Papulacandins, a new family of antibiotics with antifungal activity. Structures of papulacandins A, B, C and D.

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 long-chain 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 1 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.