STRUCTURE-ACTIVITY RELATIONSHIP OF LEPIDIMOIDE AND ITS ANALOGS

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.