Convenient Synthesis and Anticancer Activity of Methyl 2-[3-(3-Phenyl-quinoxalin-2-ylsulfanyl)propanamido]alkanoates and N-Alkyl 3-((3-Phenyl-quinoxalin-2-yl)sulfanyl)propanamides

[Image: see text] A series of methyl 2-[3-(3-phenyl-quinoxalin-2-ylsulfanyl)propanamido]alkanoates and their corresponding hydrazides and N-alkyl 3-((3-phenylquinoxalin-2-yl)sulfanyl)propanamides were prepared on the basis of the chemoselective Michael reaction of acrylic acid with the parent substrate 3-phenylquinoxaline-2(1H)-thione. The parent thione was produced by a convenient novel thiation method from the corresponding 3-phenylquinoxalin-2(1H)-one. The chemical structures of the newly synthesized compounds were confirmed by elemental analyses, (1)H and (13)C NMR. The antiproliferative activity of the synthesized compounds was tested against human HCT-116 and MCF-7 cell lines. Out of 25 screened derivatives, 10 active compounds exhibited IC(50)’s in the range 1.9–7.52 μg/mL on the HCT-116, and 17 active compounds exhibited IC(50)’s in the range 2.3–6.62 μg/mL on the MCF-7 cell lines compared to the reference drug doxorubicin (IC(50) 3.23 μg/mL). The structure–activity relationship of the tested compounds was studied through their binding affinity to the human thymidylate synthase allosteric site in silico using molecular docking and proved the quinoxaline ring as a suitable scaffold carrying a peptidomimetic side chain in position 3.