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In the course of our screening for new antibiotic, newmembersof benz[a]anthraquinone antibiotics (I and II), which showed antibacterial activity against Gram-positive bacteria were isolated from a culture broth of Streptomyces tsusimaensis MI310-38F7. This strain produced nonactin and a minor yellow compound (III) which was identical with X-14881 E1}. This report describes the isolation, characterization and structure determination of these compounds, named 6-deoxy-8-0-methylrabelomycin (I) and 8-0-methylrabelomycin (II).

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Novel chlorosis-inducing substances, AB5046Aand B, were isolated from the culture broth of a fungal strain. The producing organism, designated AB5046, was identified as a member of Nodulispor ium.AB5046Aand B were purified by extraction with EtOAc and silica gel chromatography. The structure of AB5046Aand B were determined to be 2-butyryl-3,5-dihydroxy-cyclohex-2-ene-l-one and 2-acetyl-3,5-dihydroxy-cyclohex-2-enel-one, respectively, by spectroscopic analyses. AB5046Aand B induced chlorosis against Japanese barnyard millet in vitro. The chlorosis activity of these compoundswas stronger against monocotyledonsthan dicotyledons. Inhibitionsof chloroplast formation, photosynthesis and essential amino acid's biosynthesis are considered as the important and attractive targets in the development of new herbicides with low toxicity to mammals. Some herbicides such as pyrazolate1}, methoxy-phenone2), fluridone3) are practically used as the inhibitors of chloroplast formation (chlorosis-inducing chemicals). Although it is known that some natural products (virdomic acids4), alternaric acid5), rhizobitoxin6), l -amino-2-nitrocyclopentanecarboxylic acid7), tentoxin8), etc.) have chlorosis-inducing activity, they are not utilized for control of weeds. In the course of screening for new herbicides, we found that a soil fungus produced new herbicidal substances, named AB5046A(1) and B (2), which induced chlorosis against Japanese barnyard millet in vitro. The color of generating foliage of the barnyard millet became completely white, as if they were bleached, whenthe seeds were treated with these compounds.In this paper, we describe the identification of the producing organism together with the isolation, fermentation, structure determination and biological activities of 1 and 2. Materials and Methods TaxonomyThe AB5046Aand B producing organism, strain AB5046, was isolated from a soil sample collected at Seta-gun in Gummaprefecture. Morphological observations of the strain grownon malt extract agar were carried out with a light microscope (Olympus Model BHS) and a scanning electron microscope (Hitachi S-430). The characteristics of the culture on potato -dextrose agar and malt extract agar were determined after 2 weeks of incubation