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Biomedical subjects

R X Tan

Publications and source records attributed to R X Tan.

At least 55 records · Page 3Linked to original sources
PubMed2000

Terpenoids and flavonoids from Artemisia species.

A phytochemical reinvestigation of the aerial parts of Artemisia sieversiana gave a new guaianolide and two known flavones (chrysosplenetin and 5-hydroxy-3',4',6,7-tetramethoxyflavone). Antifungal fractions derived from the chloroform extract of A. annua afforded two cadinane derivatives (arteannuin B and artemisinin), oleanolic acid, beta-sitosterol, stigmasterol, and the four flavones artemetin, bonanzin, eupalitin and chrysosplenetin. Their structures were elucidated by spectral methods. All isolates from the two species were tested in vitro for antifungal activity. Arteannuin B, a main sesquiterpenoid in A. annua, showed antifungal activity against one human (Candida albicans, MIC: 100 micrograms/ml) and four plant pathogenic fungi (Gaeumannomyces graminis var. tritici, Rhizoctonia cerealis, Gerlachia nivalis and Verticillium dahliae, MICs: 150, 100, 150 and 100 micrograms/ml, respectively) whereas others showed no antifungal activity. The MIC value of ketoconazole to C. albicans was 1.0 microgram/ml, and those of triadimefon to G. graminis var. tritici and R. cerealis 150 and 100 micrograms/ml.

Antifungal Agents↗
PubMed2000

New antimicrobial mono- and sesquiterpenes from Soroseris hookeriana subsp. erysimoides.

A new monoterpene and a new guaianolide were isolated from the aerial parts of the Tibetan medicinal plant Soroseris hookeriana subsp. erysimoides (Asteraceae), in addition to (1R,4R,5R)-5-hydroxybornan-2-one 5-O-beta-D-glucopyranoside, beta-sitosterol, daucosterol, diosmetin, isoluteolin, p-methoxybenzoic acid, isovanillic acid, two phenylmethanol derivatives (vanilioloside and phenylmethanol glucopyranoside), and five guaianolides [3 beta,8 beta-dihyroxyguaia-4(15),10(14),11(13)-triene-12,6 alpha-olide, dentalactone, 10 alpha-hydroxy-8-deoxy-10,14-dihydrodeacylcinaropicrin, glucozaluzanin C and 8-epideacylcinaropicrin glucoside]. By a combination of spectroscopic methods (IR, EI-MS, 1H- and 13C-NMR, and DEPT), the structure of the new guaianolide was established as 3 beta,8 beta-dihydroxy-11 alpha H-guaia-4(15),10(14)-diene-12,6 alpha-olide, and that of the new monoterpene as (1R,4R,5R)-5-benzoyloxybornan-2-one. The antimicrobial activity of all isolates except the two sterols were measured using Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Candida albicans, Aspergillus niger, and Trichophyton rubrum as test microorganisms. The new guaianolide was shown to be equally active (MIC: 50 micrograms/ml) against E. coli, B. subtilis and A. niger. The new monoterpene inhibited exclusively the growth of B. subtilis with MIC at 25 micrograms/ml. p-Methoxybenzoic acid and isovanillic acid were inhibitory against A. niger (MIC: 25 micrograms/ml), the latter being also active against B. subtilis with MIC at 25 micrograms/ml. The flavonoids diosmetin and isoluteolin almost equally inhibited the growth of B. subtilis (MIC: 25 micrograms/ml) and the human pathgenic fungus T. rubrum (MIC: 50 micrograms/ml).

Anti-Bacterial Agents↗
PubMed2000

Apoptosis in human hepatoma cell line SMMC-7721 induced by water-soluble macromolecular components of Artemisia capillaris Thunberg.

The aim of this study was to investigate the effect of water-soluble macromolecular components of Artemisia capillaris Thunberg (ACT) on human hepatoma cell line SMMC-7721 (SMMC-7721). The morphological changes of SMMC-7721 were observed under a light microscope and an electron microscope. Inhibition of proliferation was measured with a colorimetric MTT assay. It was discovered that ACT extract-treated cells exhibit morphological changes typical of apoptosis, including condensed chromatin and a reduction in volume. ACT extract at 25-200 microg/ml dose-dependently inhibited the proliferation of SMMC-7721. The 50% effective dose, evaluated on day 3 of exposure to the extract, was 64.52+/-3.53 microg/ml. Upon gel electrophoresis, the fragmented DNA showed a characteristic ladder pattern. Cell cycle analyses revealed that ACT induced cell cycle arrest at the G0/G1 phase.

Apoptosis↗
PubMed2000

Antioxidant activity of polyphenols from seeds of Vitis amurensis in vitro.

