7-Substituted 2-Nitro-5,6-dihydroimidazo[2,1-b][1,3]oxazines: Novel Antitubercular Agents Lead to a New Preclinical Candidate for Visceral Leishmaniasis

J Med Chem. 2017 May 25;60(10):4212-4233. doi: 10.1021/acs.jmedchem.7b00034. Epub 2017 May 11.


Within a backup program for the clinical investigational agent pretomanid (PA-824), scaffold hopping from delamanid inspired the discovery of a novel class of potent antitubercular agents that unexpectedly possessed notable utility against the kinetoplastid disease visceral leishmaniasis (VL). Following the identification of delamanid analogue DNDI-VL-2098 as a VL preclinical candidate, this structurally related 7-substituted 2-nitro-5,6-dihydroimidazo[2,1-b][1,3]oxazine class was further explored, seeking efficacious backup compounds with improved solubility and safety. Commencing with a biphenyl lead, bioisosteres formed by replacing one phenyl by pyridine or pyrimidine showed improved solubility and potency, whereas more hydrophilic side chains reduced VL activity. In a Leishmania donovani mouse model, two racemic phenylpyridines (71 and 93) were superior, with the former providing >99% inhibition at 12.5 mg/kg (b.i.d., orally) in the Leishmania infantum hamster model. Overall, the 7R enantiomer of 71 (79) displayed more optimal efficacy, pharmacokinetics, and safety, leading to its selection as the preferred development candidate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antiprotozoal Agents / chemistry*
  • Antiprotozoal Agents / pharmacokinetics
  • Antiprotozoal Agents / pharmacology
  • Antiprotozoal Agents / therapeutic use*
  • Antitubercular Agents / chemistry
  • Antitubercular Agents / pharmacokinetics
  • Antitubercular Agents / pharmacology
  • Antitubercular Agents / therapeutic use
  • Cricetinae
  • Drug Discovery
  • Female
  • Humans
  • Leishmania donovani / drug effects*
  • Leishmania infantum / drug effects*
  • Leishmaniasis, Visceral / drug therapy*
  • Male
  • Mesocricetus
  • Mice
  • Mice, Inbred BALB C
  • Nitroimidazoles / chemistry*
  • Nitroimidazoles / pharmacokinetics
  • Nitroimidazoles / pharmacology
  • Nitroimidazoles / therapeutic use*
  • Oxazines / chemistry
  • Oxazines / pharmacology
  • Oxazines / therapeutic use
  • Rats, Sprague-Dawley


  • Antiprotozoal Agents
  • Antitubercular Agents
  • Nitroimidazoles
  • Oxazines