Phytotoxic compounds from Xanthocephalum gymnospermoides var. eradiatum

Investigation of the aerial parts of Xanthocephalum gymnospermoides var era diatum led to the isolation of two new labdane-type of diterpenes, namely, 8 alpha ,13S-epoxylabdane14S,15-diol (1) and methyl grindelate (2). In addi tion, grindelic acid (3), 7 alpha ,8 alpha -epoxygrindelic acid (4), 7 alph a -hydroxy-8(17)dehydrogrindelic acid (5), 17-hydroxygrindelic acid (6) and 4,5-epoxy-beta -caryophyllene (7) were obtained. The isolated compounds we re characterized by spectral means. The absolute configuration of compound 1 was established by chemical correlation with 8 alpha ,13S-epoxy-15-nor-la bdan-14-oic acid methyl ester of known absolute stereochemistry and by usin g the advanced Mosher's ester methodology. The results of the present inves tigation indicated that the known compound barbatol (8) could be an enantio mer of compound 1. Compounds 1-3 and 7 caused significant inhibition of the radicle growth of seedlings of Amaranthus hypochondriacus.