New maplexins F–I and phenolic glycosides from red maple (Acer rubrum) bark

Four new gallotannins, maplexins F–I (1–4), two new phenolic glycosides, rubrumosides A–B (5,6), and eleven known compounds were isolated from red maple (Acer rubrum) bark. Their structures were elucidated based on spectroscopic analysis. The maplexins contained three galloylated derivatives attached to different positions of 1,5-anhydro-glucitol and were 10–20 fold more potent α-glucosidase inhibitors than the clinical drug, Acarbose (IC50=7–16 vs 161 μM), in vitro. These results support previous data suggesting that gallotannins are the main contributors to the α-glucosidase inhibitory activities of maple plant part extracts and that three substituents on the 1,5-anhydro-glucitol moiety are important for activity.