AIM: To study the antioxidant action of five polyphenols (+) catechin, procyanidin B2, procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin isolated from the seeds of Vitis amurensis. METHODS: The mouse liver homogenate lipid peroxidation assay was applied for the evaluation of the antioxidant activity in vitro. RESULTS: (+) Catechin, procyanidin B2, procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin showed antioxidant activity with the IC50 values of 0.47, 0.25, 0.10, 0.02, and 0.03 mmol/L, respectively. The IC50 value of vitamin E used as a positive control was 0.13 mmol/L. The structural activity relationship was also analyzed. Procyanidins carrying a galloyl group possessed higher anti-lipid peroxidation activities. All dimers were found to be more potent than the non-galloylated momomer such as (+) catechin. However, the activity of the 4-->6 linked dimer seemed more preferable than 4-->8 linked dimer. CONCLUSION: Procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin showed a more antioxidant activity than vitamin E did, and their activity is dependent on their substitution and polymerization patterns.

Animals↗
PubMed2000

In vitro inhibition of rat monoamine oxidase by liquiritigenin and isoliquiritigenin isolated from Sinofranchetia chinensis.

AIM: To study the inhibition of liquiritigenin (1) and isoliquiritigenin (2) isolated from Sinofranchetia chinensis on rat monoamine oxidase A and B (MAO A and B). METHODS: Rat brain mitochondrial fraction, prepared by differential centrifugation, was utilized as a source of MAO activity. MAO activity was determined radiochemically with [14C]5-hydroxytryptamine (5-HT) and [14C]beta-phenylethylamine (beta-PEA) used as MAO A or B specific radiolabled substrates, respectively. The Ki and KI values were obtained from Lineweaver-Burk plot using linear regression analysis. RESULTS: Liquiritigenin and isoliquiritigenin were found to be inhibitory against both MAO A and B in a dose-dependent manner. IC50 (95% of confidence limits) of liquiritigenin and isoliquiritigenin were 32 (26-36) and 13.9 (12.8-15.6) mumol/L for the inhibition of MAO A, and 104.6 (89.0-118.9) and 47.2 (39.5-54.5) mumol/L for that of MAO B, respectively. Lineweaver-Burk transformation of the MAO A inhibition data indicated that the inhibition was non-competitive for both liquiritigenin and isoliquiritigenin whereas their inhibition of MAO B was of mixed type. Regarding MAO A inhibition, the Ki values of liquiritigenin and isoliquiritigenin were 31.5 mumol/L and 14.3 mumol/L, respectively. As to the inhibition of MAO B, the Ki and KI data for liquiritigenin were 164.7 and 15.2 mumol/L, and those for isoliquiritigenin were 62.2 and 9.3 mumol/L, respectively. CONCLUSION: Liquiritigenin and isoliquiritigen inhibited the activity of MAO A and B in rat brain mitochondria, and the latter was more active than the former.

Animals↗
PubMed1999

Mono- and sesquiterpenes and antifungal constituents from Artemisia species.

In addition to beta-sitosterol and alpha-amyrin detected in all the investigated species, the extract of the aerial parts of Artemisia giraldii var. giraldii gave stigmasterol, daucosterol, sesamine, luteolin, eupafolin, hispidulin, eupatilin, belamcanidin, pinitol, artemin, ridentin, and a new antifungal monoterpene (named santolinylol) while that of the aerial parts of A. mongolica afforded sesamine, eupafolin, eupatilin, matricarin, and a new germacranolide (3-oxo-11 alpha H-germacra-1(10)E,4Z-dien-12,6 alpha-olide), and that of the aerial parts of A. vestita yielded stigmasterol, daucosterol, umbelliferone, scopolin, scoparone, and isoscopoletin-O-glucoside. Pinitol, first reisolated from Artemisia genus, was shown to inhibit the growth of the human pathogenic fungi Candida albicans, Aspergillus flavus, A. niger, Geotrichun candidum, Trichophyton rubrum, and Epidermophyton floccosum. Umbelliferone was also active against Candida tropicalis, A. flavus, G. candidum, T. rubrum, and E. floccosum. The flavones hispidulin and belamcanidin were almost equally inhibitory to the growth of A. flavus, G. candidum, T. rubrum, and E. floccosum, and santolinylol to C. albicans, A. flavus, A. niger, G. candidum, T. rubrum, and E. floccosum. In addition, ridentin was active against the growth of the plant pathogenic fungus Cladosporium cucumerinum.

Antifungal Agents↗
PubMed1999

Xanthine oxidase inhibitors from Brandisia hancei.

