Stereoselective β-labelling of aromatic amino-acids with deuterium and tritium

Tyrosine and phenylalanine, labelled stereoselectively with deuterium and tritium in the β-methylene groups, have been prepared via cis-hydrogenation of appropriate, β-labelled α-acylaminocinnamic acids obtained from the corresponding benzylideneoxazolinones. The configuration of (βR)-L-[β-2H]tyrosine was confirmed by ozonolysis of its racemate to give the racemate of (βS)-L-[β-2H]aspartic acid of known stereochemistry.The incorporation of the (βR)-[β-3H]- and (βS)-[β-3H]-forms of tyrosine into haemanthamine in ‘Texas’ daffodils was studied to show that hydroxylation of the original methylene group occurred highly stereospecifically with retention of configuration.