The development of novel LTA4H modulators to selectively target LTB4 generation

The pro-inflammatory mediator leukotriene B4 (LTB4) is implicated in the pathologies of an array of diseases and thus represents an attractive therapeutic target. The enzyme leukotriene A4 hydrolase (LTA4H) catalyses the distal step in LTB4 synthesis and hence inhibitors of this enzyme have been actively pursued. Despite potent LTA4H inhibitors entering clinical trials all have failed to show efficacy. We recently identified a secondary anti-inflammatory role for LTA4H in degrading the neutrophil chemoattractant Pro-Gly-Pro (PGP) and rationalized that the failure of conventional LTA4H inhibitors may be that they inadvertently prevented PGP degradation. We demonstrate that these inhibitors do indeed fail to discriminate between the dual activities of LTA4H, and enable PGP accumulation in mice. Accordingly, we have developed novel compounds that potently inhibit LTB4 generation whilst leaving PGP degradation unperturbed. These novel compounds could represent a safer and superior class of LTA4H inhibitors for translation into the clinic.


Compound synthesis
Compounds were custom synthesized by Peakdale Molecular as described below.

Synthesis of methyl 3-hydroxy-5-ethoxybenzoate (a)
To a stirred suspension of methyl 3,5-dihydroxybenzoate (4 g, 23.8 mmol) and potassium carbonate (9.05 g, 26.1 mmol) in acetone (130 mL) was added iodoethane (1.9 mL, 23.8 mmol) at 0 °C. The mixture was stirred at RT for 18 h, and then refluxed for a further 24 h. The mixture was then cooled to RT, and filtered

Synthesis of (3-(benzyloxy)-5-ethoxyphenyl)methanol (c)
To a suspension of lithium aluminium hydride (147 mg, 3.88 mmol) in THF (10 mL) was added b (1.11 g, 3.88 mmol) in THF (15 mL), dropwise, with ice/salt bath cooling to ensure internal temperature did not rise above 10°C during addition. After addition was complete, the mixture was stirred at RT for 2 h. Excess lithium aluminium hydride was then quenched by careful addition of sodium sulfate decahydrate. After stirring the suspension for 15 min, ethyl acetate (50 mL) was added, and the suspension filtered through Celite. The filtrate was evaporated to give c (968 mg, 97% yield) as a colourless oil.
A solution of e (500 mg, 0.856 mmol) in THF (10 mL) was cooled to -78 °C, and n-butyl lithium (2M in hexanes, 0.45 mL, 0.90 mmol) was added dropwise, maintaining internal temperature below -65 °C. This afforded a bright yellow suspension. After stirring for 2 h at -78 °C, a solution of 4-(benzyloxy)benzaldehyde (181 mg, 0.856 mmol) in THF (10 mL) was added dropwise. After addition was complete, the yellow suspension was allowed to warm slowly to RT, during which time the bright yellow suspension became a pale yellow solution. Two h after the addition, the mixture was diluted with water (50 mL), and extracted with dichloromethane (3 x 40 mL); the combined organic extracts were dried over sodium sulfate and evaporated to give a yellow oil, which was purified by flash chromatography (eluant:
Methanesulfonyl chloride (0.9 ml; 11.5 mmol) was then added and the reaction mixture heated at 80 °C for
Methanesulfonyl chloride (116 μl; 1.50 mmol) was then added in one portion and the reaction mixture