Homobifunctional Imidoesters

Carboxylate groups activated with NHS esters are highly reactive toward amine nucleophiles. In the mid-1970s, NHS esters were introduced as reactive ends of homobifunctional crosslinkers (Bragg and Hou, 1975 Fomant and Fairbanks, 1976). Their excellent reactivity at physiological pH quickly established NHS esters as viable alternatives to the imidoesters predominating at the time (Section 2, this chapter). 

The following list of homobifunctional imidoesters represent compounds that are commonly used for protein crosslinking and are currently available from commercial sources. 

Dimethyl pimelimidate (DMP) is a homobifunctional crosslinking agent that has imidoester groups on either end (Thermo Fisher). The imidoesters are amine reactive to give stable amidine linkages with target molecules. The 7-atom bridge created by DMP crosslinks is non-cleavable and... 

Dimethyl suberimidate, DMS, is a homobifunctional crosslinking agent-containing amine-reactive imidoester groups on both ends. The compound is reactive toward the s-amine groups... 

Bz s-imidoesters like DMS may be used to couple proteins to PE-containing liposomes by crosslinking with the amines on both molecules (Figure 22.24). However, single-step crosslinking procedures using homobifunctional reagents are particularly subject to uncontrollable polymerization of protein in solution. Polymerization is possible because the procedure is done with the liposomes, protein, and crosslinker all in solution at the same time. 

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