1-(tert-Butoxycarbonyl)-piperidine4-carboxylic acid (0.53 g), (S)-1-benzyloxycarbonyl-3-methylpiperazine (D19)(0.5 g), HOBt (0.29 g) and diethylaminomethyl polystyrene (1.78 g) were stirred in DCM (30 ml), then EDC (0.53 g) was added and the reaction was stirred at rt ovemight. The mixture was filtered and washed with saturated sodium hydrogen carbonate solution (3×50 ml) and brine (30 ml). The organic layer was dried (MgSO4) and evaporated to give a crude yellow oil which was purified by chromatography [silica gel; 0-100% ethyl acetate/hexane) to give the tide compound (D20) as a clear oil which crystallised on standing (0.88 g).
