Focusing on new monoamine oxidase inhibitors

1. Introduction

2. Recent discoveries on MAO

inhibitors

3. New targets of MAO inhibitors

4. New associations with other

drugs of classical MAO

inhibitors

5. New administration routes of

classical MAO inhibitors

6. New synthetic process of MAO

inhibitors

7. Expert opinion

Review

Focusing on new monoamineoxidase inhibitorsAdriana Bolasco†, Simone Carradori & Rossella FioravantiDipartimento di Chimica e Tecnologie del Farmaco, Universita degli Studi di Roma

“La Sapienza” , P.le Aldo Moro, 5 00185 Rome, Italy

Importance of the field: Monoamine oxidase (MAO) plays a significant role

in the control of intracellular concentration of monoaminergic neurotrans-

mitters or neuromodulators and dietary amines. The rapid degradation of

these molecules ensures the proper functioning of synaptic neurotransmission

and is critically important for the regulation of emotional and other brain

functions. Furthermore, modulators of neurotransmitters exert pleiotropic

effects on mental and cognitive functions. The by-products of MAO-mediated

reactions include several chemical species with neurotoxic potential. It is

widely speculated that prolonged or excessive activity of these enzymes

may be conducive to mitochondrial damages and neurodegenerative distur-

bances. In keeping with these premises, the development of human MAO

inhibitors has led to important breakthroughs in the therapy of several

neuropsychiatric disorders.

Areas covered in this review: This review highlights the recent MAO inhibi-

tors related patents published from July 2005 to December 2009. It also

reports on new associations of already known MAO inhibitors with other

drugs, innovative therapeutic targets, MAO inhibitors obtained by plants

extraction, alternative administration routes and synthetic processes.

What the reader will gain: The reader will gain an overview of the main

structures being investigated and their biological activities.

Take home message: Several of these MAO inhibitors appear promising for

further clinical development.

Keywords: Alzheimer’s disease, depression, MAO inhibitor, neuroprotection,

Parkinson’s disease

Expert Opin. Ther. Patents (2010) 20(7):909-939

1. Introduction

Monoamine oxidase (MAO) (EC 1.4.3.4) is an outer mitochondrial membrane-bound enzyme involved in the oxidative degradation of biogenic amines, such asneurotransmitters, and xenobiotic arylalkylamines to aldehydes, by using O2 asan electron acceptor. To complete the catalytic cycle, the reduced flavin adeninedinucleotide cofactor reacts with O2 to generate oxidized flavin and hydrogenperoxide (H2O2). All mammals contain both isoforms of MAO, namedMAO-A and MAO-B, which are localized in different tissues. Human MAO-A(hMAO-A) and human MAO-B (hMAO-B) are encoded by separate genes shar-ing a common intron/exon organization and are constituted by different amino-acid sequences that are ~ 70% identical. The A isoform preferentially metabolizesnorepinephrine (NA) and 5-HT and is inhibited by clorgyline, whereas theB isoform prefers benzylamine as substrate and is inhibited by (R)-deprenyl

10.1517/13543776.2010.495716 © 2010 Informa UK Ltd ISSN 1354-3776 909All rights reserved: reproduction in whole or in part not permitted

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and rasagiline. Tyramine and dopamine are equally metab-olized by both forms of the enzyme [1,2]. Selective MAO-A inhibitors are used clinically as antidepressants and anxio-lytics, while MAO-B inhibitors are used for the reductionof the progression of Parkinson’s disease and of symptomsassociated with Alzheimer’s disease. In Figure 1, all clinicalMAO inhibitors reported in the literature are depicted.The past 30 years have witnessed the discovery of severalselective MAO inhibitors, which display greater affinitytowards only one isoform. They could be classified intoreversible or irreversible [3]. Compounds belonging to thefirst generation of MAO inhibitors were mechanism-based inactivators: they acted via formation of reactive elec-trophilic intermediates which covalently modified the pro-tein structure. Most of these derivatives also interactedwith P450s leading to hepatotoxicity. A second seriousside effect that occurs with irreversible ones is theso-called ‘cheese effect’ which is characterized by hyper-tensive crises induced by elevated dietary tyramine levelsresulting from MAO inhibition [4]. Such disadvantages ledto the identification of new reversible inhibitors ofMAO-A (i.e., RIMAs).The recent discovery of three-dimensional structures of

hMAO-A and hMAO-B with their corresponding inhibitorsshows overall similarity in their crystalline forms, but impor-tant differences can be outlined in oligomeric states and activesite structures [5,6]. In fact, hMAO-B crystallizes as a dimer,whereas hMAO-A as a monomer. In detail, the active siteof hMAO-B is characterized by a generally hydrophobicdipartite cavity with a substrate entrance cavity (~ 290 A3)connected to a larger substrate-binding cavity (~ 420 A3).Ile199 was identified as an important structural elementbecause it acts as a gate that allows the accessibility to thesecond cavity. In the closed conformation, Ile199 physicallyseparates the two cavities, whereas in the presence ofbulky ligands it adopts an open conformation. Bindingof clinical inhibitors such as rasagiline and (R)-deprenylinduces a midspan type of cavity pushing Ile199 into theopen conformation.

Although MAOs are widely distributed in various organs,most of the studies concerning their functional propertiesand involvement in pathological processes have been mainlyfocused on the CNS. In the periphery, MAO-A andMAO-B are differently expressed in a variety of organs:MAO-A is predominant in heart, adipose tissue and skinfibroblasts, MAO-B is the major form found in platelet andlymphocytes, whereas both isoenzymes are expressed inkidney and liver.

Due to the importance of these isoforms in modulatingneurotransmitter physiological activity, MAO inhibitorshave been developed as important tools in the therapy of sev-eral neuropsychiatric diseases and important breakthroughshave been reached. In fact, it is well known that impairedneurotransmission is connected to mental diseases such asdepression and generalized anxiety disorders, and susceptibil-ity to stress. The majority of antidepressants presently used aredesigned to affect one or both of the most important neuro-transmitter systems of the brain (NA and 5-HT): it is possibleto inhibit their neuronal re-uptake or limit their degradationleading to an increase in their synaptic concentration(MAO-A inhibitors) [7].

Currently, a new molecule named CX157 (3-fluoro-7-(2,2,2-trifluoroethoxy)phenoxathiin-10,10-dioxide) is indevelopment for the treatment of major depressive disorder.This investigational compound is a unique molecule withpotent and specific MAO-A inhibiting activity in mammaliantissues (3.3 nM in human brain) [8].

Furthermore, the observation that hMAO-B levels inhumans increase four to fivefold on aging represents arationale for the involvement of hMAO-B in age-relatedneurological disorders such as Parkinson’s and Alzheimer’sdiseases [9-11]. Increased hMAO-B activity would be expectedto diminish dopamine concentration and to release catalyticreaction products (H2O2). While dopamine seems to beinvolved in (R)-synuclein aggregation which is implicated inthe etiology of Parkinson’s disease, high levels of H2O2 inthe cell may promote apoptotic signaling events and thedevelopment of Parkinson’s disease. Therefore, inhibition ofhMAO-B should allow a sort of neuroprotection against thiskind of bioactivation. In fact, agents that specifically limitthe activity of hMAO-B are likely to act as neuroprotectants.Indeed, treatment of pre-Parkinson’s patients with selec-tive hMAO-B inhibitors has been shown to be effective inreducing the development of this neurodegeneration.

A disadvantage of the first selective hMAO-B inhibitor,(R)-deprenyl, was related to its chemical structure: it is meta-bolized in vivo to methamphetamine compounds which areknown to be endowed with a strong sympathomimetic acti-vity. One advantage of rasagiline, therefore, was that it wasnot an amphetamine derivative and showed no sympathomi-metic activity. Rasagiline [N-propagyl-1(R)-aminoindan] isnow approved by the FDA in the US for treatment of patientswith beginning stages of Parkinson’s disease [11]. In particular,rasagiline potently suppresses apoptotic cell death initiated by

Article highlights.

. The development of human monoamine oxidase (MAO)inhibitors has led to important breakthroughs in thetherapy of several neuropsychiatric disorders andneurodegenerative diseases.

. Several heterocyclic structures were reported to displayselective MAO inhibitory activity.

. Known clinical MAO inhibitors were also evaluated forthe treatment of other therapeutic targets.

. MAO inhibitors were often associated with other drugsas co-adjuvants.

This box summarizes key points contained in the article.

Focusing on new monoamine oxidase inhibitors

910 Expert Opin. Ther. Patents (2010) 20(7)

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mitochondria [12] and inhibits mitochondrial permeabilitytransition by preventing pre-apoptotic swelling of mitochon-dria, caspase-3 and nuclear PARP-1 activation, translocationof GADPH and nucleosomal DNA fragmentation. Further,rasagiline induces an increase of the anti-apoptotic Bcl-2and Ccl-xL expression [13]. Recent studies have demonstratedthat, in addition to its MAO-B inhibitor activity, it alsopossesses potent neuroprotective activity. This target wasachieved in different animal models [14]. The (S)-enantiomer

is a much less potent (three orders of magnitude) inhibitorof hMAO-B than the (R)-enantiomer of rasagiline but retainsits neuroprotective properties. The inverted chirality leads to adifferent binding of the indan ring, which is rotated by 180�

with respect to the conformation observed in the rasagilinecomplex and coupled to a shift of the Tyr326 side chain sothat the overall balance of interactions is less favorable. Thisreduced efficacy may also result from steric hindrance.These data reveal that the binding mode of (S)-enantiomer

N

O NH

HN

O

N

HN

O

Cl

N

OO

OH

Iproniazide (I) (A/B) R-(-)-Deprenyl (I) (B) Pargyline (I) (A/B)

Moclobemide (R) (A) CX157 (R) (A)

Toloxatone (R) (A)

N

N

H

Cl

Cl

O N

Clorgyline (I) (A)

Isocarboxazide (I) (A/B)

HN

NH

O

N

O

Rasagiline (I) (B)

NH

Cimoxatone (R) (A)

N

OO

O

ONC

Befloxatone (R) (A)

N

OO

O

OF3C

OH

F

S

O O CF3

O O

Figure 1. Irreversible (I), reversible (R), and selective hMAO-A and/or MAO-B (A or B or A/B) inhibitors.

