Initially, the Fmoc group was removed and Cto N-direction extension of the peptide was performed to create N-acetyl tetrapeptide resin 47. Hydrazinolysis of benzyl ester 48 using 20% hydrazine hydrate in DMF gave hydrazide 49, which was transformed to acyl azide 50 using acidified sodium nitrite. Reaction with H-Ser-OBn gave N-acetyl peptide benzyl ester 51, which was elongated by sequential hydrazinolysis, followed by activation and aminolysis of acyl azide intermediates. Finally, resin cleavage and side chain protecting group removal were performed using a cocktail of TFA/H2O/triisopropylsilane (TIPS). Peptide 52 was claimed to be prepared by this route with similar purity and yield as product from C-N-SPPS. In a related activation method, dipeptides were synthesized without epimerization by way of acyl nitroso intermediates which were generated from oxidation of N-protected hydroxamates in the presence of amino esters using iodine in DMSO.