Synthesis and application of N-[1-(4-(4-fluorophenyl)-2,6-dioxocyclohexylidene)ethyl] (Fde)-protected amino acids for optimization of solid-phase peptide synthesis using gel-phase (19)F NMR spectroscopy.

N-[1-(4-(4-fluorophenyl)-2,6-dioxocyclohexylidene)ethyl] (Fde) protected amino acids have been prepared and applied in solid-phase peptide synthesis monitored by gel-phase (19)F NMR spectroscopy. The Fde protective group could be cleaved with 2% hydrazine or 5% hydroxylamine solution in DMF as determined with gel-phase (19)F NMR spectroscopy. The dipeptide Ac-L-Val-L-Val-NH(2) 12 was constructed using Fde-L-Val-OH and no noticeable racemization took place during the amino acid coupling with N,N'-diisopropylcarbodiimide and 1-hydroxy-7-azabenzotriazole or Fde deblocking. To extend the scope of Fde protection, the hydrophobic nonapeptide LLLLTVLTV from the signal sequence of mucin MUC1 was successfully prepared using Fde-L-Leu-OH at diagnostic positions.