Bolasco, Carradori & Fioravanti

Expert Opin. Ther. Patents (2010) 20(7) 911

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is clearly distinguished from that of rasagiline and theother (R)-inhibitors.Another important inhibitor, currently in Phase III clinical

trials for Parkinson’s disease and in Phase II for restless legssyndrome, is safinamide ((S)-2-(4-(3-fluorobenzyloxy)benzyl-amino)propionamide methanesulfonate) [15], which com-bines multiple mechanism of action, including reversibleinhibition of hMAO-B, sodium channel blocking activity,calcium channel modulation, dopamine re-uptake inhibitionand glutamate level modulation. Inhibition of hMAO-Breduces the metabolic inactivation of dopamine in patients,while the Na+ channel blockade selectively affects those neu-rons with abnormal firing patterns and leaves normal activityunaltered. Instead, ralfinamide ((S)-2-[4-(2-fluorobenzyloxy)benzylamino] propanamide) is a sodium channel blockeruseful in the treatment of pain conditions, including chronicand neuropathic pain, migraine, bipolar disorders anddepression [16].Ladostigil ([(3R)-3-(prop-2-ynylamino)indan-5-yl]-N-pro-

pylcarbamate) is a novel neuroprotective agent being investi-gated for the treatment of neurodegenerative disorders suchas Alzheimer’s disease, Lewy body disease and Parkinson’sdisease. It acts as a reversible acetylcholinesterase (AChE)and butyrylcholinesterase (BuChE) inhibitor (in doses of35 -- 100 µmol/kg administered orally to rats, it inhibits

cholinesterase (ChE) by 25 -- 40% and antagonizesscopolamine-induced impairments in spatial memory), andas an irreversible MAO inhibitor, and combines the mecha-nism of action of drugs such as rivastigmine and rasagilineinto a single molecule. After daily administration of75 µmol/kg for 2 weeks, ladostigil does not show any motorstimulant effects but significantly reduces immobility in theforced swim test, an action consistent with that of known anti-depressants. This could result from the inhibition of bothMAO-A and MAO-B in rat brain that, under these conditions,reaches > 70%. Ladostigil also shows selectivity for brainMAO, even after 2 months of daily administration, with littleor no effect on the enzyme located in the intestinal tract or inthe liver. This property reduces the likelihood of producingthe ‘cheese effect’. Ladostigil also has antidepressant effectsand may be useful for treating depression and anxiety. In addi-tion to its neuroprotective properties, ladostigil enhances theexpression of neurotrophic factors and may be capable ofreversing some of the damage seen in neurodegenerativediseases via the induction of neurogenesis [17].

Both stereoisomers of ladostigil protect against ischemia-induced cytotoxicity in PC12 cells and reduce edema, deficitsin motor function and memory after closed head injuryin mice. These neuroprotective effects do not result fromMAO inhibition.

Lazabemide (R) (B)

N

NH

Cl

O

NH2

O

NH

NH2

OF

Safinamide (R) (B)

Ralfinamide (R) (B)

O

NH

NH2

O

F

Ladostigil (I) (B)

NH

O

O

N

R/S-Desmethylseligiline (I) (B)

HN

Figure 1. Irreversible (I), reversible (R), and selective hMAO-A and/or MAO-B (A or B or A/B) inhibitors (continued).



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However, the use of these drugs has been limited by somecentrally mediated side effects such as the serotonin syn-drome, dizziness, light-headedness, blurred vision and weak-ness. In addition, it has been reported that MAO inhibitorsmay potentiate the effects of alcohol and other drugs thatslow the CNS, such as antihistamines, cold medicine, allergymedicine, sleep aids, medicine for seizures, tranquilizers,some pain relievers and muscle relaxants. So far, there is aneed for new compounds which do not show the reportednegative side effects [16].

2. Recent discoveries on MAO inhibitors

In this section, we collect all patents dealing with new hMAOinhibitors reported in the literature between July 2005 andDecember 2009, continuing our previous work in thisfield [18]. We also reported on structures and IC50 values ofthe most representative compounds.

2.1 b-CarbolinesThis invention relates to the preparation and biologicalevaluation of b-carboline type molecules from natural anddietary amino acids [19]. b-Carbolines are bioactive alkaloidsderived from indole endowed with neuropharmacologicaland neuromodulating properties. Aromatic b-carbolineshave also been studied for their effects on serotoninergic,opioide and benzodiazepine receptors and for theireffects on MAO activity [20-22]. Starting from the inhibitionresults obtained for natural b-carbolines (IC50 MAO-A~ 6.5 µM and IC50 MAO-B ~ 4.7 µM for b-carboline(R1 = R2 = R3 = H), IC50 MAO-A ~ 0.34 µM for1-methyl-b-carboline and IC50 MAO-A ~ 0.009 µM for7-methoxy-1-methyl-b-carboline) using the kynuraminebiological assay [23], these authors proposed new derivativesof general formula 1 in Figure 2 with the ability of inhibit-ing MAOs. 1,2,3,4-Tetrahydro-b-carbolin-3-carboxylic acidshowed, at 25 µM concentration, 60% of MAO-A inhibitionand 71% of MAO-B inhibition, while 1-methyl-1,2,3,4-tetrahydro-b-carbolin-3-carboxylic acid displayed only 90%of MAO-A inhibition.

2.2 Propargylated aminoindansScientists at Cooper & Dunham LLP disclosed and synthe-sized a ladostigil ester derivative (formula 2 in Figure 2) whichacts as MAO, AChE, and BuChE inhibitor in vitro [24]. MAOinhibition has been extrapolated from a radioactivity mea-surement. It can also be used as a reference standard or markerto investigate the pharmacokinetic and metabolic profile ofladostigil. Indeed, chronic administration of 2 and ladostigiltartrate to rats indicated that the former is responsible forbrain-selective MAO inhibition. MAO inhibition in plasmasamples from patients was determined by HPLC analysis.The composition may be prepared as medicament to beadministered orally, parenterally, rectally or transdermally orcould be provided with suitable delivery systems.

2.3 IsoxazolesResearchers at Helicon Therapeutics, Inc. discovered severalisoxazole derivatives of general formula 3 in Figure 2 asMAO-B inhibitors in the micromolar range useful forimproving cognitive function [25]. They also described thesynthesis and the pharmaceutical formulations of these mole-cules. They tested them in established animal models such ascontextual memory assay in mice (to investigate the neuralsubstrates mediating fear-motivated learning and study theimpact of various mutations on hippocampus-dependentmemory) [26] and object recognition assay (to evaluatedrug--compound effects on cognitive tasks) [27].

2.4 DiterpenesThe present invention refers to dietary or pharmaceutical com-positions containing tricyclic diterpenes and their derivatives ofgeneral formulas 4 and 5 in Figure 2 for the treatment of depres-sion [28]. Among several compounds reported in this patent,only three have been tested for their ability to inhibit MAOsusing benzylamine as substrate. Carnosic acid, 20-deoxo carno-sol and carnosic acid-12-methyl ether presented MAO-A inhib-itory activity in the micromolar range (4.4, 4.3 and 40.6 µM,respectively) with a discrete selectivity over MAO-B. Carnosicacid, isolated from plants (rosemary and sage) or synthesizedaccording to literature [29]; 20-deoxo-carnosol, isolated fromplants (Lepechinia urbaniana and wild sage) or synthesized;and carnosic acid 12-methyl ether, extracted from plants(sage, rosemary and Hyptis martiusii) possessed a biologicalactivity against disorders connected to impaired neurotrans-mission. The same three derivatives were also evaluated in theserotonin uptake inhibition test, in the Porsolt’s swim test [30]

in comparison with fluoxetine, and in the Marble buryingtest [31] in comparison with fluoxetine and venlafaxin. Carnosicacid has been also assayed in the light dark box test in themouse after subchronic, oral gavage described by Crawley [32]

to test its anxyolitic effect. Finally, researchers disclosedseveral pharmaceutical compositions for administering thesederivatives to humans and animals.

2.5 ImidazolesBayer Pharmaceuticals Corp. has synthesized a novel class ofimidazole derivatives of general formula 6 in Figure 2 asselective MAO-A inhibitors [33].

MAO inhibitory activity was not specifically assessed butthe biological evaluation of this scaffold as MAO-A inhibitorswas accomplished through in vitro, ex vivo and in vivo assaysthat are well known in the art to evaluate depression (forcedswim test, tail suspension test), schizophrenia (prepulse inhi-bition) and anxiety (elevated plus maze) [34] in establishedanimal models.

