1-Hydroxy-7-azabenzotriazole (HOAt) and N-[(dimethylamino)-1H-1,2,3-triazolo-[4,5-b]pyridin-1-yl-methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HATU)

Peptide coupling methods based on aminium salts of 1-hydroxyazabenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt) such as N-[(dimethylamino)-1H-1,2,3-triazolo-[4,5-b]pyridin-1-yl-methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HATU) are currently being used more frequently than classical carbodiimide methods. Reactions with HOAt and HATU are generally faster and show less racemization than reactions with HOBt because of the anchimeric assistance of the 7-nitrogen atom in the active HOAt-ester intermediate. They are especially useful for difficult couplings like those of N-methyl and α,α-disubstituted amino acids and for amide bond formation where time is a critical issue.