A new tetracycline-type antibiotic named viridicatumtoxin B along with the known compound viridicatumtoxin has been isolated from the mycelium of liquid fermentation cultures of Penicillium sp. FR11. The structure of viridicatumtoxin B was determined on the basis of MS and NMR data. Viridicatumtoxin B inhibited the growth of Staphylococcus aureus including methicillinresistant S. aureus and quinolone-resistant S. aureus with MIC (m g/ml) of 0.5, which is similar with that of vancomycin, but 8ϳ64 times higher activity than that of tetracycline.

Aceriphyllum rossii Engler (Saxifragaceae) have been used as a nutritious food in Korea. We found that the methanol extract of the root portion of A. rossii potently inhibited the growth of Staphylococcus aureus , with a minimal inhibitory concentration (MIC) value of 8 microg/mL. Using mass spectrometry and nuclear magnetic resonance (NMR) studies, four active constituents were isolated and identified: aceriphyllic acid A, 3-oxoolean-12-en-27-oic acid, 3alpha-hydroxyolean-12-en-27-oic acid, and 3beta-hydroxyolean-12-en-27-oic acid. Aceriphyllic acid A and 3-oxoolean-12-en-27-oic acid showed a potent antibacterial activity against several strains of S. aureus , including methicillin-resistant S. aureus and quinolone-resistant S. aureus , with MIC values of 2-8 microg/mL, while 3alpha-hydroxyolean-12-en-27-oic acid and 3beta-hydroxyolean-12-en-27-oic acid exhibited a very weak activity, with MIC values of 128 microg/mL. The methyl ester derivative of aceriphyllic acid A lost its antibacterial activity. The time-kill study against S. aureus indicated that aceriphyllic acid A had rapid bactericidal activity. These results indicated that aceriphyllic acid A and 3-oxoolean-12-en-27-oic acid are the most active principles, and both the carboxylic group at C-27 and the hydroxyl group at C-24 in aceriphyllic acid A are critical for the rapid bactericidal activity.

Antibiotics U 1200Viridicatumtoxin B, a New anti-MRSA Agent from Penicillium sp. FR11. -The new tetracycline-type antibiotic viridicatumtoxin B (I) is isolated from the mycelium of liquid fermentation cultures of Penicillium sp. FR11 together with the known viridicatumtoxin. Both compounds show potent antibacterial activity against several strains of S. aureus including MRSA and QRSA, which is higher than that of tetracycline and similar to that of vancomycin.