Abstract
Two new substances, neoastilbin (II) and isoastilbin (III), were obtained by heating astilbin ((+)-dihydroquercetin 3-L-rhamnoside) (I) with 10% pyridine water for a few hours or by heating in water for 40-50 hours and fractional crystallization of the residue, obtained after evaporation of the solvent, from 30% ethanol. Another new substance, neoisoastilbin (IV), was obtained on application of ethanolic sodium acetate solution to (I) (cf. Table I). All (I), (II), (III), and (IV) afforded quercitrin (quercetin 3-L-rhamnoside) on dehydrogenation and 2′-hydroxy-α-(L-rhamnosyioxy)-3, 4, 4′, 6′-tetramethoxychalcone by application of hot alkali solution to the respective tetramethyl ethers formed by reaction with ether solution of diazomethane (cf. Chart 1). These facts indicate that (II), (III), and (IV) are dihydroquercetin 3-L-rhamnoside, same as (I), and are considered to be stereoisomers arising from asymmetry at 2- and 3-positions in the aglycone.