2.6 DithiolethionesSolvay Pharmaceuticals B.V. developed anethole dithiole-thione and other dithiolethiones (Figure 3) for the treatmentof conditions associated with dysfunction of monoamine



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NH

NR1

R2R3

2

A2A3

A1R1

B X

Y

R1 = H, C1-6-alkyl; R2 = OH, C3-5-acyloxy, hydroxymethyl,1,3-dihydroxypropyl, C1-6-alkyl; R3 = R4 = H, OH, hydroxymethyl,C1-5-acyloxy, C1-6-alkoxy; R5 = C1-6-alkyl, hydroxymethyl, carboxy,methoxycarbonyl; R6 = H; R7 = R8 = C1-6-alkyl, carboxy, 1-6-hydroxy-C1-6-alkyl, C1-6-alkoxycarbonyl; R9 = H, hydroxymethyl, OCH3, oxo,C1-5-acyloxy; R10 = H; R11 = R12 = H, oxo

R1

R2

R3

R4

R5

R9

R10

R11

R6R7

R8

R12

O

R2

R3

O

R5

R9

R10

R11

R6R7

R8

R12

R1 = R2 = phenyl group (substituted with one or more halogens, alkyl, alkoxy, CF3, CN, NO2, Ph, alkyl sulfonyl, alkyl sulfonyl-amino,alkyl carbonyl-amino, alkyl amino-carbonyl-amino); alkyl; cyclohexyl (unsubstituted or substituted with alkyl, alkoxy, CF3, CN, one ormore fluorine); 1-naphtyl or 2-naphtyl (unsubstituted or substituted with alkyl, alkoxy, CF3, CN); benzyl (unsubstituted or substitutedon the phenyl ring with alkyl, alkoxy, CF3, CN); a5- or a 10-membered saturated, unsaturated or aromatic heterocyclic radical(unsubstituted or substituted with one or more halogens, alkyl, alkoxy, CF3, CN, NO2, Ph). R3 = H. alkyl, benzyl, chloro, bromo.X = -CONR4R5 or -CONHSO2R6. R4 = H, alkyl. R5 = alkyl or bicycloalkyl (unsubstituted or substituted with phenyl, hydroxy, benzyloxy,alkoxy, alkyl amino, F); benzyl or benzocycloalkyl (unsubstituted or substituted with hydroxy, benzyloxy, hydroxyalkyl, one or morehalogens, alkyl, alkoxy, CF3, CN, NO2). R6 = alkyl, phenyl, or benzocycloalkyl (unsubstituted or substituted with phenyl, hydroxy,benzyloxy, alkoxy, halogen)

NN

R1

R2

R3

X

R1 = R2 = H, halogen, alkyl, OCH3R3 = H, alkyl

1R1 = H, aryl, C1-6-alkyl; A1 = N,substituted alkyl; A2 = A3 = O, N;B = aryl, heteroaryl; X = carbonyl,thiocarbonyl, sulfonyl,substituted alkyl; Y = H, OH, C1-6-alkyl, aryl, heteroaryl

3

4 5

6

NH

OHN

O

HO

Figure 2. General structures of derivatives 1 -- 6.



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neurotransmission (in particular, MAO-B activity) [35]. Thegoal of this invention is to develop new bioactive molecules,structurally unrelated to those presently available and withfew side effects. Some related compounds were said to inhi-bit D-amino-acid oxidase, the enzyme that stereoselectivelydeaminates D-amino acids generating H2O2 as MAOs. Ithas now been found that this scaffold potently inhibitsMAO-B activity in cellular extracts derived from culturedrat striatal astroglial cells, whereas no significant effect isobserved on MAO-A activity (Table 1).

In addition, 3H-1,2-dithiole-3-thione (7) and its lipo-philic analog 5-(4-methoxyphenyl)-3H-1,2-dithiole-3-thione(8, anethole dithiolethione) [36] have been tested for theirability of inhibiting MAO activity (Table 2).

All synthesized compounds were fully characterized andembodied in different pharmaceutical formulations in orderto be administered at 0.1 -- 100 mg/kg of patient’s bodyweight.MAO activity was determined using the Amplex Red MAO kitassay based on the fluorescence method described by Zhou andPanchuk-Voloshina [37]. Neonatal rat striatal cells were used as a

source of both MAO isoforms and clorgyline and L-deprenylwere considered as reference drugs.

2.7 OxoisoaporphinesThis invention relates to the synthesis (with high yields in atwo-steps process) and biological evaluation of selectivehMAO-A inhibitors of oxoisoaporphine derivatives (9 inFigure 3), isomers of widely distributed natural oxoaporphinesafter oxidation of specific alkaloids (aporphines) [38,39]. Thesecompounds have been little characterized for their biologicalproperties and could represent the first example of isoquino-line alkaloids able to inhibit hMAO activity [40]. In the past,these derivatives have been synthesized because of their abilityto act as photoconductors or semiconductors. The effects ofthe test compounds on the enzymatic activity of hMAO iso-forms have been evaluated by a fluorimetric method follow-ing an experimental protocol previously described by theauthors [41]. The biological evaluation on hMAO activity hasbeen investigated by measuring their effects on the productionof H2O2 from p-tyramine (a common substrate for both

SS

S

SS

S

H3CO

D3T

N

O

R

R1

R2

R3

9R = R1 = R3 = H, OCH3;R2 = H, OCH3, NH2, NHCH2CH2 (4-HO-Ph);R1 = R2 = -OCH2O-

X

NH

N

O

R1

R2

R4

R3

R7

R6

R5

O

O

OCH3

NH

S

O

O

NH2

1110R1 = R2 = H, C1-6-alkyl, fused heterocycleR3 = R4 = H, fused cyclopropane ringX = CH, N; R5 = R6 = R7 = C1-3-alkyl, alkoxy,alkylaryl

7

Anethole dithiolethione8




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Table 1. hMAO-B inhibition of dithiolethione derivatives.

SS

S

R1

R2

R1 R2 MAO-B % inhibition

(10-5 M)

4-Hexyloxyphenyl H 100

H ON

O

81

H ON

83

Phenyl

O

ON

N

65

4-Methylphenyl

O

ON

N

74

4-Methylphenyl 4-Methylpiperazinyl 54

H -CH=CH-(4-diethylaminophenyl) 52

H -CH=CH-(2-quinolinyl) 56

Phenyl -S(CH2)2CH(CH3)NH-2-propynyl 25



Phenyl -S(CH2)2CH(CH3)N(CH3)-2-propynyl 81

Phenyl -S(CH2)2CH(CH3)N(CH3)-2-propynyl 75

Phenyl -S-CH2-(4-methylphenyl) 71

Table 2. Percent inhibition of MAO activity after administration of ADT, D3T and reference drugs.

Concentration (mM) Total MAO activity

(% inhibition)

MAO-B activity

(% inhibition)

MAO-A activity

(% inhibition)

L-Deprenyl ADT L-Deprenyl ADT D3T Clorgyline ADT

0.1 56 14 80 15 - 100 -0.3 73 35 97 40 - - -1 79 60 100 73 2 - -3 - 70 - 89 6 - -10 - 81 - 96 24 - 330 - 85 - 100 59 - 14100 - - - - 82 - -300 - - - - 92 - -1000 - - - - 91 - -

3DT: 3H-1,2-dithiole-3-thione; ADT: Anethole dithiolethione.



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hMAO-A and hMAO-B), using the Amplex Red MAO assaykit and microsomal MAO isoforms prepared from insect cellsinfected with recombinant baculovirus containing cDNA(BTI-TN-5B1 -- 4) inserts for hMAO-A or hMAO-B. Theproduction of H2O2 catalyzed by MAO isoforms can bedetected using 10-acetyl-3,7-dihydroxyphenoxazine (AmplexRed reagent), a non-fluorescent and highly sensitive probethat reacts with H2O2 in the presence of horseradish peroxi-dase to produce a fluorescent product, resorufin. The testdrugs (new compounds and four reference inhibitors) wereunable to react directly with the Amplex Red reagent,which indicates that these drugs do not interfere withthe measurements.

Structure--activity relationships were inferred from the dataof enzymatic experiments reported in Table 3. One compounddisplayed MAO-A picomolar inhibitory activity (inferior tothe most active reference drug) and, for it, the authors alsoreported ‘dose-concentration’ responses against hMAO-A.Other derivatives showed the best activity and selectivitytowards this isoform.

2.8 Prolinamide derivativesResearchers at Glaxo Group Ltd proposed, in some embodi-ments, new prolinamide derivatives of general formula 10

in Figure 3 as dual agents (sodium channel modulators andMAO-B inhibitors), which are said to be useful in the treat-ment of different conditions such as Alzheimer’s disease andsenile dementia [42]. They synthesized and characterizedthem by 1H NMR, HPLC and mass spectral studies. Therationale of this association could be found in the importanceof modulating the use-dependent voltage-gate sodium chan-nels in several CNS pathologies (bipolar disorders, mania,depression, schizophrenia). They affect neuron depolariza-tion, calcium influx and release of neurotransmitters. Theprotocol also described the test for evaluating MAO-B inhibi-tion by a fluorescent-based end point assay using benzylamineas substrate (Amplex Red reagent) but biological data arenot reported.

2.9 Benzo-heteroarylsulfonamidesThese two inventions by Janssen Pharmaceutica N.V weredirected to the use of benzo-heteroaryl sulfamide derivativesfor the treatment of depression, including both monotherapyand co-therapy with at least one antidepressant [43,44]. In2007, compounds of general formula 11 in Figure 3 were syn-thesized, characterized and assayed in vivo to predict theirability to treat mood disorders (dominant--submissive compe-tition) [45] and antidepressant activity (mouse tail suspensionand mouse forced swim tests). It is important to note thatthe NMRI mice used in these tests do not respond to allantidepressants in this model; rather, they exhibit selectivesensitivity to 5-HT re-uptake inhibitors and some tricyclicantidepressants. The lack of activity of tested drugs in thismodel would only suggest that the compound does notinhibit 5-HT re-uptake. In 2009, instead, researchers

synthesized a new class of anxiolytic agents based on this phar-macophore and tested them in vivo (mice): elevated plusmaze [34] and four plate tests [46]. MAO inhibitory activitywas not specifically assessed for all compounds.

2.10 Diphenyl ether derivativesResearchers at Orchid Research Laboratories Ltd pro-posed new MAO-A inhibitors of formulas 12 -- 22 in Figure 4

assayed by the kynuramine deamination test [47]. Com-pounds 12 -- 17 exhibited MAO inhibitory activity lowerbut still comparable to clorgyline at 1 µM concentration,while compounds 18 -- 22 reached the same results only at10 µM concentration.

2.11 Benzopyran derivatives7-Hydroxycoumarin derivatives also represented an effectivestrategy in the generation of reversible MAO inhibitors [48-50].Functionalization of the hydroxyl group modulated the MAOinhibitory activity and selectivity [51-53].

Researchers at Newron Pharmaceuticals SpA synthesizedand fully characterized novel aminoalkyl- and amidoalkyl-benzopyran derivatives of general formula 23 in Figure 5 asreversible MAO-B inhibitors, with IC50 in the nano- ormicromolar range, assayed in vivo (mice) and in vitro for theprevention and the treatment of CNS degenerative disorders.They did not possess any relevant effect on MAO-A activity.They could be administered alone or in conjunction withone or more therapeutic agents.

