in which R29 represents a hydrogen atom, a CH3O, CH3CH2O or phenyl radical, R30 denotes hydrogen or a lower alkyl radical such as methyl or ethyl, R31 denotes hydrogen or a lower alkyl radical such as methyl or ethyl, R32 denotes a lower alkyl radical such as methyl or ethyl or a radical corresponding to the formula: ???R33???N(R31)2, R33 representing a group ???CH2???CH2???, ???CH2???CH2???CH2???