A mixture of 6-(4-oxo-3,4-dihydro-phthalazin-1-ylmethyl)-pyridine-2-carboxylic acid (ivb)(0.3 g, 1.1 mmol), triethylamine (0.3 ml, 2.1 mmol), tert-butyl-1-piperazine carboxylate (0.23 g, 1.3 mmol) and 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (0.5 g, 1.3 mmol) in dimethylformamide (10 ml) was stirred for 18 hours. The reaction mixture was precipitated on the addition of water (50 ml) and air-dried. The white precipitate was dissolved in ethanol (3 ml) and 12 M hydrochloric acid (6 ml) was added to the solution and the reaction was stirred for 30 minutes. The reaction was then concentrated in vacuo, redissolved in water (10 ml) and washed with dichloromethane (2×10 ml). The aqueous layer was basified with ammonium hydroxide and extracted into dichloromethane (2×10 ml). The combined organic layers was dried with MgSO4, filtered and evaporated to yield the expected product (va) as a pink solid (0.23 g, 73%). m/z [M+1]+ 250 (96% purity)
