Investigation of the importance of the C-2 oxygen function in the transformation of stemodin analogues by Rhizopus oryzae ATCC 11145

A new stemodinoside, stemodin-a-L-arabinofuranoside (5), was isolated from the plant Stemodia maritima. Incubation of stemodin (2) with Rhizopus oryzae ATCC 11145 gave 2alpha,7beta,13(S)-trihydroxystemodane (17) and 2alpha,3beta,13(S),16alpha-tetrahydroxystemodane (18) whilst stemodinone (8) afforded 6alpha,13(S)-dihydroxystemodan-2-one (19). The bioconversion of 2beta,13(S)-dihydroxystemodane (10) by the fungus yielded 2beta,7beta,13(S)-trihydroxystemodane (20) whereas stemod-12-en-2-one (9) provided 7beta,17-dihydroxystemod-12-en-2-one (21). The results provide useful information about the relationship between the functional groups of the substrates and their potential for bioconversion. (C) 2004 Elsevier Ltd. All rights reserved.