Isolation and identification of alectrol as (+)-orobanchyl acetate, a germination stimulant for root parasitic plants

Alectrol, a germination stimulant for root parasitic plants, was purified from root exudates of red clover (Trifolium pratense L.) and identified as a strigolactone, (+)-orobanchyl acetate [(3aS,4S,8bS,E)-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-octahydro-2H-indeno[1,2-b]furan-4-yl acetate], by 1D and 2D NMR spectroscopy and ESI- and EI-MS spectrometry. Orobanchyl acetate afforded an [M-42](+) ion in EI-MS and thus had been recognized as an isomer of strigol. Orobanchyl acetate was detected in root exudates of soybean (Glycine max L.) and cowpea (Vigina unguiculata L.) along with orobanchol.