1134 Sulfur Analogs of Pyrimidine

Bases: Synthesis of 2-Alkylthio-and 4-Alkylthio-5-bromouracils and In Silico Evaluation of Their

Biological Activity

Vol 50

Grażyna Bartkowiak,* Elżbieta Wyrzykiewicz, and Grzegorz Schroeder

Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznań, Poland

*E-mail: gbartkow@amu.edu.pl

Received March 13, 2011DOI 10.1002/jhet.1098

Published online 27 August 2013 in Wiley Online Library (wileyonlinelibrary.com).

The general reactivity of alkylthiouracils under bromination conditions has been examined. Twenty2-alkylthio- and 4-alkylthio-5-bromouracils of potential biological activity have been prepared. Thestructures of these compounds were confirmed by elemental and spectral (UV/vis, IR, and 1H-NMR)analyses. The pharmacotherapeutical potential of the synthesized compounds has been predicted usingPrediction of Activity Spectra for Substances (i.e., PASS) program.

J. Heterocyclic Chem., 50, 1134 (2013).

INTRODUCTION

Thiouracils are an important class of modifiednucleobases because of their spectroscopic properties andbiological activity. 2-Thiouracil, 4-thiouracil, 5-methyl-2-thiouracil (i.e., 2-thiothymine), and 2,4-dithiouracilhave been found as minor components of nucleic acids1–3. 2-Thiouracil and 4-thiouracil are well known for theirpharmacological applications as anticancer agents [4], [5]as well as in heart diseases treatment [6], [7]. 6-Methyl-2-thiouracil and 6-propyl-2-thiouracil have been known tobe effective antithyroid drugs [8]. A series of derivativesof 2-thiouracil and 4-thiouracil can also be found in manypharmacological drugs for cancer [9], HIV [10], andthyroid [11], [12] treatments.In continuation of our works on bromothiouracil deriva-

tives [13] and in search for novel biologically activecompounds, we have performed a series of brominationreactions of alkyl derivatives of 2-thiouracil (I–V), 2-thio-6-methyluracil (VI–X), 2-thioorotic acid (XI–XV), 4-thio-uracil (XVI–XX), and 4-thio-6-methyluracil (XXI–XXV).

© 2013 HeteroC

To ensure good cell barrier permeability in order to improvepharmacokinetic properties of brominated thiouracils, thesulfur atoms in the substrates chosen have been substitutedby long alkyl chains containing 10–18 carbon atoms,that is, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl,and n-octadecyl. The sulfur position was 2 or 4 and thesubstituent in position 6 of uracil ring was hydrogen, methyl,or carboxylic group (Scheme 1). The 2-alkylthiouracils and2-alkylthioorotic acids have been obtained earlier [14] andanalyzed as to their antibacterial activity; 4-alkylthiouracilshave also been synthesized previously [15].

The aim of our work was to introduce a substituent tothe alkylthiouracil molecule that will enable further easymodification through the substitution reaction. Bromineatom was chosen as it was known to cause formation of areactive site in the molecule as a result of making a polarbond. It was of interest to evaluate the easiness of introduc-ing bromine atom to position 5 of alkylthiouracil ring whenthe electron-donating group is located on the sulfur atomS-2 or S-4 and to observe the effect of the character of sub-stituent in position 6 (neutral hydrogen, electron-donating

orporation

Scheme 1. Bromination of 2-alkylthiouracils (I–X), 2-alkylthiooroticacids (XI–XV), and 4-alkylthiouracils (XVI–XXV).

September 2013 1135Sulfur Analogs of Pyrimidine Bases: Synthesis of 2-Alkylthio- and4-Alkylthio-5-bromouracils and In Silico Evaluation of Their Biological Activity

CH3, or electron-withdrawing COOH) on brominationeffectiveness. It was also interesting to predict possiblebiological activity of alkylthiouracils after insertingbromine atom to position 5 of the molecule.Biological activity of 2- or 4-alkylthio-5-bromouracils

can be predicted by means of computer-assisted methods[16]. The computer-aided prediction of possible activitiesof resulting compounds has recently attracted a lot ofattention [17] because it permits saving a lot of time andfinancial expenses (unavoidable during biological testsin vivo and in vitro) and makes it possible to eliminatepotentially toxic, harmful, or pharmacologically unsafecompounds. Among the computer programs used for theestimation of biological activity spectrum of substances,particularly impressive is the Prediction of Activity Spectrafor Substances (PASS) program. A basic principle of thisprogram is that the activity of the chemical compound isa function of its structure, and by comparing the structureof a new substance with the structures of compounds withknown activity, it is possible to predict if the new com-pound may be useful for the treatment of a particulardisease.The computer system PASS Inet encloses data of about

