Design and Synthesis of Zanamivir Derivatives against Influenza Virus Neuraminidase
Date Issued
2009
Date
2009
Author(s)
Wen, Wen-Hsien
Abstract
Influenza remains a major health problem. The worldwide occurrences of the fatal H5N1 avian flu and the recent outbreak of the new type H1N1 flu (swine flu) have increased public awareness of the potential global influenza pandemics. Oseltamivir phosphate and zanamivir are popular drugs for the treatment of influenza. Both drugs inhibit influenza virus propagation by cleaving the linkage between the progeny virus from the surface sialo-receptor of host cells. However, the emergence of drug-resistant influenza viruses has also caused another problem in medical treatment. In comparison, oseltamivir phosphate is more susceptible to the newly evolved resistant viruses than zanamivir. However, zanamivir is made in powder for administration by nasospray in low bioavailability, thus modification of zanamivir to improve its therapeutic use has been pursued. In this thesis, we designed and synthesized novel zanamivir derivertives to improve activities against influenza virus. Part I: Based on the report that N1 neuraminidase contains a cavity adjacent to their active site that closes on ligand binding, we designed and synthesized a series of zanamivir derivatives 12−24 possessing substituents on 4-guanidino groups. Among these compounds, compound 12 exhibited the best inhibitoin against influenza (IC50 = 2.15 μM, EC50 = 0.77 μM). In order to improve the activity, we designed 65, an analog of 12 with reduced entropy, as a new inhibitor. So far, we have been unable to synthesize 65 due to its highly reactive carbon−carbon double bond. Part II: We prepared several zanamivir analogs 79−81 by conjugation of zanamivir with porphyrin in a ratio of 4:1. These analogs in general are less potent than zanamivir in inhibition of influenza virus neuraminidase, but they are significantly more potent than zanamivir in inhibition of the proliferation of influenza viruses. The enhanced anti-influenza properties of these analogs are thought to be due to the synergistic effect on neuraminidase inhibition and viral inactivation. The influenza virus inactivation is contributable to porphyrin, which is brought to close proximity of viral particle by the binding of Zanamivir with neuraminidase, to generate cytotoxic singlet oxygen to destruct the virus on irradiation (850 Lux). After illumination of influenza viruses for 0.5 h by stronger LED light (10,000 Lux), in the presence of 81 at 30 pM, the influenza virus titer is reduced by 95%. We also confirm that influenza virus neuraminidase undergoes cross-linking to generate dimeric or aggregate of high molecular weight by photo-sensitization of 81. Part III: The phosphonate group is generally used as a bioisoster of carboxylate in drug design. In comparison with the carboxylate−guanidinium ion pair, a phosphonate ion exhibits stronger electrostatic interactions with the guanidinium ion. In 2007, Shie and coworkers has synthesized Tamiphosphor, the phosphonate congener of Tamiflu , to show better anti-influenza activity than GS4071. We thus aim to synthesize a target compound 116, which is a phosphonate analog of zanamivir by different approaches. So far, synthesis of 116 using indium-mediated allylation or iodine-promoted phosphorylation is unsatisfactory. On the other hand, using sialo-lactone 134 as a precursor may be a better strategy to prepare the target compound 116. Part IV: We have successfully prepared the zanamivir−dansyl conjugate 142 and zanamvir−biotin conjugate 143 as novel sensor molecules. We have demonstrated that 143 has high affinity with influenza virus neuraminidase and is localized on the surface of virus-infected cells. Conjugates 142 and 143 may be used in detection, purification, analysis and high-throughtput screening of neuraminidase as well as in neuraminidase kinetic study. Furthermore, we believe that the high affinity between zanamivir conjugate and neuraminidase may be applied to study the subjects in cell biology and drug delivery.
Subjects
influenza virus
neuraminidase
zanamivir
PDT
Type
thesis