Hofmannolin, a cyanopeptolin from Scytonema hofmanni PCC 7110

Two depsipeptide metabolites, scyptolin A and B, were reported recently from the axenically grown terrestrial cyanobacterium Scytonema hofmanni PCC 7110. A related, novel depsipeptide was isolated from this Scytonema and designated hofmannolin. The amino acid analysis in context with infrared, mass and 1H/13C-NMR spectroscopies revealed a cyclic depsipeptide structure of M(r) 1073 belonging to the class of cyanopeptolins. Two peculiar features distinguish hofmannolin from other cyanopeptolins: O-methylated tyrosine forms the sixth moiety from the amino terminus, and the N-terminus is blocked by 2-hydroxy-3-methyl-valeric acid, a residue that has not yet been reported as a component in other cyanopeptolins. Preliminary assays of peptidase inhibitory and antimicrobial activities suggested negligible bioactivities for hofmannolin.