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Your search keyword '"Tan, Siow-Ping"' showing total 28 results
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28 results on '"Tan, Siow-Ping"'

15. A Simple BF3•Et2O-mediated Cycloaddition Reaction to the Formation of Cyclic Monoterpenoid Pyrano[3,2-a]carbazole Alkaloids

Author

Tan Siow-Ping and Nafiah Mohd Azlan

Subjects
chemistry.chemical_compound, Simple (abstract algebra), Chemistry, Carbazole, Organic Chemistry, Organic chemistry, Biochemistry, Cycloaddition
Abstract

Abstract: A Lewis acid BF3•Et2O-mediated intramolecular cycloaddition reaction of mahanimbine (1) is described. Three cycloadducts, bicyclomahanimbine (2), cyclomahanimbine (3) and murrayazolinine (4) were obtained. The structural characterization of these compounds was determined by 1D and 2D NMR experiments. These compounds showed no cytotoxic activity against human MRC-5 cells (IC50 > 60 μg/mL). Compound 3 showed the highest inhibition cytotoxic effects against HeLa and HL-60 cancer cells with IC50 values of 10.0 and 28.7 μg/mL, respectively. This strategy opens a new approach for the synthesis of biologically significant cyclic monoterpenoid pyrano[3,2-a]carbazole alkaloids.

Published
2021

18. Morphinan Alkaloids from the Leaves of Alphonsea cylindrica and Their Antibacterial Properties.

Author

Cho, Kin-Hau, Tan, Siow-Ping, Tan, Hui-Yin, Liew, Sook Yee, and Nafiah, Mohd Azlan

Subjects
*ESCHERICHIA coli, *MEDICINAL plants, *HETEROCYCLIC compounds, *ALKALOIDS, *ANTI-infective agents, *PHYTOCHEMICALS, *LEAVES, *PLANT extracts, *MOLECULAR structure, *ANTIBIOTICS, *MICROBIAL sensitivity tests
Abstract

A phytochemical study has been carried out on CH2 Cl2 extract of Alphonsea cylindrica leaves, resulting in the isolation of three new morphinan alkaloids. They are kinomenine (1), N -methylkinomenine (2), and hydroxymethylkinomenine (3). The structures of these compounds were elucidated by extensive spectroscopic analysis (1D and 2D NMR, IR, UV, HRESIMS) and comparison with the data reported in literature for similar alkaloids. Kinomenine (1) and N -methylkinomenine (2) showed weak inhibition against S. aureus (MIC values of 1 and 2 = 500 µg/mL; pIC50 values in 95% C. I. of: 1 = 2.9 to 3.0; 2 = 2.9 to 3.1), while kinomenine (1) also showed weak inhibition against E. coli (MIC values of 1 = 500 µg/mL; pIC50 value in 95% C. I. of: 1 = 2.9) by broth microdilution method. The results obtained can be used as future referencefor the discovery of morphinans and the potential of A. cylindrica as an antibacterial source. [ABSTRACT FROM AUTHOR]

Published
2023
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21. A Simple BF3•Et2O-mediated Cycloaddition Reaction to the Formation of Cyclic Monoterpenoid Pyrano[3,2-a]carbazole Alkaloids

Author

Tan, Siow-Ping and Nafiah, Mohd Azlan

Abstract

A Lewis acid BF3•Et2O-mediated intramolecular cycloaddition reaction of mahanimbine (1) is described. Three cycloadducts, bicyclomahanimbine (2), cyclomahanimbine (3) and murrayazolinine (4) were obtained. The structural characterization of these compounds was determined by 1D and 2D NMR experiments. These compounds showed no cytotoxic activity against human MRC-5 cells (IC50> 60 μg/mL). Compound 3 showed the highest inhibition cytotoxic effects against HeLa and HL-60 cancer cells with IC50 values of 10.0 and 28.7 μg/mL, respectively. This strategy opens a new approach for the synthesis of biologically significant cyclic monoterpenoid pyrano[3,2-a]carbazole alkaloids.

