Analysis of condensed tannins in Populus spp. using reversed phase UPLC-PDA-(-)esi-MS following thiolytic depolymerisation.

INTRODUCTION: Condensed tannins (CTs) are proanthocyanidin heteropolymers that are widely distributed among plants. Their biochemical properties are determined by molecular structure (e.g. polymer size, hydroxylation, stereochemistry). In Populus, genetically and environmentally-determined CT concentrations have been related to ecological effects, while the potential role of CT molecular structure has received little attention. OBJECTIVE: Evaluate CT polymerisation, major constituent monomers, stereochemistry and overall content in Populus tremuloides foliage using ultra-high-performance liquid chromatography with photodiode array and mass spectrometry (UPLC-PDA-(-)esi-MS) detection following thiolytic depolymerisation of the CTs. METHODOLOGY: CTs were extracted from dried foliage of six P. tremuloides genotypes into methanol and thiolytically depolymerised into constituent monomers. Calibration standards were prepared by thiolysis of CT mixtures isolated from P. tremuloides foliage on Sephadex LH-20, followed by preparative high-performance liquid chromatography (HPLC). RESULTS: Populus tremuloides CTs contained predominantly repeating subunits of three putative stereoisomers each of catechin and gallocatechin. Linear calibrations for standards of these subunits and their thioethers (purities 44-87%, UPLC-(-)esi-MS) were generally stable over the course of 10 months. CT polymer size, hydroxylation, stereochemistry and concentrations differed among genotypes. CONCLUSION: This thiolysis-UPLC-PDA-(-)esiMS method was optimised for analysis of CT polymer size, hydroxylation, stereochemistry, and total concentration in Populus foliage. It revealed significant variation in each of these properties among P. tremuloides genotypes, and will facilitate evaluation of how environmental factors affect CT molecular structures.

Ishophloroglucin A, a Novel Phlorotannin for Standardizing the Anti-α-Glucosidase Activity of Ishige okamurae.

Nutraceutical use of algae requires understanding of the diversity and significance of their active compositions for intended activities. Ishige okamurae (I. okamurae) extract is well-known to possess α-glucosidase inhibitory activity; however, studies are needed to investigate its active composition in order to standardize its α-glucosidase inhibitory activity. In this study, we observed the intensity of the dominant compounds of each I. okamurae extract harvested between 2016 and 2017, and the different potency of each I. okamurae extract against α-glucosidase. By comparing the anti-α-glucosidase ability of the dominant compounds, a novel Ishophloroglucin A with highest α-glucosidase inhibitory activity was identified and suggested for standardization of anti-α-glucosidase activity in I. okamurae extract. Additionally, a validated analytical method for measurement of Ishophloroglucin A for future standardization of I. okamurae extract was established in this study. We suggest using Ishophloroglucin A to standardize anti-α-glucosidase potency of I. okamurae and propose the significance of standardization based on their composition for effective use of algae as marine-derived nutraceuticals.