The retro-Mannich cleavage of delta1,delta1'-tryptophan dimers

Under acidic conditions tryptophan sidechains crosslink to form delta1,delta1'-tryptophan dimers through a Mannich-type mechanism. Tryptophan dimers are readily cleaved at high temperatures under acidic conditions making it impossible to isolate tryptophan dimers under standard conditions of acidic protein hydrolysis. In a prescriptive sense this cleavage can be used to recover peptides that have undergone tryptophan crosslinking, although the yields drop with increasing peptide length due to competitive cleavage of the amide bonds. The best conditions for cleavage involve heating the dimeric peptides in dilute ethanolic HCl at 150 degrees C in the presence of ten equivalents of ethanedithiol.