Xanthine oxidase is a key enzyme associated with the incidence of hyperuricemia-related disorders. Repeated chromatography of the enzyme inhibitory part of the water extract of the twigs and leaves of Brandisia hancei (Scrophulariaceae) gave a flavone luteolin, an iridoid glycoside mussaenoside, two beta-sitosterol glycosides daucosterol and beta-sitosterol gentiobioside, and five phenylethanoids arenarioside, brandioside, acteoside, 2'-O-acetylacteoside and isoacteoside. Luteolin and isoacteoside inhibited the xanthine oxidase (XO, EC 1.2.3.2) with the IC50 values at 7.83 and 45.48 microM, respectively. Isoacteoside was found to be the first phenylethanoid that decreased substantially the formation of uric acid by inhibiting competitively xanthine oxidase (Ki value: 10.08 microM). Furthermore, the study suggested that the caffeoylation of the 6'-hydroxyl group of the phenylethanoids was essential for the enzyme inhibitory action.

Carbohydrate Conformation↗
PubMed1999

Intestinal absorption of cefixime in rats.

AIM: To study the intestinal absorption characters of cefixime (Cef) and the factors affecting Cef absorption. METHODS: A rat intestine loop in situ technique was used to investigate the disappearance rate of Cef from the intestine. Cef concentration in the flux was measured by the reversed phase HPLC. RESULTS: Cef was mainly absorbed from the upper part of the intestine. Its disappearance rate was apparently pH-dependent [(5.8 +/- 0.6) nmol.h-1/(g wet tissue) at pH 7.4, (8.9 +/- 1.4) nmol.h-1/(g wet tissue) at pH 5.0, P < 0.05)]. The uptake rate of Cef was curvilinear at 0.01-0.5 mmol.L-1. The values of apparent Kt, Jmax, and Kd were 0.114 mmol, 78.41 nmol.h-1/(g wet tissue), and 43.70 nmol.h-1.mmol-1/(g wet tissue), respectively. Sodium edetate markedly promoted the disappearance rate of Cef from the intestine. CONCLUSION: Cef was transported partly via carrier-mediated transport system and partly via the paracellular transport system.

Animals↗
PubMed1998

Secoiridoid glycosides and an antifungal anthranilate derivative from Gentiana tibetica.

Repetitive chromatography of the methanol extract of the roots of Gentiana tibetica afforded two new secoiridoid glycosides and a novel antifungal anthranilic acid derivative, together with beta-sitosterol, daucosterol, oleanolic acid, loganic acid, gentiopicroside, sweroside, 2'-(2,3-dihydroxybenzoyl)sweroside, trifloroside, rindoside and macrophylloside A. The structures of the new products were determined mainly by spectroscopic methods as 8-hydroxy-10-hydrosweroside, isomacrophylloside and ethyl N-docosanoylanthranilate. Ethyl N-docosanoylanthranilate inhibited the growth of the human pathogenic fungi Candida albicans and Aspergillus flavus. The taxonomic significance of the constituent is discussed briefly.

Antifungal Agents↗
PubMed1998

Lignans and sesquiterpene lactones from Artemisia sieversiana and Inula racemosa.

The aerial parts of Artemisia sieversiana afforded, in addition to beta-sitosterol, stigmasterol and daucosterol, two novel lignans as well as one known and three new guaianolides. The roots of Inula racemosa gave beta-sitosterol, daucosterol and isoalantolactone. The structures were determined by a combination of spectral methods (IR, EIMS, 1H and 13C NMR, DEPT, COSY, NOESY and HETCOR). All isolates were subjected to antifungal tests. Isoalantolactone, a major sesquiterpene lactone of I. racemosa, was found to be active against the human pathogenic fungi. Aspergillus flavus, A. niger, Geotrichum candidum, Candida tropicalis and C. albicans at concentrations of 50, 50, 25, 25 and 25 micrograms/ml, respectively. The taxonomic significance of the characterized constituents is discussed briefly.

Antifungal Agents↗
PubMed1998

Biologically active substances from the genus Artemisia.

Artemisia species, widespread in nature, are frequently utilized for the treatment of diseases such as malaria, hepatitis, cancer, inflammation, and infections by fungi, bacteria, and viruses. Furthermore, some Artemisia constituents were found to be potential insecticides and allelopathic chemicals. This genus is receiving growing attention presumably due to: (i) the diversified biology and chemistry of the constituents, (ii) the frequent application in traditional medical practice, and (iii) the rich source of the plant material. This review summarizes mainly the biological results obtained in the past decade. The significance and trends in this field are briefly discussed.

Animals↗
PubMed1997

A clerodane diterpene with antibacterial activity from Ajuga lupulina.

The structure of a new diterpene, C30H46O11, with antibacterial activity against Pseudomonas aeruginose and Escherichia coli, isolated from the fresh whole plants of Ajuga lupulina (Labiatae) was established to be 2 beta-hydroxy-2-methylbutanoyl-3 alpha-lupulin (3-deoxy-14,15-dihydro-2-hydroxy-15-methoxycaryoptinol 2-methylbutanoate), by means of X-ray crystallographic analysis. The present study confirms that the two six-membered rings are in ideal chair conformations.

