Activity of Thiazine substituted 9-anilinoacridines against Corona virus (COVID19): An In-silico approach

CoronavirusDisease2019 (COVID-19), a life-threatening viral disease affected irst in Wuhan, China, and quickly spread to more than 200 countries in the world in the year 2020. So many scientists are trying to discover novel drugs and vaccines for coronavirus and treatment for COVID-19. In the present article, in-silico studies have been performed to explore the bindingmodes of Thiazine substituted 9-anilinoacridines (1a-z) against SARS CoV 2main protease (PDB id 5R82) targeting the coronavirus using Schrodinger suit 2019-4. The molecular docking studies are performed by Glide module, in-silico ADMET screening was performed by Qik prop module, and the binding free energy of ligands was calculated using PRIME MM-GB/SA module of Schrodinger suite 2019-4, Maestro 21.2 version. From the in-silico results, Thiazine substituted 9-anilinoacridines like 1m, 1j, 1s and 1b are signi icantly active against SARS CoV 2 main protease with Glide score more than -5.4 when compared with the currently recommended drug for COVID19, Hydroxychloroquine (G score -5.47). The docking results of the Thiazine substituted 9-anilinoacridines exhibited similarmode of interactionswith COVID19 and the residues GLN19, THR24, THR25, THR26, LEU27, HIE41, SER46, MET49, ASN142, GLN143, HIE164, MET165, ASP187, ARG188 and GLN189, play a crucial role in binding with ligands.


INTRODUCTION
The coronavirus Disease 2019 , a lifethreatening viral disease, Gu et al., 2020) which affected irst in Wuhan, China and spread throughout the world (Holshue et al., 2020;To et al., 2020). According to the data from WHO, as on June 2 nd week of 2020, more than 76 lakh people in the world affected by COVID19, out of these more than 4.3 lakhs peoples have died (Lu et al., 2020;Zhou et al., 2020). With more asymptomatic infections being found among COVID-19 cases (Zhou et al., 2020;Huang and Herrmann, 2020), with the details and understanding of the transmission of SARS-CoV, MERS-CoV, and SARS-CoV-2 and discussion of the pathogen inactivation methods are essential (Zhang et al., 2020).
Amsacrine which is a 9-anilinoacridine derivative with primary DNA-inter collating agent, which is more signi icant and the chromophore intercalates with DNA base pairs (Rastogi et al., 2002;Kalira-jan et al., 2012a). Likewise, thiazine derivatives also reported for various biological activities (Sondhi et al., 2005;Plouvier et al., 1994) like antimicrobial (Kalirajan et al., 2009), anticancer (Kalirajan et al., 2019a) analgesic, antiin lammatory (Sondhi et al., 2005), antimycobacterial (Indumathi et al., 2009) As a part of our ongoing research (Kalirajan et al., 2011(Kalirajan et al., , 2019b on searching the potent biological molecules against various disease by in-silico (Kalirajan et al., 2017a,b) and wet lab methods Kalirajan et al. (2018a) we have designed some thiazine substituted 9-anilinoacridines (1a-z) against COVID19 (PDB id -5R82) targeting corona virus using Schrodinger suit 2019-4.  Using different modules (Glide, Qikprop and Prime) of Schrödinger suite LLC various computational methods like molecular docking, ADMET screening and binding free energy calculations were performed to ind the interactions responsible for COVID19 inhibition. The outcomes of the research that the recently designed Thiazine substituted 9anilinoacridines showed signi icant hindrance with COVID19. These studies will provide the requirement of critical structural features in the design of potential drug candidates against COVID19.

MATERIALS AND METHODS
The 3D crystal structure of COVID19 protein called SARS-CoV-2 primary protease receptor co-crystallized with 6-(ethylamino) pyridine-3-carbonitrile (PDB ID: 5R82, Resolution: 1.31 Å) was retrieved from the RSCB protein data bank. The protein was prepared using the protein preparation wizard of an epic module (Sastry et al., 2013) of Schrödinger suite 2019-4. The protein structure is a monomer, having similar binding sites were removed with deleting waters, re ining bond orders and addition of hydrogens. Missing chain atoms are included by (Jacobson et al., 2004) using Prime module of Schrödinger suite 2019-4.
Protein-energy minimization was performed using OPLS3 (Optimized Potentials for Liquid Simulations) molecular force ield with RMSD of crystallographic heavy atoms kept at 0.30 Å. A grid box was generated to de ine the centroid of the active site.
All the compounds were docked into catalytic pocket The energy for minimized XP docked pose of the ligand-receptor complex was calculated using the OPLS3 force ield and generalized-Born/surface area (GB/SA) continuum VSGB 2.0 solvent model (Li et al., 2011).

RESULTS AND DISCUSSION
Results are summarized in Tables 1 and 2 and Fig- The docking studies of the ligands to COVID19 protein active sites were performed by an advanced molecular docking program Glide module of Schrodinger suite 2019 Maestro-12.2 version for determining the binding af inities of the compounds. The designed analogues were docked towards the COVID19 (PDB id: 5R82) to ascertain their inhibitory activity. The analogues show the best-it Root Mean Square Difference (RMS) value of 0.18.
As shown in Table 1, it is demonstrated that thiazine substituted 9-anilinoacridines like 1m, j, s, b are signi icantly active against COVID19 with Glide score more than -5.4 when compared with the currently recommended drug for COVID19 Hydroxychloroquine (G score -5.47). The above compounds have good af inity to the receptor due to more lipophilic character and also due to hydrogen bonding interactions.
The ADMET screening for the molecules can be predicted in-silico by using qikprop module of Schrödinger suite 2019-4. From the in-silico, ADMET screening results of all the compounds are within the recommended values.
Molecular docking was additionally assessed with MM-GBSA free restricting vitality which is identi ied with the post scoring approach for COVID19 (PDB ID: 5R82) target. From the results of MM-GB/SA studies Table 2 the dG bind values were observed in the range of -22.90 (1h) to -56.797 Kcal/mol (1n) and also dGCoulomb, dG vdw values, dG lipophilic values and the energies are positively contributing towards total binding energy.
The accuracy of docking is con irmed by examining the lowest energy poses predicted by the scoring function. The docking of ligands obtains the Glide score, and MM-GBSA free energy into the coupling pocket is more stable.

CONCLUSIONS
From the results of docking study that the Thiazine substituted 9-anilinoacridines like 1m, j,s, b demonstrated better arrangement at a dynamic site of the COVID19 protein. The in-silico structuring strategy embraced in the present investigation helped for recognizing some lead molecules such as 1m,j, s, b and furthermore may somewhat clarify their beneicial impact for the further determinations like in vitro and in vivo assessments.
Results from the in-silico study revealed that many of the Thiazine substituted 9-anilinoacridines like 1m, j, s, may be useful against COVID19and are probably going to be helpful after further re inement. tion. A bioinformatics analysis based on single-cell transcriptomes. Posted online January 30, bioRxiv 927806. Zhou, P., Yang, X. L., Wang, X. G. 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature.