Catalytic asymmetric total synthesis of (S)-(-)-zearalenone, a novel lipoxygenase inhibitor

Total Synthesis of (-)-Zearalenone and (-)-Zearalanone: A Macrocyclization Strategy by Ni/Zr/Cr-Mediated Reductive Ketone Coupling

The total synthesis of the resorcylic acid lactones (-)-zearalenone and (-)-zearalanone is described. Our synthetic strategy relies on Ni-, Zr-, and Cr-mediated intramolecular reductive ketone coupling to create 14-membered macrolactones. Notably, the use of CrCl2 in addition to Ni/Zr-mediated reductive ketone coupling conditions was key for the success of the macrocyclization.

A 2,2-Difluoroimidazolidine Derivative for Deoxyfluorination Reactions: Mechanistic Insights by Experimental and Computational Studies

A N-heterocyclic deoxyfluorinating agent SIMesF2 was synthesized by nucleophilic fluorination of N,N-1,3-dimesityl-2-chloroimidazolidinium chloride (3) at room temperature. SIMesF2 was applied to deoxyfluorinate carboxylic acids and alcohols and convert benzaldehyde into difluorotoluene. Mechanistic studies by NMR spectroscopy suggest reaction pathways of the carboxylic acid to acyl fluoride via outer-sphere fluorinations at an imidazolidinium ion by polyfluoride. DFT studies give further insight by exploring mechanistic details which distinguish the fluorination of aldehydes from that of carboxylic acids. Furthermore, a consecutive reaction sequence for the oxidation of an aldehyde followed by in situ fluorination of the generated carboxylic acid was developed.

Four-Step Total Synthesis of (+)-Euphococcinine and (±)-Adaline

A four-step enantiospecific total synthesis of bicyclic homotropinone alkaloid euphococcinine and a racemic synthesis of adaline were reported. Key reactions in the synthesis are the diastereoselective addition of a Wittig phosphorene to the ketimines derived from Davis-Ellman sulfinamides, ring-closing metathesis, and intramolecular Michael reactions.

Applications of Transition-Metal-Catalyzed Asymmetric Allylic Substitution in Total Synthesis of Natural Products: An Update

Metal-catalyzed asymmetric allylic substitution (AAS) reaction is one of the most synthetically useful reactions catalyzed by metal complexes for the formation of carbon-carbon and carbon-heteroatom bonds. It comprises the substitution of allylic substrates with a wide range of nucleophiles or S_N 2'-type allylic substitution, which results in the formation of the above-mentioned bonds with high levels of enantioselective induction. AAS reaction tolerates a broad range of functional groups, thus has been successfully applied in the asymmetric synthesis of a wide range of optically pure compounds. This reaction has been extensively used in the total synthesis of several complex molecules, especially natural products. In this review, we try to highlight the applications of metal (Pd, Ir, Mo, or Cu)-catalyzed AAS reaction in the total synthesis of the biologically active natural products, as a key step, updating the subject from 2003 till date.

Synthesis of 3D-Rich Heterocycles: Hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones and Octahydro-2H-2a,2a1-diazacyclopenta[cd]inden-2-ones

Two cyclic azomethine imines, 7-methyl- and 7-phenyl-2-oxo-Δ⁷-hexahydropyrazolo[1,5-a]pyridin-8-ium-1-ide, were prepared in seven steps from the respective commercially available δ-keto acids. The addition of Grignard reagents followed by N-alkylation at position 1 afforded the 1,7,7-trisubstituted hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones, whereas 1,3-dipolar cycloadditions of these dipoles to typical acetylenic and olefinic dipolarophiles gave 4a-substituted 2a,2a¹-diazacyclopenta[cd]indene derivatives as the first representatives of a novel heterocyclic system. Regio- and stereoselectivity as well as the mechanism of these [3 + 2]-cycloadditions were evaluated using computational and experimental methods. The data obtained were in agreement with the polar concerted cycloaddition mechanism via the energetically favorable syn/endo-transition states.

Inflammation, Cancer and Oxidative Lipoxygenase Activity are Intimately Linked

Cancer and inflammation are intimately linked due to specific oxidative processes in the tumor microenvironment. Lipoxygenases are a versatile class of oxidative enzymes involved in arachidonic acid metabolism. An increasing number of arachidonic acid metabolites is being discovered and apart from their classically recognized pro-inflammatory effects, anti-inflammatory effects are also being described in recent years. Interestingly, these lipid mediators are involved in activation of pro-inflammatory signal transduction pathways such as the nuclear factor κB (NF-κB) pathway, which illustrates the intimate link between lipid signaling and transcription factor activation. The identification of the role of arachidonic acid metabolites in several inflammatory diseases led to a significant drug discovery effort around arachidonic acid metabolizing enzymes. However, to date success in this area has been limited. This might be attributed to the lack of selectivity of the developed inhibitors and to a lack of detailed understanding of the functional roles of arachidonic acid metabolites in inflammatory responses and cancer. This calls for a more detailed investigation of the activity of arachidonic acid metabolizing enzymes and development of more selective inhibitors.