Synthetic disproof against the structure proposed for alectrol, the germination stimulant from Vigna unguiculata

Structure and function of natural and synthetic signalling molecules in parasitic weed germination

“…Another strigolactone, orobanchol ( 3 ), was isolated from red clover, Trifolium pretense L., an Orobanche host 15. The structures of compounds 1 to 3 have been confirmed by total synthesis;16–25 however, the spectroscopic data of the synthetic compound26, 27 with structure 4 were not in accordance with those reported for natural alectrol 12. Since then, the true structure of alectrol has remained controversial, and a bridged structure 5 for this stimulant was proposed 28.…”

“…Therefore, confirmation of structural analysis/elucidation of these strigolactones through total synthesis is desirable and indispensable. Alectrol is such a case, where the proposed structure 4 was refuted by synthesis26, 27 (see above). In order to assist the identification of stimulants from root exudates, the authors propose to prepare a library of strigolactones covering all stereoisomers, which then can serve as reference compounds in analysing HPLC chromatograms and mass and NMR spectra (see also Section 11.1).…”

Germination stimulant from root exudates of Vigna unguiculata

“…Three other strigolactones (2-4) have been isolated from root exudates of host plants, namely (+)-sorgolactone (2) from sorghum (Sorghum bicolor) ), (+)-orobanchol (3) from red clover (Trifolium pratense) (Yokota et al 1998), and alectrol (4) from cowpea (Vigna unguiculata) and red clover Yokota et al 1998). The deduced structures of 1-3 have been reconfirmed by synthetic studies (Sugimoto et al 1998;Matsui et al 1999;Hirayama and Mori 1999), although the structure of 4 proposed by Müller et al (1992) was pointed out to be in error by the synthetic studies of Mori et al (1998). The active compound which acts as a germination stimulant for the parasites, Striga gesnerioides, from cowpea has been isolated, but the determination of its chemical structure remains to be solved.…”

Biosynthetic considerations could assist the structure elucidation of host plant produced rhizosphere signalling compounds (strigolactones) for arbuscular mycorrhizal fungi and parasitic plants

“…6, compound (1) and compound (4) have already been identified as strigol and orobanchol, respectively. Compound (10) was previously suggested to be alectrol [34], which was excluded on the basis of mismatching spectra of the synthetic structure and the natural alectrol [29,32]. Muller et al also considered the structure with the gem-methyl groups at C-5 instead of at C-8 (12) (Figs.…”