Published
2021
Full Text
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22. New Indole Alkaloids from Kopsia Singapurensis (RIDL.)

Author

Koichi Takeya, Yusuke Hirasawa, A. Hamid A. Hadi, Alfarius Eko Nugroho, Tan Siow Ping, Noel F. Thomas, Hiroshi Morita, Khalijah Awang, Mohd Azlan Nafiah, and Kartini Ahmad

Subjects
Indole test, Kopsia singapurensis, biology, Apocynaceae, Chemistry, Stereochemistry, Chemical constituents, Organic chemistry, biology.organism_classification
Abstract

Study on chemical constituents from Kopsia singapurensis (Apocynaceae) yielded four new aspidofractinines: Singaporentine A (1), N(1)-formylkopsininic acid (2), N(1)-formylkopsininic acid-N(4)-oxide (3), 15-hydroxykopsamine (4); a new aspidospermatan: 14α-hydroxy-N(4)-methylcondylocarpine (5) and a new akuamiline: singaporentinidine (6) together with 18 known indole alkaloids from different parts of the plant. The structures of these compounds were elucidated by combination of various spectroscopic methods.

Published
2013

24. Cytotoxic and anti-tumour promoting activities of carbazole alkaloids from Malayan Murraya koenigii (L.) Spreng

Author

Ahmad, Kartini, Tan, Siow Ping, Md. Sukari, Mohd. Aspollah, Ali, Abdul Manaf, Nafiah, Mohd Azlan, Ahmad, Kartini, Tan, Siow Ping, Md. Sukari, Mohd. Aspollah, Ali, Abdul Manaf, and Nafiah, Mohd Azlan

Abstract

Murraya koenigii (L.) (Rutaceae) is an indigenous medicinally important herb of Indian origin and now is widely distributed throughout southern Asia. The stem bark, leaves and roots of Malayan Murraya koenigii were selected for phytochemical investigation. Eight carbazole alkaloids was isolated and identified using spectroscopic methods including NMR, IR, UV, MS spectra data. Crude extract and isolated compounds from the roots of this plant were screened for cytotoxic activity and antitumor promoting activity. All crude extracts of the roots including the isolated compounds, mahanimbine, mahanine and murrayafoline-A exhibited significant cytotoxic activity against CEM-SS cell line with IC50 3mg/mL. Girinimbine inhibited EBV-activation in the antitumor promoting assay.

Published
2014

26. The Study of Caffeine as Novel Quorum Sensing Inhibitor

Author

Siti Nur Maisarah Norizan, Kok-Gan Chan, Wai-Fong Yin, Mohd Azlan Nafiah, and Tan Siow Ping

Subjects
Communication, biology, business.industry, Biofilm, Virulence, biochemical phenomena, metabolism, and nutrition, biology.organism_classification, chemistry.chemical_compound, Quorum sensing, Biochemistry, chemistry, Gene expression, Bioassay, Bioluminescence, Caffeine, business, Bacteria
Abstract

Quorum sensing enables bacterial to communicate and at the same time control the gene expression in response to the cell density [1]. It is widely used by both gram-positive and gram-negative bacteria to regulate variety of bacterial physiological functions such as biofilm formation [2], bioluminescence [3], virulence factors [4] and swarming [5] which has been shown contribute to bacterial pathogenesis. With this knowledge, the use of QS inhibitor would be a particular value in treating bacterial pathogenicity and infections. In this work we have tested caffeine as quorum sensing inhibitor by using C.violaceum CV026 as a bioassay. This C.violaceum CV026 mutant strain is incapable of producing the purple pigment called violacein unless there are exogenous supply of N-hexanoylhomoserine lactone (C6-HSL) or other short chain AHL .The Inhibitory activity was measured by quantifying violacein production using a spectrophotometer. The results have revealed that Caffeine significantly reduced violacein production in a concentration dependent manner, indicating inhibition of quorum sensing. The presence of caffeine that exhibit anti-quorum sensing activity may be useful as the lead of anti-infective drugs.

Published
2013

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