Acylated Flavonoids from Spiraea Genus as Inhibitors of α-Amylase

Abstract

Spiraea L. belongs to a genus of deciduous-leaved shrubs in the Rosaceae family that is abundant in Eastern Siberia. The study of six species of Spiraea growing in the Baikal region revealed that they were characterized with high content of phenolic compounds and their extracts demonstrated an inhibitory effect on α-amylase. It was established using correlation analysis that flavonoids were the leading components associated with this biological effect of the extracts. The extracts from S. salicifolia leaves demonstrated the highest activity with IC₅₀ 69.30 μg/mL. Fractionation and chromatographic separation of the extracted compounds from the ethyl acetate fraction of S. salicifolia allowed isolation of 18 compounds with 15 of those isolated for the first time from this species including trifolin, 6′′-O-caffeoyl-hyperoside, 6′′-O-caffeoylisoquercitrin, 6′′-O-caffeoyl-astragalin, 1-O-p-hydroxybenzoyl-6-O-p-coumaroyl-β-d-glucopyranoside, 3,4,5-tri-O-caffeoylquinic acid, isoramnetinin-3-O-β-d-glucopyranoside, tiliroside, isoramnetin-3-O-α-lrhamnopyranoside, 1-O-cis-cinnamoyl-6-O-(2′-methylene-4′-hydroxybutyroyl)-β-d-glucopyranose, 1-О-(4′′-hydroxy-3′′-methylfurane-2′′-one)-6-О-trans-cinnamoyl-β-d-glucopyranose, 1-О-(4′′-hydroxy-3′′-methylfurane-2′′-one)-6-О-cis-cinnamoyl-β-d-glucopyranose, 6-tuliposide A, and tulipalin A. Flavonoid caffeoyl glycosides were identified as the most active inhibitors of α-amylase with 6′′-O-caffeoyl-hyperoside demonstrating the maximum IC₅₀ of 46.18 μg/mL that determined total anti-α-amylase effect of the S. salicifolia extract. The total content of 6′′-О-caffeoyl-hyperoside in S. salicifolia leaves was 0.60–10.53 mg/g and of flavonoids, 12.02–23.17 mg/g. The study showed that the acylated flavonoids from Spiraea were effective inhibitors of α-amylase.