Expanding the Toolbox for Peptide Disulfide Bond Formation via l-Methionine Selenoxide Oxidation

l-Methionine Selenoxide as an Oxidizing and Deprotection Reagent for the Synthesis of Multiple Disulfide Bonds in Peptides

The regioselective synthesis of multiple disulfide bonds in peptides has been a significant challenge in synthetic peptide chemistry. In this work, two disulfide bonds in peptides were regioselectively synthesized via an approach of MetSeO oxidation and deprotection reaction (SeODR), in which the first disulfide bond was constructed through oxidation of dithiol by MetSeO in a neutral buffer, and the second disulfide bond was then directly constructed through the deprotection of two Acm groups or one Acm group and one Thz group by MetSeO in acidic media. Synthesis of two disulfide bonds by the SeODR approach was achieved through a one-pot manner. Moreover, the SeODR approach is compatible with the synthesis of peptides containing methionine residues. Both H+ and Br- drastically promoted the reaction rate of SeODR. The mechanistic picture for the SeODR approach was delineated, in which the formation of a stable Se-X-S bridge as the transition state plays a critical role. The SeODR approach was also utilized to construct the three disulfide bonds in linaclotide, conferring a reasonable yield.

Synthesis and biological evaluation of novel all-hydrocarbon cross-linked aza-stapled peptides

Novel all-hydrocarbon cross-linked aza-stapled peptides were designed and synthesized for the first time by ring-closing metathesis between two aza-alkenylglycine residues. Three aza-stapled peptidic analogues based on the peptide dual inhibitor of p53-MDM2/MDMX interactions were synthesized and screened for biological activities. Among the three aza-stapled peptides, aSPDI-411 displayed increased anti-tumor activity, binding affinities to both MDM2 and MDMX, and cell membrane permeability compared to its linear peptide counterpart.

Deprotection of S-Acetamidomethyl and 1,3-Thiazolidine-4-Carbonyl Protecting Groups from Cysteine Side Chains in Peptides by trans-[PtX2(CN)4]2-: One-Pot Regioselective Synthesis of Disulfide Bonds

In this study, we developed an efficient approach for disulfide bond formation in peptides utilizing the Pt(IV) complex trans-[PtBr₂(CN)₄]^2- to mediate Acm and Thz deprotections. [PtBr₂(CN)₄]^2- can oxidatively deprotect two Acm groups or deprotect one Thz group and one Acm group to directly form an intramolecular disulfide bond in peptides. Several disulfide-containing peptides with excellent yields were achieved via the deprotection method in an aqueous medium under aerobic conditions. Kinetic studies indicated that the dominant path of the reaction is of first-order in both [Pt(IV)] and [peptide]; moreover, the deprotection rate increased dramatically with the addition of NaBr. A mechanism including a bromide-bridge-mediated electron transfer process was proposed. Apamin, α-conotoxin SI, and the parallel homodimer of oxytocin, all containing two disulfide bonds, were synthesized regioselectively through a one-pot method by the combined use of the above deprotection approach with oxidants l-methionine selenoxide and [PtBr₂(CN)₄]^2-. All of the reactions were completed within 30 min to afford good yields for these peptides.