DHA e prodotti di degradazione termica: isolamento, caratterizzazione spettroscopica e studi di stereodinamica

Drug development may be defined as a series of specialized events performed to satisfy criteria, internal (i.e. competitive industry benchmarks) and external (i.e. regulatory compliance), to yield a novel drug. Much attention has so far been given to the various activities in drug development. In particular Ph.D. research involved a systematic study on analytical methods to analyze Dihydroartemisinin (DHA) the active ingredient for a drug for antimalarian activity. Artemisinin (qinghaosu), an endoperoxide sesquiterpene lactone, is considered the most important secondary metabolite and bioactive constituent (Klaiman, 1985; van Agtmael et al., 1999; Heppner and Ballou, 1998). Its relatively low yields can vary considerably, depending on the plant material, growing conditions and seasonal and geographic variations: in the plant it is generally present in the shoots and seeds (Abdin et al., 2003) with highest levels in field grown leaves and flowers (0.01e1.4% dry weight; van Agtmael et al., 1999) where artemisinin is sequestered in glandular trichomes (Duke et al., 1994). Artemisinin is considered a potent antimalarial drug, even against chloroquine- and quinineresistant Plasmodium falciparum and other malaria-causing parasites. At the moment, artemisinin is the basis of a large family of drugs recommended by the World Health Organization (WHO) to fight malaria in the countries where highly resistant strains of the protozoan have been certified. The combination of artemisinin derivatives with other effective antimalarial medicines (artemisininbased combination therapies or ACTs) is currently the most effective treatment for falciparum malaria – the most lethal form of the disease. Since its identification in the 1970s, artemisinin as well as semisynthetic derivatives and synthetic trioxanes have been utilized in therapy. Reduction of artemisinin by sodium borohydride produced dihydroartemisinin (DHA,), which is also its main metabolite and provides improved antimalarial potency and a major route of elimination. The only drawback is that DHA is a highly neurotoxic compound as well, as demonstrated by both in vitro and in vivo studies. The conversion of the lactone carbonyl group at C-10 of artemisinin into the hydroxyl (hemiacetal) group in DHA yielded a new stereochemically labile centre in the molecule, which in turn provided two lactol hemiacetal epimers, namely 2α and 2β During Ph.D activities were performed several studies on DHA . In particular: 1) Chemical, stereochemical and spectroscopic characterization of DHA. 2) Pyrolisis in different experimental conditions. 3) Evaluation of International Pharmacopoeia method for DHA analysis. 4) Development of analytical chemo and stereo selective method able to separate DHA epimers and thermal degradation impurities mixture 5) Stereodinamic characterization of DHA and study of epimerization process in solution by reverse phase dynamic HPLC. 6) Isolation and characterization of the main impurity in drug substance (DKA) and of the most important thermal degradation impurity (MKA). 7) Chemical and spectroscopic characterization of DKA and MKA. 8) Stereodinamic characterization of MKA and study of epimerization process in solution by reverse phase dynamic HPLC.