ester bond or a peptide bond the novel compound can be designated as benzyl esters of aromatic amino acids and they can be synthesized by reacting such amino acid with phosgene at room temperature in dioxane to form the corresponding n carboxy anhydride hydrochloride which latter is reacted with the aromatic alcohol such as for example c 6 h 5 ch 2 oh to form the desired product in the form of its hydrochloride in the present specification and claims the following abbreviations are used alanine ala arginine arg asparagine asn aspartic acid asp cysteine cys glycine gly glutamic acid gln glycine gly histidine his isoleucine ilu leucine leu lysine lys methionine met phenylalanine phe proline pro sernine ser threonine thr tryptophan trp tyrosine tyr valine val hydrochloric acid hcl benzyl ester obz and p toluene sulphonate pts it is clear that the above method is by illustration only and that various other routes of preparation can be resorted to the novel compounds defined above are effective agents for the intended purposes further improved compounds which have a lower degree of hydrolysis can be prepared as follows str2 where r is an amino acid residue as amino acid there can be used any amino acid listed or any modification thereof or any other acid which enhances the product with hydrolysis stability instead.