Synthesis and application in SPPS of a stable amino acid isostere of palmitoyl cysteine

(S)-2-Amino-4-(2-pentadecyl-1,3-dioxolan-2-yl)-butanoic acid, 11, Pdiob, a synthetic analogue C-isostere of palmitoylated cysteine, has been prepared starting from tetrabenzyl glutamic acid. The less hindered benzyl carboxylate ester was transformed into the corresponding β-ketophosphonate and subjected to a Horner-Wadsworth-Emmons reaction followed by hydrogenation/hydrogenolysis. This product was used for the preparation on solid phase and under microwave dielectric heating of a highly lipidated peptide that can be considered as an acid stable analogue of the C-terminus of the H-Ras heptapeptides 180-186.