Poonam Taneja

Phytochemistry of the genus Piper

Abstract The secondary metabolites isolated from Piper species for the period 1907 to June 1996 have been reviewed. Nearly six hundred chemical constituents belonging to different classes of bioactive compounds are listed together with their source(s) and references.

Review Article Number 138: Constituents of the yew trees

Yew trees, taxonomically classified under the genus Taxus, are sources of a number of physiologically active compounds of different classes. Taxane derivatives with various carbon skeletons, lignans, flavonoids, steroids and sugar derivatives have been isolated from different Taxus species. Compounds isolated from the genus Taxus between 1908 and December 1997 have been comprehensively reviewed.

An aristolactam from Piper acutisleginum and revision of the structures of piperolactam B and D

Abstract A new aristolactam, 10-amino-4-hydroxy-2,3-dimethoxyphenanthrene-1-carboxylic acid lactam, was isolated from the stem of Piper acutisleginum . The structures of two related alkaloids, piperolactam B and D, have been revised.

Highly oxygenated bioactive flavones from Tamarix

Abstract Two new flavones, 5,7,2′-trihydroxy-6,4′-dimethoxyflavone (tamaridone) and 5,2′,4′-trihydroxy-6,7,8-trimethoxyflavone (tamadone) have been isolated from the aerial parts of Tamarix dioica, along with hexacosyl-p-coumarate, gardenins A, B, C and E, nevadensin A and apigenin. Gardenin B exhibited antiviral activity and anti-invasive activity against solid tumours.

Absolute configuration of epi-rhododendrin and (-)-rhododendrol [=(-)-betuligenol] and X-ray crystal and molecular structure of rhododendrin [=betuloside], a hepatoprotective constituent of Taxus baccata

Rhododendrin (= betuloside) has been isolated from the leaves of Taxus baccata L. From its X-ray diffraction studies, the absolute configuration at the chiral centre in the aglucone portion has been found to be R. These results establish the stereochemical assignments to different samples of this glucoside isolated from different plants. Our sample of rhododendrin exhibited hepatoprotective activity against two hepatotoxins in rats.

Regioselective esterification of diols and triols with lipases in organic solvents

Abstract Lipases from porcine pancreas (PPL) and Candida cylindracea (CCL) in different organic solvents allow discrimination of the primary and secondary hydroxyl groups, and also between two primary hydroxyl groups towards acylation with 2,2,2-trifluoroethyl butyrate in diols and triols with high regioselectivity.

Potential applications of enzyme-mediated transesterifications in the synthesis of bioactive compounds

The yeast lipase Candida cylindracea (CCL) and porcine pancreatic lipase (PPL) have been used for regioselective deacylation of peracetylated benzopyrones, diphenylpropenones and acetophenones for the first time. The deacylation study on different classes of polyphenols has revealed that the presence of carbonyl group attached to the aromatic ring is needed by the lipases to exhibit regioselectivity towards hydrolysis of acetoxyl groups. The acetoxyl groups at positions other than the one at ortho position to the carbonyl group get selectively hydrolysed by PPL in orgnnic solvents. The trnnsesterification reactions using triflouroethylbutyrate (TFEB), catalysed by PPL and CCL on some polyols in dry organic solvents were also performed. It was found that the primary hydroxyl is acylated. In D-panthenol, the oxidised dextrorotatory form of which is a major constituent of vitamin B-complex, the primary hydroxyl group at the far end of the asymmetric carbon atom gets exclusively acylated. This work should be of importance in the synthesis of building blocks of biologically active natural products which may provide structural leads to anti AIDS and anticancer agents.