Bis(4,6-dimethoxy-1,3,5-triazin-2-yl) ether as coupling reagent for peptide synthesis

Bis(4,6-dimethoxy-1,3,5-triazin-2-yl) ether (4) was prepared by treatment of 2-hydroxy-4,6-dimethoxy-1,3,5-triazine with 2-chloro-4,6-dimethoxy-1,3,5-triazine in 61% yield. Ether 4, isoelectronic with pyrocarbonates, was found capable to activate carboxylic acids in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) to yield, under mild reaction conditions, superactive triazine esters. Versatility of this new coupling reagent was confirmed by condensation of lipophilic and sterically hindered carboxylic acids with amines in 71-98% yield, and by synthesis of peptides, including those containing Aib-Aib sequence, in solution with high yield and high enantiomeric purity.