Showing papers by "Kirpal S. Bisht published in 1997"
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.
849 citations
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: Lipase-catalyzed ring-opening bulk polymerizations of ω-pentadecalactone (PDL) were investigated. Screening of selected commercial lipases as catalysts for PDL polymerization at 80 °C was carried out. The results of this work showed that polymerizations catalyzed by lipases PS-30, AK, Lipozyme-IM and Novozym-435 gave % PDL conversions ranging from 80 to 100% for 24 h reactions (Mn = 15 000−34 400). Lipase PS-30 both physically immobilized onto Celite-521 (I-PS-30) and in the crude powder or nonimmobilized form (NI-PS-30) was selected for further study. 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. In fact, the % monomer conversion to poly(PDL) was nearly quantitative (>98%) for 8 h polymerizations catalyzed by I-PS-30. Furthermore, for reactions conducted at 70 °C with careful removal of water, substantially greater poly(PDL) molecu...
174 citations
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 ...
141 citations
TL;DR: It is indicated that among the alkaloids and polyphenolics a number of molecules can inhibit growth and invasion of human mammary cancer cells via selective cytotoxicity.
61 citations
TL;DR: Exclusive de-esterification of the ester groups derived from the phenolic hydroxy and aliphatic acid over theEster group of the aromatic acid andAliphatic alcohol has been achieved affording the corresponding esters of phenolic acids in as high yields as 90–97%.
36 citations
Patent•
28 Mar 1997TL;DR: An oligomer composed of a carbohydrate head group and an oligomer chain is described in this article, and methods for increasing the oligomerization rates of lactones and cyclic carbonates are also disclosed.
Abstract: An oligomer composed of a carbohydrate head group and an oligomer chain is disclosed. Methods for increasing the oligomerization rates of lactones and cyclic carbonates are also disclosed.
13 citations
TL;DR: Porcine pancreatic lipase (PPL) has been immobilized in microemulsion-based gels (MBGs) and highly selective and efficient deacylation of di/trihydric phenolic perpropanoates has been observed on incubating them with immobilized PPL as mentioned in this paper.
Abstract: Porcine pancreatic lipase (PPL) has been immobilized in microemulsion-based gels (MBGs). Highly selective and efficient deacylation of di/trihydric phenolic perpropanoates has been observed on incubating them with immobilized PPL. These reactions can find general utility in Synthetic Organic Chemistry.
TL;DR: In this paper, the authors describe a variety of substrates accepted by these hydrolytic enzymes to produce compounds in high enantiomeric excess which can be used as chiral building blocks for the synthesis of compounds of pharmaceutical and synthetic interest.
Abstract: Enantioselection effected by commercially available hydrolytic enzymes reported in recent years from our own laboratory and those published by other groups is described. The discussion is confined to enantioselection in symmetric diols, amino acids and benzopyran derivatives only. The paper describes a variety of substrates accepted by these hydrolytic enzymes to produce compounds in high enantiomeric excess which can be used as chiral building blocks for the synthesis of compounds of pharmaceutical and synthetic interest.