Sodium Hydroxide → 4-[bis(tert-Butoxy)phosphoryl-fluoromethyl]-D,L-phenylalanine

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Reaction Steps

To compound 21 (690 mg, 1.71 mmol) in dioxane (17 mL) is added 1N NaOH (8.6 mL, 5 eq.) and stirred at ambient temperature (25 minutes), yielding a solution of crude 4-[bis(tert-Butoxy)phosphoryl-fluoromethyl]-D,L-phenylalanine (22), which is not isolated. The pH is adjusted to 8 by bubbling in CO2 gas, Fmoc-OBT (673 mg, 1.88 mmol) is added and the mixture stirred at ambient temperature (3 hours). Ice-cold 5% citric acid (30 mL) is added and the resultant solution is extracted with CHCl3 (3×30 mL). The combined extracts are dried (MgSO4) and evaporated under reduced pressure to yield crude 23 (1.48 g). Purification by silica gel chromatography affords pure 23 as a colorless foam (407 mg, 40%).

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