Chemotaxonomy of kōwhai: leaf and seed flavonoids of New Zealand Sophora species

Abstract

ABSTRACTChemotaxonomic analysis of kōwhai leaf extracts in New Zealand are limited with previous reports of Sophora tetraptera having a flavonoid profile distinct from S. microphylla sensu lato and S. prostrata. Eight Sophora species are now recognised in New Zealand: S. chathamica, S. fulvida, S. godleyi, S. longicarinata, S. microphylla, S. molloyi, S. prostrata and S. tetraptera. We now report liquid chromatography-ultraviolet-mass spectrometry (LC-UV-MS) analyses of leaf and seed extracts of individual plants (2–16) from each of these eight species, plus the Chilean S. cassioides. All of the S. tetraptera leaf extracts had similar LC-UV-MS profiles, different from all of the other Sophora samples, consisting of four predominant compounds, characterised by MS and nuclear magnetic resonance (NMR) spectroscopy as: luteolin-7-O-rutinoside 1, luteolin-7-O-glucoside 2, apigenin-7-O-rutinoside 3, and apigenin-7-O-glucoside 4. The other Sophora leaf extracts showed complex flavonoid compositions, with no clear distinction between species. Most of the Sophora seed samples, including those of S. tetraptera, showed one major phenolic compound, but a few had a related compound. These were purified and characterised by MS and NMR spectroscopy as 3′,4′,7-trihydroxyisoflavone 5 (in most seeds) and its 7-O-glucoside 6 (in a few seeds), neither of which has been previously reported from these Sophora species.