Swapan K. Chaudhuri

Flavonols from Heterotheca inuloides: tyrosinase inhibitory activity and structural criteria.

Tyrosinase inhibitory activity of flavonols, galangin, kaempferol and quercetin, was found to come from their ability to chelate copper in the enzyme. In contrast, the corresponding flavones, chrysin. apigenin and luteolin, did not chelate copper in the enzyme. The chelation mechanism seems to be specific to flavonols as long as the 3-hydroxyl group is free. Interestingly, flavonols affect the enzyme activity in different ways. For example, quercetin behaves as a cofactor and does not inhibit monophenolase activity. On the other hand, galangin inhibits monophenolase activity and does not act as a cofactor. Kaempferol neither acts as a cofactor nor inhibits monophenolase activity. However, these three flavonols are common to inhibit diphenolase activity by chelating copper in the enzyme.

Quantification of insect growth and its use in screening of naturally occurring insect control agents.

In studies of the effects of allelochemicals or other factors on the development of different insect species, comparison of growth-inhibiting activities is difficult using the parameters currently employed. We introduce two new parameters, growth index (GI) and relative growth index (RGI), which can unify the quantification of insect development. This quantification can also eliminate the effects of different growth characteristics due to the genetic differences between insect species. By measuring growth-inhibiting effects of two phytochemicals, chaparrin and chaparrinone, on the tobacco budworm,Heliothis virescens, and the beet armyworm,Spodoptera exigua, bioassay procedures and GI and RGI calculations are demonstrated.

Tyrosinase inhibitory flavonoids fromheterotheca inuloides and their structural functions

Abstract By bioassay-guided fractionations, quercetin was isolated as the principal tyrosinase inhibitor from the dried flowers of Heterotheca inuloides Cass (Compositae). This flavonol inhibited the oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA) by mushroom tyrosinase (EC 1.14.18.1) with an ID 50 of 22 μg/ml (0.07 mM). Interestingly, quercetin 3-β-glucoside did not inhibit this oxidation up to 1 mg/ml. Kinetic study have found quercetin to be a characteristic competitive inhibitor for the L-DOPA oxidation by the mushroom tyrosinase. Based on the above findings, several related flavonoids were also examined for comparison.

Two quassinoid glucosides from Castela tortuosa

Abstract The structures for two new bitter-tasting quassinoid glucosides, casteloside A (chaparrin-2- O -β- d -glucopyranoside) and casteloside B (glaucarubol-2- O -β- d -glucopyranoside) isolated from the bark of Castela tortuosa , a medicinal plant known as ‘chaparro amargo’ in Mexico, were determined by spectral analyses, in particular, NMR data.

Structure of chaparramarin, a quassinoid from Castela tortuosa

Abstract A new quassinoid, chaparramarin has been isolated and identified as an insect growth inhibitor against the lepidopteran pest insect, Heliothis virescens (tobacco budworm), from the bark of Castela tortuosa.

A plant growth inhibitory sesquiterpenoid from Heterotheca inuloides

Abstract A new sesquiterpenoid, inuloidin, isolated from the dried flower of Heterotheca inuloides has been characterized as 2,7-dihydroxy-β-calacoren or 7-hydroxy-5,6,7,8-tetrahydro-3-methyl-8-methylene-5-(1-methylethyl)-2-naphthalenol by means of spectroscopic method. It exhibited plant growth inhibitory activity in lettuce seedling assay.

A quassinoid glucoside from the bark of Castela tortuosa

Abstract A new minor quassinoid glucoside, castelalene-11- O -β- d -glucopyranoside has been isolated from the bark of Castela tortuosa . The structure and stereochemistry of this new glucoside has been established from spectral analyses.

Castelalin, a quassinoid from Castela tortuosa

Abstract A new quassinoid, castelalin, was isolated together with the known quassinoid, glaucarubolone, two flavanoids and methyl gallate from ‘chaparro amargo’, the bark of Castela tortuosa . Their structures were deduced by extensive use of NMR spectroscopy.

A xanthone from Clusia insignis

Abstract A new xanthone, clusone, isolated from the fresh flowers of an Amazonian medicinal plant, Clusia insignis, has been characterized as 1,3,4,5,6-pentamethoxy 9H-xanthen-9-one by means of spectroscopic evidence.

Structure of maesaquinone

Abstract Structure of a benzoquinone, maesaquinone, isolated from Maesa lanceolata (Myrsinaceae), has been characterized as 2,5-dihydroxy-3-(Z)-10′-pentadecenyl-6-methyl-1,4-benzoquinone (1) by means of spectroscopic method. It has been found to exhibit in vitro cytotoxicity against several solid tumor cells. Structure of a benzoquinone, maesaquinone, isolated from Maesa lanceolata (Myrsinaceae), has been characterized as 2,5-dihydroxy-3-(Z)-10′-pentadecenyl-6-methyl-1,4-benzoquinone by means of spectroscopic method. The 13C NMR spectrum of maesaquinone showed only four higher values of chemical shifts due to the very rapid interconversion between the exchange forms. Maesaquinone has been found to exhibit in vitro cytotoxicity against several solid tumor cells.