2,4-Dimethoxybenzyl as a Protecting Group for Glutamine and Asparagine in Peptide Synthesis

The properties of 2,4-dimethoxybenzyl (Dmb) as a protecting group for the amide side chain of glutamine and asparagine during peptide synthesis are described. 2,4-Dimethoxybenzylamine was prepared by the reduction of 2,4-dimethoxybenzyaldoxime with sodium bis(2-methoxyethoxy)aluminum hydride. The Dmb derivatives obtained by reaction of 2,4-dimethoxybenzylamine and either N,N'-dicyclohexylcarbodiimide or N-diethyl-amino-1-propyne with the appropriate amine acid derivatives are crystalline and the Dmb group can be removed by trifluoroacetic acid or anhydrous hydrogen fluoride to give the free amide. No formation of pyroglutamyl peptides or of other side reactions was detected with Dmb-protected glutamyl derivatives, even during saponification. On the contrary, use of alkali with either 2,4-dimethoxybenzyl- or bis(2,4-dimethoxybenzyl)-protected asparaginyl peptides resulted in a mixture of products and is not recommended.