Abstract
Chiral 2-octanol is one of the key intermediates for preparation of liquid crystal materials, as well as many optically active pharmaceuticals. Lipase catalyzed kinetic resolution has proved to be an efficient technique for synthesis of enantiomerically enriched compounds. In the present study, optimization and kinetic modeling of kinetic resolution of (±)-2-octanol was done by using vinyl acetate as an acyl donor in n-heptane as a solvent. Response surface methodology (RSM) and four-factor-five-level Centre Composite Rotatable Design (CCRD) were employed to evaluate the effect of various parameters such as speed of agitation, enzyme loading, temperature and acyl donor/alcohol molar ratio on conversion, enantiomeric excess (ee), enantioselectivity and initial rate of reaction. Acylation of 2-octanol with vinyl acetate catalyzed by Novozyme 435 follows the ternary complex mechanism (ordered bi-bi mechanism) with inhibition by 2-octanol.
Highlights
Enzymatic catalysis in non-aqueous media has been greatly pursued these days for the synthesis of a wide variety of pharmaceuticals, agrochemicals, perfumes, flavors and other fine-chemicals [1,2,3,4]
All chemicals were procured from firms of repute and used without any further purification: Novozyme 435 (Candida antarctica lipase B immobilized on a macroporous polyacrylic resin, activity 10 PLU/g; (1 μmol propyl laurate formed/min/g-enzyme)), Lipozyme RM IM (Mucor miehei lipase immobilized on anionic resin, activity 6 BAUN (Acidolysis Unit Novo) and Lipozyme TL IM (Thermomyces lanuginosus immobilized on silica, activity 75 IUN/g) were procured as gift samples from Novo Nordisk, Denmark. (±)-2-Octanol was procured from Merck, India
Lipase catalyzed kinetic resolution of (±)-2-octanol with vinyl acetate as an acyl donor in n-heptane as a solvent produces ester and acetaldehyde is given in Scheme 1
Summary
Enzymatic catalysis in non-aqueous media has been greatly pursued these days for the synthesis of a wide variety of pharmaceuticals, agrochemicals, perfumes, flavors and other fine-chemicals [1,2,3,4]. In this regard, our group has contributed extensively to mechanistic studies, kinetic modeling and separation of enantiomers, covering several industrially relevant classes of reactions such as epoxidation/oxidation [5,6], hydrolysis [7], esterification [8,9,10], transesterification [11,12,13], amidation [14] and hydrazinolysis [15]. Various immobilization techniques for lipase immobilization have been reported; for instance, hexagonal mesoporous silica (HMS) [12], magnetic nanoparticles, Diaion HP20, ultrastable-Y molecular sieve [27], SBA 15 [29], and Sol-gel method [31]
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