Nipecotic and iso-nipecotic amides as potent and selective somatostatin subtype-2 receptor agonists.

N-Substituted nipecotic and iso-nipecotic amides of beta-methylTrpLys tert-butyl ester were found to be novel, selective and potent agonists of the somatostatin subtype-2 receptor in vitro. For example iso-nipecotic amide 8a showed high hsst2 binding affinity (Ki = 0.5 nM) and good selectivity (h5/h2 = 832).

Phosphorylated morpholine acetal human neurokinin-1 receptor antagonists as water-soluble prodrugs.

The regioselective dibenzylphosphorylation of 2 followed by catalytic reduction in the presence of N-methyl-D-glucamine afforded 2-(S)-(1-(R)-(3, 5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluoro)phenyl-4-(5-(2- phosphoryl-3-oxo-4H,-1,2,4-triazolo)methylmorpholine, bis(N-methyl-D-glucamine) salt, 11. Incubation of 11 in rat, dog, and human plasma and in human hepatic subcellular fractions in vitro indicated that conversion to 2 would be expected to occur in vivo most readily in humans during hepatic circulation. Conversion of 11 to 2 occurred rapidly in vivo in the rat and dog with the levels of 11 being undetectable within 5 min after 1 and 8 mg/kg doses iv in the rat and within 15 min after 0.5, 2, and 32 mg/kg doses iv in the dog. Compound 11 has a 10-fold lower affinity for the human NK-1 receptor as compared to 2, but it is functionally equivalent to 2 in preclinical models of NK-1-mediated inflammation in the guinea pig and cisplatin-induced emesis in the ferret, indicating that 11 acts as a prodrug of 2. Based in part on these data, 11 was identified as a novel, water-soluble prodrug of the clinical candidate 2 suitable for intravenous administration in humans.

Substance P receptor antagonist I: conversion of phosphoramidate prodrug after i.v. administration to rats and dogs.

A water-soluble phosphoramidate prodrug (L-758,298, compound I) of the potent and selective human Substance P receptor antagonist L-754, 030 (compound II) is under development as an i.v. drug for treatment of emesis, migraine, and chronic pain. Compound I undergoes hydrolysis readily to II under acidic conditions. In the studies reported herein, we investigated the stability of I in blood and hepatic subcellular fractions from rats, dogs, and humans as well as the conversion of I to II in rats and dogs after i.v. dosing. Compound I was converted to II rapidly in rat blood but was stable in dog and human blood. However, the conversion was rapid in liver microsomes prepared from dogs and humans. As expected from the results of in vitro studies, the in vivo conversion of I to II was rapid after i.v. dosing of I to rats and dogs. The relative extent of exposure of II after i.v. dosing of I was estimated by comparing the dose-adjusted area under the plasma concentration versus time curve values of II after i.v. dosing of I with those after i.v. dosing of II. In rats, the extent of exposure was estimated to be approximately 90 and approximately 100% at 1 and 8 mg/kg, respectively; in dogs, that was approximately 59% at 0.5 mg/kg. A nonproportional increase in the area under the concentration versus time curve value of II with dose was observed after i.v. administration of I in dogs from 0.5 to 32 mg/kg, suggesting that the elimination of II might have been saturated at higher doses.

Potent, orally bioavailable somatostatin agonists: good absorption achieved by urea backbone cyclization.

Backbone cyclization of urea-based somatostatin agonists resulted in novel, orally bioavailable agonists. Binding assays confirmed that the resulting conformationally constrained cyclic ureas retained the potency of their acyclic counterparts. SAR studies subsequently led to highly potent analogs, selective for receptor subtype 2, and having good oral bioavailability.

N-glucuronidation reactions. I. Tetrazole N-glucuronidation of selected angiotensin II receptor antagonists in hepatic microsomes from rats, dogs, monkeys, and humans.

