Urinary metabolites of (R),(R)-labetalol

Dilevalol, the (R),(R)-isomer of labetalol, is a novel antihypertensive agent with both beta-adrenoreceptor activity and direct vasodilatory action. The biotransformation of dilevalol was studied in the rat, dog, monkey, and human. Nine metabolites were isolated and characterized by NMR spectroscopy and MS. The simple benzylic glucuronide is the major metabolite in the dog, monkey, and human, whereas the phenolic glucuronide is the major metabolite in the rat. Seven other metabolites that arise from phase 1 oxidation were also isolated, including a family of catechol-like metabolites formed by hydroxylation at the C3 position of the benzamide ring. This catechol also undergoes ring cyclization forming two novel indolic metabolites.