Studies on griseolic acid derivatives. III. Synthesis and biological activities of the adducts of griseolic acid and their base exchanged derivatives.
Addition reactions across the double bond of griseolic acid were investigated. Dihydrogriseolic acid was obtained by a reduction of the adduct having halogen at 4' position. The ring juncture of the two five membered rings of the dihydro derivatives was all "cis" configuration. An acetolysis of the protected dihydro derivative gave corresponding 1'-acetoxy sugar. A glycosidation of this sugar derivative with silylated bases gave base exchanged derivatives of the dihydrogriseolic acid. The influence of the base moiety and the double bond to the PDE inhibitory activity was investigated. As a result, we found that this type of compounds had a weaker inhibitory activity than the corresponding compounds which had an original double bond or a dihydro bond that made the ring juncture of the two five membered ring "trans".