Design and synthesis of isoforskolin derivatives and evaluation of cAMP activation with mechanistic investigation.

To overcome poor adenylyl cyclase (AC) selectivity and weak cyclic adenosine monophosphate (cAMP) agonistic activity of isoforskolin (ISOF), eleven derivatives were synthesised using ISOF as the parent compound. cAMP agonistic activity suggested that compound 10 possessed cAMP activation potency and preferential activation towards AC5 (92.8%), similar to the 96.8% of the positive control forskolin (FSK) and higher than the 90.0% of ISOF. Dose-response curves further demonstrated that the EC50 value of compound 10 was 1.85 μM, slightly higher than the 1.05 μM of FSK. Preliminary structure-activity suggested that substitution at the C7 position contributed to AC5-preferential activation. Network pharmacology and molecular docking predicted that compound 10 was associated with cAMP signalling, calcium signalling, and adrenergic signalling in cardiomyocytes, and formed a putative complex with AC5 (-9.21 kJ/mol) via hydrogen bonds, π-alkyl stacking, and hydrophobic interactions. Overall, compound 10 preferentially activates AC5, representing a promising candidate for developing AC5-preferential agonists.