3678 possible activities, including pharmacological effects,mechanisms of action, and adverse side effects (e.g., toxic-ity and mutagenicity) and predicts biological activityspectrum of a compound studied on the basis of its struc-tural formula. The leave-one-out (LOO) cross-validationhas been used to validate this prediction method. Theprediction is based on the training set containing more than260,000 compounds of known biological activity. The

Journal of Heterocyclic Chemi

mean accuracy of LOO cross-validation is about 90%,and the activity is described qualitatively (active orinactive). The results of prediction are presented as the listsof activities with appropriate probable activity (Pa) andprobable inactivity (Pi) in descending sequence of thedifference (Pa − Pi) > 0. If Pa for the particular type ofactivity is more than 0.7, the compound is very likely toexhibit this kind of activity in tests; however, it is alsohighly probable that similarly active pharmaceutical agentsare already known. If 0.5 < Pa < 0.7, the compound islikely to reveal this type of activity, but with lower proba-bility, and the compound is supposedly not very similar toa known pharmaceutical agent. If Pa < 0.5, the compoundis unlikely to reveal this kind of activity; however, if thisactivity would be confirmed in experiment, the compoundmight be a precursor of the new class of pharmacologicallyvaluable compounds.

RESULTS AND DISCUSSION

The biological activities of compounds 1–20 obtainedwere predicted using the computer program PASS [18].The bromination of alkylthiouracils was performed at roomtemperature using a 10% (v/v) bromine solution intetrachloromethane and a suspension of respective thioura-cil derivative in tetrachloromethane. 2-Alkylthiouracils I–X underwent the reaction easily in a short reaction time(30–60 min) and at a sixfold excess of bromine. Theproducts 1–10 were easily purified through crystallizationfrom methanol. 4-Alkylthiouracils XVI–XXV reacted withbromine with difficulty and demanded higher excess ofbromine (30-fold) or longer reaction times (to 24 h).Extension of reaction time or high excess of brominenot only leads to a mixture of products containing the target4-alkyl-5-bromothiouracils (11–20, about 20%) but also5-bromouracil (about 30%) and intact substrate, that is,4-alkylthiouracil (about 50%). Isolation of pure 11–20 wasrealized by column chromatography on columns filled withsilica gel 60 and eluted with chloroform (100%) and chloro-form–methanol with increasing percentage of CH3OH from1 to 30%. The eluate compositions were monitored by thinlayer chromatography (TLC) using chloroform–methanol9:1 as a mobile phase. The products 11–20 were eluted first[Rf = 0.68 (11–15); Rf = 0.72 (16–20)], next unreactedsubstrate (Rf = 0.45–0.55), and finally dealkylthiolated sideproduct, that is, 5-bromouracil (Rf = 0.25) or 5-bromo-6-methyluracil (Rf = 0.31), respectively. The physicochemicalproperties of 1–20 are given in Table 1.

The bromination of 2-alkylthioorotic acids XI–XVfailed. Using the same reaction conditions as foralkylthiouracils I–X or XVI–XXV, we did not obtain 2-alkylthio-5-bromoorotic acid but only unreacted substrateswere recovered. Increasing the bromine excess to 50:1 andthe reaction time to 3–5 days resulted in the appearance of

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Table 1

Physical and analytical data of compounds 1–20.

Compound n Formula (MW) Yield (%) m.p. (°C) Rf TLCa

Analysis (calcd./found, %)

