Flavonoid 8-O-Glucuronides from the Aerial Parts of Malva verticillata and Their Recovery Effects on Alloxan-Induced Pancreatic Islets in Zebrafish.

<italic>Malva verticillata</italic> (Cluster mallow), a leafy vegetable that has been popular in East Asia for a long time, has also been used in herbal teas and medicines. The aqueous fraction of the aerial parts of <italic>Malva verticillata</italic>, exhibiting a very high quantity of flavonoids compared to the EtOAc and <italic>n</italic>-BuOH fractions, exhibited significant recovery effects on pancreatic islets damaged by alloxan in zebrafish larvae. Thus, the bioactive components responsible for this anti-diabetic activity were investigated. A new flavonoid glucuronide (<bold>1)</bold> and five known flavonoids were isolated from the aqueous fraction. Based on several spectroscopic methods, compound <bold>1</bold> was identified to be nortangeretin-8-<italic>O</italic>-β-d-glucuronide, and was named malvaflavone A. The A-ring of compound <bold>1</bold> had a 5,6,7,8-tetrahydroxy moiety, which rarely occurs in plant systems. Also 8-<italic>O</italic>-glucuronide attached to the flavonoid moiety was rarely occurred in plant system. Compounds <bold>1</bold>, <bold>3</bold>, <bold>4</bold>, and <bold>6</bold> significantly improved the pancreatic islet size in zebrafish at 0.1 μM, and compounds <bold>1</bold> and <bold>6</bold> were found to block β-cell K⁺ channels in experiments with diazoxide. In ABTS, ORAC, and SOD assays, compounds <bold>1</bold>–<bold>5</bold> exhibited high anti-oxidant activities compared with quercetin and BHA (positive controls), indicating that the 8-<italic>O</italic>-glucuronide attached to the flavonoid moiety is a key structure for the expression of anti-oxidant activity. This is the first report of the isolation of compounds <bold>1</bold>–<bold>6</bold> from <italic>M. verticillata</italic> as well evaluated for anti-diabetic and anti-oxidant ativities. [ABSTRACT FROM AUTHOR]