Further dihydrochalcone C-glycosides from the fruit of Averrhoa carambola

- Six new dihydrochalcone C-glycosides were isolated from star fruit.
- Their structures were determined by spectroscopic and chemical methods.
- All the compounds demonstrated potent ABTS radical cation scavenging activity.

Further study on the chemical constituents present in the fruit of Averrhoa carambola L. (Oxalidaceae), commonly called star fruit or carambola, led to the isolation of six new dihydrochalcone C-glycosides, carambolasides E∼J (1∼6). Their structures were determined by spectroscopic and chemical methods, including low temperature nuclear magnetic resonance (NMR). Compounds 1∼6 and two alkaline hydrolysates, 5a and 6a, exhibited more potent 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) radical cation (ABTS+) scavenging activity with IC50 values ranging from 4.52 to 2.54 μM than l-ascorbic acid (14.21 μM). However, they were inactive in scavenging 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and in ferric reducing antioxidant power (FRAP).