Synthesis of functionalized salicylate esters and amides by photochemical acylation

Synthesis of the monomeric counterpart of Marinomycin A and B

The synthesis of polyketide natural products has been a captivating pursuit in organic chemistry, with a particular focus on selectively introducing 1,3-polyol units. Among these natural products, Marinomycins A-D have garnered substantial interest due to their exceptional structural features and potent cytotoxicity. In this paper, we present a novel approach for synthesising the monomeric counterparts of Marinomycin A and B. Our method employs a previously established iterative cycle in conjunction with a standardised polyketide building block. Through this strategy, we showcase a promising pathway towards total and partial syntheses of these intriguing natural products.

Interfacial Ultraviolet Cross-Linking of Green Bilayer Dielectrics

Electronic waste is a growing challenge which needs to be addressed through the integration of high-performance sustainable materials. Green dielectric polymers such as poly(vinyl alcohol) (PVA) have favorable electrical properties but are challenging to integrate into thin film electronics due to their physical properties. For example, PVA suffers from poor film formation and is hygroscopic. Bilayer dielectrics with interfacial cross-linking can enable the use of high-performance PVA with favorable surface chemistry by using a hydrophobic poly(caprolactone) (PCL) layer. In this study, we developed a benzodioxinone-terminated PCL layer, which can be UV cross-linked to the hydroxy groups of the PVA dielectric. This air-stable UV-cross-linking PCL dielectric was able to effectively cross-link with PVA, leading to high-performance capacitors and single-walled carbon nanotube-based thin film transistors. This UV cross-linking PCL dielectric led to significant improvements in shelf-life, ease of processing, and similar device performance compared to our previously reported thermally cross-linking PCL layer. The UV cross-linking at the interface between these bilayers can allow for the integration of high-speed roll-to-roll processing, which enables low-cost, sustainable, and high-performance electronics.

Synthesis and characterization of benzodioxinone mono-telechelics and their use in block copolymerization

Poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) methyl ether (mPEG)-based monotelechelics were quantitatively prepared by copper (I)-catalyzed azide/alkyne cycloaddition (CuAAC) click reactions using azido-terminated polymers and alkyne functional benzodioxinones. The monotelechelic containing dimethyl moities (2,2-dimethyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was heat-sensitive, whereas the monotelechelic containing diphenyl moieties (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was UV light sensitive. Based on the FT-IR, 1H-NMR, and GPC investigations, the CuAAC click reactions enable the quantitative syntheses of monotelechelics under mild conditions. Moreover, the photosensitive mPEG-based monotelechelic was further utilized for the block copolymer synthesis upon UV-light irradiation. The photoinduced acylation of mPEG monotelechelic consist of (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) in the presence of hydroxy-terminated poly(epsilon caprolactone) enabled the successful block copolymer formation.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Catalyst-free synthesis of 3,1-benzoxathiin-4-ones/1,3-benzodioxin-4-ones

An unambiguous and precise method for the synthesis of 3,1-benzoxathiin-4-ones/1,3-benzodioxin-4-ones by the reaction of propargylic alcohols and salicylic/thiosalicylic acids under a catalyst-free and open-air atmosphere is described. This strategy is found to be quite general using various 2-mercapto and 2-hydroxybenzoic acids providing benzoxathiinones/benzodioxinones in good yields.

Synthesis of functionalized benzo[1,3]dioxin-4-ones from salicylic acid and acetylenic esters and their direct amidation

Direct synthesis of 4H-benzo[d][1,3]dioxin-4-one derivatives from salicylic acids and acetylenic esters (both mono- and disubstituted) has been described. The reaction is mediated by CuI and NaHCO₃ in acetonitrile. Room temperature amidation of the synthesized 1,3-benzodioxinones with primary amines readily afforded the corresponding salicylamides in moderate to good yields.

An efficient method for the synthesis of the active core 4H-benzo[d][1,3]dioxin-4-one followed by its direct room temperature amidation is reported.