C H N

1 9 C14H23N2OSBr (347.32) 51 100–102 0.67 48.41/47.85 6.67/6.29 8.07/7.622 11 C16H27N2OSBr (375.37) 45 104–106 0.67 51.20/51.13 7.25/7.27 7.46/7.193 13 C18H31N2OSBr (403.43) 36 109–112 0.68 53.59/53.31 7.75/7.42 6.94/6.724 15 C20H35N2OSBr (431.48) 35 106–108 0.68 55.67/55.39 8.18/8.02 6.49/6.175 17 C22H39N2OSBr (459.53) 13 104–105 0.70 57.50/57.29 8.55/8.43 6.10/5.886 9 C15H25N2OSBr (361.35) 55 110–113 0.77 49.86/49.44 6.97/6.99 7.75/7.567 11 C17H29N2OSBr (389.40) 58 110–111 0.80 52.44/51.99 7.51/7.81 7.19/6.998 13 C19H33N2OSBr (417.45) 60 112–116 0.80 54.67/54.32 7.97/7.70 6.71/6.459 15 C21H37N2OSBr (445.51) 57 113–115 0.80 56.62/56.33 8.37/8.79 6.29/6.0110 17 C23H41N2OSBr (473.56) 40 114–116 0.80 58.34/58.09 8.73/8.42 5.92/5.8811 9 C14H23N2OSBr (347.32) 20 76–78 0.68 48.41/48.50 6.67/6.68 8.07/7.7912 11 C16H27N2OSBr (375.37) 18 78–80 0.68 51.20/50.91 7.25/6.95 7.46/7.5813 13 C18H31N2OSBr (403.43) 21 79–82 0.68 53.59/53.33 7.75/8.00 6.94/7.1214 15 C20H35N2OSBr (431.48) 22 80–83 0.68 55.67/55.60 8.18/7.99 6.49/6.4215 17 C22H39N2OSBr (459.53) 20 81–84 0.68 57.50/57.35 8.55/8.48 6.10/6.0116 9 C15H25N2OSBr (361.35) 23 87–89 0.72 49.86/49.57 6.97/7.20 7.75/7.5617 11 C17H29N2OSBr (389.40) 18 88–90 0.72 52.44/52.30 7.51/7.69 7.19/7.0118 13 C19H33N2OSBr (417.45) 22 89–92 0.72 54.67/54.59 7.97/7.88 6.71/6.6019 15 C21H37N2OSBr (445.51) 19 88–91 0.72 56.62/56.54 8.37/8.29 6.29/6.3520 17 C23H41N2OSBr (473.56) 18 87–90 0.72 58.34/58.09 8.73/8.65 5.92/5.87

aSolvent (mobile phase): CHCl3 CH3OH (9:1).

1136 G. Bartkowiak, E. Wyrzykiewicz, and G. Schroeder Vol 50

respective 2-alkylthio-5-bromouracil in the reaction prod-ucts. The reaction time longer than 6 days leads to theformation of almost pure 2-alkylthio-5-bromouracil usingthe same or higher excess of bromine. It proves that decar-boxylation of the starting 2-alkylthioorotic acid takes placeat the attempted bromination.The UV/vis spectra of 1–5 (Table 2) show three absorp-

tion bands of λmax in the range 220.0–294.2 nm andbatochromic shifts relative to the corresponding UV/visdata for the substrates. The electronic spectra of 6–10reveal three bands in the range 210.0–292.8, alsobatochromically shifted with respect to the 205.0–286.4nm for the substrate. The UV/Vis spectra of 11–15 showλmax in the range 210.4–290.0, whereas for 16–20, thecorresponding range is 217.6–290.0.The IR spectra of all compounds studied (Table 2) show

absorption bands of medium intensities in the two charac-teristic regions: 1041–1017 cm−1 and 670–621 cm−1,assigned to νC Br vibrations (Table 2). These bands arenot found in the IR spectra of substrates. Intensive νC O

bands are present in the range 1650–1660 cm−1 andνC5=C6 between 1557 and 1620 cm−1.The 1H-NMR spectra (Table 3) of compounds 1–20 do

not show the characteristic signals of proton at C5 of thepyrimidine rings when referred to the 1H-NMR spectra ofthe substrates (i.e., doublets at 6.22–6.25 ppm for 2-alkylthiouracils I–V [14] and 4-alkylthiouracils XVI–XX[15] and singlets at 7.26–7.27 ppm for 2-alkylthio-6-methyluracils (VI–X) [14] and 6.10 ppm for 4-alkylthio-6-methyluracils XXI–XXV [15]), which confirms that the

Journal of Heterocyclic Chemi

bromination reaction is completed and the product issufficiently pure.

