Deprotection of t-Butyl Esters of Amino Acid Derivatives by Nitric Acid in Dichloromethane

The extension of the deprotection procedure of t-butylated carboxyl function using HNO3 in CH2Cl2 to a number of appropriately selected N-Z-derivatives of natural amino acid esters was investigated. The method was found to work effectively with alanine, phenylalanine, serine and the dipeptide aspartame, but the reagent brought about a number of unwanted transformations with tyrosine, methionine and tryptophan. Suitable protection of functions present in the latter ones allowed selective ester dealkylation, but tyrosine underwent unavoidable fast preliminary ring nitration.