Bioorganic & Medicinal Chemistry Letters 21 (2011) 4836–4843

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Bioorganic & Medicinal Chemistry Letters

journal homepage: www.elsevier .com/ locate/bmcl

Biphenyl/diphenyl ether renin inhibitors: Filling the S1 pocket of reninvia the S3 pocket

Jing Yuan a,⇑, Robert D. Simpson a, Wei Zhao a, Colin M. Tice a, Zhenrong Xu a, Salvacion Cacatian a, Lanqi Jia a,Patrick T. Flaherty a, Joan Guo a, Alexey Ishchenko a, Zhongren Wu a, Brian M. McKeever a, Boyd B. Scott a,Yuri Bukhtiyarov a, Jennifer Berbaum a, Reshma Panemangalore a, Ross Bentley b, Christopher P. Doe b,Richard K. Harrison a, Gerard M. McGeehan a, Suresh B. Singh a, Lawrence W. Dillard a, John J. Baldwin a,David A. Claremon a

a Vitae Pharmaceuticals, 502 West Office Center Drive, Fort Washington, PA 19034, USAb GlaxoSmithKline, 709 Swedeland Road, King of Prussia, PA 19406, USA

a r t i c l e i n f o

Article history:Received 18 April 2011Revised 8 June 2011Accepted 10 June 2011Available online 17 June 2011

Keywords:Renin inhibitorsHypertensionBiphenylDiphenyl etherStructure-based designX-ray crystallography

0960-894X/$ - see front matter � 2011 Elsevier Ltd.doi:10.1016/j.bmcl.2011.06.043

⇑ Corresponding author.E-mail address: jyuan@vitaerx.com (J. Yuan).

a b s t r a c t

Structure-based design led to the discovery of a novel class of renin inhibitors in which an unprecedentedphenyl ring filling the S1 site is attached to the phenyl ring filling the S3 pocket. Optimization for severalparameters including potency in the presence of human plasma, selectivity against CYP3A4 inhibitionand improved rat oral bioavailability led to the identification of 8d which demonstrated antihypertensiveefficacy in a transgenic rat model of human hypertension.

� 2011 Elsevier Ltd. All rights reserved.

The renin angiotensin aldosterone system (RAAS) is a centralmechanism by which mammalian blood pressure is controlled.1

The aspartyl protease renin performs the first and rate-limitingstep in the RAAS, cleavage of the decapeptide angiotensin I fromthe N-terminus of the glycoprotein angiotensinogen (Fig. 1).Although renin has long been viewed as a desirable target for anti-hypertensives, identification of orally bioavailable, low molecularweight inhibitors proved challenging. Efforts by many researchgroups during the 1980s focused on modified peptides, leading tothe identification of potent compounds such as remikiren (1).2,3

However, none of these compounds was ultimately deemed suit-able for full development.4 Finally in 2007, Novartis brought thefirst renin inhibitor, aliskiren (2), to market.5,6

Comparison of the structural features of remikiren (1, Fig. 1) tothe amino acid residues surrounding the cleavage site of the natu-ral substrate angiotensinogen illustrates the correspondencebetween groups occupying the S1, S2 and S3 pockets7 in therespective structures (PDB code: 3D91). Publication of the firstX-ray structure of human renin (PDB code: 1RNE)8 revealed thatthe S1 and S3 pockets form a contiguous superpocket, suggesting

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that it might be possible to attach the group filling S3 to the groupoccupying S1. Early attempts to reduce this idea to practice led tocompounds with substantially reduced potency.9,10 However,extensive structure-based design work at Ciba-Geigy, includingdeletion of the peptide backbone, led to the identification of2.11–13 The X-ray crystal structure of 2 bound to renin (PDB code:2V0Z) confirmed that the methoxyphenyl group occupies S3 andthat the two i-Pr groups occupy S1 and S10.

