α‑Arylidene Diacylglycerol-Lactones (DAG-Lactones) as Selective Ras Guanine-Releasing Protein 3 (RasGRP3) Ligands

Diacylglycerol-lactones have proven
to be a powerful template for
the design of potent ligands targeting C1 domains, the recognition
motif for the cellular second messenger diacylglycerol. A major objective
has been to better understand the structure activity relations distinguishing
the seven families of signaling proteins that contain such domains,
of which the protein kinase C (PKC) and RasGRP families are of particular
interest. Here, we synthesize a series of aryl- and alkyl-substituted
diacylglycerol-lactones and probe their relative selectivities for
RasGRP3 versus PKC. Compound 96 showed 73-fold selectivity
relative to PKCα and 45-fold selectivity relative to PKCε
for in vitro binding activity. Likewise, in intact cells, compound 96 induced Ras activation, a downstream response to RasGRP
stimulation, with 8–29 fold selectivity relative to PKCδ
S299 phosphorylation, a measure of PKCδ stimulation.