These coumarin analogs have shown to possess differentpharmacological properties and similar compounds, whereinthe substituents on the pyran ring do not contain either anamido or an amino group, and have been patented recently.MAO enzyme activity was evaluated in vitro after extractionof both isoforms from rat brain and administration of14C-serotonin (for MAO-A) and 14C-phenylethylamine (forMAO-B) through a radioenzymatic assay (Table 4). In orderto investigate whether the test compounds were irreversibleor reversible MAO-B inhibitors, the authors performedtime-dependent experiments for calculating their associationkinetics. At last, they also evaluated ex vivoMAO-B inhibitionadministering such compounds orally to mice. Results showedthat this scaffold acted as a potent, reversible and short-acting MAO-B inhibitor with full recovery of the enzymaticactivity 8 -- 16 h after the administration.

Structurally similar benzopyranone derivatives (24 inFigure 5) were also designed by Ache Laboratorios Farmaceu-ticos S/A for preventing or treating diseases associated withMAOs. These compounds could be obtained syntheticallyby conventional chemical routes or be contained in a stan-dardized pharmaceutical product (plants belonging to thefamily of Passifloraceae) and for this reason they could existas C-glycosylated flavonoids (schaftoside, isoschaftoside, vitexin,isovitexin, isovitexin-2¢¢-O-b-glucopyranoside, isoorientin-2¢¢-O-b-glucopyranoside). The authors considered that thequantity of active principle may vary between ~ 1 and



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Table 3. hMAO inhibition reported for oxoisoaporphine derivatives and reference drugs.

Compound IC50 hMAO-A IC50 hMAO-B Ratio

N

O

H3CO

H3CO

OCH3

27.32 ± 1.18 µM* z > 3.66#

N

O

H3CO

H3CO

OCH3

OCH3

13.65 ± 0.34 nM* z > 7326#

N

O

H3CO

OCH3

44.37 ± 2.25 nM* z > 2253.77#

N

O

OCH3

O

O

723.48 ± 52.36 µM* * > 0.14#

N

O

H3CO

OCH3

HO

OCH3 835.75 ± 49.75 pM* z > 119,653.01#

N

O

H3CO

H3CO

OCH3

1.23 ± 0.08 µM* z > 81.30#

Ratio: hMAO-A selectivity index = IC50 (hMAO-B)/IC50 (hMAO-A). Each IC50 value is the mean ± s.e.m. from five experiments.

Level of statistical significance: *P < 0.01 versus the corresponding IC50 values obtained against hMAO-B, as determined by ANOVA/Dunnett´s.zInactive at 100 µM (the highest concentration tested).§50 µM (the highest concentration tested).{Inactive at 1 mM (the highest concentration tested).#Values obtained under the assumption that the corresponding IC50 against hMAO-B is the highest concentration tested.



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500 mg and, for ease of demonstration, reported on in vitroMAO activity inhibition tests carried out with a standardizedpharmaceutical Passiflora incarnata product using kynuramineas substrate.

Another invention relates to novel, synthetic or isolatedfrom plant, coumarin ether derivatives of general formula 25

in Figure 5 for preventing and treating disorders connectedto impaired neurotransmission. DSM Ip Assets B.V. thought

these dietary/pharmaceutical compositions as ‘conditionimprovers’. Among them, they reported biological data aboutMAO inhibition of the racemic obliquin (26), isolated fromplants [54] or synthesized according to literature (Table 5) [55].The colorimetric MAO assay and the higher specificity forMAO-B were reported. Obliquin displayed, in the concen-tration range 10-7 -- 10-4, a better inhibition of MAO-B(8.3 -- 91.5%) over MAO-A (2 -- 24.1%). Further, it has

Table 3. hMAO inhibition reported for oxoisoaporphine derivatives and reference drugs (continued).

Compound IC50 hMAO-A IC50 hMAO-B Ratio

N

O

H3CO

OCH3

HO

34.75 ± 1.28 nM* z > 2877.70#

N

O

H3CO

H3CO

OCH3

OCH3 13.36 ± 0.54 nM* z > 7485.03#

N

O

OCH3

NH

H3CO

OCH3 HO 2.12 ± 0.07 µM* § > 23.58#

N

O

OCH3

H2N

H3CO

OCH3 9.81 ± 0.26 µM* § > 5.10#

Clorgyline 3.97 ± 0.75 nM* 63.41 ± 1.20 µM 15,972.29

(R)-deprenyl 68.73 ± 4.21 µM* 17.32 ± 1.96 nM 0.00025

Iproniazid 6.56 ± 0.76 µM 7.54 ± 0.36 µM 1.15

Moclobemide 361.38 ± 19.37 µM* { > 2.77#

Ratio: hMAO-A selectivity index = IC50 (hMAO-B)/IC50 (hMAO-A). Each IC50 value is the mean ± s.e.m. from five experiments.

Level of statistical significance: *P < 0.01 versus the corresponding IC50 values obtained against hMAO-B, as determined by ANOVA/Dunnett´s.zInactive at 100 µM (the highest concentration tested).§50 µM (the highest concentration tested).{Inactive at 1 mM (the highest concentration tested).#Values obtained under the assumption that the corresponding IC50 against hMAO-B is the highest concentration tested.



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been assayed even in the Porsolt’s swim test, a validated animalmodel for depression which responds to enhancement of thetransmission of serotonin, dopamine and NA [30], in theMarble burying test for anxiety-like or obsessive behavior [31]

and in the serotonin uptake inhibition and labeled citalopramdisplacement test.

2.12 a-Aminoamides (safinamide derivatives)Safinamide, as described above, combines multiple mecha-nisms of action and could present unexpected side effects [56].For these reasons, new mono or polydeuterated derivatives(27 in Figure 5) have been synthesized, characterized andassayed for their ability of inhibiting MAO-B and modulatingNa+ and Ca+2 channel activity. It has been proven thatsuch derivatives can be administered alone or with a secondtherapeutic agent having the same mechanism of action of

safinamide. This invention relates to the manufacturing ofdifferent kits to treat Parkinson’s disease and restless legs syn-drome. A number of studies suggest that the fundamentalpathophysiology of this last syndrome involves mechanismsof iron and dopamine transport and turnover (in particulariron deficiency and its potential effects on dopamine systemactivity), thus, demonstrating the clinical use of dopaminepromoting MAO-B inhibitors such as selegiline, rasagilineand safinamide. These disclosed compounds were evaluatedonly for metabolic stability in vitro against human livermicrosomes (20 mg/ml) by calculating their t1/2 values [57].

2.13 Pyrazole derivativesBayer Pharmaceuticals Corp. has synthesized novel substi-tuted pyrazole derivatives (including their enantiomers andconformers) of general formula 28 in Figure 5 useful in the

HCl HCl HCl

12 13

O

S

NH

H2N

O OCH3

S

O

14

O

S

NH

H2N

O OCH3

O

O

F

15

O

NH

Cl

N

O

O

O

16

O

NH

Cl

N

O

O

O

O

S

NH

H2N

O

S

O

OCH3

17

O

NH

Cl O

O

NH

O

Figure 4. Diphenyl ether derivatives 12 -- 22.



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treatment of psychiatric disorders including schizophrenia,depression and anxiety [58,59]. Demonstration of their activityhas been accomplished through in vitro, ex vivo and in vivoassays well known in the art about established animal models.The forced swim [30] and the tail suspension tests have beenused to assess the efficacy of antidepressant compounds, whileeffects on schizophrenia and anxiety have been studiedthrough the prepulse inhibition and the elevated plus mazetests [60,61]. MAO inhibitory activity was not specificallyassessed for all compounds.

Other pyrazole compounds were evaluated as inhibitors ofMAO-B enzyme activity and could be useful for improvingcognitive function and for treating psychiatric disorders inanimals. The MAO enzymatic assay was performed accordingto the fluorometric method described by Matsumoto et al. [23]with slight modifications. These compounds showed MAO-B

inhibitory properties at 0.1 -- 10 µM, typically at 5 -- 100%.Most of them demonstrated selectivity for MAO-B overMAO-A. The ability of a compound to modulate cognitivebehavior can be evaluated using a specific assay which meas-ures memory after contextual fear conditioning. Compoundswere dissolved in 1% DMSO/PBS and administered intra-peritoneally in a volume of 8 ml/kg 20 min before training.The ability of a compound to modulate cognitive behaviorcan also be evaluated using the object recognition assay.Specifically, some compounds of this scaffold, injected20 min before training, significantly enhanced contextualmemory in mice.

2.14 Pyridine derivativesThese two patents, written in Japanese, reported on thesynthesis, characterization and biological evaluation of

O

NH

18

Cl O

H2N

O OCH3

HCl

20

O

N

O

O

S

NO

S

COOH

21

O

N

O

O

S

NHO

S

Cl

22

HCl

O

H2N

S

NHO

O

OH3CO

O

S

NH

H2N

O

HCl

OCH3

O

O

19

Cl

Figure 4. Diphenyl ether derivatives 12 -- 22 (continued).



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O R4

R3

N

O

R1

R2

OR

O

OOH

R2

HO

R1

R3

OH

23

3

ROO

R1

R

O3

25R1 = H,OH,(E )-methyl-but-2-enyl;R2 = methyl, 3-(4,5-dihydro-5,5-dimethyl-4-furanon-2-yl)-2-(E/Z )-butenyl, (E/Z )-3,7-dimethylocta-2,6-dienyl,7-hydroxy-3,7-dimethyl-2-octen-6-on-yl,(E/Z , E/Z )-11-acetyl-oxy-3,7,11,11-tetramethyl-undeca-2,7-dien-10-onyl; -R3 = H, -O-C(H)(C(CH3)2(H)-O-C(O)CH3)-CH2-

O O

O

O

26

FO

NHY1 Y2

Y3 Y4

O

NH2

R1Y5 N

N

R

R1

R2

A B

X

29R = H, alkyl, alkenyl, alkynyl, halo; R1 = alkyl, aryl, alkoxy, aryloxy,

halogen; X = CO, SO2; Y = alkylene; A = saturated ring, aromatic ring

N

R

NX

Y

R1

A

N

R

N

R1

XY

A

for substituents see Table 4 24

R1 = R2 = H, carbohydrate;R3 = H, OH

27R1 = CH3, polideuterated CH3Y = H, D

28R = R1= unsusbstitutedor substituted aryl and heteroaryl;R2 = H,OH,C1-3-alkoxy;A = different-linkers;B = sulfonyl,carbonyl;X = benzyl, aryl, heteroaryl, C1-8-alkyl




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pyridine derivatives of general formula 29 in Figure 5 asselective MAO-B inhibitors useful for treatment ofParkinsonism [62,63].

