The structure-activity relationship of lepidimoide and its analogues w
as investigated by means of the Amaranthus caudatus L. hypocotyl elong
ation test. In addition, the activities of alpha-D-galacturonic acid a
nd L-(+)-rhamnose, which are component sugars of lepidimoide, were als
o studied. The carboxylic acid free type of lepidimoide showed growth-
promoting activity as high as the original lepidimoide (sodium type).
The acetylated compound showed considerably higher activity than lepid
imoide, whereas the methylated lepidimoide did not show any activity.
The hydroxylated lepidimoide without a double bond in the C-4,5 positi
on showed lower activity. The sugar alcohol type of lepidimoide [2-O-(
alpha-D-glucopyranosyl)-L-rhamnose] showed the highest activity in all
the compounds studied. alpha-D-Galacturonic acid, L-(+)-rhamnose and
their mixtures, which are component sugars of lepidimoide, exhibited o
nly slight or no activity, respectively. D-Glucose and the mixture of
D-glucose and L-(+)-rhamnose were also slightly active or inactive. Th
ese data suggest that the active sites in the chemical structure of th
e lepidimoide are the uronic acid derivative bearing an alpha,beta-uns
aturated carboxylate bonded to rhamnose via an alpha-glucoside linkage
and a double bond in the C-4,5 position in the uronic acid.