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. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.