The second series of pyridine derivatives is claimed to haveBBB permeability as centrally acting drugs and contrast agentsfor MRI.

2.15 PolyprenolsThis invention, written in Russian, referred to therapeuticagents for reducing MAO over activity based on a scaffoldof polyprenols of general formula 30 in Figure 6 [64]. The treat-ment is characterized by one or more doses of polyprenols inamounts ranging from 1 to 150 mg/day. Biological data foreach compound are reported in Russian.

2.16 Biphenyl derivativesMerck Frosst Canada Ltd synthesized and characterized138 biphenyl derivatives of general formula 31 in Figure 6 asreversible inhibitors of recombinant hMAOs using thekynuramine assay. They could be used alone or in associa-tion with other therapeutic agents [65]. Biological data arenot reported.

2.17 Benzyloxy derivativesThe invention related to benzyloxy derivatives of general for-mula 32 in Figure 6 was prepared enantiomerically pure andcharacterized with mass spectrometry [66-68]. The tested com-pounds acted as MAO-B inhibitors and were especially usefulfor the treatment and prevention of Alzheimer’s diseaseand senile dementia. MAO enzymatic assay was performedusing a spectrophotometric method described by Zhou andPanchuk-Voloshina [37]. Clorgyline and L-deprenyl wereused as reference drugs. Data were not reported but theauthors stated that the IC50 values ranged from 1 to 0.02 µMagainst MAO-B.

2.18 Oxazolidinone derivativesThe structural template for this scaffold was derived fromcimoxatone, toloxatone and befloxatone (currently in

Phase III clinical trials for depression) [69-74]. Isozyme selectiv-ity is dramatically improved by replacing the central phenylgroup of befloxatone with larger heteroaromatic moieties.SAR studies demonstrated the strict requirement for theR-configuration of the stereogenic center of the methoxy-methyloxazolidinone group and a para-substituent on the arylring for good inhibition activity. In particular, oxazolidinoneswith amine and ether substituents in the 5-position ofthe nucleus have been described as having potent MAOinhibitory activity [75-77].

Certain antibacterial compounds containing an oxazolidi-none ring have been described in the literature and theirmechanism of action has been fully investigated [78]. Line-zolid, N-[[(5S)-3-[3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]acetamide, was the first approvedantimicrobial oxazolidinone for clinical use in the US. How-ever, inhibition of MAO is a potential cause of manyunwanted side effects, and so this property was minimizedin each potential antibacterial agent.

The first invention related to a scaffold of sulfur-containing substituted 2,3,5-trifluorophenyl oxazolidinonesof general formula 33 in Figure 6 and to the process of theirsynthesis. The enzymatic assay for hMAO-A was performedby a spectrophotometer and was based on the formation ofa colored reaction product [79].

In this patent, the authors at AstraZeneca UK Ltddescribed a class of bi-aryl compounds containing one oxazo-lidinone and one isoxazoline ring, bearing ether or substitutedether side chains on the isoxazoline and a triazole ring onthe oxazolidinone, endowed with acceptable levels of MAOinhibition whilst having useful antibacterial activity. Theysynthesized and characterized novel compounds of generalformula 34 in Figure 6 and also provided a process for pre-paring a pharmaceutically-acceptable salt or an in vivo hydro-lysable ester thereof. These molecules displayed a goodspectrum of activity in vitro against pathogenic bacteria interms of the MIC, but they were also assayed on humanliver MAO enzymes expressed in yeast as described in theliterature [80]. From the results, it was possible to extrapolate

Table 4. MAO inhibition of coumarin derivatives.

Compound IC50 MAO-A (mM) IC50 MAO-B (mM)

4-[(Hydrazinocarbonyl)methyl]-7-benzyloxy-2H-chromen-2-one 1.4 0.04

4-[(Aminocarbonyl)methyl]-7-(3-fluoro-benzyloxy)-2H-chromen-2-one 70 0.05

4-[(Dimethylaminocarbonyl)methyl]-7-(3-chloro-benzyloxy)-2H-chromen-2-one > 100 0.04

4-[(Dimethylaminocarbonyl)methyl]-7-benzyloxy-2H-chromen-2-one 15.3 0.08

4-Aminoethyl-7-(3-chloro-benzyloxy)-2H-chromen-2-one 1.9 0.01

4-[(Methylamino)methyl]-7-(3-fluoro-benzyloxy)-2H-chromen-2-one 13.5 0.02

4-(2-Aminoethyl)-7-(3-chloro-benzyloxy)-2H-chromen-2-one 31.8 0.25

4-[(Methylamino)methyl]-7-(3-chloro-benzyloxy)-2H-chromen-2-one 5.9 0.01

4-[2-(Methylamino)ethyl]-7-(3-chloro-benzyloxy)-2H-chromen-2-one 74 0.30



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Table 5. MAO inhibition of pyridine derivatives.

Compound Concentration MAO-A

(% inhibition)

MAO-B

(% inhibition)

O

Cl

N

N

10 µM 13 87

O

Cl

N

N

10 µM -- 59

O

N

N

F

F

10 µM -- 39

O

N

N

F

10 µM 6 92

O

N

N

Cl

10 µM -- 80

O

Cl

F

N

N

10 µM -- 92



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Table 5. MAO inhibition of pyridine derivatives (continued).


(% inhibition)

MAO-B

(% inhibition)

O

N

N

Cl

Cl

10 µM 9 77

O

N

N

CF3

10 µM 5 31

O

OCH3

OCH3

N

N

10 µM 4 --

SO

Cl

O

N

N

10 µM 4 6

O

Cl

N

N

10 µM 9 11

H

O

Cl

N

N

N

1 µM 10 1



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that the introduction of a 4-alkyltriazole generally demon-strated lower MAO-A inhibition than the unsubstitutedtriazole analogs. The most active derivative is (5S)-3-[3-fluoro-4-[6-((5S)-5-[[(2-hydroxyethyl)]methyl]-4,5-dihydroisoxazol-3-yl)pyridin-yl]phenyl]-5-(1H-1,2,3-triazol-1-ylmethyl)-1,3-oxazolidin-2-one.Successively, researchers at Ferrer Internacional, SA devel-

oped a novel class of cyano piperidinyl-phenyl-oxazolidinonesand 1(2H)-tetrazol-5-yl-phenyl-oxazolidinones, which wereactive against bacteria, but with a weak MAO inhibitory acti-vity. They also investigated and characterized different poly-morphic forms of some of them by X-ray diffractionspectrum, equilibrium solubility and differential scanningcalorimetry. MAO inhibition assay was performed on com-pounds reported in Table 6 using membranes from SF9 cells(a cell line derived from pupal ovarian tissue of Spodopterafrugiperda) expressing both isoforms. Kynuramine was usedas substrate for the fluorimetric reaction.Metaxalone (35 in Figure 6), 5-[(3,5-dimethylphenoxy)

methyl]-2-oxazolidinone, is an orally administered skeletalmuscle relaxant with a relatively low toxicity [81]. Researchersat Auspex Pharmaceuticals, Inc. synthesized and fully charac-terized novel metaxolone derivatives of general formula 36

in Figure 6 substituted with hydrogen or deuterium. Deutera-tion of pharmaceuticals to improve pharmacokinetic, phar-macodynamic and toxicity profiles has been demonstratedwith some classes of drugs. These derivatives were assayedfor their in vitro liver microsomal stability and the resultsshowed that the deuterated ones possessed an improved degra-dation half-life (37%), compared to the non-isotopicallyenriched drug. This invention also related to the inhibition

of CYPs or MAO isoforms by this scaffold itself or in com-bination with other agents (i.e., MAO inhibitors). MAO-Ainhibition and oxidative turnover were carried out spectro-photometrically using the method described by Weyler [82,83],while MAO-B inhibition was performed as reported byUebelhack et al. [82,83].

2.19 Deuterated derivativesResearchers at Auspex Pharmaceuticals, Inc. studied and dis-closed two classes of deuterated compounds which are usefulfor the management of psychological or post-traumatic stressdisorders of general formulas 37 and 38 in Figure 6 [84,85].These derivatives were synthesized and characterized to actthrough different mechanism of actions, and their ability toinhibit MAOs was also investigated. Biological data are notreported, but they stated that the decrease in activity ofMAO isoform, in some embodiments, was greater than about50% when compared to the corresponding non-isotopicallyenriched compounds.

2.20 Fluoro substituted amphetamine derivativesResearchers at the University of Tubingen proposednovel fluoro substituted derivatives of amphetamine (39in Figure 6) endowed with low neurotoxicity or hallucinogeneffects, which could have a therapeutic action againstParkinson’s disease in animal models [86,87]. They stated thatthese compounds possess a better pharmacological profileand could be administered alone or in association withother drugs (i.e., MAO inhibitors, selegiline). In the patent,they reported on synthesis, characterization data of newcompounds and biological assays to evaluate their effects on

Table 5. MAO inhibition of pyridine derivatives (continued).


