The present invention relates to a compound of formula (I), or a pharmaceutically acceptable salt thereof, wherein Z is OR.sup.1 or NR.sup.1R.sup.2 wherein each of R.sup.1 and R.sup.2 is independently H, or a hydrocarbyl group; X is an alkylene, alkenylene, or alkynylene group, each of which may be optionally substituted by one or more substituents selected from alkyl, COOH, CO.sub.2-alkyl, alkenyl, CN, NH.sub.2, hydroxy, halo, alkoxy, CF.sub.3 and nitro; Y is a polar functional group selected from OH, NO.sub.2, CN, COR.sup.3, COOR.sup.3, NR.sup.3R.sup.4, CONR.sup.3R.sup.4, SO.sub.3H, SO.sub.2--R.sup.3, SO.sub.2NR.sup.3R.sup.4 and CF.sub.3, where each of R.sup.3 and R.sup.4 is independently H or a hydrocarbyl group; A is an aryl or heteroaryl group, each of which may be optionally substituted; and B is (CH2).sub.n where n is 0, 1, 2, 3, 4 or 5; with the proviso that: (i) when A is phenyl, n is 0, and Z is OH, X--Y is other than meta-C.ident.--C--(CH.sub.2).sub.2CO.sub.2H, meta-C.ident.--C--(CH.sub.2).sub.2OH, meta-C.ident.C--(CH.sub.2).sub.2CO.sub.2Me, meta-(CH.sub.2).sub.4CO.sub.2H, ortho-CH.sub.2CO.sub.2H, ortho-(CH.sub.2).sub.2CO.sub.2H and ortho-(CH.sub.2).sub.4CO.sub.2H; and (ii) when A is phenyl, n is 0, and Z is OMe, X--Y is other than meta-C.ident.C--(CH.sub.2).sub.4OH. Further aspects of the invention relate to the use of such compounds in the preparation of a medicament for the treatment of a muscular disorder, a gastrointestinal disorder, or for controlling spasticity or tremors.