After 1 h 30 min at rt, the reaction was acidified by adding a 10% v/v TFA solution (371 µL) to reach a final TFA concentration of 2% v/v. AcOEt remaining on top of the aqueous solution was carefully removed. Purification of the crude peptide alkyl thioester 6e by RP-HPLC (BEH C18 column, eluent A 0.25% TFA in water, eluent B 0.25% TFA in CH3CN, gradient 0-10% B in 6 min and then 10-25% B in 54 min, 6 mL/min, T = 60 °C, λ = 215 nm) furnished the target peptide alkyl thioester 6e (4.36 mg, 51%) as a white powder after lyophilization.