The invention provides reagents and methods for conjugating polymers specifically
to the -amine of polypeptides in high yield. The invention provides monofunctional,
bifunctional, and multifunctional PEGs and related polymers having a thioester
moiety capable of specifically conjugating to the -amine of a polypeptide
having a cysteine or histidine at the N-terminus. The invention provides active
thioester derivatives of PEG that have suitable reactivity with an N-terminal cysteine
or histidine residue of a polypeptide to produce an amide bond between the PEG
and polypeptide. Use of these active esters to prepare PEG-proteins and PEG-peptides
is described.
