Synthesis of novel curcumin analogues and their evaluation as selective cyclooxygenase-1 (COX-1) inhibitors

Curcumin, a major yellow pigment and active component of turmeric, has been shown to possess anti-inflammatory and anti-cancer activities. Recent studies have indicated that cyclooxygenase-1 (COX-1) plays an important role in inflammation and carcinogenesis. In order to find more selective COX-1 inhibitors a series of novel curcumin derivatives was synthesized and evaluated for their ability to inhibit this enzyme using in vitro inhibition assays for COX-1 and COX-2 by measuring PGE(2) production. All curcumin analogues showed a higher rate of COX-1 inhibition. The most potent curcumin compounds were (1E,6E)-1,7-di-(2,3,4-trimethoxyphenyl)-1,6-heptadien-3,5-dione (4) (COX-1: IC(50) = 0.06 microM, COX-2: IC(50) > 100 microM, selectivity index>1666) and (1E,6E)-methyl 4-[7-(4-methoxycarbonyl)phenyl]-3,5-dioxo-1,6-heptadienyl]benzoate (6) (COX-1: IC(50) = 0.05 microM, COX-2: IC(50) > 100 microM, selectivity index > 2000). Curcumin analogues therefore represent a novel class of highly selective COX-1 inhibitors and promising candidates for in vivo studies.     

A potent bicyclic inhibitor of a family 27 alpha-galactosidase

Two isomeric bicyclo[4.1.0]heptane analogues of the glycosidase inhibitor galacto-validamine, (1R*,2S,3S,4S,5S,6S*)-5-amino-1-(hydroxymethyl)bicyclo[4.1.0]heptane-2,3,4-triol, have been synthesized in 13 steps from 2,3,4,6-tetra-O-benzyl-D-galactose. The inhibitory activities of the two conformationally restricted amines, and their corresponding acetamides, were measured against commercial alpha-galactosidase enzymes from coffee bean and E. coli. The activity of the glycosyl hydrolase family GH27 enzyme (coffee bean) was competitively inhibited by the 1R,6S-amine (7), a binding interaction that was characterized by a K(i) value of 0.541 microM. The GH36 E. coli alpha-galactosidase exhibited a much weaker binding interaction with the 1R,6S-amine (IC(50)= 80 microM). The diastereomeric 1S,6R-amine (9) bound weakly to both galactosidases, (coffee bean, IC(50)= 286 microM) and (E. coli, IC(50)= 2.46 mM).     

A new stilbene with tyrosinase inhibitory activity from Chlorophora excelsa

A new stilbene, 4-[(2"E)-7"-hydroxy-3",7"-dimethyloct-2"-enyl]-2',3,4',5-tetrahydroxy-trans-stilbene (1), and the known compound chlorophorin (2) were isolated from the heartwood of Chlorophora excelsa. Both 1 and 2 showed tyrosinase inhibitory activity with IC(50) values of 96 and 1.3 microM, respectively.     

Two new triterpenes from the Rhizome of Dryopteris crassirhizoma, and inhibitory activities of its constituents on human immunodeficiency virus-1 protease

Two new hopane type triterpenes, named dryopteric acids A (1) and B (2), were isolated from the Rhizome of Dryopteris crassirhizoma (Aspiadaceae) together with sixteen known compounds (3-18). Of isolated compounds, ursolic acid (15), and dryopteric acid A (1) and B (2) showed potent inhibitory activities against HIV-1 protease with IC50 values of 8.9-44.5 microM. In addition, acetylated compounds 1 and 2 appreciably increased inhibitory activities with their IC50 values of 1.7 and 10.8 microM, respectively.     

COX-1, COX-2 inhibitors and antifungal agents from Croton hutchinsonianus

Two new compounds, 3'-(4'-hydroxy-3',5'-dimethoxyphenyl)-propyl benzoate (1) and 3'-(4'-hydroxyphenyl)-propyl benzoate (3) together with known compounds, 3'-(4'-hydroxy-3'-methoxyphenyl)-propyl benzoate (2), poilaneic acid (4), farnesyl acetone (5) and 4-hydroxybenzaldehyde (6) were isolated and identified from the branches of Croton hutchinsonianus. Their structures were determined by spectroscopic methods. The three phenylpropyl benzoates (1-3) were found to exhibit antifungal activity against Candida albicans (IC(50) 5.36-11.41 microg/ml). Compounds 1-2 (IC(50) 2.11-4.95 microg/ml) exhibited potent but non-selective activity against the enzymes cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) whereas 3 (IC(50) 1.88 microg/ml) preferentially inhibited the enzyme COX-2.     

