Using a diacylglycerol-lactone (DAG-lactone) template previously developed in our laboratory as a scaffold with high binding affinity for C1 domains, we describe herein a series of novel DAG-lactones containing heterocyclic moieties (pyridines, quinolines, and indoles) as alpha-arylidene fragments. Some of the DAG-lactones obtained show selective binding to RasGRP3 as compared to PKCalpha by more than 2 orders of magnitude and possess subnanomolar affinities. Because activated C1 domains bound to their ligands (DAG or DAG-lactones) insert into membranes, the lipid composition of membranes (cellular, nuclear, and those of internal organelles) is an important determinant for specificity. Therefore, reaching a proper hydrophilic/lipophilic balance for these molecules is critical. This was achieved by carefully selecting partnering acyl fragments for the DAG-lactones with the appropriate lipophilicity. The results clearly show that the combination of chemical and physical properties in these molecules needs to be perfectly balanced to achieve the desired specificity.