O.O.[C:3]([OH:8])(=[O:7])[C:4]([OH:6])=[O:5].[CH2:9]([O:16][NH:17][CH:18]1[CH2:23][NH:22][C@H:21]([C:24]#[N:25])[CH2:20][CH2:19]1)[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1>C(OCC)(=O)C.CC(C)=O.C(OCC)(=O)C>[C:3]([OH:8])(=[O:7])[C:4]([OH:6])=[O:5].[CH2:9]([O:16][NH:17][CH:18]1[CH2:23][NH:22][C@H:21]([C:24]#[N:25])[CH2:20][CH2:19]1)[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1A solution of oxalic acid dihydrate (5.28 gm, 0.0418 mol) in a mixture of ethyl acetate: acetone (1:1, 28 ml:28 ml) was slowly added to a stirred solution of (2S)-5-[(benzyloxy)amino]-2-cyanopiperidine (X) (8.8 gm, 0.0380 mol, prepared according to the procedure described in step 7) in ethyl acetate (35 ml) at 25° C. After 3 hour of stirring, the separated solid was filtered under suction, washed with additional 50 ml of v/v mixture of ethyl acetate: acetone solution (1:1, 25 ml:25 ml) and the solid dried under reduced pressure to obtain 6.7 gm of (2S)-5-[(benzyloxy)amino]-2-cyanopiperidine ethanedioate (1:1) (XI) in 55% yield.
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