J . Med. Chem. 1994,37,2071-2078
2071
New Potent Prolyl Endopeptidase Inhibitors: Synthesis and Structure-Activity Relationships of Indan and Tetralin Derivatives and Their Analogues Yoshiaki Tanaka, Seiichi Niwa, Hiroyasu Nishioka, Takeshi Yamanaka, Motoki Torizuka, Koji Yoshinaga, Naomi Kobayashi, Yugo Ikeda, and Heihachiro Arai' Central Research Laboratories, Zeria Pharmaceutical Company, Ltd., 2512-1 Oshikiri, Kohnan-machi, Ohsato-gun, Saitama-ken 360-01, Japan Received October 22, 1 9 9 9
New compounds were synthesized.bystructural modification of 1-[l-(4-phenylbutanoyl)-~-prolyl]pyrrolidine (SUAM-1221,l) or 1-[1-(benzyloxycarbonyl)-~-prolyl]prolinal (Z-Pro-prolinal, 2) and were tested for in vitro inhibitory activities against purified prolyl endopeptidase (PEP) from canine brain. In a series of compounds which lack a formyl or a cyano group, 3-[3-[(S)-2-(1,2,3,4tetrahydronaphthy1)acetyll-~-thioprolyll thiazolidine (13) exhibited an approximately 20-fold (ICs0 = 2.3 nM) increase in potency compared with 1. Compounds having a formyl or a cyano group showed much more potent inhibitory activities than those which lack such a functional group. Among all compounds tested in uitro, 1-[1-(2-indanylacetyl)-~-prolyllprolinal (27), 1-[1-[(S)-2(1,2,3,4-tetrahydronaphthyl)acetyll -~-prolyllprolinal(B), 1-[3-[(S)-2-(1,2,3,4-tetrahydronaphthyl)acetyl] -L-thioprolyllprolinal (301, (S)-2-cyano-l-[2- [(S)-2-(1,2,3,4-tetrahydronaphthyl)acetyl]-Lprolyll pyrrolidine (341, and (S)-2-cyano-l-[3-[(S)-2-(1,2,3,4-tetrahydronaphthy1)acetyll-~-thioprolyl] pyrrolidine (36) showed an approximately 2-fold (ICs0 0.5 nM) increase in potency compared with 2. The structure-activity relationships of these compounds are discussed.
Introduction Prolyl endopeptidase (PEP) [EC 3.4.21.261 is a serine protease that specificallycleavespeptidyl proline bonds.' This enzyme hydrolyzes many biologicallyactive peptides, including thyrotropin-releasing hormone, substance P, angiotensin 11,oxytocin, and bradykinin.- The enzyme also degrades arginine vasopressin which may facilitate learning and m e m ~ r y . ~Yoshimoto -~ et al. reported that the PEP inhibitor 1- [1-(benzyloxycarbonyl)-~-prolyl] prolinal (Z-Pro-prolinal, 2) reversed scopolamine-induced amnesia in the passive avoidance learning test in rats.lOJ1 They also found that the antiamnesic effects of such compoundswere approximately parallelto their inhibition potencies toward PEP in uitro.lOJ1 Furthermore, Saito et al. reported that PEP plays an important role in the regulation of learning and memory consolidation in the brain, since in the passive avoidance test using amnesic rats treated with scopolamine,the pyrrolidinederivatives, which had potent inhibitory activities toward PEP, also showed strongantiamnesiceffecta.12 These studies suggest that inhibitors of the enzyme are possible candidates for antiamnesic drugs for preventing and/or curing amnesia. These lines of evidence have prompted us to search for novel PEP inhibitors. It is known that the PEP inhibitors having either a formyl:J1-'8 a chlor0acety1,~~J~ or a diazoacetyP group exhibit very potent inhibitory activities. The chloroacetyl or diazoacetyl derivatives irreversibly inhibit PEP in response to chemical reactivity of the functional group. Recently the formyl derivative2 was reported to be a tightbinding reversible inhibitor.18 It has ala0 been reported that PEP inhibitors without such a functional group have reversible and competitive inhibitory manner~.l~J7*2~-23 Furthermore, a non-peptide PEP inhibitor, 2-[[8(dimethy1amino)octyll thiol -6-isopropyl-3-pyridyl-2-thienyl ketone citrate (Y-29794), was also reported by Nakajima et al.% Tsuru et al. reported that introduction ~~
e Abstract published in Advance ACS Abstracts, May 16, 1994.