The introduction of Br into C5 position of pyrimidinering causes a change in the C6-H signal from doublet at7.84–7.85 ppm for 2-alkylthiouracils I–V into singlet at8.12–8.17 ppm for 2-alkylthio-5-bromouracils (1–5) andresults in replacement of a C6-H doublet at 7.3–7.4 ppmfor 4-alkylthiouracils XVI–XX by a singlet at 8.02–8.03for 4-alkylthio-5-bromouracils 11–15 (downfield shift).The C6-CH3 signals are shifted downfield under theinfluence of bromine atom in position C5 in the spectraof 2-alkylthio compounds [from 2.25–2.27 ppm (VI–X)to 2.54–2.58 ppm (6–10)] and slightly upfield shift in thespectra of 4-alkylthio compounds [from 2.30–2.35 ppm(XXI–XXV) to 2.28 ppm (16–20)]. The influence ofbromine atom in C5 position on the chemical shift ofSCH2 triplet is not very significant; it causes a ∼0.1 ppmdownfield shift for 2-thiouracil and no effect in the spectraof 4-thiouracil derivatives.

For all synthesized compounds (1–20), their biologicalactivity spectra were predicted using PASS [19], [20],and the types of activities with the highest probability(focal activities) for particular compounds were selected.The values obtained for representative compounds (theones with n-decyl group were chosen) are presented inTable 4 It should be noted that the results for the otheralkyl groups were very similar. According to the dataobtained, 5-bromo-2-thiouracil derivatives are likely to bespermicidic, whereas 5-bromo-4-thiouracil derivatives areexpected to be mucomembraneous protectors and antiviral

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Table 2

UV and IR spectral data of compounds 1–20.

Compound

UV/vis IR (cm−1)

λmax (nm) Log ε νC O νC Br νC5 = C6 νC S

νN3C4, νC4C5

δN1C2N3νC2N3, νN1C6

1 292.6 3.87 1658 1019 1557 2525 1471 715248.4 3.84 669 1428220.0 3.95

2 292.2 3.86 1658 1018 1557 2532 1472 715250.6 3.84 669 1428220.0 3.97

3 294.2 3.85 1658 1019 1558 2540 1472 715250.2 3.83 670 1428220.0 3.94

4 294.2 3.84 1657 1019 1558 2541 1472 715250.6 3.82 1428219.8 3.93 670

5 294.0 3.84 1657 1020 1575 2541 1472 716∼250 3.82 670 1428220.0 3.92

6 290.0 3.88 1650 1041 1573 2456 1469 723248.0 3.92 1423210.4 3.81 621

7 289.4 3.83 1650 1035 1620 ∼2450 1470 721247.8 3.85 624 1423

∼210 3.778 291.6 3.83 1650 1020 1620 ∼2450 1473 721

247.8 3.81 628 1423∼210 3.96

9 292.8 3.81 1660 1018 1570 ∼2450 1471 720247.8 3.82 629 1430

∼210 3.9510 280.6 3.80 1639 1017 1566 ∼2450 1466 721

250.2 3.78 1423210.0 4.10 630

11 280.8 3.81 1649 1025 1607 ∼2600 1470 717249.8 3.79 665 1425217.6 4.09

12 280.8 3.81 1650 1025 1607 ∼2600 1470 717250.6 3.78 667 1428218.4 4.08

13 281.4 3.79 1652 1025 1605 ∼2600 1471 717250.2 3.72 666 1432218.4 4.05

14 281.4 3.75 1652 1026 1605 ∼2600 1472 718250.2 3.72 664 1434218.4 4.02

15 281.4 3.74 1652 1023 1605 ∼2600 1472 718250.2 3.71 662 1436218.4 4.01

16 289.6 3.63 1659 1020 1601 2576 1468 725248.2 3.52 661 1440210.4 3.91

17 290.0 3.64 1659 1026 1600 2580 1468 725247.8 3.50 660 1440210.6 3.93

18 290.0 3.62 1658 1026 1600 ∼2600 1469 725248.0 3.50 662 1440210.8 3.90

19 290.4 3.62 1657 1026 1600 ∼2600 1468 725248.1 3.48 662 1445210.8 3.90

20 290.4 3.61 1657 1026 1600 ∼2600 1470 726248.1 3.48 1446210.9 3.89 663

September 2013 1137Sulfur Analogs of Pyrimidine Bases: Synthesis of 2-Alkylthio- and4-Alkylthio-5-bromouracils and In Silico Evaluation of Their Biological Activity

Journal of Heterocyclic Chemistry DOI 10.1002/jhet

Table 4

Pa values for predicted biological activities of compounds 1, 6, 11, and 16 as representative examples.

