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Kirpal S. Bisht

Bio: Kirpal S. Bisht is an academic researcher from University of South Florida. The author has contributed to research in topics: Lipase & Candida antarctica. The author has an hindex of 26, co-authored 137 publications receiving 3360 citations. Previous affiliations of Kirpal S. Bisht include University of Massachusetts Lowell & University of Massachusetts Boston.


Papers
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Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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.

131 citations

Journal ArticleDOI
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.
Abstract: Water-soluble polycarbonate having pendent carboxyl groups on the main-chain carbons is reported for the first time. This paper describes synthesis and enzyme-catalyzed ring-opening polymerization of a novel carbonate monomer, 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (1). Various commercially available lipases were screened for their ability to polymerize 1 in bulk at 80 °C. Monomer conversion and molecular weight of the polymer were significantly influenced by the source of the enzyme. For example, of the seven lipases screened, lipase AK (from Pseudomonas fluorescens) gave the highest monomer conversion (97%) and molecular weight (Mn = 6100). In reactions carried out under identical experimental conditions, no polymerization was observed when thermally deactivated lipase AK was used. Debenzylation of 2 by catalytic hydrogenation led to the corresponding linear polycarbonate, 3, with pendent carboxyl groups. Presence of pendent carboxyl groups is expected to enhance the biodegradability of the polyc...

123 citations


Cited by
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Journal ArticleDOI
TL;DR: Privileged substructures are believed to achieve this through the mimicry of common protein surface elements that are responsible for binding, such as β- and gamma;-turns.
Abstract: Privileged substructures are of potentially great importance in medicinal chemistry. These scaffolds are characterized by their ability to promiscuously bind to a multitude of receptors through a variety of favorable characteristics. This may include presentation of their substituents in a spatially defined manner and perhaps also the ability to directly bind to the receptor itself, as well as exhibiting promising characteristics to aid bioavailability of the overall molecule. It is believed that some privileged substructures achieve this through the mimicry of common protein surface elements that are responsible for binding, such as β- and gamma;-turns. As a result, these structures represent a promising means by which new lead compounds may be identified.

2,620 citations

Journal ArticleDOI
TL;DR: Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells.

2,424 citations

Journal ArticleDOI
TL;DR: This review presents the various methods of the synthesis of polyesters and tailoring the properties by proper control of molecular weight, composition, and architecture so as to meet the stringent requirements of devices in the medical field.

1,441 citations

Journal ArticleDOI
TL;DR: This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems).
Abstract: Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: e-caprolactone (e-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

1,247 citations

Journal ArticleDOI
Huayu Tian1, Zhaohui Tang1, Xiuli Zhuang1, Xuesi Chen1, Xiabin Jing1 
TL;DR: This review presents a comprehensive introduction to various types of synthetic biodegradable polymers with reactive groups and bioactive groups, and further describes their structure, preparation procedures and properties.

1,088 citations