Synthesis of pentafluorophenyl, 2,4,5-trichlorophenyl and pentachlorophenyl esters of Fmoc-amino acids using Fmoc-amino acid chlorides as intermediates

The synthesis of pentafluorophenyl,2,4,5-trichlorophenyl and pentachlorophenyl esters ofFmoc-amino acids has been accomplished via Fmoc-amino acidchlorides as intermediates. A two phase system with a mildin-organic base (3% NaHCO₃) in the aqueous layer was used. The esterification reaction was clean and complete in about2–3 hr. All the esters prepared have been obtained in goodyield and are fully characterised.