NO-CARRIER-ADDED CARBON-11-LABELED SN-1,2-DIACYLGLYCEROLS AND SN-1,3-DIACYLGLYCEROLS BY [C-11] PROPYL KETENE METHOD

This article describes the preparation of sn-1,2-[C-11]diacylglycerols and sn-1,3-[C-11]diacylglycerols by a no-carrier-added reaction based on a labeling method using [1-C-11]propyl ketene, which is one of the most potent acylating agents. [1-C-11]Propyl ketene was produced by pyrolytic decomposition of [1-C-11]butyric acid and was trapped in pyridine containing L-alpha-palmitoyl-lysophosphatidylcholine, producing L-alpha-palmitoyl-2-[1-C-11]butyryl-sn-glycero-3-phosphorylcholine. We adopted an enzymatic reaction to remove the phosphorylcholine, in which L-alpha-palmitoyl-2-[1-C-11]butyryl-sn-glycero-3-phosphorylcholine was incubated with phospholipase C, hydrolyzing to produce 1-palmitoyl-sn-2-[1-C-11]butyrylglycerol. Total synthesis time was about 50 minutes and the specific activity was estimated at 93 GBq/mu-mol (2.5 Ci/mu-mol) at end of synthesis. Radiochemical yield was 3.8% based on the trapped (CO2)-C-11. sn-1,3-[C-11]Diacylglycerol was also synthesized by [1-C-11]propyl ketene reaction with 1 -palmitoyl-sn-glycerol in a single procedure. The regional brain tissue radioactivities obtained in sn-1,2-[C-11]diacylglycerol were higher than those of sn-1,3-[C-11]diacylglycerol, and the regional values varied widely. In autoradiography of brain slices from conscious rats, sn-1,2-[C-11]diacylglycerol incorporation sites were discretely localized, especially in the amygdala, cerebral cortex, and hippocampus, suggesting that intensive neuronal processing occurred in these areas on the basis of phosphatidylinositol turnover.