A facile synthesis of 2-oxazolines using a PPh3–DDQ system

Modulation of the Meisenheimer complex metabolism of nitro-benzothiazinones by targeted C-6 substitution

Tuberculosis, caused by Mycobacterium tuberculosis, remains a major public health concern, demanding new antibiotics with innovative therapeutic principles due to the emergence of resistant strains. Benzothiazinones (BTZs) have been developed to address this problem. However, an unprecedented in vivo biotransformation of BTZs to hydride-Meisenheimer complexes has recently been discovered. Herein, we present a study of the influence of electron-withdrawing groups on the propensity of HMC formation in whole cells for a series of C-6-substituted BTZs obtained through reductive fluorocarbonylation as a late-stage functionalization key step. Gibbs free energy of reaction and Mulliken charges and Fukui indices on C-5 at quantum mechanics level were found as good indicators of in vitro HMC formation propensity. These results provide a first blueprint for the evaluation of HMC formation in drug development and set the stage for rational pharmacokinetic optimization of BTZs and similar drug candidates.

Synthesis and characterization of dendritic compounds containing nitrogen: monomer precursors in the construction of biomimetic membranes

In this article, we synthesized a novel dendritic 2-oxazoline, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole), and its amide precursor N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide. Of the distinct synthetic routes explored, it was established that the direct amidation of esters with sodium methoxide followed by the dehydrative cyclisation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as oxidizing agent and triphenylphosphine was the most efficient route to synthesize the dendritic 2-oxazoline. Besides, N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide exhibited a monotropic columnar mesophase, whilst the dendritic 2-oxazoline does not exhibited a liquid crystalline mesophase. At the end, the first attempts to polymerize the 2-oxazoline monomer via cationic ring opening polymerization showed promising results. Therefore, the dendritic 2-oxazoline could be used as a mesogenic monomer in the synthesis of side-chain liquid-crystalline polyoxazolines that might self-assembly into columnar structures.

Phosphorus-Based Organocatalysis for the Dehydrative Cyclization of N-(2-Hydroxyethyl)amides into 2-Oxazolines

A metal-free, biomimetic catalytic protocol for the cyclization of N-(2-hydroxyethyl)amides to the corresponding 2-oxazolines (4,5-dihydrooxazoles), promoted by the 1,3,5,2,4,6-triazatriphosphorine (TAP)-derived organocatalyst tris(o-phenylenedioxy)cyclotriphosphazene (TAP-1) has been developed. This approach requires less precatalyst compared to the reported relevant systems, with respect to the phosphorus atom (the maximum turnover number (TON) ∼ 30), and exhibits a broader substrate scope and higher functional-group tolerance, providing the functionalized 2-oxazolines with retention of the configuration at the C(4) stereogenic center of the 2-oxazolines. Widely accessible β-amino alcohols can be used in this approach, and the cyclization of N-(2-hydroxyethyl)amides provides the desired 2-oxazolines in up to 99% yield. The mechanism of the reaction was studied by monitoring the reaction using spectral and analytical methods, whereby an ¹⁸O-labeling experiment furnished valuable insights. The initial step involves a stoichiometric reaction between the substrate and TAP-1, which leads to the in situ generation of the catalyst, a catechol cyclic phosphate, as well as to a pyrocatechol phosphate and two possible active intermediates. The dehydrative cyclization was also successfully conducted on the gram scale.

Copper N-Heterocyclic Carbene Complexes As Active Catalysts for the Synthesis of 2-Substituted Oxazolines from Nitriles and Aminoalcohols

The reaction between nitriles and aminoalcohols to access 2-substituted oxazolines was investigated. Using copper-NHC complexes, various nitriles were successfully converted into the corresponding oxazolines, under milder and less wasteful conditions than those of previously reported methods.

A direct synthesis of oxazoles from aldehydes

An expedient method for the direct conversion of aldehydes to 2,4-disubstituted oxazoles is presented. The method relies on the oxidation of an oxazolidine formed from the condensation of serine with an aldehyde and proceeds through a 2,5-dihydrooxazole intermediate. In contrast to standard methods that start from carboxylic acids, the use of aldehydes as starting materials does not require intermediate purification and affords the oxazoles under relatively mild conditions.