Natural and Nature Inspired Compounds Targeting the Replication Cycle of RNA Viruses and GABAA Receptor

In the PhD work, a bioassay-guided approach was used to isolate bioactive secondary metabolites from four different plants. Two Indian plants namely, O. sanctum and T. cordifolia were studied targeting HIV-1 RT associated RNase H function. Among the twenty one secondary metabolites isolated from these plants, the triterpenoids Ursolic acid and Lupeol were the most potent inhibitors of RNase H function with a IC50 of 5.5 ± 0.3 µM and 5.9 ± 0.24 µM, respectively. Rabdosiin, from O. sanctum, was found as a most potent natural compound against RNase H (IC50= 2.16 ± 0.11µM). Also, Rabdosiin was able to inhibit RDDP function (IC50= 4.0 ± 0.8) of reverse transcriptase, resulted as a dual inhibitor of HIV-1 RT. Using tetradecyl ferulate as lead compound, a series of ferulic acid and caffeic acid esters and amides were synthesized. Newly synthesized compounds resulted as dual inhibitor of HIV-1 RT. Molecular modeling studies, together with Yonetani-Theorell analysis, demonstrated that one of the most active compounds, n-oleyl caffeamide, is able to bind both RNase allosteric site and NNRTI binding pocket. Bioguided isolation of the anti-Human Rhinovirus (HRV) DCM extract of Bupleurum fruticosum L., a plant growing in Sardinia, gave ten compounds. Among all, Fruticotriol and (-)-Eucamanol are new to the literature. An ester of 3,4-dimethoxycinnamyl alcohol was found the most active metabolite inhibiting the replication of HRV 39 serotype with an EC50 of 0.9 µg/mL with moderate toxicity (CC50 = 7.6 µg/mL). A time-of-drug addition assay suggested that the ester of 3,4-dimethoxycinnamyl alcohol behave as capsid binder towards HRV39 and also acts by another mode of action, probably based on the uncoating of viral genome. The methanol extract of Withania somnifera was studied for its GABAA modulation activity. Two new compounds named Withasomniferolide A and Withasomniferolide B have been isolated besides seven known compounds. Among all, docosanyl ferulate showed positive modulation of GABAA receptor while octadecyl ferulate and withasomniferolide B have shown negative modulation. In summary, this PhD work permitted to discover some natural and natural-derived compounds that may offer a new class of interesting lead compounds for further optimization.