Recent advancements in the use of Bobbitt's salt and 4-acetamidoTEMPO

Aerobic Oxidation of PMB Ethers to Carboxylic Acids

The first aerobic protocol of direct transformation of p-methoxybenzyl (PMB) ethers to carboxylic acids efficiently with Fe(NO3)3 ⋅ 9H2O and TEMPO as catalysts at room temperature has been developed. The reaction accommodates C-Br bond, terminal/non-terminal C-C triple bond, amide, cyano, nitro, ester, and trifluoromethyl groups. Even highly selective oxidative deprotection of different benzylic PMB ethers has been realized. The reaction has been successfully applied to the total synthesis of natural product, (R)-6-hydroxy-7,9-octadecadiynoic acid, demonstrating the practicality of the method. Based on experimental studies, a possible mechanism involving oxygen-stabilized benzylic cation has been proposed.

Oxoammonium Salt-Mediated On-DNA Alcohol Oxidation for DEL Synthesis

On-DNA carboxylic acids are important synthetic intermediates in the synthesis of DNA-encoded library (DEL) structures. Herein, we report an oxoammonium salt-mediated, room temperature, solution-phase oxidation of DNA-linked primary alcohols into carboxylic acids. This method exhibits a wide substrate scope, encompassing aliphatic, benzylic, and heterobenzylic alcohols, and is compatible with DEL encoding strategies. This advancement facilitates a DEL strategy to utilize unprotected alcohols as inert, masked carboxylic acids and enables access to noncommercial bifunctional carboxyl intermediates to enhance the accessible chemical diversity within DELs.

Advances in the investigation of N6-isopentenyl adenosine i6A RNA modification

Prenylation (isopentenylation), a key post-transcriptional modification with a hydrophobic prenyl group onto the biomacromolecules such as RNA and proteins, influences their localization and function. Prenyltransferases mediate this process, while cytokinin oxidases degrade the prenylated adenosine in plants. This review summarizes current progress in detecting prenylation modifications in RNA across species and their effects on protein synthesis. Advanced methods have been developed to label and study these modifications in vitro and in vivo, despite challenges posed by the inert chemical properties of prenyl groups. Continued advancements in bioorthogonal chemistry promise new tools for understanding the precise biological functions of prenylated RNA modifications and other related proteins.

Green Oxidation of Aromatic Hydrazide Derivatives Using an Oxoammonium Salt

Aromatic diazenes are often prepared by oxidation of the corresponding hydrazides using stoichiometric quantities of nonrecyclable oxidants. We developed a convenient alternative protocol for the oxidation of aromatic hydrazides using Bobbitt's salt (1), a metal-free, recyclable, and commercially available oxoammonium reagent. A variety of aryl hydrazides were oxidized within 75 min at room temperature using the developed protocol. Computational insight suggests that this oxidation occurs by a polar hydride transfer mechanism.

Asymmetric Synthesis of Nidulalin A and Nidulaxanthone A: Selective Carbonyl Desaturation Using an Oxoammonium Salt

Nidulaxanthone A is a dimeric, dihydroxanthone natural product that was isolated in 2020 from Aspergillus sp. Structurally, the compound features an unprecedented heptacyclic 6/6/6/6/6/6/6 ring system which is unusual for natural xanthone dimers. Biosynthetically, nidulaxanthone A originates from the monomer nidulalin A via stereoselective Diels-Alder dimerization. To expedite the synthesis of nidulalin A and study the proposed dimerization, we developed methodology involving the use of allyl triflate for chromone ester activation, followed by vinylogous addition, to rapidly forge the nidulalin A scaffold in a four-step sequence which also features ketone desaturation using Bobbitt's oxoammonium salt. An asymmetric synthesis of nidulalin A was achieved using acylative kinetic resolution (AKR) of chiral, racemic 2H-nidulalin A. Dimerization of enantioenriched nidulalin A to nidulaxanthone A was achieved using solvent-free, thermolytic conditions. Computational studies have been conducted to probe both the oxoammonium-mediated desaturation and (4 + 2) dimerization events.