Application of azide–alkyne cycloaddition ‘click chemistry’ for the synthesis of Grb2 SH2 domain-binding macrocycles

Copper (I) promoted [3+2] Huisgen cycloaddition of azides with terminal alkynes was used to prepare triazole-containing macrocycles based on the Grb2 SH2 domain-binding motif, ‘Pmp-Ac6c-Asn’, where Pmp and Ac6c stand for 4-phosphonomethylphenylalanine and 1-aminocyclohexanecarboxylic acid, respectively. When cycloaddition reactions were conducted at 1 mM substrate concentrations, cyclization of monomeric units occurred. At 2 mM substrate concentrations the predominant products were macrocyclic dimers. In Grb2 SH2 domain-binding assays the monomeric (S)-Pmp-containing macrocycle exhibited a Kd value of 0.23 μM, while the corresponding dimeric macrocycle was found to have greater than 50-fold higher affinity. The open-chain dimer was also found to have affinity equal to the dimeric macrocycle. This work represents the first application of ‘click chemistry’ to the synthesis of SH2 domain-binding inhibitors and indicates its potential utility.