α‐Glucosidase (AG) inhibitors, one of the classes of oral antidiabetics used to treat type 2 diabetes mellitus, delay digestion and absorption of glucose, which in turn, has a lowering effect on postprandial blood glucose and insulin levels. Natural products are a great source for the development of new AG inhibitory drug candidates. We aim to summarize advances in natural AG inhibitors according to their secondary metabolite groups in the last decade. Their mechanisms of action and structure–activity relationships will especially be discussed.

Introduction: Analysis of biochemical pathways typically involves feeding a labelled precursor to an organism, and then monitoring the metabolic fate of the label. Initial studies used radioisotopes as a label and then monitored radioactivity in the metabolic products. As analytical equipment improved and became more widely available, preference shifted the use stable ‘heavy’ isotopes like deuterium ( ² H)‐, carbon‐13 ( ¹³ C)‐ and nitrogen‐15 ( ¹⁵ N)‐atoms as labels. Incorporation of the labels could be monitored by mass spectrometry (MS), as part of a hyphenated tool kits, e.g. Liquid chromatography (LC)–MS, gas chromatography (GC)–MS, LC–MS/MS. MS offers great sensitivity but the exact location of an isotope label in a given metabolite cannot always be unambiguously established. Nuclear magnetic resonance (NMR) can also be used to pick up signals of stable isotopes, and can give information on the precise location of incorporated label in the metabolites. However, the detection limit for NMR is quite a bit higher than that for MS. Objectives: A number of experiments involving feeding stable isotope‐labelled precursors followed by NMR analysis of the metabolites is presented. The aim is to highlight the use of NMR analysis in identifying the precise fate of isotope labels after precursor feeding experiments. As more powerful NMR equipment becomes available, applications as described in this review may become more commonplace in pathway analysis. Conclusion and Prospects: NMR is a widely accepted tool for chemical structure elucidation and is now increasingly used in metabolomic studies. In addition, NMR, combined with stable isotope feeding, should be considered as a tool for metabolic flux analyses.

Background: Aboveground parts and bulbs of Ornithogalum species are consumed as food and used in traditional medicine in worldwide. Objective: It is aimed to report the antioxidant capacity and phenolic compounds content of Ornithogalum sigmoideum , Ornithogalum orthophyllum and Ornithogalum oligophyllum for the first time. Materials and methods: Antioxidant activity of the crude methanol extracts of the aerial parts and the bulbs of the species were determined with 1,1-diphenyl-2-picryl-hydrazyl, superoxide radical scavenging, ferrous ion-chelating effect, phosphomolybdenum-reducing antioxidant power and ferric-reducing antioxidant power assay. The ethylacetate, diethylether and water subextracts from leaf and flower were analyzed to quantify selected phenolic compounds by HPLC-UV. Results: Among the six extracts, the methanol extract of the aerial parts of O. orthophyllum contained the highest amount of phenolic compounds (GAE, 11.0 mg/g extract). The aerial parts of O. orthophyllum showed higher DPPH and SOD activities than the other extracts with the SC ₅₀ values of 0.39±0.05 mg/mL and 0.44±0.08 mg/mL, respectively. Protocatechuic acid, p -hydroxybenzoic acid, vanillic acid and p -coumaric acid were the most abundant compounds at all the subextracts. Conclusion: The antioxidant activity is found to be in accordance with the levels of phenolic content in the extracts.