Method for producing maleimide polyethylene glycol lipid

A method for producing a maleimide polyethylene glycol lipid represented by the following general formula (2), the method comprising:

• a reaction step of deprotecting a maleimide polyethylene glycol lipid having a protective group, which is represented by the following general formula (1), by heating the maleimide polyethylene glycol lipid having a protective group in a solvent in the presence of silica gel,
• wherein R1, R2, R3, and R4 are each independently a group selected from a hydrogen atom, an alkyl group, a halogen, a cyano group, a formyl group, an acyl group, a carboxy group, an acyloxy group, and an alkylcarbonyloxymethyl group, n is an integer of 2 to 10 which represents a repeating unit number of a methylene group, m is an integer of 10 to 2000 which represents a repeating unit number of polyethylene glycol, Z represents a group selected from an ether group, a methylene group, and a dimethylvinylidene group, Y is any group represented by the following general formulas (3) to (6):
• wherein M represents Na or K, and 1 represents an integer of 1 to 5 which represents a repeating unit number of a methylene group, and
• A is a group represented by the following general formula (7) or (8):
• wherein R5 and R6 are each independently a group selected from a hydrogen atom, a saturated or unsaturated acyl group having 8 to 24 carbon atoms, or a saturated or unsaturated alkyl group having 8 to 24 carbon atoms.