Verbascoside and rare flavone glucosides from Citharexylum spinosum L. flowers as antihyperglycemic agents: Isolation, α-amylase inhibition, molecular docking and drug-likeness prediction

Abstract

Human concern for its public health has been a cornerstone since ancient times, with humans exploring natural resources in their environment for medicinal purposes. Plants have long served as the primary source of medicinal compounds, reflecting centuries of exploration and experimentation. Today, leveraging cognitive and technological advancements, researchers continue to deepen their studies towards achieving optimal health conditions. In pursuit of antihyperglycemic phyto-alternatives, a phytochemical investigation of EtOAc and n-BuOH flower extracts of Citharexylum spinosum L. yielded four rare flavone glucosides viz. cirsilineol 4′-glucoside, jaceoside, 5,4′-dihydroxy-7,3′-dimethoxyflavone 6-glucoside and pedaliin. Additionally, the flavone aglycone apigenin, and the phenylethanoid glycoside verbascoside were isolated. The flavonoid compounds were isolated for the first time from C. spinosum tree. The extracts underwent silica gel column chromatography for simplification, followed by compound purification using preparative HPLC. Molecular structures were elucidated through NMR spectroscopic experiments, spectrometric ESI-HRMS analysis, and comparisons with existing literature data. Subsequently, extracts and isolated compounds were evaluated for their antihyperglycemic activities by assessing their ability to inhibit α-amylase enzymatic activity. EtOAc and n-BuOH extracts displayed important anti-α-amylase properties with IC50 values of 52.5 ± 1.2 and 36.3 ± 1.1 µg/mL, respectively. The results demonstrated promising inhibitory properties of the α-amylase enzyme by the polyphenols isolated in this study. IC50 values ranged from 12.8 ± 0.1 to 23.2 ± 0.1 µM for the isolated compounds, comparable to the reference standard acarbose (IC50= 12.3 ± 0.1 µM). Furthermore, a structure-activity relationship study was conducted, with all isolated molecules docked to the α-amylase enzyme (PDB: 7TAA) and their drug-likeness properties predicted.