Anti-plasmodial and cholinesterase inhibiting activities of some constituents of Psorospermum glaberrimum

Glaberianthrone (1), a new bianthrone was isolated from the hexane extract of the stem bark of Psorospermum glaberrimum together with thirteen known compounds: 3-geranyloxyemodin anthrone (2), friedelan-3-one (3), 3-prenyloxyemodin anthrone (4), 3-geranyloxyemodin (5), 3-prenyloxyemodin (6), friedelan-3-ol (7), acetylvismione D (8), betulinic acid (9), 2-geranylemodin (10), bianthrone A2b (11), bianthrone 1a (12), emodin (13) and 2-prenylemodin (14). The structures of the isolated compounds were established by means of spectroscopic methods. The extracts and the isolated compounds were tested in vitro for their anti-plasmodial activity against Plasmodium falciparum (chloroquine resistant strain W2) and for their acetyl- and butyrylcholinesterase inhibitory properties. The n-hexane extract showed good anti-plasmodial activity against P. falciparum W2 strain, with IC(50) of 0.87 microg/ml. It also exhibited 65.5% and 98.2% of acetyl- and butyrylcholinesterase inhibition at 0.2 mg/ml, respectively. Compounds 2 and 8 showed the best potencies against P. falciparum W2 strain with IC(50) of 1.68 microM and 0.12 microM, (0.66 microg/ml and 0.054 microg/ml) respectively. All tested compounds showed good butyrylcholinesterase inhibition activities with compound 12 displaying the best potency (IC(50) 9.25+/-0.25 microM). All the tested compounds showed weak inhibitory activity against acetylcholinesterase.     

Cholinesterase inhibiting and antiplasmodial steroidal alkaloids from Sarcococca hookeriana

Bioguided phytochemical investigation of Sarcococca hookeriana with respect to the cholinesterase enzyme inhibitory assay yielded two new pregnane-type steriodal alkaloids hookerianamide H (1) and hookerianamide I (2), along with three known alkaloids N(a)-methylepipachysamine D (3), sarcovagine C (4) and dictyophlebine (5). Their structures were determined with the aid of extensive spectroscopic analysis. All compounds showed good inhibitory activities against the enzymes acetylcholinesterase (IC(50) 2.9-34.1 microM) and butyrylcholinesterase (IC(50) 0.3-3.6 microM). These compounds also showed moderate antiplasmodial activity (IC(50) 2.4-10.3 microM) against the Plasmodium falciparum chloroquine resistant W2 strain.     

Corylucinine, a new alkaloid from Corydalis cava (Fumariaceae), and its cholinesterase activity

A new benzyldihydroisoquinoline alkaloid (1) was isolated from the tubers of Corydalis cava and named corylucinine. Additionally, 8-trichloromethyl-7,8-dihydropalmatine (2), an isolation artifact of tetrahydropalmatine, was obtained. The structures were established by spectroscopic (including 2D NMR and optical rotation) and HR-ESI-MS methods. Both compounds were tested for human blood acetylcholinesterase (HuAChE) and human plasma butyrylcholinesterase (HuBuChE) inhibitory activity. In comparison with the used standards, both compounds showed only moderate inhibitory activity against HuAChE (IC50,. HuAChE = 127.6 +/- 5.2 microM for 1, and IC50, HuAChE = 82.9 +/- 3.9 microM for 2) and none against HuBuChE.     

Prediction of cyclooxygenase inhibitory activity of curcuma rhizome from chromatograms by multivariate analysis

The potential use of partial least square regression (PLS-R) models for the prediction of biological activities of a herbal drug based on its liquid chromatography (LC) profile was verified using various extracts of Curcuma phaeocaulis and their cyclooxygenase-2 (COX-2) inhibitory activities as the model experiment. The correlation of practically measured inhibitory activities and predicted values by PLS-R analysis was quite good (correlation coefficient=0.9935) and the possibility of transforming chromatographic information into a measure of biological activity was confirmed. In addition, furanodienone and curcumenol were identified as the major active anti-inflammatory constituents of C. phaeocaulis, through detailed analysis of the regression vector, followed by isolation of these compounds and their COX-2 inhibitory assays. The selectivity indices (SI), IC(50) of COX-1/IC(50) of COX-2, of both compounds were higher than that of indomethacin and it is considered that furanodienone and curcumenol are the most promising compounds as lead anti-inflammatory agents.     

