A conjugate compound of the formula: ##STR13## wherein m has a value of from 0 to 3;n has a value of from 0 to 3; d has a value of from 0 to 3; q has a value of from 0 to 6; X is oxygen or sulphur; R4 is hydrogen, alkyl, or alkoxy; L is a linker group; and Z is a reactive functional group; Z1 is the residue of a reactive functional group; w is 0 or 1; z is an integer 1 or more; and Ab is an antibo