Non-peptide fibrinogen receptor antagonists. 7. Design and synthesis of a potent, orally active fibrinogen receptor antagonist

The design, synthesis, and pharmacological evaluation of L-734,217, a potent, low-molecular weight, orally active fibrinogen receptor antagonist, is reported. A strategy for producing low-molecular weight inhibitors from the peptide c-[(Ac)CRGDC] A, previously reported from these laboratories, is outlined. This strategy combines a retrodesign analysis of the conformationally defined cyclic peptide A with stereochemical information present in the arginine-glycine-aspartic acid (RGD) tripeptide sequence, culminating with the discovery of L-734,217. L-734,217 inhibited the aggregation of human, dog, and chimpanzee platelets at concentrations below 100 nM and was found to be > 15000-fold less effective at inhibiting the attachment of human umbilical vein endothelial cells to fibrinogen, fibronectin, and vitronectin than it was at inhibiting the aggregation of platelets. L-734,217 showed significant ex vivo antiplatelet activity following oral administration in dogs and chimpanzees at doses of 1.0 and 2.0 mg/kg, respectively, and has been selected as a clinical candidate for development as an antithrombotic agent.

Development of inhibitors of protein farnesylation as potential chemotherapeutic agents

Protein prenylation, adding either the 15-carbon isoprenoid farnesyl or the 20-carbon isoprenoid geranylgeranyl to cysteine residue(s) at or near the C-termini of proteins, is a recently identified post-translational modification that localizes some proteins to a membrane compartment. One of the most intensely studied prenylated proteins is Ras, a low molecular weight GTP-binding protein that plays an important role in the regulation of cell proliferation. Proteins encoded by ras genes with oncogenic mutations are capable of transforming cells in culture. Such mutated ras genes are frequently found in a wide variety of human tumors. Localization of the Ras oncoprotein to the cytoplasmic face of the plasma membrane via farnesylation is essential for efficient cell transforming ability. Thus, inhibition of the Ras farnesylation reaction is a possible anti-cancer strategy. Several strategies have been employed to inhibit Ras farnesylation, including inhibition of isoprenoid biosynthesis and inhibition of the enzyme which catalyzes the farnesylation reaction, farnesyl-protein transferase (FPTase). Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate limiting enzyme in isoprenoid biosynthesis, inhibit Ras farnesylation and block the growth of ras-transformed cells. However, antiproliferative effects do not result from specific inhibition of Ras farnesylation; they are also observed in cells transformed by raf, which is independent of Ras farnesylation. A more specific approach to inhibiting Ras farnesylation is to inhibit FPTase. Using random screening of natural products and a rational design approach, a variety of compounds that specifically inhibit FPTase have been isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-peptide fibrinogen receptor antagonists. 2. Optimization of a tyrosine template as a mimic for Arg-Gly-Asp

Inhibitors of platelet-fibrinogen binding offer an opportunity to interrupt the final, common pathway for platelet aggregation. Small molecule inhibitors of the platelet fibrinogen receptor GPIIb/IIIa were prepared and evaluated for their ability to prevent platelet aggregation. Compound 23m (L-700,462/MK-383) inhibited in vitro platelet aggregation with an IC50 of 9 nM and demonstrated a selectivity of > 24,000-fold between platelet and human umbilical vein endothelial cell fibrinogen receptors. Dose-dependent inhibition of ex vivo platelet aggregation induced by ADP was achieved with i.v. infusions of 0.1-10 micrograms/kg/min of 23m in anesthetized dogs, with 10 micrograms/kg/min completely inhibiting platelet aggregation during the entire 6 h infusion protocol. Platelet aggregatability returned rapidly after the termination of the 23m infusions. These features suggest that 23m may be useful in the treatment of arterial occlusive disorders.