0022-262319411837-2071$04.50/0
of a sulfur atom into the proline ring and/or pyrrolidine ring of 1-[1-(4-phenylbutanoyl)-~-prolyl]pprolidine (SUAM-1221)12(1) resulted in increased inhibitory activity.17J1 It is also known that the inhibitory activities of prolinal, thioprolinal, or 2-cyanopyrrolidine derivatives with a formyl or a cyano26group are greater than those of compounds without the functional group. We have recently reported the synthesis and structure-activity relationships of a series of Carylbutanoyl derivatives having potent inhibitory effects against the PEP from canine brain.26 In the present paper, the synthesis of a new series of PEP inhibitors with high inhibitory activities was attempted since it was desired to find a PEP inhibitor suitable for clinical use. The compounds,general formula [AI, of which the phenylbutanoyl or benzylosycarbonyl group of 1 or 23J1-18was replaced by 2-indanoyl, 3-(2indanyl)p~panOyl,4-(2-indanyl)butanoyl, 2-indanylacety, (R)-and (S)-2-tetralinylacetyl,2-indenylacetyl, 2-benzosubenylacetyl,2-benzo[bIfurylacetyl, 2-benzo[bI thienylacetyl, or 5 ( 4 , 5 , 6 , 7 - t e t r [ b l ~ e n y l )g~ro~upl ings, were synthesized, and their inhibitory activities against PEP were evaluated. We also examined the inhibitory activities of the compounds with a formyl or a cyano group at the 2-position of the pyrrolidine or thiazolidine ring of the indan or the tetralin derivative, and structure-activity relationships of these compounds are discussed. Novel compounds 3-26 and 27-36 were prepared as outlined in Charta 2 and 3, respectively. Their potencies of PEP inhibition are listed in Tables 1and 2, respectively. Chemistry For the synthesis of benzo- or thienocycloalkanylacetic acid derivatives, compound 37 was prepared in moderate yield from the corresponding ketone 36 by heating with glyoxylicacid in the presence of a smallamount of sulfuric acid. Catalytic hydrogenation of 37 in the presence of
0 1994 American Chemical Society
New Potent Prolyl Endopeptidase Inhibitors
2072 Journal of Medicinal Chemistry, 1994, Vol. 37, No. 13
chart 3a
chart 1
Ar-CH2COOH
388, 39
-
Ar-CH2COCI
42
i
1, SUAM 1221
0
44 X
43
CH20CON QCOQCHO
2, Z-Pro-prolinal
Y
Ar--CH2CdLC&lCHO
27-31 43
-?L%
Ar-CH2CON ' k C & k C N
32-35 (Y = CH2)
Chart
Ar: a, 2-indanyl;b, (S)-2-(1,2,3,44etrahydronaphthyl) X, Y: (1) X = CH2, (2)X =S, (3) X = Y = CH2, (4) X = S, Y = CH,, (5) X = Y = S
2s
0
36
0 (i) SOCl2, CH2C12; (ii) L-proline or L-thioproline, Na2COs; (iii) pivaloyl chloride or WSCeHC1; (iv) L-prolinol or L-thioproliiol; (v) pyridine408 complex, triethylamine,DMSO;(vi) pivaloyl chloride, triethylamine, CH2Cl2; (vii) (S)-2-cyanopyrrolidine.
