Phosphoramidate-peptide synthesis by solution- and solid-phase Staudinger-phosphite reactions

Bioorthogonal Reactions of Triarylphosphines and Related Analogues

Bioorthogonal phosphines were introduced in the context of the Staudinger ligation over 20 years ago. Since that time, phosphine probes have been used in myriad applications to tag azide-functionalized biomolecules. The Staudinger ligation also paved the way for the development of other phosphorus-based chemistries, many of which are widely employed in biological experiments. Several reviews have highlighted early achievements in the design and application of bioorthogonal phosphines. This review summarizes more recent advances in the field. We discuss innovations in classic Staudinger-like transformations that have enabled new biological pursuits. We also highlight relative newcomers to the bioorthogonal stage, including the cyclopropenone-phosphine ligation and the phospha-Michael reaction. The review concludes with chemoselective reactions involving phosphite and phosphonite ligations. For each transformation, we describe the overall mechanism and scope. We also showcase efforts to fine-tune the reagents for specific functions. We further describe recent applications of the chemistries in biological settings. Collectively, these examples underscore the versatility and breadth of bioorthogonal phosphine reagents.

Direct access to site-specifically phosphorylated-lysine peptides from a solid-support

Phosphorylation is a key process for changing the activity and function of proteins. The impact of phospho-serine (pSer), -threonine (pThr) and -tyrosine (pTyr) is certainly understood for some proteins. Recently, peptides and proteins containing N-phosphorylated amino acids such as phosphoarginine (pArg), phosphohistidine (pHis) and phospholysine (pLys) have gained interest because of their different chemical properties and stability profiles. Due to its high intrinsic lability, pLys is the least studied within this latter group. In order to gain insight into the biological role of pLys, chemical and analytical tools, which are compatible with the labile P(=O)-N bond, are highly sought-after. We recently reported an in-solution synthetic approach to incorporate pLys residues in a site-specific manner into peptides by taking advantage of the chemoselectivity of the Staudinger-phosphite reaction. While the in-solution approach allows us to circumvent the critical TFA cleavage, it still requires several transformations and purification steps to finally deliver pLys peptides. Here we report the synthesis of site-specific pLys peptides directly from a solid support by using a base labile resin. This straightforward and highly efficient approach facilitates the synthesis of various site-specific pLys-containing peptides and lays the groundwork for future studies about this elusive protein modification.

Bis(arylmethyl)-substituted unsymmetrical phosphites for the synthesis of lipidated peptides via Staudinger-phosphite reactions

With this study we introduce new unsymmetrical phosphites to obtain lipidated peptide-conjugates starting from easily accessible azide-modified amino acid or peptide precursors.

Site-specific PEGylation of proteins: recent developments

The attachment of linear polyethylene glycol (PEG) to peptides and proteins for their stabilization for in vivo applications is a milestone in pharmaceutical research and protein-drug development. However, conventional methods often lead to heterogeneous PEGylation mixtures with reduced protein activity. Current synthetic efforts aim to provide site-specific approaches by chemoselective targeting of canonical and noncanonical amino acids and to improve the PEG architecture. This synopsis highlights recent work in this area, which also resulted in improved pharmacokinetics of peptide and protein therapeutics.

Staudinger ligation as a method for bioconjugation

In 1919 the German chemist Hermann Staudinger was the first to describe the reaction between an azide and a phosphine. It was not until recently, however, that Bertozzi and co-workers recognized the potential of this reaction as a method for bioconjugation and transformed it into the so-called Staudinger ligation. The bio-orthogonal character of both the azide and the phosphine functions has resulted in the Staudinger ligation finding numerous applications in various complex biological systems. For example, the Staudinger ligation has been utilized to label glycans, lipids, DNA, and proteins. Moreover, the Staudinger ligation has been used as a synthetic method to construct glycopeptides, microarrays, and functional biopolymers. In the emerging field of bio-orthogonal ligation strategies, the Staudinger ligation has set a high standard to which most of the new techniques are often compared. This Review summarizes recent developments and new applications of the Staudinger ligation.