The aspartimide problem in Fmoc‐based SPPS. Part I

Abstract

A variety of Asp β-carboxy protecting groups, Hmb backbone protection and a range of Fmoc cleavage protocols have been employed in syntheses of the model hexapeptide H-VKDGYI-OH to investigate the aspartimide problem in more detail. The extent of formation of aspartimide and aspartimide-related by-products was determined by RP-HPLC. This study included three new Fmoc-Asp-OH derivatives: the β-(4-pyridyl-diphenylmethyl) and β-(9-phenyl-fluoren-9-yl) esters and also the orthoester Fmoc-β-(4-methyl-2,6,7-trioxabicyclo[2.2.2]-oct-1-yl)-alanine. 3-Methylpent-3-yl protection of the Asp side chain resulted in significant improvements with respect to aspartimide formation. Complete suppression was achieved using the combination OtBu side chain protection and Hmb backbone protection for the preceding Gly residue.

Design of a Specific Colonic Mucus Marker Using a Human Commensal Bacterium Cell Surface Domain

“…Moreover, MS analysis of the identified peak revealed the presence of a complex mixture of similar peptides with a mass deviation of Ϫ18 or ϩ67, reflecting the presence of aspartimide and piperidide byproducts in a highly significant amount. Aspartimide formation (26) and subsequent base-catalyzed ring opening during Fmoc solid phase peptide synthesis has been described to be strongly dependent on the previous coupled amino acid (27) in relation with the global mixing time of the Asp-containing peptide resin in the Fmoc deprotection solution (28). Along this line, the MUB 70 sequence accumulates eight highly sensitive occurrences (three Asp-Gly, two Asp-Asn, two Asp-Asp, one Asp-Thr), among which the Asp-Gly sequences are particularly prone to aspartimide formation.…”

Synthesis and folding of a mirror-image enzyme reveals ambidextrous chaperone activity

“…4B), it will be important to improve their quality and yield to expand application of this work to even larger synthetic proteins. We speculate that subtle synthetic defects in our proteins include single-residue deletions, racemization (50), and aspartamide formation (51,52).…”

Solid‐phase synthesis of tailed cyclic RGD peptides using glutamic acid: unexpected glutarimide formation

“…For example, allyl (All) and allyloxycarbonyl (Aloc) groups, for protecting carboxylic and amino groups, respectively, enable the construction of a lactam bridge selectively between carboxylic and amino groups while the peptide is still attached to the resin. One major problem with using aspartic acid for orthogonal peptide synthesis is the formation of aspartimide [14][15][16][17]. Glutamic acid has a similar structure to aspartic acid.…”