4.4.4. Benzo[*a*]pyran[2,3-*c*]phenazine Derivatives

This class of phenazine derivatives, which contain phenazine, pyran and benzo core, possess grea<sup>t</sup> anticancer activity but rarely reported. Inspired by **XR11576** (Figure 1), benzophenazine derivative has been proved to be a grea<sup>t</sup> antitumor compound which could be further modified. Gao et al. synthesized a series of benzo[*a*]pyran[2,3-*c*] phenazine derivatives and evaluated their biological activities. Some of them (compounds **188**–**191**) are listed in Figure 20. Among these compounds, **189** and **191** possessed a *p*-dimethylamino substituted group in benzo ring and the apparent differences between their structures possessed cyan group and ethyl acetate group, respectively, in 3-position of *γ*-pyran ring. Compared to the positive control drug (hydroxycamptothecin), **189** showed better inhibition activity against tested cancer cell line HepG2. However, **191** demonstrated no inhibitory activity against all selective cell lines. These experimental data proved that cyan group played an important role in antiproliferative activity: **189** and **190**, possessing a *p*-dimethylamino group and *p*-hydroxyl group, respectively, demonstrated some cytotoxic activity to HCT116 cell line, IC50 of 0.22 μM and 15.32 μM, respectively; **189** showed cytotoxic activity against HepG2 cell line with IC50 of 6.71 μM; **188**–**191** showed weak or no activity against MCF-7 and A549 cell lines. SAR studies showed that cyan group and *p*-dimethylamino group played a significant role in antiproliferative activity and resulted in the decrease of cytotoxic activity [79].

**Figure 20.** The chemical structures of compounds **188**–**191**.

#### 4.4.5. Benzo[*a*]chromeno[2,3-*c*] phenazine Derivatives

Chromenes are also an important class of heterocyclic compounds which exhibit attractive pharmacological properties, such as antitumor, anti-vascular, antioxidant, antimicrobial, sex pheromone, tumor necrosis factorα (TNFα) inhibitor, cancer therapy and central neuroprotective activities [80]. Chromenes and phenazine derivatives both have attracted attention, but benzo[*a*]chromeno[2,3-*c*] phenazine derivatives have rarely been investigated [81].

Reddy et al. synthesized a series of phenazine-chromene hybrid molecules by protocol of one pot multi-component reaction. Compounds **192**–**194** (Figure 21) showed excellent in vitro antioxidant activity which was benefit to the treatment of cancer and prevention of cardiovascular diseases. Compared with anticancer drugs etoposide and camptothecin, **192**–**194** showed similar antiproliferative activity against selective cancer cell lines with IC50 values of 3.28 μM, 4.31 μM and 4.01 μM against HeLa cell line and 2.24 μM, 3.81 μM and 3.12 μM against SK-BR-3 cell line, respectively. These compounds did not show significant toxicity against normal human breast cells (HBL 100) at lower concentrations [19].

**Figure 21.** The chemical structures of compounds **192**–**194**.

#### 4.4.6. Derivatives Derived from 2-Phenazinamine

Inspired by previous reports, Gao et al. isolated a natural derivative derived from 2-phenazinamine, showing high cytotoxicity against selective cancer cell lines. A series of 2-phenazinamine derivatives, including compounds **195**–**202** (Figure 22), were synthesized. The antiproliferative activity results showed that IC50 values of **195** and **197** against HepG2 cell line were 16.46 μM and 15.21 μM, respectively. IC50 values of **195** and **198** against K562 cell line were 33.43 μM and 49.20 μM, respectively. In addition, IC50 value of **196** against MCF-7 cell line was 11.63 μM. Notably, these active compounds showed no cytotoxicity on the epithelial cells from the 293T non-cancer cells. Moreover, mechanism of **195** was similar to control drug (cisplatin), inhibiting cancer proliferation by inducing apoptosis [82].

**Figure 22.** The chemical structures of compounds **195**–**202**.

According to the report of Gao et al., Kale et al. selected some 2-phenazinamines derivatives and further utilized computational methods to investigate their protein targets. The experimental data of **199**–**202** showed grea<sup>t</sup> binding energy against BCR-ABL tyrosine kinase by Autodock 4.2. Scores of **199**–**202** were −7.6 kcal/mol, −8.8 kcal/mol, −7.2 kcal/mol and −7.1 kcal/mol, respectively. In addition, the score of imatinib was −8.7 kcal/mol. All the computational data showed 2-phenazinamine derivatives would be inhibitors against BCR-ABL tyrosine kinase and needed to be further investigated [25].

#### 4.4.7. Derivatives Derived from 2,3-Diaminophenazine

Protein kinases (PKs) are essential in many cellular processes, which catalyze phosphorylation of different cellular substrates. Then, phosphorylation in turn regulates various cellular functions. Normally, their activity is strictly regulated. Under pathological conditions, PKs can be deregulated, leading to changes in the phosphorylation, resulting in uncontrolled cell division, inhibiting apoptosis and other abnormalities. Various cancers are known to be caused or accompanied by deregulation of the phosphorylation. Screening new potent, selective and less toxic compounds to inhibit PKs has been proved to be a promising cancer treatment strategy [83].

Mahran et al. prepared some phenazine derivatives, such as compound **203** and its analogues (Figure 23). Among these derivatives, compounds **203**–**207** displayed antiproliferative activity with IC50 values of 8.8 μM, 7.7 μM, 8.4 μM, 6.8 μM and 8.8 μM against A549 cell line and 6.0 μM, 4.4 μM, 5.2 μM, 16 μM and 6.8 μM against HCT116 cell line, respectively. These compounds also showed inhibitory activity of human tyrosine kinases. The experimental results of inhibiting human tyrosine kinase were consistent with cell cytotoxicity activity [20].

**Figure 23.** The chemical structures of compounds **203**–**207**.
