No abstract

We report on the spontaneous, reversible intramolecular transesterification of natural labdane lactones. Through extensive spectroscopic analysis, the interconversion between the two tautomers was investigated, which could be retarded when the free hydroxy group was acetylated or the exocyclic double bond of the lactone ring was mutated. Besides, a conversion mechanism was postulated, and the energy barriers were calculated by density functional theory calculations. Furthermore, the tautomers were found to inhibit the virulence of the efflux pump-deficient Candida albicans DSY654.

The first total synthesis of penicimutanin A (1) was achieved within 10 steps (LLS).

A divergent synthetic approach to biogenetically related diterpenoids such as ent-kauranes, ent-trachylobanes, ent-beyerane, and ent-atisane has been developed. The unified synthetic route involves the De Mayo reaction to rapidly generate the bicyclo[3.2.1]-octane moiety of ent-kaurane. The key reactions also include bioinspired nucleophilic cyclopropanation generating the [3.2.1.0 2,7 ]-tricyclic core of ent-trachylobane and regioselective cyclopropane fragmentation furnishing ent-beyerane and ent-atisane through the nucleophilic attack and protonation of the cyclopropane ring. This strategy enables the asymmetric total syntheses of six diterpenoids from the commercially available geraniol.