Privileged Scaffold Hybridization in the Design of Carbonic Anhydrase Inhibitors

Abstract

Human Carbonic Anhydrases (hCA) are enzymes that contribute to cancer's development and progression. Isoforms IX and XII have been identified as potential anticancer targets, and, more specifically, hCA IX is overexpressed in hypoxic tumor cells, where it plays an important role in reprogramming the metabolism. With the aim to find new inhibitors towards IX and XII isoforms, the hybridization of the privileged scaffolds isatin, dihydrothiazole, and benzenesulfonamide was investigated in order to explore how it may affect the activity and selectivity of the hCA isoforms. In this respect, a series of isatin thiazolidinone hybrids have been designed and synthesized and their biological activity and selectivity on hCA I, hCA II, hCA IX, and hCA XII explored. The new compounds exhibited promising inhibitory activity results on isoforms IX and XII in the nanomolar range, which has highlighted the importance of substituents in the isatin ring and in position 3 and 5 of thiazolidinone. In particular, compound 5g was the most active toward hCA IX, while 5f was the most potent inhibitor of hCA XII within the series. When both potency and selectivity were considered, compound 5f appeared as one of the most promising. Additionally, our investigations were supported by molecular docking experiments, which have highlighted the putative binding poses of the most promising compound.

Keywords: benzenesulfonamide-based zinc binders; carbonic anhydrases inhibitors; scaffold hybridization.

Figure 1

Representative previously reported compounds and design of 5a–i derivatives obtained by combining different fragments of biologically active molecules.

Scheme 1

Reaction conditions: (a) hydrazine monohydrate, MW, 40 min; (b) phenyl isothiocyanate, ethanol, reflux, overnight; (c) ethyl bromoacetate, sodium acetate, ethanol, reflux, 4 h; (d) appropriate isatin, sodium acetate, acetic anhydride, and acetic acid, reflux for 16 h.

Figure 2

HMBC spectrum of compound 4. In the horizontal axis, the ¹H NMR spectrum is shown, and, in the vertical axis, the ¹³C NMR is shown. The significative coupling between NH with carbons is highlighted in blue.

Figure 3

HMBC spectrum of compound 3. In the horizontal axis, the ¹H NMR spectrum is shown, and, in vertical axis, the ¹³C NMR is shown. No coupling was observed.

Figure 4

Putative binding mode of ZZ-5f (yellow sticks, panel (A)) and ZE-5f (pink sticks, panel (D)) on hCA IX (5FL4). Panels (B,C) show 3D and 2D interactions of compound ZZ-5f in the hCA IX catalytic site. Panels (E,F) show 3D and 2D interactions of compound ZE-5f in the hCA IX catalytic site.

Figure 5

Putative binding mode of ZZ-5f (yellow sticks, panel (A)) and ZE-5f (pink sticks, panel (D)) on hCA XII (5MSA). Panels (B,C) show 3D and 2D interactions of compound ZZ-5f in the hCA XII catalytic site. Panels (E,F) show 3D and 2D interactions of compound ZE-5f in the hCA XI catalytic site.

Figure 6

Putative binding mode of ZZ-5f (yellow sticks, panel (A)) and ZE-5f (pink sticks, panel (D)) on hCA II (3F8E). Panels (B,C) show 3D and 2D interactions of compound ZZ-5f in the hCA II catalytic site. Panels (E,F) show 3D and 2D interactions of compound ZE-5f in the hCA II catalytic site.