We recently described the discovery of potent, orally bioavail-able alkyl amine renin inhibitor 3 (Fig. 1).14 This compound con-nects the residues filling the S1 and S3 pockets through abridging piperidine linker. Inspection of the X-ray structure of 3bound to renin (PDB code: 3GW5) suggested an alternate inhibitordesign strategy where S1 could be filled by direct attachment of asuitable group to the ortho-position of the phenyl ring occupyingS3. In this Letter, we describe the successful realization of this de-sign strategy to afford potent, orally bioavailable renin inhibitors.

Application of Contour™, a proprietary computational struc-ture-based drug design program, initially identified the phenoxygroup represented in general structure 4 as a candidate to fill theS1 site, when combined with an appropriate group at R1 (Table 1).Introduction of the phenoxy group while retaining thecyclohexylmethyl group at R1 (4a) substantially reduced potency

Figure 1. The N-terminal sequence of angiotensinogen is shown highlighting the amino acids in the P3–P10 positions. The P1, P2 and P3 groups in 1 (remikiren), the P10 , P1and P3 groups in 2 (aliskiren) and the P1 and P3 groups in 3 are indicated.

Table 1SAR of diphenyl ethers 4

NHN

NHMeO

H

OHMeO

OR1

4

R2

Compd R1 R2 IC50a,b,c (nM) PRAa,b,d (nM) CYP 3A4e (lM)

3c — — 0.5 13 14a c-hexCH2 H 5964b i-Bu H 8.8 313 1.14c t-BuCH2 H 4204d Me H 126 1340 1.94e Me Me 2900

a See Ref. 14 for assay protocols.b IC50 values are the average of at least two replicates.c Inhibition of 0.3 nM of purified recombinant human renin in buffer was

measured.d IC50 in the presence of human plasma.e Inhibition of CYP3A4 in human liver microsomes was measured.

J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843 4837

compared to 3, as expected. However, truncation of R1 to i-Bu (4b),the P1 sidechain in the natural substrate, greatly increased potency.The closely related t-BuCH2 group (4c) was much less potent. Fur-ther reducing the size of R1 to Me (4d) reduced potency comparedto 4b. The geminal dimethyl substitution was also unfavorable (4e).

The identification of potent compound 4b provided the first valida-tion of our design.

As a next step, we surveyed replacement of the substituted eth-ylene diamine chain in 4 with various cyclic moieties incorporatingbasic amines to give compounds of general structure 5 (Table 2.R3 = aminocycloalkyl, azacycloalkyl, etc.). Presentation of the basicamine as part of a cyclic structure was intended to retain the keycoulombic interactions with the catalytic aspartates and provideentropic benefit by removing torsional degrees of freedom presentin the earlier compound 4. From this effort, we identified (3S,1R)-3-aminocyclopentane-1-carboxylic acid derivative 5a with modestpotency (Table 2). By contrast, the (3R,1R) and (3R,1S)-isomers5b and 5c were substantially less potent. Modeling of 5a in the re-nin binding site suggested that additional hydrophobic interac-tions with the protein could be attained by introduction of asmall lipophilic substituent at the ortho-position of the distal ringof the diphenyl ether which occupies S1. 2-Methylphenoxy com-pound 5d proved to be 10�more potent than 5a. Further examina-tion of our model indicated that a hydroxyl group at the 4-positionof the cyclopentane ring syn to the 3-amino group would enjoy afavorable interaction with the Asp32 carboxylate. Thus, 5e exhib-ited 7� greater potency than 5d, while the epimer 5f was onlyslightly more potent than 5d. Unfortunately, the more potent ana-logs of general structure 5 also inhibited CYP3A4 with IC50 values61 lM.

