Conjugated biological molecules and their preparation

1. A process for the preparation of a compound of the general formula

in which one of X and X′ represents a polyethylene glycol, and the other represents a hydrogen atom;

each Q independently represents a linking group,

W represents a keto group or a CH(OH) group,

each of Z 1 and Z 2 independently represents a protein,

A is a C 1-5 alkylene or alkenylene chain, and

B is a bond or a C 1-4 alkylene or alkenylene chain;

which comprises reacting either:

(i) a compound of the general formula

in which X, X′, Q, A and B have the meanings given above;

W′ represents a keto group and

each L independently represents a leaving group; or

(ii) a compound of the general formula

in which X, X′, Q, W′, A and L have the meanings given above and m represents an integer 1 to 4;

with compounds of the general formula Z 1 SH and Z 2 SH.

2. A process as claimed in claim 1 , in which the or each leaving group L represents —SR, —SO 2 R, —OSO 2 R, —N + R 3 , —N + HR 2 , —N + H 2 R, halogen, or —Oø, in which R represents an alkyl or aryl group and ø represents a substituted aryl group containing at least one electron withdrawing substituent.

3. A process as claimed in claim 1 , in which Z 1 and Z 2 represent different proteins.

4. A process as claimed in claim 1 , carried out in an aqueous medium.

5. A process as claimed in claim 1 , in which each linking group Q independently represents a direct bond, an alkylene group, or an optionally-substituted aryl or heteroaryl group, any of which may be terminated or interrupted by one or more oxygen atoms, sulphur atoms, —NR groups in which R represents an alkyl or aryl group, keto groups, —O—CO— groups and/or —CO—O— groups.