Conjugates of pharmaceutically useful proteins

Claim 1

A conjugate of formula (II): ##STR12## where X is a pharmaceutically useful protein and the NH moiety is derived from a protein amino group in X; and either: (i) R1 and R 2 are each a non-polymeric organic group or a group of formula --R 3 --P wherein P is a water-soluble polymer selected from the group consisting of polyethylene glycol, polypropylene glycol and methoxy polyethylene glycol and R 3 is a bridging group selected from the group consisting of straight or branched C 1-10 aliphatic hydrocarbon chains and straight or branched C 1-10 aliphatic hydrocarbon chains interrupted or terminated by an amide moiety, an ester moiety or at least one hetero atom selected from oxygen, sulphur or nitrogen, said moiety being unsubstituted or substituted by C 1-16 alkyl; or (ii) R 1 and R 2 together are C 3-5 polymethylene to complete a 5- to 7-membered alicyclic ring or together complete an aromatic ring, wherein the alicyclic or aromatic ring is substituted by groups R 4 and R 5 which are each of non-polymeric organic group or a group of formula --R 3 --P; provided that at lease one of RI and R 2 or of R 4 and R 5 is a group --R 3 --P.