Ac2O (2.0 mL, 21 mmol) was added to tert-butyl [(3R,4R,5S)-4-hydroxy-5-methyl-1-(3-nitro-1-oxido-6,7-dihydro-5H-cyclopenta[b]pyridin-4-yl)piperidin-3-yl]carbamate (0.090 g, 0.22 mmol) in a tube that was then sealed. The reaction mixture was heated in the sealed tube with stirring in an oil bath at 90° C. oil bath. The reaction mixture was allowed to cool to room temperature and acetyl chloride (0.10 mL) and DIPEA (0.2 mL) were then added. The resulting mixture was stirred at room temperature for 15 min. After removal of the solvents under reduced pressure, the resulting residue was diluted with EtOAc and aq. Na2CO3 and stirred at room temperature for 30 min. The organic layer was separated, dried and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (eluting with 0-70% EtOAc in hexanes) to give the sub-title compound (86 mg, 79%) as a foamy brown powder. LCMS calc. for C23H33N4O8 (M+1)+: m/z=493.2. Found: 493.2.
