Showing papers by "Kirpal S. Bisht published in 2005"

Enantioenriched substituted polycaprolactones by enzyme catalysis

Abstract: The kinetic resolution of racemic seven-membered lactones substituted either at the 4- or the 6-position is achieved in bulk (solvent free) conditions, by lipase-catalysed butanolysis. Novozym-435 lipase (from Candida antarctica) induced (S)-selective butanololysis, and (R)-lactones were recovered unreacted with >97% enantiomeric excess (e.e.). The (S)-selective Novozyme-435 catalysis is also employed for the ring opening polymerization of 4-methyl-e-caprolactone (4-MeCL) and 4-ethyl-e-caprolactone (4-EtCL) to obtain highly (S)-enriched substituted poly E-caprolactones. 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 (ee p ) have been prepared. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. The optically enriched (R)- 4-MeCL and 4-EtCL obtained were mixed with rac-4-MeCL and 4-EtCL to prepare mixtures of variable enantiopurities and the mixtures were subjected to chemical polymerization initiated by Sn(Oct) 2 to obtain poly (4-EtCL) and poly (4-MeCL) of variable enantiopurities. The effects of optical purity of the polymers glassy state were evaluated by DSC.

Enantioselective Synthesis of Imperanene via Enzymatic Asymmetrization of an Intermediary 1,3‐Diol.

Abstract: [reaction: see text] Using a chemoenzymatic synthetic strategy, (S)-imperanene and its (R)-enantiomer has been synthesized from vanillin in nine steps. The key step in the synthesis involves the use of Pseudomonas cepacia lipase (PS-30) to induce asymmetrization of the intermediary prochiral 1,3-diol in >97% ee.