Microbial metabolism part 9. Structure and antioxidant significance of the metabolites of 5,7-dihydroxyflavone (chrysin), and 5- and 6-hydroxyflavones

5,7-Dihydroxyflavone (chrysin) (1) when fermented with fungal cultures, Aspergillus alliaceous (ATCC 10060), Beauveria bassiana (ATCC 13144) and Absidia glauco (ATCC 22752) gave mainly 4 '-hydroxychrysin (4), chrysin 7-O-beta-D-4-O-methylglucopyranoside (5) and chrysin 7-sulfate (6), respectively. Mucore ramannianus (ATCC 9628), however, transformed chrysin into six metabolites: 4 '-hydroxy-3 '-metboxychrysin (chrysoeriol) (7), 4 '-hydroxychrysin (apigenin) (4) 3 ',4 '-dihydroxychrysin (luteolin) (8), 3 '-methoxychrysin 4 '-O-alpha-D-6-de-oxyallopyranoside (9), chrysin 4 '-O-alpha-D-6-deoxyallopyranoside (10), and luteolin 3 '-sulfate (11). Cultures of A. alliaceous (ATCC 10060) and B. bassiana (ATCC 13144) metabolized 5-hydroxyflavone (2) into 5,4 '-dihydroxyflavone (12) and 4 '-hydroxyflavone 5-O-beta-D-4-O-methylglucopyranoside (13), respectively. 6-Hydroxyflavone (3) was transformed into 6-hydroxyflavanone (14), flavone 3-O-beta-D-4-O-methylglucopyranoside (15) and (+/-)-flavanone 6-O-beta-D-4-O-methylglucopyranoside (16) by cultures of Beauveria bassiana (ATCC 13144). The structures of the metabolic products were elucidated by means of spectroscopic data. The significance of the metabolites as antioxidants in relation to their structure is briefly discussed.