RT Journal Article SR Electronic T1 The metabolism of avermectin-H2B1a and -H2B1b by pig liver microsomes. JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 464 OP 469 VO 12 IS 4 A1 S H Chiu A1 E Sestokas A1 R Taub A1 J L Smith A1 B Arison A1 A Y Lu YR 1984 UL http://dmd.aspetjournals.org/content/12/4/464.abstract AB The avermectins are a new class of macrocyclic lactone disaccharide antiparasitic agents derived from Streptomyces avermitilis. On incubation of avermectin-H2B1a and avermectin-H2B1b with pig liver microsomes, a group of metabolites slightly more polar than the parent compounds were generated. Two major metabolites have been isolated and purified by repetitive reversed phase and normal phase HPLC. Their structures were established to be the O-demethylation products of the parent compounds, i.e. 3''-O-desmethyl-H2B1a and 3''-O-desmethyl-H2B1b. The structure assignments were based on spectral results of UV, NMR, fast atom bombardment-mass spectrometry, and chemical derivatization studies including acid hydrolysis as well as fluorogenic reaction. Among the in vitro metabolites, there was only a trace amount of the polar metabolites 24-hydroxymethyl-H2B1a and 24-hydroxymethyl-H2B1b which were the major in vitro metabolites of avermectin-H2B1a and -H2B1b by steer or rat liver microsomes.