Total Synthesis of (+)-Pochonin D and (+)-Monocillin II via Chemo- and Regioselective Intramolecular Nitrile Oxide Cycloaddition

Manganese-Catalyzed 5-Endo-trig Oxygenative Cyclization of α,β-Unsaturated Oximes under Air and Ambient Conditions for the Synthesis of 4,5-Dihydroisoxazoles

The stereoselective 5-endo-trig oxygenative cyclization of α,β-unsaturated oximes was achieved using molecular oxygen (O2) and a manganese catalyst. Several 4-hydroxy-4,5-dihydroisoxazoles were obtained in high yields by directly incorporating O2 from the atmosphere (eliminating the necessity for a pure oxygen environment) and using an unprecedentedly low loading of Mn(acac)3 (as little as 0.020 mol %) without additional additives. Because of its desirable features, such as operational simplicity, inexpensive catalyst, mild reaction conditions (open flask conditions at room temperature), and broad substrate compatibility, this novel reaction provides an attractive synthetic approach to producing 4-hydroxy-4,5-dihydroisoxazoles.

Total synthesis of 14-membered ring β-resorcylic acid lactone (+)-monocillin II

This study outlines the total synthesis of (+)-monocillin II, wherein a cis-isomer selectively produces a trans-isomer during the ring-closing metathesis. The Mitsunobu reaction conducted at -60 °C, facilitating the formation of an ester bond, was the key to completing the total synthesis, which was accomplished in the longest linear sequence of 10 steps with an overall yield of 9.3%.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Regio- and diastereoselective access to densely functionalized ketones via the Boekelheide rearrangement of isoxazoline N-oxides

In this work, the classical "isoxazoline route" toward aldols involving the [3 + 2]-cycloaddition of nitrile oxide to alkenes and hydrogenolysis of the oxime group was revisited. To avoid regioselectivity issues, [4 + 1]-annulation of nitroalkenes with sulfonium ylides was used to construct the isoxazoline ring bearing an N-oxide moiety. Subsequent deoxygenative C-H functionalization using the Boekelheide rearrangement and hydrogenolysis of the isoxazoline ring afforded α'-acyloxy-substituted aldols, which are difficult to access both by the classical aldol reaction and the "isoxazoline route". The products are formed in good to high overall yields and as single diastereomers in most cases. The synthetic use of these aldols was showcased by their smooth transformation into diastereomerically pure triols and a 2,3-diaryl-4-hydroxy-substituted tetrahydrofuran derivative, which is structurally related to cinncassin B.

3-Benzoylisoxazolines by 1,3-Dipolar Cycloaddition: Chloramine-T-Catalyzed Condensation of α-Nitroketones with Dipolarophiles

In this study, 3-benzoylisoxazolines were synthesized by reacting alkenes with various α-nitroketones using chloramine-T as the base. The scope of α-nitroketones and alkenes is extensive, including different alkenes and alkynes to form various isoxazolines and isoxazoles. The use of chloramine-T, as the low-cost, easily handled, moderate base for 1,3-dipolar cycloaddition is attractive.

A three-component approach to isoxazolines and isoxazoles under metal-free conditions

A 1,3-dipolar cycloaddition of 2-methylquinoline, tert-butyl nitrite (TBN) and alkynes or alkenes for the synthesis of biheteroaryls containing both isoxazoline/isoxazole and quinoline motifs has been developed. In this protocol, TBN serves as a convenient N-O source to convert 2-methylquinoline into intermediate nitrile oxides in situ.

Total Synthesis of trans-Resorcylide via Macrocyclic Stille Carbonylation

The resorcylic macrolides are important natural products with a wide range of remarkable biological activities. So far, most of the reported resorcylic macrolide syntheses use either macrolactonization or ring closing metathesis to build the corresponding macrocycle. In continuation of our efforts in developing novel carbonylation reactions to facilitate natural product total synthesis, we report herein a total synthesis of trans-resorcylide (1) featuring a palladium-catalyzed macrocyclic Stille carbonylation to build its 12-membered macrocycle.

Stereoconfining macrocyclizations in the total synthesis of natural products

This review covers selected examples of point chirality-forming macrocyclizations in natural product total synthesis in the past three decades.

In Situ Generation of Nitrile Oxides from NaCl-Oxone Oxidation of Various Aldoximes and Their 1,3-Dipolar Cycloaddition

Reported is a new green protocol for the efficient in situ generation of nitrile oxides through NaCl/Oxone oxidation of aldoximes and their dipolar cycloaddition. The key feature is the use of a green chemistry approach to address the substrate scope of aldoximes: broad scope (aliphatic, aromatic, and alkenyl aldoximes) without production of organic byproducts derived from oxidant and/or catalyst. Importantly, NaCl/Oxone-promoted three-component cycloaddition of aldehyde, hydroxylamine hydrochloride, and alkene was demonstrated to be competent (63-81%).

Antiviral and Anti-Inflammatory Activities of Pochonin D, a Heat Shock Protein 90 Inhibitor, against Rhinovirus Infection

Human rhinoviruses (HRV) are one of the major causes of common cold in humans and are also associated with acute asthma and bronchial illness. Heat-shock protein 90 (Hsp90), a molecular chaperone, is an important host factor for the replication of single-strand RNA viruses. In the current study, we examined the effect of the Hsp90 inhibitor pochonin D, in vitro and in vivo, using a murine model of human rhinovirus type 1B (HRV1B) infection. Our data suggested that Hsp90 inhibition significantly reduced the inflammatory cytokine production and lung damage caused by HRV1B infection. The viral titer was significantly lowered in HRV1B-infected lungs and in Hela cells upon treatment with pochonin D. Infiltration of innate immune cells including granulocytes and monocytes was also reduced in the bronchoalveolar lavage (BAL) by pochonin D treatment after HRV1B infection. Histological analysis of the lung and respiratory tract showed that pochonin D protected the mice from HRV1B infection. Collectively, our results suggest that the Hsp90 inhibitor, pochonin D, could be an attractive antiviral therapeutic for treating HRV infection.