Chiral Chromatographic Isolation on Milligram Scale of the Human African Trypanosomiasis Treatment d- and l-Eflornithine

Mikael Boberg; Anna C Jonson; Hanna Leek; Rasmus Jansson-Löfmark; Michael Ashton

doi:10.1021/acsomega.0c03121

Chiral Chromatographic Isolation on Milligram Scale of the Human African Trypanosomiasis Treatment d- and l-Eflornithine

ACS Omega. 2020 Sep 11;5(37):23885-23891. doi: 10.1021/acsomega.0c03121. eCollection 2020 Sep 22.

Authors

Mikael Boberg¹, Anna C Jonson², Hanna Leek², Rasmus Jansson-Löfmark^{1

3}, Michael Ashton¹

Affiliations

¹ Unit for Pharmacokinetics and Drug Metabolism, Sahlgrenska Academy, University of Gothenburg, Gothenburg 41390, Sweden.
² Early Chemical Development, Pharmaceutical Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg 43183, Sweden.
³ DMPK, Research and Early Development Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg 43183, Sweden.

Abstract

Eflornithine is a recommended treatment against the otherwise fatal parasitic disease late stage human African trypanosomiasis (HAT), also known as Gambian sleeping sickness. It is administered repeatedly as a racemic mixture intravenously (IV) together with oral nifurtimox. Racemic eflornithine has been investigated in clinical trials for oral dosing. However, due to low systemic exposures at a maximum tolerated oral dose, the drug is continued to be administered IV. The eflornithine enantiomers, d- and l-eflornithine, have different affinities to the target enzyme ornithine decarboxylase, suggesting that the pharmacodynamics of the enantiomers may differ. The aim of this study was to develop a method for isolation of d- and l-eflornithine from a racemic mixture. Several chiral stationary phases (CSPs) were evaluated for enantioselectivity using supercritical fluid chromatography (SFC) or high-performance liquid chromatography (HPLC). None of the tested CSPs rendered separation of the enantiomers in SFC mode. Separation of the enantiomers with SFC on the CSP Chiralpak IG was only achieved on an analytical scale after derivatization with ortho-phthalaldehyde (OPA). This was the first reported enantioselective SFC method for an eflornithine derivate. However, due to poor stability, the eflornithine-OPA derivates degraded and no chemically pure enantiomers were obtained. The CSP that showed enantioselectivity in HPLC mode was Chirobiotic R, which resulted in a successful isolation on a semipreparative milligram scale. The isolated eflornithine enantiomers will be tested in nonclinical in vitro and in vivo studies to support and assess the feasibility of a future clinical program with an oral HAT treatment.