Synthesis and Evaluation of 3-Aryl-4(1H)-Quinolones as Orally Active Antimalarials: Overcoming Challenges in Solubility, Metabolism, and Bioavailability

• Main Author: Monastyrskyi, Andrii
• Format: Others
• Published: Scholar Commons 2014
• Subjects: 4(1H)-quinolone; malaria; prodrug; solubility; Organic Chemistry
• Online Access: https://scholarcommons.usf.edu/etd/5080; https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=6276&context=etd

Infectious diseases are the second leading cause of deaths in the world with malaria being responsible for approximately the same amount of deaths as cancer in 2012. Despite the success in malaria prevention and control measures decreasing the disease mortality rate by 45% since 2000, the development of single-dose therapeutics with radical cure potential is required to completely eradicate this deadly disease. Targeting multiple stages of the malaria parasite is becoming a primary requirement for new candidates in antimalarial drug discovery and development. Recently, 4(1H)-pyridone, 4(1H)-quinolone, 1,2,3,4-tetrahydroacridone, and phenoxyethoxy-4(1H)-quinolone chemotypes have been shown to be antimalarials with blood stage activity, liver stage activity, and transmission blocking activity. Advancements in structure-activity relationship and structure-property relationship studies, biological evaluation in vitro and in vivo, as well as pharmacokinetics of the 4(1H)-pyridone and 4(1H)-quinolone chemotypes is discussed in the first chapter of the dissertation. Convenient synthetic approaches to 3-aryl-4(1H)-quinolones via metal-catalyzed and metal-free arylation of β-keto carbonyl compounds is addressed in Chapter 2. A clean arylation protocol of ethyl acetoacetate was developed by using hypervalent diaryl iodonium salts under mild and metal-free conditions. The scope of the reaction, using symmetric and unsymmetric iodonium salts varying in sterics and electronics was examined. This method has been applied for the synthesis of antimalarial compound ELQ-300, which is currently in preclinical development. Additionally, a first gram scale synthesis of ELQ-300 and its structurally related 4(1H)-quinolone P4Q-391 using operationally simple and highly yielding metal-catalyzed conditions have been shown. Despite of 3-aryl-4(1H)-quinolone chemotypes displaying potent antimalarial activities against Plasmodium species in vitro and in vivo, their development is also associated with risks. 4(1H)-quinolones are known to be poorly soluble and thus represent challenging drug candidates for pharmacokinetic and bioavailability reasons. Disrupting of molecular crystal packing and prodrug approaches were employed to overcome solubility and bioavailability issues in current series. Quantum mechanics torsion profile calculations, 13C T1 spin-lattice relaxation experiments as well as X-ray studies were conducted with the objective to determine possible effects improving key physicochemical properties such as solubility and stability. As a backup strategy, a prodrug approach was developed enabling the 4(1H)-quinolone scaffold to be functionalized at the quinolone's oxygen. In order to avoid any enzymatic dependences, an approach was developed in which the prodrug moiety was removed via a pH-triggered decay. Additionally, phosphate prodrugs regenerating the active compound via extrahepatic enzymes such as the ubiquitous alkaline phosphatase were investigated. The development of orally bioavailable prodrugs enabled an advance overcoming in vivo efficacy limitations and has been confirmed by pharmacokinetic profiling studies. The herein presented approaches present viable options for any pyridone quinolone antimalarial chemotype which are currently studied.