Synthesis of potential cytotoxic quaternary ammoniums by oxidation of eburnane alkaloids

Oxidation of vincamine and substituted analogs on ring-A was carried out in two steps: benzylic oxidation by Jones reagent and aromatization of ring-C with Hg(OAc) 2 or Tl(OCOCF 3 ) 3 in trifluoroacetic acid. Final compounds are quaternary ammoniums which exhibited weak cytotoxicity or no cytotoxicity according to substituents on ring-A and nature of ring-E