The general procedure for the synthesis of L-leucinamide hydrochloride from L-leucine methyl ester hydrochloride is as follows: the synthesis is an improvement on a previously published method. The raw material L-leucine methyl ester hydrochloride can be purchased from Alfa Aesar. L-Leucine methyl ester hydrochloride (1.0 g, 5.5 mmol) and methanol (10 mL) were added to a glass pressure tube, followed by a methanol solution of 7N ammonia (7.9 mL, 55 mmol). The reaction tube was sealed, heated to 50 °C and kept for 2 days. After completion of the reaction, the mixture was concentrated in vacuum. The crude product was suspended in 1,4-dioxane (10 mL) and converted to hydrochloride by addition of 1,4-dioxane solution (1.7 mL, 6.8 mmol) in 4N HCl. Mixing was facilitated by sonication. The solvent and excess HCl were removed using a rotary evaporator, 1,4-dioxane (10 mL) was added during the process to help remove excess HCl.The product was purified by recrystallization from hot isopropanol, allowing crystals to form slowly at room temperature. The recrystallized solid was placed under high vacuum to remove residual solvent. The final yield was 0.55 g (60%). The product had a melting point of 216-218 °C, a specific spin [α]D24 of +12.0° (c 0.50, methanol), and an HPLC purity (200 nm) greater than 99% and significantly lower than 0.5% of the parent leucine.1H NMR ((CD3)2SO) δ 8.29 (broad single peak, 3H), 7.96 (single peak, 1H), 7.48 (single peak, 1H), and 3.66 (multiple peaks, 1H), 1.67 (multiple peaks, 1H), 1.56 (multiple peaks, 2H), 0.92 (double peaks, J=3Hz, 3H), 0.90 (double peaks, J=3Hz, 3H).
