Na[(tert-Butoxy)carbonyl]-2-diazo-~-histidine methyl ester 1 was synthesized starting from the corresponding L-histidine derivative. The physico-chemical properties of this new photoactivatable amino-acid derivative were established. The synthetic precursor of 1,2-amino-~-histidine derivative 3, was best isolated and characterized as 2-amino-Nr-[(tert-butoxy)carbonyl]-~T-tosyl-~-histidine methyl ester (4). Selective deprotections of 4 (N"-Boc, N'-Tos, COOMe) were achieved, thus allowing the use of the corresponding products in peptide synthesis. The optically active dipeptides 8 and 9 were synthesized by coupling 2-amino-Nr-tosyl-~-histidine methyl ester ( 5 ) with 6) with L-alanine methyl ester, respectively. The question of selective diazotization of a 2-aminohistidine residue in a synthetic peptide was studied using competitive diazotizations between 2-amino-lH-imidazole and several amino-acid derivatives susceptible to undergo nitrosylation. The results show that synthetic photoactivatable peptides incorporating a 2-diazohistidine residue might become useful photoaffinity probes.
N-[(tert-butoxy)cdrbonyl]-L-alanine and N'-[(rert-buto~y)carbonyl]-N~-tosyl-~-histidine (