Abstract A series of new analogues of 1-β- d-ribofuranosylbenzimidazole 3′,5′-phosphate (cBIMP) has been designed according to the properties predicted by the MNDO method, and synthesised from substituted benzimidazoles. Dipole vectors and HOMO and LUMO energies for each benzimidazole base were calculated by the MNDO method and the lipophilicities of the cBIMP derivatives were determined. In general, the cBIMP derivatives activate cAMP-dependent protein kinases I and II and preferentially bind to site B, especially for the type II kinase, with 2-trifluoromethyl-cBIMP and 5,6-difluoro-cBIMP exhibiting the highest site selectivity. Each cBIMP derivative can stimulate cGMP-stimulated cyclic phosphodiesterase (cGS-PDE), with 5,6-dimethyl-cBIMP being as potent as cGMP, and also inhibit cGMP-inhibited phosphodiesterase (cGI-PDE). Only the 2-trifluoromethyl-cBIMP and the Rp-phosphorothioates (cBIMPS) (equatorial P=S) were resistant to hydrolysis by cPDE. The Sp-phosphorothioates were hydrolysed slowly, if at all. In addition to exhibiting a high lipophilicity, the most active compounds for the induction of apoptosis and inhibition of proliferation were also resistant to cPDE (Sp-5,6-dichloro-cBIMPS) and / or were potent activators of cAMP-dependent protein kinase (5,6-dichloro-cBIMP).