Different inflammatory diseases and allergic reactions are mediated by leukotrienes, which arise from the oxygenation of arachidonic acid catalyzed by 5-lipoxygenase (5-LO). One promising approach for an effective anti-leukotriene therapy is the inhibition of this key enzyme. This study presents the synthesis and development of a potent and direct 5-LO inhibitor based on the well characterized 5-benzylidene-2-phenylthiazolone C06, whose further pharmacological investigation was precluded due to its low solubility. Through optimization of C06, evaluation of structure-activity relationships including profound assessment of the thiazolone core and consideration of the solubility, the 5-benzyl-2-phenyl-4-hydroxythiazoles represented by 46 (ST-1829, 5-(4-chlorobenzyl)-2-p-tolylthiazol-4-ol) were developed. Compound 46 showed an improved 5-LO inhibitory activity in cell-based (IC50 values 0.14 μM) and cell-free assays (IC50 values 0.03 μM) as well as a prominent enhanced solubility. Furthermore, it kept its promising inhibitory potency in the presence of blood serum, excluding excessive binding to serum proteins. These facts combined with the non-cytotoxic profile mark a major step towards an effective anti-inflammatory therapy.