In vitro conditions for the preparation of tetrazole N2-glucuronides using liver microsomes (enriched with UDP-glucuronic acid) from rats, dogs, monkeys, and humans have been developed and optimized. The structures of tetrazole N2-glucuronides of 3 biphenyl tetrazole-containing angiotensin II (AII) receptor antagonists MK-954 (I), L-158,338 (II), and L-158,809 (III), and a model compound methyl biphenyl tetrazole (IV) were determined either by NMR and mass spectrometry or by comparison of HPLC retention times with that from authentic compounds. The species difference as well as gender difference in the rate of the in vitro reaction were compared. The optimal pH for the reaction was determined to be 5.0 with liver microsomes from monkeys and humans, and 6.2 with those from rats and dogs. For the model compound IV, the rate of N2-glucuronidation by liver microsomes from rats, dogs, and monkeys was approximately 10-fold faster than that by humans. For the AII receptor antagonists I, II, and III, the rate of the same reaction by liver microsomes from dogs and monkeys was much faster than that by humans. The relative intrinsic rate of this reaction for these three substrates ranked similarly in rats and humans as II > III > I. With compound I, a biphenyl tetrazole-containing imidazole derivative that has potential sites for both O- (primary hydroxyl) and N2-(tetrazole) glucuronidation, both O- and tetrazole N2-glucuronides were formed by liver microsomes from rats and monkeys (at neutral pH), whereas N2-glucuronide was the only product from dogs and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Site-directed mutagenesis of glutathione S-transferase YaYa. Important roles of tyrosine 9 and aspartic acid 101 in catalysis.

The roles of tyrosine 9 and aspartic acid 101 in the catalytic mechanism of rat glutathione S-transferase YaYa were studied by site-directed mutagenesis. Replacement of tyrosine 9 with phenylalanine (Y9F), threonine (Y9T), histidine (Y9H), or valine (Y9V) resulted in mutant enzymes with less than 5% catalytic activity of the wild type enzymes. Kinetic studies with purified Y9F and Y9T mutants demonstrated poor catalytic efficiencies which were largely due to a drastic decrease in kcat. The estimated pK alpha values of the sulfhydryl group of glutathione bound to Y9F and Y9T mutant enzymes were 8.5 to 8.7, similar to the chemical reaction, in contrast to the estimated pK alpha value of 6.7 to 6.8 for the glutathione enzyme complex of wild type glutathione S-transferase. These results indicate that tyrosine 9 is directly responsible for the lowering of the pKa of the sulfhydryl group of glutathione, presumably due to the stabilization of the thiolate anion through hydrogen bonding with the hydroxyl group of tyrosine. To examine the role of aspartic acid in the binding of glutathione to YaYa, 4 conserved aspartic acid residues at positions 61, 93, 101, and 157 were changed to glutamic acid and asparagine. All mutant enzymes retained either full or partial activity except D157N, which was virtually inactive. Kinetic studies with four mutant enzymes (D93E, D93N, D101E, and D101N) indicate that only D101N exhibited a 5-fold increase in Km toward glutathione. Also, the binding of this mutant to the affinity column was greatly reduced. These results demonstrate that aspartic acid 101 plays an important role in glutathione interaction to YaYa. The role of aspartic acid 157 in catalysis remains to be determined.

Expression in Escherichia coli of rat liver cytosolic glutathione S-transferase Yc cDNA.

An expression plasmid, pKK-GTB2, containing the complete coding sequence of a rat liver glutathione S-transferase Yc subunit was constructed and expressed in Escherichia coli. The entire Yc cDNA sequence from plasmid pGTB42 (Telakowski-Hopskins et al., 1985, J. Biol. Chem. 260, 5820-5825) was amplified by the polymerase chain reaction, subcloned into modified expression vector A6316 (Schoner et al., 1986, Proc. Natl. Acad. Sci. USA 83, 8506-8510 and Linemeyer et al., 1987, Bio/Technology 5, 960-965) and transformed into E. coli strain AB1899. The colonies were screened by hybridization to pGTB42 and the production of Yc subunit was detected by immunoblot analysis. The purified recombinant Yc subunit was active in the conjugation and peroxidation reactions, and appeared homogeneous as judged by sodium dodecyl sulfate gel electrophoresis. Amino acid sequencing of the expressed Yc subunit revealed that about 40% of the expressed protein was blocked at the N-terminus. Approximately 25% of the sequenceable protein (15% of total protein) contained the initiation methionine residue at the amino terminus whereas the rest of the sequenceable protein had proline as the N-terminus. In contrast, only one molecular species with Pro as the first amino acid was identified when the inducer isopropyl-beta-D-thiogalactopyranoside was omitted in the growth medium. Our observation indicated that under certain growth conditions, the enzymes responsible for protein maturation were not able to complete the processing of the overproduced recombinant Yc in E. coli.