FORSKOLIN CARBAMATES - BINDING AND ACTIVATION STUDIES WITH TYPE-I ADENYLYL-CYCLASE

Three series of analogs were regioselectively prepared from a protecte d forskolin precursor to afford 7-carbamoyl-7-desacetylforskolins (ser ies 1), 6-carbamoyl-7-desacetylforskolins (series 2), and 6-carbamoylf orskolins (series 3). The analogs were pharmacologically evaluated for binding (IC50) to and activation (EC(50)) of type I adenylyl cyclase in membranes from stably transfected Sig cell lines expressing a singl e adenylate cyclase subtype. The following ranges were determined for the IC50's and EC(50)'s of each individual series: series 1, IC50 = 43 -1600 nM, EC(50) = 0.5-9.6 mu M; series 2, IC50 = 65-680 nM, EC(50) = 0.63-6.5 mu M; series 3, IC50 = 21-271 nM, EC(50) = 0.5-8.1 mu M (fors kolin IC50 = 41 nM and EC(50) = 0.5 mu M). Activation paralleled bindi ng; however, some analogs exhibited poor binding and good activation w hereas others demonstrated good binding but poor activation. Steric bu lk tended to diminish binding and activation when at the 6- or 7-posit ion, although bulk was accommodated at the 6-position if the 7-site wa s reacetylated. Acylation of the 7-position by the carbamoyl linker or acetyl was important for obtaining good binding and activation; howev er, the effect was more pronounced with binding. For both binding and activation, small, linear, lipophilic substituents (propyl, allyl, iso propyl) are well tolerated at the 7-position but less so in the 6-posi tion, even when the 7-site is reacetylated. Planar aromatic moieties ( phenyl and 2-pyridinyl) demonstrated moderate to good potency for bind ing and activation when located at either the 6- or 7-positions. There is an overall trend toward increasing potency for both binding and ac tivation with polar substituents.