Abstract: Compounds of formula I are described, ##STR1## wherein n is equal to one or two, R.sub.1 stands for hydrogen or an amino protecting group, R.sub.2 represents hydrogen or a carboxyl protecting group and R.sub.3 4-methyltriphenylmethyl, 4,4'-dimethyltriphenylmethyl, 4,4',4"-trimethyltriphenylmethyl. Furthermore described are compounds of formula I which are reactive and suitable for coupling reactions and are derived from I with R.sub.2 =H by activation of the carboxyl group.The compounds mentioned above can be used as starting materials for the synthesis of peptides. They are more suitable than analogous compounds of formula I, wherein R.sub.3 represents hydrogen or a carbamoyl protecting group used hitherto.