A convergent approach toward fidaxomicin: Syntheses of the fully glycosylated northern and southern fragments

Efficient approaches that enable the synthesis of analogs of natural product antibiotics are needed to keep up with the emergence of multiply-resistant strains of pathogenic organisms. One promising candidate in this area is fidaxomicin, which boasts impressive in vitro anti-tubercular activity but has poor systemic bioavailability. We designed a flexible synthetic route to this target to enable the exploration of new chemical space and the future development of analogs with superior pharmacokinetics. We developed a robust approach to each of the key macrocyclic and sugar fragments, their union via stereoselective glycosylation, and a convergent late-stage macrolide formation with fully glycosylated fragments. Although we were able to demonstrate that the final Suzuki cross-coupling and ring-closing metathesis steps enabled macrocycle formation in the presence of the northern resorcylic rhamnoside and southern novioside sugars, these final steps were hampered by poor yields and the formation of the unwanted Z-macrocycle as the major stereoisomer.

Combining benzoxazine and ketene chemistries for self-healing of high performance thermoset surfaces

The use of oxoketene chemistry for self-healable polybenzoxazines is described.

Benzodioxinone Photochemistry in Macromolecular Science: Progress, Challenges, and Opportunities

This paper reviews the photoinduced reactions of benzodioxinones and how they function in polymer synthesis and UV curing applications. The mechanistic characteristics of the ketene and benzophenone production from the photolysis of benzodioxinone indicate that, under certain conditions, each intermediate may undergo further reactions expedient for the formation of various polymeric structures. While ketenes are efficient contributors to step-growth polymerization when subjected to reaction with the compounds possessing hydroxyl or amine groups, the released benzophenone can be utilized as a photoinitiator in both the free radical and cationic polymerizations. It has been shown that the photolysis of heterobifunctional monomers equipped with benzodioxinone and aliphatic hydroxyl groups leads to the formation of oligoesters with a narrow molecular weight distribution. We also validated the photochemical ability of benzodioxinone to induce the synthesis of block and graft copolymers, hybrid and branched polymers, and cross-linked monofunctional vinyl monomers or hydroxyl group-containing linear polymers.

Stereoselective Total Syntheses of (3R,5R)-Sonnerlactone and (3R,5S)-Sonnerlactone

A highly convergent and concise total syntheses of (3 R,5 R)-Sonnerlactone and (3 R,5 S) Sonnerlactone from a readily available L-malic acid is described. The following series of reactions such as Barbier allylation, photochemical esterification and Ring Closing Metathesis (RCM) are utilized as key steps to accomplish their syntheses.

Oxidative cyclization of alkenoic acids promoted by AgOAc

Alkenoic acids derived from salicylic acid and analogues undergo an unexpected oxidative cyclization process triggered by AgOAc leading to 4H-benzo[d][1,3]dioxin-4-ones. The process is affected by the substitution on the aryl and the allyl units.

Macrolactam analogues of macrolide natural products

The chemical modification of macrolide natural products into aza- or lactam analogues is a strategy employed to improve their metabolic stability and biological activity.

Synthesis and structure-activity studies of the V-ATPase inhibitor saliphenylhalamide (SaliPhe) and simplified analogs

An efficient total synthesis of the potent V-ATPase inhibitor saliphenylhalamide (SaliPhe), a synthetic variant of the natural product salicylihalamide A (SaliA), has been accomplished aimed at facilitating the development of SaliPhe as an anticancer and antiviral agent. This new approach enabled facile access to derivatives for structure-activity relationship studies, leading to simplified analogs that maintain SaliPhe's biological properties. These studies will provide a solid foundation for the continued evaluation of SaliPhe and analogs as potential anticancer and antiviral agents.