Compound Focal predicted activity (Pa > 0.6)

1 Spermicide (0.800), protein kinase (CK1) inhibitor (0.740), thioredoxin inhibitor (0.622)6 Spermicide (0.746), leukopoiesis stimulant (0.719), antiulcerative (0.686), antiviral (Arbovirus) (0.657)11 Mucomembranous protector (0.731), antineoplastic (0.675), antiviral (Arbovirus) (0.662)16 Leukopoiesis stimulant (0.723), thrombocytopoiesis inhibitor (0.669), mucomembranous protector (0.689), antiviral (Arbovirus)

(0.675), protein kinase (CK1) inhibitor (0.645)

Table 31H‐NMR shifts of 1–20 (ppm).

CompoundC6‐H(s, 1H)

C6‐CH3(s, 3H)

S–CH2(t, 2H)

SCH2CH2(quint, 2H)

(CH2)x(s broad, 2×H)

–(CH2)xCH3(t, 3H)

1 8.17 – 3.22 1.72 1.26 0.882 8.15 – 3.20 1.72 1.26 0.883 8.14 – 3.18 1.72 1.26 0.884 8.12 – 3.17 1.71 1.26 0.885 8.12 – 3.17 1.71 1.26 0.886 – 2.54 3.30 1.72 1.26 0.887 – 2.58 3.24 1.72 1.26 0.888 – 2.56 3.18 1.72 1.26 0.889 – 2.54 3.17 1.71 1.26 0.8810 – 2.54 3.17 1.71 1.26 0.8811 8.03 – 3.05 1.62 1.25 0.8512 8.03 – 3.02 1.62 1.25 0.8513 8.03 – 3.00 1.62 1.25 0.8514 8.02 – 3.00 1.62 1.25 0.8515 8.02 – 3.00 1.62 1.25 0.8516 – 2.28 3.04 1.59 1.20 0.8017 – 2.28 3.02 1.59 1.20 0.8018 – 2.28 3.00 1.59 1.20 0.8019 – 2.28 3.00 1.59 1.20 0.8020 – 2.28 3.00 1.59 1.20 0.80

Spectra determined in dimethyl‐d6 sulfoxide at 25°C and chemical shifts are reported in ppm (δ) downfield from tetramethylsilane.

1138 G. Bartkowiak, E. Wyrzykiewicz, and G. Schroeder Vol 50

agents against Arbovirus. The compounds studied, which have6-methyl substituent, that is, 2-alkylthio and 4-alkylthio-5-bromo-6-methyluracils, are expected to act as potentleukopoiesis stimulants. It ought to be pointed out thatthe group of compounds (1–20) comprises also potentialantineoplastic and antiulcerative agents as well as vari-ous enzyme inhibitors.

CONCLUSIONS

The reactions of 2-alkylthiouracils and 4-alkylthiouracils1–10 with sixfold excess of bromine at room tem-perature led easily to the corresponding 2-alkyl-5-bromouracils. To obtain 4-alkyl-5-bromouracils 11–20,

Journal of Heterocyclic Chemi

higher excess of bromine (30-fold) is needed anddealkylthiolation as a side reaction occurs. Directbromination of 2-alkylthioorotic acids XI–XV doesnot occur in analogous conditions. The use of 50-foldbromine excess and long reaction time (several days)leads to the formation of corresponding 2-alkylthio-5-bromouracils. It is suggested that the first step of thereaction is decarboxylation of 2-alkylthioorotic acid tothe 2-alkylthiouracil, which undergoes bromination inthe next step consecutively.

The results obtained using PASS program for predictionof activity spectrum of substances on the basis of theirchemical structure show the possibility of pharmacologicalapplication of compounds 1–20.

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September 2013 1139Sulfur Analogs of Pyrimidine Bases: Synthesis of 2-Alkylthio- and4-Alkylthio-5-bromouracils and In Silico Evaluation of Their Biological Activity

EXPERIMENTAL

The purity of compounds 1–20 was determined by meltingpoints, TLC, and elemental analyses. Melting points(uncorrected) were determined using Boetius microscopeapparatus. Rf values refer to silica gel F254 TLC plates(Merck) developed with CHCl3 CH3OH 9:1 and observedunder UV light (λ = 254 nm). UV/vis spectra were recordedwith a Specord UV/vis spectrophotometer in methanol. IRspectra were recorded with a FTIR Bruker ISF-113 spectro-photometer in KBr pellets. The 1H-NMR spectra were mea-sured in DMSO-d6 as a solvent with Varian Gemini 300(300 MHz) spectrometer at ambient temperatures using TMSas an internal standard. Chemical shifts are given in δ scale(ppm). Elemental analyses were performed with Vector EuroEA 3000 analyzer.