37
38
a, E = CH=CH. m = 0 ; b. E = CH=CH, m = 1; c, E = CH =CH, m = 2 ; d, E = S, m= 1
41 : a, 2-indancarboxylicacid; b, 3-(2-indanyl)prqionicacid; c, 4-(2-indanyl)butyricacid; d, 2-indenylaceticacid; e, 2-benzdbjfurylaceticadd;f, 2-benzo[b)hienylaceticadd
(i) Glyoxylic acid, HzSO4, dioxane, 80 OC; (ii) 5% Pd-C, HBO,, dioxane, 60 OC; (iii) pivaloyl chloride CHZC12,triethylamine; (iv)Propyrrolidine, Prethiazolidine, thioPro-pyrrolidine, or thioprethiazolidme, triethylamine, CHzClz.
sulfuricacid under a hydrogen atmospheregave the benzoor thienocycloalkanylaceticacid 38 in moderate yield. In the case of optically active tetralinylacetic acid, treatment of (RS)-2-(1,2,3,4-tetrahydronaphthyl)acetic acid38b with0.5 molof (S)-(-)or (R)-(+)-l-(l-naphthyI)ethylamine in AcOEt produced the corresponding salt. Each salt was then treated with base followed by acidification with HCl to afford optically active 39 or 40, which was then purified by recrystallizationfrom isopropylether. The absolute configuration of 39, which was resolved with (S)-(-)-l-(l-naphthyl)ethylamine,was confirmed by comparing the rotation ([CUID = -80') of ita methyl ester of 99% ee with the rotation ([CUID = -32.2O) of the known S-configured (S)-2-(1,2,3,4-tetrahydronaphthyl)aceticacid methyl ester.27 Opticalrotation of 40 of 99 % ee was +79.8'. Compounds3-26 were prepared from the corresponding carboxylic acids 38a,c,d and 39-41 by treatment with pivaloyl chloridein the presence of triethylamine followed by condensation with L-proline or L-thioproline deriva-
tives.= The yields and the physical and analytical data for 3-26 are summarized in Table 1. Novel formyl and cyano derivatives 27-31 and 32-36 were also synthesized as outlined in Chart 3. Acetyl chloride derivatives 42, which were prepared from 38a or 39 with thionyl chloride, were treated with L-proline or L-thioproline in the presence of sodium carbonate to afford 43, which was condensed with L-prolinol or L-thioprolinol using pivaloyl chloride and triethylamine to give 44. The formyl derivatives27-31 were synthesized by oxidationof 44 with pyridine sulfur trioxide.The cyano derivatives 32-36 were prepared from carboxylicacid 43 by treatment with pivaloyl chloride in the presence of triethylamine followed by condensation with (S)-2-~yanopyrrolidine.~l The yields and the physical and analytical data for 27-31 and 32-35 are summarized in Table 2.
Results and Discussion In our in vitro PEP inhibition assay, 1showed inhibitory activity with an ICs0 of 49 nM. Z-Pro-pyrrolidine, which lacke the formyl group of 2, showed an ICs0 of 86 nM. However, the potency of Y-29794,which is a non-peptide inhibitor, showed only an ICs0 of 3.5 NM. To estimate the effectof the number of methylenes (n)for indau derivatives of general formula [AI on the inhibitory activity, we examined 3-6, each having a different number of methylene groups. The 2-indanylacetyl derivative (n = 1)had the m a t potent inhibitoryactivity. The activity gradually decreased as n increased.26 Compound 3, which lacks a methylene group, had only about one-fiftieth of the inhibitory activity of 4. Using this result, it was decided to set n = 1for the synthesis of a series of arylcycloalkane derivatives. It has been reported that in the amino acid moiety, the L-form shows a much greater potency than the D-form,and the introduction of a sulfur atom into the proline and/or pyrrolidine ring increased the inhibitory activity.21*28On the basis of these results, the structureactivity relationship of arylcycloalkanyl series [AI was studied. In a series of compounds containing a 2-indanylacetyl group, the activity increased with increasing number of sulfur atoms. Chiefly,the thioprolylthiazolidinederivative 8 gave the most potent inhibitory activity in this series. This is part of a general trend.21y26For example, 10-13
Tanaka et al.
Journal of Medicinal Chemistry, 1994, Vol. 37, No.13 2073
Table 1. Structures, Physical Properties, and PEP Inhibitory Activities of the Synthesized Compounds 3-26 Ar-(CH2)&0N
compd no.
Ar 3
n
0
X S
Y
*
CH2
R
