Rhodium-Catalyzed Oxidation of Unprotected Peptide Thiols to Disulfides with Oxygen in Water

Nickel-catalyzed selective disulfide formation by reductive cross-coupling of thiosulfonates

Developing innovative methodologies for disulfide preparation is of importance in contemporary organic chemistry. Despite significant advancements in nickel-catalyzed reductive cross-coupling reactions for forming carbon-carbon and carbon-heteroatom bonds, the synthesis of S-S bonds remains a considerable challenge. In this context, we present a novel approach utilizing nickel catalysts for the reductive cross-coupling of thiosulfonates. This method operates under mild conditions, offering a convenient and efficient pathway to synthesize a wide range of both symmetrical and unsymmetrical disulfides from readily available, bench-stable thiosulfonates with exceptional selectivity. Notably, this approach is highly versatile, allowing for the late-stage modification of pharmaceuticals and the preparation of various targeted compounds. A comprehensive mechanistic investigation has been conducted to substantiate the proposed hypothesis.

Trace cisplatin adsorption by thiol-functionalized sponge (TFS) and Sn/SnO2-coated TFS: Adsorption study and mechanism investigation

To remove trace cisplatin from aqueous solution, commercial sponges were functionalized by esterification with 3-mercaptopropionic acid, followed by reduction with Na2S·9H2O or SnCl2·2H2O. The resulting thiol-functionalized sponges (TFSs), TFS_1 and TFS_2, were tested for the removal of cisplatin (235 μg L-1) achieving maximum removal of 95.5 ± 0.8% and 99.5 ± 0.1% respectively, which were significantly higher than the non-functionalized counterpart. The successful grafting of thiol groups, verified through FTIR, elemental analysis, SEM-EDS, and XPS characterization, facilitated Pt-S complexation during adsorption. The aqua-derivatives of cisplatin, formed through hydration, complexed with thiol sites through ligand displacement. Additionally, the presence of Sn/SnO2 coating on TFS_2 further enhanced the adsorption process. The rapid adsorption process conformed to pseudo-second-order kinetic model, involving both diffusion and chemisorption. While the Langmuir isotherm model generally described the monolayer adsorption behavior of cisplatin, the aggregation of Sn/SnO2 onto TFS_2 at 343 K introduced surface heterogeneity, rendering the Freundlich model a better fit for the adsorption isotherm. Differential pH dependence and the evaluation of mean free energy, derived from the Dubinin-Radushkevich isotherm model, indicated that cisplatin adsorption onto TFS_1 involved physisorption, including electrostatic attraction, while chemisorption predominated for TFS_2. Increasing the temperature notably promoted adsorption by facilitating the thermal-favored formation of Pt-S bonds.

Synthesis of Unprotected Cyclic Peptide Methylene Dithioacetals by Rhodium-Catalyzed Oxidation of Methanol to Formaldehyde

In the presence of a rhodium catalyst, unprotected peptide dithiols possessing two cysteine residues are efficiently converted to their corresponding cyclic methylene dithioacetals in a mixed solvent of methanol and water (4:1) under an oxygen atmosphere (1 atm). The slow formation of formaldehyde inhibits side reactions by maintaining its concentration at a low level, which is a key feature of this reaction. This method can be applied to peptide dithiols containing amino acids such as Gly, Ala, Ser, Lys, Met, Phe, Tyr, and His and provides cyclic methylene dithioacetals without being affected by other functional groups. Primary alcohols, such as ethanol and isopropanol, can also be employed. Oxytocin can be cyclized to provide a cyclic methylene dithioacetal.

Fluorogenic Protein Labeling by Generation of Fluorescent Quinoliziniums Using [Cp*RhCl2]2

Fluorogenic labeling has received considerable attention as a result of the high demand in chemical biology and synthetic biology applications. Herein, we develop a new strategy for fluorescent turn-on ligation targeting alkyne- and quinoline-linked peptides and proteins (λ_em of 515 nm and up to Φ_F of 0.20) using the [Cp*RhCl₂]₂ catalyst. The good conversion, high flexibility, broad utility, ease of use, and mild reaction conditions are great advantages to extend the rhodium-mediated turn-on fluorogenic bioconjugation for further applications.

Application of Bulky NHC-Rhodium Complexes in Efficient S-Si and S-S Bond Forming Reactions

The efficient and straightforward syntheses of silylthioethers and disulfides are presented. The synthetic methodologies are based on new rhodium complexes containing bulky N-heterocyclic carbene (NHC) ligands that turned out to be efficient catalysts in thiol and thiol-silane coupling reactions. These green protocols, which use easily accessible reagents, allow obtaining compounds containing S-Si and S-S bonds in solvent-free conditions. Additionally, preliminary tests on coupling of mono- and octahydro-substituted spherosilicates with selected thiols have proved to be very promising and showed that these catalytic systems can be used for the synthesis of a novel class of functionalized silsesquioxane derivatives.

PdCl2/DMSO-Catalyzed Thiol-Disulfide Exchange: Synthesis of Unsymmetrical Disulfide

Unsymmetrical disulfides have been effectively prepared through thiol exchange with symmetrical disulfides employing a simple PdCl₂/DMSO catalytic system. The given method features excellent functional group tolerance, a broad substrate scope, and operational simplicity. This reaction is especially useful for late-stage functionalization of bioactive scaffolds such as peptides and pharmaceuticals. Disulfide-containing organic dyes have also been prepared. This transformation could be extended to thiol-diselenide or thiol-ditelluride exchange affording RS-SeR' or RS-TeR'.