2-Alkylthiouracils (I–V), 2-alkyl-6-methyluracils (VI–X), and2-alkylthioorotic acids (XI–XV) were obtained according to ref.[14]. 4-Alkylthiouracils (XVI–XXV) were also obtained using aprocedure described earlier [15].

Synthesis of 5-bromo-2-alkylthiouracils 1–10. A sample (1mmol) of appropriate 2-alkylthiouracil (1–8) was suspended in20 mL of CCl4 and stirred magnetically at room temperature.To the stirred suspension, a solution of Br2 in CCl4 (10% v/v)was added dropwise (6 equivalents of bromine for 1 equivalentof 2-alkylthiouracil). The reaction mixture was next stirred atroom temperature for 30 min. The obtained crude product wasfiltered off, washed twice with warm tetrachloromethane (2 × 5mL) and dried. The resulting powder was crystallized frommethanol.

Synthesis of 5-bromo-4-alkylthiouracils 11–20. A solutionof bromine in tetrachloromethane (10% v/v) was addeddropwise to the stirred solution of 4-alkylthiouracil (1mmol) in 20 mL CCl4 at room temperature, using 30-foldexcess of bromine (30 equivalents of bromine for 1equivalent of 4-alkylthiouracil). The obtained reaction mixturewas stirred magnetically for 30–60 min. The precipitate werefiltered off, washed twice with warm CCl4 (2 × 5 mL) and dried.The crude product after column-chromatographic isolation wascrystallized from methanol.

Journal of Heterocyclic Chemi

REFERENCES AND NOTES

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[2] Yaniv, M.; Folk, W. R. J Biochem 1979, 250, 3243.[3] Jeffrey, G. A.; Saenger, W. Hydrogen Bonding in Biological

Structures; Springer: New York, 1991.[4] Miller, W. H.; Robin, R. O.; Astwood, E. B. J Am Chem Soc

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2001, 35, 417.[7] Ortiga-Carvalho, T. M.; Hashimoto, K.; Pazos-Moura, C. C.;

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[8] Palumbo, A.; d’Ishia, M. Biochem Biophys Res Commun2001, 282, 793.

[9] Sulkowska, A.; Równicka, J.; Bojko, B.; Sulkowski, W. J MolStruct 2003, 651, 133.

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[11] Elias, A. N. Med Hypotheses 2004, 62, 431.[12] Antoniadis, C. D.; Corban, G. J.; Hadjikakou, S. K.; Hadjiliadis,

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[14] Wyrzykiewicz, E.; Bartkowiak, G.; Nowakowska, Z.; Kędzia,B. Farmaco 1993, 48, 979.

[15] Wyrzykiewicz, E.; Nowakowska, Z.; Bartkowiak, G.; Kędzia,B. Pol J Chem 1997, 71, 201.

[16] Poroikov, V. V.; Filimonov, D. A. In Rational Approaches toDrug Design; Holtje, H.-D.; Sippl, W., Eds.; Prous Science: Barcelona,2001; p 403.

[17] Poroikov, V. V.; Filimonov, D. A.; Ihlenfeldt, W.-D.;Gloriozova, T. A.; Lagunin, A. A.; Borodina, Y. V.; Stepanchikova, A.V.; Nicklaus, M. C. J Chem Inf Comput Sci 2003, 43, 228.

[18] PASS program was available online at http://195.178.207.203/PASS (accessed on February 2011); currently at http:// www.pharmaexpert.ru/PASSOnline/

[19] Poroikov, V. V.; Filimonov, D. A. In Predictive Toxicology;Helma, C., Ed.; Taylor & Francis: New York, 2005; p 459.

[20] Lagunin, A. A.; Gomazkov, O. A.; Filimonov, D. A.; Gureeva,T. A.; Kugaevskaya, E. V.; Eliseeva, Y. E.; Solovyeva, N. I.; Poroikov, V.V. J Med Chem 2003, 46, 3326.

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