title: Efficient Photochemical Synthesis of Peptide-α-Phenylthioesters.
abstract: Low yields and substantial epimerization of peptide-α-thioesters often compromise the overall efficiency of native chemical ligation (NCL). Peptide arylthioesters are more reactive than peptide alkylthioesters in NCL, but are also more difficult to handle due to their propensity to hydrolyze, and are therefore often generated in situ. However, pre-prepared peptide arylthioesters are required for some NCL applications. Here we present a 7-nitroindoline-based photochemical method that generates protected peptide phenylthioesters under neutral reaction conditions via their activated esters from photoreactive peptide precursors in high isolated yields, and with low levels of epimerization. This method is fully compatible with Fmoc-strategy solid-phase peptide synthesis. Global deprotection with trifluoroacetic acid furnishes peptide phenylthioesters for NCL. Photoreactive peptide precursors can also be converted into their hydrazides in two steps by this method.
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Andrew
authors.initials: A
authors.lastname: Pardo
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Tyrone J
authors.initials: TJ
authors.lastname: Hogenauer
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Zhefeng
authors.initials: Z
authors.lastname: Cai
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Julian A
authors.initials: JA
authors.lastname: Vellucci
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Efrain M
authors.initials: EM
authors.lastname: Castillo
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Carl W
authors.initials: CW
authors.lastname: Dirk
authors.affiliation: Department of Chemistry, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211 (USA).
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Franz
authors.affiliation: Department of Chemistry, University of Texas at El Paso, 500 W University Avenue, El Paso, TX 79968 (USA).
authors.forename: Katja
authors.initials: K
authors.lastname: Michael
keywords: acylation; hydrazides; peptides; photochemistry; thioesters