Integration of In Vitro and In Silico Results From Chemical and Biological Assays of <i>Rheum turkestanicum</i> and <i>Calendula officinalis</i> Flower Extracts

In this study, we conducted a thorough analysis of <i>Rheum turkestanicum</i> (RT) and <i>Calendula officinalis flowers</i> (COF) extracts with varying polarities using LC-MS chemical profiling and biological tests (antioxidant, antimicrobial, enzyme inhibition, and cytotoxic effects). The highest level of total phenolic content in the ethanol extract of RT with 75.82 mg GAE/g, followed by the infusions of RT (65.00 mg GAE/g) and COF (40.99 mg GAE/g). A total of 20 bioactive compounds were identified and quantified. The ethanol extract of COF was rich in terms of 5-O-caffeoylquinic acid (2780.56 μg/g), isorhamnetin-O-rutinoside (1653.59 μg/g), and rutin (1356.97 μg/g). However, RF extracts were rich in catechin gallate (21.66-80.01 μg/g) and 5-O-caffeoylquinic acid. Except for metal chelating ability, the ethanol extract of RT exhibited the strongest ability (DPPH: 171.5 mg TE/g; ABTS: 387.35 mg TE/g; CUPRAC: 449.80 mg TE/g; FRAP: 195.60 mg TE/g; and PBD: 1.52 mmol TE/g). In the enzyme inhibition tests, the tested ethanol extracts for both species were more active than the infusion. The highest values for tyrosinase were recorded as 72.47 mg KAE/g (in RT extracts) and 71.74 mg KAE/g (in COF extracts). Furthermore, all extracts underwent assessment for their antibacterial and antifungal properties, targeting both Gram-positive and Gram-negative bacteria, as well as clinical yeast and fungal microorganisms. In silico studies yielded valuable insights into the potential therapeutic applications of the bioactive compounds identified in COF and RT extracts. Stable interactions were observed between key compounds, such as isorhamnetin 3-O-glucoside and 3-O-caffeoylquinic acid, with crucial target proteins (AChE, BChE, and MurE). These compounds formed stable hydrogen bonds with minimal root mean square deviation (RMSD) fluctuations, particularly in the isorhamnetin 3-O-glucoside-<i>Staphylococcus aureus</i> MurE and 3-O-caffeoylquinic acid-MurE of <i>S. aureus</i> complexes. These findings further underscore the potential of these compounds as promising candidates for therapeutic development.