A mixture of tert-butyl {(3R,4R,5S)-1-[3-({[6-(4-ethoxy-2,6-difluorophenyl)-5-fluoropyridin-2-yl]carbonyl}amino)-7-hydroxy-6,7-dihydro-5H-cyclopenta[b]pyridin-4-yl]-4-hydroxy-5-methylpiperidin-3-yl}carbamate (6 mg, 0.01 mmol) and 4.0 M TFA in DCM (2.0 mL) was stirred at room temperature for 1 h. After removal of the solvent under reduced pressure, the residue was diluted with MeOH, filtered and purified by preparative LC-MS (XBridge™ preparative C18 5 μm OBD™ column, 30×10 mm, 60 mL/min., eluting with a gradient of MeCN and water with 0.1% NH4OH) to give both diastereoisomers as white powders. On analytical HPLC (Waters SunFire™ C18, 2.1×50 mm, 5 μm; flow rate 3 mL/min.; injection volume 2 μL; gradient from 2 to 80% B in 3 minutes (A=water with 0.025% TFA, B=MeCN)), the diastereoisomers had the following properties:
