Triazolopyrimidines identified as reversible myeloperoxidase inhibitors

Abstract

Myeloperoxidase, a mammalian peroxidase involved in the immune system as an anti-microbial first responder, can produce hypochlorous acid in response to invading pathogens. Myeloperoxidase has been implicated in several chronic pathological diseases due to the chronic production of hypochlorous acid, as well as other reactive radical species. A high throughput screen and triaging protocol was developed to identify a reversible inhibitor of myeloperoxidase toward the potential treatment of chronic diseases such as atherosclerosis. The identification and characterization of a reversible myeloperoxidase inhibitor, 7-(benzyloxy)-3H-[1,2,3]triazolo[4,5-d]pyrimidin-5-amine is described.

Fig. 1. MPO catalytic mechanism.

Fig. 2. Literature MPO inhibitors (1–5) and HTS hits (6, 7).

Fig. 3. HTS testing and triaging operations.

Fig. 4. A–C: Multiwavelength stopped-flow scans over 50 ms after mixing 1 uM MPO, 5 uM peroxide and 80 uM compound 1 (4A), 40 uM compound 6 (4B), and 7 (4C). D–F: Single wavelength traces from separate stopped-flow experiments showing the change in 430 nm and 450 nm wavelengths over 200 s after mixing for compound 1 (4D), 6 (4E), and 7 (4F).

Fig. 5. Co-crystal structure of 6 with MPO. The carbons of compound 6 are colored in yellow and the carbons for heme are colored in green. Light chain residues of MPO are shown in cyan and heavy chain in magenta. Oxygens are colored red and nitrogens are blue. Hydrogen bonds are indicated with dashed lines.

Fig. 6. Inhibition of MPO mediated chlorination by 6 (blue) rescued ApoA1 cholesterol efflux capacity (red).

Fig. 7. Inhibition of MPO-mediated formation of HOCl after dosing 6 at 30 and 100 mpk as measured by luminol chemiluminescence. *P < 0.05, vs. vehicle, t test.

Fig. 8. SAR of the triazolopyrimidine core of lead 6.