Discovery of 2-substituted benzoxazole carboxamides as 5-HT3 receptor antagonists.

A new class of 2-substituted benzoxazole carboxamides are presented as potent functional 5-HT(3) receptor antagonists. The chemical series possesses nanomolar in vitro activity against human 5-HT(3)A receptors. A chemistry optimization program was conducted and identified 2-aminobenzoxazoles as orally active 5-HT(3) receptor antagonists with good metabolic stability. These novel analogues possess drug-like characteristics and have potential utility for the treatment of diseases attributable to improper 5-HT(3) receptor function, especially diarrhea predominant irritable bowel syndrome (IBS-D).

A new reaction manifold for the Barton radical intermediates: synthesis of N-heterocyclic furanosides and pyranosides via the formation of the C(1)-C(2) bond.

The first radical intermediate in the thiourethane-mediated deoxygenation of an alcohol (Barton-McCombie reaction) can participate in an exo-hex-5-enyl- or exo-hept-6-enyl-type radical cyclization when a suitable radical acceptor (e.g., alpha,beta-unsaturated ester, oxime ether, or hydrazone) is appropriately placed. Carbohydrate-derived imidazolyl and triazolyl thiourethanes with such acceptors, upon addition to excess of a good hydride donor (reverse addition), undergo efficient cyclization reactions to give N-heterocyclic furanosides, and, surprisingly even N-pyranosides. Depending on the acceptor, glycosides with either a C(2)()-amino or a C(2)()-carbon substituent are formed.