Assessment of a pretomanid analogue library for African trypanosomiasis: Hit-to-lead studies on 6-substituted 2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine 8-oxides

Bioorg Med Chem Lett. 2018 Jan 15;28(2):207-213. doi: 10.1016/j.bmcl.2017.10.067. Epub 2017 Oct 27.

Abstract

A 900 compound nitroimidazole-based library derived from our pretomanid backup program with TB Alliance was screened for utility against human African trypanosomiasis (HAT) by the Drugs for Neglected Diseases initiative. Potent hits included 2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine 8-oxides, which surprisingly displayed good metabolic stability and excellent cell permeability. Following comprehensive mouse pharmacokinetic assessments on four hits and determination of the most active chiral form, a thiazine oxide counterpart of pretomanid (24) was identified as the best lead. With once daily oral dosing, this compound delivered complete cures in an acute infection mouse model of HAT and increased survival times in a stage 2 model, implying the need for more prolonged CNS exposure. In preliminary SAR findings, antitrypanosomal activity was reduced by removal of the benzylic methylene but enhanced through a phenylpyridine-based side chain, providing important direction for future studies.

Keywords: African trypanosomiasis; In vivo efficacy; Library screening; Nitroimidazole; Pharmacokinetics; Pretomanid.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Animals
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Humans
  • Mice
  • Molecular Structure
  • Nitroimidazoles / administration & dosage
  • Nitroimidazoles / chemistry
  • Nitroimidazoles / pharmacology*
  • Small Molecule Libraries / administration & dosage
  • Small Molecule Libraries / chemistry
  • Small Molecule Libraries / pharmacology*
  • Structure-Activity Relationship
  • Trypanosomiasis, African / drug therapy*

Substances

  • Nitroimidazoles
  • Small Molecule Libraries
  • pretomanid