To a stirred diastereomeric mixture containing (2R*,3R*) and (2R*,3S*)-2-amino-3-hydroxy-pentanoic acid (0.107 g, 0.81 mmol) and NaHCO3 (0.102 g, 1.21 mmol) in H2O (2.0 mL), at rt, the isomeric mixture containing 5-phenyl-pentyl-2-pyridyl-carbonate and 5-phenyl-pentyl-2-oxopyridine-1-carboxylate (0.346 g, 1.21 mmol) [prepared as for example 32, step 1] in THF (2.0 mL) was added. After 15 h at rt, the crude mixture was rotary evaporated to remove the organics and subsequently extracted with Et2O (3×10 mL). The aqueous phase was acidified with 2.0 M HCl solution to pH 2-3 and subsequently extracted with AcOEt (3×20 mL). The organic fraction was dried over Na2SO4, filtered and concentrated to dryness to afford the title compound (0.155 g, 60% over 2 steps), as a diastereoisomeric mixture (anti:syn=8:2), as an off-white solid, which was used in the next step without further purification. MS (ESI) m/z: 324[M−H]+; (ESI) m/z: 322 [M−H]−. 1H NMR (DMSO-d6) δ 0.86 (t, J=7.41 Hz, 3H), 1.27-1.50 (m, 4H), 1.51-1.67 (m, 4H), 2.57 (t, J=7.69 Hz, 2H), 3.52-3.66 (m, 1H), 3.93 (t, J=6.63 Hz, 3H), 4.83 (s, 1H), 7.10 (d, J=8.73 Hz, 1H), 7.13-7.22 (m, 3H), 7.22-7.30 (m, 2H), 12.35 (s, 1H) (reported data refer to the major anti diastereoisomer).
