Protein kinase C (PKC) is a family of closely related serine and threonine kinases. Overactivation of some PKC isozymes has been postulated to occur in several disease states, including diabetic complications. Selective inhibition of overactivated PKC isozymes may offer a unique therapeutic approach to disease states such as diabetic retinopathy. A novel series of 14-membered macrocycles containing a N−N‘-bridged bisindolylmaleimide moiety is described. A panel of eight cloned human PKC isozymes (α, βI, βII, γ, δ, ε, ζ, η) was used to identify the series and optimize the structure and associated activity relationship. The dimethylamine analogue LY333531 (1), (S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno-1H,13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene-1,3(2H)-dione, inhibits the PKCβI (IC₅₀ = 4.7 nM) and PKCβII (IC₅₀ = 5.9 nM) isozymes and was 76- and 61-fold selective for inhibition of PKCβI and PKCβII in comparison to PKCα, respectively. The additional analogues described in the series are also selective inhibitors of PKCβ. LY333531 (1) exhibits ATP dependent competitive inhibition of PKCβI and is selective for PKC in comparison to other ATP dependent kinases (protein kinase A, calcium calmodulin, caesin kinase, src tyrosine kinase). The cellular activity of the series was assessed using bovine retinal capillary endothelial cells. Retinal endothelial cell dysfunction has been implicated in the development of diabetic retinopathy. Plasminogen activator activity stimulated by a phorbol ester (4β-phorbol 12,13-dibutyrate) in endothelial cells was inhibited by the compounds in the series with ED₅₀ values ranging from 7.5 to 0.21 μM. A comparison of the PKC isozyme and related ATP dependent kinase inhibition profiles is provided for the series and compared to the profile for staurosporine, a nonselective PKC inhibitor. The cellular activity of the series is compared with that of the kinase inhibitor staurosporine.