Amooru G. Damu

Isolation of a Natural Antioxidant, Dehydrozingerone from Zingiber officinale and Synthesis of Its Analogues for Recognition of Effective Antioxidant and Antityrosinase Agents

In the present study, the antioxidative and inhibitory activity of Zingiber officinale Rosc. rhizomes-derived materials (on mushroom tyrosinase) were evaluated. The bioactive components of Z. officinale rhizomes were characterized by spectroscopic analysis as zingerone and dehydrozingerone, which exhibited potent antioxidant and tyrosinase inhibition activities. A series of substituted dehydrozingerones [(E)-4-phenyl-3-buten-2-ones] were prepared in admirable yields by the reaction of appropriate benzaldehydes with acetone and the products were evaluated in terms of variation in the dehydrozingerone structure. The synthetic analogues were examined for their antioxidant and antityrosinase activities to probe the most potent analogue. Compound 26 inhibited Fe2+-induced lipid peroxidation in rat brain homogenate with an IC50 = 6.3±0.4 μM. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical quencher assay, compounds 2, 7, 17, 26, 28, and 29 showed radical scavenging activity equal to or higher than those of the standard antioxidants, like a-tocopherol and ascorbic acid. Compound 27 displayed superior inhibition of tyrosinase activity relative to other examined analogues. Compounds 2, 17, and 26 exhibited non-competitive inhibition against oxidation of 3,4-dihydroxyphenylalanine (L-DOPA). From the present study, it was observed that both number and position of hydroxyl groups on aromatic ring and a double bond between C-3 and C-4 played a critical role in exerting the antioxidant and antityrosinase activity.

Anti-HBV and cytotoxic activities of pyranocoumarin derivatives.

Four natural pyranocoumarins clausenidin (1), nordentatin (2), clausarin (3), and xanthoxyletin (4) were isolated from the medicinal plant Clausena excavata. Recently, we found that 1 and 2 suppressed hepatitis B virus surface antigen in HepA2 cells, and in addition, 1-3 showed cytotoxic activity against four human cancer cell lines (A549, MCF7, KB, and KB-VIN). To explore the SAR of 1-4, 17 pyranocoumarin analogues (5-21) were designed and synthesized. Among these analogues, 5 and 10 were the most potent against hepatitis B virus with EC(50) values of 1.14 and 1.34microM, respectively. The most interesting result in the cytotoxicity assay was the significant activity of 1, 5, and 6 against the multi-drug resistant cell line, KB-VIN, without activity against the KB cell line. These data suggest that these three compounds could be useful hits for developing MDR-inverse drugs.

A rapid and simple determination of protoberberine alkaloids in Rhizoma Coptidis by 1H NMR and its application for quality control of commercial prescriptions

Simple, convenient, sensitive and accurate analytical methods are needed for the analysis of alkaloid components in Rhizoma Coptidis in traditional Chinese herbal medicine, which has important bioactivity. In the present study, a highly specific and sensitive method using (1)H NMR has been developed for the quantitative determination of protoberberine alkaloids berberine, palmatine, coptisine and jatrorrhizine in Coptis species and their commercial traditional Chinese medicine prescriptions. A (1)H NMR analysis of the H-13 signals of target protoberberine alkaloids was performed. By comparing the solvent effects on the resolution of these signals, methanol-d(4)-benzene-d(6) (75:25) is selected as an optimal (1)H NMR solvent. The quantity of the compounds is calculated by the relative ratio of the integral values of the target peak for each compound to the known amount of the internal standard anthracene. This method allows rapid and simple quantitation of protoberberine alkaloids from Coptis species and the more complex commercial prescriptions in 5 min without any pre-purification steps. The recoveries of these alkaloids from Coptis chinensis are in the range of 93-105%. Limit of detection of berberine in the plant material or prescription is 0.03 mg/mL. The advantages of this method are that no reference compounds are required for calibration curves, the quantification can be directly realized on a crude extract, and the better selectivity for protoberberine alkaloids and a very significant time-gain can be achieved, in comparison to conventional HPLC methods, for instance.

Constituents of the Roots of Clausena lansium and Their Potential Anti-inflammatory Activity

Eight new carbazole alkaloids, claulamines C (1), D (2), and E (5) and clausenalines B-F (3, 4, 6-8), four new coumarins, clausemarins A-D (9-12), and 43 known compounds were isolated from the roots of Clausena lansium. The structures of the new compounds were established on the basis of 2D-NMR spectroscopic analysis, and their absolute configurations were established from their ECD spectra. The configuration of wampetin was revised as E using a NOESY experiment. Most of the isolated compounds were evaluated for their potential anti-inflammatory activity. The results showed that compounds 9, 13-18, and 20-22 exhibited strong inhibition of superoxide anion generation with IC50 values ranging from 1.9 to 8.4 μM, while compounds 18, 19, and 21 inhibited elastase release with IC50 values in the range from 2.0 to 6.9 μM.

