Flavokawain B (1) is a natural chalcone extracted from the roots of Piper methysticum, and has been proven to be a potential cytotoxic compound. Using the partial structure of flavokawain B (FKB), about 23 analogs have been synthesized. Among them, compounds 8, 13 and 23 were found in new FKB derivatives. All compounds were evaluated for their cytotoxic properties against two breast cancer cell lines, MCF-7 and MDA-MB-231, thus establishing the structure–activity relationship. The FKB derivatives 16 (IC50 = 6.50 ± 0.40 and 4.12 ± 0.20 μg/mL), 15 (IC50 = 5.50 ± 0.35 and 6.50 ± 1.40 μg/mL) and 13 (IC50 = 7.12 ± 0.80 and 4.04 ± 0.30 μg/mL) exhibited potential cytotoxic effects on the MCF-7 and MDA-MB-231 cell lines. However, the methoxy group substituted in position three and four in compound 2 (IC50 = 8.90 ± 0.60 and 6.80 ± 0.35 μg/mL) and 22 (IC50 = 8.80 ± 0.35 and 14.16 ± 1.10 μg/mL) exhibited good cytotoxicity. The lead compound FKB (1) showed potential cytotoxicity (IC50 = 7.70 ± 0.30 and 5.90 ± 0.30 μg/mL) against two proposed breast cancer cell lines. It is evident that the FKB skeleton is unique for anticancer agents, additionally, the presence of halogens (Cl and F) in position 2 and 3 also improved the cytotoxicity in FKB series. These findings could help to improve the future drug discovery process to treat breast cancer. A molecular dynamics study of active compounds revealed stable interactions within the active site of Janus kinase. The structures of all compounds were determined by 1H-NMR, EI-MS, IR and UV and X-ray crystallographic spectroscopy techniques.

A chalcone derivative, (E)-3-(2,3-dimethoxyphenyl)-1-(5-methylfuran-2-yl)-prop-2-en-1-one (DMMF) was synthesized and evaluated against various cancerous cell lines including colon adenocarcinoma (HT-29), myloplasticleukemia (HL60), breast cancer (MCF-7 and MDA-MB231), normal hepatic cell (WRL-68) and normal breast cell (MCF-10A). The structure of DMMF was determined by EI-MS, 1H NMR and single X-ray crystallographic techniques. The DMMF possessed the highest cytotoxic effect against MCF-7 breast cancer cell (2.01 ± 1.53 μg/mL) and lowest against normal hepatic WRL-68 and breast cell lines after 24 h of treatment. Induction of apoptosis and regulation of cell cycle progression results indicates the significant increase in early apoptosis and G2/M arrest after 48 h of treatment in MCF-7 cells. Meanwhile, in MDA-MB231 cells, there was an increase in Sub G0/G1 cells population and early/late apoptotic cells upon treatment with DMMF. Additionally, DMMF effectively induced G2/M cell cycle arrest in MCF-7 cells and apoptosis in both MCF-7 and MDA-MB231 cells.