Stereochemical Assignment of Strigolactone Analogues Confirms Their Selective Biological Activity

Strigolactones (SLs) are new plant
hormones with various developmental
functions. They are also soil signaling chemicals that are required
for establishing beneficial mycorrhizal plant/fungus symbiosis. In
addition, SLs play an essential role in inducing seed germination
in root-parasitic weeds, which are one of the seven most serious biological
threats to food security. There are around 20 natural SLs that are
produced by plants in very low quantities. Therefore, most of the
knowledge on SL signal transduction and associated molecular events
is based on the application of synthetic analogues. Stereochemistry
plays a crucial role in the structure–activity relationship
of SLs, as compounds with an unnatural D-ring configuration may induce
biological effects that are unrelated to SLs. We have synthesized
a series of strigolactone analogues, whose absolute configuration
has been elucidated and related with their biological activity, thus
confirming the high specificity of the response. Analogues bearing
the R-configured butenolide moiety showed enhanced
biological activity, which highlights the importance of this stereochemical
motif.