In the course of our HPLC screening program, we investigated freshly isolated actinomycete strains from selected terrestrial and limnetic habitats with the aim of detecting novel drugs for pharmaceutical applications. The strains were grown in submerged culture in different media, and extracts prepared from mycelia and culture filtrates at various fermentation times. The metabolite patterns of the strains were analyzed by HPLC-diode array monitoring (HP 1090; Agilent, Waldbronn, Germany) in combination with our in-house HPLC-UVvisible database. Strain Acta 2259 was of special interest because of the presence of a prominent peak in the mycelium extract at a retention time of 12.9 min in our standardized gradient elution profile (Figure 1). It also showed an unusual UV-visible spectrum that differed from those of 933 reference compounds stored in our HPLC-UV-visible database. During the isolation and purification procedure, it became obvious that compounds 1–4 co-eluted in the same peak at a retention time of 12.9 min.