Natural and Synthetic Derivatives Targeting Microbial and Cancer-Related Key Enzymes

The present study is focused on the isolation and structure elucidation of bioactive natural compounds as well as on the semi-synthesis and synthesis of new derivatives as inhibitors of HIV-1 Reverse Transcriptase, Carbonic Anhydrase, DNA Gyrase, and human Rinoviruses replication. As regards the first target, we found that the EtOAc extract of the Sardinian plant Teucrium flavum subp. glaucum was able to inhibit the HIV-1 RT associated RNase H function. A bioassay-guided fractionation of the extract yielded six secondary metabolites and, among all, the flavone Cirsiliol was the most potent inhibitor of RNase H function with an IC50 of 8.2 μM. Furthermore, the hydrolysis of the inactive Teuflavoside led to one known and three new neo-clerodanes. Among all, Flavuglaucin B was the most potent inhibitor with an IC50 of 9.1 μM. Site-directed mutagenesis and docking studies indicated that Flavuglaucin B bind to the RT allosteric pocket close to RNase H site. Concernig carbonic anhydrases (CAs), the phytochemical investigation of two extracts of the plant Magydaris pastinacea, endowed with inhibitory activity toward this enzyme, resulted in the isolation of one new and fourteen known coumarins. All compounds were selective toward the tumor-associated CA IX and CA XII since none was active against the off target CA I and CA II up the concentration of 100 μM. Some coumarins revealed a strong inhibitory effect toward CA IX and CA XII with Kis in the range of 74.5-5.7 nM. Molecular docking experiments revealed that the most potent coumarin could be hydrolyzed by the Zn2+ activated water molecule of the enzyme cavity and the open compound is stabilized by several hydrogen bonds and π-π interactions in the catalytic site of CA XII. Based on the evidence that the phenylpropanoid (E)-3-(3,4-dimethoxyphenyl)-2-propen-1-yl(Z)-2-[(Z)-2-methyl-2-butenoyloxymethyl)butenoate isolated from Bupleurum fruticosum, behaved as a potent capsid binder, three series of derivatives were synthesized modifying both the phenylpropyl group and the aliphatic ester chain. Interestingly, biological tests revealed that the most part of the synthesized compounds exhibited no cellular toxicity up to 100 μM and showed a reversal of selectivity towards the viral species B, HRV-14. Among all, some of the phenylpiperazine or piperidinylpyridine derivative amides, inhibited the replication of HRV-14 with EC50 values in the low micromolar range. Bacterial DNA gyrase is an interesting target for the discovery of new antibacterial compounds, overcoming bacterial resistance, insufficient penetration and effluxing and boosting antibacterial activity. Based on this evidence, Ciprofloxacin, a well known Gyrase A inhibitor, was combined with benzothiazole-based gyrase B inhibitors. All dual compounds displayed potent antibacterial activity against E.coli due to the interaction of the hybrids with the GyrA and/or topoisomerase IV vi ParC subunits, while inhibition of GyrB was not strong enough to provide a substantial contribution to the observed antibacterial activity.