Ginkgo (Ginkgo biloba) is one of the oldest living tree species and has been widely used in traditional medicine. Leaf extracts of ginkgo, such as the standardized extract EGb761, have become one of the best-selling herbal products. However, no bioactive compound directed at plants has been reported in this species. Therefore, we investigated possible allelopathic activity and searched for allelopathically active substances in ginkgo leaves. An aqueous methanol leaf extract inhibited the growth of roots and shoots of garden cress (Lepidium sativum), lettuce (Lactuca sativa), timothy (Phleum pratense) and ryegrass (Lolium multiflorum) seedlings. The extract was purified by several chromatographic runs and an allelopathically active substance was isolated and identified by spectral analysis to be the novel compound 2-hydroxy-6-(10-hydroxypentadec-11-enyl)benzoic acid. The compound inhibited root and shoot growth of garden cress and timothy at concentrations greater than 3. μM. The activity of the compound was 10- to 52-fold that of nonanoic acid. These results suggest that 2-hydroxy-6-(10-hydroxypentadec-11-enyl)benzoic acid may contribute to the allelopathic effect caused by ginkgo leaf extract. The compound may also have potential as a template for the development of new plant control substances.
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