**4. Conclusions**

A series of novel *<sup>N</sup>*−benzylisatin−aryl−hydrazones were designed and synthesized with good to moderate yields for their antimicrobial and antiproliferative activity evaluation, for the development of potent anticancer therapeutics with no or minimal side effects. Six bacterial strains and a fungal strain were used for the antimicrobial screening of the synthesized compounds and no inhibitory effect was found on different microbes in concentration up to 100-μg/disc. On the other hand, four compounds showed two−to−four-fold antiproliferative activity than the FDA approved first−line treatments for lung cancer drug gefitinib. For example, IC50 of compound **6c** is 4.35 μM, whereas gefitinib shows 15.23**-**μM concentration against non−small cell lung cancer cell lines 'A549.' In case of HeLa cell lines, antiproliferative activity of compound **6c** also showed two-fold higher than the gefitinib. The strong inhibitory effect of **6c**, among the tested compounds, on the growth of cancerous cells accompanied by their complete safety on the growth of microbial cells, indicate a high level of target selectivity and a unique mechanism of action. Higher predicted ADME values were obtained than the known gefitinib. In our observation, this *<sup>N</sup>*−benzylisatin−aryl−hydrazones can be a potential agen<sup>t</sup> for anticancer therapeutics. Studies on the mechanism of action of antiproliferative activity of these derivative are ongoing and the results will be explored in due courses.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3417/10/11/3669/s1, Figure of the 13CNMR spectra of **6a**–**j**.

**Author Contributions:** Conceptualization, A.F.M.M.R. and H.S.A.-S.; data curation, H.A.A., I.S.I., A.Z.M., A.A. and M.A.; formal analysis, I.S.I., A.Z.M. and M.A.; funding acquisition, H.S.A.; investigation, H.S.A. and A.F.M.M.R.; methodology, H.A.A., I.S.I., A.Z.M., A.A. and M.A.; resources, H.S.A.−S. and A.F.M.M.R.; supervision, H.S.A.−S. and A.F.M.M.R; validation, H.S.A.-S.; writing—original draft, H.S.A.-S. and A.F.M.M.R.; writing—review and editing, H.S.A.−S. and A.F.M.M.R.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the King Saud University, Research Center of the Female Campus for Scientific and Medical Studies.

**Acknowledgments:** This research project was supported by a gran<sup>t</sup> from the research center of the Female Campus for Scientific and Medical Studies, King Saud University, Riyadh, Saudi Arabia.

**Conflicts of Interest:** The authors declare no conflict of interest.
