Discovery and structural elucidation of novel antioxidant Scoparioate A from Artemisia scoparia using spectroscopic analysis and DFT computational techniques

The Artemisia scoparia Waldst. & Kit plant powder was extracted using methanol. Ethyl acetate, chloroform, and n-hexane were used to separate the crude methanolic extract. Two known chemicals α-amyrin (2) and scopoletin (3), and one new aromatic ester, Scoparioate A (1), were isolated from the chloroform fraction. Clarification of the structures of the separated compounds was achieved using spectroscopic analysis. The test compound 1 exhibited potent antioxidant potential by scavenging more than 80% of the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) radicals at a dose of 70 µg/mL. Using the 6-311++g(d,p) Density Functional Theory (DFT) approach, the geometry was optimised using the B3LYP approach. Also, to implement the Frontier Molecular Orbital's (FMO) intentions at the TD-DFT level, the same methodology (B3LYP) and basis set were employed. The test compound has higher ionisation potential (I) value (7.272), in comparison to electron affinity (A) value (1.639 eV). This study demonstrated the examined compound's exceptional ability to donate electrons, which is attributed to the HOMO-LUMO energies. The compound has high value (i.e. 3.524) of global electrophilicity (ω), having greater tendency towards nucleophile, because the electrophile accepts electrons. Moreover, the Nuclear Magnetic Resonance (NMR) and Ultra Violet (UV) spectroscopic experimental data was in agreement with the DFT computational data generated for an isolated molecule. There was a perfect correlation between the experimental and theoretical UV and ¹H NMR results.