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

地衣产生多种地衣物质，其中一些已被发现表现出广泛的潜在有用的生物活性。最近，地衣菌群的培养物被证明能够产生某些地衣物质或新的代谢产物在逆境胁迫条件下。在我们寻找新的生物活性化合物的过程中，我们培养了几种地衣的孢子来源的真菌生物体，并从它们的培养物中分离出不同的化合物。在日本收集的Graphis cognata的培养地衣真菌生物体产生altemariol沿着graphislactones A和C。在美国收集的G.prunicola的真菌生物体产生graphislactones A-D。<13>乙酸乙酯与培养的Prunicola的真菌生物体的分离导致两个新的代谢产物的分离和通过altemariol到graphislactones的生物合成途径的确定。从日本的日本核壳菌（Pyrenulajaponica）和美国的拟蟾蜍核壳菌（P.pseudobufonia）中分离得到4个新的3位甲基氧杂蒽酮和一种真菌代谢产物核壳菌素。此外，培养的真菌Lecanora cinereocarenea产生了三个新的二苯并呋喃，而培养的真菌Xanthoria polycarpa和Caloplaca elegans产生了五个已知的蒽醌。虽然分离的代谢产物尚未在地衣化条件下发现，但它们似乎通常在从高度不相关的位置分离的真菌中产生。代谢产物产生的生物学意义尚不清楚。然而，在真菌培养物中出现的各种产物可能解释了真菌在地衣化前的条件下更好的生存机会，并提供了有关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.