Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl Phosphonodiamidate prodrugs of N-alkoxy analogs of a fosmidomycin surrogate as antimalarial and antitubercular agents Charlotte Courtens a , Martijn Risseeuw a , Guy Caljon b , Paul Cos b , Anandi Martin c , Serge Van Calenbergh a, ⁎ a Laboratory for Medicinal Chemistry, Ghent University, Ottergemsesteenweg 460, B-9000 Ghent, Belgium b Laboratory for Microbiology, Parasitology and Hygiene, University of Antwerp, Universiteitsplein 1 (S7), B-2610 Wilrijk, Belgium c Medical Microbiology, Institute of Experimental and Clinical Research, Université catholique de Louvain, Avenue Hippocrate 55, B-1200 Woluwe-Saint-Lambert, Belgium ARTICLE INFO Keywords: Fosmidomycin Prodrugs Non-mevalonate pathway Isoprenoid biosynthesis Malaria Tuberculosis ABSTRACT A series of N-alkoxy analogs of a L-leucine ethyl ester phosphonodiamidate prodrug of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. These compounds originate by merging a previously reported successful phosphonate derivatisation with fa- vorable modifications of the hydroxamate moiety. None of the synthesized compounds showed enhanced ac- tivity against either P. falciparum or M. tuberculosis in comparison with the parent free hydroxamate analog. Despite international efforts, malaria and tuberculosis (TB) remain among the most problematic infectious diseases worldwide. According to the World Health Organization (WHO), malaria incidence has de- creased significantly since 2010. Since 2014, however, the number of malaria cases is steadily increasing, while the number of deaths remains comparable. 1 Resistance to antimalarial drugs is a persisting problem and, alarmingly, elevated resistance to artemisinin combination therapy (ACT) drugs has been observed in recent years. 2,3 Despite a significant drop in TB mortality rates since 2010, the proportion of multidrug-resistant (MDR) TB cases is steadily increasing. Approxi- mately 5% of active TB cases are multidrug-resistant (MDR), of which 6% are extensively drug-resistant (XDR). Treatment success rates of drug-resistant TB cases are relatively low, being 50% for MDR-TB and 30% for XDR-TB. 4,5 In 2009, the first totally drug-resistant (TDR) strains have been detected in India. 6 In order to halt the upsurge of infections with drug-resistant pathogen strains, there is an urgent need for antimalarial and antitubercular agents with a novel mechanism of action (MOA). In this respect, the non-mevalonate pathway (NMP) for isoprenoid biosynthesis represents an interesting potential drug target. Isoprenoids form the largest class of natural compounds and are es- sential to all living organisms. They are built up of the five-carbon isoprene units isopentenyl pyrophosphate (IPP) and dimethylallyl pyr- ophosphate (DMAPP). These building blocks can be synthesized via two evolutionary distinct pathways: the mevalonate (MVA) pathway and the NMP, also known as the methylerythritol phosphate (MEP) pathway. Both malaria-causing Plasmodium parasites and Myco- bacterium tuberculosis (Mtb), the causative agent of TB, rely entirely on the NMP, while it is absent in humans. 1-Deoxy-D-xylulose-5-phosphate reductoisomerase (DXR, also known as IspC), catalyzes the second step of the MEP pathway and is the most extensively investigated enzyme of this pathway. 7,8 L-leucine ethyl ester based prodrug derivatives of N-alkoxy analogs of a fosmidomycin surrogate are the focus of this work. Fosmidomycin (1, Fig. 1) and FR900098 (2, Fig. 1), the N-acetyl analog of fosmidomycin, are natural antibiotics originally isolated from Streptomyces lavendulae and Streptomyces rubellomurinus, respectively. 9 Fosmidomycin was originally evaluated for the treatment of urinary tract infections. In 1998, however, fosmidomycin and FR900098 were https://doi.org/10.1016/j.bmcl.2019.03.008 Received 10 February 2019; Received in revised form 4 March 2019; Accepted 6 March 2019 Abbreviations: AA, amino acid; ACT, artemisinin-based combination therapy; DCM, dichloromethane; DMAPP, dimethylallyl pyrophosphate; DXP, 1-deoxy-D- xylulose 5-phosphate; DXR, 1-deoxyxylulose 5-phosphate reductoisomerase; EDC, N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide; Et 3 N, triethylamine; GlpT, glycerol-3-phosphate transporter; HOBt, hydroxybenzotriazole; HRMS, high-resolution mass spectrometry; MDR, multidrug-resistant; MEP, methylerythritolpho- sphate; MIC, minimal inhibitory concentration; MOA, mechanism of action; Mtb, Mycobacterium tuberculosis; MVA, mevalonate; NADPH, nicotinamide adenine dinucleotide phosphate; NMP, non-mevalonate pathway; PK, pharmacokinetic; POM, pivaloyloxymethyl; SD, standard deviation; SI, selectivity index; TB, tu- berculosis; TDR, totally drug-resistant; TFA, trifluoroacetic acid; THF, tetrahydrofuran; WHO, world health organization; XDR, extensively drug-resistant ⁎ Corresponding author. E-mail address: serge.vancalenbergh@ugent.be (S. Van Calenbergh). Bioorganic & Medicinal Chemistry Letters 29 (2019) 1051–1053 Available online 07 March 2019 0960-894X/ © 2019 Elsevier Ltd. All rights reserved. T