Dehydro-para-asebotin, a New Chalcone Glucoside in the Flowers of Gnaphalium affine D. DON

TLDR: Examination of the methanolysis products of III permethylate (XV) and the spectral data of XV evidenced that III is 4'-O-β-D-glucopermethylate of 2', 4, 4'-trihydroxy-6'-methoxychalcone (dehydro-para-asebotin), from which V is yielded on acid treatment.

Abstract: Besides luteolin 4'-D-glucoside (I) and luteolin (II), a chalcone glycoside (III), C22H24O10·1 1/2 H2O, mp 199-200°, [α]30D-85.2°(methanol), ultraviolet spectrum (UV) λEtOHmax 368 nm, was isolated from the flowers of Gnaphalium affine D. DON. III was acid hydrolyzed to give glucose and a flavanone (V), mp 256°, UV λEtOHmax 228, 284 nm, which was identified as 4', 7-dihydroxy-5-methoxyflavanone by chemical and spectral data and by direct comparison of the diethyl ether (VIII) with an authentic sample. The sample, 4', 7-diethoxy-5-methoxyflavanone (VIII) was prepared, according to the result of a preliminary experiment (Table I), by stepwise alkylations of naringenin (IX) with an ether solution of diazoethane in absolute methanol for 3 hr and then with diazomethane in 70% methanol for 24 hr. Further examination of the methanolysis products of III permethylate (XV) and the spectral data of XV evidenced that III is 4'-O-β-D-glucopermethylate of 2', 4, 4'-trihydroxy-6'-methoxychalcone (dehydro-para-asebotin), from which V is yielded on acid treatment. This is the first isolation of III and V from natural sources.