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.

Ethyl Glucoside as a Multifunctional Initiator for Enzyme-Catalyzed Regioselective Lactone Ring-Opening Polymerization

Abstract: The one-pot biocatalytic synthesis of novel amphiphilic products consisting of an ethyl glucopyranoside (EGP) headgroup and a hydrophobic chain is described. The porcine pancreatic lipase (PPL) catalyzed ring-opening polymerization of e-caprolactone (e-CL) by the multifunctional initiator EGP was carried out at 70 °C in bulk. Products of variable oligo(e-CL) chain length (Mn = 450, 2200) were formed by variation of the e-CL/EGP ratio. Extension of this approach using Candida antarctica lipase (Novozym-435) and EGP as the initiator for trimethylene carbonate (TMC) ring-opening polymerization also resulted in the formation of an EGP−oligo(TMC) conjugate (Mn = 7200). Structural analysis by 1H, 13C, and COSY (13C-13C) NMR experiments showed that the reaction was highly regiospecific; i.e., the oligo(e-CL)/oligo(TMC) chains formed were attached by an ester/carbonate link exclusively to the primary hydroxyl moiety of EGP.

Enzyme-Mediated Regioselective Acylations of Sophorolipids.

Abstract: Enzymatic synthesis of well-defined sophorolipid analogues for evaluation of their bioactivities and as new building blocks for the preparation of glycolipid-based amphiphilic polymers is described. Lipase Novozym 435 from Candida antarctica has been shown to be an efficient catalyst for acylation of sophorolipids esters. A mixture of sophorolipids produced by Torulopsis bombicola was esterified by reaction with sodium alcoxide. The alkyl esters of sophorose lipids were subjected to Novozym 435 catalyzed acylation in dry tetrahydrofuran (THF) with vinyl acrylate and vinyl acetate to diacyl derivatives. The reactions were highly regioselective, and exclusive acylation of the hydroxyl groups on C-6‘ and C-6‘ ‘ took place. Methyl ester in the absence of the acylating agent, or with the agent at a concentration less than equimolar, gave sophorolactone (9). Careful analysis of the spectral data revealed it to be a synthetic analogue of microbially produced macrolactone. Sophorolactone (9) differs in the site a...

Solventless Enantioelective Ring-Opening Polymerization of Substituted ∊-Caprolactones by Enzymatic Catalysis

Abstract: Highly (S)-enriched substituted poly(e-caprolactone)s were synthesized from 4-methyl-e-caprolactone (4-MeCL) and 4-ethyl-e-caprolactone (4-EtCL) by lipase Novozym-435 (from Candida antarctica) catalyzed ring-opening polymerizations. The polymerizations were performed in bulk, thus eliminating the need for solvents in the polymerization process. Poly(4-EtCL) and poly(4-MeCL) having >95% enantiomeric purity (eep) have been prepared. Number-average molecular weights of the poly(4-EtCL) and poly(4-MeCL) were 4400 and 5400, respectively. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. Contrary to many literature reports and conventional wisdom, the enantioselectivity of the lipase was greater at 60 °C, the higher reaction temperature. The solventless polymerization process appeared to be diffusion-controlled in which the monomer conversion and polymer molecular weight increased at higher reaction temperature.

The combinatorial synthesis of bicyclic privileged structures or privileged substructures

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.

Synthesis of polycaprolactone: a review

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).