Pharmacokinetics and pharmacodynamics of L-703,014, a potent fibrinogen receptor antagonist, after intravenous and oral administration in the dog

The pharmacokinetics and pharmacodynamics of L-703,014, a fibrinogen receptor antagonist, have been examined in the dog. An analytical method which utilizes methanol precipitation of dog plasma proteins followed by HPLC with an automated column switching technique using the chemical analogue L-704,326 as internal standard was developed for the determination of L-703,014 in dog plasma. The compound was not metabolized in the dog and was eliminated in the kidneys and into bile. Of the administered dose, 68.9 +/- 1.3% (i.v.) and 80.5 +/- 11.9% (p.o.) were recovered in the feces; 20.3 +/- 1.3% (i.v.) and 2.2 +/- 0.2% (p.o.) were recovered in the urine by 72 hr. L-703,014 was 23 +/- 3.4% bound in dog plasma protein and the mean ratio of plasma/whole blood was 1.22 +/- 0.05. The mean terminal half-life was 118 +/- 36 min, the mean steady-state volume of distribution was 0.61 +/- 0.22 L/kg, and the mean plasma clearance was 8 +/- 2 mL/min/kg. Ex vivo platelet aggregation measurements were made by inducing platelet aggregation with 10 micrograms/mL collagen in the presence of 1 microM epinephrine as an agonist. The mean C50 was 44.4 +/- 6.0 ng/mL, and the mean Hill coefficient was 1.5 +/- 0.3. The mean bioavailability was 4.9 +/- 1.4% in dogs administered 2.0 mg/kg (p.o.).

4-substituted thiophene- and furan-2-sulfonamides as topical carbonic anhydrase inhibitors

A series of 4-substituted thiophene- and furan-2-sulfonamides was prepared and was found to possess nanomolar-level potency for inhibition of human carbonic anhydrase II in vitro. Selected examples from this group were further evaluated for their potential to act as topically effective ocular hypotensive agents in the ocular normotensive albino rabbit and the ocular alpha-chymotrypsinized rabbit. Solubility studies in water and pH 7.4 buffer were carried out to estimate the ability of compounds to be formulated in solution. The sensitization potential of key representative structures was determined by in vitro glutathione reactivity studies and guinea pig maximization testing.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 9. The synthesis and biological evaluation of novel simvastatin analogs

Substitution of hydroxy and hydroxyalkyl functionality at C-7 of the hexahydronaphthalene nucleus of simvastatin has provided novel analogs. The synthetic strategy employed epoxidation or Lewis acid-catalyzed aldol reaction of the 8-keto silyl enol ether as a key reactive intermediate. These analogs were evaluated as potential hypocholesterolemic agents via initial determination of their ability to inhibit HMG-CoA reductase in vitro. Oral activity of these compounds was determined in an acute rat model and a three-week study in cholestyramine-primed dogs. Compounds were identified that possessed in vitro and in vivo activity comparable to that of simvastatin.

Thieno[2,3-b]furan-2-sulfonamides as topical carbonic anhydrase inhibitors

Novel 5-[(alkylamino)methyl]thieno[2,3-b]furan-2-sulfonamides were prepared and evaluated in vitro for inhibition of human carbonic anhydrase II (CA II) and ex vivo for their ability to inhibit Ca II in the albino rabbit eye after topical administration. Compound 11a was found to lower intraocular pressure (IOP) in both the alpha-CT ocular hypertensive albino rabbit and the normal albino rabbit, but was ineffective at lowering IOP in a hypertensive, pigmented monkey model. Since 11a was highly bound to ocular pigment, a series of less basic analogs was prepared. Examples in this series were both less extensively bound to ocular pigment and more active at reducing IOP in pigmented rabbits after topical dosing. Key examples displayed moderate reactivity toward glutathione.

3-Hydroxy-3-methylglutaryl-coenzyme a reductase inhibitors. 7. Modification of the hexahydronaphthalene moiety of simvastatin: 5-oxygenated and 5-oxa derivatives

Modification of the hexahydronaphthalene ring 5-position in simvastatin 2a via oxygenation and oxa replacement afforded two series of derivatives which were evaluated in vitro for inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and acutely in vivo for oral effectiveness as inhibitors of cholesterogenesis in the rat. Of the compounds selected for further biological evaluation, the 6 beta-methyl-5-oxa 10 and 5 alpha-hydroxy 16 derivatives of 3,4,4a,5-tetrahydro 2a, as well as, the 6 beta-epimer 14 of 16 proved orally active as hypocholesterolemic agents in cholestyramine-primed dogs. Subsequent acute oral metabolism studies in dogs demonstrated that compounds 14 and 16 evoke lower peak plasma drug activity and area-under-the-curve values than does compound 10 and led to the selection of 14 and 16 for toxicological evaluation.

