## 4 Conclusions  
The synthesis of dipyridothiazine dimers with an \(m\)-xylene moiety is presented in the light of a comparative analysis with their anticancer active analogs containing a lutidine linker in their structure. The structure of the new compounds was clearly confirmed by the NMR and HRMS spectroscopic techniques. The compounds were subjected to initial in silico screening using the Way2 Drug server to determine the molecular targets and the likelihood of cytotoxicity against various types of cancer cells. In the next stage, cytotoxicity tests were performed against normal cell lines (HaCaT) and five cancer cell lines (SW480, SW620, MDA-MB-231, A-549, and LN-229), which showed weak anticancer activity and low cytotoxicity compared to the previously described structural analogs with the lutidine system. Quantum mechanical calculations of the electron density and bond length were performed to elucidate the structural differences that directly affected the conformation of the molecule, as well as interactions with the molecular targets. In addition, preliminary molecular docking studies were performed on histone deacetylase, showing different binding sites to the selected molecular target. Quantum mechanical calculations and molecular docking explained the anticancer activity research results to some extent.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14167263/s1](https://www.mdpi.com/article/10.3390/app14167263/s1)]([https://www.mdpi.com/article/10.3390/app14167263/s1](https://www.mdpi.com/article/10.3390/app14167263/s1)), File S1: Supporting materials on spectral analysis of all compounds and the results of quantum mechanical calculations are included.  
Figure 7: Position of dimer **8a** in the binding pocket obtained using DifffDock docking and the interaction with amino acids, which are indicated by black dashed lines. The dark-blue sphere indicates the zinc atom. The orange sticks indicate the following amino acids: Phe168, Phe277, His153, and His198.  
**Author Contributions:** Conceptualization, B.M.-M. and E.M.; methodology, E.M., P.S.-L., M.S., K.Z., A.K. and W.B.; software, E.M., B.M.-M., M.J., P.S.-L., M.S., K.Z., A.K. and W.B.; validation, E.M.; formal analysis, E.M., B.M.-M., M.J., P.S.-L., M.S., K.Z., A.K. and W.B.; investigation, E.M. and B.M.-M.; resources, E.M., B.M.-M., M.J., P.S.-L., M.S., K.Z., A.K. and W.B.; data curation, E.M. and B.M.-M.; writing--original draft preparation, E.M. and B.M.-M.; writing--review and editing, B.M.-M., E.M. and M.J.; visualization, B.M.-M.; supervision, E.M. and B.M.-M.; project administration, B.M.-M.; funding acquisition, E.M. and B.M.-M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** [PERSON] was supported by a research subsidy from the Medical University of Silesia in Katowice (grant BNW-2-015/N/3/F, BNW-2-051/K/4/F); A.P.C. was funded by the Metropolis of Upper Silesia and Zaglebie Basin as part of the implementation of the project entitled \"Support for scientific activity of doctoral students and employees at the doctoral level of the Silesian Medical University in Katowice\", which was implemented within the framework of the Metropolitan Science Support Fund program for 2022-2024 (grant agreement nos. RW/27/2024 and PCTT/621/2024).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article and Supplementary Materials.  
**Conflicts of Interest:** The authors declare no conflicts of interest.