110 mg of D-cysteine is dissolved in 2 mL of water, the solution is made alkaline with a solution of 0.17 g of sodium hydroxide in 1 mL of water. After deoxygenating the solution, the reaction vessel is wrapped with aluminum foil to protect the solution from exposure to light. Subsequently, 120 mg of 6-hydroxybenzothiazole-2-carbonitrile dissolved in 4.5 mL of methanol are added, the solution stirred for 1 h at room temperature and then the pH is adjusted to pH 2.5 with 2 M hydrochloric acid and allowed to stand for at least 20 h in a refrigerator. The precipitate is filtered and dried in a vacuum. The crude product is sufficiently pure, yet impurities are still present at this time, which should be separated by column chromatography.
The mixture after acidification
The crude product