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With benzotriazol-1-ol; N-ethyl-N,N-diisopropylamine; dicyclohexyl-carbodiimide; In N,N-dimethyl-formamide; at 20.0℃; for 12.0h;
Example 25; (2- ( (3-Benzyloxy-6- (tert-butyl-dimethyl- silanyloxymethyl) -4-oxo-4H-pyran-2-carbonyl) - (4-fluoro- benzyl) -amino) -ethyl) -carbamic acid tert-butyl ester; To the solution of the above-mentioned acid (753 g, 2 mmol) in DMF (20 ml) were added (2-(4- fluorobenzylamino) -ethyl) -carbamic acid tert-butyl ester (644, 2.4 mmol), DIPEA (0.66 mL, 4 mmol), DCC(619 mg, 3 mmol), and HOBt.H20 (405 mg, 3 mmol) . The EPO <DP n="140"/>reaction mixture was stirred at rt for 12 h. After removal of the solvent under reduced pressure, the residue was suspended into 50 mL of water and the mixture was extracted with chloroform (3 x 50 ml) . The combined organic phases were washed with brine, dried over anhydrous sodium sulfate. Evaporation of the solvent under reduced pressure gave a residue, which was purified using silica gel chromatography with hexane and ethyl acetate (4:1) to provide the title compound as a white solid in the form of two rotamers(610 mg) .
Example 24; 3-Benzyloxy-6- (tert-butyl-dimethyl-silanyloxymethyl) -4- oxo-4H-pyran-2-carboxylic acid.; Starting from the known kojic acid, compound 3- benzyloxy-6- (tert-butyl-dimethyl-silanyloxymethyl) -4- oxo-4H-pyran-2-carbaldehyde was prepared using the procedure described in Kiyama, R. WO 03/016275 Al. EPO <DP n="139"/>To a solution of this aldehyde (774 ing, 2.15 mmol) in acetonitrile/water (10 mL/10 ml) were added NaH2PO4(516 mg, 4.3 mmol) and NaClO2 (80%, 850 mg, 7.25 mmol) .The reaction mixture was stirred at rt for 12 h. After removal of the solvent under reduced pressure, the residue was suspended into 30 ml of water and the pH was adjusted to 3. The mixture was extracted with methylene chloride (3 x 15 ml) . The combined organic phases were washed with brine, dried over anhydrous sodium sulfate. Evaporation of the solvent under reduced pressure afforded a white solid of 730 mg, which was used in the next step without further purification.
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