Redução fenilcetonas por fermento de pão imobilizado

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

We have studied the stereospecific reduction of phenylketones by IMBY (immobilized baker s yeast) that not only gives alcohols with high optical yields but can be reused in further reactions after regeneration of the cofator NADH. The chiral alcohols are valuable intermediates for pharmaceuticals synthesis. We have used chrysotile and montmorillonite as supports and two methods for the culture medium: method 1 - IMBY and water; method 2 - IMBY, sugar and 2% KCI solution (IMBY/sugar 1:1). We have reduced PhCOCH2X compounds where X=CI or N3. The a-chloroacetophenone was reduced (chrysotile-IMBY) to the corresponding (R)-chlorohydrin with chemical and optical yields very close to those obtained with FBY (free baker s yeast). The subsequent reuse of the catalyst was possible only with method 2 and gave the (S)-chlorohydrin. The IMBY was not active for further recycle after the 3rd cicIe. By this methodology is possible to efficiently control the stereochemistry of the reduction of the ketones. The reduction of a-azidoacetophenone with montmorillonite K10-IMBY gave higher chemical yields of the azidoalcohol than those obtained with FBY. The isoladed azidoalcohol was reduced to (-)-(R)-2-amino-1-phenylethanol in order to compare its optical purity with the literature value. Compouds of the type PhCOCXCH3 where X=O (94), NOH (93), NOCOCH3 (95) and NOCH2Bz (96) were also studied. With (93) and using method 1 (chrysotile-IMBY), we have recover the starting ketone; with (94) and method 1 we have isolated. (-)-(S)-2-hydroxi-1-phenylpropanone (97) (in 27-31% yield) and (-)-(1R,2S)-1-phenyl-1,2-propanediol (98) (5%). The reuse was only achieved after leaving the IMBY overnight in the refrigerator with sugar and a 2% solution of KCI. Using method 2 we have obtained the diol (98) (15-47%) and the alcohol (97) (1-5%). With chrysotile as support, the chemical yields were lower than those with K10 but the optical yields were higher. Compound (95) was hydrolised to (93) when reacted with (chrysotile-IMBY). The compound (96) was reduced to O-benzil-1-hydroxi-1-phenyl-2-oxime-2-propanone in 23% yield. The optical purity of the isoladed compouds was determinaded by comparison with the values of especific optical rotation.

ASSUNTO(S)

quimica organica - sintese quimica organica

ACESSO AO ARTIGO

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