Enzymatic resolution of (±)-5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester and its transformations into polyfunctionalised amino acids and dipeptides |
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Authors: | Giuseppe Cremonesi Piero Dalla Croce Alessandra Forni Maddalena Gallanti Raffaella Gandolfi Concetta La Rosa |
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Institution: | 1. DISMAB—Sezione di Chimica Organica, Università degli Studi di Milano, ‘A. Marchesini’, V. Venezian 21, I-20133 Milano, Italy;2. Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, V. Venezian 21, I-20133 Milano, Italy;3. C.N.R.—I.S.T.M., Università degli Studi di Milano, V. Golgi,19, I-20133 Milano, Italy |
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Abstract: | Enantiomerically pure (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester was obtained via enzymatic resolution of the corresponding racemic mixture using a lipase from hog pancreas (PPL). The following reduction of the ester group to the corresponding alcohol and the oxidation of the latter led to (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carbaldehyde, and the reaction between this and Schöllkopf’s reagent, (2R)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine, gave mixtures of adducts with a good syn/anti ratio. The steric configurations of the major diastereoisomer were assigned on the basis of spectroscopic data and X-ray analysis. The subsequent controlled hydrolysis of the pyrazine ring led to β-(5-phenyl-4,5-dihydroisoxazol-3-yl)-serine methyl esters and the corresponding dipeptides with (R)-valine. Finally, reductive cleavage of the 4,5-dihydroisoxazole ring under hydrolytic conditions made it possible to obtain the corresponding polyfunctionalised dipeptides. |
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