Synthesis
The general procedure for the synthesis of L-tryptophan methyl ester hydrochloride from methanol and L-tryptophan was as follows: L-tryptophan (18.2 mmol) was dissolved in methanol (20 mL) at 0 °C with stirring. Thionyl chloride (1.6 mL, 22 mmol) was added slowly and dropwise over 10 min. Subsequently, the reaction mixture was gradually warmed to room temperature and heated under reflux conditions for 3 hours. Upon completion of the reaction, the solvent and volatiles were removed by distillation under reduced pressure. The resulting product was ground with ethyl acetate to give L-tryptophan methyl ester hydrochloride as a colorless solid in 100% yield. The product was a white solid with a yield of 4.63 g. Its 1H NMR (400 MHz, CD3OD) and 13C NMR (100 MHz, CD3OD) data were consistent with those reported in the literature, confirming the structure and purity of the product.
References
[1] Tetrahedron, 2001, vol. 57, # 51, p. 10181 - 10189
[2] Patent: US2014/206741, 2014, A1. Location in patent: Paragraph 0111
[3] European Journal of Medicinal Chemistry, 2016, vol. 114, p. 318 - 327
[4] New Journal of Chemistry, 2018, vol. 42, # 16, p. 13549 - 13557
[5] Organic and Biomolecular Chemistry, 2014, vol. 12, # 41, p. 8280 - 8287
