Cl.[Cl:2][CH2:3][CH2:4][NH:5][CH2:6][CH2:7][Cl:8].CS(O[C@@H:14]([CH3:20])[C:15]([O:17][CH2:18][CH3:19])=[O:16])(=O)=O.FC(F)(F)S([O-])(=O)=O>[OH-].[Na+].O1CCCC1>[CH2:18]([O:17][C:15](=[O:16])[C@@H:14]([CH3:20])[N:5]([CH2:6][CH2:7][Cl:8])[CH2:4][CH2:3][Cl:2])[CH3:19]A suspension of bis(2-chloroethyl)amine hydrochloride (0.392 g; 2.1 mmol) in 5N aqueous sodium hydroxide (3 mL) is extracted with ether (2×10 mL) and the combined extracts are washed with a minimum amount of water and saturated brine. The ethereal solution is dried quickly over magnesium sulfate and filtered. Tetrahydrofuran (2 mL) is added to the filtrate, and ether is carefully removed under reduced pressure on a rotavapor unit without heating. The residue is mixed with a solution of ethyl (S)-2-[(methylsulfonyl)oxy]-propionate (0.5 g; 2 mmol) in tetrahydrofuran (1 mL). After stirring the reaction mixture for 24 hrs at room temperature, there is no visible precipitate. The volatiles are removed under reduced pressure and the remaining viscous oil is dissolved in ether (8 mL), and the slightly turbid solution is filtered after 60 minutes. The filtrate is treated dropwise with n-heptane to induce crystallization; the final ratio of n-heptane/ether is 1:3. The crystalline salt is collected by filtration and washed quickly with a small portion of ether. There is obtained 0.653 g (yield 83.3%) of N,N-bis(2-chloroethyl)-(R)-alanine ethyl ester, trifluoromethanesulfonate; mp 73-74.5° C.; 1H NMR (300 MHz, CDCl3) δ 1.35 (t, J=7.1 Hz, 3H), 1.76 (d, J=7.2 Hz, 3H), 3.87 (m, 2H), 4.00 (m, 2H), 4.35 (q, J=7.1 Hz, 2H), 4.57 (q, J=7.2 Hz, 1H), 9.02 (b, 1H).
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