Preparation and properties of Nα-trityl amino acid 1-hydroxybenzotriazole esters

Nα-Trityl amino acid 1-hydroxybenzotriazole active esters, in contrast to HOBt esters of other protected amino acids, exhibit high hydrolytic stability and can be isolated in excellent yields and purity. The derivatives occur in three isomeric forms (an ester=I, two amides=II and III). All active ester forms react at high concentrations within 2 h with various alkyl amino acid esters to produce the corresponding protected dipeptides in high yields. Amorphous active esters on prolonged storage at — 20° rearrange partially towards form III without any sign of decomposition.