Dear Anwar,

The purpose is to have a degradable hydrogel for cell culture purpose.

The peptide (13 amino acids) contains protease sensitive sequence. This PEG functionalization has been done with PEG-VS, so I do not have question about other parts except the carboxy-PEG in situ activation.

Saba, if your peptide has only an N-terminal amino group, just go ahead with the activated ester (NHS..). To prepare it, use a simple and cheap approach with DCC or EDC and NHS before trying more complex and expensive chemistries. I just can speculate about the scale; if you plan to prepare more than a few milligrams, it might be reasonable to isolate the NHS-PEG. For a few milligrams, activation in situ with EDC in MES buffer pH5 (kind of standard approach for aqueous systems) will do the job.

Usually, coupling should work in PBS or bicarbonate, just make sure you have no amines (Tris...) present. If you have internal lysines however, talk to the people who synthesize your peptide in order to develop a good strategy (probably it will be using the PEG-derivative of the N-terminal AA or coupling the PEG-NHS ester before the lysines are deprotected).

Thanks a lot, Wolfgang!