Structure of human alpha-thrombin complexed with RWJ-51438 at 1.7 A: unusual perturbation of the 60A-60I insertion loop.

The three-dimensional structure of the ternary complex consisting of human alpha-thrombin, hirugen and the active-site inhibitor RWJ-51438 has been determined at 1.7 A resolution. The crystals of the complex belong to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 62.98, b = 117.52, c = 47.99 A. The refined R and R(free) values are 0.196 and 0.232, respectively. The ketone carbonyl group of the inhibitor is covalently linked to the hydroxyl O atom of Ser195, forming a tetrahedral intermediate hemiketal structure; the benzothiazole ring N atom of RWJ-51438 forms a hydrogen bond with His57. Surprisingly, the carboxylate substituent on the benzothiazole group forms salt bridges with Lys60F NZ and the NZ of the symmetry-related residues Lys236 and Lys240, which introduces steric effects that perturb the 60A-60I insertion loop, especially at residues Trp60D and Phe60H.

Antithrombotic properties of RWJ-50353, a potent and novel thrombin inhibitor.

The antithrombotic, anticoagulant, and kinetic properties of RWJ-50353, a novel, reversible, active-site-directed thrombin inhibitor, were evaluated. RWJ-50353 inhibited the catalytic activity of human alpha-thrombin with a K(i) of 0.19+/-0.02 nM. It showed a 16-fold selectivity relative to inhibition of trypsin and at least 330-fold selectivity relative to inhibition of other biologically important serine proteases. In a gel-filtered platelet preparation, RWJ-50353 inhibited alpha-thrombin-induced aggregation with an IC(50) of 32+/-6 nM. In a canine arteriovenous shunt antithrombotic model, RWJ-50353 demonstrated a significant dose-related (0.1-1.0 mg/kg, i.v.) reduction in thrombus formation with 50% inhibition (ID(50)) obtained at 0.46+/-0.1 mg/kg. In a rabbit deep vein thrombosis model, RWJ-50353 dose-dependently (0.1-1. 0 mg/kg, i.v.) reduced thrombus formation with an ID(50) of 0.25+/-0. 03 mg/kg. The antithrombotic activity in both of these models was associated with only mild prolongations in bleeding time and coagulation parameters. These results demonstrate that RWJ-50353 is a potent, selective thrombin inhibitor that is an effective antithrombotic agent after intravenous administration in models of arterial and venous thrombosis and may be useful in the management of various thrombotic disorders.

Potent, orally active GPIIb/IIIa antagonists containing a nipecotic acid subunit. Structure-activity studies leading to the discovery of RWJ-53308.

Although intravenously administered antiplatelet fibrinogen receptor (GPIIb/IIIa) antagonists have become established in the acute-care clinical setting for the prevention of thrombosis, orally administered drugs for chronic use are still under development. Herein, we present details from our exploration of structure-activity surrounding the prototype fibrinogen receptor antagonist RWJ-50042 (racemate of 1), which was derived from a unique approach involving the gamma-chain of fibrinogen (Hoekstra et al. J. Med. Chem. 1995, 38, 1582). Our analogue studies culminated in the discovery of RWJ-53308 (2), a potent, orally active GPIIb/IIIa antagonist. To progress from RWJ-50042 to a suitable candidate for clinical development, we conducted a series of optimization cycles that employed solid-phase parallel synthesis for the rapid, efficient preparation of nearly 250 analogues, which were assayed for fibrinogen receptor affinity and inhibition of platelet aggregation induced by four different activators. This strategy produced several promising analogues for advanced study, including 3-(3,4-methylenedioxybenzene)-beta-amino acid analogue 3 (significant improved in vivo potency) and 3-(3-pyridyl)-beta-amino acid 2 (significantly improved potency, oral absorption, and duration of action). In dogs, 2 displayed significant ex vivo antiplatelet activity on oral administration at 1.0 mg/kg, 16% systemic oral bioavailability, minimal metabolic transformation, and an excellent safety profile. Additionally, 2 was found to be efficacious in three in vivo thrombosis models: canine arteriovenous (AV) shunt (0.01-0.1 mg/kg, iv), guinea pig photoactivation-induced injury (0.3-3 mg/kg, iv), and guinea pig ferric chloride-induced injury (0.3-1 mg/kg, iv). On the basis of its noteworthy preclinical data, RWJ-53308 (2) was selected for clinical evaluation.

