DIPEA (2.504 mL, 14.38 mmol) was added to a stirred suspension of 4-cyanobenzoic acid (0.670 g, 4.55 mmol) and TBTU (1.462 g, 4.55 mmol) in DCM (10 mL) at rt. The suspension was stirred for 5 min before it was cooled on an ice-bath. A solution of (S)-1-(2-cyclobutyl-2-(methylamino)ethyl)azetidin-3-ol (Compound Z2.1) (0.960 g, 4.79 mmol) in DCM (10 mL) was added over 5 min. The ice-bath was removed after 10 min and the reaction was stirred at rt for 3 h. The reaction mixture was diluted with DCM (20 mL), washed with NaHCO3 (8% aq., 35 mL), filtered through a phase separator and concentrated under reduced pressure. The residue was purified by preparative HPLC. The selected fractions were concentrated and NaHCO3 (saturated, 40 mL) was added. The water layer was extracted with DCM (3×75 mL) and the combined organic layers were filtered through a phase separator and concentrated under reduced pressure to give the title compound (0.925 g, 62%). Mixture of rotamers: 1H NMR (400 MHz, DMSO-d6) δ 1.32-1.62, 1.65-1.97, 1.97-2.08, 2.17-2.28, 2.32-2.60, 2.62-2.74, 3.16-3.27, 3.39-3.45, 3.46-3.52, 4.07-4.18, 4.40-4.52, 5.19-5.24, 7.42-7.46, 7.57-7.62, 7.87-7.95.
