Figure 1.
Structures of calanquinone A and denbinobin.
Figure 2.
Structural sets used in the pharmacophore study.
CA-1∼CA-11 and 3a-9b are noted as natural and synthesized compounds, respectively.
Figure 3.
Synthetic procedure of phenanthrene derivatives.
Reagents and conditions: (i) DDQ, benzene, RT. (ii) TFA, ether, RT. (iii) Me2SO4, K2CO3, acetone, reflux. (iv) P4-tBu, benzene, 140°C. (v) AgO, 6 N HNO3, acetone, 60°C.
Figure 4.
Synthesis of methoxy-phenanthrenequinones.
Reagents and conditions: (i) MeOH, Fe2(SO4)3, PTSA, 70°C.
Figure 5.
Selective demethylation and acetylation of phenanthrenequinones.
Reagents and conditions: (i) TMSI, CH2Cl2, RT or 60°C. (ii) Ac2O, pyridine, RT.
Figure 6.
Demethylation of phenanthrenes.
Reagents and conditions: (i) AlCl3, benzene, 70°C.
Table 1.
Cytotoxicity data of natural phenanthrenes isolated from C. arisanensis.
Table 2.
Cytotoxicity data of synthesized phenanthrenes.
Figure 7.
The mutual distances of the hydrogen bond triad and the distances between hydrogen bonds and hydrophobic group in the best HypoGen pharmacophore model.
The pharmacophore features are colored with green, as are the hydrogen-bond acceptors (HBA1, HBA2 and HBA3). The hydrophobic aromatic feature (HYD) is denoted in cyan. Distances between features are in Ångström units.
Figure 8.
The best HypoGen pharmacophore model mapping onto calanquinone A (6a) and its derivatives.
The light and dark green represent active and inactive features, respectively. The models mapped with the compounds 6a (A), 6b (B), 7a (C), 7b (D), 5a (E) and 5b (F) are shown here. Pharmacophore features are colored as in Figure 7.
Figure 9.
ChemGPS-NP analysis of calanquinone A (6a) and denbinobin (6b).
Score plot of the three dimensions (principal components 2–4) consisting of PC2 (yellow; aromaticity etc.), PC3 (green; lipophilicity etc.) and PC4 (orange; flexibility/rigidity), from analysis of most potent compounds 6a and 6b as medium seagreen cubes in the ChemGPS-NP model addressed by Rosén et al. in 2009 for prediction of MOA. A reference set of known anticancer agents includes alkylating agents (red), anti-metabolites (lime), proteasome inhibitions (cyan), tyrosine kinase inhibitors (orange), topoisomerase I (blue), topoisomerase II (magenta), and tubulin inhibitors (black).
Figure 10.
Topoisomerase II DNA cleavage assay.
An in vitro assay was used to assess the effect of compounds 6a and 5a on the DNA cleavage activity of human TopoII. Etoposide was the positive control. Control lane: TopoIIα + plasmid DNA. DMSO lane: TopoIIα + plasmid DNA + DMSO.