Marine-derived fungi are to excellent resources for novel secondary metabolites and many lead compounds have for drug development. Aspergillus versicolor, a slow-growing filamentous fungus, normally are found in air, soil, marine sediment, corrupted plants, and agricultural products. Previous chemical investigations on the fungus Aspergillus versicolor from different environments have resulted in the identification of new secondary metabolites with a variety of structures; such as alkaloids, anthraquinones, xanthones, diphenyl ethers, lactones, peptides, polyketide, terpenoids, and varicuothiols.
Therefore during our continuous screening of new secondary metabolites from marine Aspergillus versicolor; six new diketopiperazines named as -7,8-epoxy-brevianamide Q, -8-hydroxy-brevianamide R; -8-epihydroxy-brevianamide R along with four known compounds -brevianamide R, versicolorin B; so averufin were isolated from the culture material of a marine-derived fungus strain Aspergillus versicolorMF180151.
The preliminary bioactivities
The compound is the first sample of brevianamides with an epoxy moiety. But in this paper, they describe the fermentation, isolation, structure elucidation and preliminary bioactivities of these compounds. Brevianamides belong to a class of naturally occurring 2,5-diketopiperazine alkaloids, which are mainly produced by fungi of Penicillium and Aspergillus. In this research, three pairs of new brevianamides and their relative configurations according to the 1D, 2D NMR, HRESIMS, UV.
But, the specific optical rotation analysis and CD showed that these compounds racemic mixtures. In more than 24 brevianamides, the hydroxy-substitution have mainly occurred at C-8 or/and C-9. In our research; -7,8-epoxy-brevianamide Q as the first brevianamide analogs with an epoxy substitution. But compounds did not exhibit antifungal and antibacterial activities against C. albicans, B. subtilis, S. aureus, MRSA, P. aeruginosa and Bacillus Calmette-Guérin (MIC >100 µg/mL).
The strain Bacillus
Versicolorin B exhibited moderate activities against S. aureus and MRSA with the MIC values of 6.25 µg/mL and 12.5 µg/mL. Simultaneously; averufin exhibited moderate activities against S. aureus and MRSA with the MIC values of 6.25 µg/mL and 25 µg/mL. The strain Bacillus Calmette–Guérin used for the anti-BCG assay was with a green fluorescent protein; constitutive expression plasmid pUV3583c with direct readout of fluorescence as a measure of bacterial growth.
The strain was to mid-log phase at 37 °C in Middle brook 7H9 broth supplemented with 10% OADC enrichment; 0.05% Tween-80 and 0.2% glycerol and then diluted to an OD600 of 0.025 with broth. Aliquots (80 μL) of the bacterial suspension to each well of the 96-well microplates (clear flat-bottom); followed by adding compounds (2 μL in DMSO); which serially twofold diluted.
Therefore isoniazid served as positive control and DMSO as the negative control. The plate at 37 °C for 3 days; GFP fluorescence with Multi-label Plate Reader using the bottom read mode; with excitation at 485 nm and emission at 535 nm. MIC is the minimum concentration of drug that inhibits more than 90% of bacterial growth by fluorescence value.