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The structures of the papulacandins A, B, C and D, new antibiotics of Papularia sphaerosperma have been established by means of spectral analysis and degradation reactions. Base catalysed hydrolysis of the main product papulacandin B (1) gave two new hydroxylated longchain unsaturated fatty acids 5 and 6 along with a hitherto unknown spirocyclic diglycoside 7. The structure of 7 was determined by further degradation reactions. The positions of attachment of the two fatty acids to the spirocyclic diglycoside 7 through ester-bonds were established by selective base catalysed hydrolysis of 1 and spectral analysis of I and some derivatives and degradation products thereof. The structures of papulacandin A (2), papulacandin C (3) and papulacandin D (4) were determined in an analogous way.

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A number of rifamycin non-producing UV-mutants derived from Nocardia mediterranei strains N813 (rifamycin B producer) and A101) (aro-mutant excreting shikimate derived from strain N813) were found to accumulate an identical complex of aromatic components instead of rifamycin B. The main component of this aromatic complex, product P8/1-OG, was isolated from six of these P--mutant strains and identified spectroscopically as a very early precursor in the biosynthesis of rifamycins.As described in parts I and II of this series of papers1 ,2) This approach has not yet led to the isolation of mutants blocked in one of the four enzyme activities mentioned above. All the P--mutants derived from strain N813 are aro+, rifamycin-, whereas the P--mutants derived from strain A10 are aro, rifamycin-.As all the mutants from A 10 still excrete shikimate and no other shikimate pathway intermediates, the rifamycin--mutation is not due to a second block in the shikimate pathway before the branch point but is due to additional blocks in the rifamycin biosynthesis behind the branch point.