J. Med. Chem. 1983,26, 394-403
394
(Mercaptopropanoyl)indoline-2-carboxylic Acids and Related Compounds as Potent Angiotensin Converting Enzyme Inhibitors and Antihypertensive Agents Dong H. Kim,*.?Charles J. Guinosso,t George C. Buzby, Jr.,+David R. Herbst,? Ronald J. McCaully,? Thomas C. Wicks,’ and Robert L. Wendtt Medicinal Chemistry Section and Cardiovascular Pharmacology Section, Wyeth Laboratories, Inc., Philadelphia, Pennsylvania 19101. Received J u n e 21, 1982 1-(3-Mercapto-2-methyl-l-oxopropyl)indoline-2-carboxylic acids (7b) and related compounds were synthesized in order to examine their ability to inhibit angiotensin converting enzyme (ACE) and to reduce the systolic blood pressure of spontaneously hypertensive rats (SHR). All four possible stereoisomers of the precursor 1-[3-(benzoylthio)-2methyl-l-oxopropyl]indoline-2-carboxylicacid (6b) were characterized with absolute stereochemical assignment. The removal of the benzoyl group of the precursor to give 7b was conveniently carried out by treatment with 2-methoxyethylamine. Three of the four stereoisomers of the benzoyl derivative 6 showed in vitro ACE inhibitory activity in the following order: Gb(S,S) > 6b(S,R) > 6b(R,S). The stereoisomer having the R,R configuration was essentially inactive. The substitution at the Csof the indoline nucleus with the Et or OMe group caused only marginal changes in the inhibitory activity. The mercaptan 7b(S,S) was the most active ACE inhibitor synthesized in this study, showing in vitro potency 3 times that of captopril. The augmentation of the potency may be due to the increased hydrophobicity of 7b(S,S) compared with captopril and suggests the presence of a hydrophobic pocket at the active site of ACE. When tested in spontaneously hypertensive rats, 7b(S,S) exhibited oral antihypertensive activity 27 times that of captopril. The corresponding benzoyl derivative 6b(S,S) was 24 times as potent as captopril. The thio lactone 10 obtained by cyclization of 7b(S,S) as a potential prodrug was less potent than the parent compound, 7b(S,S), in the ACE inhibitory and antihypertensive tests.
Captopri11i2 is a highly potent, orally effective, and
’
HSCHzCHCO-N
Scheme I
C02H
1 iCAPTOPRlLi
nonpeptidic inhibitor of angiotensin converting enzyme (ACE). I t is clinically useful for the treatment of hypert e n ~ i o n . Since ~ the discovery of this compound, numerous analogues have been preparedP13 in the hope of improving its pharmacological profile and/or to probe the hypothetical active-site model of the enzyme proposed by Ondetti and Cushman.lp2 The basic structural requirements for the ACE inhibition of these compounds involve (a) a carboxylic acid group or its isosteres at one end of the molecule, (b) a carbonyl group, preferably of an amidic nature, (c) a methyl group CK to the carbonyl bond, (d) a group such as sulfhydryl or phosphoryl that chelates with zinc in the enzyme, and (e) S,S absolute configuration at both chiral centers. Furthermore, (f) the presence of pyrrolidine at the COzH terminus of the molecules was found to be an important requirement for high inhibitory potency.2J2P1415 Hydrophobicity is known to play an important role in the binding of substrate or inhibitor to the active site of an enzyme.16 The effect of improved hydrophobic character, especially at the pyrrolidine portion of the therapeutically effective ACE inhibitor (captopril), on the enzyme inhibitory activity was of interest to us. This paper describes the synthesis and preliminary pharmacology of (-)-(S)-l[ (S)-&mercapto-2-methyl-l-oxopropyl]indoline2-carboxylic acid and related compounds. Chemistry. Ethyl indoline-2-carboxylate (2)17 was acylated in excellent yield with methacryloyl chloride to give 3, which was then hydrolyzed to 5 under basic conditions. The acid 5 was alternatively obtained by the + Medicinal
Chemistry Section. Cardiovascular Pharmacology Section. (1) M. A. Ondetti, B. Rubin, and D. W. Cushman, Science, 196, t
441 (1977). (2) D. W. Cushman, H. S. Cheung, E. F. Sabo, and M. A. Ondetti, Biochemistry, 16, 5484 (1977).