Rat pharmacokinetic parameters were determined for 5e; thecompound showed good oral bioavailability but rapid clearance(Table 3). The rat liver microsome half life (RLM t1/2) of 5e was18 min, suggesting that oxidative metabolism might well be themechanism of clearance. Introduction of an ortho-fluorine on theproximal phenyl ring was expected to lock the diphenyl ether into

Table 2SAR of 3-aminocyclopentane carboxamides 5

N R3

OH

OHMeO

OXY3

45

6

Compd R3 X Y IC50a,b,c (nM) PRAa,b,d (nM) CYP 3A4e (lM) RLM t1/2 (min)

5a NH2H H 195

5b NH2H H 1437

5c NH2H H >5000

5d NH2H 2-Me 19 306 0.4

5e

NH2

OHH 2-Me 2.7 32 0.5 18

5f

NH2

OHH 2-Me 11 233 1.0

5g

NH2

OH3-F 2-Me 1.2 19 0.4 31

a See Ref. 14 for assay protocols.b IC50 values are the average of at least two replicates.c Inhibition of 0.3 nM of purified recombinant human renin in buffer was measured.d IC50 in the presence of human plasma.e Inhibition of CYP3A4 in human liver microsomes was measured.

4838 J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843

a favorable conformation and reduce oxidative metabolism; amodest increase in potency and RLM t1/2 of 31 min were observed(5g).

In peptidomimetic renin inhibitors, analogs with aryl rings at P1are much less potent than compounds with aliphatic groups.15 Fur-thermore, the majority of the previously described classes of po-tent, non-peptidic renin inhibitors that bind to the closed form ofrenin fill S1 with an aliphatic group;16 however, workers at Sano-fi-Aventis have recently described inhibitors which deploy a phe-nyl ring in S1.17 Modeling suggested that replacement of thediphenyl ether with a biphenyl system would be tolerated while,potentially, offering superior intrinsic metabolic stability. Unsub-stituted biphenyl analog 6a demonstrated moderate overall po-tency (Table 4). Modeling indicated that small lipophilicsubstituents could be accomodated at the 3-position of the distal

Table 3Rat pharmacokinetic parametersa,b

Compd Oral Cmax (ng/mL) Oral tmax (h) Oral AUC(0–t) ng h/m

3 73 3.3 4725e 185 4.3 7286i 60 3.3 2647bc 5.6 0.2 238a 45 2.7 1868b 71 2.3 2958d 111 3.3 338

a All compounds were dosed as fumarate salts at 2 mg/kg iv.b All compounds were dosed as fumarate salts at 10 mg/kg po except 7b.c Oral dose 7 mg/kg.

phenyl ring of the biphenyl ring system. Thus, 6c (Y = 3-Me) wasmore potent than both the unsubstituted biphenyl 6a and the 2-and 4-methyl isomers 6b and 6d. Another improvement in potencywas obtained with 3-chloro compound 6e. Modeling indicated thatthe chlorine interacted favorably with Val30 and Val120 in the S1pocket. Unfortunately, 6e suffered a greater loss in potency in thepresence of plasma than 6c. However, both 6c and 6e were morestable in RLM than 5e. Introduction of small lipophilic substituentsat the 3-position of the proximal phenyl ring was predicted to in-crease potency by locking the biphenyl system into a favorableconformation for binding to renin; this was borne out with fluoroanalog 6f and chloro analog 6i. Introduction of fluorine at the 4-po-sition (6g) and particularly the 5-position (6h) reduced potency. Asseen with 6e, chloro analogs 6i–k, while potent when assayed inbuffer, suffered >20� losses in potency in presence of plasma.

