Improved preparation of amyloid-β peptides using DBU as Nα-Fmoc deprotection reagent

Previous studies have shown the amyloid peptides, A beta 1-40/42, to be exceptionally difficult to assemble by Fmoc-solid phase peptide synthesis due to the high hydrophobicity of the C-terminal segment and resulting on-resin aggregation. We found that the use of the stronger and more efficient base, DBU. at a concentration of 2% in DMF for N-alpha-Fmoc deprotection allowed substantially improved continuous flow solid phase assembly of the model peptide A beta 29-40/42 fragments. This suggested that. at least for these sequences. incomplete deprotection was a greater problem than Incomplete amino acid acylation. This base was then used during the synthesis of both A beta 1-40 and A beta 1-42, up to and including Ser(8), from which point 20% piperidine in DMF was utilized so as to avoid potential aspartimide formation at Asp(7). By this means, the deprotection efficiency through the difficult C-terminal portion of the sequence was much improved and resulted in increased availability of terminal amino groups for acylation. This simple strategy that obviates the need for special conditions significantly improved crude peptide quality and allowed considerable facilitation of subsequent purification. Copyright (C) 2001 European Peptide Society and John Wiley & Sons, Ltd.