Subsequently, the carboxylate activations were performed using ynamide 78 in dichloroethane (DCE) or in 7:3 DCE:sulfolane to provide vinyl esters (e.g., 81). Aminolysis reactions employed amino silyl esters in DCE or MeTHF. The amino silyl esters were prepared using 1-(trimethylsilyl)pyrrolidone and the resulting peptide silyl esters (e.g., 82) were cleaved using N-to C-SPPS Ghosh and Lubell 16 citric acid in methanol to provide carboxylates (e.g., 83) for subsequent activation. Side chain alcohol (Ser), phenol (Tyr) and carboxylate (Glu) functions were respectively protected with tert-butyl groups and the -amine of lysine was Boc protected. Resin cleavage and side chain liberation was performed on protected peptide 84 using a TFA/H2O/TIPS cocktail. Peptide 85 was obtained in 50% purity, which was comparable with the 57% purity achieved in the preparation of the same product using conventional C-N-SPPS. 51