Chirality induction and chiron approaches to enantioselective total synthesis of α-lipoic acid

Ligand-modulated nickel-catalyzed regioselective silylalkylation of alkenes

Organosilicon compounds have shown tremendous potential in drug discovery and their synthesis stimulates wide interest. Multicomponent cross-coupling of alkenes with silicon reagents is used to yield complex silicon-containing compounds from readily accessible feedstock chemicals but the reaction with simple alkenes remains challenging. Here, we report a regioselective silylalkylation of simple alkenes, which is enabled by using a stable Ni(II) salt and an inexpensive trans-1,2-diaminocyclohexane ligand as a catalyst. Remarkably, this reaction can tolerate a broad range of olefins bearing various functional groups, including alcohol, ester, amides and ethers, thus it allows for the efficient and selective assembly of a diverse range of bifunctional organosilicon building blocks from terminal alkenes, alkyl halides and the Suginome reagent. Moreover, an expedient synthetic route toward alpha-Lipoic acid has been developed by this methodology.

Review of lipoic acid: From a clinical therapeutic agent to various emerging biomaterials

Lipoic acid (LA), an endogenous small molecule in organisms, has been extensively used for the highly efficient clinical treatment of malignant diseases, which include diabetes, Alzheimer's disease, and cancer over the past seven decades. Tremendous progresses have been made on the use of LA in nanomedicine for the development of various biomaterials because of its unique biological properties and highly adaptable structure since the first discovery. However, there are few reviews thus far, to our knowledge, summarizing this hot subject of research of LA and its derived biomaterials. For this purpose, we present herein the first comprehensive summary on the design and development of LA and its derived materials for biomedical applications. This review first discusses the therapeutic use of LA followed by the description of synthesis and preclinical study of LA-derived-small molecules. The applications of various LA and poly (lipoic acid) (PLA)-derived-biomaterials are next summarized in detail with an emphasis on the use of LA for the design of biomaterials and the diverse properties. This review describes the development of LA from a clinical therapeutic agent to a building unit of various biomaterials field, which will promote the further discovery of new therapeutic uses of LA as therapeutic agents and facile development of LA-based derivates with greater performance for biomedical applications.

Effects of Silver Carbonate and p-Nitrobenzoic Acid for Accelerating Palladium-Catalyzed Allylic C-H Acyloxylation

An allylic C-H acyloxylation of terminal alkenes with 4-nitrobenzoic acid was assisted by a bidentate-sulfoxide-ligated palladium catalyst combined with 1,4-benzoquinone and Ag₂CO₃ under mild reaction conditions. The catalytic activity was remarkably enhanced by Ag₂CO₃ as an additive and 4-nitrobenzoic acid as a carboxylate source; both components were essential to exhibiting high catalytic activity, high branch selectivity, and a wide substrate scope with low loading of the palladium catalyst. Branch-selective allylic acyloxylation of ethyl 7-octenoate (1a) gave the product which was led to ethyl 6,8-dihydroxyoctanoate (5), a useful synthetic intermediate of (R)-α-lipoic acid.

Rational Design and Experimental Research on the Self-Assembled System of Thermosensitive Molecularly Imprinted Polymers Formed by α-Lipoic Acid and N-Vinyl Caprolactam

In this paper, the main work was to study the theoretical self-assembly process of thermosensitive molecularly imprinted polymers (MIPs) for α-lipoic acid and to investigate thermosensitive functional monomers through density functional theory calculations (DFT) and intermolecular weak interaction analysis. The M06-2X/6-311+G (d, p) level was used to study the structural parameters, bonding sites, natural population analysis, binding energies ( $\Delta E$ ), atom in molecules (AIM), independent gradient model (IGM), and imprinted molar ratio. The results revealed that α-lipoic acid mainly interacted with N-vinyl caprolactam (NVCL) by weak hydrogen bonds, and the best conditions for MIP synthesis were an optimum molar ratio of 1 : 4 (α-lipoic acid/NVCL). The thermosensitive properties showed that the highest adsorption was at 40°C and the lowest adsorption was at 20°C; also, the MIPs released the intercepted α-lipoic acid inside polymers, and the lower critical solution temperatures (LCST) of MIPs and nonimprinted polymers (NIPs) are 25.7°C and 19.4°C, respectively. In this study, the thermosensitive MIPs displayed a different adsorption capacity towards NVCL, which could be applied for controlled separation and release of α-lipoic acid in different temperatures in a complex matrix.

Preparation of Chitosan Molecularly Imprinted Polymers and the Recognition Mechanism for Adsorption of Alpha-Lipoic Acid

Two effective molecularly imprinted polymers for the adsorption of alpha-lipoic acid (ALA) were synthesized by the cross-linking of chitosan with epichlorohydrin (ECH) and glutaraldehyde (GLU), respectively, in the presence of ALA as template molecules. Investigations on the molar ratios of ALA and chitosan (–NH₂) in the preparation of chitosan molecularly imprinted polymers (MIPs) were carried out with a factor of ALA rebinding capabilities. The surface morphology and chemical properties of the polymers were characterized. The optimized MIPs crosslinked by ECH (MIPs–ECH) and MIPs crosslinked by GLU (MIPs–GLU) had adsorption capabilities of 12.09 mg/g and 19.72 mg/g for ALA, respectively. The adsorption behaviors of two kinds of chitosan MIPs including adsorption kinetics and isotherms were investigated in detail. Adsorption and kinetic binding experiments showed that the prepared MIPs–ECH and MIPs–GLU had selective adsorption and excellent affinity for ALA. In addition, the possible binding models between ALA and chitosan oligosaccharide were predicted by molecular dynamics simulation.