Synthesis and antimicrobial evaluation of nitazoxanide-based analogues: identification of selective and broad spectrum activity

Abstract

A library composed of nitazoxanide-based analogues was synthesized and assayed for increased antibacterial efficacy against the pyruvate-ferredoxin oxidoreductase (PFOR) using microorganisms Helicobacter pylori, Campylobacter jejuni and Clostridium difficile. Derivatives were found to recapitulate and improve activity against these organisms and select analogues were tested for their ability to disrupt the PFOR enzyme directly. The library was also screened for activity against staphylococci and resulted in the identification of analogues capable of inhibiting both staphylococci and all PFOR organisms at low micromolar minimum inhibitory concentrations with low toxicity to human foreskin cells.

Figure 1

Representative Nitro Drugs.

Figure 2

Binding of pyruvate to the activated vitamin co-factor thiamine pyrophosphate (TPP). Pyruvate is then converted to acetyl-CoA. Nitazoxanide is believed to bind to and abstract a proton from the activated TPP, essentially out competing pyruvate and inhibiting the enzymatic reaction. PP: Pyrophosphate.

Figure 3

Pyruvate:ferredoxin oxidoreductase (PFOR) enzymatic reaction. Acetyl-CoA and CO2 are the oxidative by-products of the PFOR enzymatic reaction which requires ferredoxin (Fd) or flavodoxin (Fld) as electron acceptors. NADP oxidases or hydrogenases oxidize the reduced Fd/Fld to complete the cycle. Solid arrows indicate the forward reaction; hollow arrows indicate the reverse reaction.

Scheme 1

Synthesis of aryl furans and aryl thiophenes. With the synthesis of a few simple pyridines and a more elaborate furan library, thiophenes were the final group to be assessed for activity. Thiophene analogues were synthesized and assayed following the established routes and several phenyl thiophene derivatives were also synthesized through Suzuki cross coupling reactions (Scheme 1).