1-ACETYL-7-DEACETYLFORSKOLIN - A POTENTIAL NONSPECIFIC INACTIVE ANALOG OF FORSKOLIN FOR ESTIMATION OF ITS SPECIFIC HIGH-AFFINITY BINDING AND ADENYLYL-CYCLASE STIMULATION IN-VITRO

Labeled and unlabeled 1-acetyl-7-deacetylforskolin and forskolin were synthesized by acetylation of 7-deacetylforskolin with labeled and unl abeled acetyl chloride. The binding of 1-acetyl[1-acetyl-C-11]-7-deace tylforskolin ([C-11]1-acetyl-7-deacetylforskolin) and [7-acetyl-C-11]f orskolin ([C-11]forskolin) to rat brain membranes was studied using fi ltration assay. The [C-11]forskolin binding was decreased with an incr easing load of unlabeled forskolin, whereas [C-11] 1-acetyl-7-deacetyl -forskolin binding was always very low, the level of which agreed with that of the non-specific binding in forskolin. However, binding of [7 -acetyl-C-11]1,9-dideoxyforskolin, which has been used as a nonspecifi c inactive analog of forskolin, had a higher binding ratio than that o f the non-specific binding of forskolin. The binding of [C-11]forskoli n was not affected by an increased load of cold 1-acetyl-7-deacetylfor skolin. Forskolin activated adenylyl cyclase (AC) in cultured human en dothelial cells, whereas 1-acetyl-7-deacetylforskolin did not. These d ata show that the 1-acetyl-7-deacetylforskolin lacks specific binding affinity and the ability to stimulate AC, while it has similar physica l properties with forskolin. The compound 1-acetyl-7-deacetylforskolin would be a suitable ''non-specific inactive analog'' of forskolin wit h which to estimate its specific high-affinity binding capacity and to validate forskolin-specific AC stimulation in vitro.