Structure−Activity Relationships of Synthetic Cordycepin Analogues as Experimental Therapeutics for African Trypanosomiasis Suman K. Vodnala, † Thomas Lundba ̈ ck, ‡,⊥ Esther Yeheskieli, † Birger Sjö berg, ‡,⊥ Anna-Lena Gustavsson, ‡,⊥ Richard Svensson, §,⊥ Gabriela C. Olivera, † Anthonius A. Eze, ∥ Harry P. de Koning, ∥ Lars G. J. Hammarströ m, ‡,⊥,# and Martin E. Rottenberg* ,†,# † Department of Microbiology, Tumor and Cell Biology and ‡ Division of Translational Medicine and Chemical Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 171 77 Stockholm, Sweden § Uppsala University Drug Optimization and Pharmaceutical Profiling Platform (UDOPP), Department of Pharmacy, Uppsala University, 753 12 Uppsala, Sweden ∥ Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, U.K. ⊥ Chemical Biology Consortium Sweden, Sweden ABSTRACT: Novel methods for treatment of African trypanosomiasis, caused by infection with Trypanosoma brucei are needed. Cordycepin (3′-deoxyadenosine, 1a) is a powerful trypanocidal compound in vitro but is ineffective in vivo because of rapid metabolic degradation by adenosine deaminase (ADA). We elucidated the structural moieties of cordycepin required for trypanocidal activity and designed analogues that retained trypanotoxicity while gaining resistance to ADA-mediated metabolism. 2-Fluorocordycepin (2-fluoro- 3′-deoxyadenosine, 1b) was identified as a selective, potent, and ADA-resistant trypanocidal compound that cured T. brucei infection in mice. Compound 1b is transported through the high affinity TbAT1/P2 adenosine transporter and is a substrate of T. b. brucei adenosine kinase. 1b has good preclinical properties suitable for an oral drug, albeit a relatively short plasma half-life. We present a rapid and efficient synthesis of 2-halogenated cordycepins, also useful synthons for the development of additional novel C2-substituted 3′-deoxyadenosine analogues to be evaluated in development of experimental therapeutics. ■ INTRODUCTION Human African trypanosomiasis (HAT) is caused by infection with the extracellular protozoan parasite Trypanosoma brucei. Parasites are transmitted through the bite of the tsetse fly (Glossina sp.) vector, which infests vast areas of sub-Saharan Africa. Infection with T. brucei causes a debilitating wasting disease in livestock, and sleeping sickness in humans. The subspecies T. b. gambiense causes a protracted human infection prevalent in Western and Central Africa, while human T. b. rhodesiense infection, with a more rapid disease progression, dominates in Eastern and Southern Africa, where it also infects wild and domestic animals. 1 The human disease is characterized by two stages. In the early stage the parasite is found in the blood and lymph; infected individuals show fever, joint pain, headaches, and itching as clinical symptoms. In the late stage, the parasite invades the central nervous system (CNS) after crossing the blood−brain barrier (BBB), causing severe neurological symptoms, sensory alterations such as hyperalgesia and allodynia, poor coordination, and sleep disturbances. 2 The disease eventually results in coma and is invariably lethal if left untreated. The incidence of African trypanosomiasis has been reduced from an estimated 300 000 cases per year 12 years ago to 21 000 cases in 2012. 3 Despite this positive trend, the limited number of safe and efficacious drugs available for treatment and the difficulties in administration of current therapies warrant continued investigation of new methods to treat this devastating disease. It is worth remembering that sleeping sickness was almost eradicated in the late 1950s/early 1960s but returned to epidemic proportions in the 1990s. 4 Management of HAT is critically dependent on an accurate diagnosis of the stage of infection, since most current trypanocidal drugs do not transverse the BBB and are thus unsuitable for treatment of late stage infections. The few drugs that are BBB penetrating and thereby efficacious for treatment of late stage infection are associated with severe side effects, require a complicated treatment regimen, and/or are subspecies specific. Melarsoprol, an arsenic derivative discovered in 1949, is used for treatment of late stage infection with both T. brucei subspecies. This drug, together with eflornithine, 5 which targets T. b. gambiense polyamine synthesis, is currently first-line therapy for treating late stage infection. Treatment with Received: July 15, 2013 Published: November 27, 2013 Article pubs.acs.org/jmc © 2013 American Chemical Society 9861 dx.doi.org/10.1021/jm401530a | J. Med. Chem. 2013, 56, 9861−9873