title: Backbone Amide Linker (BAL) Strategy for N(alpha)()-9-Fluorenylmethoxycarbonyl (Fmoc) Solid-Phase Synthesis of Unprotected Peptide p-Nitroanilides and Thioesters(1).
abstract: A novel and general backbone amide linker (BAL) strategy has been devised for preparation of C-terminal modified peptides containing hindered, unreactive, and/or sensitive moieties, in concert with N(alpha)()-9-fluorenylmethoxycarbonyl (Fmoc) solid-phase synthesis protocols. This strategy comprises (i) start of peptide synthesis by anchoring the penultimate residue, with its carboxyl group orthogonally protected, through the backbone nitrogen, (ii) continuation with standard protocols for peptide chain elongation in the C --> N direction, (iii) selective orthogonal removal of the carboxyl protecting group, (iv) solid-phase activation of the pendant carboxyl and coupling with the desired C-terminal residue, and (v) final cleavage/deprotection to release the free peptide product into solution. To illustrate this approach, several model peptide p-nitroanilides and thioesters have been prepared in excellent yields and purities, with minimal racemization. Such compounds are very difficult to prepare by standard Fmoc chemistry, including the BAL strategy as originally envisaged.
authors.affiliation: Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, and Department of Organic Chemistry, University of Barcelona, 08028 Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Alsina
authors.forename: T. Scott
authors.initials: TS
authors.lastname: Yokum
authors.forename: Fernando
authors.initials: F
authors.lastname: Albericio
authors.forename: George
authors.initials: G
authors.lastname: Barany