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In the preceding papers' the isolation and characterization of the new antibiotic haloquinone, produced by Streptomyces venezuelae ssp. xanthophaeus were described. In the following we report the structural data and some chemical reactions of the antibiotic. Mass spectral and elemental analysis of haloquinone (1a) are in agreement with the formula C17H12O,. The presence of two C-methyl groups is proved by KUHN-ROTH oxidation. Haloquinone is an indicator substance. The dark red antibiotic gives a blue solution in NaOH, the color immediately turns yellow by reducing it with zinc dust, the reduced form is reoxidized by air. This behaviour is typical for a hydroxyquinone. This observation is supported by the fact that haloquinone forms a bluegreen color in 0.001 N ethanolic magnesium acetate or, after heating, in acetic anhydride/pyroboracetate. The pigment is insoluble in sodium hydrogencarbonate solution and does not react quickly with diazomethane at room temperature. Evidently there are no carboxy or unchelated phenolic hydroxyl groups. A characteristic reaction of haloquinone is the quick (1 minute) decolorization of its alkaline solution with hydrogen peroxide caused by the ortho-quinone structure (see below). The spectral data of haloquinone (1a) are very similar to those of piloquinone (2a), isolated from Streptomyces pilosus2"3•'). Comparisons of the UV and the PMR data are given in Tables 1 and 2. The PMR-signals of the side chain of 2a are missing in the spectrum of haloquinone (la). The chemical reactions of haloquinone (la) and piloquinone (2a) are quite similar2.3), i.e. with ophenylenediamine the yellow quinoxaline-derivative 3 can be obtained, which proves the ortho-quinone structure. The reaction of haloquinone with methyliodide/silver(I)-oxide leads to the yellow dimethyl ether 1b, acetylation with acetic anhydride/sodium acetate yields the unstable yellow diacetate lc. The

Metabolic products of microorganisms. 208 Haloquinone, a new antibiotic active against halobacteria. II. Chemical structure and derivatives.