Vijaya Kumar

Antimicrobial alkaloids from Zanthoxylum tetraspermum and caudatum.

Two benzophenanthrene alkaloids, 8-acetonyldihydronitidine and 8-acetonyldihydroavicine were isolated from Zanthoxylum tetraspermum stem bark along with liriodenine, sesamin, lichexanthone and (+)-piperitol-gamma,gamma-dimethylallylether. The species endemic to Sri Lanka, Z. caudatum, contained sesamin, savinin, liriodenine, decarine and 8-O-desmethyl-N-nornitidine. 8-Acetonyldihydronitidine and 8-acetonyldihydroavicine showed significant antibacterial activity while the former along with liriodenine was strongly antifungal. Savinin exhibited potent spermicidal activity. Both savinin and sesamin exhibited significant insecticidal activity.

Sesquiterpene lactones from Michelia champaca

Five sesquiterpene lactones were isolated from Michelia champaca root bark. One of these, michampanolide (2,7-dihydroxy-3,7-dimethyl-11-methylene-13-oxatricyclo[8,3,0,0,3,b]tridecan-12-one), possessed a new skeleton, while two others, 8-acetoxyparthenolide and magnograndiolide, were isolated for the first time from M. champaca.

The cowpea aphid, Aphis craccivora, host plant odours and pheromones

Olfactometer experiments were conducted with apterae and alatae of the cowpea aphid, Aphis craccivora, Koch (Hom.:Aphidoidea). The occurrence of density dependent related pheromones and odour response to their host plant Vigna unguiculata was studied. Apterae responded with positive anemotaxis to air passed over both small groups of apterae and alatae (≤10 individuals) but negatively to air that passed over a bigger group (≥20 individuals). Alatae responded in the same way to groups of apterae but were repelled by alatae independent of the size of the group applied as odour source in the olfactometer, except when exposed to air passing ten alatae feeding on cowpea leaves. This may be due to interaction between aphid pheromones and host plant odour. Both apterae and alatae showed a general attraction to green plants and were also able to distinguish between other host plants and cowpea, which was the original host of the aphid clone used in the experiments. When attacked by aphids, the cowpea plant responded with a temporal increase in attractivity that reached a maximum after 48 h and had disappeared after one week.

Separation of proanthocyanidins isolated from tea leaves using high-speed counter-current chromatography

The proanthocyanidin extract from tea (Camellia sinensis) leaves was purified for the further study of the biological role of proanthocyanidins in blister blight leaf disease of tea, which is caused by the fungus Exobasidium vexans. An aqueous acetone extract of proanthocyanidins prepared from healthy tea leaves was partially purified using Sephadex LH-20 chromatography. The crude proanthocyanidin extract obtained was fractionated with high-speed counter-current chromatography (HSCCC) using the solvent system n-hexane-EtOAc-MeOH-water (1:5:1:5). The purity of the each isolated fraction after a single HSCCC run was evaluated by high-performance liquid chromatography (HPLC). Seven fractions of high purity were isolated. The identity of the compound present in each fraction isolated was established using electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy. Five proanthocyanidins and two flavanol digallates, (-)-epigallocatechin digallate (EGCDG) and (-)-epicatechin digallate (ECDG) were isolated. Comparison of spectral data of the proanthocyanidins isolated with those previously reported indicated that all five were known B-type proanthocyanidins with 2,3-cis stereochemistry in both the upper (u-unit) and the terminal (t-unit) units, and 4R configuration of the C-ring in the u-unit. The proanthocyanidins were established to be dimers composed of (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and (-)-epiafzelechin gallate (EAG) units with the following structures: EGCG-(4beta-->6)-EGCG, ECG-(4beta-->6)-EGCG, EGCG-(4beta-->6)-ECG, EAG-(4beta-->6)-EGCG, ECG-(4beta-->6)-ECG by analysis of spectral data. Therefore HSCCC offers a powerful method for the separation of a group of closely related naturally occurring compounds.

Evaluation of the Ethnomedical Claims of Murraya koenigii.

