A compound of formula (I), ** Formula ** in which R 1 represents phenyl which is unsubstituted or mono-substituted with halogen, (C 1 -C 4) alkyl, (C 1 -C 4) alkoxy, (C 1 -C 2) fluoroalkyl ) or fluoroalkoxy (C1-C2)； R2 represents hydrogen, methyl or cyclopropyl； R3 and R4 are identical and represent hydrogen or methyl； and R5 represents (C1-C2) alkyl； and a salt of such a compound.Un compuesto de fórmula (I), **Fórmula** en la que R1 representa fenilo el cual está no sustituido o mono-sustituido con halógeno, alquilo (C1-C4), alcoxi (C1-C4), fluoroalquilo (C1-C2) o fluoroalcoxi (C1-C2)； R2 representa hidrógeno, metilo o ciclopropilo； R3 y R4 son idénticos y representan hidrógeno o metilo； y R5 representa alquilo (C1-C2)； y una sal de tal compuesto.
