Stereochemistry and putative origins of flavanones found in post-administration urine of the traditional Chinese remedies shosaiko-to and daisaiko-to.

Optically active flavanones, dihydrowogonin and dihydrooroxylin A, were found in the urine of healthy volunteers who orally received the traditional Chinese remedies Shosaiko-to and Daisaiko-to on separate occasions. These remedies, which consisted of dried extracts of Scutellariae Radix and other herbs, contained the metabolic precursors of the flavanones, but not the flavanones themselves, in stoichiometrically sufficient amounts. Structures and stereochemistry of the flavanones were elucidated by UV, circular dichroism (CD), electron impact (EI)-MS and 1H-NMR analyses, showing that the biotransformations from the corresponding flavones, wogonin and oroxylin A, were stereoselective with a preference for the S-enantiomers. The putative origins of the flavanones were confirmed in terms of pharmacokinetics. Renal excretion-time data of the flavanones and the flavones suggested that the stereoselective transformations might have occurred in the intestinal tract as a result of microfloral metabolism before absorption.