. . . . . . "In formula I the optional substitution on X, which preferably is an optionally mono-unsaturated C2-3 chain, may for example take the form of halogen atoms or oxo, amino, carboxyl, hydroxy or alkyl groups or combinations or derivatives thereof such as for example amide, ester, ether or N-attached heterocyclic, e.g. 2,5-dioxo-pyrrolidino, groups." . . . . .