ɑ-SQA-ω-Tritylthio PEGs

The squaric acid PEGs are chemoselective towards the amino groups of Lysin in protein PEGylation whereas the guanidine function of Arginine, the hydroxyl group of Serine and the imidazole function of Histidine are not affected. PEG tritylthio derivatives feature a protected thiol at on chain end. Trityl groups are easily removed with acid. Pure TFA or TFA/DCM mixtures cleave trityl from thiols quantitatively.