A compound of formula: wherein: ▪ A represents a linear or branched (C 1 -C 6) alkyl chain; ▪ R 1 represents: • a hydrogen atom, • a halogen atom, • an acyl group CO-R 7 or a sulfonyl group SO 2 -R 7, wherein R 7 represents a (C 1 -C 6) alkyl group, • a sulfonamide group SO 2 -NR 8 R 9 wherein R 8 and R 9 independently represent a hydrogen atom, or a (C 1 -C 6) alkyl group, or • a (C 1 -C 6) alkyl, (C 1 -C 6) alkoxy, (C 1 -C 6) alkylmercapto, thio-(C 1 -C 6)alkyl or (C 1 -C 6) alkylsulfonyl group, said groups being optionally substituted by at least one halogen atom; ▪ R 1 ' represents a hydrogen atom or a hydroxyl group, preferably a hydrogen atom; ▪ R 2, R 3, R 4 and R 5 are identical or different and each represents a hydrogen atom or a (C 1 -C 6) alkyl group; and ▪ R 6 represents: • a hydrogen atom, • a (C 1 -C 6) alkyl group, optionally substituted by at least one hydroxyl group at the end of the alkyl chain, • a (C 1 -C 4) alkylacyloxy group, • a (C 1 -C 4) alkyl-ORio group, wherein R 10 represents: - a (C 1 -C 4) alkyl group, optionally substituted by at least one hydroxyl group at the end of the chain, - or a COR 11 group, R 11 being a (C 1 -C 6) alkyl group optionally substituted by an amino group at end of the alkyl chain; or one of its pharmaceutically acceptable salts, for a use for treating spasticity. ▪ A represents a linear or branched (C 1 -C 6) alkyl chain; ▪ R 1 represents: • a hydrogen atom, • a halogen atom, • an acyl group CO-R 7 or a sulfonyl group SO 2 -R 7, wherein R 7 represents a (C 1 -C 6) alkyl group, • a sulfonamide group SO 2 -NR 8 R 9 wherein R 8 and R 9 independently represent a hydrogen atom, or a (C 1 -C 6) alkyl group, or • a (C 1 -C 6) alkyl, (C 1 -C 6) alkoxy, (C 1 -C 6) alkylmercapto, thio-(C 1 -C 6)alkyl or (C 1 -C 6) alkylsulfonyl group, said groups being optionally substituted by at least one halogen atom; • a hydrogen atom, • a halogen atom, • an acyl group CO-R 7 or a sulfonyl group SO 2 -R 7, wherein R 7 represents a (C 1 -C 6) alkyl group, • a sulfonamide group SO 2 -NR 8 R 9 wherein R 8 and R 9 independently represent a hydrogen atom, or a (C 1 -C 6) alkyl group, or • a (C 1 -C 6) alkyl, (C 1 -C 6) alkoxy, (C 1 -C 6) alkylmercapto, thio-(C 1 -C 6)alkyl or (C 1 -C 6) alkylsulfonyl group, said groups being optionally substituted by at least one halogen atom; ▪ R 1 ' represents a hydrogen atom or a hydroxyl group, preferably a hydrogen atom; ▪ R 2, R 3, R 4 and R 5 are identical or different and each represents a hydrogen atom or a (C 1 -C 6) alkyl group; and ▪ R 6 represents: • a hydrogen atom, • a (C 1 -C 6) alkyl group, optionally substituted by at least one hydroxyl group at the end of the alkyl chain, • a (C 1 -C 4) alkylacyloxy group, • a (C 1 -C 4) alkyl-ORio group, wherein R 10 represents: - a (C 1 -C 4) alkyl group, optionally substituted by at least one hydroxyl group at the end of the chain, - or a COR 11 group, R 11 being a (C 1 -C 6) alkyl group optionally substituted by an amino group at end of the alkyl chain; • a hydrogen atom, • a (C 1 -C 6) alkyl group, optionally substituted by at least one hydroxyl group at the end of the alkyl chain, • a (C 1 -C 4) alkylacyloxy group, • a (C 1 -C 4) alkyl-ORio group, wherein R 10 represents: - a (C 1 -C 4) alkyl group, optionally substituted by at least one hydroxyl group at the end of the chain, - or a COR 11 group, R 11 being a (C 1 -C 6) alkyl group optionally substituted by an amino group at end of the alkyl chain; - a (C 1 -C 4) alkyl group, optionally substituted by at least one hydroxyl group at the end of the chain, - or a COR 11 group, R 11 being a (C 1 -C 6) alkyl group optionally substituted by an amino group at end of the alkyl chain;