The invention concerns a compound of the general formula (I): ##STR1## in which Bi denotes a residue derived by cleavage of a carboxyl group from biotin or from a biotin derivative, R.sup.1 and R.sup.2 denote independently of one another hydrogen or C.sub.1 --C.sub.4 alkyl,n denotes an integer from 4 to 10 andX denotes an alkylene residue with a chain length of 5 to 20 atoms substituted by one or several O or/and S atoms and a conjugate of this compound with a substance that has at least one primary or/and secondary amino group NHR.sup.3.