Proanthocyanidins from Ginkgo biloba leaf extract and their radical scavenging activity

Abstract

Context: Ginkgo biloba L (Ginkgoaceae) is a traditional herbal medicinal plant for the treatment of mild to moderate cognitive disorders, tinnitus, and dementia. These uses may be correlated with the presence of radical scavenging compounds.

Objective: The chemical composition and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the flavan-3-ols and proanthocyanidins from G. biloba were studied.

Material and methods: The compounds have been isolated using column chromatography on Sephadex LH-20 and MCI gel and the structures were determined on the basis of 1D- and 2D-NMR (HSQC, HMBC) experiments of their peracetylated derivatives, MALDI-TOF-MS and by acid-catalyzed degradation with phloroglucinol. The DPPH radical scavenging activities of the compounds were investigated.

Results: The new trimeric prodelphinidin, epigallocatechin-(4β→8)-epigallocatechin-(4β→8)-catechin (compound 7), has been isolated from the air-dried leaves of the title plant, in addition to catechin, epigallocatechin, gallocatechin, and three dimeric proanthocyanidins. The dimeric prodelphinidin epigallocatechin-(4β→8)-epigallocatechin (compound 6) showed the strongest DPPH radical scavenging activity, with IC₅₀ 1.7 μg/mL, 10 times more active than the positive control, BHT (IC₅₀ 17.3 µg/mL), followed by the new trimeric proanthocyanidin epigallocatechin-(4β→8)-epigallocatechin-(4β→8)-catechin with IC₅₀ 2.1 µg/mL. The crude extract exhibited high DPPH radical scavenging activity with IC₅₀ 15.5 µg/mL comparable with that of BHT.

Discussion and conclusion: The results showed that all the isolated compounds from the tannin fraction exhibited potent free radical scavenging activities, which were higher than that of BHT, suggesting that the condensed tannins from G. biloba leaves strongly contribute to the overall antioxidant effects.

Keywords::

• Polyphenols
• tannins
• Ginkgoaceae
• trimeric prodelphinidin

Acknowledgements

We wish to acknowledge the help of Prof. Dr. R. Anwander (Inst. f. anorganische Chemie, Tuebingen) for the NMR spectra, Dr. H. Luftmann (Inst. f. organische Chemie, Muenster) for the MALDI-MS-spectra and Prof. Dr. V. Buß (Theoretische Chemie, Duisburg) for the CD spectra.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing the paper.