α-amylase and α-glucosidase inhibitor activities of secondary metabolites from Arcytophyllum thymifolium

Plants belonging to Arcytophyllum genus are widespread in Central and South America mainly in Costa Rica, Panama, Venezuela, Colombia, Ecuador, Peru and Bolivia [1]. Aerial parts infusion and/or decoction are used in traditional medicine for the treatment of colic and indigestion [2]. Only one study was previously reported in the literature, showing the presence of flavonoids and triterpenoids from Arcytophyllum genus [3]. A. thymifolium (Ruiz & PAV) Standl (Rubiaceae) is a shrub growing in Ecuador in the typical Ande mountain ecosystem [1]. In the present study, a phytochemical investigation of A. thymifolium aerial parts was performed for the first time. The dried and powdered plant material was sequentially extracted with n-hexane, CHCl3, CHCl3-MeOH (9:1) and MeOH. The CHCl3 extract was first subjected to a flash chromatography through Biotage Isolera™, and fractions obtained were successively eluted on RP-HPLC and HPCPC. The MeOH extract was partitioned between n-BuOH and H2O and the n-BuOH fraction was preliminary chromatographed on Sephadex LH-20 column, subsequently, fractions obtained were submitted to RP-HPLC. Twenty-three compounds (8 coumarins, 4 flavonoids, 9 iridoids, 2 caffeic acid derivatives), including five new secondary metabolites, were finally isolated and identified by NMR and MS analyses. The hypoglycaemic properties of known and new compounds were also evaluated measuring extracts and pure compounds α-amylase and α-glucosidase inhibitory effects, by using acarbose as positive control [4]. The iridoid asperulosidic acid showed the higher activity as α-amylase inhibitor, having an IC50 of 70 μM, moderately higher than acarbose (IC50 26.3 µM), while the new flavanone 7-O-(3-metylbut-2-enyl)oxy eriodictyol resulted to be the most active as α-glucosidase inhibitor with an IC50 of 30 μM, sensibly lower than acarbose (IC50 402.7 µM). A molecular docking study is in progress to gain information on β-glucosidase-7-O-(3-metylbut-2-enyl)oxy eriodictyol interaction.