Structural highlights
Function[IMDH_CRYPV] Catalyzes the conversion of inosine 5'-phosphate (IMP) to xanthosine 5'-phosphate (XMP), the first committed and rate-limiting step in the de novo synthesis of guanine nucleotides, and therefore plays an important role in the regulation of cell growth (By similarity).[1] Publication Abstract from PubMedCryptosporidium 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 muM) against a panel of four mammalian cells lines. Optimization of Benzoxazole-Based Inhibitors of Cryptosporidium parvum Inosine 5'-Monophosphate Dehydrogenase.,Gorla SK, Kavitha M, Zhang M, Chin JE, Liu X, Striepen B, Makowska-Grzyska M, Kim Y, Joachimiak A, Hedstrom L, Cuny GD J Med Chem. 2013 May 23;56(10):4028-43. doi: 10.1021/jm400241j. Epub 2013 May 13. PMID:23668331[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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