Swee-Hock Goh

Novel cytotoxic polyprenylated xanthonoids from Garcinia gaudichaudii (Guttiferae)

Abstract Cytotoxicity guided phytochemical analysis of the leaf extract of the Malaysian medicinal plant Garcinia gaudichaudii led to the isolation of 15 novel cytotoxic compounds, gaudichaudiones A - H ( 1,2,8 – 10 and 12 ), gaudichaudiic acids A - E ( 3 – 6 ), including the known morellic acid ( 7 ) and forbesione ( 11 ). All are mainly tetraprenylated xanthonoids but gaudichaudione H ( 12 ) is a novel bridgehead methoxylated triprenylated xanthonoid. The novel caged structures were determined by detailed NMR spectral analysis and the compounds were found to exhibit significant cytotoxicity against several cancer cell lines.

Griffipavixanthone, a novel cytotoxic bixanthone from Garcinia griffithii and G. pavifolia

Abstract A bioactivity-directed fractionation of the extracts of the Malaysian plant Garcinia pavifolia and a phytochemical study of G. griffithii led to the discovery of griffipavixanthone ( 1 ), a novel cytotoxic bixanthone with cyclized prenyl groups providing the xanthone-xanthone linkage. Spectroscopic data and preparation of methylated derivatives allowed for the complete structural elucidation of 1 .

CYTOTOXIC CAGED TETRAPRENYLATED XANTHONOIDS FROM GARCINIA GAUDICHAUDII (GUTTIFERAE)

Abstract Leaves of the Malaysian medicinal plant Garcinia gaudichaudii yielded novel and cytotoxic gaudichaudiones A-D which are pentacyclic tetra-isoprenylated xanthonoids. These compounds which exhibited significant cytotoxicity to several cancer cell lines, had their structures determined by detailed spectral analysis.

Eicosenones and methylated flavonols from Amomumkoenigii

Abstract Two novel eicosenones, 1-methoxy-cf11>Efy1>cf1>-4-eicosen-3-one and1-(4-hydroxyphenoxy)-cf11>Efy1>cf1>-4-eicosen-3-one, together with eleven knownmethylated flavonols were isolated from the fruits of cf11>Amomum koenigiify1>cf1>. Theirstructures were elucidated by spectroscopic techniques.

Lateriflorone, a cytotoxic spiroxalactone with a novel skeleton, from Garcinia lateriflora BL

Abstract Lateriflorone ( 1 ), a cytotoxic natural product with an unprecedented spiroxalactone skeleton isolated from Garcinia lateriflora , has been characterized by NMR and X-ray crystallography studies as 6,21-bis(3-methylbut-2-enyl)-19-hydroxy-2,2,23,23-tetramethyl-13,15,22-trioxaspiro[6,7-dihydro-2H-chromene-7,4′-tetracyclo[7.4.1.0 2,7 .0 2,11 ] tetradecane]-17-ene-5,8,16,20-tetraone.

Modes of action of fraxinellone against the tobacco budworm, Heliothis virescens

Fraxinellone significantly reduced the relative growth rate, food consumption rate as well as the efficiency of conversion of ingested food into biomass of Heliothis virescens when incorporated into artificial diets at concentrations of 4.31 × 10−5 mol/L and above. After being fed with fraxinellone‐treated diets for 24 h, the larval midguts of H. virescens possess significantly lower activities of α‐amylase and non‐specific proteases and higher activities of cytochrome P450s. In vitro, the compound did not inhibit the activities of α‐amylase and non‐specific proteases extracted from the larval midguts. Clear evidence of post‐ingestive toxicity of fraxinellone to midgut cells was observed under an electron microscope. The modes of action of the compound against insects were discussed.

Coumarins from Calophyllum teysmannii

Abstract During a chemotaxonomic survey of several Malaysian Calophyllum species, two new coumarins were isolated from the bark of Calophyllum teysmannii var. inophylloide . Structure elucidation of the new coumarins, teysmanones A and B are presented and species varieties are discussed. The known calanone and inophyllums C and E were also isolated.

Larvicidal Activity of Malaysian Goniothalamus Species

Abstract Extracts of thirteen Malaysian Goniothalamus plants and two other annonaceous plants (Disepalum and Mezzetia species) were screened for bioactive components. Larvicidal principles include four classes of natural products (acetogenins, styrylpyrone derivatives, dioxoaporphines and flavanones) which account for their ethnobotanical uses.

A remote substituent as a control element in indium-mediated allylation reactions in aqueous media: highly diastereoselective synthesis of 1,3-amino alcohols

Abstract A new method for the stereoselective synthesis of 1,3-amino alcohols based on the indium-mediated allylation of keto ester (R,S)-2 in aqueous media, resulting from shielding of one face by a remote substituent, was developed to be a useful method for acyclic stereocontrol in the absence of any obvious steric interaction.

Prenylated xanthones from Garcinia opaca

Abstract Macluraxanthone, 1,3,5-trihydroxy-6′,6′-dimethylpyrano-(2′,3′:6,7)-4-(1,1-dimethylprop-2-enyl)xanthone and two new prenylated xanthones, 1,3,5-trihydroxy-6′,6′-dimethylpyrano(2′,3′:6,7)-2-(3-methylbut-2- enyl)-4-(1,1- dimethylprop-2-enyl)xanthone and 4″,5″-dihydro-1,5-dihydro-1,5-dihydroxy-6′,6′- dimethylpyrano(2′,3′:6,7)-2-(3- methylbut-2-enyl)-4″,4″,5″-trimethylfurano(2″,3″:3,4) xanthone, have been isolated from the leaf extract of Garcinia opaca . The structures of these compounds were established on the basis of 2D NMR and other spectroscopic techniques.