Polyketides with antimicrobial activity from the solid culture of an endolichenic fungus Ulocladium sp.

Two new polyketides, 7-hydroxy-3, 5-dimethyl-isochromen-1-one (1) and 6-hydroxy-8-methoxy-3a-methyl-3a,9b-dihydro-3H-furo[3,2-c]isochromene-2,5-dione (2), along with eleven known compounds, 5′-methoxy-6-methyl-biphenyl-3,4,3′-triol (3), 7-hydroxy-3-(2-hydroxy-propyl)-5-methyl-isochromen-1-one (4), rubralactone (5), isoaltenuene (6), altenuene (7), dihydroaltenuenes A (8), altenusin (9), alterlactone (10), 6-O-methylnorlichexanthone (11), norlichexanthone (12), and griseoxanthone C (13) were isolated from the culture of the endolichenic fungus Ulocladium sp. Compound 2 was obtained as a racemate with an unprecedented chemical skeleton. The NMR data assignments for 3 and 4 were achieved for the first time. Compounds 1–13 were screened for their antimicrobial and radical scavenging activities. Compound 1 showed some antifungal activity against Candida albicans SC 5314 with IC50 of 97.93 ± 1.12 μM. Compounds 11–13 showed strong activity against Bacillus subtilis with IC50 in the range of 1–5 μM. Compound 12 significantly inhibited the growth of methicillin-resistant Staphylococcus aureus with IC50 of 20.95 ± 1.56 μM. Compounds 9 and 10 showed strong radical scavenging activity in comparison with vitamin C. The plausible biosynthetic pathways for compounds 1, 2, and 4–8 were discussed.

Graphical abstractTwo new polyketides (1–2) along with eleven known compounds (3–13) were isolated from the culture of the endolichenic fungus UlocladiumXylaria sp. Compound 2 was obtained as a racemate with an unprecedented chemical skeleton. All the compounds were evaluated for their antimicrobial and radical scavenging activities.Figure optionsDownload full-size imageDownload high-quality image (69 K)Download as PowerPoint slide