To 1-(4-ethyl-3-methoxy-benzoyl)spiro[piperidine-4,4′-pyrrolo[2,1-c][1,4]benzoxazine]-7′-carboxylic acid (550 mg, 1.2 mmol) in tetrahydrofuran (2.2 mL) at 0° C. was added triethylamine (200 μL, 1.4 mmol) then isobutyl chloroformate (180 μL, 1.4 mmol). The mixture was stirred for 30 min then filtered. The filtrate was added dropwise to a solution of sodium borohydride (70 mg, 1.8 mmol) in water (770 μL) at 0° C. The mixture was allowed to slowly reach room temperature before it was concentrated to ⅓ volume, diluted with ethyl acetate and washed with 1M HCl. The organics were dried over sodium sulfate, filtered and evaporated to yield (4-ethyl-3-methoxyphenyl)(7-(hydroxymethyl)spiro[benzo[b]pyrrolo[1,2-d][1,4]oxazine-4,4′-piperidine]-1′-yl)methanone (330 mg, 62%). ESI-MS m/z calc. 432.5, found 433.5 (M+1)+; Retention time: 1.78 minutes (3 min run).
