General procedure: L-leucine hydrochloride (1 eq.), formic acid (5 eq.), sodium bicarbonate (10 eq.) and glycerol ketone-oxide 1 (2 eq.) were dissolved in H2O (0.2-0.3 M), followed by the addition of EDCI (2 eq.). The reaction mixture was stirred for 3 h. Upon completion of the reaction, it was quenched with 1% HCl aqueous solution. The aqueous phase was extracted with EtOAc (or CHCl3, or CHCl3-MeOH (10/1). The organic extracts were combined and dried with Na2SO4, followed by vacuum evaporation of the solvent. Purification by silica gel chromatography (or Sephadex LH20) afforded N-formyl-DL-leucine (see Table 1 for yields). Similarly, the N-formylation reaction was carried out using oxide 1 in DMF-H2O (9/1).