Abstract Based on sethnomedicine, Murraya koenigii. (L.) Spreng. is used as a stimulant, antidysentery, and for the management of diabetes mellitus. Twelve carbazole alkaloids were isolated from the stem, seed, and leaf of the plant growing in Nigeria and Sri Lanka. The methanol extracts were devoid of hypoglycemic activity, and some isolates decreased insulin secretion when they were subjected to both in vivo. and in vitro. (insulin secretion from INS-1 cells) antidiabetic tests. The cytotoxicity of the leaf and stem methanol extracts determined by the brine shrimp lethality bioassay were LC50 61.5 and 14.5 µg/ml, respectively. These extracts caused CNS depression in albino mice at the dose levels of 25–400 mg/kg. Also, they had an IC50 of 34.0 and 35.0 µg/ml at 24 h, respectively, against trichomonas. These results confirmed the use of the plant as an antidysentery caused by trichomonas but refute the antidiabetic and stimulant ethnomedical claims for the plant. The differences observed in their alkaloidal composition suggested probable influence of geographical location on the elaboration of carbazole alkaloids in the plant and differences in the localization of carbazole alkaloids in the plant parts.

1-[2′,4′-dihydroxy-3′,5′-di-(3″-methylbut-2″-enyl)-6′-methoxy] phenylethanone from Acronychia pedunculata root bark

Abstract A new arylketone, 1-[2′,4′-dihydroxy-3′,5′-di-(3″-methylbut-2″-enyl)-6′-methoxy] phenylethanone, was isolated together with acronylin, acrovestone, bergapten, β-amyrin and three furoquinoline alkaloids from the root bark of Acronychia pedunculata .

Two fungicidal phenylethanones from Euodia lunu-ankenda root bark.

Abstract Euodia lunu-ankenda root bark contained two fungicidal phenylethanones, 1-[2′,4′-dihydroxy-6′-(3′-methyl-2′-butenyloxy)-5′-(3′-methyl-2′-butenyl)]phenylethanone and

21α,26-dihydroxy-D:A-friedooleanan-3-one from Salacia reticulata var. Diandra (celastraceae)

Abstract Carbon-13 NMR has been used to detect the position of angular methyl oxygenation and determine the structure of 21α,26-dihydroxy-D:A-friedooleanan-3-one, a new trioxygenated friedooleanane from Salacia reticulata var. diandra and the assignment has been confirmed chemically.

Calocalabaxanthone, the putative isoprenyl precursor of calabaxanthone from Calophyllum calaba

Abstract The bark of Calophyllum calaba var. calaba contains a new xanthone, 2,8-di-(3-methylbut-2-enyl)-1,3-dihydroxy-7-methoxyxanthone (calocalabaxanthone), the precursor of 5-hydroxy-8-methoxy-2,2-dimethyl-7-(3-methylbut-2-enyl)-2H,6H-pyano-(3,2-b)-xanthen-6-one (calabaxanthone). In addition the bark contains calabaxthone and the other constituents isolated earlier from Calophyllum calaba var. worthingtonii .

Preformed and Induced Chemical Resistance of Tea Leaf Against Exobasidium vexans Infection

Levels of (−)-epicatechin in tea cultivars resistant to blister blight leaf disease were significantly higher than those in susceptible cultivars, while the reverse was true for (−)-epigallocatechin gallate, suggesting that epicatechin was involved in the resistance mechanism. The content of the methylxanthines, caffeine and theobromine, in the leaf increased in the initial translucent stage of the disease, probably as a defense response to fungal attack. Epicatechin and epigallocatechin levels were less than in healthy tissues at this stage, but increases in the corresponding gallate esters suggested that they were being converted into esters. Although epicatechin and epigallocatechin levels decreased from translucent to mature blister stages, the decrease was not significant. The decrease in levels of epicatechin, epigallocatechin, and their esters on infection and the formation of cyanidin and delphinidin on oxidative depolymerization of the blisters suggests that proanthocyanidins may play a role in the defense mechanism. The high resistance of a purple green leafed cultivar is attributed to the additional catechin source provided by the high levels of anthocyanins present.