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By bioactivity-directed fractionation, six cytotoxic constituents have been characterized from the bark of Plumeria rubra collected in Indonesia. Three iridoids, fulvoplumierin 1, allamcin 2, and allamandin 3, as well as 2,5-dimethoxy-p-benzoquinone 4, were found to be active constituents of the P. rubra petroleum-ether- and CHCl3-soluble extracts. Cytotoxic compounds isolated from the H2O-soluble extract of the bark were the iridoid plumericin 5, and the lignan liriodendrin 6. Each of these substances was found to demonstrate general cytotoxic activity when evaluated with a panel of cell lines composed of murine lymphocytic leukemia (P-388) and a number of human cancer cell-types (breast, colon, fibrosarcoma, lung, melanoma, KB). Five additional iridoids, 15-demethylplumieride 7, plumieride 8, alpha-allamcidin 9, beta-allamcidin 10, and 13-O-trans-p-coumaroylplumieride 11, were obtained as inactive constituents. Compound 7 was found to be a novel natural product, and its structure was determined by spectroscopic methods and by conversion to plumieride 8. The configuration of the C-4 stereocenter was unambiguously assigned for compounds 9 and 10, and certain nmr reassignments have been provided for compound 1.
Kardono et al. (1990) studied this question.