While screening fermentations of fungal cultures for activity against antibiotic-resistant bacteria, a methanolic extract of the mycelial mass of an unidentified and non-sporulating fungal culture, LL-49F233, was found to exhibit activity against antibiotic-resistant bacteria. The active molecule was identified as a novel antibiotic, LL-49F233α, containing an N-methyltetramic acid attached to a bicyclic hydrocarbon skeleton (Figure 1)1). This compound was not cytotoxic against a panel of tumor cell lines and was inactive in a screen detecting DNA damage in Escherichia coli. Microbial metabolites containing a tetramic acid moiety have been known to have diverse biological activities2~10). Equisetin (a potent antibacterial and leukemogenic agent produced by a Fusarium equiseti)4), MBP049 (a proline hydroxylase inhibitor produced by a Ophiobolus rubellus)5), antibiotic PF1052 (an antibacterial agent produced by Phoma species)6) and lydicamycin (a novel antibacterial agent containing tetramic acid and amidinopyrrolidine moities)10) are some of the chemically related compounds. Streptolydigin and tirandamycin A are other typical members of the naturally occurring class of 3-dienoyl tetramic acids that possess potent antibacterial activity, particularly against anaerobes, and have been shown to inhibit bacterial RNA polymerase3,9). Some tetramic acid derivatives are also reported to be DNA gyrase inhibitors11). Since antibiotic LL-49F233α was structurally different from all known tetramic acid-containing compounds, we investigated its microbiological and mechanistic profiles.