Synthetic Transformations of Higher Terpenoids. 41. Synthesis and Anti-Inflammatory Activity of 4-(Carboxyalkyl)-18-nor-isopimara-7,15-Dienes

Synthetic methods were developed for isopimaric acid derivatives, the terminal carboxylic acid of which was separated by two or three methylenes from the tricyclic skeleton. Their anti-inflammatory activity was studied. A Wittig reaction of isopimarinal (obtained from isopimaric acid) with the phosphorus ylide generated from methoxymethyl(triphenyl)phosphonium chloride using butyllithium formed a mixture of (Z)- and (E)-alkenes (54% yield) and 4-[(Z)-pentenyl]-18-nor-isopimara-7,15-diene (17% yield). Hydrolysis of the mixture of enol ethers by p-toluenesulfonic acid in Me2CO produced 4-(2-oxoethyl)-18-nor-isopimara-7,15-diene. Olefination of pimarinal and its homolog by a Horner-Wadsworth-Emmons reaction led to the corresponding ethers of (E)-alkenes (81-85% yield). Reduction of the double bond by Mg in MeOH and hydrolysis of the ethers proceeded smoothly to the corresponding 4-(carboxyalkyl)-18-nor-isopimara-7,15-dienes (74 and 88% yield). The structure of 4-(2-carboxyethyl)-18-nor-isopimara-7,15-diene was established by an X-ray crystal structure analysis. Significant anti-inflammatory activity of the new C4-modified isopimaric acid derivatives was found in in vivo tests.

Automated summary

A synthetic method was developed for isopimaric acid derivatives, and their anti-inflammatory activity was studied. Significant anti-inflammatory activity was found in the new C4-modified isopimaric acid derivatives.