Automated solid‐phase synthesis of metabolically stabilized triazolo‐peptidomimetics

Abstract

The use of 1,4‐disubstituted 1,2,3‐triazoles as trans‐amide bond surrogates has become an important tool for the synthesis of metabolically stabilized peptidomimetics. These heterocyclic bioisosters are generally incorporated into the peptide backbone by applying a diazo‐transfer reaction followed by CuAAC (click chemistry) with an α‐amino alkyne. Even though the manual synthesis of backbone‐modified triazolo‐peptidomimetics has been reported by us and others, no procedure has yet been described for an automated synthesis using peptide synthesizers. In order to efficiently adapt these reactions to an automated setup, different conditions were explored, putting special emphasis on the required long‐term stability of both the diazo‐transfer reagent and the Cu(I) catalyst in solution. ISA·HCl is the reagent of choice to accomplish the diazo‐transfer reaction; however, it was found instable in DMF, the most commonly used solvent for SPPS. Thus, an aqueous solution of ISA·HCl was used to prevent its degradation over time, and the composition in the final diazo‐transfer reaction was adjusted to preserve suitable swelling conditions of the resins applied. The CuAAC reaction was performed without difficulties using [Cu (CH3CN)4]PF6 as a catalyst and TBTA as a stabilizer to prevent oxidation to Cu(II). The optimized automated two‐step procedure was applied to the synthesis of structurally diverse triazolo‐peptidomimetics to demonstrate the versatility of the developed methodology. Under the optimized conditions, five triazolo‐peptidomimetics (8–5 amino acid residues) were synthesized efficiently using two different resins. Analysis of the crude products by HPLC‐MS revealed moderate to good purities of the desired triazolo‐peptidomimetics (70–85%). The synthesis time ranged between 9 and 12.5 h.

Solid Phase Synthesis and TAR RNA-Binding Activity of Nucleopeptides Containing Nucleobases Linked to the Side Chains via 1,4-Linked-1,2,3-triazole

“…In many cases, the newly obtained triazole derivatives of known chemical structures showed greater biological activity than their unmodified counterparts [ 57 , 58 , 59 ]. In most cases, the triazole ring was introduced into small-molecule compounds, although examples of the introduction of this system into large macromolecules such as peptides or nucleic acids are known [ 60 , 61 , 62 ]. The molecular basis of such modifications underlying the changes in physicochemical properties and biological activity of such modified biomolecules is poorly understood.…”

Amide-to-Triazole Switch in Somatostatin-14-Based Radioligands: Impact on Receptor Affinity and In Vivo Stability

“…Among the many mimics of amide bonds reported (e.g., sulfonamides, semicarbazides, etc. ), triazole heterocycles have emerged as reliable amide bond surrogates that can be incorporated efficiently into the backbone of peptides by convenient manual or automated solid-phase peptide synthesis (SPPS), utilizing the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) [ 22 , 23 , 24 ]. Metabolically, stable 1,4-disubstituted 1,2,3-triazoles (Tz) effectively mimic trans -amide nbonds whereas the 1,5-disubstituted regioisomers can serve as surrogates of cis -amide bonds [ 25 ].…”