0022-2623/83/ 1826-0394$01.50/0
1
I’ c
a:X;H, b: X H, I
c: X d. X
: i
R
~
H
R hle Ohle, R Me Et, R Me i
:
i
R
p:
v-cOc6HI
7: v-li
acylation of 4 in the presence of Et3N. The acid 4 was readily prepared from 2 by mild basic hydrolysis. Subsequent treatment of 5 with thiobenzoic acid afforded 6
(3) (a) H. Gavras, H. R. Brunner, G. A. Turini, G. R. Kershaw, C. P. Tifft. S. Cuttelod. I. Gavras, R. A. Vukovich, and D. N. McKinstry, N. Engl. J. Med., 298, 991 (1978). (b) H. R. Brunner, H. Gavras, G. A. Turini, B. Waeber, P. Chappuis, and D. M. McKinstry, Clin. Sci. Mol. Med., 55, 293s (1978). (c) D. B. Case, S. A. Atlas, J. H. Laragh, J. E. Sealey, P. A. Sullivan, and D. N. McKinstry, Progr. Cardiouasc. Dis., 21, 195 (1978). (4) I. Mita, J.-I. Iwao, M. Oya, T. Chiba, and T. Iso, Chem. Pharm. Bull., 26, 1333 (1978). (5) E. W. Petrillo, Jr., M. A. Ondetti, D. W. Cushman, E. R. Weaver, and J. E. Heikes, “Abstracts of Papers”, 176th National Meeting of the American Chemical Society, Miami Beach, FL, Sept 11-14, 1978, American Chemical Society, Washington, DC, 1978, Abstr MEDI 27. (6) A. Sugie and J. Katsube, Chem. Pharm. Bull., 27,1708 (1979).
0 1983 American Chemical Society
Journal of Medicinal Chemistry, 1983, Vol. 26, No. 3 395
(Mercaptopropanoyl)indoline-2-carboxylicAcids
Scheme I11
Scheme I1
0 HOE
lfl->b
,U,d-
5COC6HS
1 11 HSCOC& 21 DCHA 31 FRACTIONAL RECRYSTALLIZATION 41 Aq.KHS04 SOLN.
11 DCHA 21 i Q A C T I O Y H L R E C R Y S T A L L I Z A l l G h ! 31 A q KHSOP SOLN.
!-l-$b!S,SI
!+I-@b!R, SI
I
I*I-IMR S I DHAA
.Dehydrcdbietylamlne
I-L-!blS.SI
Scheme IV
in a resinous form, from which crystalline racemic 6b(R,R + S,S) was deposited upon addition of a small amount of ethanol. The other racemic diastereomer, 6b(R,S + S,R) was isolated from the mother liquor (for stereochemical assignments, see below). The diastereoisomeric ratio of the thiobenzoic acid addition product was highly dependent on the nature of the reaction medium. Whereas 6b(R,S + S a ) was the predominant product (70%)when the reaction was carried out in CHzClz,6b(R,R S,S) was the major product in acetone solution. The formation of the latter in acetone medium was further enhanced by the
+
(7) M. E. Condon, J. A. Reid, K. A. Losse, D. W. Cushman, and
M. A. Ondetti, "Abstracts of Papers", ACS/CSJ Chemical Congress, Honolulu, HI, Apr 2-6, 1979, American Chemical Society, Washington, DC, 1979, Abstr MEDI 64. (8) E. W. Petrillo, Jr., and E. R. Spitzmiller, Tetrahedron Lett., 4929 (1979). (9)
