Kirpal S. Bisht

TL;DR: The secondary metabolites isolated from Piper species for the period 1907 to June 1996 have been reviewed in this paper, where nearly six hundred chemical constituents belonging to different classes of bioactive compounds are listed together with their source(s) and references.

TL;DR: Comparison of % conversion vs time for bulk PDL polymerizations at 70 °C catalyzed by NI- and I-PS-30 showed that for short reaction times, the immobilized catalyst gave % conversions that were more than 10 times greater.

Abstract: This work was directed at extending the use of lipase-catalyzed ring-opening polymerizations to cyclic carbonate monomers. Of the seven lipases screened for bulk trimethylene carbonate (TMC) polymerization (70 °C, 120 h), Novozym-435 from Candida antarctica gave almost quantitative monomer conversion (97%) and poly(TMC) with a Mn = 15 000 (Mw/Mn = 2.2) with no apparent decarboxylation during propagation. The lipases from Pseudomonas species (AK and PS-30) and porcine pancreas (PPL) also exhibited high monomer conversions (>80%, 120 h) but gave lower molecular weight polymers with broad polydispersity. Analyses by 1H-NMR spectroscopy suggested that poly(TMC) prepared by Novozym-435-catalyzed polymerization had terminal −CH2OH functionalities at both chain ends. A monotonic increase in monomer conversion with time and the rapid increase in Mn as a function of monomer conversion for Novozym-435-catalyzed TMC bulk polymerization at 70 °C suggest that the polymerization has chain-type propagation kinetics. An ...

TL;DR: In this article, taxonomically classified under the genus Taxus, a number of physiologically active compounds of different classes have been extracted from yew trees, including lignans, flavonoids, steroids and sugar derivatives.

TL;DR: In this article, an enzyme-catalyzed ring-opening polymerization of a novel carbonate monomer, 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one, was reported.