Fabacyl acetate, a germination stimulant for root parasitic plants from Pisum sativum

A germination stimulant, fabacyl acetate. was purified from root exudates of pea (Pisum sativum L.) and its structure was determined as ent-2'-epi-4a,8a-epoxyorobanchyl acetate [(3aR,4R,4aR,8bS,E)-4a,8a-epoxy-8,8-dimethyl-3-(((R)-4-methyl-5-oxo-2,5-dihydrofuran-2-yloxy)methylene)-2-oxo- 3,3a,4,5,6,7,8,8b-decahydro-2H-indeno[1,2-b]furan-4-yl acetate], by 1D and 2D NMR spectroscopic, ESI-and E1-MS spectrometric, X-ray crystallographic analyses, and by comparing the H-1 NMR spectroscopic data and relative retention times (RRt) in LC-MS and CC-MS with those of synthetic standards prepared from (+)-orobanchol and (+)-2'-epiorobanchol. The H-1 NMR spectroscopic data and RRt of fabacyl acetate were identical with those of an isomer prepared from (+)-2'-epiorobanchol except for the opposite sign in CD spectra. This is the first natural ent-strigolactone containing an epoxide group. Fabacyl acetate was previously detected in root exudates of other Fabaceae plants including faba bean (Vicia faba Q and alfalfa (Medicago sativa L). (C) 2008 Elsevier Ltd. All rights reserved.