spirolactone

Spiro-lactones are a class of spiro compounds in which a lactone ring—an cyclic ester—shares a single atom (the spiro center) with a second, typically saturated or unsaturated, ring. The two rings are linked at this spiro carbon, generating a rigid, three-dimensional framework. The spiro center is usually a quaternary carbon, and the overall topology may be chiral if the rings are unsymmetrical.

Structural diversity arises from the size of the lactone ring and the nature of the second ring, which can be carbocyclic or heterocyclic. The term spirolactone is used for both simple mono-lactones with a spiro connection and more complex, fused systems that incorporate additional rings or functionalities. Nomenclature follows the spiro notation, for example spirolactone derived from spiro[A.B], where A is the lactone-containing ring and B the second ring.

Occurrence and synthesis: Spirolactones appear in natural products and in synthetic libraries as constrained three-dimensional scaffolds. They are typically prepared by intramolecular esterification (lactonization) of hydroxy acids or by cyclization strategies that forge the lactone ring while setting the spiro junction. Enantioselective routes exist to access individual stereoisomers, using organocatalysis, metal catalysis, or substrate-controlled approaches.

Properties and applications: The spiro center imparts rigidity and defined geometry, which can enhance binding selectivity in biological targets. Spirolactones are studied as motifs in medicinal chemistry, natural product synthesis, and as building blocks for conformationally restricted molecules. Stability depends on ring sizes and substituents; hydrolysis under acidic or basic conditions is possible for many lactones.

See also: spiro compounds, lactones.