Efficient access to peptidyl ketones and peptidyl diketones via C-alkylations and C-acylations of polymer-supported phosphorus ylides followed by hydrolytic and/or oxidative cleavage

Chemically Stable Diazo Peptides as Selective Probes of Cysteine Proteases in Living Cells

Diazo peptides have been described earlier, however, due to their high reactivity have not been broadly used until today. Here, we report the preparation, properties, and applications of chemically stable internal diazo peptides. Peptidyl phosphoranylidene-esters and amides were found to react with triflyl azide primarily to novel 3,4-disubstituted triazolyl-peptides. Nonaflyl azide instead furnished diazo peptides, which are chemically stable from pH 1-14 as amides and from pH 1-8 as esters. Thus, diazo peptides prepared by solid phase peptide synthesis were stable to final deprotection with 95 % trifluoroacetic acid. Diazo peptides with the recognition sequence of caspase-3 were identified as specific, covalent, and irreversible inhibitors of this enzyme at low nanomolar concentrations. A fluorescent diazo peptide entered living cells enabling microscopic imaging and quantification of apoptotic cells via flow cytometry. Thus, internal diazo peptides constitute a novel class of activity-based probes and enzyme inhibitors useful in chemical biology and medicinal chemistry.

Integration of C-Acylation in the Solid-Phase Synthesis of Peptides and Peptidomimetics Employing Meldrum’s Acid, Phosphorus, and Sulfur Ylides

The modification of native peptides to peptidomimetics is an important goal in medicinal chemistry and requires, in many cases, the integration of C-acylation steps involving amino acids with classical peptide synthesis. Many classical C-acylation protocols involving Claisen condensations and the use of ylides are not compatible with peptide synthesis, mostly due to the requirements for strong bases leading to epimerization or deprotection of peptides. Meldrum’s acid as well as several specific phosphorus and sulfur ylides, however, are acidic enough to provide reactive C-nucleophiles under mildly basic conditions tolerated during peptide synthesis. This review provides an overview of peptide-compatible C-acylations using Meldrum’s acid and phosphorus and sulfur ylides, and their application in the medicinal chemistry of peptides.

1 Introduction

2 C-Acylation of Meldrum’s Acid

2.1 C-Acylation of Meldrum’s Acid on Solid Phase

3 Ylides as Substrates for C-Acylation

3.1 C-Acylation of Phosphorus Ylides in Solution Phase

3.2 C-Acylation of Solid-Supported Phosphorus Ylides

3.3 C-Acylation of Sulfur Ylides

3.4 C-Acylation of Solid-Supported Sulfur Ylides

4 Miscellaneous Ylides as Acyl Anion Equivalents

5 Summary

Side-Chain Modification of Peptides Using a Phosphoranylidene Amino Acid

The flexible variation of peptidomimetics is of great interest for the identification of optimized protein ligands. Here we present a general concept for introducing side-chain modifications into peptides using triarylphosphonium amino acids. Building blocks 4a and 4b are activated for amidation and incorporated into stable peptides. The obtained phosphoranylidene peptides undergo Wittig olefinations and 1,3-dipolar cycloaddition reactions, yielding peptidomimetics with vinyl ketones and 5-substituted 1,2,3-triazoles as non-native peptide side chains.

Polymer-supported triphenylphosphine: application in organic synthesis and organometallic reactions

This comprehensive review highlights the diverse chemistry and applications of polymer-supported triphenylphosphine (PS-TPP) in organic synthesis since its inception. Specifically, the review describes applications of the preceding reagent in functional group interconversions, heterocycle synthesis, metal complexes and their application in synthesis, and total synthesis of natural products. Many examples are provided from the literature to show the scope and selectivity (regio, stereo, and chemo) in these transformations.

A microwave-assisted highly practical chemoselective esterification and amidation of carboxylic acids

The ubiquitousness of esters and amide functionalities makes their coupling reaction one of the most sought-after organic transformations.

Selective Monoesterification of Symmetrical Diols Using Resin-Bound Triphenylphosphine

Coupling reactions to make esters and amides are among the most widely used organic transformations. We report efficient procedures for amide bond formation and for the monoesterification of symmetrical diols in excellent yields without any requirement for high dilution or slow addition using resin-bound triarylphosphonium iodide. Easy purification, low moisture sensitivity, and good to excellent yields of the products are the major advantages of this protocol.

Gilheany D. First ever observation of the intermediate of phosphonium salt and ylide hydrolysis: P-hydroxytetraorganophosphorane

P-Hydroxytetraorganophosphorane, the putative intermediate in phosphonium salt & ylide hydrolysis reactions, has been observed and characterised for the first time, thus establishing unequivocally its existence & involvement in these reactions.

Ethyl acrylate conjugated polystyryl-diphenylphosphine — An extremely efficient catalyst for Henry reaction under solvent-free conditions (SolFC)

Over the last few decades, the fast-growing development of polymer supported reagents has led to the synthesis of a variety of reagents on solid support. Some of the major advantages of using such reagents are that they are less hygroscopic, easy to recover, and can be recycled. Here, we have demonstrated that in situ generated ethyl acrylate conjugated polystyryl-diphenylphosphine (PDPP–EA) derived from the reaction of a mixture of polystyryl-diphenylphosphine and ethyl acrylate in a stoichiometric ratio can efficiently catalyze the synthesis of β-nitroalcohols from the reaction of aldehydes and nitroalkanes under solvent-free conditions (SolFC).