Design Of Fluoro-furoxan Derivatives Targeting Schistosoma Japonicum TGR And N-oxide Moiety Restricts The Conformation Of Short Peptides

1.Design of Fluorofuroxan Derivatives Targeting Schistosoma japonicum Thioredoxin-Glutathione Reductase(TGR)Schistosoma is a major neglected tropical epidemic that is prevalent in 78 countries and regions around the world.About 261 million people are infected with schistosomiasis and 600 million individuals are at risk of infection.However,the treatment of schistosomiasis relies solely on praziquantel,which may accelerate the development of drug-resistant parasites.Therefore,it is of great significance to find drugs that can replace praziquantel in the treatment of schistosomiasisDavid L Williams et al identified that oxadiazole 2-oxide(furoxan)can inhibit TGR activity through quantitative high-throughput screening.Furoxan kills schistosomiasis at different growth stages in the body,and its activity is better than praziquantel,but unfortunately furoxan has serious cell cytotoxicity.In this work,furoxan is used as the parent compound for structural modification.The design of the compound mainly includes the introduction of different substituents in the meta and para positions of the benzene ring,and the replacement of the cyano group on the right side of furoxan with different groups which contain fluorine atom.The fluorine atom may change the compound's efficacy and pharmacokinetic properties.Based on the above concepts,this subject used cinnamic acid or benzaldehyde as the starting material,and synthesized 37 novel fluorine-containing compounds through esterification or Wittig-Horner reaction,reduction reaction,cyclization reaction,esterification reaction,and nucleophilic substitution reaction.Furoxan derivatives have been characterized by 1H-NMR,13C-NMR and HRMS.The compound 4b,7d,7h and 7i have good inhibitory activity against recombinant SjTGR selenium protease(SjTGR-Sec)of Schistosoma japonicum in vitro,laying the foundation for the development of anti-schistosomiasis drugs.2.N-oxide moiety restricts the conformation of short peptidesN-oxide is a kind of special functional group.The uneven distribution of electrons results in the oxygen atom being partially negatively charged,suggesting that the oxygen atom has a strong proton binding ability and can be used as a hydrogen bond acceptor in short peptides.N-oxide is competitive binding with jacent amide proton with carbonyl oxygen,and restrict the conformation of the short peptide.The previous studies introduced N-oxide into amino acids or short peptides by oxidizing the nitrogen atoms of proline residues.However,proline residues are important inducers of peptide folding,yielding secondary structures with ?-tum or a-helix character.In order to eliminate the proline residue on the conformation of N-oxide peptide(NOP),we design and synthesis glycine N-oxide peptide(g-NOP)for the first time,proline N-oxide peptide(p-NOP)was also synthesized for comparison and for further exploration.In the previous work,our research group confirmed that the N-oxide in p-NOP and g-NOP can both formed a six-membered ring intramolecular hydrogen bond with jacent amide proton through DMSO-d6 titration experiment,concentration dependent experiment,two-dimensional nuclear magnetic hydrogen spectrum,single crystal data and simulation calculation.In this work,the stability of the intramolecular hydrogen bond in protic solvents is further explored through the CD3OH titration experiment.The experimental results confirm that the intramolecular hydrogen bonds in p-NOP4 and g-NOP9 can be stable in CD3OH,while the intramolecular hydrogen bond in g-NOP12 was destroy,this may relate to the extremely high solubility of g-NOP12 in methanol.The results of the variable temperature nuclear magnetic experiment indicate that the sequence of intramolecular hydrogen bond strength was p-NOP>g-NOP9>g-NOP 12,consistent with the results of CD3OH titration experiment,which is confirmed that the proline ring can increase the strength of hydrogen bonding.The research in this subject confirmed that the NOP has a completely different secondary structure from the normal peptide.The strong electron-withdrawing of the N-oxide restricts the formation of a short peptide into a helical conformation.Therefore,N-oxide is an effective tool for restricting the conformation of short peptides.