Marine-derived fungi have been shown in recent years to produce a plethora of new bioactive secondary metabolites, some of them featuring new carbon frameworks hitherto unprecedented in nature. These compounds are of interest as new lead structures for medicine as well as for plant protection. The aim of this protocol is to give a detailed description of methods useful for the isolation and cultivation of fungi associated with various marine organisms (sponges, algae and mangrove plants) for the extraction, characterization and structure elucidation of biologically active secondary metabolites produced by these marine-derived endophytic fungi, and for the preliminary evaluation of their pharmacological properties based on rapid 'in house' screening systems. Some results exemplifying the positive outcomes of the protocol are given at the end. From sampling in marine environment to completion of the structure elucidation and bioactivity screening, a period of at least 3 months has to be scheduled.

Bioactive natural products from endophytic fungi, isolated from higher plants, are attracting considerable attention from natural product chemists and biologists alike as indicated by the steady increase of publications devoted to this topic during recent years (113 research articles on secondary metabolites from endophytic fungi in the period of

Two new 10-oxo-10H-phenaleno[1,2,3-de]chromene-2-carboxylic acids, xanalteric acids I (1) and II (2), and 11 known secondary metabolites were obtained from extracts of the endophytic fungus Alternaria sp., isolated from the mangrove plant Sonneratia alba collected in China. The metabolites were confirmed to be of fungal origin, and the structures of the new natural products were unambiguously elucidated on the basis of extensive one- and two-dimensional NMR spectroscopic studies and mass spectrometric analysis. The two new compounds 1 and 2 exhibited weak antibiotic activity against multidrug-resistant Staphylococcus aureus. Altenusin (3) displayed broad antimicrobial activity against several additional multidrug-resistant bacterial and fungal strains.