Preparation of menisdaurigenin and related compounds

Menisdaurin (1), a cyano glucoside, was first isolated in 1978 from Menispermum dauricum (Menispermaceae) and named after the plant. It has been also isolated from several plant sources. The stereochemistry of the aglycone part was first reported as (Z,4R,6S)-enantiomer of (4,6-dihydroxy-2-cyclohexen-1-ylidene)acetonitrile based on the CD spectrum of menisdaurilide (2), the α,β-unsaturated γ-lactone obtained by an acid hydrolysis of menisdaurin. Later, the absolute stereochemistry was revised as (Z,4S,6R) by X-ray crystal analysis of 1 isolated from Saniculiphyllum guangxiens. The aglycone part of menisdaurin (1) has not been obtained from 1, because an acid hydrolysis of 1 gave menisdaurilide (2), and enzymatic hydrolysis with emulsin did not give the aglycone. On the other hand, a compound named coculauril (3) was isolated from Cocculus lauriforius. This compound has the same planner structure corresponding to the aglycone of 1, but the stereochemistry was reported to be (E,4R,6S). Here, we confirmed the absolute stereochemistry of 1 by Mosher's method to be (Z,4S,6R), and prepared the aglycone of 1, i.e., menisdaurigenin (4) by an enzymatic hydrolysis of 1. We also revealed that 4 is a different compound from 3 and unstable in water and MeOH.