Formation of grindelane dimers by microbial transformation

The material balance for the biotransformation of grindelic acid by Aspergillus niger was determined along with the isolation of two novel dimers identified as methyl-8α-hydroxy-grindelate-7β-O-7′β-ether hydrate and methyl-3β-acetoxy-8α-hydroxy-grindelate-7β-O-7′β-ether hydrate. Also identified were the known 19-hydroxy-grindelic acid and the novel 6α,17-dihydroxy-grindelic acid. All compounds were isolated as their methyl ester acetate derivatives. The known 3β-hydroxy-7α,8α-epoxy grindelic acid was the sole product formed when 3β-hydroxy-grindelic acid was used as the substrate for biotransformation.