Synthesis of Tetra(2-hydroxyethoxy)-Substituted Dibenzocyclooctyne Derivatives as Novel, Highly Hydrophilic Tool Compounds for Strain-Promoted Alkyne-Azide Cycloaddition Applications

The synthesis of a novel, hydrophilic dibenzocyclooctyne derivative for strain-promoted alkyne-azide cycloaddition (SPAAC) is described. Starting from 2-(3,4-dimethoxyphenyl)acetaldehyde, the corresponding activated carbonate of 2,3,8,9-tetrakis(2-hydroxyethoxy)-5,6-dihydro-11,12-didehydrodibenzo[a,e][8]annulene, termed THE-DIBO, was prepared in seven steps and 24% overall yield. A water-soluble THE-DIBO analogue showed a k(2) value of (21.9 +/- 0.2) x 10(-2) M-1 s(-1) for SPAAC with 2-azidoethanol in water. The high hydrophilicity and steric bulk of THE-DIBO derivatives should to suppress nonspecific thiol-yne addition of proteins to strained alkynes observed for SPAAC labeling in complex proteomes.