Rates of racemization and coupling of cysteine active ester derivatives

Active ester-based peptide bond formation and its application in peptide synthesis

“…114,117 A variety of aryl esters have been examined to gain additional insight, 118 among which the pentafluorophenyl (PFP) esters (Scheme 25, 25-8) appeared to be of significant advance. [119][120][121] The van der Waals radius of fluorine is smaller than that of chlorine and slightly larger than that of hydrogen, yet its electronegativity far surpasses chlorine and hydrogen atoms. Given a better electron-withdrawing effect delivered by the fluorine atom without causing bulkiness, PFP esters are efficient even in a crowded environment.…”

“…Given a better electron-withdrawing effect delivered by the fluorine atom without causing bulkiness, PFP esters are efficient even in a crowded environment. 120,121 The advances of these active esters in solution-phase peptide synthesis prompted chemists to explore their applicability in SPPS. 122 A decapeptide ACP(65-74) and a dodecapeptide were prepared via SPPS with Fmoc-amino-acid PFP esters as the building blocks (Scheme 28).…”

Synthesis, Structure, and Biological Properties of Sequential Polypeptides

“…The pentafluorophenyl esters are considerably more reactive than the pentachlorophenyl esters, whereas the trichlorophenyl esters are slightly less so (87,88). The increased reactivity of the pentafluorophenyl esters makes them useful as alternatives for the backing-off procedure of Goodman and Stueben (89); however, their low melting points and ease of hydrolysis can be unfavorable characteristics (90,91).…”