Synthesis of spirocyclic heterocycles from α,ß-unsaturated N-acyliminium ions.

The reactions of α,ß-unsaturated N-acyliminium ions, generated in situ from 4(S)-O-substitutedhydroxy-5-hydroxy-5-vinyl-N-alkylpyrrolidin-2-ones, with allylsilanes and indoles leading to the formation of spirocyclic heterocycles, are reported. Six single crystal X-ray structures and extensive 2D NMR experiments confirmed the structures and stereochemistries of these products. In addition, computational studies provided mechanistic insights and an understanding of the stereochemical outcomes of these reactions.

Polyoxygenated Cyclohexenes and Their Chlorinated Derivatives from the Leaves of Uvaria cherrevensis.

The chemical study of leaf extracts from Uvaria cherrevensis resulted in the identification of 11 new polyoxygenated cyclohexenes, cherrevenols A-K (1-11), and a new seco-cyclohexene derivative, cherrevenol L (12). Nine known compounds (13-21) were also isolated. Three of the isolated compounds are chlorinated polyoxygenated cyclohexenes. The structures of these compounds were determined using spectroscopic methods and, in some cases (compounds 2, 6, 8, and 10), single-crystal X-ray crystallographic structural analysis or chemical correlation (compounds 6 and 7). Compounds 6 and 7 were both isolated as scalemic mixtures (ee 23-24%).

A new xanthone and a biphenyl from the flower and twig extracts of Garcinia mckeaniana.

The phytochemical investigation of the flower and twig extracts of Garcinia mckeaniana yielded a new xanthone, mckeanianone F (1) and a new biphenyl, mckeaniabiphenyl (2) together with 15 known compounds. The isolated compounds were characterized using spectroscopic techniques and mass spectrometry. Some of the isolated compounds from the twigs exhibited antimalarial and cytotoxic activities.

Four new C-benzyl flavonoids from the fruit of Uvaria cherrevensis.

The phytochemical investigation of the fruit extracts of Uvaria cherrevensis led to the isolation and characterization of four new C-benzyl flavonoids; cherrevenones A-D (1-4) together with 11 known compounds. The isolated compounds were characterized using spectroscopic techniques. Compounds 1, 3, 5 and 11 showed moderate inhibitory activities against the P. falciparum strains TM4/8.2 and K1CB1 with IC50 values ranging from 21.0 ±â€¯3.10 - 33.7 ±â€¯7.69 and 21.0 ±â€¯5.44 - 43.5 ±â€¯11.9 µM, respectively. Compounds 1, 2, 5, 10 and 11 exhibited strong cytotoxic activities against KB cells with IC50 values ranging from 0.60 ±â€¯0.17 - 4.91 ±â€¯2.69 µM which were similar to their cytotoxic activities found against Vero cells, except for compound 5, which was non-toxic to Vero cells.

2-Phenylnaphthalenes and a polyoxygenated cyclohexene from the stem and root extracts of Uvaria cherrevensis (Annonaceae).

Three new 2-phenylnaphthalene derivatives, cherrevenaphthalenes A-C (1-3), and a new polyoxygenated cyclohexene derivative, (-)-uvaribonol F (4) together with six known compounds, 5-10, were isolated from the stem and root extracts of Uvaria cherrevensis (Annonaceae). The structures of all isolated compounds were elucidated by spectroscopic analysis. The structures of 3 and 4 were further confirmed by single crystal X-ray diffraction methods. Compound 2 exhibited modest antiplasmodial activity against the P. falciparum stains TM4/8.2 and K1CB1 with IC50 values of 18.8±3.63 and 23.4±4.08µM, respectively, and weak cytotoxicity to a Vero cell line. Furthermore, compound 4 displayed cytotoxic activity against a KB cell line with an IC50 value of 22.1±0.42µM but was non-cytotoxic to the Vero cell line. Compound 5 revealed stronger cytotoxicity towards the KB cell line, with an IC50 value of 5.05±0.86µM and was nearly equally cytotoxic to the Vero cell line.

Antibacterial tetraoxygenated xanthones from the immature fruits of Garcinia cowa.

A phytochemical investigation of the acetone extract from the immature fruits of Garcinia cowa led to the isolation of two novel tetraoxygenated xanthones, garcicowanones A (1) and B (2), together with eight known tetraoxygeanted xanthones. Their structures were determined by spectroscopic analysis. All isolated compounds were evaluated for their antibacterial activity against Bacillus cereus TISTR 688, Bacillus subtilis TISTR 008, Micrococcus luteus TISTR 884, Staphylococcus aureus TISTR 1466, Escherichia coli TISTR 780, Pseudomonas aeruginosa TISTR 781, Salmonella typhimurium TISTR 292 and Staphylococcus epidermidis ATCC 12228. α-Mangostin showed potent activity (MIC 0.25-1 µg/mL) against three Gram-positive strains and garcicowanone A and ß-mangostin exhibited strong antibacterial activity against B. cereus with the same MIC values of 0.25 µg/mL.