Bender Tobias, Schuhmann Tim, Magull Jörg, Grond Stephanie, von Zezschwitz Paultheo
Institut für Organische und Biomolekulare Chemie and Institut für Anorganische Chemie der Georg-August-Universität Göttingen, Tammannstrasse 2-4, D-37077 Göttingen, Germany.
J Org Chem. 2006 Sep 15;71(19):7125-32. doi: 10.1021/jo060149e.
The new spiro[4.5]acetal okaspirodiol (4) was isolated from Streptomyces sp. Gö TS 19 as a secondary metabolite in yields up to 380 mg/L. The structure of this cryptic ketotetrol was elucidated by different methods including X-ray analysis, and its equilibration under mildly acidic conditions furnishing three additional isomers was thoroughly studied. Although metabolite 4 is not the thermodynamically favored isomer, a high-yielding total synthesis was accomplished comprising a stereoselective spiroacetalization under equilibrium conditions. This approach benefits from the important influence of an intramolecular hydrogen bond on the stabilization of the spiro[4.5]acetal moiety. The biosynthesis of 4 was investigated by feeding experiments with 13C-labeled precursors proving its origin from a new type of the rare mixed acetate-glycerol biosynthetic pathway. All results are discussed on the basis of the structural diversity of spiroacetals in nature and their chemical properties.