L Oral t1/2 (h) iv CL (mL/min.kg) Vss (L/kg) F (%)

nd 33 nd 133.8 66 12 344.1 39 9 850 50 39 215.3 80 25 144.9 58 19 133.1 53 83 19

Table 4SAR of biphenyls 6

NOH

HMeO

OH

NH2

O

X Y3

45

6

Compd X Y IC50a,b,c (nM) PRAa,b,d (nM) CYP 3A4e (lM) RLM t1/2 (min)

6a H H 37 420 4.06b H 2-Me 23 126 0.56c H 3-Me 10 137 1.6 676d H 4-Me 20 405 0.96e H 3-Cl 2.1 79 0.2 736f 3-F 3-Me 1.4 12 0.86g 4-F 3-Me 7.1 506h 5-F 3-Me 47006i 3-Cl 3-Me 1.6 35 0.2 1026j 3-F 3-Cl 1.9 47 0.56k 3-Cl 3-Cl 3.7 131 2.0

a See Ref. 14 for assay protocols.b IC50 values are the average of at least two replicates.c Inhibition of 0.3 nM of purified recombinant human renin in buffer was measured.d IC50 in the presence of human plasma.e Inhibition of CYP3A4 in human liver microsomes was measured.

J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843 4839

Many analogs of general structure 6 posessed submicromolar IC50

values against CYP3A4.An X-ray structure of unsubstituted biphenyl 6a complexed to

renin (PDB code: 3Q3T) confirmed the modeled binding pose(Fig. 2). Strong electrostatic interactions of the protonated cyclo-pentylamine with the Asp32 and Asp215 side chain carboxylatesprovide a key, anchoring interaction. In addition, the hydroxyl sub-stituent on the cyclopentane donates a hydrogen bond to theAsp32 carboxylate. The tertiary alcohol moiety hydrogen bondswith Ser219, as observed in the crystal structure of 3 bound to re-nin (PDB code: 3GW5). The ether oxygen at the terminus of themethoxybutyl chain occupying the S3 subpocket forms a hydrogenbond with the backbone NH of Tyr14, as seen for the analogousgroups in 2 (PDB code: 2V0Z) and 3 (PDB code: 3GW5). The S3–S1 superpocket filled by the biphenyl moiety, has the phenyl ringin the S3 pocket interacting with the positive edge of Phe117 and

Figure 2. X-ray structure of 6a bound to renin (PDB code: 3Q3T). The molecular surface cprovide an unobstructed view of the inhibitor and its interactions.

the second phenyl ring in the S1 pocket interacting with Tyr75.Modeling based on 3Q3T predicted that the m-positions of boththe phenyl rings have ample room to allow small substituents tooccupy hydrophobic spaces in the S1 and S3 pockets and provideimproved affinity as observed for 6c, 6e–g and 6i–k.

In rat, 6i demonstrated reduced iv clearance, consistent with itslonger RLM t1/2, but reduced orally bioavailability, compared to 5e(Table 3). In addition, the IC50 value for 6i in the presence of humanplasma (PRA) was unsatisfactory due to projected inferior efficacyin vivo. Our subsequent efforts were directed to identify analogswith improved PRA, reduced CYP3A4 inhibition and increased oralbioavailability.

In earlier work with related compounds, our general approachto improving PRA and reducing CYP inhibition was to introduceadditional polar functionality into the molecule.18 Specifically, inthese earlier compounds, removal of the hydroxyl group and

orresponding to certain amino acid residues of the binding site was not rendered to

4840 J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843

replacement of the 4-methoxybutyl chain occupying S3sp with anacylated 2-aminoethoxy chain greatly improved PRA inhibition.By contrast, in this series, the same modification decreased po-tency both in buffer and in the PRA (7a vs 6f). On the other hand,retention of the hydroxyl and replacement of the 4-methoxybutylchain with a 3-(methoxycarbonylamino)propyl chain afforded 7bwith improved PRA (Table 5). Replacement of fluorine with chlo-rine (7c) was well tolerated. 3-(Acetylamino)propyl analogs 7dand 7e also had good activity in the PRA and offered a modestreduction in CYP3A4 inhibition. Compound 7b was advanced torat PK. Despite its long RLM t1/2, 7b was subject to rapid clearancein vivo and had low oral bioavailability (Table 3).

