Concise synthesis of (+)-subersic acid from (−)-Sclareol

CuLi2Cl4 catalysed cross-coupling strategy for the formal synthesis of the diterpenoid (+)-subersic acid from (–)-sclareol

A CuLi2Cl4-catalysed regioselective cross-coupling is used in a key step leading to the concise synthesis of (+)-subersic acid with an overall yield of 25.7% from commercially available (–)-sclareol. The coupled product 15-(2-methoxy-5-carbomethoxy)phenyl-labda-8(9),13 E-diene was obtained in 62% yield under CuLi2Cl4 conditions starting from 2-iodo-4-carbomethoxyanisole and 15-acetoxy-labda-8(9),13 E-diene. These were derived from 4-hydroxybenzoic acid and (–)-sclareol respectively. The 15-(2-methoxy-5-carbomethoxy)phenyl-labda-8(9),13 E-diene was easily transformed into (+)-subersic acid by demethylation of the phenol ether and ester. This cross-coupling strategy showed a good functional group tolerance and various (+)-subersic acid derivatives were obtained in moderate yields.

Terpenoids with Special Pharmacological Significance: A Review

Terpenoids are a very prominent class of natural compounds produced in diverse genera of plants, fungi, algae and sponges. They gained significant pharmaceutical value since prehistoric times, due to their broad spectrum of medical applications. The fragrant leaves of Eucalyptus trees are a rich source of terpenoids. Therefore this review starts by summarizing the main terpenoid compounds present in Eucalyptus globulus, E. citriodora, E. radiata and E. resinifera and describing their biosynthetic pathways. Of the enormous number of pharmaceutically important terpenoids, this paper also reviews some well established and recently discovered examples and discusses their medical applications. In this context, the synthetic processes for (–)-menthol, (–)- cis-carveol, (+)-artemisinine, (+)-merrilactone A and (–)-sclareol are presented. The tricyclic sesquiterpene (–)-englerin A isolated from the stem bark of the Phyllanthus engleri plant ( Euphorbiaceae) is highly active against certain renal cancer cell lines. In addition, recent studies showed that englerin A is also a potent and selective activator of TRPC4 and TRPC5 calcium channels. These important findings were the motivation for several renowned research labs to achieve a total synthesis of (–)-englerin A. Two prominent examples – Christmann and Metz – are compared and discussed in detail.