A pharmaceutical compound of the formula: ##STR1## in which n is 1 or 2, R.sup.1 is --CO.sub.2 H, R.sup.2 is hydrogen or C.sub.1-4 alkyl andR.sup.3 is hydrogen, C.sub.1-10 alkyl, C.sub.2-10 alkenyl, optionally substituted phenyl, optionally substituted phenyl-C.sub.1-4 alkyl, optionally substituted phenyl C.sub.2-10 alkenyl,(optionally substituted phenyl).sub.2 -C.sub.1-4 alkyl, optionally substituted C.sub.3-7 cycloalkyl, optionally substituted C.sub.3-7 cycloalkyl-C.sub.1-4 alkyl or optionally substituted C.sub.3-7 cycloalkyl-C.sub.2-10 alkenyl, orR.sup.2 and R.sup.3, together with the carbon atom to which they are attached, form an optionally substituted C.sub.4-7 cycloalkyl group;or a salt or ester thereof other than the compounds .gamma.-propylidene-L-glutamic acid, .gamma.-ethylidene-L-glutamic acid and .gamma.-methylidene-L-glutamic acid.