To a solution of (R)-3-hydroxypiperidine-1-carboxylic acid tert-butyl ester (209 mg, 1.04 mmol), triphenylphosphine (327 mg, 1.249 mmol), 1-amino-isoquinolin-6-ol (200 mg, 1.249 mmol) in THF (4 ml) and DMF (394 μL) at 0° C., under argon, was added dropwise diethylazodicarboxylate (197 mL) over 5 min. The mixture was then warmed to ambient temperature and stirred for 48 h. Water was then added and the mixture basified with dilute NaOH. The mixture was extracted with ethyl acetate (X3), dried (sodium sulphate) filtered and evaporated under reduced pressure to give a residue. Flash chromatography of the residue on silica (eluent: 2-10% methanol in dichloromethane with 1% aqueous ammonia) gave (S) 3-(1-amino-isoquinolin-6-yloxy)piperidin-1--carboxylic acid tert-butyl ester (72 mg), El-MS: m/z=344.1 [M+H]+.
