BI 1002494 [(R)-4-{(R)-1- [7-(3,4,5-trimethoxy-phenyl)- [1,6] napthyridin-5-yloxy]-ethyl}pyrrolidin-2-one] is a novel, potent, and selective spleen tyrosine kinase (SYK) inhibitor with sustained plasma exposure after oral administration in rats, which qualifies this molecule as a good in vitro and in vivo tool compound. BI 1002494 exhibits higher potency in inhibiting highaffinity IgE receptor-mediated mast cell and basophil degranulation (IC 50 5 115 nM) compared with B-cell receptor-mediated activation of B cells (IC 50 5 810 nM). This may be explained by lower kinase potency when the physiologic ligand B-cell linker was used, suggesting that SYK inhibitors may exhibit differential potency depending on the cell type and the respective signal transduction ligand. A 3-fold decrease in potency was observed in rat basophils (IC 50 5 323 nM) compared with human basophils, but a similar species potency shift was not observed in B cells. The lower potency in rat basophils was confirmed in both ex vivo inhibition of bronchoconstriction in precision-cut rat lung slices and in reversal of anaphylaxis-driven airway resistance in rats. The different cellular potencies translated into different in vivo efficacy; full efficacy in a rat ovalbumin model (that contains an element of mast cell dependence) was achieved with a trough plasma concentration of 340 nM, whereas full efficacy in a rat collageninduced arthritis model (that contains an element of B-cell dependence) was achieved with a trough plasma concentration of 1400 nM. Taken together, these data provide a platform from which different estimates of human efficacious exposures can be made according to the relevant cell type for the indication intended to be treated.

A series of chromene derivatives was synthesized and evaluated for their in vitro and ex vivo 5-lipoxygenase (5-LO) inhibitory activity. These compounds were prepared by condensation of appropriate salicyl aldehydes with alpha, beta-unsaturated carbonyl compounds, followed by transformation to the corresponding hydroxamic acids or N-hydroxyureas. Placement of phenoxy or p-fluorophenoxy substituents at the 6 position of the chromene ring led to a dramatic increase in the in vitro potency as demonstrated by the guinea pig PMN 5-LO assay. Chromene hydroxamic acids, in general, behaved poorly in the ex vivo dog model. On the other hand, replacement of the hydroxamic acid function with N-hydroxyurea yielded potent and long-lasting 5-LO inhibitors in the dog model. In most cases, the oral efficacy of the chromene N-hydroxyureas correlated very well with their in vitro activity. Compounds 43 (CGS 23885) and 55 (CGS 24891) are among the most potent inhibitors prepared, showing IC50 values of 48 and 51 nM, respectively. The values for the duration of action (DA) for compounds 43 and 55 are 21 and 20 h, respectively, following intravenous (i.v.) administration of 1.0 mg/kg. In the oral (po) experiments, 43 and 55 have DA's of 14 and 15 h, respectively, at a 1.0 mg/kg dose. In both iv and po experiments, 43 and 55 showed sustained maximal inhibition (> 95%) at earlier time points. The oral ED50 values of 43 and 55 in the ex vivo dog model are 0.23 and 0.23 mg/kg, respectively, at 6.0 h, and 2.37 and 1.63 mg/kg, respectively, at 24 h. Compound 43, which inhibits sheep seminal vesicle cyclooxygenase (CO) with an IC50 value of 36 microM, was shown to be a selective 5-lipoxygenase inhibitor in the ex vivo study. These compounds compare favorably with zileuton (A-64077) in all the parameters examined.