Synthesis and characterization of phenanthrene derivatives with anticancer property against human colon and epithelial cancer cell lines

A variety of polycyclic aromatic hydrocarbons have been synthesized and structurally characterized in our laboratory. Phenanthrene derivatives were efficiently prepared in excellent yields and high purity via a two-step sequence. Heck coupling yielded the corresponding diarylethenes, followed by classical oxidative photocyclization to achieve the expected phenanthrenes. First, we envisioned to synthesize a variety of substituted phenanthrenequinones. Second, we investigated the possibility of a dibenz[a,c]phenazine formation by addition of o-phenylenediamine after completion of the oxidation process. Moreover, because phenanthrenequinones are available so simply, it is likely that other uses will be found for these compounds. For example, 9,10-phenanthrenequinone can be sequentially reduced, alkylated, acetylated, and sulfonated. All the synthesized derivatives were evaluated for cytotoxic activity in vitro against the human epidermoid carcinoma epithelial cells Hep-2 and human colon carcinoma cells Caco-2 using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. From the structure–activity point of view, position and nature of the electron donating and electron withdrawing functional groups attached to the phenanthrene skeleton may contribute to the anticancer action. Interestingly, the analysis of the IC₅₀ values suggests that most compounds exerted cytotoxic effects with selectivity against both cancer cells. Among them, methyl 8-methyl-9,10-phenanthrenequinone-3-carboxylate 11d showed the highest potency with IC₅₀ values of 2.81 and 0.97 μg/mL.