Stereochemistry of the rearrangement of 2-aminoethanol by ethanolamine ammonia-lyase.

Abstract

(1R)-2-Amino[1-2H1]ethanol and (1S,2RS)-2-amino[1,2-2H2]ethanols have been synthesised by decarboxylation of (2S,3R)-[3-2H1]serine and (2S,3S)-[2,3-2H2]serine respectively. The stereochemical integrity of these labelled 2-aminoethanols has been ascertained from the 1H-NMR spectra of their N,O-dicamphanoyl derivatives. This assay has also been used to confirm that samples of (2R)- and (2S)-2-amino [2-2H1]ethanols prepared from (2R)- and (2S)-[2-2H1]glycines are stereochemically pure. Ethanolamine ammonia-lyase rearranges (1R)-2-amino[1-2H1]ethanol to acetaldehyde at approximately the same rate as it rearranges unlabelled 2-aminoethanol, whilst (1S,2RS)-2-amino[1,2-2H2]ethanol is rearranged at the same rate as the (1,1-2H2)-labelled substrate. The isotope effect is approximately kH/k2H = 8. The 2H-NMR spectra of the 3,5-dinitrobenzoates of the ethanol produced by reduction in situ of the acetaldehyde formed in the rearrangements show that the 1-2H1 label migrates in (1S,2RS)-2-amino-[1,2-2H2]ethanol and 2-amino[1,1-2H2]ethanol but not in (1R)-2-amino[1-2H1]ethanol. The above results indicate that the adenosylcobalamin-dependent ethanolamine ammonia-lyase catalyses the rearrangement of 2-aminoethanol with migration of the 1-pro-S-hydrogen atom.