R. E. Galardy, Biochem. Biophys. Res. Commun., 97, 94 (1980).
(10) R. G. Almquist, W.-R. Chao, M. E. Ellis, and H. L. Johnson, J . Med. Chem., 23, 1392 (1980). (11) D. H. Kim, J. Heterocycl. Chem., 17, 164 (1980). (12) S. Klutchko, M. L. Hoefle, R. D. Smith, A. D. Essenburg, R. B. Parker, V. L. Nemeth, M. J. Ryan, D. H. Dugan, and H. R. Kaplan, J . Med. Chem., 24, 104 (1981). (13) A. A. Patchett, E. Harris, E. W. Tristram, M. J. Wyvratt, M.
(14)
(15) (16) (17)
T. Wu, D. Taub, E. R. Peterson, T. J. Ikeler, J. ten Broeke, L. G. Payne, D. L. Ondeyka, E. D. Thorsett, W. J. Greenlee, N. S. Lohr, R. D. Hoffsommer, H. Joshua, W. V. Ruyle, J. W. Rothrock, S. D. Aster, A. L. Maycock, F. M. Robinson, R. Hirschmann, C. S. Sweet, E. H. Ulm, D. M. Gross, T. C. Vassil, and C. A. Stone, Nature (London),288, 280 (1980). (a) D. W. Cushman and M. A. Ondetti, Prog. Med. Chem., 17, 41 (1980). (b) D. W. Cushman, J. Pluscec, N. J. Williams, E. R. Weaver, E. F. Sabo, 0. Kocy, H. S. Cheung, and M. A. Ondetti, Enperientia, 29, 1032 (1973). D. W. Cushman, H. S. Cheung, E. F. Sabo, and M. A. Ondetti, Progr. Cardiovasc. Dis., 21, 176 (1978). B. R. Baker, in "Medicinal Chemistry", 3rd ed., Part I, A. Burger, Ed., Wiley-Interscience, New York, 1970, Chapter 12. E. J. Corey, R. J. McCaully, and H. S. Sachdev, J. Am. Chem. SOC.,92, 2476 (1970).
addition of a catalytic amount of 4-(dimethylamino)pyridine to give 6b(R,R + S,S) and 6b(R,S + S,R) in a ratio of 31. Removal of the benzoyl group by treatment of both racemic 6b's with NH,-MeOH by a conventional method afforded the corresponding 7b(R,R + S,S) and 7b(R,S S,R),respectively. The use of acryloyl chloride instead of methacryloyl chloride in the above synthesis gave 6a and 7a (Scheme I). The use of resolved 5b afforded all four possible stereoisomers of 6b and 7b (Scheme 11). When racemic 5b was treated with an 0.5 molar equiv amount of dehydroabietylamine, (+)-5b preferentially formed a crystalline salt, leaving the (-) enantiomer in solution. Treatment of (-)-5b, obtained from the mother liquor of (+)-5b dehydroabietylamine salt, with thiobenzoic acid afforded a diastereoisomeric mixture of 6b(S,S) and 6b(S,R),which was readily separated by fractional recrystallization of the dicyclohexylamine (DCHA) salts from ethanol or 2propanol. Similarly, 6b(R,S) and 6MR,R) were prepared. Amminolysis of the benzoyl derivatives with 2-methoxyethylamine afforded the corresponding mercapto compounds (7b). Unlike benzamide or benzoic acid generated in the conventional debenzoylation reaction, the N (methoxyethy1)benzamide that is formed by the brief contact with 2-methoxyethylamine is a liquid and was readily separable from 7b. The NMR spectrum of 6b(S,S) deserves comment: Although the spectrum obtained in MezSO-ds showed the
+
396 Journal of Medicinal Chemistry, 1983, Vol. 26, No. 3
Kim et al.