Structure of the RWJ-51084-bovine pancreatic beta-trypsin complex at 1.8 A.

The three-dimensional structure of bovine pancreatic trypsin complexed with the inhibitor RWJ-51084 has been determined at 1.8 A resolution. These crystals belong to the trigonal space group P3(1)21, with unit-cell parameters a = b = 53.43, c = 107.76 A. The refined R and R(free) values are 0.175 and 0.237, respectively. The carbonyl group bonded to the benzothiazole group of the inhibitor is covalently linked to the hydroxyl O atom of Ser195, forming a tetrahedral intermediate hemiketal structure. The other carbonyl O atom of the inhibitor forms a hydrogen bond with the Gln192 side-chain amide group. The benzothiazole group is oriented with the aromatic N atom of RWJ-51084 accepting a hydrogen bond from His57 NE2. The arginine side chain of the inhibitor extends into the deep and narrow pocket of the S1 specificity site of trypsin, forming a network of hydrogen bonds.

Structure-activity studies on anticonvulsant sugar sulfamates related to topiramate. Enhanced potency with cyclic sulfate derivatives.

We have explored the structure-activity relationship (SAR) surrounding the clinically efficacious antiepileptic drug topiramate (1), a unique sugar sulfamate anticonvulsant that was discovered in our laboratories. Systematic structural modification of the parent compound was directed to identifying potent anticonvulsants with a long duration of action and a favorable neurotoxicity index. In this context, we have probed the pharmacological importance of several molecular features: (1) the sulfamate group (6-8, 22-25, 27, 84), (2) the linker between the sulfamate group and the pyran ring (9, 10, 21a,b), (3) the substituents on the 2,3- (58-60, 85, 86) and 4, 5-fused (30-38, 43, 45-47, 52, 53) 1,3-dioxolane rings, (4) the constitution of the 4,5-fused 1,3-dioxolane ring (2, 54, 55, 63-68, 76, 77, 80, 83a-r, 84-87, 90a, 91a, 93a), (5) the ring oxygen atoms (95, 96, 100-102, 104, 105), and (6) the absolute stereochemistry (106 and 107). We established the C1 configuration as R for the predominant alcohol diastereomer from the highly selective addition of methylmagnesium bromide to aldehyde 15 (16:1 ratio) by single-crystal X-ray analysis of the major diastereomer of sulfamate 21a. Details for the stereoselective syntheses of the hydrindane carbocyclic analogues 95, 96, 100, and 104 are presented. We also report the synthesis of cyclic imidosulfites 90a and 93a, and imidosulfate 91a, which are rare examples in the class of such five-membered-ring sulfur species. Imidosulfite 93a required the preparation and use of the novel sulfur dichloride reagent, BocN=SCl2. Our SAR investigation led to the impressive 4,5-cyclic sulfate analogue 2 (RWJ-37947), which exhibits potent anticonvulsant activity in the maximal electroshock seizure (MES) test (ca. 8 times greater than 1 in mice at 4 h, ED50 = 6.3 mg/kg; ca. 15 times greater than 1 in rats at 8 h, ED50 = 1.0 mg/kg) with a long duration of action (>24 h in mice and rats, po) and very low neurotoxicity (TD50 value of >1000 mg/kg at 2 h, po in mice). Cyclic sulfate 2, like topiramate and phenytoin, did not interfere with seizures induced by pentylenetetrazole, bicucculine, picrotoxin, and strychnine; also, 2 was not active in diverse in vitro receptor binding and uptake assays. However, 2 turned out to be a potent inhibitor of carbonic anhydrase from different rat tissue sources (e. g., IC50 of 84 nM for the blood enzyme and 21 nM for the brain enzyme). An examination of several analogues of 2 (83a-r, 85-87, 90a, 91a, 93a) indicated that potent anticonvulsant activity is associated with relatively small alkyl substituents on nitrogen (Me/H, 83a; Me/Me, 83m; Et/H, 83b; allyl/H, 83e; c-Pr/H, 83j; c-Bu/H, 83k) and with limited changes in the cyclic sulfate group, such as 4,5-cyclic sulfite 87a/b. The potent anticonvulsants 83a and 83j had greatly diminished carbonic anhydrase inhibitory activity; thus, inhibition of this enzyme may not be a significant factor in the anticonvulsant activity. The alpha-L-sorbopyranoses 67, 68, and 80, which mainly possess a skew conformation (ref 29), were nearly twice as potent as topiramate (1). The L-fructose enantiomers of 1 (106) and 2 (107), synthesized from L-sorbose, were found to have moderate anticonvulsant activity, with eudysmic ratios (MES ED50 in mice at 4 h, po) of 1:106 = 1.5 and 2:107 = 3.5. The log P values for 1 and 2 were determined experimentally to be 0.53 and 0.42, respectively, which are less than the optimal 2.0 for CNS active agents. However, analogues with more favorable calculated log P (clogP) values, in conjunction with just minor steric perturbation according to the developed SAR profile, such as 47 (clogP = 2.09), 83m (1.93), and 86 (1.50), did not display improved potency: 47 is less potent than 1, 83m is equipotent with 2, and 86 is less potent than 2. Although the measured log P value for diethyl analogue 31 is 1.52, this did not translate into enhanced potency relative to 1. (ABSTRACT TRUNCATED)

