HPTLC Bioautography Guided Isolation of α‐Glucosidase Inhibiting Compounds from Justicia secunda Vahl (Acanthaceae)

α‐Glucosidase inhibitors form an essential basis for the development of novel drugs in diabetes type 2 treatment. Searching for α‐glucosidase inhibitors in plants, TLC bioautographic assays have been established and improved within the last years. In traditional medicine, extracts from the leaves of Justicia secunda Vahl are used to treat diabetes mellitus symptoms. Objective To screen for α‐glucosidase inhibitors in J. secunda via HPTLC bioautography. Methodology – Extracts from the leaves of J. secunda and fractions thereof were evaluated in terms of their α‐glucosidase inhibiting potential by subjecting them to HPTLC bioautography. The aqueous (AQ) fraction deriving from the methanol extract was further fractionated via column chromatography on polystyrene Diaion® HP‐20. Two AQ subfractions revealed active compounds, which were isolated via preparative HPTLC and semipreparative HPLC. Their identification and structure elucidation was achieved employing HPLC‐ESI‐MS n , HRESI‐MS, and NMR analyses. Results α‐Glucosidase inhibitors were visualised as white zones on violet background on the TLC plate. The crude water extract, the methanol extract, and the methanol extract derived AQ fraction showed α‐glucosidase inhibiting effects. In the latter, two diastereomeric mixtures responsible for the α‐glucosidase inhibition were enriched. They were identified as the novel 2‐caffeoyloxy‐4‐hydroxy‐glutaric acid and the diastereomers secundarellone B and C. Conclusion The current study presents the α‐glucosidase inhibiting potential of J. secunda supporting its traditional medicinal use in diabetes mellitus treatment. HPTLC bioautography screening for α‐glucosidase inhibitors provides a simple and effective method for the investigation of complex samples, such as plant extracts. Copyright © 2016 John Wiley & Sons, Ltd.