A CuAAC–Hydrazone–CuAAC Trifunctional Scaffold for the Solid-Phase Synthesis of Trimodal Compounds: Possibilities and Limitations

Abstract

Abstract:We present a trifunctional scaffold designed for the solid-phase synthesis of trimodal compounds. This scaffold holds two alkyne arms in a free and TIPS-protected form for consecutive CuAAC (copper(I)-catalyzed azide-alkyne cycloaddition), one Fmoc-protected hydrazide arm for reaction with aldehydes, and one carboxylic acid arm with CF2 groups for attachment to the resin and 19 F-NMR quantification. This scaffold was attached to a resin and derivatized with model azides and aliphatic, electron-rich or electron-poor aromatic aldehydes. We identified several limitations of the scaffold caused by the instability of hydrazones in acidic conditions, in the presence of copper during CuAAC, and when copper accumulated in the resin. We successfully overcame these drawbacks by optimizing synthetic conditions for the derivatization of the scaffold with aromatic aldehydes. Overall, the new trifunctional scaffold combines CuAAC and hydrazone chemistries, offering a broader chemical space for the development of bioactive compounds.

Synthesis and Evaluation of a Library of Trifunctional Scaffold-Derived Compounds as Modulators of the Insulin Receptor

“…For the solid-phase synthesis of the library, we used the PEG-based ChemMatrix resin , because it gave satisfactory results for CuAACs with the CuSO 4 /sodium ascorbate system in tBuOH/H 2 O. , We used the Ramage linker, which can be cleaved by low concentrations of TFA (3–5%) to generate the terminal amides …”

“…First, based on the concentrations determined by 19 F NMR, we prepared 1 mM stock solutions of individual libraries in 100 mM Hepes/NaOH buffer, pH 7.5 (see Experimental Methods). The concept and the methodology of the determination of the concentration of scaffold I -derived compounds were described in detail in our previous papers. , …”

“…The strategy of orthogonal TIPS/TES protection of terminal alkynes was first developed in Aucagne’s group, who selectively deprotected the TES group by using Ag­(I) salts and these conditions were recently applied by Liskamp’s group. , However, under our experimental conditions, silver deposits appeared on the resin, which disabled further synthesis. We solved this problem by performing the CuAAC directly on the TES-protected terminal alkyne and by using an excess of copper­(II) and sodium ascorbate. , Under these conditions, the TES group is selectively deprotected and the cycloaddition with the azide occurs in one-pot. The mechanism of the TES cleavage during high copper load CuAAC is unclear and is currently being investigated in our laboratory.…”

A Trifunctional Linker for Palmitoylation and Peptide and Protein Localization in Biological Membranes

“…A very elegant option is a molecule based on a tri‐orthogonal “click” scaffold, combining inverse electron demand Diels–Alder (iEDDA) between a cyclooctyne and a tetrazine moiety with a copper‐catalyzed alkyne–azide click (CuAAC) reaction as well as maleimide coupling . The combination of two CuAAC click reactions with an aldehyde and/or activated ester coupling is an alternative option . Herein we report the synthesis of a tyrosine‐based trifunctional linker in which the palmitoyl chains, fluorophore and peptide are conjugated onto one scaffold via amide, CuAAC and maleimide coupling, respectively.…”

Tri‐Orthogonal Scaffolds for the Solid‐Phase Synthesis of Peptides

“…For this purpose, we previously developed two tripodal scaffolds, which enable stepwise attachment of three different moieties to individual scaffold arms by Cu I -catalyzed click chemistry (scaffold I) [7] or by a reaction of aldehydes with a hydrazide group of scaffold Ia [8] (Figure 1). Recently, we synthesized a combinatorial library of 1 000 compounds based on the structure of scaffold I modified with 30 different azides.…”