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With triethylamine; In 1,4-dioxane; water; at 0 - 20℃;
EXAMPLE 4 N-(tert-butoxycarbonyl)-DL-aspartic acid DL aspartic acid acid (1 g) was dissolved in 20 mL of dioxane/water 1:1 and 4.15 mL of triethylamine was added. The mixture was cooled to 0 C. and 2.4 g of di-tert-butyl dicarbonate added. The solution was left at room temperature overnight. The suspension was concentrated and extracted with ethyl acetate and water. The aqueous extract was acidified with 5% aq. NaHSO4 and then extracted with AcOEt three times. The organic extracts were dried over anh. sodium sulfate and the solvent evaporated under vacuum to provide 1.53 g of the title compound. 1H NMR (400 MHz, DMSO-D6) delta ppm 1.36 (s, 9 H) 2.45-2.57 (m, 1 H) 2.60-2.72 (m, 1 H) 4.19-4.31 (m, 1 H) 7.01 (d, J=8.50 Hz, 1 H) 12.45 (bs, 2 H).
With dmap; benzotriazol-1-ol; dicyclohexyl-carbodiimide In dichloromethane at 0 - 20℃; for 25h;
Preparation of compound 5a~5d
General procedure: Oleyl alcohol (5.3g, 19.8mmol) was added to the anhydrous dichloromethane solution (200mL) of 4 (9.01 mmol), dicyclohexylcarbodiimide (DCC, 4.1 g, 19.8 mmol), HOBt (2.97g, 22mmol) and N, N-dimethylaminopyridine (DMAP, 24 mg, 1.8 mmol) in ice-salt-bath at 0C for 1h and then 24 h at room temperature and filtered. The filtrate was evaporated under reduced pressure, and a little ethyl acetate was added. The mixture was maintained at 0 oC for half an hour and filtered. The filtrate was evaporated under reduced pressure to give the crude products which were purified by chromatography over silica (EA/PE, 1:20, v/v) as colorless oil yields 5b and 5d (Rf = 0.7, EA/PE = 1 : 8).