Crystal structures of thrombin with thiazole-containing inhibitors: probes of the S1' binding site.

Structures of the blood clotting enzyme thrombin complexed with hirugen and two active site inhibitors, RWJ-50353 10080(N-methyl-D-phenylalanyl-N-[5-[(aminoiminomethyl)amino]-1- [[(2-benzothiazolyl)carbonyl]butyl]-L-prolinamide trifluoroacetate hydrate) and RWJ-50215 (N-[4-(aminoiminomethyl)amino-1-[2- (thiazol-2-ylcarbonylethyl)piperidin- 1-ylcarbonyl]butyl]-5-(dimethylamino)naphthalenesulfonamide trifluoroacetate hydrate), were determined by x-ray crystallography. The refinements converged at R values of 0.158 in the 7.0-2.3-A range for RWJ-50353 and 0.155 in the 7.0-1.8-A range for RWJ-50215. Interactions between the protein and the thiazole rings of the two inhibitors provide new valuable information about the S1' binding site of thrombin. The RWJ-50353 inhibitor consists of an S1'-binding benzothiazole group linked to the D-Phe-Pro-Arg chloromethyl ketone motif. Interactions with the S1-S3 sites are similar to the D-phenylalanyl-prolyl-arginyl chloromethylketone structure. In RWJ-50215, a S1'-binding 2-ketothiazole group was added to the thrombin inhibitor-like framework of dansylarginine N-(3-ethyl-1,5-pentanediyl)amide. The geometry at the S1-S3 sites here is also similar to that of the parent compound. The benzothiazole and 2-ketothiazole groups bind in a cavity surrounded by His57, Tyr60A, Trp60D, and Lys60F. This location of the S1' binding site is consistent with previous structures of thrombin complexes with hirulog-3, CVS-995, and hirutonin-2 and -6. The ring nitrogen of the RWJ-50353 benzothiazole forms a hydrogen bond with His57, and Lys60F reorients because of close contacts. The oxygen and nitrogen of the ketothiazole of RWJ-50215 hydrogen bond with the NZ atom of Lys60F.

2-Substituted 1-azabicycloalkanes, a new class of non-opiate antinociceptive agents.

2-Substituted 1-azabicycloalkanes (3- and 5-aryloctahydroindolizines 2 and 11, 3-cyclohexyloctahydroindolizine 12, 4-aryloctahydroquinolizines 13, and 3-arylhexahydropyrrolizines 14) constitute a new class of non-opiate antinociceptive agents. These compounds demonstrated activity in the mouse abdominal constriction test and many were active in the mouse tail-flick test. trans-3-(2-Bromophenyl)octahydroindolizine (2a) did not bind to the opiate receptor nor did it affect arachidonate metabolism. 3-Aryloctahydroindolizines were prepared by catalytic hydrogenation of 1-aryl-3-(2-pyridinyl)-2-propen-1-ones. The X-ray crystal structure of (-)-2a was determined and absolute stereochemistry assigned as 3-R,8a-R.

