2.2.3. Synthesis of N-carboxyanhydride (NCA) of l-alanine (NCA-Ala)

l-Alanine (5.00 g, 56.1 mmol) and α-pinene (17.58 g, 129 mmol) were dissolved in dry THF (60 mL) in a 250 mL 3-neck round-bottom flask. The solution was heated under inert reflux conditions. Triphosgene (11.16 g, 37.6 mmol) was dissolved in dry THF (24 mL) and added dropwise to the reaction mixture once reflux started. After 3 h, all solids had dissolved to leave a clear solution. The solution was reduced to a quarter of the volume and the same purification was followed as for NCA-Lys(Boc) (50%). ¹H NMR (500 MHz, DMSO-d₆) δ 8.98 (s, 1H), 4.48 (q, J = 7.0 Hz, 1H), 1.33 (d, J = 7.1 Hz, 2H).