ABSTRACT
The leaves of Ginkgo biloba L. contain a variety of chemical compounds, some of which are unique to this ancient tree. Various substances including long-chain hydrocarbons and derivatives, alicyclic acids, cyclic compounds, carbohydrates and derivatives, lectins, carotenoids, isoprenoids (sterols, terpenoids), and flavonoids can be found in its leaves. Several of these compounds have antibiotic and antifungal properties or afford protection against herbivores, attributes that may very well have contributed to the long survival of this unique plant [1, 2]. From a pharmacological perspective, flavonoids and terpenoids are probably the most interesting components. In dried Ginkgo leaves, the content of the flavonoid glycosides is around 0.5-1% w/w, whereas the content of terpenoids is often below 0.1% w/w [2]. The phenolic aglycon moiety of the flavonoid glycosides is made up predominantly of the flavonols quercetin or kaempferol, the occurence of isorhamnetin being significantly smaller. The flavonols myricetin, 3′-O-methylmyricetin, and tamarixetin and the flavones luteolin, apigenin, and 4′-O-methylapigenin are found only in small amounts (Fig. 1A). The glycoside moiety consists of mono-, di-, or triglycosides (mainly D-glucose and L-rhamnose units), which are connected to the aglycon at position 3, 3′, or 7 via O-glycosidic bonds. Some of these glycosides are additionally acylated by p-coumaric acid (Fig. 1B) [3]. Since these latter compounds are distinctive to Ginkgo biloba leaves and extracts, they are considered to be lead substances in this species. Other compounds with a flavonoid-like structure, such as nonglycosidic biflavonoids, catechins, and proanthocyanidins, have also been isolated from this plant [1, 2, 4].