(% inhibition)

MAO-B

(% inhibition)

H

O

Cl

N

N

N

1 µM 9 2

O

N

N

F

10 µM 14 63

1 µM 5 17

0.1 µM 1 8



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https://www.researchgate.net/publication/13455123_Inhibition_of_Platelet_MAO-B_by_Kava_Pyrone-Enriched_Extract_from_Piper_Methysticum_Forster_Kava-Kava?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy


https://www.researchgate.net/publication/11139270_Ecstasy_counteracts_catalepsy_in_rats_anti-parkinsonian_effect?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

H ( )n

OH

n = 8 – 2030

R1

R2

R

R3

R = CONH2, CN; R1= CH3, -CH2-CH2-;R2 = OH, NH2; R3 = polyfluoroalkyl, polyfluorophenyl

31

Y X NO

O

HN

F

F F

R

O

NO

O

R2

N

NN

R

R1

N

NO

O

R3

ONH

OO

35 36R = H, D

ON

OOR

RR

R

R

R

R

R

R

R R

R

RR

O

NR2

R3

R4

R5

O

NH

O

R1

33X = CH, N; Y = O, SO, SO2,

HOCH2CON; R = alkyl, alkoxy, NH-alkyl

34R = H, halogen, CN, halomethyl, methylthio, alkynyl;R1 = R2 = H, F, Cl, CF3; R3 = alkyl, substituted alkyl

32R1 = halogen, haloalkyl, haloalkoxy,cyano; R2 = R3 = R4 = R5 = H, halogen




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the Parkinson-induced symptoms on mice. MAO inhibitoryactivity was not specifically assessed for all compounds.

2.21 MAO inhibitors obtained from plantsFive additional inventions relate strictly to methods and com-positions involving the inhibition of MAO and/or otherenzymes using processed plant products.The Morinda citrifolia fruit juice is reported to be able to

increase the inhibition of the MAO enzyme and/or cathecol-O-methyl transferases without causing negative side effectswhen the composition is administered to a mammal. Extractsmay be also obtained from the leaves, stem, seeds and roots byfirst chopping the raw material. After removing insolublecomponents through filtering, the solvent is removed and acomplex mixture is obtained (quercetin and rutin are pre-sent in amounts by weight ranging from 0.01 to 10% of thetotal formulation or composition). This formulation couldbe administered to a patient orally, intravenously andsystemically [88].Gingko biloba extracts and compositions, which contain

20 -- 30% flavonoid glycosides, 2.5 -- 4.5% gyngkolides,2 -- 4% bilobalides, < 10% proanthocyanidines and < 10 ppmalkylphenol type compounds (EGb 761), could act as regulat-ing MAO activity agents and dopamine restoring nutraceuticalsfor the treatment of Parkinson’s disease and MPTP-inducedParkinsonism [89].

A dry and a fluid extract of Rhodiola rosea L., free of undesir-able tannins of the pyrogallol group, could possess inhibitoryactivity against MAOs and other enzymes (phosphodiesterasesand COMT) [90]. According to the method of Zhou andPanchuk-Voloshina [37], the fluid extract inhibited MAO-Awith an IC50 ~ 4.5 µM and MAO-B with an IC50 ~ 3.5 µM.

Another invention [91] relates to the use of Chinese herbsBuguzhi (Psoralea corylifolia L.) and Fuling (Poria cocosWolf.) extracts in formulations for the treatment of depres-sion and related symptoms (the weight portion of Buguzhiextract and Fuling extract ranges from 1:1 to about 1:7).The pharmaceutical composition comprises about 95% furo-coumarins (7 -- 9% of psoralen and about 6 -- 8% of isopsor-alen) and about 57 -- 62% of polysaccharides. The inventionrelates to the field of pharmaceutical composition, dietarysupplements, health products and related formulations.Kong et al. [92] reported on in vitro experiments designed totest inhibition of rat brain MAO activity by psoralen and iso-psoralen. However, the actual effectiveness thereof is not yetproven. Rat brain mitochondrial fractions were prepared fol-lowing the procedure described by Schurr and Livne [93].MAO activity was assessed by the spectrophotometer asdescribed by Yu et al. [94]. It can be noticed that oral adminis-tration of the extract at doses of 200 and 150 mg/kg sig-nificantly inhibited MAO-A and MAO-B activities intreated animals, 45.49 and 64.01%, respectively. In order to

N

N

N

O

O

R

R

R

R

R

R

O

OR

R

RR

R

R

R

R

R

37R = H, D

O

O

N

RR

R

RR

R

R

RR

R

R

R

R

R

38R = H, D

R

R

NR1

R1R

R

39R = H, F, CH3R1 = H, CH3

Figure 6. General structures of derivatives 30 -- 39 (continued).



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https://www.researchgate.net/publication/22215506_Different_inhibition_of_mitochondrial_monoamine_oxidase_from_brain_by_hashish_components?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

https://www.researchgate.net/publication/222021963_Antidepressant_activity_of_aqueous_extracts_of_Curcuma_longa_in_mice?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

https://www.researchgate.net/publication/12161461_Inhibition_of_rat_brain_monoamine_oxidase_activities_by_psoralen_and_isopsoralen_Implications_for_the_treatment_of_affective_disorders?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

investigate the antidepressant effects of the pharmaceuticalcomposition, tail suspension test [95], forced swimmingtest [30] in mice and chronic mild stress (CMS) were used.In the CMS model, the recovery of sucrose intake, inhibitionof brain MAO-A and -B activities, and reduction in cortisol

level in CMS-treated rats are used as indicators of effectivenessof antidepressant drugs [96]. The reversal of CMS-inducedbehavioral change reported is the result of MAO activity inhi-bition and normalization of the hypothalamic-pituitary-adrenalaxis hyperactivity. The antidepressant actions could make

Table 6. Ki values for both MAO isoforms by some oxazolidinone derivatives and linezolid.

Compound MAO-A Ki (mM) MAO-B Ki (mM)

SO

O

HCH3

O

NNN

F F

F 84 --

SO

O

HCH3

O

O

O

N NN

F

F F

3000 --

N NNN

O

O

HCH3

O

O

OH

F

F F

195 --

OO

O

HCH3

O

N NN

F

FF

268 --

O

O

HCH3

O

NC N NN

F

1.05 2.45

NO

O

HN

FCH3

O

NN

N N

74.20 14.20

NO

O

HN

FCH3

O

NN

N N

O

37.10 10.10

NO

O

HN

FCH3

O

NN

N N

OH

28.80 8.10

O N NO

O

HN

FCH3

O

Linezolid

6.96 0.48



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https://www.researchgate.net/publication/19237463_The_tail_suspension_test_A_new_method_for_screening_antidepressants_in_mice?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

https://www.researchgate.net/publication/13778894_Willner_P_Validity_reliability_and_utility_of_the_chronic_mild_stress_model_of_depression_a_10-year_review_and_evaluation_Psychopharmacology_Berl_134_319-329?el=1_x_8&enrichId=rgreq-99010b00-fe3a-4fdd-851e-8b273d5997e9&enrichSource=Y292ZXJQYWdlOzQ0Njc4MDI1O0FTOjEwNTAyMzE0OTE4Mjk4MkAxNDAyMDUwODc4ODEy

Buguzhi and Fuling extracts potentially valuable drugs for thetreatment of elderly depression. The components (psoralenand isopsoralen) of the produced Buguzhi extract were analyzedby HPLC, using ultraviolet as detection.Finally [97], some authors investigated the inhibitory acti-

vity against MAO-B, superoxide dismutase, NOS and AchEof an extract of Lotus enriched in procyanidins. Biologicaldata and methods are reported in Chinese.

3. New targets of MAO inhibitors

MAO inhibiting agents have also been extensively studied fortreating or preventing other pathologies they are validated for.

3.1 Isocarboxazid and migraineA pharmaceutical composition of isocarboxazid (Figure 1) in arapid-release formulation (sublingual or intranasal spray, fastdissolving tablets, biphasic or injectable formulations, viscouscontrolled release formulations), which enables the release ofisocarboxazid within 30 sec after being administered sub-sequently to onset of symptoms, has been patented for itscapability of preventing or treating migraines alone or in asso-ciation with other agents [98,99]. In fact, it has been suggestedthat MAOIs (phenelzine and isocarboxazid) may also have abeneficial effect against certain symptoms associated withmigraines, even if their mechanism of action is not very welldefined. The authors reported on a double-blind, multi-center, placebo-controlled study performed to evaluate theeffect of 20 or 40 mg doses of isocarboxazid in the acutetreatment of migraine (with or without aura) and chronictension-type headache.

3.2 Safinamide and its derivatives in the therapy of

glaucomaThe present invention is directed to compounds of generalformula 40 in Figure 7, which are MAO inhibitors, and totheir use in treating disorders of the outer retina resultingfrom acute or chronic degenerative conditions of the eye [100].Certain MAO inhibitors, especially the selective

MAO-B ones, have demonstrated possessing neuroprotective/neurorescuing properties in a number of models and to beable to inhibit induction of apoptosis. In fact, in the retina,selegiline and desmethylselegiline protected ganglion cellsfrom NMDA-induced excitotoxicity [101], while L-deprenylpreserved the same cells after optic nerve crush [102], andclorgyline had an effect on photoreceptor rhythms of diskshedding and autophagic degradation [103]. Safinamide andits synthesized derivatives were potent and selective inhibitorsof MAO-B with an IC50 in the submicromolar--nanomolarrange and no relevant effect on MAO-A in vitro (Table 7).After oral administration in mice, the tested compoundsbehaved as short-acting MAO-B inhibitors with full recoveryof activity 8 -- 16 h after a single-dose administration.The neuroprotective activity of these selective MAO-B

inhibitors was evaluated in the rat photo-oxidative-induced

retinopathy model, because cellular damage resulting fromthis kind of stress leads to cell death by apoptosis [104]. Dosingwith safinamide resulted in a dose-dependent protection ofretinal function, which was demonstrated through differentexperiments. Such compounds can be also incorporated intovarious types of ophthalmic formulations for selective deliveryto the eye.

