Chemoselective Ligation

Tiefenbrunn TK, Dawson PE (2010) Chemoselective ligation techniques modem applications of time-honored chemistry. Biopolymers 94 95-106... 

The following sections briefly describe three cycloaddition reactions that can be used to form bioconjugates. These reactions represent highly specific reactant pairs that have a chemoselec-tive nature, meaning they mainly react with each other and not other functional groups, such as those found on biomolecules. For a complete discussion of chemoselective ligation reactions, see Chapter 17. 

Figure 17.3 Maleimide-modified glass slides (1) can be derivatized using two chemoselective ligation reactions to create biotin modifications. In the first step, alkyne-PEG4-cyclopentadiene linkers (2) are added to the maleimide groups using a Diels-Alder reaction. In the second reaction, an azido-PEG4-biotin compound (3) is reacted with the terminal alkyne on the slide using click chemistry to result in another cycloaddition product, a triazole ring.

Once a molecule is modified with a hydrazine reagent and another molecule is modified with the benzaldehyde compound, they may be combined to form the final conjugate, which will result in a hydrazone linkage between the two molecules. In addition, chemoselective ligation using aldehyde/hydrazine reactions may be done to immobilize biomolecules. In this regard, one modified component may be a surface and the other one an antibody, protein, or oligonucleotide destined for immobilization onto the surface. 

In another application of coupling proteins to surfaces using click chemistry, Duckworth et al. (2006) carried out prenylation of a protein using a farnesyl azide derivative and the enzyme farnesyl transferase for subsequent chemoselective ligation to alkyne-functionalized agarose beads. The result is a highly discrete, site-specific attachment of the protein to the solid phase at a single location. 

Lemieux, G.A., and Bertozzi, C.R. (1998) Chemoselective ligation reactions with proteins, oligosaccharides and cells. Trends Biotechnol. 16(12), 506-513. 

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