Microbiological transformation of two labdane diterpenes, the main constituents of Madia species, by two fungi

Microbial transformation of 13R,14R,15-trihydroxylabd-7-ene (5) and 13R,14R,15-trihydroxylabd-8,17-ene (6) by the fungus Debaryomyces hansenii gave 1 and 3, respectively. While, microbial transformation of 5 by Aspergillus niger afforded 2, and 13R,14R,15-trihydroxylabd-8,17-ene (6) gave 3 and 4. The structures of the new compounds, 1 and 2, were assigned by 1D and 2D high-field NMR spectroscopic methods. Antimicrobial activity of these compounds were tested and their MIC were determined.