Replacement of the piperidine ring in 6 with morpholine offeredan alternative strategy to increase overall polarity. Effecting thischange in 6f gave 8a, with a 3� reduction in renin potency but a30� reduction in CYP3A4 inhibition (Table 6). Changing fluorine

Table 5SAR of polar side chain analogs 7

NR5R4

HO

X

Compd X Y R4 R5 IC5

7a F Me H MeOCONHCH2CH2O– 5.27b F Me OH MeOCONH(CH2)3– 1.67c Cl Me OH MeOCONH(CH2)3– 1.17d F Me OH MeCONH(CH2)3– 1.67e Cl Me OH MeCONH(CH2)3– 2.1

a See Ref. 14 for assay protocols.b IC50 values are the average of at least two replicates.c Inhibition of 0.3 nM of purified recombinant human renin in buffer was measured.d IC50 in the presence of human plasma.e Inhibition of CYP3A4 in human liver microsomes was measured.

Table 6SAR of morpholine analogs 8

OOH

HMeO

X

Compd X Y IC50a,b,c (nM)

8a F Me 3.88b Cl Me 1.88c F Et 2.58d Cl Et 1.18e Cl i-Pr 0.78f Cl MeS 2.3

a See Ref. 14 for assay protocols.b IC50 values are the average of at least two replicates.c Inhibition of 0.3 nM of purified recombinant human renin in buffer was measured.d IC50 in the presence of human plasma.e Inhibition of CYP3A4 in human liver microsomes was measured.

to chlorine (8b) and methyl to ethyl (8c) improved renin potency(Table 6). Combining, these afforded 8d with an excellent in vitroprofile. Interestingly, replacing the ethyl group in 8d with isopro-pyl (8e) had little effect on renin potency but led to a substantialincrease in CYP3A4 inhibition. Oral bioavailability was demon-strated for 8a, 8b and 8d, but clearance remained high for all threecompounds (Table 3). Compounds 8a–f also demonstrated excel-lent selectivity for renin over three other aspartyl proteases: b-secretase, cathepsin D and cathepsin E (<10% inhibition at 10 lM).

The antihypertensive efficacy of 8d was demonstrated in a dou-ble transgenic rat (dTGR) model of human hypertension, in whichthe animals express both human renin and human angiotensino-gen (Fig. 3).19,20 Oral administration of 10 mg/kg of 8d led to a sta-tistically significant reduction in mean arterial blood pressure(MABP) sustained for more than 12 h. At the nadir, MABP was re-duced by >20 mm Hg.

OH

NH2

Y

0a,b,c (nM) PRAa,b,d (nM) CYP 3A4e (lM) RLM t1/2 (min)

52 0.54.4 3.8 5672.8 1.11.7 5.3 4604.4 3.5 2033

N

OH

NH2

OY

PRAa,b,d (nM) CYP 3A4e (lM) RLM t1/2 (min)

17 25 9911 188.1 174.0 105.2 0.426 2

-40

-30

-20

-10

0

10

20

30

0 6 12 18 24Time (hrs)

Ch

ang

e fr

om

Bas

elin

e(m

mH

g)

Vehicle (n=6)

10mg/kg po (n=6)

Figure 3. Effect of 8d on mean arterial blood pressure in dTGR.

J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843 4841

The syntheses of piperidines 12 and 16, which comprise the lefthand sides of the target compounds 5, 6 and 7, are shown inScheme 1.21 (R)-Boc-nipecotic acid 9 was converted to the corre-sponding Weinreb amide and treated with various substituted di-phenyl ether (10a) or biphenyl (10b) lithiums to afford ketone 11.Addition of (4-methoxybutyl)magnesium chloride to ketone 11afforded the desired Boc-protected alcohol as the major product(75–80%). To avoid elimination of the tertiary alcohol, the Bocgroup was removed under mild aqueous conditions to afford keyintermediate 12.

