Displaying publications 1 - 20 of 92 in total

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  1. Al-Majedy YK, Al-Amiery AA, Kadhum AA, Mohamad AB
    PLoS One, 2016;11(5):e0156625.
    PMID: 27243231 DOI: 10.1371/journal.pone.0156625
    The synthesis of derivatives of 4-Methylumbelliferone (4-MUs), which are structurally interesting antioxidants, was performed in this study. The modification of 4-Methylumbelliferone (4-MU) by different reaction steps was performed to yield the target compounds, the 4-MUs. The 4-MUs were characterized by different spectroscopic techniques (Fourier transform infrared; FT-IR and Nuclear magnetic resonance; NMR) and micro-elemental analysis (CHNS). The in vitro antioxidant activity of the 4-MUs was evaluated in terms of their free radical scavenging activities against 2,2-diphenyl-1-picrylhydrazyl (DPPH), Nitric oxide radical scavenging activity assay, chelating activity and their (FRAP) ferric-reducing antioxidant power, which were compared with a standard antioxidant. Our results reveal that the 4-MUs exhibit excellent radical scavenging activities. The antioxidant mechanisms of the 4-MUs were also studied. Density Function Theory (DFT)-based quantum chemical studies were performed with the basis set at 3-21G. Molecular models of the synthesized compounds were studied to understand the antioxidant activity. The electron levels, namely HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), for these synthesized antioxidants were also studied.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  2. Shah SH, Kar RK, Asmawi AA, Rahman MB, Murad AM, Mahadi NM, et al.
    PLoS One, 2012;7(11):e49788.
    PMID: 23209600 DOI: 10.1371/journal.pone.0049788
    Exotic functions of antifreeze proteins (AFP) and antifreeze glycopeptides (AFGP) have recently been attracted with much interest to develop them as commercial products. AFPs and AFGPs inhibit ice crystal growth by lowering the water freezing point without changing the water melting point. Our group isolated the Antarctic yeast Glaciozyma antarctica that expresses antifreeze protein to assist it in its survival mechanism at sub-zero temperatures. The protein is unique and novel, indicated by its low sequence homology compared to those of other AFPs. We explore the structure-function relationship of G. antarctica AFP using various approaches ranging from protein structure prediction, peptide design and antifreeze activity assays, nuclear magnetic resonance (NMR) studies and molecular dynamics simulation. The predicted secondary structure of G. antarctica AFP shows several α-helices, assumed to be responsible for its antifreeze activity. We designed several peptide fragments derived from the amino acid sequences of α-helical regions of the parent AFP and they also showed substantial antifreeze activities, below that of the original AFP. The relationship between peptide structure and activity was explored by NMR spectroscopy and molecular dynamics simulation. NMR results show that the antifreeze activity of the peptides correlates with their helicity and geometrical straightforwardness. Furthermore, molecular dynamics simulation also suggests that the activity of the designed peptides can be explained in terms of the structural rigidity/flexibility, i.e., the most active peptide demonstrates higher structural stability, lower flexibility than that of the other peptides with lower activities, and of lower rigidity. This report represents the first detailed report of downsizing a yeast AFP into its peptide fragments with measurable antifreeze activities.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  3. Sivasothy Y, Loo KY, Leong KH, Litaudon M, Awang K
    Phytochemistry, 2016 Feb;122:265-269.
    PMID: 26712615 DOI: 10.1016/j.phytochem.2015.12.007
    A dimeric acylphenol and a potent α-glucosidase inhibitor, giganteone D (IC50 5.05μM), was isolated and characterized from the bark of Myristica cinnamomea King. The bark also yielded an acylphenol with an unprecedented skeleton for which the name cinnamomeone A (IC50 358.80μM) was proposed. Their structures were established by means of NMR and MS spectrometric analyses. The Lineweaver-Burk plot of giganteone D indicated that it was a mixed-type inhibitor. This is the first report on the α-glucosidase inhibiting potential of acylphenols.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  4. Gan CY, Yoganathan K, Sim KS, Low YY, Lim SH, Kam TS
    Phytochemistry, 2014 Dec;108:234-42.
