Design, Synthesis And Biological Evaluation Of Novel Thiadiazine Derivatives As HIV-1NNRTIs

Human Immunodefeciency Virus type1(HIV-1) is the etiologic agent responsible for the onset of the Acquired Immunodeficiency Syndrome (AIDS) which has developed into a worldwide pandemic of disastrous proportions. In the treatment of HIV patients, the non-nucleoside reverse transcriptase inhibitors (NNRTIs) have been widely used for their high selectivity, relatively low toxicity, and potent activity. However, NNRTI therapy is suffered from inevitable emergence of drug resistant virul strains due to the rapid mutations of the residues in RT. Therefore, further development of novel NNRTIs with improved pharmacological and anti-resistance profile is critical for a more successful application of NNRTIs in anti-HIV therapy.DABO and DAPY analogues represented two important and promising classes of HIV-1NNRTIs. They have very potent activities against not only wild virus but also strains with different mutants. And it is worth noting that two compounds of DAPY series have been approved by U.S. Food and Drug Administration.Based on the structural features, binding mode and SAR study of these two pyrimidine containing NNRTIs, we made several modifications of the nucleus and the substituents of the DABO. According to the bioisosterism of drug design, we replaced the4-oxopyrimidine by1,2,6-thiadiazine-1,1-dione ring with an attempt to improve the hydrogen bond between the ligand and amino acids of RT. And we used the substituents which are similar to’wings’of DAPY to keep the key structural requirements that were responsible for potent enzyme inhibition. We chose various substituted aniline, benzylamine, phenylethylamine and aliphatic amine as the groups connecting to the C-3position of thiadiazine in order to explored the effects of linker and steric, electrical, hydrophobic factors. Besides, benzyl and1-naphtylmethyl were used as the substituents of C-5position to form the π-π interaction with Tyr181, Tyr188and hydrophobic interaction with conservative Trp229. Finally, we designed two series novel3,5-disubstituted-1,2,6-thiadiazine-1,1-dione derivatives.We also used the dock module of CADD (Computer Aided Drug Design) software Sybyl-X1.1to evaluate our compounds. The result indicates that the scores of several compounds are very similar to the original ligand TMC125. And the binding mode shows new compounds can overlap the original ligand well. While nearly all these necessary interactions with key residues in the NNIBP (Non-nucleoside inhibitor binding pocket) are remained, new hydrogen bond forms between oxygen atom of sulfone and Lysine101.For the preparation of the two newly designed series, we chose phenylacetyl chloride and1-naphthlcetic acid as the starting material respectively. After reacted with Meldrum’s acid and sulfonamide, the important intermediates5-disubstituted-1,2,6-thiadiazine-1,1,3-trione were obtained by cyclization. Finally, different aromatic or aliphatic amine nucleophilic attack the C-3position connecting a chloride atom which was introduced by POC13involved halogenation reaction, giving the50title compounds (Ⅰa-Ⅰx, Ⅱa-Ⅱz). All of them were identified by MS and ’H-NMR spectral analysis respectively.15specifically chosen compounds were evaluated for their inhibitory activity against RT by colorimetric reverse transcriptase assay. The results indicated that the target compounds showed a wide range of activities against HIV-1. Among them, two compounds Ⅰh and Ⅱh displayed inhibitory activity at the lower micromolar concentration (EC50=5.39and1.54μM, respectively), comparable to that of positive control drug Nevirapine (EC50=1.50μM) and TMC125(EC50=0.55μM). Preliminary SAR analysis indicated that the substitutions at C-2position contributed to antiviral activity in the following order:aniline> benzylamine> cyclopropylamine> phenylethylamine. And the substituents of aniline should be ranked as cyano> chloro->methoxy->bromo-> sulfonylamdie, and para->meta->ortho-in position. In term of substituents of C-5position, the activity of compounds with1-naphtylmethyl is better than that with benzyl. Additionally, all these target compounds are evaluated for their activity against wild&mutated HIV-1and cytotoxicity in MT-4cells, and the result will be obtained as soon as possible.In summary, based on the structural features, binding mode and S AR study of two pyrimidine containing NNRTIs, we designed and synthesized two series of novel1,2,6-thiadiazine-1,1-dione derivatives using the principle of bioisosteric replacement. And the compounds were identified by MS,1H-NMR and13C-NMR spectral analysis. Biological evaluation for their anti-RT activity assay revealed that several compounds were effective at low micromolar concentration, which are worth further investigation and development. The preliminary SAR analysis among the newly synthesized compounds are discussed briefly and rationalized by docking studies. We hope that the knowledge and insight on the NNRTI research learnt from this work will provide valuable information for the development of novel potent NNRTIs.