Modification de la tyrosine lors de l'elimination par acidolyse du groupe protecteur o-benzyle

A photolabile protecting group for the phenolic hydroxyl function of tyrosine

The ortho-nitrobenzyl group (ONBzl) was utilized to protect the phenolic functions of the side chain of tyrosine. Optimal conditions for its mild photolyti removal were established. This paper describes the preparation and properties of some (O-ONBzl)-tyrosine derivatives of potential value in the synthesis of tyrosine-containing peptides. Their use in the synthesis of the dipeptide, N-benzyloxycarbonyl-L-tyrosyl-glycine ethyl ester is presented as an example.

SN 1 and SN 2 mechanisms for the deprotection of synthetic peptides by hydrogen fluoride. Studies to minimize the tyrosine alkylation side reaction

Studies on the side reaction leading to ring alkylation during HF deprotection of tyrosine revealed that under SN 1 conditions the formation of by-product can be reduced by using protecting groups that either provide only weakly electrophilic carbocations or give rise to an intermediate that deactivates the tyrosine ring and allows scavengers to suppress the formation of 3-alkyltyrosine. The effectiveness of the scavenger can be qualitatively predicted by its pKa value. A new reagent (HF: dimethylsulfide, 1:3, v/v) provides an SN2 cleavage mechanism that removes the danger of carbocation formation and suppresses the electrophilic alkylation side reaction.