New Bitter-Tasting Hemiterpene Glycosides from the Japanese Fern Hymenophyllum barbatum

Abstract

Hymenosides G—J were newly isolated from the Japanese fern Hymenophyllum barbatum, in addition to hymenosides A—F. The structures of hymenosides were elucidated by extensive two-dimensional nuclear magnetic resonance and/or chemical evidence. The structures of those aglycones were divided into three types, 1,4-dihydroxy-2-hydroxymethyl-but-2-ene, 1,4-dihydroxy-2-methyl-but-2-ene, and 3-hydroxy-5-hexanolide. The sugar moieties were also established by chemical and spectroscopic methods, which were acylated by phenylacetic acid derivatives. These glycosides had a bitter or weakly pungent taste.