General procedure for the synthesis of (S)-2-aminobut-3-enoic acid hydrochloride from (S)-2-(benzyloxycarbonylamino)-3-butenoic acid methyl ester: (S)-2-(benzyloxycarbonylamino)-3-butenoic acid methyl ester (0.905 g, 3.61 mmol) was suspended in 6 M hydrochloric acid solution (20 mL). The reaction mixture was heated to reflux for 2 hours and subsequently cooled to room temperature. Extraction was partitioned with dichloromethane (DCM) and the aqueous phase was again washed with DCM. After combining the organic phases, the aqueous phase was concentrated under vacuum to give a white solid product. Purification by acetone recrystallization resulted in the white crystalline product (S)-2-aminobut-3-enoic acid hydrochloride in a yield of 0.350 g and 71% yield. The structure of the product was confirmed by 1H-NMR (500 MHz, DMSO-d6): δ 8.32 (2H, broad single peak, NH2), 6.02-6.11 (1H, multiple peaks, CH=CH2), 5.50-5.75 (2H, multiple peaks, CH=CH2), 4.68-4.73 (1H, multiple peaks, CHCO2H).
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