Phytochemical and biosynthetic studies on the products from the cultures of isolated lichen mycobionts

地衣可产生多种地衣物质，其中几种已被发现具有广泛的潜在生物活性。最近，地衣真菌的培养被证明能够在渗透胁迫条件下产生某些地衣物质或新的代谢物。在寻找新的生物活性物质的过程中，我们对几种地衣的孢子源真菌进行了培养，并从其培养物中分离出了不同的化合物。从日本采集的地衣真菌生物体产生了石墨内酯，在美国采集的青海植物的真菌生物体产生了石墨内酯A-D。从日本和美国采集的龟甲地衣真菌中分离到4个新的含甲基口山酮类化合物和一种真菌代谢产物菌核蛋白。此外，培养的Cecanora cinerecarenea真菌产生了3个新的二苯并呋喃，而培养的多果桑和Caloplaca elegans培养的真菌产生了5个已知的蒽醌类化合物。虽然分离的代谢物还没有在地衣形成的条件下被发现，但它们似乎通常产生于从高度无关的地点分离出来的真菌生物体。代谢物产生过程中的生物学意义尚不清楚。然而，真菌培养物中各种产物的出现可能解释了真菌在地衣前状态下生存的更好机会，并提供了关于它们进化和共生的信息。

Lichens produce a variety of lichen substances, several of which have been found to exhibit a wide range of potentially useful biological activities. Recently, cultures of lichen mycobionts were shown to be capable of producing certain lichen substances or novel metabolites under osmotically stressed conditions. In the course of our searches for new bioactive compounds, we cultivated the spore-derived mycobionts of several species of lichens and isolated diverse compounds from their cultures.The cultured lichen mycobionts of Graphis cognata collected in Japan, yielded altemariol along with graphislactones A and C.Mycobionts of G.prunicola, which were collected in USA, produced graphislactones A-D.Feeding experiments of ^<13>C-acetate with the cultured mycobionts of G.prunicola resulted in the isolation of two new metabolites and determination of the biosynthetic pathway to graphislactones via altemariol. From the cultured lichen mycobionts of Pyrenulajaponica collected in Japan and P.pseudobufonia collected in USA, four new xanthones with a methyl group at C-3 as well as a fungal metabolite sclerotiorin were isolated and characterized. Furthermore, the cultured mycobionts of Lecanora cinereocarenea yielded three new dibenzofurans, while the cultured mycobionts of Xanthoria polycarpa and Caloplaca elegans yielded five known anthraquinones.It is of great interest to know that lichen mycobionts of the same genus are able to produce the same secondary substances. Although the isolated metabolites have not yet been found in lichenized conditions, they appear to be commonly produced in mycobionts isolated from highly unrelated locations. The biological significance in the production of the metabolites is still unknown. However, the occurrence of various products in the cultures of mycobionts may account for a better chance of survival of the mycobiont in pre-lichenized condition and give informations about their evolution and symbiosis.