Synthesis of the Spirocyclic Imine Fragment of Portimines Using a γ-Hydroxymethyl-αβ-butenolide Dienophile in a Diastereoselective Diels-Alder Reaction.

The synthesis of the spirocyclic imine fragment of the portimine family of marine toxins has been achieved. A densely functionalized key lactone-ester intermediate was assembled via a highly diastereoselective Diels-Alder cycloaddition, involving a novel γ-hydroxymethyl-α,β-butenolide dienophile. A Stille coupling was employed to install the vinyl group.

Synthesis of the spiroimine fragment of portimines A and B.

Portimines A and B are spirocyclic imine natural products, which display remarkable anticancer, anti-HIV, and antifouling activities. Herein, we report a facile synthesis of the spirocyclic core of portimines A and B. Our strategy utilized a scalable Diels-Alder addition of a 2-bromo-1,3-butadiene to a symmetrical malonate dienophile, coupled with a diastereoselective lactonization of the resulting malonate that enabled differentiation of the two carbonyl groups.

Synthesis of the C4-C16 Polyketide Fragment of Portimines A and B.

Stereoselective synthesis of the C4-C16 polyketide fragment of portimines A and B is reported, enabled by our previously established method for the stereoselective synthesis of -α,α'-dihydroxyketones. The preparation of this advanced fragment provides insights useful for the total synthesis of portimines A and B. An asymmetric Evans aldol reaction was used to install the C10-C11 adjacent stereogenic centers before incorporation of indantrione, followed by epoxidation and epoxide opening to forge the challenging -α,α'-dihydroxyketone functionality.

Clinical characteristics of intrahepatic biliary papilloma: A case report.

Background: Intrahepatic bile duct papilloma (IPNB) is a rare benign tumour from the bile duct epithelium and has a high malignant transformation rate. Early radical resection can obviously improve the prognosis of patients, but it is difficult to be sure of the diagnosis of IPNB before operating.

Case Summary: This study included 28 patients with intraductal papilloma admitted to the First Hospital of Jilin University from January 2010 to November 2020 and recorded their clinical manifestations, imaging features, complications and prognosis.

Clinical characteristics of adult-type annular pancreas: A case report.

Background: Annular pancreas (AP) is a rare congenital abnormal rotation of the pancreas. AP rarely occurs in adults. Pancreatic tumors and ampullary tumors are related to AP, so the discovery and treatment of AP are essential.

Zinc, sulfur and nitrogen co-doped carbon from sodium chloride/zinc chloride-assisted pyrolysis of thiourea/sucrose for highly efficient oxygen reduction reaction in both acidic and alkaline media.

Zn and N co-doped carbon (Zn-N-C) shows encouraging catalytic stability for oxygen reduction reaction (ORR) because of the fulfilled d orbital of Zn, but its catalytic activity is not satisfactory. Herein, hierarchically porous Zn, S and N co-doped carbon (Zn-S-N-C) with large specific surface area (2433 m g) and pore volume (3.007 cm g) is synthesized by using NaCl/ZnCl-assisted pyrolysis of sucrose and thiourea.

A ZIF-derived hierarchically porous Fe-Zn-N-C catalyst synthesized via a two-stage pyrolysis for the highly efficient oxygen reduction reaction in both acidic and alkaline media.

A ZIF-derived Fe-Zn-N-C catalyst with sufficient exposure of bimetallic active sites and well-balanced micro/mesopores is synthesized by a two-stage pyrolysis process and exhibits superior oxygen reduction activity with high half-wave potentials of up to 0.819 V in 0.1 M HClO and 0.

Highly Diastereoselective Synthesis of Syn-1,3-Dihydroxyketone Motifs from Propargylic Alcohols via Spiroepoxide Intermediates.

Syn dihydroxyketone motifs are embedded in a wide range of biologically active natural products, however the development of stereoselective synthetic methods to assemble these structures has proven a challenging task. We report a highly diastereoselective method for the synthesis of syn dihydroxyketones from propargylic alcohols, with wide scope for application in natural product synthesis. The reaction sequence involves regioselective cyclisation of propargylic alcohols with incorporation of a triketone to give enol dioxolanes that are then diastereoselectively epoxidised to form unusual spiroepoxide intermediates.

Reactivity of 2-Nitropyrrole Systems: Development of Improved Synthetic Approaches to Nitropyrrole Natural Products.

Fundamental study of the reactivity of 2-nitropyrrole systems has enabled the identification of effective methods for incorporation of this unusual motif into advanced natural product frameworks. The presence of electron-rich pyrrole N-protecting groups (BOM, Boz) was demonstrated to enable a variety of previously unsuccessful palladium-mediated cross-couplings to be carried out in high yield. Based on this foundation, a series of regio- and stereoselective synthetic routes toward the nitropyrrolin and heronapyrrole families of natural products was developed by our group (G1-3).

Synthesis and biological evaluation of novel teixobactin analogues.

The cyclic depsipeptide, teixobactin, possesses promising activity against a range of antimicrobial-resistant (AMR) pathogenic bacteria, including Staphylococcus aureus and Mycobacterium tuberculosis. Teixobactin contains a number of non-canonical residues, including the synthetically challenging amino acid, l-allo-enduracididine, complicating clinical application of this peptide. Herein, we report the synthesis of six analogues of teixobactin, in which the non-canonical l-allo-enduracididine amino acid is replaced by isosteric, commercially available Fmoc-amino acid building blocks.

General Synthesis of the Nitropyrrolin Family of Natural Products via Regioselective CO-Mediated Alkyne Hydration.

The total synthesis of the 2-nitropyrrole natural products nitropyrrolins A and B and the formal synthesis of nitropyrrolin D are reported. The key 2-nitro-4-alkylpyrrole core was efficiently assembled by Sonogashira cross-coupling, with complete control of regioselectivity. An unusual carboxylative cyclization, sulfonylcarbamate formation, and base-promoted cleavage sequence enabled access to the key hydroxy ketone without affecting the protected 2-nitropyrrole unit.

2-Nitropyrrole cross-coupling enables a second generation synthesis of the heronapyrrole antibiotic natural product family.

The heronapyrroles are a family of antibiotic natural products containing the rare 2-nitropyrrole motif. We report here a second generation total synthesis that circumvents problems of selective pyrrole nitration and alkene formation that limited the utility of previous approaches. Stille sp-sp cross coupling of a novel 2-nitropyrrole fragment was developed to install the key C7,8 olefin with complete regiochemical control.

Nitropyrrole natural products: isolation, biosynthesis and total synthesis.

Nitropyrrole-containing natural products are relatively rare in nature. Known examples are limited to the β-nitropyrrole-containing pyrrolomycins and α-nitropyrrole-containing nitropyrrolins and heronapyrroles. Their unique structures and interesting bioactivity are of ongoing interest to the chemistry community.

Total synthesis of heronapyrrole C.

A flexible total synthesis of the 2-nitropyrrole-derived marine natural product, (+)-heronapyrrole C, is reported. The approach is based on regioselective access to key building blocks containing the rare 4-substituted 2-nitropyrrole motif. Sharpless asymmetric epoxidation and dihydroxylation and a Shi epoxidation were used to introduce the five stereogenic centers of the bis-THF-diol side chain.