Asperlactone

Five new polyketides, asperochrapyran (1) and asperochralactones A-D (2-5), along with 12 known polyketides (6-17), were obtained from the fungal strainAspergillus ochraceopetaliformis. Structures of all isolates were elucidated by their spectroscopic parameters. The relative configurations of the new compounds were deduced by the data of coupling constants and NOESY spectra. The absolute configurations were determined by the comparison of experimental and calculated ECD spectra. Moreover, the plausible biosynthesis pathway of major isolates was proposed as well. Anti-inflammatory activity of compounds5and7-17were evaluated with human neutrophils in response to the stimulation of formyl-methionyl-leucyl phenylalanine (fMLP). Asperlactone (9), aspyrone (13), and (-)-(3R)-mellein (14) exerted superoxide anion inhibition at 30 ± 9%, 29 ± 9%, and 26 ± 12%, respectively, at 10 μM. The capacities of asperlactone (9), aspilactonol B (10), penicillic acid (12), and (-)-(3R)-mellein (14) in elastase release inhibition were revealed as 25 ± 4%, 38 ± 8%, 25 ± 5%, and 34 ± 9%, respectively, at 10 μM.

Chlorohydroaspyrones A (1) and B (2), antibacterial aspyrone derivatives, and the previously described aspyrone (3), asperlactone (4), and penicillic acid (5) have been isolated from the broth of a marine isolate of the fungus Exophiala. The structure and absolute stereochemistry of the compounds were determined on the basis of the physicochemical data analysis and chemical reactions. Compounds 1 and 2 exhibited a mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The MIC values of each strain are as follows: compound 1 showed 62.5 microg/mL for S. aureus and 125 microg/mL for methicillin-resistant S. aureus and multidrug-resistant S. aureus, and compound 2, 62.5 microg/mL for S. aureus and methicillin-resistant S. aureus and 125 microg/mL for multidrug-resistant S. aureus.

Aspergillus westerdijkiae is the main producer of several biologically active polyketide metabolites including isoasperlactone and asperlactone. A 5298bp polyketide synthase gene "aomsas" has been cloned in Aspergillus westerdijkiae by using gene walking approach and RACE-PCR. The predicted amino acid sequence of aomsas shows an identity of 40-56% with different methylsalicylic acid synthase genes found in Byssochlamys nivea, P. patulum, A. terreus and Streptomyces viridochromogenes. Based on the reverse transcription PCR and kinetic secondary metabolites production studies, aomsas expression was found to be associated with the biosynthesis of isoasperlactone and asperlactone. Moreover an aomsas knockout mutant "aoDeltamsas" of A. westerdijkiae, not only lost the capacity to produce isoasperlactone and asperlactone, but also 6-methylsalicylic acid. The genetically complemented mutant ao+msas restored the biosynthesis of all the missing metabolites. Chemical complementation through the addition of 6-methylsalicylic acid, aspyrone and diepoxide to growing culture of aoDeltamsas mutant revealed that these compounds play intermediate roles in the biosynthesis of asperlactone and isoasperlactone.