Chemistry 259Medicinal Chemistry of Modern AntibioticsSpring 2008Lecture 7:Antibiotics Classes & TargetsLecture 7: Antibiotics Classes & TargetsPart II: Drugs Targeting Fatty Acid and Folic Acid Biosynthesis,Cell DivisionThomas HermannThomas HermannDepartment of Chemistry & BiochemistryUniversity of California San DiegoUniversity of California, San Diego Antibacterial Targets: OverviewBacterial Fatty Acid BiosynthesisBacterial Fatty Acid BiosynthesisBacterial Fatty Acid BiosynthesisBacterial Fatty Acid BiosynthesisBacterial Fatty Acid BiosynthesisBacterial Fatty Acid BiosynthesisBacterial Fatty Acid Biosynthesis: InhibitorsBP1Decynoyl-NACBacterial Fatty Acid Biosynthesis: FabI Inhibitors(broadspectrum antibacterial; used in soap disinfectant)(used to treat M. tuberculosisfor over 50 years)(Gram -, M. tuberculosis;not used in human; toxic)used in soap, disinfectant)for over 50 years)not used in human; toxic)FabIFabIBacterial Fatty Acid Biosynthesis: FabI Inhibitors(broadspectrum antibacterial; used in soap disinfectant)(used to treat M. tuberculosisfor over 50 years)(Gram -, M. tuberculosis;not used in human; toxic)used in soap, disinfectant)for over 50 years)not used in human; toxic)NAD NAD NADIsoniazidFabI inhibitors bind to theFabI inhibitors bind to the active site of the reductase and form a tight complex with the NAD cofactor.Triclosan, DiazaborineNAD (nicotinamide adenine dinucleotide)Bacterial Fatty Acid Biosynthesis: FabI Inhibitors: Isoniazid(Broussy et al., Org. Biomol. Chem. 2005, 3, 670)Bacterial Fatty Acid Biosynthesis: FabI Inhibitors: TriclosanNADTriclosanNAD(Stewart et al., JMB 1999, 290, 859)Bacterial Fatty Acid Biosynthesis: FabI Inhibitors: DiazaborinesNADNAD(Levy et al., JMB 2001, 309, 171)Bacterial Fatty Acid Biosynthesis: FabB Inhibitors(isolated from fungus Cephalosporium ceruleans; inhibits also mammalian fatty acid(isolated from fungus Nocardia sp.; efficacious against G+/in mouseceruleans; inhibits also mammalian fatty acid synthases -> not used)efficacious against G+/-in mouse models)FabBThiolactomycinoccupies malonate portion of the substrateCeruleinmimics the covalently bound condensation intermediate; nonpolarof the substrate binding site in FabB.intermediate; nonpolar tail is located in a hydrophobic tunnel.(Heath et al., Appl. Microbiol. Biotechnol. 2002, 58, 695)Bacterial Fatty Acid Biosynthesis: FabA Inhibitors: Decynoyl-NACAnalog of cis-3-decenoyl-ACPFabA:FabAFabAHistorical importance: First example of a suicide enzyme inhibitor (Helmkamp et al., JBC 1969, 244, 6014)Bacterial Fatty Acid Biosynthesis: FabF Inhibitors: PlatensimycinBacterial Fatty Acid Biosynthesis: FabF Inhibitors: PlatensimycinBacterial Fatty Acid Biosynthesis: FabF InhibitorsBacterial Fatty Acid Biosynthesis: FabF InhibitorsBacterial Fatty Acid Biosynthesis: FabF InhibitorsBacterial Folic Acid BiosynthesisGTPFolic acidBacterial Folic Acid BiosynthesisFolic acidBacterial Folic Acid BiosynthesisFolic acidBacterial Folic Acid BiosynthesisFolic acidBacterial Folic Acid BiosynthesisFolic acidBacterial Folic Acid Biosynthesis: InhibitorsFolic acidDHPSDHFRBacterial Folic Acid Biosynthesis: Inhibitors – Combination TherapySulfamethoxazole inhibits bacterial synthesis of dihydrofolicTrimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting dihydrofolate reductase (DHFR)bacterial synthesis of dihydrofolic acid by competing with para -aminobenzoic acid (PABA) at the 7,8-dihydropteroate synthase (DHPS).dihydrofolate reductase (DHFR).• Pathway inhibition by synergistic use of two drugs that act on different targets within the same pathwayRit d l h l lFolic acid•Resistance develops much more slowly than with either of the components alone• H. influenzae, S. pneumomoniae, Neisseria species, S. aureus; urinary tract infections (Bactrim; $0 15/day)DHPSDHFRtract infections (Bactrim; $0.15/day)Bacterial Folic Acid Biosynthesis: SulfamethoxazoleSulfamethoxazole inhibits bacterial synthesis of dihydrofolicbacterial synthesis of dihydrofolic acid by competing with para -aminobenzoic acid (PABA) at the 7,8-dihydropteroate synthase (DHPS).(Babaoglu et alStructure2004 12 1705)• DHPS is unique to bacteria, not found in mammalian cells(Babaoglu et al., Structure2004, 12, 1705)First Antibiotics: Domagk Discovers Sulfonamides (“Sulfa-Drugs”)Prontosil (red azo dye) Sulfanilamide(Bayer 1935) (1936)Prontosil is a prodrug that is not active in vitro. Cleavage in the tit ti lt tl dtth ti dGerhard J. P. Domagk(Wuppertal, 1895-1964)gastrointestinal tract leads to the active compound sulfanilamide which is competes with p-aminobenzoic acid, the substrate of dihydropteroate synthetase in the bacterial synthetic pathway to folic acid.Worked at Bayer (IG Farben) where he discovered and developed sulfonamides (Prontosil), the first drugs effective against bacterial infections. Nobel Price in Medicine 1939 for discovery of sulfonamides.Bacterial Folic Acid Biosynthesis: TrimethoprimTrimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting dihydrofolate reductase (DHFR)dihydrofolate reductase (DHFR).NAD• DHFR is essential to both bacteria and eukaryotes but trimethoprim isand eukaryotes but trimethoprim is selective for the bacterial targetDHFR(Matthews et al., JBC 1985, 260, 392)NADBacterial Folic Acid Biosynthesis: IclaprimIclaprim• currently in Phase III testing• active against trimethoprim-resistant S. aureus (Phe98->Tyr98)(Hawser et al., Biochem. Pharmacol. 2006, 71, 941)Antibacterial Targets: OverviewCell Division InhibitionFtsZ/ZipABacterial Cell DivisionSeptal ring model for cell division in E. coli:• FtsZ polymerizes and forms a ring in the cytoplasm.Th i b i t d ith th ll b i•The ring becomes associated with the cell membrane via the ZipA protein and FtsA.• Penicillin-binding protein 3 (PBP3) is required for the production of the murein layer at the site of septal division.Ft K i i d f l li ti f th l•FtsK is required for localization of the complex.• The roles for FtsL, N, Q and W are not clear.• TG, transglycosylase.(Hate & DeBoer, J. Bact. 1999, 181, 167)Bacterial Cell Division: FtsZ Polymerization InhibitorsViriditoxin from Aspergillus sp.fermentation broth.Discovered in high-throughput screen of >100,000 microbial and (Stokes et al., JBC 2005, 280, 39709)FtsZ inhibitors discovered in high-throughput screen of ~100,000