A new α-glucosidase inhibitor from Achillea fragrantissima (Forssk.) Sch. Bip. growing in Egypt.

α-Glucosidase inhibitors (AGIs) represent a class of oral antidiabetic drugs that delay the absorption of ingested carbohydrates, reducing the postprandial glucose and insulin peaks to reach normoglycaemia. In this study, a bioassay-guided fractionation of the ethanolic extract of the aerial parts of Achillea fragrantissima (Forssk.) Sch. Bip. growing in Egypt led to the isolation of a new potent AGI; acacetin-6-C-(6″-acetyl-β-D-glucopyranoside)-8-C-α-L-arabinopyranoside (5) alongside with four known compounds: chondrillasterol (1), quercetin-3,6,7-trimethyl ether (chrysosplenol-D) (2), isovitexin-4'-methyl ether (3) and isovitexin (4). The structure of the new compound (5) was elucidated on the basis of its spectral data, including HR-FAB-MS, UV, (1)H NMR, (13)C NMR, (1)H-(1)H COSY, HSQC and HMBC. The new compound (5) exhibited the most significant α-glucosidase inhibitory activity (IC₅₀ 1.5 ± 0.09 μg/mL). Under the assay conditions, all the tested compounds were more potent than the positive control acarbose (IC50 224 ± 2.31 μg/mL).