ABSTRACT
Figure 6.1 A schematic process of PEGylation: (1) PEGylation reactor. (2) Membrane separator. (3) Chromatographic columns.
For protein or other biomolecules, the common PEGylation route is shown as Fig. 6.1. Monomethoxy PEG (mPEG) was activated to form a derivative with active end group. Here we use mPEG-O-ACT to illustrate various derivatives that are formed through different
chemistry (6). These can be aldehyde, maleimide, or NHS ether, which can react subsequently with a biomolecule, such as a protein, at mild reaction condition to preserve the biological activity of the biomolecule. The derivative, mPEG-O-ACT, is added to the solution of biomolecule to be PEGylated. The whole process involves two stages: reaction and separation. In the reaction stage, mPEG-OACT reacts with the corresponding group of the biomolecule, usually amine, thio, or N terminal of a protein. In most cases of protein PEGylation, the reaction is not very specific because there could be more than one group reacting with the PEG molecule. As a consequence, isomers of different PEGylation sites could be formed. If the reaction is not controlled at the optimum condition, a complex mixture might be produced, which contains mono-, di-, or tri-PEGylated products.
