| abstract |
A compound of formula (VIII): ##STR1## in which Alk is a (C 1 -C 4 )alkyl group, R• is hydrogen or a protecting group cleavable by hydrolysis and R is hydrogen, a protecting group cleavable by reduction or a heterocycle of structure (IX): ##STR2## in which Hal is a halogen atom and X, Y and Z are each --CH═ or one of them is a nitrogen atom and the others are --CH═, and its salts, R• being other than hydrogen if R is hydrogen or a group of structure (IX). |