Compounds of the formula I, ##STR1## in which 'R.sub.1 is an amino protective group, and n stands for 1 or 2, R.sub.1 denotes hydrogen or an amino protective group, R.sub.2 denotes hydrogen or a carboxyl protective group and R.sub.3 denotes triphenylmethyl, 4-monomethoxy-trityl or 4,4'-dimethoxy-trityl, and reactive carboxylic acid derivatives of such compounds of the formula I in which R.sub.2 stands for hydrogen, are described.These compounds can be used as starting materials for the preparation of peptides. They are more suitable for this than are analogous compounds of the formula I in which R.sub.3 denotes hydrogen or one of the carbamoyl protective groups hitherto customary.