The invention relates to a compound of formula (I), where: R1 is a phenyl group optionally substituted by one or more halogen atoms; R2 is: a hydrogen atom or a halogen atom or a cyano group; a -C(=O)Y group where Y is a hydrogen atom, or a -NH2 or -OR3 group; a -C(=S)NH2 group; a -C(=NH)NH-OH group; a -CH2OH or -CH2F group; a -CH=N-OH group; a -CH=CH2 or -C=C-R3 group; a H or H R1 group being a hydrogen or (C1-C4)alkyl group; R3 is a hydrogen atom or (C1-C4)alkyl group; and R4 is a -NH2, (C1-C4)alkyl, (C1-C4)fluoroalkyl or (C3-C7)cycloalkyl group.