Overcoming Challenges in Automated Long Peptide Synthesis — A Multi-pronged Approach

Abstract

Introduction Over the past 20 years peptides have been identified as a promising source for novel pharmaceutical drug candidates, most recently evidenced by approval of Fuzeon for treatment of HIV [1]. However, delivery and manufacturing challenges have impeded widespread development of peptide related therapeutics. Historically, the synthesis of longer peptides has been prohibited by synthetic inefficiencies associated with peptide aggregation. New strategies have tempered the resources required to achieve economically viable preparation of longer and “difficult” peptides. Recently, Abgent has substantially increased the success for synthesis of long and difficult peptides, working in conjunction with EMD Biosciences and Protein Technology Inc. to apply pseudoproline dipeptides in automated synthesis. Pseudoproline dipeptides consist of ψP-X, where X is any amino acid and ψP is a serine or threonine modified via reversible linkage of amino and side chain hydroxy groups to form an oxazolidine ring [2,3]. Structural perturbation from pseudoproline dipeptides incorporated into protein or peptide structures disrupts adoption of helices and -sheets, and this function has been successfully exploited to efficiently inhibit aggregation of hydrophobic peptides in solid-phase peptide synthesis (SPPS). Mild TFA cleavage post-synthesis lead to full recovery of the native serine or threonine amino acid structure. Pseudoproline dipeptides have proven indispensable to markedly improved yield, solubility and ease of HPLC purification., thereby rendering accessible to SPPS many previously infeasible long or difficult peptide sequences of biological value [4-7].