The present invention relates to a compound of formula I, or a pharmaceutically acceptable salt thereof : (I) wherein : n is 0 or 1; R1 is selected from H, alkyl and aralkyl, wherein said alkyl and aralkyl groups may be optionally substituted by one or more OH groups; X is a group selected from -C≡C-(CH2)p-; -C(R5)=C(R6)-(CH2)q-; and -C(R5)(R6)C(R7)(R8)-(CH2)r-; where each of R5, R6, R7 and R8 is independently H or alkyl, and each of p, q and r is independently 1, 2, 3, 4 or 5; Y is a group selected from : CN; COOR2; CONR3R4; SO2NR9R10; NR12COR13; NR14SO2R15; and a heterocyclic group selected from oxadiazolyl, thiazolyl, iso- thiazolyl, oxazolyl, iso-oxazolyl, pyrazolyl and imidazolyl; where each of R2, R3 and R4 is independently H or alkyl; or R3 and R4 are linked, together with the nitrogen to which they are attached, to form a 5 or 6-membered heterocycloalkyl or heterocycloalkenyl group, said heterocycloalkyl or heterocycloalkenyl group optionally containing one or more further groups selected from O, N, CO and S, and where each of R9, R10, R11, R12, R13, R14 and R15 is independently H or alkyl. 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, pain, or for controlling spasticity or tremors, for example, spasticity in MS.