    PMID: 25442910 DOI: 10.1016/j.phytochem.2014.09.014
    Eleven indole alkaloids, comprising four corynanthean, two eburnane, one aspidofractinine, one secoleuconoxine, one andranginine, and two pauciflorine type alkaloids were isolated from the stem-bark and leaf extracts of Kopsia pauciflora. Their structures were determined using NMR and MS analyses. The catharinensine type alkaloid kopsirensine B and the secoleuconoxine alkaloid arboloscine A showed moderate to weak activity in reversing MDR in vincristine-resistant KB cells. The alkaloid content was markedly different compared to that of a sample from Malaysian Borneo.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  5. Gan CY, Low YY, Robinson WT, Komiyama K, Kam TS
    Phytochemistry, 2010 Aug;71(11-12):1365-70.
    PMID: 20542302 DOI: 10.1016/j.phytochem.2010.05.015
    Leucofoline and leuconoline, representing the first members of the aspidospermatan-aspidospermatan and eburnane-sarpagine subclasses of the bisindole alkaloids, respectively, were isolated from the Malayan Leuconotis griffithii. The structures of these bisindole alkaloids were established using NMR and MS analysis, and in the case of leuconoline, confirmed by X-ray diffraction analysis. Both alkaloids showed weak cytotoxicity towards human KB cells.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  6. Lukaseder B, Vajrodaya S, Hehenberger T, Seger C, Nagl M, Lutz-Kutschera G, et al.
    Phytochemistry, 2009 May;70(8):1030-7.
    PMID: 19535116 DOI: 10.1016/j.phytochem.2009.05.007
    Fifteen prenylated or geranylated flavanones and flavanonols were isolated from the leaf extracts of different Glycosmis species collected in Thailand and Malaysia. All structures were elucidated by spectroscopic methods, especially 1D and 2D NMR. Six compounds were described for the first time and two were only known so far as synthetic products. The chemotaxonomic significance of flavanoid accumulation within the genus Glycosmis is highlighted.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  7. Lim KH, Sim KM, Tan GH, Kam TS
    Phytochemistry, 2009 Jun;70(9):1182-1186.
    PMID: 19643450 DOI: 10.1016/j.phytochem.2009.06.010
    Four tetracyclic oxindole alkaloids, 7(R)- and 7(S)-geissoschizol oxindole (1 and 2), 7(R),16(R)- and 7(S),16(R)-19(E)-isositsirikine oxindole (3 and 4), in addition to a taberpsychine derivative, N(4)-demethyltaberpsychine (5), were isolated from the Malayan Tabernaemontana corymbosa and the structures were established using NMR and MS analysis.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  8. Rahmani M, Susidarti RA, Ismail HB, Sukari MA, Hin TY, Lian GE, et al.
    Phytochemistry, 2003 Oct;64(4):873-7.
    PMID: 14559284
    In a continuation of our study of the Rutaceae, detailed chemical investigation on Micromelum minutum (Rutaceae) collected from Sepilok, Sabah, Malaysia gave four new coumarins. The structures of the coumarins have been fully characterised by spectroscopic methods as 3",4"-dihydrocapnolactone 1, 2',3'-epoxyisocapnolactone 2, 8-hydroxyisocapnolactone-2',3'-diol 3 and 8-hydroxy-3",4"-dihydrocapnolactone-2',3'-diol 4.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  9. Kam TS, Choo YM
    Phytochemistry, 2004 Mar;65(5):603-8.
    PMID: 15003424
    Six new alkaloids, viz., alstolactone, affinisine oxindole, lagumicine, N(4)-demethylalstonerine, N(4)-demethylalstonerinal, and 10-methoxycathafoline N(4)-oxide, in addition to 36 other known alkaloids, were obtained from the leaf extract of Alstonia angustifolia var. latifolia. The structures of the new alkaloids were determined using NMR and MS analysis.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  10. Hung Ho S, Wang J, Sim KY, Ee GC, Imiyabir Z, Yap KF, et al.
    Phytochemistry, 2003 Apr;62(7):1121-4.
