Soulamarin, a new coumarin from stem bark of Calophyllum soulattri

The extracts of the stem bark of Calophyllum soulattri gave a new pyranocoumarin, soulamarin (1), together with five other xanthones caloxanthone B (2), caloxanthone C (3), macluraxanthone (4), trapezifolixanthone (5) and brasixanthone B (6) one common triterpene, friedelin (7), and the steroidal triterpene stigmasterol (8). The structures of these compounds were established based on spectral evidence (1D and 2D NMR).     

<em>Mesua beccariana </em>(Clusiaceae), A Source of Potential Anti-cancer Lead Compounds in Drug Discovery

An investigation on biologically active secondary metabolites from the stem bark of Mesua beccariana was carried out. A new cyclodione, mesuadione (1), along with several known constituents which are beccamarin (2), 2,5-dihydroxy-1,3,4-trimethoxy anthraquinone (3), 4-methoxy-1,3,5-trihydroxyanthraquinone (4), betulinic acid (5) and stigmasterol (6) were obtained from this ongoing research. Structures of these compounds were elucidated by extensive spectroscopic methods, including 1D and 2D-NMR, GC-MS, IR and UV techniques. Preliminary tests of the in vitro cytotoxic activities of all the isolated metabolites against a panel of human cancer cell lines Raji (lymphoma), SNU-1 (gastric carcinoma), K562 (erythroleukemia cells), LS-174T (colorectal adenocarcinoma), HeLa (cervical cells), SK-MEL-28 (malignant melanoma cells), NCI-H23 (lung adenocarcinoma), IMR-32 (neuroblastoma) and Hep-G2 (hepatocellular liver carcinoma) were carried out using an MTT assay. Mesuadione (1), beccamarin (2), betulinic acid (5) and stigmasterol (6) displayed strong inhibition of Raji cell proliferation, while the proliferation rate of SK-MEL-28 and HeLa were strongly inhibited by stigmasterol (6) and beccamarin (2), indicating these secondary metabolites could be anti-cancer lead compounds in drug discovery.     

Isolation and structural modifications of ananixanthone from Calophyllum teysmannii and their cytotoxic activities

Two naturally occurring xanthones, ananixanthone (1) and β-mangostin (2), were isolated using column chromatographic method from the n-hexane and methanol extracts of Calophyllum teysmannii, respectively. The major constituent, ananixanthone (1), was subjected to structural modifications via acetylation, methylation and benzylation yielding four new xanthone derivatives, ananixanthone monoacetate (3), ananixanthone diacetate (4), 5-methoxyananixanthone (5) and 5-O-benzylananixanthone (6). Compound 1 together with its four new derivatives were subjected to MTT assay against three cancer cell lines; SNU-1, K562 and LS174T. The results indicated that the parent compound has greater cytotoxicity capabilities against SNU-1 and K562 cell lines with IC₅₀ values of 8.97 ± 0.11 and 2.96 ± 0.06 μg/mL, respectively. Compound 5 on the other hand exhibited better cytotoxicity against LS174T cell line with an IC₅₀ value of 5.76 ± 1.07 μg/mL.     

Enantioselective organocatalytic synthesis of medicinally privileged 2-amino-4H-chromene-3-carbonitriles via a cascade process

An efficient organocatalytic cascade approach toward medicinally privileged 2-amino-4H-chromene-3-carbonitriles is reported. The enantioselective synthesis of these compounds is achieved in high yields and good to high ee values (up to 96% yield and 89% ee) using bifunctional amine-thiourea organocatalysts developed in our laboratory.     

Asymmetric organocatalytic cascade Michael/hemiketalization/retro-Henry reaction of β,γ-unsaturated ketoesters with α-nitroketones

An unprecedented enantioselective organocatalytic Michael/hemiketalization/retro-Henry cascade sequence is described, which catalyzed by a simple bifunctional indane amine-thiourea catalyst. This process provides a new route to the enantioselective synthesis of 5-nitro-pent-2-enoates, a precursor to α-ketolactam.     

A novel cyclodione coumarin from the stem bark of Mesua beccariana

Our ongoing investigations on the stem bark of Mesua beccariana afforded a novel cyclodione coumarin, beccamarin, together with two known xanthones, mesuarianone, mesuasinone, two anthraquinones, 4-methoxy-1,3,5-trihydroxy-anthraquinone and 2,5-dihydroxy-1,3,4-trimethoxyanthraquinone and one coumarin, mammea A/AB. The structures were elucidated by 1D and 2D NMR and MS techniques.     

Synthesis and Characterization of Three Isomeric Hepta-Nuclear Ruthenium Clusters

Reactions of 1,2,3,4-tetraphenyl-1,2,3,4-tetraphospholane(Ⅰ) with triruthenium Dodecacarbonyl in 1:2 molar ratio at different temperatures resulted in the cleavage of P-P bonds in Ⅰ to afford three new isomeric heptnuclear ruthenium clusters containing phosphido and phosphinidene ligands with the formula of[Ru₇(CO)₁₅(μ₄-PPh)₂{(μ₂-PPH)₂CH₂}]. All these new obtained clusters have been characterized by elementary analysis, IR, ¹H, and ¹³P NMR spectroscopy methods, and their molecular structures have been established by single crystal X-ray diffraction analysis, Cluster 1 is a chiral molecule alnd two enantiomers (la,lb) are present in it, The structure of 1 is found to contain two square pyramids skeleton sharing a triangular face.