Synthesis of hydrophilic Fischer carbene complexes as organometallic marker and PEGylating agent for proteins

Syntheses of Fischer carbene complexes with various hydrophilic tethers (4, 6a, 6b, 6c, 8a, 8b, 14a, 14b, 15 and 19) are described. The water-soluble carbene complex, 14b, was used to label and pegylate bovine serum albumin (BSA) without affecting its conformation. The red complex, 19, underwent a sharp color change to yellow on reaction with BSA, a feature that is potentially useful for developing assay methods.