Dicyclohexylcarbodiimide (21 g) was added to a solution of 5-hydroxy-12H-benzo[a]phenothiazine (4.2 g) and N-tert-butyloxycarbonyl glycine (8.4 g) in THF (150 ml) followed by the addition of DMAP (0.2 g). The reaction mixture was stirred for 15 minutes, filtered and the filtrate evaporated to dryness. The residue was dissolved in EtOAc, washed with a solution of NaHCO3, dried and evaporated to dryness. The resulting oily residue was chromatographed on silica gel (5% EtOAc/CH2Cl2) to afford 5-tert-butyloxycarbonylamino acetoxy-12H-benzo[a]phenothiazine. m.p. 175° as an intermediate.
