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With water; sodium hydroxide; In tetrahydrofuran; methanol; at 0 - 20℃; for 4.0h;
To a solution of (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-(5-fluoro-1 H-indol-3- yl)propanoic acid (3 g, 6.75 mmol) in THF (20 ml), MeOH (10 ml_) , and water (20.00 ml) at 0 C was added NaOH (20.25 ml, 20.25 mmol) and the resulting solution was stirred at ambient temperature for 4 hours, then the volatile was evaporated. To the aqueous mixture was added dioxane (50 ml) and water (20 ml_), the resulting solution was cooled to 0 C and B0C2O (1.881 ml, 8.10 mmol) was added to the above solution. The resulting solution was stirred at 0 C for 3 hours, the volatile was removed and the aqueous phase was extracted with Et20 (3x40 ml_), acidified to pH 3, then extracted with DCM (3x100ml_), followed by 30%IPA/DCM (2x80 mL). The combined organic phase was dried over Na2S04 and concentrated to give 69. LC/MS: (M+1 )+: 322.9.