Flavonoids are important secondary plant metabolites that have been studied for a long time for their therapeutic potential in inflammatory diseases because of their cytokine-modulatory effects. Five flavonoid aglycones were isolated and identified from the hydrolyzed aqueous methanol extracts of Anastatica hierochuntica L., Citrus reticulata Blanco, and Kickxia aegyptiaca (L.) Nabelek. They were identified as taxifolin (1), pectolinarigenin (2), tangeretin (3), gardenin B (4), and hispidulin (5). These structures were elucidated based on chromatographic and spectral analysis. In this study, molecular docking studies were carried out for the isolated and identified compounds against SARS-CoV-2 main protease (Mpro) compared to the co-crystallized inhibitor of SARS-CoV-2 Mpro (α-ketoamide inhibitor (KI), IC50 = 66.72 µg/mL) as a reference standard. Moreover, in vitro screening against SARS-CoV-2 was evaluated. Compounds 2 and 3 showed the highest virus inhibition with IC50 12.4 and 2.5 µg/mL, respectively. Our findings recommend further advanced in vitro and in vivo studies of the examined isolated flavonoids, especially pectolinarigenin (2), tangeretin (3), and gardenin B (4), either alone or in combination with each other to identify a promising lead to target SARS-CoV-2 effectively. This is the first report of the activity of these compounds against SARS-CoV-2.

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Pterygota Schott & Endl. (Sterculiaceae) consists of about 15 species distributed in Tropical Asia and Africa. Pterygota alata (Roxb) R. Br. is a large deciduous tree known as Budah coconut tree. The plant is naturally distributed in South Asia and Myanmar. For a long time, P. alata has been controversial from a systematic point of view. On the bases of various morphological features, Sterculia alata Roxb. had been revised to the genus Pterygota and hence the name was revised to P. alata [1][2][3][4]. The seeds of P. alata are consumed, possess a narcotic like effect and utilized as an alternate for opium in India. The bark juice of Pterygota species was used traditionally in the management of hemorrhoids, dropsy, swelling oedema, gout, leprosy and pain [2]. The tree heartwood was used in the production of cement-bonded wood for floor boards [2]. The first phytochemical study on the leaves and stems of P. alata was carried out by Lin et al.[5] yielding four phenylpropanoids (cinnamic acid, p-methoxy cinnamic acid, 1,6-O-dicinnamoyl glucose and 1-O-p-coumaroyl 6-O-cinnamoyl-β-D-galactoside), four triterpenes (taraxeryl acetate, fridelin, epifriedelanol and oleanolic acid), two lignans (epieudesmin and diayangambin), one steroid ( stigmasterol), an anthraquinones (thespeson) and a flavonoid (apigenin). Jahan et al. [6] reported that the chloroform fraction of the crude ethanol extract of P. alata bark showed high concentrations of phenolics and flavonoids as well as free radical scavenging property. Chatterji [7], Qin [8] and Hussain et al. [9] found that the leaves of S. urens, S. lychnophora and S. foetida possessed significant anti-hyperglycemic activity with an improvement of body weight. Recently, in developing nations and industrialized countries the occurrence of diabetes is escalating. Imbalance between ROS (Reactive oxygen species) and the antioxidant defense system mediated oxidative stress which is a key factor in the mechanism of several diseases including diabetes [10]. Thus, apart from traditional treatment a suitable antioxidant therapy would benefit in diabetes.

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