Huisgen cycloaddition, "click"-type

There are four different chemical reactions that have been used to crosslink polymers with peptide sequences (Fig. 6.8) (i) amide bond formation (ii) Michael-type addition (iii) Huisgen cycloaddition (click reaction) and (iv) radical polymerisation. The amide bond formation follows typical solid phase peptide synthesis (SPPS) protocols and does not require functionalisation of the termini of the peptide sequence. Fluorenyhnethoxycarbonyl (Fmoc) protection of the N-terminus allows attachment of the peptide sequence to an amine-bearing polymer. After removal of the Fmoc group, the amine-terminated peptide-polymer conjugate can be reacted with a second polymer bearing carboxylic acid functionalities using the same coupling chemistry (Maier et al, 2011). For Michael-type additions the peptide... 

Among the chemical procedures listed above, click chemistry can be considered an efficient method that covers a wide range of different, requested functionalizations. The key reaction, called Sharpless-type click reaction , is a variant of the Huisgen 1,3-dipolar cycloaddition reaction between C—C triple bonds, C—N triple bonds, and alkyl-, aryl-, and sulfony 1-azides. 

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