1,3-Dioxepine and spiropyran derivatives of viomellein and other dimeric naphthopyranones from cultures of Aspergillus elegans KUFA0015 and their antibacterial activity

Two undescribed viomellein derivatives, xanthoelegansin and spiroxanthoelegansin, were isolated together with clavatol, sitosteanone, vioxanthin, xanthomegnin, viomellein, rubrosulphin, rubrosulphin diacetate, viopurpurin, ochratoxin A, ochratoxin A methyl ester, ochratoxin B and ochratoxin beta, from cultures of the marine spongeassociated fungus Aspergillus elegans KUFA0015. The structures of the undescribed compounds were established based on an extensive analysis of 1D and 2D NMR spectra as well as HRMS data. The structure of xanthoelegansin and the absolute configuration of its stereogenic carbons were confirmed by X-ray analysis. The change in conformation of xanthoelegansin was interpreted using quantum mechanical theoretical calculation data in combination with the observation of the change of the proton signals of the 1,3-dioxepine ring in 1HNMR spectra at varying temperatures. The mechanisms of the formation of xanthoelegansin and spiroxanthoelegansin from viomellein were proposed. Clavatol, sitosteanone, vioxanthin, xanthomegnin, viomellein, xanthoelegansin, rubrosulphin, rubrosulphin diacetate, ochratoxin A, ochratoxin A methyl ester, ochratoxin B and ochratoxin beta were assayed for their antibacterial activity against reference strains and multidrug-resistant isolates from the environment. The tested compounds were also evaluated for their capacity to inhibit biofilm formation in the reference strains.

Automated summary

Two new viomellein derivatives, xanthoelegansin and spiroxanthoelegansin, were isolated from a marine sponge-associated fungus. Xanthoelegansin's structure and chiral configuration were confirmed using X-ray analysis, while its conformational change was explained through quantum mechanical theoretical calculations. The compounds were also evaluated for antibacterial activity and biofilm inhibition, providing valuable information for future drug research.