¹H NMR-Based Biochemometric Analysis of Morus alba Extracts toward a Multipotent Herbal Anti-Infective

Mulberry Diels–Alder-type adducts (MDAAs) derived from the white mulberry tree were discovered recently as dual inhibitors of influenza viruses and pneumococci. For the development of a natural product based remedy for respiratory infections, the aim was to (i) identify the most prolific natural source of MDAAs, (ii) develop a protocol to maximize the content of MDAAs in Morus alba extracts, (iii) unravel constituents with the highest anti-infective potential within multicomponent mixtures, and (iv) select and characterize a hit extract as a candidate for further studies. Validated quantitative UPLC-PDA analysis of seven MDAAs (1–7) revealed the root bark as the best starting material and pressurized liquid extraction (PLE) as the optimum technique for extraction. Extracts enriched in MDAAs of a total content above 20% exerted a potent dual anti-influenza virus and antipneumococcal activity. For a detailed analysis of the most bioactive chemical features and molecules within the extracts, 1H NMR-based heterocovariance analysis (HetCA) was used. According to the multivariate statistical analysis procedure conducted, MDAAs exclusively accounted for the in vitro anti-influenza viral effect. The anti-infective profile of one hit extract (MA60) investigated showed a good tolerance by lung cells (A549, Calu-3) and pronounced in vitro activities against influenza viruses, S. pneumoniae, S. aureus, and inflammation.