title: A Backbone Linker for BOC-Based Peptide Synthesis and On-Resin Cyclization: Synthesis of Stylostatin 1(,).
abstract: We have developed a new 4-alkoxybenzyl-derived linker that anchors the C-terminal amino acid to the resin through the alpha-nitrogen atom. The linker allows BOC solid-phase peptide assembly and peptide cleavage using standard HF protocols. This linking strategy provides a versatile on-resin route to cyclic peptides and avoids the diketopiperazine formation that is prominent when using FMOC chemistry on backbone linkers. The linker was prepared by forming the aryl ether from 4-hydroxybenzaldehyde and bromovaleric acid. Subsequent reductive amination of the aldehyde with an allyl-protected amino acid ester and acylation of the resulting secondary amine provided the tertiary amide. After linking the amide to the resin, standard BOC SPPS, followed by allyl deprotection, cyclization, and HF cleavage gave cyclic peptides in high purity. To exemplify the strategy, the cytotoxic heptapeptide, stylostatin 1, was synthesized from two linear precursors. For comparison purposes, the yields of the on-resin and solution-phase cyclization were determined and found to be dependent upon the linear precursor. This linker technology provides new solid-phase avenues in accessing libraries of cyclic peptides.
authors.affiliation: Centre for Drug Design and Development, The University of Queensland, St. Lucia 4072, Brisbane, Australia.
authors.forename: Gregory T.
authors.initials: GT
authors.lastname: Bourne
authors.forename: Wim D. F.
authors.initials: WD
authors.lastname: Meutermans
authors.forename: Paul F.
authors.initials: PF
authors.lastname: Alewood
authors.forename: Ross P.
authors.initials: RP
authors.lastname: McGeary
authors.forename: Martin
authors.initials: M
authors.lastname: Scanlon
authors.forename: Andrew A.
authors.initials: AA
authors.lastname: Watson
authors.forename: Mark L.
authors.initials: ML
authors.lastname: Smythe