    PMID: 12591266
    We screened more than 60 Malaysian plants against two species of insects and found that Melicope subunifoliolata (Stapf) T.G. Hartley (Rutaceae) showed strong feeding deterrent activity against Sitophilus zeamais Motsch. (Curculionidae) and very good larvicidal activity against Aedes aegypti L. (Diptera). One anti-insect compound, meliternatin (3,5-dimethoxy-3',4',6,7-bismethylendioxyflavone) (6) and six other minor polyoxygenated flavones were isolated from M. subunifoliolata.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  11. Nge CE, Gan CY, Low YY, Thomas NF, Kam TS
    Org. Lett., 2013 Sep 20;15(18):4774-7.
    PMID: 23991636 DOI: 10.1021/ol4021404
    Two new indole alkaloids, voatinggine (1) and tabertinggine (2), which are characterized by previously unencountered natural product skeletons, were isolated from a Malayan Tabernaemontana species. The structures and absolute configuration of these alkaloids were determined using NMR and MS analysis, and X-ray diffraction analysis. A possible biogenetic pathway to these novel alkaloids from an iboga precursor, and via a common cleavamine-type intermediate, is presented.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  12. Gan CY, Robinson WT, Etoh T, Hayashi M, Komiyama K, Kam TS
    Org. Lett., 2009 Sep 3;11(17):3962-5.
    PMID: 19708704 DOI: 10.1021/ol9016172
    A cytotoxic bisindole alkaloid possessing an unprecedented structure constituted from the union of an eburnan half and a novel vinylquinoline alkaloid has been isolated from Leuconotis griffithii. The structure was established by analysis of the spectroscopic data and confirmed by X-ray diffraction analysis. A possible biogenetic pathway to the novel quinolinic coupling partner is presented from an Aspidosperma precursor.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  13. Kam TS, Tan SJ, Ng SW, Komiyama K
    Org. Lett., 2008 Sep 4;10(17):3749-52.
    PMID: 18683934 DOI: 10.1021/ol801354s
    A cytotoxic bisindole alkaloid possessing an unprecedented structure in which two indole moieties are bridged by an aromatic spacer unit has been isolated from Alstonia angustifolia. The structure was established by analysis of the spectroscopic data and confirmed by X-ray diffraction analysis. A possible biogenetic pathway from pyrocatechuic acid and pleiocarpamine is presented.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  14. Feng X, Jiang G, Xia Z, Hu J, Wan X, Gao JM, et al.
    Org. Lett., 2015 Sep 18;17(18):4428-31.
    PMID: 26315849 DOI: 10.1021/acs.orglett.5b02046
    The first enantioselective synthesis of (-)-conolutinine was achieved in 10 steps. The synthesis featured a catalytic asymmetric bromocyclization of tryptamine to forge the tricycle intermediate. Hydration of an alkene catalyzed by Co(acac)2 was also employed as a key step to diastereoselectively introduce the tertiary alcohol moiety. The absolute configuration of (-)-conolutinine was established to be (2S,5aS,8aS,13aR) based on this asymmetric total synthesis.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  15. Wong SP, Gan CY, Lim KH, Ting KN, Low YY, Kam TS
    Org. Lett., 2015 Jul 17;17(14):3628-31.
    PMID: 26183592 DOI: 10.1021/acs.orglett.5b01757
    A new monoterpene indole alkaloid characterized by an unprecedented pentacyclic cage skeleton, arboridinine (1), was isolated from a Malaysian Kopsia species. The structure and absolute configuration of the alkaloid were determined based on NMR, MS, and X-ray diffraction analysis. A possible biogenetic pathway from a pericine precursor is presented.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  16. Kam TS, Pang HS, Lim TM
    Org Biomol Chem, 2003 Apr 21;1(8):1292-7.
    PMID: 12929658
    The ethanol extract of the leaves of Tabernaemontana divaricata (double flower variety) provided a total of 23 alkaloids, including the new aspidosperma alkaloids, taberhanine, voafinine, N-methylvoafinine, voafinidine, voalenine and the new bisindole alkaloid, conophyllinine in addition to the previously known, biologically active bisindole, conophylline and its congener, conofoline. The structures of the new alkaloids were established by spectroscopic methods. The preparation and characterization of the corresponding quinones of the biologically active bisindoles are also described in relation to a structure-activity study of these compounds with respect to their action in stimulating insulin expression.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  17. Jamila N, Yeong KK, Murugaiyah V, Atlas A, Khan I, Khan N, et al.
