Synthesis, HPLC enantioresolution and X-ray analysis of a new series of C5-methyl pyridazines as N-formyl peptide receptor (FPR) agonists

The synthesis of three racemates and the corresponding non-chiral analogues of a C5-methyl pyridazine series is described here, as well as the isolation of pure enantiomers and their absolute configuration assignment. In order to obtain optically active compounds, direct chromatographic methods of separation by HPLC-UV were investigated using four chiral stationary phases (CSPs: Lux Amylose-2, Lux Cellulose-1, Lux Cellulose-2 and Lux Cellulose-3). The best resolution was achieved using amylose tris(5-chloro-2-methylphenylcarbamate) (Lux Amylose- 2), and single enantiomers were isolated on a semipreparative scale with high enantiomeric excess, suitable for biological assays. The absolute configuration of optically active compounds was unequivocally established by X-ray crystallographic analysis and comparative chiral HPLCUV profile. All compounds of the series were tested for formyl peptide receptor (FPR) agonist activity, and four were found to be active, with EC50 values in the micromolar range.