Synthesis and secondary structural studies of penta(acetyl-Hmb)A beta(1-40).

: The Fmoc solid phase synthesis of Aβ(1–40), a strongly aggregating peptide found in Alzheimer’s disease brain, was performed using 2-hydroxy-4-methoxybenzyl (Hmb) backbone amide protection. Hmb-Gly residues were incorporated using Nα-Fmoc-Hmb-Gly-OH rather than N,O-bisFmoc-Hmb-Gly-OPfp. Amino acid acylation of the sterically hindered Hmb-amino acids was monitored using ‘semi-on-line’ MALDI-TOF-MS in a novel application of this technique which significantly simplified the successful incorporation of these residues. Standard coupling conditions in N,N-dimethylformamide (DMF) were used throughout the synthesis. Comparative structural studies of acetyl-Hmb-protected and native Aβ(1–40) were performed to investigate the structural basis of Hmb-mediated disaggregation. The incorporation of backbone amide protection was observed by circular dichroism spectroscopy and gel electrophoresis to strongly affect the solution structure of Aβ(1–40). Despite the reported structure-breaking activity of Hmb groups, penta(acetyl-Hmb)Aβ(1–40) was found to adopt both α-helix and intermolecular β-sheet conformations. In 100% TFE a mixed α-helix/random coil structure was formed by the protected peptide indicating reduced α-helical propensity relative to Aβ(1–40). The protected peptide formed β-sheet structures in aqueous buffer. Gel electrophoresis indicated that, unlike native Aβ(1–40), penta(acetyl-Hmb)Aβ(1–40) did not form large aggregate species.