New isomeric classes of topically active ocular hypotensive carbonic anhydrase inhibitors: 5-substituted thieno[2,3-b]thiophene-2-sulfonamides and 5-substituted thieno[3,2-b]thiophene-2-sulfonamides

A series of 5-substituted thieno[2,3-b]- and thieno[3,2-b)- and thieno[3,2-b)thiophene-2-sulfonamides was prepared and evaluated for topical ocular hypotensive activity in glaucoma models. The 5-substituents were varied to maximize both inhibitory potency against carbonic anhydrase and water solubility. At the same time, these substituents were varied in order to obtain compounds with the appropriate pKa to minimize pigment binding in the iris. All of these variables were optimized in the best compound, 5-[[(methoxyethyl)[(methoxyethyl)ethyl] amino]methyl]thieno[2,3-b]thiophene-2-sulfonamide hydrochloride (55).

Iminium ion-mediated cyclizations of 4-aryl-1,4-dihydropyridines. Alternate cyclization pathways

Acid-catalyzed cyclization of dimethyl 2,6-dimethyl-4-[(2-ethenyl-5-methoxy)phenyl]-1,4-dihydropyridine-3,5-dicarboxy-late affords novel products via competing intramolecular processes. The present mechanistic pathways differ from previous iminium ion-mediated cycloadditions, to afford conformationally constrained dihydropyridine analogs for study as calcium antagonists. These results illustrate the ability of the dihydropyridine nucleus to function as either a nucleophile or an electrophile, depending upon substituents in the aryl ring.

Synthesis and activity of novel nitropyrazines for use as hypoxic cell radiosensitizers

A series of eight novel nitropyrazines has been prepared by oxidation of sulfoximine intermediates. The partition coefficient, one-electron reduction potential, sensitizer enhancement ratio, and chronic and acute aerobic cytotoxicity have been measured for each. Two representatives of this series were tested in the Ames test and were not found to be mutagenic.

Non-mutagenic nitroheterocycles. The lack of correlation between bacterial mutagenicity and one-electron reduction potential

The bacterial mutagenicity (Ames test) and the one-electron reduction potential for several nitropyridines, nitropyrazines and nitropyrimidines were determined. It was found that, although these nitroheterocycles underwent one-electron reduction more easily than metronidazole, they were not mutagenic in the Ames test. Six-membered ring nitroheterocycles, will, in general, exhibit diminished mutagenic potential compared to five-membered ring nitroheterocycles, and it is postulated that this effect is due to differences in the electronic nature and potential chemical reactivity of their respective nitrenium ions.

The relationship of the carcinogenic/mutagenic potential of arylamines to their singlet-triplet nitrenium ion energies

Utilizing intermediate neglect of differential overlap (INDO) and ab initio methodology, trends in the energy differences between the singlet and triplet states for mono- and polycyclic aryl nitrenium ions have been estimated. Calculations reveal an empirical correlation between the energy separation of the singlet and triplet states of the nitrenium ion and the ability of the parent amine to behave as a carcinogen or mutagen. Non-carcinogenic/non-mutagenic arylamines were characterized by nitrenium ions whose singlet states were much less stable than the triplet. Carcinogenic/mutagenic amines were characterized by nitrenium ions whose singlet states were of similar or greater stability than the triplet. By examination of the charge density at key ring atoms of the singlet and triplet species, a rational approach to the stabilization of one species relative to the other has merged and forms the basis for prediction of genotoxicity in closely related structures. The application of this empirical correlation to the prediction of the carcinogenic/ mutagenic potential of arylamines is discussed.