Flavonoids and ent-labdane diterpenoids from Andrographis paniculata and their antiplatelet aggregatory and vasorelaxing effects

Two new flavones, designated as andropaniculosin A (1) and andropaniculoside A (2), and 30 known compounds were isolated as a result of detailed chemical examination on the whole plants of Andrographis paniculata. Their structures have been elucidated mainly by 1D and 2D NMR, and MS spectroscopic methods. Among them, four flavonoids showed potent inhibition of collagen, arachidonic acid, thrombin, and platelet activation factor induced platelet aggregation. Furthermore, a diterpenoid demonstrated moderate vasorelaxing effect in isolated rat thoracic aorta.

Total synthesis of phenanthroindolizidine alkaloids (+/-)-antofine, (+/-)-deoxypergularinine, and their dehydro congeners and evaluation of their cytotoxic activity.

Due to their limited natural abundance and significant biochemical effects, we synthesized the alkaloids (+/-)-antofine (1a), (+/-)-deoxypergularinine (1b), and their dehydro congeners (2 and 3) starting from the corresponding phenanthrene-9-carboxaldehydes. We also evaluated their in vitro cytotoxic activity. Compounds 1a and 1b showed significant potency against various human tumor cell lines, including a drug-resistant variant, with EC(50) values ranging from 0.16 to 16ng/mL. Structure-activity correlations of these alkaloids and some of their synthetic intermediates were also ascertained. The non-planar structure between the two major moieties, phenanthrene and indolizidine, plays a crucial role in the cytotoxic activity of phenanthroindolizidines. Increasing the planarity and rigidity of the indolizidine moiety significantly reduced potency. A methoxy group at the 2-position (1a) was more favorable for cytotoxic activity than a hydrogen atom (1b).

Cardiac glycosides from Antiaris toxicaria with potent cardiotonic activity.

An ethanolic extract of Antiaris toxicaria trunk bark showed potent in vitro cardiotonic effect on isolated guinea pig atria. Bioassay-guided fractionation of the extract led to identification of nine new cardiac glycosides (1-9, named antiarosides A-I), antiarotoxinin A (10), and 18 known compounds. Their structures were established using MS and NMR spectroscopic studies, including homonuclear and heteronuclear correlation experiments. The ability of these cardiotonic compounds to produce positive inotropic action and their safety indexes were examined in comparison with those of ouabain, a classical inhibitor of Na(+)/K(+)-ATPase. Malayoside (23) was nearly equipotent and had a similar safety index to ouabain in guinea pig atria. However, the maximal positive inotropic effect and safety index of 23 in papillary muscle were better than those of ouabain. An electrophysiological recording showed that 23 inhibited the sodium pump current in a concentration-dependent manner.

Constituents of leaves of Phellodendron chinense var. glabriusculum

The leaves of Phellodendron chinense var. glabriusculum yielded three new flavanones, phellodensin D (1), phellodensin E (2), and phellodensin F (3) along with five known compounds, amurensin (4), phellamurin (5), methyl caffeate (6), beta-sitosterol (7), and pheophytin-a (8). The structural assignment of new compounds was based on spectroscopic studies.

Chemical constituents and pharmacology of the Formosan Aristolochia species

Aristolochia is an important genus widely cultivated and used in traditional Chinese medicine. The genus has attracted much interest and has been the subject of numerous chemical studies. In the last twelve years, all the Formosan species of Aristolochia have been investigated by our group for their chemical constituents and biological activities. They are sources of a number of physiologically active compounds of different classes, and various types of phenanthrene derivatives, terpenes, alkaloids, flavonoids, lignoids, benzenoids, and steroids have been isolated from Formosan Aristolochia species. The nature of these constituents is compiled in this review together with their bioactivities in an effort to show the rapid development in the phytochemistry and the therapeutic applications of the Aristolochia species.

Chemical Constituents from Andrographis echioides and Their Anti-Inflammatory Activity

Phytochemical investigation of the whole plants of Andrographis echioides afforded two new 2′-oxygenated flavonoids (1) and (2), two new phenyl glycosides (3) and (4), along with 37 known structures. The structures of new compounds were elucidated by spectral analysis and chemical transformation studies. Among the isolated compounds, (1–2) and (6–19) were subjected into the examination for their iNOS inhibitory bioactivity. The structure-activity relationships of the flavonoids for their inhibition of NO production were also discussed.