    Nat Prod Res, 2015;29(1):86-90.
    PMID: 25219673 DOI: 10.1080/14786419.2014.952228
    Garcinia species are reported to possess antimicrobial, anti-inflammatory, anticancer, anti-HIV and anti-Alzheimer's activities. This study aimed to investigate the in vitro cholinesterase enzyme inhibitory activities of garcihombronane C (1), garcihombronane F (2), garcihombronane I (3), garcihombronane N (4), friedelin (5), clerosterol (6), spinasterol glucoside (7) and 3β-hydroxy lup-12,20(29)-diene (8) isolated from Garcinia hombroniana, and to perform molecular docking simulation to get insight into the binding interactions of the ligands and enzymes. The cholinesterase inhibitory activities were evaluated using acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. In this study, compound 4 displayed the highest concentration-dependent inhibition of both AChE and BChE. Docking studies exhibited that compound 4 binds through hydrogen bonds to amino acid residues of AChE and BChE. The calculated docking and binding energies also supported the in vitro inhibitory profiles of IC50. In conclusion, garcihombronanes C, F, I and N (1-4) exhibited dual and moderate inhibitory activities against AChE and BChE.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  18. Mah SH, Ee GC, Teh SS, Sukari MA
    Nat Prod Res, 2015;29(1):98-101.
    PMID: 25229947 DOI: 10.1080/14786419.2014.959949
    Extensive chromatographic isolation and purification of the extracts of the stem bark of Calophyllum inophyllum and Calophyllum soulattri have resulted in 11 xanthones. C. inophyllum gave inophinnin (1), inophinone (2), pyranojacareubin (5), rheediaxanthone A (6), macluraxanthone (7) and 4-hydroxyxanthone (8), while C. soulattri afforded soulattrin (3), phylattrin (4), caloxanthone C (9), brasixanthone B (10) and trapezifolixanthone (11). The structures of these compounds were determined on the basis of spectroscopic analyses such as 1D and 2D NMR, GC-MS, IR and UV. Cytotoxicity screening (MTT assay) carried out in vitro on all the xanthones using five human cancer cell lines indicated good activities for some of these xanthones. The structure-activity relationship study revealed that the inhibitory activities exhibited by these xanthone derivatives to be closely related to the existence and nature of the pyrano and the prenyl substituent groups on their skeleton.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  19. Al Muqarrabun LM, Ahmat N, Aris SR, Shamsulrijal N, Baharum SN, Ahmad R, et al.
    Nat Prod Res, 2014;28(9):597-605.
    PMID: 24568340 DOI: 10.1080/14786419.2014.886211
    A new sesquiterpenoid, malayscaphiol (1), and three known compounds, lupeol (2), lupenone (3) and stigmasterol (4), were isolated from the methanolic extract of the stem bark of Scaphium macropodum. The structures of the isolated compounds were determined using several spectroscopic methods, including UV-vis, FT-IR, 1D and 2D NMR, and mass spectrometer. Major isolated compounds were assayed for cytotoxicity and anti-acetylcholinesterase activities. The chemotaxonomy significance of this plant was also discussed.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
  20. Daud SB, Ee GC, Malek EA, Teh SS, See I
    Nat Prod Res, 2014;28(19):1534-8.
    PMID: 24897077 DOI: 10.1080/14786419.2014.924001
    A new coumarin, hoseimarin (1), together with four other xanthones, trapezifolizanthone (2), osajaxanthone (3), β-mangostin (4) and caloxanthone A (5), were isolated from the stem bark of Calophyllum hosei. The structures of these compounds were established by using spectroscopic analysis which included (1)H NMR, (13)C NMR, COSY, DEPT, HMQC and HMBC experiments.
    Matched MeSH terms: Nuclear Magnetic Resonance, Biomolecular
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