Pyrroloisoquinoline antidepressants. 3. A focus on serotonin.

A collection of hexahydropyrroloisoquinoline derivatives (1-22), which represent a class of compounds that inhibit the neuronal uptake of dopamine (DA), norepinephrine (NE), and serotonin (5-HT), was investigated in vivo for serotonin-potentiating properties in the mouse head-twitch and rat serotonin syndrome assays. The p-methylthio compound 3b (McN-5652-Z) was found to possess exceptional activity in these assays, and the activity was attributable almost exclusively to the (+)-6S,10bR enantiomer. Ten closely related analogues were synthesized, tested, and compared among themselves and with some previously prepared compounds, both in vivo and in vitro. Several trans diastereomers exhibited strong inhibition of 5-HT uptake and substantial potentiation of 5-HT, while the cis diastereomers (3a, 4a, and 10a) tested were virtually devoid of such activity. Although 3b was only moderately selective in inhibiting the uptake of 5-HT vs NE, its 10-substituted analogues 4b, 7b-9b had improved 5-HT selectivity relative to NE, to the extent of 20-25 times (150-200 times relative to DA). Of these more selective compounds (in vitro), only 4b and 7b had substantial activity in vivo. Sulfoxide 11b appeared to function as a prodrug of 3b in vivo.

Pyrroloisoquinoline antidepressants. 2. In-depth exploration of structure-activity relationships.

A series of pyrrolo[2,1-a]isoquinolines, and related compounds, were examined for antidepressant-like activity, by virtue of their antagonism of tetrabenazine-induced ptosis and sedation, and inhibition of biogenic amine uptake. Thus, we have identified some of the most potent antagonists of TBZ-induced ptosis and some of the most potent inhibitors of the uptake of dopamine, norepinephrine, and serotonin (in rat brain synaptosomes) ever reported. Compounds of particular note, in this regard, are 52b, 29b, 22b, and 48b, respectively. Biological activity was chiefly manifested by the trans isomeric class. Also, through resolution of four compounds, 7b, 24b, 37b, and 48b, biological activity was found to be associated with the (+) enantiomer subgroup (salts measured at 589 nm in MeOH), corresponding to the 6S, 10bR absolute configuration for 7b, 37b, and 48b, and the 6R,10bR configuration for 24b. An X-ray determination on (+)-24b X HBr established its absolute configuration; configurations for the other compounds were verified by enantiospecific synthesis starting with (+)-(R)-2-phenylpyrrolidine. Regarding the pendant phenyl ring, diverse substitution patterns were investigated. Those substitutions that were particularly unfavorable were 3',4',5'-trimethoxy (20b), 2',3',4',5',6'-pentafluoro (34b), 2'-trifluoromethyl (38b), 3',5'-bis(trifluoromethyl) (42b), 4'-n-butyl (44b), 2'-cyano (47b), 4'-methylsulfonyl (50b), and 2'-carboxy (58b). Exceedingly potent compounds, in one way or another, were 10b-12b, 22b, 23b, 25b, 28b, 29b, 33b, 45b, 48b, 51b-53b. The pattern of aromatic substitution had a strong impact on selectivity in the uptake tests (NE vs. DA vs. 5-HT). Activity was significantly diminished by methyl substitution of 7b at the 5 (65, 66), 6 (61b), or 10b (60b) position, by changing the phenyl group of 7b to cyclohexyl (67b), benzyl (68b), or H (72), by moving the phenyl group of 7b to the 5 (69) or 10b (70) position, by expansion of ring B to an azepine (78b), and by modification of ring C to an azetidine (77b), piperidine (75b), or azepine (74b). The interaction of selected analogues with various CNS receptors is reported. Little affinity was shown for the muscarinic cholinergic receptor, suggesting a lack of anticholinergic side effects. Interestingly, 24b and 33b displayed a high affinity for the serotonin-2 receptor, analogous to mianserin and clomipramine. After the body of data was reviewed, derivatives 24b and 48b were chosen for advanced development.