Phenolic Compounds from Hypericum cerastoides (Spach) N. Robson: Dereplication via UHPLC-HRMS/MS, Isolation, Identification, and Preliminary Biological Evaluation Focusing on Radical-Scavenging, Anti-α-Glucosidase, and Pro-Lipase Activities

Background/Objectives: Hypericum cerastoides (Spach) N. Robson is a lesser-known species with potential pharmacological importance. This study aimed to profile phenolic compounds in its aerial parts and assess biological activities of isolated constituents, focusing on radical-scavenging, anti-α-glucosidase, and pro-lipase effects. Methods: Phenolic compounds from H. cerastoides aerial parts were dereplicated via UHPLC-HRMS/MS. The structures of isolated compounds were determined using spectroscopic methods (1D and 2D NMR, UV, and HRMS-ESI). Radical-scavenging was evaluated by DPPH and ABTS assays; anti-α-glucosidase and pro-lipase activities were measured by LC-MS. Results: UHPLC-HRMS profiling of a hydroalcoholic extract tentatively identified and quantified 39 phenolic compounds, mainly flavonoids and hydroxycinnamic acid derivatives. Furthermore, two new phenolic compounds, namely hypercerastoside A (HC4) and hypercerastoside B (HC6), together with three known compounds, coumaroylquinic acid (HC1), myricetin-3-O-glycoside (HC2), and myricetin-3-O-galactoside (HC3), as well as two artifacts, namely methyl ester of chlorogenic acid (HC5) and hypercerastoside C (HC7), were isolated from the ethylacetate extract of the aerial parts of title plant. Compounds HC2, HC3, and HC5 displayed the highest radical-scavenging activity. The anti-α-glucosidase test showed that compounds HC1 (IC50 = 44 µM) and HC3 (IC50 = 206 µM) possessed similar activity to acarbose (IC50 = 206 µM). Myricetin glycosides HC2 and HC3 enhanced lipase activity fivefold at 200 µM. Conclusions: H. cerastoides is a promising source of bioactive phenolic compounds with significant radical-scavenging and enzyme-modulating activities. These preliminary findings support further exploration of its therapeutic potential, especially for oxidative stress-related disorders, type 2 diabetes, and cachexia.