Ethyl 4-piperidinecarboxylate → 1-[2-Fluoro-5-(4-oxo-3,4-dihydrophthalazin-1-ylmethyl)benzoyl]piperidine-4-carboxylic acid

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Reaction Steps

2-Fluoro-5-(4-oxo-3,4-dihydrophthalazin-1-ylmethyl)benzoic acid (B)(3.1 g, 0.14 mol), ethyl isonipecotate (1.7 ml, 0.11 mol), 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) (5.1 g, 0.13 mol) and N,N,-diisopropylethylamine (10.0 ml, 0.55 mol) were added to dimethylacetamide (15 ml) and stirred for 18 hours. Water (100 ml) was added to the reaction mixture and the product was extracted into dichloromethane (4×50 ml). The combined organic layers were, filtered, washed with water (3×100 ml), dried over MgSO4, filtered and evaporated in vacuo to yield an orange oil. The oil was purified by flash chromatography (ethyl acetate) to yield 1-[2-fluoro-5-(4-oxo-3,4-dihydrophthalazin-1-ylmethyl)benzoyl]piperidine-4-carboxylic acid as the methyl ester (1.5 g, 33%, 96% purity). To a solution of the methyl ester in tetrahydrofuran:water (2:1, 40 ml) was added sodium hydroxide (0.3 g, 0.075 mol) and the reaction was stirred for 18 h. The reaction was concentrated, washed with ethyl acetate (2×20 ml) and acidified with 2M HCl to pH 2. The aqueous layer was extracted with dichloromethane (2×20 ml), and the combined extracts were dried over MgSO4 and evaporated to yield 1-[3-(4-oxo-3,4-dihydrophthalazin-1-ylmethyl)benzoyl]piperidine-4-carboxylic acid (D) as a yellow solid (0.6 g, 65%), m/z [M+1]+ 392 (96% purity)

Provenance & Evidence