Phenolic Constituents with Antioxidant and &alpha;-glucosidase Inhibitory Activities from Sugar Maple (<em>Acer saccharum</em> Marsh.) Fall Leaves

Abstract

To elucidate the chemical compositions of the sugar fall maple leaves, the methanol extracts were firstly fractionated by ethyl acetate and n-butanol respectively. The phenolic acids-rich fractions (ethyl acetate extracts) were further purified by various chromatographic columns including XAD macroporous resin, Sephadex LH-20, ODS and semi-preparative HPLC to yield the compounds. The isolated compounds were characterized by 1H-Nuclear Magnetic Resonance (1H-NMR), 13C-NMR, and high resolution electrospray ionisation mass spectral (HR-ESI-MS) spectroscopy. Twenty eight phenolics including fourteen flavonoids (1-14), five quinic acid derivatives (15-19), five galloyl tannins (20-24) and four other phenolic acids (25-28) were isolated and their structures were identified. The isolated compounds were evaluated for their antioxidant and &amp;alpha;-glucosidase inhibitory activities. All of the phenolics constituents showed DPPH scavenging antioxidant activities. While, glycosides of quercetin and myricetin, galloyl tannins were showed promising &amp;alpha;-glucosidase inhibitory activity. All of the compounds except 4, 11, 12 and 28 were isolated from sugar maple for the first time. Moreover, Compounds 9, 10, 14, 20, 21, 23, 25 and 26 were isolated from the Acer species for the first time.