Inhibition on HIV-1 integrase activity and nitric oxide production of compounds from Ficus glomerata

An ethanol Ficus glomerata wood extract and its purified components were investigated for their HIV-1 integrase (IN) and nitric oxide (NO) inhibitory activities. From bioassay-guided isolation, five compounds: beta-sitosterol-D-glucoside (1), aloe-emodin (2), genistein (3), 1,3,6-trihydroxy-8-methyl-anthraquinone (4) and 3-(1-C-beta-D-glucopyranosyl)-2,6-dihydroxy-5-methoxybenzoic acid (5) were isolated. Among the tested samples, at concentrations of 100 microM; compound 2 showed 31.9% inhibition of HIV-1 IN, followed by 4 (19.5%), whereas other compounds were inactive. With regard to the inhibitory effect on NO production, 3 possessed the highest activity with an IC50 value of 27.5 microM, followed by 4 (IC50 = 34.7 microM) and 2 (IC50 = 41.8 microM), respectively. This is the first time that compounds 2-5 have been isolated from Ficus glomerata.     

Inhibitory effects of constituents from Cynomorium songaricum and related triterpene derivatives on HIV-1 protease

From CH2Cl2 and MeOH extracts of the stems of Cynomorium songaricum RUPR. (Cynomoriaceae), ursolic acid and its hydrogen malonate were isolated as inhibitors of human immunodeficiency virus type 1 (HIV-1) protease, with 50% inhibitory concentrations (IC50) of 8 and 6 microM, respectively. Amongst various synthesized dicarboxylic acid hemiesters of related triterpenes, inhibitory activity tended to increase in the order of oxalyl, malonyl, succinyl and glutaryl hemiesters, for triterpenes such as ursolic acid, oleanolic acid and betulinic acid. The most potent inhibition was observed for the glutaryl hemiesters, with an IC50 of 4 microM. From the water extract of the stems of C. songaricum, flavan-3-ol polymers, consisting of epicatechin as their extender flavan units, were also found to be potent inhibitory principles against HIV-1 protease.     

Tyrosinase inhibitory and antileishmanial constituents from the rhizomes of Paris polyphylla

The search for bioactive natural products from the rhizomes of Paris polyphylla (Trilliaceae) has resulted in the isolation of four known constituents, 1,5-dihydroxy-7-methoxy-3-methylanthraquinone (1), diosgenin-3-O-[alpha-L-rhamnopyranosyl-(1 --> 3)-beta-D-glucopyranoside] (2), diosgenin-3-O-[alpha-L-rhamnopyranosyl-(1(Rha) --> 2(Glu))-alpha-L-arabinofuranosyl-(1(Ara) --> 4(Glu))]-beta-D-glucopyranoside (3), and diosgenin-3-O-[alpha-L-rhamnopyranosyl-(1(Rha) --> 2(Glu))-alpha-L-rhamnopyranosyl-(1(Ara) --> 4(Glu))]-beta-D-glucopyranoside (4). Their structures were identified by spectral comparison with the reported data. Compound 1 was isolated for the first time from this genus. The chloroform, ethyl acetate, and butanol extracts of the plant were found to have mild to moderate inhibitory potentials against the enzyme tyrosinase. Compound 1 showed strong (IC(50) = 0.23 microM), while compounds 2-4 and hydrolyzed product 4a showed mild to moderate (IC(50) = 0.93-36.87 microM) activities against the tyrosinase. Similarly, compounds 2-4 and 4a showed mild to moderate (IC(50) = 1.59-83.72 microg mL(-1)) antileishmanial activities.     

