Mixed disulfides

A composition for treating hypertension comprising a pharmaceutically acceptable carrier and an effective amount of one or more hypotensive agents or pharmaceutically acceptable salts thereof of the formula ##STR46## wherein A and A.sub.1 are each amino acid residues independently selected from the group consisting of glycyl, alanyl, valyl, leucyl, .alpha.-glutamyl, .gamma.-glutamyl, .alpha.-aspartyl, .beta.-aspartyl, phenylalanyl, tyrosyl, lysyl, arginyl, and prolyl, said A residue being joined through a carbonyl group and said A.sub.1 residue being joined through an amino group;

• X is an .alpha.-imino acid residue selected from the group consisting of ##STR47## R.sub.2 is hydrogen, hydroxy, lower alkyl, halogen, keto, ##STR48## or --Y--R.sub.5 ;
• Y is O or S;
• R.sub.5 is lower alkyl, phenyl, phenyl-lower alkylene, 1- or 2-naphthyl, biphenyl, substituted phenyl, substituted phenyl-lower alkylene, substituted 1- or 2-naphthyl, or substituted biphenyl wherein said substituent is on the phenyl ring and is one or two members selected from the group consisting of lower alkyl of 1 to 4 carbons, lower alkoxy of 1 to 4 carbons, lower alkylthio of 1 to 4 carbons, chloro, fluoro, trifluoromethyl, acetyloxy, and hydroxy;
• R.sub.6 is halogen or --Y--R.sub.7 ;
• R.sub.7 is lower alkyl, phenyl, phenyl-lower alkylene, substituted phenyl, or substituted phenyl-lower alkylene wherein said substituent is one or two members selected from the group consisting of lower alkyl of 1 to 4 carbons, lower alkoxy of 1 to 4 carbons, lower alkylthio of 1 to 4 carbons, chloro, fluoro, trifluoromethyl, acetyloxy, and hydroxy, or the R.sub.7 groups join in an alkylene chain of 2 or 3 carbons to complete a 5- or 6-membered ring or said ring in which one of the carbon atoms has a lower alkyl or di(lower alkyl)substituent;
• and
• R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen and lower alkyl.