Abstract
The lipases CAL-B, PSL, PSL-C, PSL-D, and A. niger lipase, free or immobilized in starch (obtained from two types of yam, known in Brazil as “cara” (Discorea alata L.) and “inhame” (Colocasia esculenta (L.) Schott) or gelatin films, were used in the acylation of (RS)-sec-butylamine with different acyl donors in various organic solvents applying conventional heating (CH) or microwave (MW) irradiation. In the case of free A. niger lipase, the conversion degrees were three times higher using MW irradiation when compared to conventional heating at 35 oC. Using free A. niger lipase, the (R)-amide was obtained with a conversion degree of 21%, resulting in eep > 99% and E-value (enantioselectivity value) > 200, in 1 min of reaction under MW irradiation. When the A. niger lipase was immobilized in yam starch films, the (R)-amide was obtained in moderate conversions of 8-25% after 3 or 5 min of reaction under MW irradiation, but with higher selectivity (eep > 99% and E > 200) in comparison with the free form (conversion degree of 45%, eep 81% and E value of 18).
Highlights
Biocatalysts are an attractive alternative to conventional methods for effecting asymmetric organic transformations, offering unique characteristics when compared to homogeneous or heterogeneous chemical catalysts
Five lipases from different sources were screened in the acylation of (RS)-sec-butylamine (1) with ethyl acetate in n-hexane at 35 oC, under conventional heating (CH)
Lipases produced by C. antarctica (CAL-B), P. cepacia (PSL, PSL-C and PSL-D) and the native A. niger free or immobilized in yam starch or gelatin films were selected for this study
Summary
Biocatalysts are an attractive alternative to conventional methods for effecting asymmetric organic transformations, offering unique characteristics when compared to homogeneous or heterogeneous chemical catalysts. Lipases (triacylglycerol acyl hydrolases, EC 3.1.1.3) are considered the most ubiquitous and valuable enzymes for asymmetric synthesis. The synthesis of optically pure amides is an area of growing interest in synthetic chemistry. Amines and their derived amides are important compounds in organic synthesis because of the presence of these functional groups in many pharmacologically active compounds such as (S)‐methyldopa and (S)-penicillin.[6,7,8,9,10]. The classic amide synthesis method is the reaction of carboxylic acids with amines at high temperature. Due to the low activity of carboxylic acids, various methods for
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