2-Amino-3-[(4-methoxybenzyl)thio]propanoicacid

White to off-white powder

(Step 1)To a mixed solution of diethyl ether (400 ml) and conc. hydrochloric acid (400 ml) was added in drops 4-methoxybenzyl chloride (280 g, 1780 mmol) dissolved in diethyl ether (400 ml) for 2 h, and the mixture was stirred for 1 h. The organic layer was separated and added to a solution which was prepared by dissolving L-cysteine (197 g, 1625 mmol) and 2N aqueous sodium hydroxide solution (980 ml) in ethanol (1890 ml). The mixture was stirred for 2 h at room temperature. After completion of the reaction, the mixture was cooled to 0, and neutralized to pH 7 using 3N aqueous hydrochloric acid solution. The resulting solid was filtered and dried to give (R)-2-amino-3-(4-methoxy-benzylsulfanyl)-propionic acid (250 g, 1035 mmol, Yield 64percent).4-Methoxybenzyl alcohol (280 g, 1780 mmol) dissolved in diethylether (400 mL) was added in drops to a mixture of diethylether (400 niL) and cone, hydrochloric acid (400 mL) over 2 h, and the mixture was stirred for 1 h. The organic layer was separated, and added to a solution prepared by dissolving L-cysteine (197 g, 1625 mmol) and 2N aqueous sodium hydroxide solution (980 mL) to ethanol (1890 mL).The mixture was stirred for 2 h at room temperature. After completion of the reaction, the reaction mixture was cooled to 04-Methoxybenzyl alcohol (280 g, 1780 mmol) dissolved in diethylether (400 mL) was added in drops to a mixture of diethylether (400 mL) and conc. hydrochloric acid (400 mL) over 2 h, and the mixture was stirred for 1 h. The organic layer was separated, and added to a solution prepared by dissolving L-cysteine (197 g, 1625 mmol) and 2N aqueous sodium hydroxide solution (980 mL) to ethanol (1890 mL). The mixture was stirred for 2 h at room temperature. After completion of the reaction, the reaction mixture was cooled to 0°, and neutralized to pH 7 using 3N aqueous hydrochloric acid solution. The resulting solid was filtered and dried to give the title compound (250 g, Yield 64percent).To a solvent mixture of diethylether (400 ml) and conc. hydrochloric acid (400 ml) was added in drops 4-methoxybenzylalcohol (280 g, 1780 mmol) dissolved in diethylether (400 ml) for 2 h, and the mixture was stirred for 1 h. The organic layer was separated, and added to a solution prepared by dissolving L-cysteine (197 g, 1625 mmol) and 2N aqueous sodium hydroxide solution (980 ml) in ethanol (1890 ml). The mixture was stirred for 2 h at room temperature. After completion of the reaction, the reaction solution was cooled to 0° C., and neutralized to pH 7 using 3N aqueous hydrochloric acid solution. The resulting solid was filtered, and dried to give (R)-2-amino-3-(4-methoxy-benzylsulfanyl)-propionic acid (250 g, 1035 mmol, Yield: 64percent).General procedure: A two-necked, round-bottomed flask was charged with the requisite amino acid (1 eq.) and dried under high vacuum at '30-40 mTorr for >36 h to remove as much residual moisture as possible. The reaction flask was equipped with a reflux condenser topped with a dual-connection glass adapter, with one end connected to a nitrogen source and the other vented to the top of the fume hood (to properly exhaust the HCl vapors generated). Depending on the reaction scale, either a magnetic stir bar or mechanical paddle stirrer was inserted. Anhydrous THF was added to give an amino acid concentration of 0.4-0.5 M. To the resulting heavy suspension was added neat diphosgene (0.6-1.0 eq.; see Tables 2 and 4) in one portion. The reaction was carefully warmed to 55 C with an oil bath or left to stir at ambient temperature. The reaction was considered complete when all the solids in the reaction dissolved and 1H NMR analysis of a vacuum-dried 0.3-mL aliquot indicated complete conversion to the product. Once at ambient temperature, the reaction mixture was transferred to a clean and dry round-bottomed flask, and concentrated on a rotary evaporator with the water bath maintained between 25 and 30 C. Fresh anhydrous THF (?6-8 mL/g of amino acid) was added to dissolve the material before reconcentrating. The crude product was dissolved in a minimal amount of THF (?4-6 mL/g of amino acid) and transferred to a large precipitation container. Under a blanket of nitrogen, with vigorous mechanical stirring, heptane (6-8 crude volume) was added over 10-30 min to precipitate. The resulting solid was collected by vacuum filtration, washed with additional heptane (1-2 crude volume), and dried in a vacuum oven at room temperature overnight. Anhydrous DCM (?8-10 mL/g NCA) was added to the material and stirred for 15-30 min under nitrogen in order to dissolve as much of the crude material as possible. Oven-dried celite with a bed height of 2-4 cm was prepared in a sintered glass Buchner funnel, topped with a Whatman glass microfiber filter, and rinsed with anhydrous DCM before use (taking care to avoid cracks in the bed). The DCM-NCA suspension was filtered through the celite bed and then rinsed through with additional anhydrous DCM (3-5 mL/g of NCA). The clear filtrate was concentrated on a rotary evaporator with the water bath maintained at 25-30 C. Anhydrous THF (?6-8 mL/g of NCA) was added to dissolve the product before reconcentrating. The material was dissolved in a minimal amount of THF (?4-6 mL/g of NCA), precipitated with heptane (6-8 crude volume), and collected/dried using the same method as described for the first precipitation. The final product was packaged under either nitrogen or argon in a container that was then sealed in a FoodSaver heat-seal vacuum bag and stored at 78 C until use.4 g of H-Cys(Mob)-OH was dissolved in THF, and it was reacted with 2 equivalents of triphosgene at 50 C. for 2 hours, and the obtained solution was precipitated using hexane. The obtained precipitate was dissolved in CH2Cl2, and it was purified by recrystallization using hexane. It was confirmed from LC-MS and 1H NMR that 4-methoxybenzylcysteine N-carboxy anhydride (Cys(Mob)-NCA) was synthesized.