Derivatives of di-O-octanoylglycerol and mono-O-octylglycerol as modulators of protein kinase C and diacylglycerol kinase activities.

Twelve analogs of 1,2-di-O-octanoylglycerol modified at C-3 and three quaternary N-alkyl-ammonium derivatives of glycerol were synthesized. The compounds were tested in vitro as potential modulators of the calcium activated, phospholipid dependent protein kinase C (PKC) and diacylglycerol (DAG) kinase activities in order to understand the molecular interactions of these enzymes with their natural activators, inhibitors, or substrates. PKC activity was assayed by measuring histone H1 phosphorylation, and the compounds synthesized were tested either in the presence (inhibitors) or in the absence (activators) of 1,2-di-O-octanoylglycerol analogs with the phosphatidylserine/Ca2+ mixture. DAG kinase activity was measured by the incorporation of phosphate into 1,2-di-O-oleoyl-sn-glycerol in the presence of the various analogs synthesized. In regard to PKC activity, the assays revealed that 1,2-di-O-octanoylglycerol analogs are inactive when modified at C-3 with groups which do not permit hydrogen bonding. Under our conditions, di-O-octanoylthioglycerol, which has been reported as inactive, was able to activate PKC in the presence of phosphatidylserine. It has been shown to give a synergistic activation with diacylglycerol and had no affinity for the phorbol ester receptor binding site, suggesting that O-octanoylthioglycerol interacts with the enzyme at a different site from the phorbol ester receptor binding site. PKC and DAG kinase activities are inhibited by N-alkyl-ammonium compounds (IC50 24 microM) only when either two 8-carbon alkyl or acyl chains are present at the 1- and 2-positions of the glycerol backbone.(ABSTRACT TRUNCATED AT 250 WORDS)