title: Optimization of benzoxazole-based inhibitors of Cryptosporidium parvum inosine 5'-monophosphate dehydrogenase.
abstract: Cryptosporidium parvum is an enteric protozoan parasite that has emerged as a major cause of diarrhea, malnutrition, and gastroenteritis and poses a potential bioterrorism threat. C. parvum synthesizes guanine nucleotides from host adenosine in a streamlined pathway that relies on inosine 5'-monophosphate dehydrogenase (IMPDH). We have previously identified several parasite-selective C. parvum IMPDH (CpIMPDH) inhibitors by high-throughput screening. In this paper, we report the structure-activity relationship (SAR) for a series of benzoxazole derivatives with many compounds demonstrating CpIMPDH IC50 values in the nanomolar range and >500-fold selectivity over human IMPDH (hIMPDH). Unlike previously reported CpIMPDH inhibitors, these compounds are competitive inhibitors versus NAD(+). The SAR study reveals that pyridine and other small heteroaromatic substituents are required at the 2-position of the benzoxazole for potent inhibitory activity. In addition, several other SAR conclusions are highlighted with regard to the benzoxazole and the amide portion of the inhibitor, including preferred stereochemistry. An X-ray crystal structure of a representative E·IMP·inhibitor complex is also presented. Overall, the secondary amine derivative 15a demonstrated excellent CpIMPDH inhibitory activity (IC50 = 0.5 ± 0.1 nM) and moderate stability (t1/2 = 44 min) in mouse liver microsomes. Compound 73, the racemic version of 15a, also displayed superb antiparasitic activity in a Toxoplasma gondii strain that relies on CpIMPDH (EC50 = 20 ± 20 nM), and selectivity versus a wild-type T. gondii strain (200-fold). No toxicity was observed (LD50 > 50 μM) against a panel of four mammalian cells lines.
authors.affiliation: Department of Biology, Brandeis University , 415 South Street, Waltham, Massachusetts 02454, USA.
authors.forename: Suresh Kumar
authors.initials: SK
authors.lastname: Gorla
authors.forename: Mandapati
authors.initials: M
authors.lastname: Kavitha
authors.forename: Minjia
authors.initials: M
authors.lastname: Zhang
authors.forename: James En Wai
authors.initials: JE
authors.lastname: Chin
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Liu
authors.forename: Boris
authors.initials: B
authors.lastname: Striepen
authors.forename: Magdalena
authors.initials: M
authors.lastname: Makowska-Grzyska
authors.forename: Youngchang
authors.initials: Y
authors.lastname: Kim
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
authors.forename: Lizbeth
authors.initials: L
authors.lastname: Hedstrom
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Cuny
mesh_terms: D000577:Amides / Q000138:chemical synthesis / Q000494:pharmacology; D000818:Animals; D001583:Benzoxazoles / Q000138:chemical synthesis* / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D016785:Cryptosporidium parvum / Q000187:drug effects / Q000201:enzymology*; D003460:Crystallization; D015195:Drug Design; D006207:Half-Life; D057166:High-Throughput Screening Assays; D006801:Humans; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007700:Kinetics; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014122:Toxoplasma / Q000187:drug effects
chemical_list: D000577:Amides; D001583:Benzoxazoles; D007202:Indicators and Reagents; D011725:Pyridines; D007168:IMP Dehydrogenase