Strigone, isolation and identification as a natural strigolactone from Houttuynia cordata

(+)-Strigone was described earlier in a paper on isolation of strigol and then recently examined for hyphal branching activity in arbuscular mycorrhizal fungi as a strigolactone. Herein, it was isolated from root exudates of Houttuynia cordata, and its structure was confirmed by direct comparison with synthetic standards in LC-MS/MS, GC-MS, and H-1 and C-13 NMR analyses. The stereochemistry of strigone was determined by comparing the CD spectra and RRt in chiral LC-MS/MS with those of synthetic (+)-strigone and ()-strigone. Four stereoisomers of strigone exhibited clearly different levels of stimulation activity on the seeds of three root parasitic plants, Orobanche minor, Phelipanche ramosa, and Striga hermonthica. (+)-Strigone was a highly potent germination stimulant on S. hermonthica and also on P. ramosa, but less active than ent-2'-epi-strigone on G. minor. In addition to strigone, H. cordata was found to produce strigol, sorgomol, and 5-deoxystrigol, indicating that this plant produces mainly strigol-type strigolactones derived from 5-deoxystrigol. (C) 2012 Elsevier Ltd. All rights reserved.