Table I. Physical Data and ACE Inhibitory Testing (in Vitro) Results of N-Acryloyl- and N-( 2-Methacryloyl)indoline-2-carboxylic Acids and Analogues
R
synth R method H A Me A-C Me b
deg ( e , recrystn compd X mp, "C EtOH); temp, "C solvent yield, % formulaC IC,,,d M 5a(R + S) H 167-169 EtOAc 56 C12H11N03 >io-5 5b(R t S) H 138-140 Et ,O 52, 95, 52 C,,H13N0, >lo-$ H 148-150 +133.45 Et ,O 77 C13H13N03 >10-5 5WR) (1.11);23.5 H Me b 153-154 -135.9 Et,O 69 Ci3H13N03 >10-5 5WS) (0.94); 2 5 5c(R t S) OMe Me B 115-118 EtOAc 71 c , , H , , N o , ~ * ~ ~ H , o 10-5 a Parenthetical R and S designations indicate absolute stereochemical configuration. See Experimental Section. All Molar concentration required for 50% inhibition by the method of Cushman compounds were analyzed for C, H, and N. and C h e ~ n g . , ~ [cy],,
methyl proton signals as a doublet at 6 1.28, the proton signals observed in CDC13appeared as a pair of doublets that coalesced as the temperature of the sample probe was raised, giving a broad singlet a t 6 1.14. A similar solvent-dependent NMR phenomenon was also observed with 7b(S,S) and its diasterkomers. Apparently, the compound exists as more than one rotamer,ls especially in a nonpolar solvent. A practical synthesis of 7b(S,S) starts with (-)-8(S)l9and racemic 4a (Scheme 111). Treatment of (-)-8(S) with thionyl chloride and condensation of the resulting acid chloride with 4a in the presence of 2 molar equiv of Et3N afforded an approximately equimolar mixture of 6b(S,S) and 6b(R,S).20 The rapid addition of the acid chloride was found to be extremely important for high yield of the product. Slow addition (1h) gave 12, which was presumably formed from the reaction of freshly generated 6b with the intact 4a as shown in Scheme IV. The crude diastereoisomeric mixture of 6b(S,S) and 6b(R,S) was converted into DCHA salts, and the salts were separated by repeated washing with MeCN followed by recrystallization from ethanol to give 6b(S,S).DCHA in 34% yield. Treatment of the salt with aqueous KHS04 followed by debenzoylation with 2-methoxyethylamine gave 7b(S,S). Similarly, 7b(R,S) was prepared from 6b(R,S),which was isolated from the MeCN washings. Cyclization of 7b(S,S) and 7b(R,S) with DCC in the presence of a catalytic amount of 4-(dimethy1amino)pyridineafforded thio lactones 10 and 11, respectively. The absolute stereochemistry of the indoline-2carboxylic acid moiety of 6b(S,S) and 7b(S,S) was established to be the S configuration as shown below: Acidic hydrolysis of 7b(S,S) gave (+)-4a. Reduction of the optically active 4a with lithium aluminum hydride gave (+)-2-(hydroxymethy1)indoline.The latter has been previously correlated with L-phenylalanine to have the S absolute configuration. The stereochemical assignments for racemic 6b(R,R + S,S) and 6b(R,S + S,R) were based on their chromatographic (TLC and HPLC) characteristics (18) D. H. Kim, J. Heterocycl. Chem., 13, 1187 (1976). (19) The resolved (-)-8(S) was obtained from Chemical Dynamics Corp. (20) After we had developed this synthetic procedure, a patent (EP-008831) appeared that described the synthesis of l-[D3-(benzoylthio)-2-methyl-l-oxopropyl]-~-proline (S,S) by a similar method.
