Phosphinic acid derivatives

A phosphinic acid derivative of formula (I) or a pharmaceutically acceptable salt thereof, ##STR29## in which R.sup.1 represents a linear or branched alkyl group having 1 to 10 carbon atoms which may be substituted by a hydroxyl group, a lower alkoxy-lower alkyloxy group or a halogen atom;

• a cycloalkyl-lower alkyl group having 4 to 10 carbon atoms;
• a cycloalkyl group having 3 to 6 carbon atoms in the ring which may be substituted by 1 to 4 identical or different lower alkyl groups;
• or an aralkyl group having 7 to 11 carbon atoms;
• R.sup.2 represents a hydrogen atom;
• R.sup.5 represents a hydrogen atom, a 1-(lower alkylcarbonyloxy)lower alkyl group, a phthalidyl group, a lower alkoxycarbonylmethyl group or a 1-(5-lower alkyl or phenyl-2-oxo-1,3-dioxol-4-yl)lower alkyl group;
• and
• A represents a group of the formula ##STR30## wherein R.sup.3a represents a phenyl group;
• an aralkyl group having 7 to 11 carbon atoms;
• a cycloalkyl-lower alkyl group having 4 to 10 carbon atoms;
• or a linear or branched alkyl group having 1 to 10 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms in the ring, which may be substituted by a halogen atom, a carboxyl group, a di-lower alkyl-substituted amino group, an N-methyl-N-carboxymethylamino group, a phenylthio group, a triazolythio group, a carboxy-lower alkylthio group, a lower alkoxycarbonyl-lower alkylthio group, a pyridylthio group, hydroxy substituted pyridylthio group, an imidazolylthio group, a lower alkyl substituted imidazolylthio group, a hydroxy-lower-alkylthio group, an amino-lower alkylthio group or a 2-amino-2-carboxyethylthio group;
• and the double bond at A has a Z-configuration, or a group of the formula ##STR31## wherein R.sup.4a represents a cycloalkyl group having 3 to 6 carbon atoms.