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.