3.3 Rasagiline and bruxismAnother invention related to a method for preventing ortreating bruxism by administering a therapeutically effectiveamount of an MAO inhibitor (rasagiline) that increases dopa-minergic activity [105]. Bruxism, otherwise known as teethclenching or grinding, is a commonly occurring conditioninvolving forceful contact between the biting surfaces of theupper and lower teeth. It has been found that compoundsthat act as dopaminergic agents can be effectively used inthe prevention and treatment of bruxism and thereby alleviateor eliminate one or more related symptoms. The compoundsof the present invention can be used in combination withother drugs that provide additional therapeutic benefits.Two patients with symptoms and evidence of bruxism weretreated with 0.5 -- 1.0 mg of rasagiline one time per day fora total of 30 days. Both treated patients exhibited a reductionor elimination of one or more symptoms or evidence ofbruxism, including the reduction or elimination of headache,jaw pain and migraine.

3.4 Rasagiline and multiple system atrophyResearchers at Teva Pharmaceuticals USA, Inc. disclosedseveral pharmaceutical compositions for the treatment andalleviation of symptoms of multiple system atrophy(MSA) [106]. This progressive neurodegenerative disease doesnot possess a determined cause, occurs sporadically and causesParkinsonism, cerebellar, pyramidal autonomic and urologi-cal dysfunction [107]. There is no specific treatment for thevarious features of MSA and therapy tends to be aimed atmitigating the Parkinsonism. While levodopa and dopamineagonists have been tested with mixed results, rasagiline dem-onstrated potent neuroprotective activity, in addition to itsMAO-B inhibition, in in vitro and in vivo experiments. Thisinhibitor, administered from 0.5 to 5 mg/day, was evaluatedin several established animal models to assess its neurotoxicityand its effects on rat motor behavior and in a mouse model ofMSA. Biological data are accurately reported.

3.5 Rasagiline and glaucomaRecently, rasagiline has been incorporated in a method fortreating subjects afflicted with glaucoma or suffering fromretinal ganglion cell (RGC) damage [108]. Glaucoma is a groupof ocular diseases characterized by progressive damage to theeye partly due to elevated intraocular pressure (IOP). Addi-tionally, it could be characterized by RGC death, axonloss and an excavated appearance of the optic nerve head.RGC death mechanisms in experimental animal models of



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glaucoma and human glaucoma have been shown to involveapoptosis [109]. Further, while L-deprenyl was suggested forthe treatment of glaucoma, the effects of rasagiline on thispathology had not previously been studied. Results showedthat rasagiline had a positive effect on RGC survival assay ina rat model of chronically elevated IOP. This indicates thattreatment with rasagiline eliminated some processes whichcontributed to ganglion death and increased protectionagainst loss of RGCs consequently reducing severity of glau-coma symptoms, for example, limiting atrophy of the opticnerve. In conclusion, the aims of this study were to presentevidence that rasagiline, administered in the form of eyedrops, penetrates the inner layers of the eye by examiningthe extent of MAO inhibition in the retina, determinerasagiline doses which inhibit MAO-A and MAO-B in the

retina, and assess the systemic penetration of rasagiline byexamining the extent of MAO inhibition in internal organssuch as liver and brain. The results showed that local MAOinhibition in the retina was higher than the level of inhibitionobserved in the liver, while inhibition of the brain enzymeswas similar to the retina ones.

3.6 Desmethylseligiline and ischemic/hypoxic

damageThe present disclosure is directed to methods for reducingthe neuronal damage associated with cerebrovascular diseasecaused by ischemia or hypoxia, such as stroke or cerebraledema, by administering R(-)-desmethylselegiline (R(-)DMS),S(+)-desmethylselegiline (S(+)DMS) or a combination of thetwo [110]. Selegiline can be used as a prophylactic treatment

Table 7. MAO inhibition of safinamide derivatives.

Compound IC50 MAO-A (mM) IC50 MAO-B (mM)

2-[[4-(3-Chloro-benzyloxy)-benzyl]-methyl-amino]-acetamide 50 0.04

(S)-2-[4-(2-fluoro-benzyloxy)-benzylamino]-propionamide 228 0.18

(S)-2-[4-(4-fluoro-benzyloxy)-benzylamino]-propionamide 93 0.06

(S)-2-[4-(3-chloro-benzyloxy)-benzylamino]-propionamide 114 0.03

(R)-2-[4-(3-chloro-benzyloxy)-benzylamino]-3-hydroxy-propionamide > 100 0.11

(S)-2-[4-hexylmethoxy-benzylamino)-propionamide 301 0.03

(S)-2-[4-(3-fluoro-benzyloxy)-benzylamino]-3-hydroxy-propionamide 100 0.14

(S)-2-[4-(3-chloro-benzyloxy)-benzylamino]-3-hydroxy-propionamide 84 0.04

(S)-2-[[4-(3-chloro-benzyloxy)-benzyl]-methyl-amino]-3-propionamide 82 0.06

40

O

N

RR1

R2

O

R4

R3

A1

A2

A3

A QN

R

R1

NH2

R2

41

42

RR7

R6

R5

R4R3

R2 R1

43

A1

A2

A3

A QN

R R1

Figure 7. General structures of novel MAO inhibitors 40 -- 43 with new therapeutic targets (for substituents, see the

corresponding reference).



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for brain tissue in a rat model when it is administered beforehypoxia/ischemia [111]. Specifically, it was found to exert protec-tive effects against ischemic/hypoxic damage in the striatum andthalamus areas of the brain, probably by reducing oxidativeneuronal damage, increasing the amount of the enzymesuperoxide dismutase and/or reducing dopamine catabolism.Selegiline is ~ 128 times more potent as an inhibitor ofMAO-B relative to MAO-A, whereas R(-)DMS is about97 times more potent as an inhibitor of MAO-B relative toMAO-A. The purity of both synthesized enantiomers wasdetermined by HPLC, mass spectroscopy, IR and 1H NMRstudies. The neuroprotective effect of both R(-)DMS and S(+)DMS was also examined using several experimental models(also compared with two other MAO inhibitors, pargylineand clorgyline). They resulted as effective neuroprotectants,inhibited transport of released dopamine at the neuronal syn-apse, and enhanced the relative activity of this neurotransmitterat the synapse. In this context, S(+)DMS is more potentthan selegiline which, in turn, is more potent than R(-)DMS.For these reasons, S(+)DMS is the most preferred drugwith regard to the treatment of hypodopaminergic conditionssuch as attention deficit/hyperactivity disorder (AD/HD).In vivo, both enantiomers demonstrated activity in inhibitingMAO-B, indicating that these enantiomers are able to crossthe BBB.

3.7 Ladostigil and MSLadostigil tartrate has been also studied (3.3 -- 5 mg/kg/day)for the treatment of MS, a chronic, inflammatory CNS dis-ease characterized by demyelization of neural axons in thebrain and spinal cord [112]. Among several hypotheses, anautoimmune one is supported by the experimental allergicencephalomyelitis (EAE) model of MS. Researchers reportedon in vitro and in vivo studies from which it is possible toextrapolate that this drug decreased both the incidence andseverity of EAE through the observation of its clinical signsin mice post EAE-induction. Moreover, dose-dependentMAO inhibition was observed (81 -- 99% inhibition ofMAO-B and 55 -- 60% inhibition of MAO-A). The ChEactivity recorded was mostly AChE (47 -- 52% of AChE inhi-bition in brain and 60 -- 65% in blood), while BuChE wasreduced to an extent of 35 -- 42%.

3.8 Clorgyline and cardiovascular diseasesA very interesting and innovative invention relates to theadministration of MAO inhibitors in the prevention andtreatment of heart failure, post-ischemic oxidative stress andmyocyte hypertrophy [113]. In spite of various known treat-ment and preventive methods, heart failure remains a majorcause of worldwide mortality. A variety of MAO inhibitorsare useful for practicing the methods of the present invention.MAO-A (or -B) inhibitors administered in accordance withthe invention are those which do not give rise to thepotentially harmful side-reaction called ‘cheese-effect’. Therationale for this therapy depends on the fact that MAO-A

is the prevalent isoform in the heart, and the majority of theenzyme is situated in the cardiomyocytes. In the peripheraltissues, MAO protects the body by oxidizing blood-derivedamines or by preventing their entry into the bloodstreambecause they have major implications in the progression ofcompensated hypertrophy to left ventricular (LV) dilationand failure. Accordingly, the present invention provides thatinhibition of MAOs, such as MAO-A, effectively preventsor retards this progression, improves myocardial function,and may also limit the loss of viable myocardial cells due toincreased oxidative stress and pro-apoptotic signaling. Theeffects of MAO-A inhibition under pharmacological condi-tions on the LV hypertension development were also tested.As described, after 3 weeks, wall thickness was increased inclorgyline-treated mice and LV function was significantly bet-ter. Moreover, mice showed reduced levels of hypertrophy.These results demonstrate that inhibiting MAO-A by admin-istering a therapeutically effective amount of an MAO inhib-itor prevents or reduces maladaptive LV hypertrophy,chamber dilation and LV dysfunction in pressure-overloadedhearts. Furthermore, the administration of the MAO-A inhib-itor clorgyline results in reduced levels of apoptosis in heartcells after 6 weeks: it is able to impact the pro-apoptotic sig-naling cascade preventing caspase-3 activation and oxidativestress in cardiomyocytes [114,115].

3.9 Lazabemide and pargyline derivatives in the

treatment of obesityThere are four patents related to a new application of alreadyknown or new MAO inhibitors for the treatment of obesityand/or associated pathologies (diabetes, cardiometabolicdisorders) [116-119]. In particular, MAO-B inhibitors, clinicallyuseful in the treatment of CNS disorders, have unexpectedlyshown an anti-obesity activity (reduction of adipose tissue,promotion of weight loss), alone or in association with anappetite suppressant or a lipase inhibitor (synergic effect).

The former patents by Jenrin Discovery disclosed this newtherapeutic target using several especially clinically testedMAO-B inhibitors and a large array of new synthesized andcharacterized derivatives reported in literature (see referencestherein). Specific relevance was attributed to synthesis, phar-maceutical formulations and MAO-B inhibitory activity oflazabemide derivatives of general formula 41 in Figure 7,which could be used for cardiometabolic disorders.