Structural requirements of flavonoids and related compounds for aldose reductase inhibitory activity

The methanolic extracts of several natural medicines and medicinal foodstuffs were found to show an inhibitory effect on rat lens aldose reductase. In most cases, flavonoids were isolated as the active constituents by bioassay-guided separation, and among them, quercitrin (IC(50)=0.15 microM), guaijaverin (0.18 microM), and desmanthin-1 (0.082 microM) exhibited potent inhibitory activity. Desmanthin-1 showed the most potent activity, which was equivalent to that of a commercial synthetic aldose reductase inhibitor, epalrestat (0.072 microM). In order to clarify the structural requirements of flavonoids for aldose reductase inhibitory activity, various flavonoids and related compounds were examined. The results suggested the following structural requirements of flavonoid: 1) the flavones and flavonols having the 7-hydroxyl and/or catechol moiety at the B ring (the 3',4'-dihydroxyl moiety) exhibit the strong activity; 2) the 5-hydroxyl moiety does not affect the activity; 3) the 3-hydroxyl and 7-O-glucosyl moieties reduce the activity; 4) the 2-3 double bond enhances the activity; 5) the flavones and flavonols having the catechol moiety at the B ring exhibit stronger activity than those having the pyrogallol moiety (the 3',4',5'-trihydroxyl moiety).     

Glutathione S-transferase inhibiting chemical constituents of Caesalpinia bonduc

Glutathione S-transferase inhibition assay-guided fractionations on the ethanolic extract of the bark of Caesalpinia bonduc resulted in the isolation of a new sterol, 17-hydroxy-campesta-4,6-dien-3-one (1) along with four known compounds, 13,14-seco-stigmasta-5,14-dien-3alpha-ol (2), 13,14-seco-stigmasta-9(11),14-dien-3alpha-ol (3), caesaldekarin J (4) and pipataline (5) as active constituents. Structures of compounds 1-5 were established on the basis of extensive NMR spectroscopic studies. The compounds (1-5) were isolated on the basis of their inhibitory activity against glutathione S-transferase, an enzyme that has been implicated in resistances during treatment of cancer and parasitic infections. Efforts to study structure-activity relationships of compounds 2 and 3 were also made by modifying their structures. The IC50 values of these compounds and their derivatives ranged from 57-380 microM and were compared to the inhibitory effects due to sodium taurocholate, an isoprene-derived GST inhibitor (IC50=398 microM). A plausible biosynthesis of 13,14-seco-steroids has also been proposed.     

Hydantoin derivatives of L- and D-amino acids: synthesis and evaluation of their antiviral and antitumoral activity

3,5-Disubstituted hydantoin (1,3-imidazolidinedione) derivatives 5a-h were prepared by base induced cyclization of the corresponding N-(1-benzotriazolecarbonyl)-L- and D-amino acid amides 4a-h. Compounds 5a-h were evaluated for their cytostatic and antiviral activities. Among all the compounds evaluated, 3-benzhydryl-5-isopropyl hydantoin (5a) showed a weak but selective inhibitory effect against vaccinia virus (EC(50) = 16 microg/mL; selectivity index: 25). 3-Cyclohexyl-5-phenyl hydantoin (5g) showed inhibitory activity against cervical carcinoma (HeLa, IC(50) = 5.4 microM) and breast carcinoma (MCF-7, IC(50) = 2 microM), but also cytotoxic effects towards human normal fibroblasts (WI 38). On the contrary, the 3-benzhydryl-5-phenyl substituted hydantoin derivative 5h showed moderate inhibitory activity towards HeLa, MCF-7, pancreatic carcinoma (MiaPaCa-2), lung carcinoma (H 460) and colon carcinoma (SW 620) (IC(50) = 20-23 microM), but no effect on WI 38.     

Potent inhibitory effects of N-aryl S-alkylthiocarbamate derivatives on the dopa oxidase activity of mushroom tyrosinase

This study reports the potent inhibitory effect of N-aryl S-alkylthiocarbamate derivatives on mushroom tyrosinase (MT) activity. N-Aryl S-alkylthiocarbamate derivatives were found to exhibit a potent inhibitory effect on the dopa (3,4-dihydroxyphenylalanine) oxidase activity of mushroom tyrosinase. Most of the N-aryl S-alkylthiocarbamate derivatives (compounds from A to J) exhibited higher inhibitory effects than kojic acid (IC50=318 microM), a well known tyrosinase inhibitor. Tyrosinase was the most inhibited by S-phenetyl N-phenylthiocarbamate (compound E, IC50=7.25 microM), and this inhibition was 44 times stronger than that of kojic acid. Compound E exhibited 95.0% of inhibition at 100 microM. A kinetic study of MT inhibition by compound E using the Lineweaver-Burk plots analysis was performed. And the kinetics profiles observed suggest that compound E competitively inhibits MT.