Methyl L-tryptophanate hydrochloride

• Oxamoyl derivatives of N-(2-aminobenzoyl)-L-tryptophan (dipeptides) by acylation reaction with 3,1-benzoxazinones.
• Tadalafil (Cialis), a type-V phosphodiesterase (PDE5) inhibitor.
• Isoroquefortine C.

67-56-1

73-22-3

7524-52-9

(2) Preparation of L-tryptophan methyl ester hydrochloride: 60 mL of methanol was added to a 100 mL round-bottomed flask under ice bath conditions. Subsequently, 4 mL of sulfoxide chloride (SOCl2) was slowly added dropwise through a constant-pressure dropping funnel (equipped with a drying tube at the top), and NaOH solution was used to absorb the resulting exhaust gas. After the reaction mixture was reacted under stirring conditions for 1 h, 8 mmol of L-tryptophan (3d) was added and stirring was continued for 30 min at room temperature. After that, the reaction system was warmed up to 66 °C and the reaction was refluxed for 6 hours. The reaction process was monitored by thin-layer chromatography (TLC) using 2% ninhydrin ethanol solution as a color developer until the raw material spot disappeared. Upon completion of the reaction, the solvent was removed by evaporation to give L-tryptophan methyl ester hydrochloride in 100% yield.