The last patents proposed a new mechanism of action for anovel scaffold of derivatives of general formula 42 in Figure 7

and pargyline derivatives (43, N-benzyl-N-propargyl-amines),which prevented the deposition of adipose tissue becauseMAO enzymes are located in a number of peripheral (non-CNS) tissues, including adipocytes. That is why it was neces-sary to limit the BBB permeation and reduce central sideeffects mediated by these compounds introducing polar func-tions (i.e., quaternary salts or acid substituents) in the phar-macophore. Biological data are not presented but theauthors stated that only representative compounds have been



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tested and showed to be active in the micromolar rangeagainst MAO-B isoform.

3.10 Befloxatone and its derivatives in the treatment

of capillary pigmentationEfficacy of inhibitors of MAO to fight the whiteness of hair isshown in another patent by L’Oreal, FR. A cosmetic processfor the capillary pigmentation of the superficial body growths,such as hair, could include the use of inhibitors of MAO(befloxatone and its derivatives) [120]. It is known that specificenzymes participating in the synthesis and degradation ofcatecholamines (MAO) are expressed by melanocytes, andtheir catabolism products could be toxic against the samecells [121].

3.11 Pargyline derivatives and hair follicle growthResearchers at Cutech s.r.l suggested new compositions (oralor topical application) comprising MAO inhibitors (pargylineand its derivatives) and a cosmetically acceptable carrier(water, alcohols, polyols, oil bodies) [122]. Surprisingly, it hasbeen observed that these inhibitors have a strong effect oncell proliferation and increase hair follicle growth. At thesame time, they delay the decline of the catagen phase andenlarge the anagen one during which the growth of the hairfollicles take place. Finally, the number of proliferative cellsis significantly increased, while cell apoptosis remains at thesame level. The results obtained in this study and supportedby detailed experimental data reveal that MAO inhibitorsmay represent effective agents for fighting many kinds ofdiseases associated with disorders of hair follicles.

4. New associations with other drugs ofclassical MAO inhibitors

While there is only one patent dealing with selective MAO-Binhibitors, different associations among MAO-A inhibitorsand other drugs have been published.

An alternative triple therapy, which comprehends a selec-tive re-uptake inhibitor of serotonin, an MAO inhibitor anda phosphodiesterases inhibitor (in a composition containingglabridin, resveratrol and quercetin), has been proposed fortreating mental disorders [123].

Moreover, two inventions provided pharmaceuticalcompositions comprising droxidopa ((2R,3S)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropanoic acid) alone orin association with MAO inhibitors and others drugs for thetreatment of orthostatic hypotension [124], mood disorders(depression), sleep disorders (narcolepsy, insomnia) or AD/HD [125]. Droxidopa is a psychoactive drug and a syntheticamino-acid precursor which acts as a crossing BBB prodrugto the neurotransmitters NA and epinephrine [126].

On the contrary, new indolylalkyl derivatives of pyrimidi-nylpiperazine [127] are reported to be useful for alleviating,preventing and treating anxiety, depression and sexual

dysfunction due to their effect on the serotonin system.They have been synthesized and characterized for a monother-apy or a co-therapy in conjunction with MAO inhibitors andother drugs.

Researchers at Ellneuroxx Ltd disclosed novel dihydroxy-phenylalanine derivatives and pharmaceutical compositionscontaining an association of these compounds with sele-giline and other drugs for the treatment of movement andneurodegenerative disorders [128].

Janssen Pharmaceutica, N.V. proposed new carbamatederivatives to be used in association with a conventional anti-depressant (in particular, RIMA) [129]. These compounds havebeen shown to have antidepressant action and an activating orenergizing effect in both animal models and in studies inhumans, even though the precise mechanism of action is notcompletely understood.

Dimebolin hydrochloride is an antihistamine drug whichhas been used clinically in Russia since 1983. Recently, dime-bolin has attracted renewed interest after showing positiveeffects on people suffering from Alzheimer’s disease throughmultiple mechanisms of action [130]. Subsequently, it hasbeen associated with a reversible inhibitor of MAO-A inclinical therapy for the treatment of Alzheimer’s disease [131].

At Cypress Biosciences, Inc., researchers studied the combi-nation of antidepressants (i.e., RIMAs) with a 5-HT antagonistto increase the tolerability of the latter compound [132].

Inventors at the University of Montana [133] have discov-ered that amphetamines and their derivatives, alone or in asso-ciation with MAO inhibitors or tricyclic antidepressant, couldreduce, if administered within 16 h, the occurrence of neuro-nal cell damage and death caused by transient cerebral hyp-oxia and ischemia. In the patent, in vivo and in vitroexperimental models and data were reported to justify thedose-dependent neuroprotective response.

Researchers at Janssen Pharmaceutica N.V. [134] proposednovel carbamate derivatives (25 -- 400 mg/day) with antide-pressant activity, which could also be useful, in associationwith MAO inhibitors, for the treatment of sexual dysfunctionin human female or males. The effect reported was confirmedby literature studies [135]. The precise mechanism of action isnot completely understood, but they were assayed in an animalmodel that supported an increased central catecholaminergicactivity after administration.

Researchers at Richter Gedeon Vegyeszeti Gyar RT pro-posed a new combination between voltage-gated sodiumchannel blocker and an MAO-B inhibitor to gain anincrease effect in several pathologies [136] (Alzheimer’s disease,Parkinson’s disease, chronic pain and epilepsy) [137]. In thereported experiments (inhibition of the spinal reflex, inhibi-tion of maximal electroshock seizures, behavioral study,Morris maze, in vivo neuroprotective effect in an entorhinal cor-tex lesion model), they surprisingly found a marked increase inthe sodium channel blocking activity of some compoundswhen an MAO-B inhibitor (rasagiline or (R)-deprenyl) wassimultaneously administered. In particular, an increased level



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of cholinergic synapses, which may be particularly advantageousin Alzheimer’s disease, followed the treatment.

5. New administration routes of classicalMAO inhibitors

In order to achieve prolonged and useful levels of drug in theblood without reaching adverse effects, some authors focusedtheir attention on the improvement of the manufacturing ofdosage forms (controlled-release drug delivery systems) oftransdermal patches of rasagiline [138].

6. New synthetic process of MAO inhibitors

It is known that the large scale preparations of safinamideand ralfinamide according to the methods described inthe prior art contain two undesired impurities, that is,(S)-2-[3-(3-fluorobenzyl)-4-(3-fluorobenzyloxy)-benzylamino]propanamide and (S)-2-[3-(2-fluorobenzyl)-4-(2-fluoroben-zyloxy)-benzylamino]propanamide, respectively [139,140]. Thisfact is of particular relevance as these impurities showed avery high toxicity against the CYP system which is stronglyundesirable in early preclinical phase. This patent related toa new synthetic process for the large scale production of safi-namide and ralfinamide (their salts, enantiomers and racemicmixture) with high purity degree (content of benzyl deriva-tives impurities lower than 0.01 -- 0.03%), better yields andreaction work-up, and a safer biological profile. The syntheticschemes were accurately described.

7. Expert opinion

The patents reported, published starting from July 2005 tothe end of 2009, are tripled in comparison with the previousreview [18] and show that the interest in this field is constantlyincreasing. Furthermore, the description of the three-dimensional crystallographic structure of the hMAO-B andmore recently of the hMAO-A led to the discovery of newlead compounds useful as MAO selective inhibitors.Currently, the major interest is devoted to the study

of MAO-B inhibitors used as agents for the treatment ofParkinson’s disease, Alzheimer’s disease and neurologicaldisorders probably due to the progressive ageing of the

population. Several drugs with MAO-A inhibitory activityare used for the treatment of depression and new psychiatricdisorders. The new compounds, obtained some by synthesisand others by extraction methods of processed plant, are char-acterized by different structures (b-carbolines, aminoindanes,isoxazoles, diterpenes, imidazole derivatives, dithiolethiones,oxoisoaporphines, prolinamide derivatives, benzoheteroaryl-sulfonamides, benzopyran derivatives, pyrazole and pyridinederivatives, oxazolidinones) and by reversible or irreversibleand selective inhibitory activity.

The reported patents regarding the new target of MAOinhibitors, alone or in association with other drugs, high-lighted the role of radical scavengers of the MAO inhibitorsin preventing and treating migraines, glaucoma, bruxism,MSA, ischemic/hypoxic damage, MS, cardiovascular disease,obesity, and pigmentation and growth of hair follicles.

Moreover, some patents licensed new administration routesor synthetic processes to enhance the activity of alreadyknown MAO inhibitors.

Finally, we draw attention to results obtained by usinghMAOs in comparison to those evaluated with rMAOs [141]

or established animal models. In fact, in the literature, humanbrain, liver and blood platelets have been little used as hMAOsources to screen inhibitors, because of the easy accessibility ofrat and bovine brain or liver for in vitro studies. But species-dependent differences [5] (single amino-acid substitutionsmay induce deep changes in the secondary and tertiary struc-tures of these isoforms) have been reported by differentauthors for several classes of compounds [142]. Therefore, thedivergences found, after extrapolating data on MAO inhibi-tion from different species sources to the human enzyme,could have a deep impact on the development of new andselective hMAO inhibitors.

Dedication

This paper is dedicated to the memory of our colleagueFrancisco Orallo.

Declaration of interest

The authors state no conflict of interest and have received nopayment in preparation of this manuscript.



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AffiliationAdriana Bolasco†1, Simone Carradori2 &

Rossella Fioravanti2

†Author for correspondence1Professor,

Dipartimento di Chimica e

Tecnologie del Farmaco,

Universita degli Studi di

Roma “La Sapienza”,

P.le Aldo Moro,

5 00185 Rome, Italy

Tel: +39 6 49913923;

E-mail: [email protected] di Chimica e

Tecnologie del Farmaco,

Universita degli Studi di

Roma “La Sapienza”,

P.le Aldo Moro,

5 00185 Rome, Italy



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Focusing on new monoamine oxidase inhibitors

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