Synthesis, opioid receptor binding, and bioassay of naltrindole analogues substituted in the indolic benzene moiety.

A series of analogues of the delta opioid receptor antagonist naltrindole (1) possessing a phenyl, phenoxy, or benzyloxy group at the 4'-, 5'-, 6'-, or - 7'-positions (4-15) and a 2-(2-pyridinyl)ethenyl group at the 5'-position (16) on the indolic benzene ring were synthesized through Fischer indolization of naltrexone. Compounds 4-16 were evaluated for their affinities in opioid receptor binding assays in rat or guinea pig brain membranes and for their opioid antagonist and agonist activities in vitro on the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. All of the compounds displayed delta selectivity in binding to the delta, mu, and kappa opioid receptors. The binding potencies of most of the compounds at the delta, mu, and kappa sites, however, were lower than that of 1. Among positional isomers, the 7'-substituted compounds in general had higher affinities than 6'-, 5'-, or 4'-substituted analogues, indicating that bulky groups are tolerated better at the 7'-position than at other positions. The affinity of the compounds were also determined at putative subtypes of the delta and kappa receptors: deltacx-1 (mu-like), deltacx-2 (delta-like), and the kappa2b site in an attempt to identify subtype selective agents. Although none were identified, the data revealed a different rank-order of potency beteween mu vs deltacx-1, deltacx-2 vs delta, and the kappa2b vs mu, delta, and kappa1. The antagonist potencies of the compounds in the MVD were in agreement with their binding affinities at the delta site in rat brain membrane. The most potent member of the series, the 7'-phenoxy compound 14, binds to the delta site with a Ki of 0.71 nM, shows >40-fold delta over mu and delta over kappa binding selectivity, and exhibits delta receptor antagonist potency in the MVD with a Ke of 0.25 nM, properties which are comparable to the delta receptor affinity and antagonist potency of naltrindole (Ki = 0.29 nM, Ke = 0. 49 nM). Interestingly, many members of the series were found to possess significant partial to full agonist activities in the MVD (6, 9, 10, 13, 16) or GPI (6, 11, 14, 15). Among the compounds studied, the highest agonist activity in the MVD was displayed by 16 (IC50 = 220 nM), and the highest agonist activity in the GPI was displayed by 14 (IC50 = 450 nM). The overall affinity and activity profile of compound 14 is, therefore, that of a nonpeptide ligand possessing mixed mu agonist/delta antagonist properties. Recently there has been considerable interest in such compounds possessing mu agonist/delta antagonist activities because of their potential therapeutic usefulness as analgesics with low propensity to produce tolerance and dependence side effects. The results of the present study suggest that morphinan derivatives related to 16 and 14 may provide useful leads for the development of potent nonpeptide ligands possessing delta agonist or mixed delta antagonist/mu agonist activities.

Synthesis and structure-activity relationships of 3,5-disubstituted 4,5-dihydro-6H-imidazo[1,5-a][1,4]benzodiazepin-6-ones at diazepam-sensitive and diazepam-insensitive benzodiazepine receptors.

A series of imidazobenzodiazepin-6-ones possessing varying substituents at the 3- and 5-positions were synthesized and evaluated for their affinities at diazepam-sensitive (DS) and diazepam-insensitive (DI) benzodiazepine receptors (BzR) in rat cortical and cerebellar membranes. Replacement of an ester substituent at the 3-position with a carbamate, acetylamino, formylamino, isothiocyanato, 2-oxazolinyl, 2-benzoxazolyl, or p-tolylsulfonyl groups lead to > 100-fold reductions in affinity at both DS and DI BzR. Replacement of a methyl group on the nitrogen at the 5-position with propyl, allyl, or phenethyl groups also led to significant reductions in affinity at both BzR isoforms. However, incorporation of a benzyl group yields ligands (11f,h,i and 14a-c) with moderate to high affinities at DS BzR, suggesting the presence of a hydrophobic pocket at the receptor site. Introduction of chlorine at the 7-position enhances ligand affinity at DS BzR while chlorine at the 8-position decreases affinity (IC50: 11f, 9.3 nM; 11h, 2.4 nM; 11i, 37.8 nM). In contrast, chlorine substitution at the 7- as well as the 8-position increases affinity at DI BzR (Ki: 11f, 112 nM; 11h, 20.2 nM; 11i, 10.9 nM). Compound 11 is among the few described high affinity DI-site ligands with a selectivity comparable to that of Ro 15-4513. Despite their in vitro affinities, compounds 11f, 11h, and 11i exhibit low in vivo activities that may be attributable to unfavorable metabolic or pharmacokinetic properties.

Synthesis and biologic activity of 2'-fluoro-2-halo derivatives of 9-beta-D-arabinofuranosyladenine.

The synthesis of 2-halo-9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)adenines (4b and 4d) by coupling the 2,6-dihalopurine with 3-acetyl-5-benzoyl-2-deoxy-2-fluoro-D-arabinofuranosyl bromide (2) followed by replacement of the 6-halogen with concomitant removal of the acyl blocking groups is described. 2-Fluoroadenine derivative 4g had to be prepared by the diazotization-fluorination of 2-aminoadenine nucleoside 4e. All three nucleosides provided good increases in life span of mice inoculated with P388 leukemia. The best results were obtained when the compounds were administered q3h x 8 on days 1, 5, and 9 after implantation of the leukemia cells. The 2',3'-dideoxynucleoside 5b, prepared by deacetylation of 4f and deoxygenation of the resultant 4h followed by removal of the benzoyl group of 5a, was slightly active against HIV in cell culture.

Synthesis of analogues of N-(2-chloroethyl)-N'-(trans-4-methylcyclohexyl)-N-nitrosourea for evaluation as anticancer agents.

The superior activity of N-(2-chloroethyl)-N'-(trans-4-methylcyclohexyl)-N-nitrosourea (MeCCNU) against advanced murine Lewis lung carcinoma in comparisons with the cis form and other nitrosoureas prompted the synthesis of a number of MeCCNU analogues, including several cis-trans pairs. The methyl group was replaced by a variety of substituents (CO2H, CH2CO2H, CO2Me, CH2OAc, CH2Cl, OMe); the trans-3-methylcyclohexyl, cis-2-methyl-1,3-dithian-5-yl, cis- and trans-2-methyl-1,3-dithian-5-yl-tetraoxide, and 1-methylhexyl (open-chain) analogues were also prepared. Preliminary tests against murine leukemia L1210 revealed therapeutic indices (ED50/LD10) ranging from 0.26 to 0.79; all but three analogues effected 50% cure rates at nontoxic doses, the open-chain analogue being one of the least active. In terms of therapeutic index, diequatorial (trans-4) isomers were, with one exception, as active as or, in four of the eight examples, somewhat more active than the corresponding axial-equatorial (cis-4) isomers. In this series, four of the five 2-fluoroethyl analogues prepared were clearly inferior to the corresponding 2-chloroethyl analogues.