Abstract
The genus Rhododendron is a rich source of phenolic compounds that possess a wide range of biological activities. Phytochemical investigation of the methanolic extract of the flowers of Rhododendron yunnanense Franch. led to the isolation and characterization of 13 phenolic compounds isolated for the first time from this plant species. These compounds were identified as quercetin (1), quercitrin (2), avicularin (3), taxifolin-3-O-α-L-arabinoside (4), azalein (5), kaempferol-3-O-rhamnoside (6), kaempferol-4?-methoxy-3-O-rhamnoside (7), kaempferol-3-β-D-glucopyranoside (8), catechin (9), epicatechin (10), catechin-3-O-gallate (11), 5-O-Z-p-coumaroylquinic acid methyl ester (12), and 5-O-caffoeylquinic acid methyl ester (13). The structures of compounds 1–13 were determined by 1D and 2D nuclear magnetic resonance and comparison with reported spectral data. A molecular simulation study was carried out on the binding mode of the isolated compounds as anti-inflammatory agents through cyclooxygenase 2 (COX-2) inhibition and as mediators of tumor angiogenesis through vascular endothelial growth factor inhibition. The docking results of the isolated compounds revealed promising binding affinities to the examined enzymes. Compound 2 showed predominant affinity for the two examined receptors [COX-2 (−19.4542 kcal/mol) and vascular endothelial growth factor receptor 2 (−17.6036 kcal/mol)]. The isolated compounds offered significantly active phytoconstituents for drug discovery and development.
Highlights
Natural polyphenols are widely distributed phytochemicals in the plant kingdom that are considered a significant source for drug discovery and development (Asuzu et al, 2019)
It is well established that chronic inflammation is a risk factor for cancer development which is indicated by overexpression of inflammatory mediators such as cytokines, NF-κB, cyclooxygenase (COX), and vascular endothelial growth factor (VEGF) associated with various cancers development such as pancreatic, prostate, cervical, breast, lung, and colon cancers (Wong, 2019)
Despite the fact that angiogenesis is regulated by multiple complex proangiogenic factors, the VEGF is a vital mediator of tumor angiogenesis in which its expression increases associated with tumor prognosis (Abhinand et al, 2020)
Summary
Natural polyphenols are widely distributed phytochemicals in the plant kingdom that are considered a significant source for drug discovery and development (Asuzu et al, 2019). Recent studies have shown that many isolated natural compounds exhibited antiangiogenic activity as a potential target for cancer treatments especially for solid tumors (Al Abd et al, 2017). Despite the fact that angiogenesis is regulated by multiple complex proangiogenic factors, the VEGF is a vital mediator of tumor angiogenesis in which its expression increases associated with tumor prognosis (Abhinand et al, 2020). Recent studies suggest that COX-2 inhibitors could lead to a reduction of tumorigenesis by suppression of angiogenesis through the downregulation of VEGF production and other proangiogenic factors produced by tumor cells (Liu et al, 2000; Toomey et al, 2009)
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