Sim Keng Yeow
Email Address
chmsimky@nus.edu.sg
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Publication (-)-Ledol from Calophyllum teysmanii: Structure and stereochemistry(2000) Cao, S.-G.; Sim, K.-Y.; Goh, S.H.; CHEMISTRYThe bark extracts of Calophyllum teysmannii furnished (-)-ledol (1a) and its structure and stereochemistry were established by 2D NMR and synthesis from (+)-aromadendrene. Inconsistencies of previously reported data on the stereochemistry of (-)-ledol are discussed and corrected.Publication Xanthones and benzophenones from Garcinia griffithii and Garcinia mangostana(2005-07) Nilar; Nguyen, L.-H.D.; Venkatraman, G.; Sim, K.-Y.; Harrison, L.J.; CHEMISTRYA new polyisoprenylated benzophenone, guttiferone I, together with the known compounds cambogin, 1,7-dihydroxyxanthone, 1,3,6,7-tetrahydroxyxanthone and 1,3,5,6-tetrahydroxyxanthone were isolated from the stem bark of Garcinia griffithii. The acetone extract of the heartwood of Garcinia mangostana contained one new diprenylated xanthone (mangoxanthone) and a new benzophenone (3′,6-dihydroxy-2,4,4′-trimethoxybenzophenone) as well as the known xanthones dulxanthone D, 1,3,7-trihydroxy-2-methoxyxanthone, 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran[7,6-b]xanthen-9-one. Their structures were established on the basis of spectroscopic studies and chemical correlation. © 2005 Elsevier Ltd. All rights reserved.Publication The in vitro Antitumour Activity of Substituted Dibutyl-1,3,2-dioxastannolanes(1997-07) Ng, S.C.; Parsons, P.G.; Sim, K.Y.; Tranter, C.J.; White, R.H.; Young, D.J.; CHEMISTRYSix dibutyl-l,3,2-dioxastannolanes, including two enantiomeric pairs, exhibited greater in vitro antitumour activity towards a variety of human tumour cell lines than cisplatin but with little discrimination, suggesting hydrolysis to a common cytotoxic intermediate. A cell line hypersensitive to mitochondrial inhibitors (CI80-13S) was not sensitive to any of the test compounds, suggesting that cell mechanisms other than, or in addition to, mitochondrial function are targeted by tin antitumour agents. A pigmented melanoma cell line (MM418c5) was resistant to the test compounds, which were found to be sequestered by melanin. This resistance was not observed with triphenyltin hydroxide. © 1997 by John Wiley & Sons, Ltd.Publication A highly stereoselective one-pot asymmetric synthesis of homoallylic amines and amino acids from aldehydes(1997-02-03) Loh, T.-P.; Ho, D.S.-C.; Xu, K.-C.; Sim, K.-Y.; CHEMISTRYA simple and efficient one-pot method was developed to give chiral homoallylic amines and amino acids from the respective aldehydes in high stereoselectivity.Publication Triterpenoids, tocotrienols and xanthones from the bark of Cratoxylum Cochinchinense(1993-03) Bennett, G.J.; Harrison, L.J.; Sia, G.-L.; Sim, K.-Y.; CHEMISTRYA novel bicyclic triterpenoid, polypoda-8(26),13,17,21-tetraen-3β-ol, as well as friedelin, three known tocotrienols, four known xanthones (mangostin, β-mangostin, garcinone D and tovophyllin A) and the previously unreported 2-geranyl-1,3,6-trihydroxy-4-(3,3-dimethylallyl)-xanthone and cratoxylone (1,3,6-trihydroxy-2-(3-hydroxy-3-methylbutyl)-7-methoxy-8-(3,3-dimethylallyl)-xanthone) have been isolated from the bark of Cratoxylum cochinchinense. The structures of the new compounds were determined using a combination of spectroscopic and chemical methods. © 1993.Publication Three new coumarins from Calophyllum teysmannii var. inophylloide (guttiferae)(1997) Cao, S.-G.; Sim, K.-Y.; Goh, S.-H.; CHEMISTRYA chemotaxonomic survey of Malaysian Calophyllum plants for potential bioactive compounds provided three new coumarins [12-methoxyinophyllum P (1), hydrohydroxyisocalanone (2) and 4-phenyl-5-methoxy-7-hydroxy-8-benzoylcoumarin (3)] from the bark of C. teysmannii var. inophylloide, together with known compounds calanone (4) and betulinic acid. Their structures were determined by spectroscopic analysis including 2D NMR.Publication Griffipavixanthone, a novel cytotoxic bixanthone from Garcinia griffithii and G. pavifolia(1998-12-03) Xu, Y.-J.; Cao, S.-G.; Wu, X.-H.; Lai, Y.-H.; Tan, B.H.K.; Pereira, J.T.; Goh, S.H.; Venkatraman, G.; Harrison, L.J.; Sim, K.-Y.; CHEMISTRYA 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.Publication Gracilipene: A heterocyclic seco-trisnor-oleanane from Calophyllum gracilipes (Guttiferae)(1997-07-07) Cao, S.-G.; Sim, K.-Y.; Goh, S.-H.; Xue, F.; Mak, T.C.W.; CHEMISTRYGracilipene, a novel heterocyclic trisnor-triterpene from the leaves of Calophyllum gracilipes, shows an unprecedented rearranged seco-trisnor-oleanane structure with a dihydropyran ring-A, as determined by NMR spectra and single crystal X-ray analysis. Other known triterpenes isolated include friedelin, lupeol, lupenone, β-sitosterol, stigmasterol, 3β-hydroxy-30-norlupan-20-one, lupane-3β,20-diol, (20R)-3β-hydroxylupan-29-oic acid, betulinic acid and squalene.Publication A highly prenylated xanthone from the bark of Calophyllum gracilipes (Guttiferae)(1997) Cao, S.-G.; Lim, T.-B.; Sim, K.-Y.; Goh, S.H.; CHEMISTRYPublication Screening of traditional medicines for their inhibitory activity against HIV-1 protease(1996-05) Xu, H.-X.; Wan, M.; Loh, B.-N.; Kon, O.-L.; Chow, P.-W.; Sim, K.-Y.; CHEMISTRY; BIOCHEMISTRYAqueous extracts of 75 different traditional medicines, currently used for the treatment of various human diseases in China, Japan and Indonesia, were screened for possible inhibitory activity against HIV-1 protease using fluorogenic assay. Forty extracts exhibited inhibitory activity at a concentration of 250 μg/mL, and 18 of them inhibited HIV-1 protease activity by more than 70%. Among the extracts examined, Belamcanda chinensis, Magnolia fargesii, Paeonia suffruticosa, Phellodendron amurense and Terminalia chebula were also effective at a concentration of 25 μg/mL in the fluorogenic assay.