The product was synthesized following general coupling procedure B, using Z-L-Ala as the amino acid and prolinonitrile PTSA salt as the amine, to give the product as a clear oil (59% General acid-catalyzed oxidative cyclization procedure A. The dipeptide (1 eq) was diluted in anhydrous DCM (0.02 M), and 2-3 drops of Sudan III solution (1mg/mL in DCM) were added (enough to reach a pink color). The solution was cooled to -78°C, and N2 gas was bubbled into the solution for 5 minutes, followed by ozone (~80% ozone output). When the solution turned dark blue, ozone addition was stopped, and N2 was bubbled until the solution was colorless. Polymer-bound triphenylphospine (1.5 eq, ~3mmol/g loading, CAS 39319-11-4) was added, and the mixture stirred for 5 minutes at -78°C, then at room temperature overnight under argon atmosphere, after which the mixture became slightly opaque. TFA (1.5 eq) was added at room temperature, and the mixture was stirred for 2h. The mixture was filtered through Celite®. The solid was rinsed with DCM, and the filtrate was concentrated in vacuo. The residue was redissolved in EtOAc and washed with saturated NH4Cl and brine. The organic layer was dried over Na2SO4, filtered, and concentrated in vacuo to give the crude product, which was purified by flash chromatography on a silica gel column to give the pure product.