Flavonoid glycosides from the leaves of Michelia champaca
Michelia champaca L. (Magnoliaceae) was cultivated in large scale for flowers as cosmetic raw materials, whereas the value of its leaves remains to be discovered. Our chemical study on the leaves yielded four new flavonol diglycosides, champaflavosides A–D ( 1 – 4 ), together with twenty-three known flavonoid glycosides ( 5 – 27 ). Their structures were determined by spectroscopic and chemical methods. Compounds 5 – 21 and 23 – 27 were not previously reported from the genus Michelia , and kaempferol 3- O -rutinoside ( 22 ) was obtained from this species for the first time. All the compounds were evaluated for antioxidant activity by four in vitro assays. Compounds 3 – 12 and 20 showed more potent 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity than l -ascorbic acid ( l -AA). Compounds 2 – 23 , 25 , and 27 exhibited 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical cation scavenging activity superior to l -AA. The ferric reducing antioxidant powers (FRAP) of compounds 2 – 13 , 17 , and 19 were higher than l -AA. Further, eighteen compounds demonstrated cellular reactive oxygen species (ROS) scavenging activity, of which champaflavoside D ( 4 ), rhamnetin 3- O -neohesperidoside ( 8 ), quercetin 3- O -(6- O - E - p -coumaroyl)-neohesperidoside ( 9 ), and liquiritin ( 27 ) were more potent than curcumin. The results revealed that the renewable leaves of M. champaca are a rich source of flavonoids and antioxidants.
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