Highly selective isomerization and dehydrogenation of three major bufadienolides at 3-OH by Fusarium solani

Twenty strains of filamentous fungi (from nine genera) and four species of bacteria were screened for their capabilities to transform bufadienolides. The highly stereo- and regiospecific isomerization and dehydrogenation of three major bufadienolides (resibufogenin, cinobufagin and bufalin) at 3-OH by Fusarium solani AS 3.1829 were reported. Three major transformed products were obtained and their structures were identified as 3-epi-resibufogenin (1a), 3-epi-bufalin (2a), 3-keto-cinobufagin (3a), respectively, on the basis of their spectral data. The reaction kinetics and the effects of pH, substrate concentration and incubation phase on the biotransformation were also investigated.