Investigations of Natural Products from Marine Sponge Derived Fungi
Research results described here are from experiments conducted in organic chemistry and marine microbiology. Sponge derived chemistry has provided the marine natural products field with a higher percentage of bioactive leads than temstrial plants or microorganisms. Inspection of these bioactive leads reveals structure types that occur in more than one Demosponge or invertebrate species. It has been hypothesized that this trend indicates complex biosyntheses occmring which include microorganisms associated with the sponges. This theme built on circumstantial evidence is discussed first.
Initially we investigated jasplakinolide's occurrence from unrelated sponges including Jaspis aff. johnstoni. Fungi were cultured from this sponge to test the possibility of microorganism biosynthetic involvement. From an unidentified culture we discovered the coriolins, previously known from the temstrial fungus Coriolus consors, and new sesquiterpenes named the chloriolins. We tested the biosynthetic potential of C. consors by growing it in liquid broths with varied salt and fresh water media. We characterized a new coriolin type compound and new and known piperazine diones.
Fungi were cultured from the sponge Jaspis aff. coriacea including one strain identified as Aspergillus ochraceus. This fungus produced novel chlorinated polyketides named chlorocarolides which appear to have no ecological connection with sponge's known metabolites. However they do appear analogous to the known Aspergillus metabolite carotic acid. Relative stereochemistry of the chlorocarolides was solved by 1H NMR coupling and molecular modeling analysis.
Our fungi library isolated from sponge tissue provided culture extracts screened in two ways: for bioactivity using in-house and off-campus cancer-based bioassays, and for large molecular weight compounds using electrospray ionization mass spectrometry (ESIMS). Polyketides isolated include new nectriapyrones and the novel compound 14,15-secocurvularin. ESIMS results assisted our dereplication process of known compounds isolated.
We have shown sponges are a good source for isolating fungi cultures and these cultures may be extracted and purified to provide new and bioactive metabolites from polyketide, terpene, and polypeptide structure classes. Our results indicate that the culturable fungi do not influence the biosynthesis of sponges as once hypothesized and that other classes of microorganisms may merit investigation for their ability to influence sponge metabolite biosynthesis.