PtCl2-Catalyzed Intramolecular Cyclization of α-Benzyl Allenoates to Afford Indenes and Furanones

Indene and furanone are important ring structures widely present in active pharmaceutical molecules. Here, we have developed a straightforward method for the synthesis of indene and furanone via PtCl2-catalyzed intramolecular cyclization of α-benzyl allenoates. By altering the ester substitution pattern in the α-benzyl allenoates, we can regulate the reaction site, enabling two distinct intramolecular cyclization reactions that yield both indene and furanone products, respectively. For α-benzyl-substituted ethyl allenoate, the reaction proceeds via a 5-exo cyclization to form indene derivatives. In contrast, for α-benzyl-substituted tert-butyl allenoate, the reaction involves ester hydrolysis and intramolecular cyclization, yielding furanone products. This method operates efficiently under a 5 mol % PtCl2 catalyst and exhibits good tolerance toward various functional groups. Furthermore, furanone products can be obtained on a gram scale and further smoothly converted into 1,2-disubstituted furan.

Anti-Larval and Anti-Algal Natural Products from Marine Microorganisms as Sources of Anti-Biofilm Agents

Bacteria growing inside biofilms are more resistant to hostile environments, conventional antibiotics, and mechanical stresses than their planktonic counterparts. It is estimated that more than 80% of microbial infections in human patients are biofilm-based, and biofouling induced by the biofilms of some bacteria causes serious ecological and economic problems throughout the world. Therefore, exploring highly effective anti-biofilm compounds has become an urgent demand for the medical and marine industries. Marine microorganisms, a well-documented and prolific source of natural products, provide an array of structurally distinct secondary metabolites with diverse biological activities. However, up to date, only a handful of anti-biofilm natural products derived from marine microorganisms have been reported. Meanwhile, it is worth noting that some promising antifouling (AF) compounds from marine microbes, particularly those that inhibit settlement of fouling invertebrate larvae and algal spores, can be considered as potential anti-biofilm agents owing to the well-known knowledge of the correlations between biofilm formation and the biofouling process of fouling organisms. In this review, a total of 112 anti-biofilm, anti-larval, and anti-algal natural products from marine microbes and 26 of their synthetic analogues are highlighted from 2000 to 2021. These compounds are introduced based on their microbial origins, and then categorized into the following different structural groups: fatty acids, butenolides, terpenoids, steroids, phenols, phenyl ethers, polyketides, alkaloids, flavonoids, amines, nucleosides, and peptides. The preliminary structure-activity relationships (SAR) of some important compounds are also briefly discussed. Finally, current challenges and future research perspectives are proposed based on opinions from many previous reviews.

Palladium-catalyzed double-carbonylative cyclization of propargyl alcohols and aryl triflates to expedite construction of 4-aroyl-furan-2(5H)-ones

A palladium-catalyzed double-carbonylative cyclization of propargyl alcohols and aryl triflates has been developed. Various 4-aroyl-furan-2(5H)-one scaffolds were produced in good yields with Cr(CO)₆ as the CO source.

Synthesis of the natural product descurainolide and cyclic peptides from lignin-derived aromatics

Alternative sources of potential feedstock chemicals are of increasing importance as the availability of oil decreases. The biopolymer lignin is viewed as a source of useful mono-aromatic compounds as exemplified by the industrial scale production of vanillin from this biomass. Alternative lignin-derived aromatics are available in pure form but to date examples of the use of these types of compounds are rare. Here we address this issue by reporting the conversion of an aromatic keto-alcohol to the anti- and syn-isomers of Descurainolide A. The key step involves a rhodium-catalyzed allylic substitution reaction. Enantio-enriched allylic alcohols were generated via an isothiourea-catalyzed kinetic resolution enabling access to both the (2R,3R) and (2S,3S) enantiomers of anti-Descurainolide A. In addition we show that the lignin-derived keto-alcohols can be converted into unnatural amino acid derivatives of tyrosine. Finally, these amino acids were incorporated into cyclic peptide scaffolds through the use of both chemical and an enzyme-mediated macrocylisation.

MRI micelles self-assembled from synthetic gadolinium-based nano building blocks

Synthetic self-assembled stealth Gd-micelles are a new blood pool contrast agent for magnetic resonance imaging.

Natural products and ring-closing metathesis: synthesis of sterically congested olefins

This review highlights RCM reactions towards the synthesis of sterically congested natural products throughout the recent evolution of catalysts.

Naked eye instant reversible sensing of Cu(2+) and its in situ imaging in live brine shrimp Artemia

A Cu(2+)-specific colorimetric reversible fluorescent receptor was designed and synthesized which showed a naked eye observable colour change from colourless to pink on addition of an aqueous buffer (pH 7.4) solution of 30 ppb Cu(2+). Short response time (≤5 s) and low detection limit (nearly 3 ppb) make suitable as a reliable "dip-in" open eye sensor for Cu(2+). Bio-imaging application in live brine shrimp Artemia enabled to detect Cu(2+) at as low as 10 ppb exposure.

Chemoselective access to substituted butenolides via a radical cyclization pathway: mechanistic study, limits and application

We developed a new approach to γ-lactols and methylene-γ-lactols based upon the radical cyclization of aluminium acetals obtained by reduction of α-bromoesters with DIBAL-H. The cyclic aluminium acetals resulting from the cyclization process could engage in situ in further functionalization, as illustrated by the Oppenauer-type oxidation to give the corresponding lactones and γ-butenolides. The preparation of butenolides using this strategy compared favourably with the direct, tin-mediated cyclization of α-bromoesters, for which side reactions such as epimerization via [1,5]-HAT processes have been observed.

Reporting a new siderophore based Ca2+ selective chemosensor that works as a staining agent in the live organism Artemia

A new acyclic chemosensor bearing a siderophore linked to a rhodamine 6G fluorophore showed highly selective detection of Ca²⁺ ions in 100% aqueous solution at pH 7.4. The probe showed bio-imaging applicability in the live animal Artemia.