Abstract The use of 2-nitro-4-methoxy-phenylsulfenyl-(I) as an amino protecting group which is extremely sensitive towards electrophilic attack in the synthesis of amino penicillins (amino-penicillin and DL-α-amino-benzylpenicillin) is described. Synthesis of few protected dipeptides (2-nitro-4-methoxyphenylsulfenyl-L-phenylalanyl-L-valine, 2-nitro-4- methoxyphenylsulfenyl-L-phenylalanyl-L-phenylalanine and 2-nitro-4- ...