Similarly, addition of Grignard reagent 14, which was generatedfrom protected amine 13, to ketone 11b afforded, after aqueouswork up, aminoalcohol 15 as the major product. The amino groupin 15 was treated with acetic anhydride or methyl chloroformate,followed by removal of the Boc group under mild conditions, to af-ford key piperidine intermediates 16. The stereochemistry of thenewly formed carbinol center in both 12 and 16 was initially as-signed based on the results obtained in analogous reactions re-ported previously.14 These assignments were subsequentlyconfirmed by the X-ray structure of derived compound 6a (PDBcode: 3Q3T).

The synthesis of morpholine intermediate 27 is shown inScheme 2. Epoxide 17 was opened by amine 18 under basic

Scheme 1. Synthesis of piperidine intermediates. Reagents and conditions: (a) MeNHOM10b, THF,�78 �C to rt, 16 h; (c) for 11a: MeO(CH2)4MgCl, THF, �10 �C to �78 �C to rt, 16 h(e) Mg, THF, reflux, 2.5 h; (f) 11b, THF, �78 �C to rt, 16 h; (g) for 16a: MeOCOCl, DMAP,

conditions to give intermediate 19, which was further cyclizedand protected to afford morpholine benzyl ether 21.22 The benzylgroup of compound 21 was removed by hydrogenation to affordalcohol 22, which was oxidized to acid 24 using trichloroisocyanu-ric acid (23) and TEMPO in excellent yield. It was determinedexperimentally that Grignard additions to morpholine ketonessuch as 26 occur under chelation control. This dictated that the or-der of addition of the methoxybutyl group and the biphenyl moietybe reversed from that used in the synthesis of piperidine interme-diates 12 and 16. Thus, acid 24 was converted to Weinreb amide 15and treated with (4-methoxybutyl)magnesium chloride to affordketone 26. A variety of substituted biphenyl lithiums (10b) wasadded to ketone 16 to give, after removal of the Boc group undermild conditions, the desired morpholine intermediate 27 as themajor product which was utilized in the synthesis of analogs 8.

The assembly of ureas 4 is shown in Scheme 3. Commerciallyavailable Boc-amino acids 28 were converted to the correspondingmethyl amides 29, which were reduced with Red-Al to afford sec-ondary amines 30 in reasonable yields. After protecting the sec-ondary amine with Teoc, the Boc group of compounds 31 wasselectively removed using p-toluenesulfonic acid under vaccumat 60 �C to give primary amines 32. Amines 32 were then activatedwith p-nitrophenyl chloroformate to form their p-nitrophenylcar-bamates, which were reacted with piperidine 12a (X, Y = H) to af-ford the urea. Finally, the Teoc group was removed with Et4N+F� inacetonitrile to give the desired analogs 4.

The formation of target compounds 5–8 is shown in Scheme 4.Commercially available stereoisomers of Boc-protected amino es-ters 34 were hydrolyzed to the carboxylic acids 33b under mildconditions. The Boc-protected amino acids 33 were then coupledwith piperidines 12 or 16 or morpholines 27 under standard amideformation conditions, followed by Boc removal, to afford 5–8.23

Scheme 5 shows the synthesis of target compound 7a. Ketone11b was reduced by NaBH4 to alcohol 35 as a mixture of diastere-oisomers, which was alkylated to give ester 36. Ester 36 was re-duced to alcohol 37, which was elaborated to primary amine 38in three steps. The diastereomers of 38 were separated by prepara-tive HPLC. Methyl carbamate formation and removal of the Bocgroup gave piperidine 39. Coupling the (1S,3R,4S)-isomer of 33bwith 39, followed by deprotection afforded 7a.

In conclusion, we have described the structure based design of atopologically novel class of renin inhibitors in which an unprece-dented phenyl ring filling the S1 site is attached to the phenyl ringfilling S3. The predicted binding mode was confirmed by X-ray

e�HCl, EDC; i-Pr2NEt, CH2Cl2, rt, 16 h; (b) 10a, THF, �20 to �10 �C, 30 min to 1 h; or; for 11b, MeO(CH2)4MgCl, THF, �78 �C to rt, 16 h; (d) 1:1 2 M aq HCl/MeCN, rt, 16 h;Et3N, CH2Cl2; for 16b: Ac2O, DMAP, Et3N, CH2Cl2.

