TRICOLORIN-A, MAJOR PHYTOGROWTH INHIBITOR FROM IPOMOEA-TRICOLOR

The allelopathic potential of Ipomoea tricolor (Convolvulaceae), used in Mexican traditional agriculture as a weed controller, has been demonstrated by measuring the inhibitory activity of organic extracts on seedling growth of Amaranthus leucocarpus and Echinochloa crus-galli. Bioactivity-directed fractionation of the active CHCl3 extract led to the isolation of the allelopathic principle, which turned out to be a mixture of the so-called ''resin glycosides'' of convolvulaceous plants. The structure of tricolorin A, the major phytogrowth inhibitor present in the active fraction, was elucidated as (11S)-hydroxyhexadecanoic acid 11-0-alpha-L-rhamnopyranosyl-(l-->3)-O-alpha-L-[2-0-(2S-methylbutyryl)-4-0-(2S-methylbutyryl)] rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(l-->2)-beta-D-fucopyranoside-(1,3''-lactone)(1], based on chemical methods and spectral analysis including H-1-H-1COSY, H-1-C-13 HETCOR, long range H-1-C-13 COLOC, and selective INEPT experiments. Bioassays showed that radicle elongation of the two weed seedlings rested was inhibited by tricolorin A [1] with IC50 values ranging from 12 to 37 muM. Staphylococcus aureus was sensitive to compound 1 with an MIC value of 1.8 mug/ml. Significant cytotoxic activity against cultured P-388 and human breast cancer cells (ED50 2.2 mug/ml) was demonstrated for compound 1, and it also inhibited phorbol 12,13-dibutyrate binding using calf brain homogenate as a source of protein kinase C (IC50 43 muM).