Evaluating the potential of vacuolar ATPase inhibitors as anticancer agents and multigram synthesis of the potent salicylihalamide analog saliphenylhalamide

The natural product salicylihalamide is a potent inhibitor of the Vacuolar ATPase (V-ATPase), a potential target for antitumor chemotherapy. We generated salicylihalamide-resistant tumor cell lines typified by an overexpansion of lysosomal organelles. We also found that many tumor cell lines upregulate tissue-specific plasmalemmal V-ATPases, and hypothesize that tumors that derive their energy from glycolysis rely on these isoforms to maintain a neutral cytosolic pH. To further validate the potential of V-ATPase inhibitors as leads for cancer chemotherapy, we developed a multigram synthesis of the potent salicylihalamide analog saliphenylhalamide.

Efficient and selective reduction protocols of the 2,2-dimethyl-1,3-benzodioxan-4-one functional group to readily provide both substituted salicylaldehydes and 2-hydroxybenzyl alcohols

Two complementary procedures have been developed that selectively allow for the synthesis of either substituted salicylaldehydes or the corresponding 2-hydroxylbenzyl alcohols upon treatment of the 2,2-dimethyl-1,3-benzodioxan-4-one functional group with DIBAL-H or LAH, respectively.

Acylation of different amino derivatives with fatty acids on UL-MFI-type catalysts

Acylation of different amino derivatives (ethanol amine, diethanol amine, N-aminoethylpiperazine) was carried out under green conditions with oleic acid or tail oil fatty acids. The experiments were carried out using as heterogeneous catalysts mesoporous Al-Meso and UL-ZSM-5 with Si/Al ratios between 100 and 20, in the range of the temperatures 80-180 °C without any solvent or in octane or water. The efficiency of the catalysts for the acylation of the investigated substrates appeared to be directly dependent on the Si/Al ratio and the size of the pores. The selectivity toward esters or amides was firstly controlled by temperature, and then by the Si/Al ratios. Additionally, both the conversion and selectivity were controlled by the solvent in which the reaction was carried out. The use of water led mostly to a mixture of esters and amides.

Macrolactonization via hydrocarbon oxidation

A novel Pd/sulfoxide-catalyzed macrolactonization reaction of linear omega-alkenoic acids is reported that proceeds via serial ligand-catalyzed allylic C-H oxidation. The scope of this macrolactonization appears to be very broad. Aryl, alkyl, and (Z)-alpha,beta-unsaturated acids are all competent nucleophiles for this reaction, with the latter undergoing macrolactonization with no olefin isomerization. High functional group compatibility is observed that includes biologically and medicinally relevant functionality such as ortho-substituted salicylate esters, bis(indoyl)maleimides, and peptides. Evidence is provided to support the hypothesis that macrolactonization proceeds via inner-sphere functionalization from a templated pi-allylPd carboxylate intermediate.

Efficient asymmetric synthesis of (+)-SCH 351448

An efficient and stereocontrolled total synthesis of (+)-SCH 351448, a novel activator of low-density lipoprotein receptor promoter, has been achieved with a longest linear sequence of 21 steps. Key steps include applications of the recently developed asymmetric allyl- and crotylsilane reagents and a new protodesilylative version of the tandem silylformylation/allylsilylation reaction, which provides an efficient synthesis of 1,5-syn-diols. [reaction: see text]

Radical Phosphination of Organic Halides and Alkyl Imidazole-1-carbothioates

Taking advantage of a radical-based methodology, mild and chemoselective phosphination reactions of organic halide and alkyl imidazole-1-carbothioates have been developed. The mild reaction conditions allow labile functional groups to survive during the reaction.

A Concise Synthesis of (+)-SCH 351448

[structure: see text] We describe a highly convergent synthetic approach to the natural product (+)-SCH 351448 (1)-a hexane-soluble heptacoordinate monosodium salt of a C(2)-symmetrical macrocyclic dilactone. Our approach implements a photochemical acylation as the key step to combine two nearly identical but orthogonal C1-C29 fragments, followed by a base-induced intramolecular acylation and deprotection to yield the natural product.