Suppression of alpha-carbon racemization in peptide synthesis based on a thiol-labile amino protecting group

Abstract

In conventional solid-phase peptide synthesis (SPPS), α-amino groups are protected with alkoxycarbonyl groups (e.g., 9-fluorenylmethoxycarbonyl [Fmoc]). However, during SPPS, inherent side reactions of the protected amino acids (e.g., α-C racemization and aspartimide formation) generate by-products that are hard to remove. Herein, we report a thiol-labile amino protecting group for SPPS, the 2,4-dinitro-6-phenyl-benzene sulfenyl (DNPBS) group, which is attached to the α-amino group via a S–N bond and can be quantitatively removed in minutes under nearly neutral conditions (1 M p-toluenethiol/pyridine). The use of DNPBS greatly suppresses the main side reactions observed during conventional SPPS. Although DNPBS SPPS is not as efficient as Fmoc SPPS, especially for synthesis of long peptides, DNPBS and Fmoc are orthogonal protecting groups; and thus DNPBS SPPS and Fmoc SPPS can be combined to synthesize peptides that are otherwise difficult to obtain.

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

“…In our system, there are two obvious bases present for abstraction of the proton-acetate ion from nickel (II) acetate and the imidazole ring from imidazole-2-carboxaldehyde. It has been demonstrated in solid phase peptide synthesis that the imidazole moiety is basic enough to deprotonate C α of an amino acid, especially of histidine, which is being incorporated into a peptide [46,47].…”

Solid-Phase Peptide Synthesis and 2D NMR Analysis of Unknown Tripeptides: An Advanced Undergraduate Synthesis and Spectroscopy Laboratory

“…Couplings (20 min) and deprotections (15 min) are conducted in a 75 °C water bath in a fritted syringe and do not require any specialized heating equipment (microwave, peptide synthesizer, etc.). There are challenges associated with heating during peptide synthesis, including racemization, peptide cleavage from the resin, and aspartimide formation, but we did not observe significant byproduct formation in the synthesis of 3-amino acid peptides . Resin-bound polypeptides are filtered on a filtration manifold after each coupling or deprotection.…”

Chemical Synthesis of Human Proteoforms and Application in Biomedicine

“…The NCL approach has been widely used for chemical protein synthesis, ,− but the robust acquisition of peptide thioesters that are sensitive to bases and nucleophiles has been a long-standing obstacle (Figure a-b). To overcome this hurdle, various approaches have been explored to develop peptide thioester surrogates that are compatible with Fmoc-SPPS conditions. − Among them, peptide hydrazide ligation, which was discovered by us in 2011, has been recognized as one of the most efficient technologies for de novo chemical protein synthesis . This strategy employs redox chemistry to trigger on-demand chemoselective activation of otherwise inert peptide hydrazides by sodium nitrite (NaNO 2 ) to generate reactive intermediates (acyl azide and thioester) in situ.…”