Boc-L-cysteine is the protected form of L-Cysteine (C995000), a non-essential α-amino acid that is biosynthesized in humans. L-Cysteine is also a bicarbonate-sensitive endogenous excitotoxin in rats and possibly humans.
General procedure for the synthesis of (R)-2-((tert-butoxycarbonyl)amino)-3-mercaptopropionic acid from N,N'-bis(Boc)-L-cystine: N,N'-bis(Boc)-L-cystine (2.51 mmol) was dissolved in a solvent mixture of tetrahydrofuran (29.2 mL) and water (0.8 mL). Tributylphosphine (2.76 mmol) was added to the solution under ice bath cooling conditions. The reaction mixture was gradually warmed up to room temperature and stirred continuously at this temperature for 1 hour. Upon completion of the reaction, ethyl acetate (20 mL) and 10% aqueous citric acid (10 mL) were added to the reaction mixture for extraction and separation. The organic phase was collected and washed with saturated aqueous saline solution (20 mL). Subsequently, the organic phase was concentrated and the resulting residue was purified by silica gel column chromatography (eluent: hexane-ethyl acetate mixed solvent) to afford the target compound 22 as an oily product. Yield: 99%. ESI MS m/z 220.1 [M-H]-; 1H NMR (400 MHz, CDCl3) δ: 5.47 (1H, brs), 4.65 (1H, brs), 3.09-2.97 (2H, m), 1.48 (9H, s).
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