Synthesis of the N-terminal lipohexapeptide of human G(alpha o)-protein and fluorescent-labeled analogues for biological studies

For the study of biological signal transduction via heterotrimeric N-myrist oylated and S-palmitoylated G proteins, useful reagents may be lipidated pe ptides that contain the lipid groups and amino acid sequences of their pare nt lipoproteins. The synthesis of S-palmitoylated peptides like Myr-Gly-Cys (Pal)-Thr-Leu-Ser-Ala-OH (I), which represents the characteristic N-terminu s of the alpha-subunit of human G(alpha O) protein, is complicated by the p ronounced base- lability of the thioester. Lipidated G-protein peptide I an d various fluorescent-labeled analogues thereof were built up efficiently b y employing either the Pd-0-mediated removal of the allyl ester or the buty ryl choline esterase-catalysed cleavage of the choline ester as key step. T he removal of both blocking functions proceeds under very mild conditions a nd without undesired side reactions. In the cases studied the allyl ester p roved to be superior to the enzyme-labile choline ester. The fluorescent-la beled lipopeptides were subjected to microinjection experiments in NIH-3T3 cells, which revealed that the compounds meet basic requirements for applic ation in biology.