Spirocyclic Orthoesters, Orthothioesters and Orthoaminals in the Synthesis and Structural Modification of Natural Products

摘要

Spirocyclic scaffolds are embedded in several families of rat ural products. In the spirocyclic structure, the two rings constituting the spirane are linked through a common carbon atom. This review covers families of compounds that have three heteroatoms directly attached to the spirocarbon. Common heteroatoms are nitrogen, oxygen and sulfur, constituting spirocyclic orthoesters, ortholactones, orthothioesters and orthoaminals, or combinations thereof. Embedded spirocyclic scaffolds introduce steric restrictions and thereby influence bioactivity. In polymer chemistry, synthetic ortholactones may serve as monomers. Synthesis of anomeric spironucleosides will afford molecules where the basic unit is in a fixed conformation around the N-glycosidic bond. Synthesis of glycosidic and 2-deoxyglycosidic ortholactones in disaccharides and regioselective reductive cleavage of cyclic cirthoesters result in stereoselective beta-(1 -> 4)-glycosidic bond formation. Pyra nose and fura nose free-radical chemistry via spirocyclic orthoesters can be applied in the generation of carbacyclic sugars and nucleosides.