Chemical constituents and biological activities of Alpinia mutica Roxb. and Lysiphyllum strychnifolium (Craib) A. Schmitz

Abstract

This study described the phytochemical studies, α-glucosidase inhibitory activity, and antioxidants of Alpinia mutica and Lysiphyllum strychnifolium, along with the optimal infusion conditions for L. strychnifolium leaves tea. The study is divided into three sections listed below.

First, the chemical constituents and a-glucosidase inhibitory activity of A. mutica were investigated. The dichloromethane crude extracts of pericarps and seeds were analyzed by GC-MS in this section. The main volatile constituent of the pericarp extract was diarylheptanoid, namely 1,7-diphenyl-4,6-heptadien-3-one (45.28%). The most abundant volatile components in the seed extract were 5,6-dehydrokawain (64.94%), pinocembrin (22.51%) and farnesol (9.18%). Moreover, seven known compounds, including farnesol (1), 5,6-dehydrokawain (2), pinocembrin (3), cardamomin (4), naringenin (5), pinocembrin chalcone (6), and alpinetin (7) were isolated from dichloromethane extract of A. mutica seed and evaluated for α-glucosidase inhibitory activity. The most potent isolated compound against α-glucosidase was naringenin (5) with an IC50 value of 8.77 ± 1.04 μM.

The chemical constituents, a-glucosidase inhibitory and antioxidant activities of L. strychnifolium were subsequently investigated. In this section, thirteen compounds, including astilbin (8), isoastilbin (9), neoastilbin (10), epicatechin (11), (E)-resveratrol (12), (E)-resveratrol 4'-O-β-D-glucoside (13), quercetin 3-O-β-D-arabinoside (14), phloretin (15), phloretin 4'-O-β-D-glucoside (16), phloretin 4'-O-(6''-O-galloyl)-β-D-glucoside (17), pinitol (18), gallic acid (19) and gallic acid ethyl ester (20) were isolated from the crude ethanolic extract of L. strychnifolium roots, stems, leaves and flowers. Compound 17 exhibited strong α-glucosidase inhibitory activity with an IC50 value of 16.2 ± 1.4 μM. In addition, compound 17 exhibited the highest antioxidant activity with an IC50 value of 19.26 ± 0.95 μM. The results of these two sections demonstrated that compounds 5 and 17 may provide therapeutic alternatives for type 2 diabetes.

The final part of the research focused on determining the optimal infusion conditions for L. strychnifolium leaves tea. In this section, the effects of infusion conditions, including time, temperature and water volume, as well as multiple infusions, were investigated. L. strychnifolium leaves tea had the highest extraction yield (26.99 ± 0.33%) when brewed using hot water at 70 °C with a leaf powder and water ratio of 1:40 (g/mL) for 5 min, followed by two steps of brewing. Moreover, a sweetener, phloretin 4'-O-β-D-glucoside (16) and anti-hyperglycemia agent, pinitol (18), were identified as the major components of L. strychnifolium leaves tea. This section provides evidence for the folk belief that L. strychnifolium tea promotes health and wellness.