Secondary Metabolites by Chemical Screening, 22. Gabosines, New Carba‐sugars From <i>Streptomyces</i>

Abstract

Abstract Chemical screening of different Streptomycetes strains resulted in the detection, isolation, and structure elucidation of a number of novel carba‐sugars. The constitution of these secondary metabolites, named gabosines A to K ( 1 to 11 ), was deduced from spectroscopic data as well as chemical transformation reactions. The gabosines exhibit a basic C 7 skeleton and can be characterized as hydroxylated branched cyclohexanone derivatives, which show structural similarities to carbohydrates deriving from secondary metabolism. The configuration fo the gabosines (absolute stereochemistry for 1 , 4 , 5 , and 6 ; relative configuration for the remaining metabolites) was determined by derivatization with chiral acids (Helmchen's method), NMR spectral analysis, as well as by a comparison of optical rotation values with those of the already known gabosines B ( 2 ) and C ( 3 ). The new term “ketocarbasugars” is used to characterize a typical ketone containing subgroup of carba‐sugars originating from microbial sources. The well available natural gabosines can be used as suitable chiral building blocks.