Enzymic asymmetric synthesis of .alpha.-amino acids. Enantioselective cleavage of 4-substituted oxazolin-5-ones and thiazolin-5-ones
摘要:
A general enzymatic asymmetric synthesis of L-alpha-amino acids has been developed. This method entails the use of the Pseudomonas cepacia lipase (P-30) to catalyze the enantioselective methanolysis of a variety of 4-substituted 2-phenyloxazolin-5-one derivatives in a nonpolar organic solvent to furnish optically-active N-benzoyl-L-alpha-amino acid methyl esters (ee = 66-98%), which in turn is subjected to a protease-catalyzed kinetic resolution yielding enantiomerically-pure N-benzoyl-L-alpha-amino acids. This synergistic coupling of two enzymes allows the ready preparation of L-alpha-amino acids of high enantiopurity in yields greater than 50%, an inherent advantage over conventional resolution procedures. Two proteases were found to catalyze the enantioselective hydrolysis of a variety of 4-substituted 2-phenylthiazolin-5-one derivatives to give N-(thiobenzoyl)-L-alpha-amino acids of high optical purity.
Chiral Phosphoric Acid Catalyzed Diastereo- and Enantioselective Mannich-Type Reaction between Enamides and Thiazolones
作者:Jun Kikuchi、Norie Momiyama、Masahiro Terada
DOI:10.1021/acs.orglett.6b00857
日期:2016.6.3
An enantioselective Mannich-type reaction between enamides, serving as aliphatic imine equivalents, and thiazolones or an azlactone, serving as α-amino acid derived pronucleophiles, was investigated using a chiral phosphoric acid catalyst. By using thiazolones, Mannich adducts with a tetrasubstituted chiral carbon center at the α-position and an aliphatic substituent at the β-position were efficiently
4-substituted 2-phenylthiazol-5(4H)-one and an electron-deficient alkene is shown to include a stable cycloadduct and a Michael adduct formed through the 2- or the 4-position of the thiazolone. The reaction can be diverted towards the Michael adduct entirely, by adding traces of aqueous alkali to the reactants in acetone solution. A novel type of 1:2-adduct is present in the reaction mixture, and is shown to