Glycryrrhizic acid was metabolized to 3-oxo-18 beta-glycyrrhetinic aci
d via 18 beta-glycyrrhetinic acid by Aspergillus niger, A. oryzae, A.
sojae, and A. tamarii. Two methyl esters were derived from these two m
etabolites and identified by their C-13-NMR spectra and MS data.