Anti-Bacterial Agents↗
PubMed1997

Secoiridoids from Gentiana siphonantha.

Repeated fractionations of the methanol extract of the subterranean parts (rhizomes and roots) of Gentiana siphonantha afforded two new and five known secoiridoids, in addition to the widespread plant constituents beta-sitiosterol, daucosterol and oleanolic acid. The structures of the new acyl secoiridoid glycosides were elucidated as 6'-gentisoyl 8-epikingiside and 2'-gentisoyl gelidoside mainly by a combination of high field NMR techniques. The known secoiridoids were identified as gentiolactone, gentiopicroside, sweroside, gelidoside and trifloroside. None of these constituents was active against human pathogenic fungi (Candida albican, Aspergillus flavus and Trichoderma viride). The chemotaxonomic significance of the isolates is discussed briefly.

Antifungal Agents↗
PubMed1996

Secoiridoids and antifungal aromatic acids from Gentiana algida.

Fractionation of an aqueous acetone extract of the whole herb of Gentiana algida gave one new [2'-(o,m-dihydroxybenzyl)sweroside] and five known secoiridoids, together with anofinic acid, fomannoxin acid, sitosterol, daucosterol, stigmasterol, oleanolic acid, orientin and gentianose. The structures were determined by spectral methods and a few chemical transformations. Anofinic acid and fomannoxin acid were found to be active against Cladosporium cucumerinum, a plant pathogenic fungus. Preliminary structure-activity studies indicated that the presence of carboxylic moieties in these acids was presumably a precondition for activity, whereas their methyl esters, inactive to the fungus, were active against the human pathogenic yeast Candida albicans. The chemotaxonomic significance of the isolates is discussed briefly.

Acetone↗
PubMed1996

Acyl secoiridoids and antifungal constituents from Gentiana macrophylla.

LC-UV-mass spectrometry and bioassay co-directed fractionation of an aqueous acetone extract of the roots of Gentiana macrophylla gave three new chromene derivatives and two novel and six known secoiridoids, along with kurarinone, kushenol I, beta-sitosterol, stigmasterol, daucosterol, beta-sitosterol-3-O-gentiobioside, alpha-amyrin, oleanolic acid, isovitexin, gentiobiose and methyl 2-hydroxy-3-(1-beta-D-glucopyranosyl)oxybenzoate. The structures of the new products were established from spectral and chemical evidence as 2-methoxyanofinic acid and macrophyllosides A-D. The six known secoiridoids were gentiopicroside, sweroside, 6'-O-beta-D-glucosylgentiopicroside, 6'-O-beta-D-glucosylsweroside, trifloroside and rindoside. The new acid (2-methoxyanofinic acid), its methyl ester, kurarinone and kushenol I were shown to be active against the plant pathogenic fungus Cladosporium cucumerinum. The methyl ester and kurarinone inhibited also the growth of the human pathogenic yeast Candida albicans. Structure-activity relationships were studied. Thus, addition of a methoxyl group to the benzene nucleus of anofinic acid (2,2-dimethyl-2H-1-benzopyran-6-carboxylic acid) increased the antifungal activity remarkably whereas glycosylation at the carboxylic moiety was found to remove the activity. Esterification of the new acid induced its activity against C. albicans, but decreased its growth inhibition properties against C. cucumerinum. Hydroxylation of kurarinone at the 3 beta-position removed its activity against C. albicans and decreased the inhibition of C. cucumerinum. In addition, the chemotaxonomic significance of the identified constituents is discussed.

Antifungal Agents↗
PubMed1996

Antibacterial neoclerodane diterpenoids from Ajuga lupulina.

The whole plants of Ajuga lupulina afforded five compounds, including three new clerodane diterpenes, lupulins A-C (1-3), whose structures were elucidated by spectral methods. Among these compounds, lupulins A (1) and B (2) as well as the acid hydrolysate (5) of lupulin D (4) showed antibacterial activities against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli.

Acetals↗
PubMed1996

Two flavones from Artemisia giraldii and their antimicrobial activity.

Two new flavones, 4',6,7-trihydroxy-3',5'-dimethoxy-flavone (2) and 5',5- dihydroxy-3',4',8-trimethoxyflavone (3) were isolated from Artemisia giraldii and their structures were identified by spectroscopic methods. These two new flavones showed antibiotic activity against Staphylococcus aureus, Sarcina lutea, Escherichia coli, Pseudomonas aeruginosa, Proteus sp. Aspergillus flavus, and Trichoderma viride.

Anti-Bacterial Agents↗