Scheme V
OD\rSCOCbH5 Me
?d
when compared with respective resolved enantiomers. A NMR spectral study of the thio lactones 10 and 11 warrants special comment: Examination of their molecular models indicated that whereas the C4 Me group of 10 is positioned away from the thio lactone carbonyl group, the corresponding Me group of its diastereomer 11 is situated in close proximity to the group well within the range of the deshielding zone. Thus, as expected from the model, the C4Me of 10 showed signals at 6 1.35 as a doublet, and the corresponding Me protons of 11 exhibited their signals a t 6 1.48. 1-[3-(Benzoylthio)-2-methyl-l-oxopropyl]-l~-indole-2carboxylic acid (14) was prepared as shown in Scheme V. Attempts a t the debenzoylation of 14 were unsuccessful under various conditions. Instead, cleavage of the amide bond occurred. Bis-disulfide 13 was a minute impurity found in 7b(S,S), which was possibly formed during the workup. It was also obtainable by a mild oxidation of 7b(S,S) by the method of Yiannios and Karabinos.",22
1.3
~
(21) C. N. Yiannios and J. V. Karabinos, J . Org. Chem., 28, 3246
(1963). (22) Conventional methods, such as the use of iodine, caused oxi-
dation of the indoline moiety to indole in addition to disulfide formation.
(Mercaptopropanoyl)indoline-Z-carboxylicAcids
Journal of Medicinal Chemistry, 1983, Vol. 26, No. 3 397
lArg1 F
-al 0.1
Figure 2. Active-site model of ACE.
i
10
1w
ORAL DOSE Img/kgl
Figure 1. Doseresponse relationships of antihypertensive activities of 7b(S,S) (Wy-44,221), Gb(SS) (Wy-44,088),and captopd in the SHR.
Biological Results and Discussion Compounds prepared in this study were initially tested for their in vitro ACE inhibitory activities by essentially following the procedure reported by Cushman and C h e ~ n g . 2 ~ None of the N-acryloyl- or N-(2-methacryloyl)indoline2-~arboxylic acid intermediates displayed significant ACE inhibitory activity (Table I). Of the four stereochemical isomers of [(benzoylthio)methylpropanoyl]indoline-2-carboxylicacid, three showed inhibitory activity. The most potent compound, Gb(S,S), having S,S absolute configuration, showed activity nearly equal to that of captopril. Its diastereoisomer, Gb(S,R), exhibited only 10% of the activity of Gb(S,S),and Gb(R,S) was 33 times less potent than Gb(S,S). Apparently, the correct stereochemical requirement ( S configuration) at the chiral center adjacent to the C0,H group is much more important for the activity than the one in the side chain. Compound Gb(R,R) was inactive. The importance of the stereochemical requirement for inhibitory activity was further demonstrated by the indole derivative 14,which was also inactive. The aromatic substitution with Et or Me0 did not cause a significant effect on the ACE inhibitory activity (Table 11). In the series of (mercaptopropanoy1)indoline-2carboxylic acids, 7b(S,S) showed the highest activity with ICM = 3.7 X lo4 M, which is equivalent to 3 times that of captopril. Ita diastereomer 7b(R,S) showed only weak activity, again demonstrating the importance of the chiral requirement at the indoline C2 position for the activity. As expected, racemate 7b(R,R + S,S) was less potent than 7b(S,S). The higher potency of 7b(R,S + S,R) compared with that of optically active 7 b ( R S indicates than 7b(S,R) is considerably more potent than its diastereoisomer 7b(R,S), as was observed with the benzoyl derivatives (Table 111). Selected compounds were studied for their in vivo ACE inhibitory activities and their ability to lower blood pressure in the spontaneously hypertensive rat (SHR) (Table IV). The former activity was assessed by calculating the oral dose required to inhibit 50% of the vasopressor response induced by intravenous administration of angiotensin I in conscious normotensive rats, using the method of Rubin et al. with slight modification.24 Again, (23) D. W.Cushman and H. 1637 (1971).
S. Cbeung, Biochem. Phnrmacol., 20,
7b(S,S) was the most active compound with a potency approaching 1.6 times that of captopril, whereas the potency of Gb(S,S)was about one-third that of captopril. In the SHR, 7b(S,S) reduced systolic blood pressure by 25 mmHg at 4 h posttreatment at a calculated oral dose of 0.88 mg/kg, whereas captopril required 17.78 mg/kg to effect the same result (Figure 1). When relative potencies were determined by the method of analysis of variance for a parallel line assay, 7b(S,S) was 27 times (p
