N-(Azido-PEG2)-N-Boc-PEG3-NHS ester

The possible role of phosphoryl amino acids for biomolecular origins is briefly reviewed. Peptide formation, ester formation, ester exchange on phosphorus and N to O migration occurred when the N-phosphoryl amino acid was incubated at room temperature. Short nucleotides and peptides were formed when nucleoside was reacted with N-phosphoryl amino acid at room temperature. Serine and threonine residues in their conjugate with different nucleosides (mediated with phosphorus) showed different self-cleavage activities. N-phosphoryl Histine and Ser-His dipeptide could cleave nucleic acids, proteins and esters in neutral medium. Based on a simple model, a pathway of 'co-evolution of protein and nucleic acid' was proposed.

The Bis-T series of compounds comprise some of the most potent inhibitors of dynamin GTPase activity yet reported, e. g., (2E,2'E)-N,N'-(propane-1,3-diyl)bis(2-cyano-3-(3,4-dihydroxyphenyl)acrylamide) (2), Bis-T-22. The catechol moieties are believed to limit cell permeability, rendering these compounds largely inactive in cells. To solve this problem, a prodrug strategy was envisaged and eight ester analogues were synthesised. The shortest and bulkiest esters (acetate and butyl/tert-butyl) were found to be insoluble under physiological conditions, whilst the remaining five were soluble and stable under these conditions. These five were analysed for plasma stability and half-lives ranged from ~2.3 min (propionic ester 4), increasing with size and bulk, to greater than 24 hr (dimethyl carbamate 10). Similar profiles where observed with the rate of formation of Bis-T-22 with half-lives ranging from ~25 mins (propionic ester 4). Propionic ester 4 was chosen to undergo further testing and was found to inhibit endocytosis in a dose-dependent manner with IC50 ~8 μM, suggesting this compound is able to effectively cross the cell membrane where it is rapidly hydrolysed to the desired Bis-T-22 parent compound.

In order to gain detailed insight into the biochemical behavior of proteins, researchers have developed chemical tools to incorporate new functionality into proteins beyond the canonical 20 amino acids. Important considerations regarding effective chemical modification of proteins include chemoselectivity, near stoichiometric labeling, and reaction conditions that maintain protein stability. Taking these factors into account, we discuss an N-terminal labeling strategy that employs a simple two-step "one-pot" method using N-hydroxysuccinimide (NHS) esters. The first step converts a R-NHS ester into a more chemoselective R-thioester. The second step reacts the in situ generated R-thioester with a protein that harbors an N-terminal cysteine to generate a new amide bond. This labeling reaction is selective for the N-terminus with high stoichiometry. Herein, we provide a detailed description of this method and further highlight its utility with a large protein (>100kDa) and labeling with a commonly used cyanine dye.