Scheme 2. Synthesis of morpholine intermediates. Reagents and conditions: (a) NaOH, MeOH/H2O, 40 �C, 2 h; (b) NaOH, toluene, H2O, 65 �C, 16 h; (c), (Boc)2O, K2CO3, 3:1acetone/H2O, 0 �C to rt, 30 min; (d) Pd–C, H2, MeOH, rt; (e) TEMPO, NaBr, NaHCO3, acetone; (f) MeNHOMe, HBTU, HOBt, DIEA, DMF; (g) MeO(CH2)4MgCl, THF, �20 �C, 10 min;(h) 10b, THF, toluene, �20 �C, 10 min; (i) 1:1 2 M aq HCl/MeCN, rt, 16 h.

Scheme 3. Synthesis of ureas 4. Yields are shown for 4a and are representative. Reagents and conditions: (a) MeNH2�HCl, HOBt, HBTU, i-Pr2NEt, DMF, 0 �C to rt, 2 h; (b) Red-Al, toluene, 0 �C to rt, 16 h; (c) Teoc-OSu, K2CO3, 3:1 acetone/H2O, 0 �C to rt, 1.5 h; (d) TsOH�H2O, EtOH, ether, 60–65 �C, 30 min; (e) p-NO2C6H4OCOCl, pyridine, CH2Cl2, rt,5 min; (f) 12a (X, Y = H), i-Pr2NEt, 1:1 MeCN/CH2Cl2; (g) Et4N+F�, MeCN, 50 �C, 16 h.

Scheme 4. Synthesis of amides 5–8. For definitions of X, Y, R7 and cyclopentane stereochemistry, see Tables 3–6. Reagents and conditions: (a) 1 N NaOH, 1:1 EtOH/THF; (b)HOBt, HBTU, i-Pr2NEt, DMF, rt, 5 min; (c) 1:1 2 M aq HCl/MeCN, rt, 16 h.

4842 J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843

Scheme 5. Synthesis of 7a. Reagents and conditions: (a) NaBH4, CH3OH, rt, 2 h; (b) BrCH2CO2Et, NaH, THF, 0 �C to reflux, 12 h; (c) NaBH4, CH3CH2OH, rt, 16 h; (d) MsCl, Et3N,CH2Cl2, 0 �C to rt, 1 h; (e) NaN3, DMF, 80 �C, 5 h; (f) Pd–C, H2, CH3OH, rt, 16 h; (g) preparative HPLC; (h) MeOCOCl, DMAP, Et3N, CH2Cl2; (i) 1:1 2 M aq HCl/MeCN, rt, 16 h; (j)(1S,3R,4S)-33b, HOBt, HBTU, i-Pr2NEt, DMF, rt, 5 min.

J. Yuan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4836–4843 4843

crystallography. This effort culminated in the discovery of 8d, a po-tent, selective and orally bioavailable inhibitor of renin whicheffectively lowered blood pressure in an animal model of humanhypertension.

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21. Target compounds and key intermediates gave satisfactory 1H NMR and LC–MSdata.

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23. Compound 8d gave the following spectral data: 1H NMR (400 MHz, CD3OD) d7.69–7.66 (m, 1H), 7.30–7.12 (m, 4H), 6.88–6.84 (m, 2H), 6.59 (s, 2H), 4.23–4.12 (m, 2H), 3.75–3.57 (m, 2H), 3.43–3.33 (m, 1H), 3.27–3.00 (m, 9H), 2.75–2.54 (m, 3H), 2.23–1.79 (m, 3H), 1.68–1.12 (m, 9H), 0.86–0.75 (m, 1H); MS ESI+ve ionization, m/z 545, 547 (M+H+).