Microbial biotransformation of retinoic acid by Cunninghamella echinulata and Cunninghamella blakesleeana

Vitamin A (retinol) is needed by higher animals for the maintenance of normal epithelium and growth, and retinoic acid (I) has been proposed to be the active metabolite. Microbial models are useful for the study of mammalian metabolism of xenobiotics. Two species of the fungal genus Cunninghamella afforded products of greater polarity than 1 when fed 1 in a two-stage fermentation procedure. The products obtained were principally the result of oxidation of the trimethylcyclohexenyl ring. Although most of the isolated metabolites of 1 have been previously seen in mammalian studies, two novel compounds, 2-hydroxyretinoic acid (2) and 2,3-dehydro-4-oxoretinoic acid (4), were isolated.