Two bioactive saponins from Albizia subdimidiata from the Suriname rainforest.

Bioassay-guided fractionation of a methanol extract of Albizia subdimidiata using the engineered yeast strains 1138, 1140, 1353, and Sc7 of Saccharomyces cerevisiae as the bioassay tool resulted in the isolation of the two active saponins 1 and 2; one of these, albiziatrioside A (1), is described for the first time. The structures of 1 and 2 were established on the basis of HRMS, 1D and 2D NMR spectral data, and GC--MS analysis of the sugar units. Both isolated compounds showed significant cytotoxicity against the A2780 cell line.

Bioactive saponins from Swartzia schomburgkii from the suriname rainforest.

Bioassay-guided fractionation of the MeOH extract of Swartzia schomburgkii using the engineered yeast strains 1138, 1140, and 1353 as the bioassay tool resulted in the isolation of five active (2, 4-7) and three inactive (1, 3, 8) saponins. Saponins 4 and 6 are previously unreported. The structures of all of the saponins were established based on 1D and 2D NMR spectral analysis, on acid and alkaline hydrolysis followed by TLC and GC-MS, and by comparison with literature data for known compounds. Three of the isolated compounds (4-6) showed weak cytotoxicity against the M-109 cell line.

Synthesis and biological evaluation of analogues of cryptolepine, an alkaloid isolated from the Suriname rainforest.

Bioassay-guided fractionation of an extract of a mixture of Microphilis guyanensis and Genipa americanacollected in the rainforest of Suriname yielded the known alkaloid cryptolepine (2) as the major active compound in a yeast bioassay for potential DNA-damaging agents; the same compound was later reisolated from M. guyanensis. The structure of cryptolepine was identified unambiguously by spectral data and by its total synthesis. Several cryptolepine derivatives (3-29, 32-41) were synthesized based on modifications of the C-2, N-5, N-10, and C-11 positions. Two cryptolepine dimers (30, 31) were also prepared. The structure modifications did not result in compounds with a higher potency than the parent compound cryptolepine in the yeast assay system, although some derivatives did show significant activity. Selected compounds (6, 7, 17, 22, 23, 26, and 27) were also tested for cytotoxicity in mammalian cell culture, and two compounds showed significant cytotoxic activity.

DNA-damaging steroidal alkaloids from Eclipta alba from the suriname rainforest1.

Bioassay-guided fractionation of the MeOH extract of Eclipta alba using three yeast strains (1138, 1140, and 1353) resulted in the isolation of eight bioactive steroidal alkaloids (1-8), six of which are reported for the first time from nature. The major alkaloid was identified as (20S)(25S)-22,26-imino-cholesta-5,22(N)-dien-3beta-ol (verazine, 3), while the new alkaloids were identified as 20-epi-3-dehydroxy-3-oxo-5,6-dihydro-4,5-dehydroverazine (1), ecliptalbine [(20R)-20-pyridyl-cholesta-5-ene-3beta,23-diol] (4), (20R)-4beta-hydroxyverazine (5), 4beta-hydroxyverazine (6), (20R)-25beta-hydroxyverazine (7), and 25beta-hydroxyverazine (8). Ecliptalbine (4), in which the 22,26-imino ring of verazine was replaced by a 3-hydroxypyridine moiety, had comparable bioactivity to verazine in these assays, while a second alkaloid (8) showed good activity against Candida albicans. All the alkaloids showed weak cytotoxicity against the M-109 cell line.

Bioactive iridoids and a new lignan from Allamanda cathartica and Himatanthus fallax from the Suriname rainforest.

Bioassay-guided fractionation of the EtOAc extract of both Allamanda cathartica and Himatanthus fallax (Apocynaceae) using the Sc-7 yeast strain resulted in the isolation of the weakly cytotoxic isoplumericin and plumericin. In addition, the new lignan 7(R)-methoxy-8-epi-matairesional and three known compounds, plumieride, matairesinol, and pinoresinol, were isolated from H. fallax.