5--5--5--trifluoroleucine and 4-4-4-trifluorovaline

Stereoselective syntheses of the valuable fluorinated amino acids (2S,3S)-4,4,4-trifluorovaline and (2S,4S)-5,5,5-trifluoroleucine have been achieved starting from 4,4,4-trifluoro-3-methylbutanoic acid by using a conceptually simple transformation: conversion to a chiral oxazoline, SeO2-promoted oxidative rearrangement to the dihydro-2H-oxazinone, and face-selective hydrogenation of the C=N bond, followed by hydrogenolysis-hydrolysis. The transformation is limited by the tendency of the intermediate beta-trifluoromethyldihydrooxazinone to undergo imine-enamine isomerization. Both amino acids were obtained as configurationally pure hydrochloride salts identical in all respects with those in literature reports.

Topics: Leucine; Molecular Conformation; Oxazines; Oxazoles; Oxidation-Reduction; Stereoisomerism; Valine

Topics: Amino Acids; Catalysis; Chemistry, Organic; Dipeptides; Leucine; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Stereoisomerism; Valine