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Two 3-(p-substituted phenyl)-3a,8a-dihydro-4H-cyclohepta[d]isoxazoles were synthesized by 1,3-dipolar cycloaddition of the corresponding nitrile oxides with cycloheptatriene. Two endoperoxides were synthesized as facially selective and single products in high yields (93%--95%) from the reactions of isoxazole derivatives with singlet oxygen. The exact configurations of the endoperoxide with a methyl group in the phenyl ring and the diol synthesized from it were confirmed by X-ray analysis. To elucidate the mechanism, the formation energy of the endoperoxide was investigated by simulations using the software package Gaussian 09 and density functional theory calculations via the M06-2X/6-311+G(d,p) level method in dichloromethane. The results were consistent with experimental findings showing the formation of isoxazole products. [ABSTRACT FROM AUTHOR]

Aromatic architectures able to capture, store and release singlet oxygen have sparked the interest of the scientific community as an attractive strategy to generate singlet oxygen. Among these structures, anthracenes are efficient singlet oxygen batteries with applications in various fields such as chemistry, materials science or medicine. Until now, studies have mainly focused on symmetrical 9,10‐disubstituted anthracenes bearing (hetero)aryl groups or substituted alkyne motifs. In this work, we investigated unsymmetrical anthracene molecules to explore their propensity to trap and to release singlet oxygen. Kinetic studies confirmed the impact of electron‐rich and electron‐deficient substituents on the photooxygenation step and on the release of singlet oxygen triggered by thermolysis of the endoperoxides. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of a heavy-atom-free BODIPY dye called carbonyl-BDP and its application in the photooxygenation of 1-naphthol to 1,4-naphthoquinone. BODIPY dyes are known for their strong visible-light absorption and good photochemical and thermal stabilities, making them suitable for organic transformations. The introduction of carbonyl groups into the BODIPY system enhances its ability to generate singlet oxygen, which is important for photocatalytic reactions. The researchers successfully demonstrated the photooxygenation of 1-naphthol using carbonyl-BDP as a photosensitizer under white-light irradiation. [Extracted from the article]

Histidine photooxygenation has been the subject of extensive investigation for many years. The intricate nature of histidine distinguishes it from other amino acids, as its side chain readily undergoes changes in charge state and tautomerization in response to pH, and the polarity of the imidazole ring inverts upon oxidation. This complexity gives rise to a diverse range of oxidation products and mechanisms, posing challenges in their interpretation. This review aims to provide a thorough overview of the chemistry involved in histidine photooxygenation, encompassing a comprehensive analysis of resulting products, mechanisms engaged in their formation, and analytical techniques that have contributed to their identification. Additionally, it explores a wide range of applications stemming from this transformation, offering valuable insights into its practical implications in fields such as materials science, biomedical research, and drug development. By bridging the existing gap in literature, this review serves as a resource for understanding the intricacies of histidine photooxygenation and its diverse ramifications. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic endoperoxides are important sources of singlet oxygen (1O2) and their formation from polyacenes is well established. Anthracene carboxyimides are of particular interest as they exhibit excellent antitumor activity and possess unique photochemical properties. However, the photooxygenation of the synthetically versatile anthracene carboxyimide moiety has not been reported due to its competing [4+4] photodimerization reaction. Herein, we describe the reversible photo‐oxidation of an anthracene carboxyimide. X‐ray crystallographic analysis surprisingly revealed the formation of a racemic mixture of chiral hydroperoxides, rather than the expected endoperoxide. The photoproduct undergoes both photo‐ and thermolysis to form 1O2. Activation parameters were derived for the thermolysis and the mechanisms of photooxygenation and thermolysis are discussed. The anthracene carboxyimide also showed high selectivity and sensitivity for nitrite anions in acidic aqueous media and possessed stimuli‐responsive behaviour. [ABSTRACT FROM AUTHOR]

In the quest for new therapies targeting hypoxia, aromatic endoperoxides have intriguing potential as oxygen releasing agents (ORAs) able to free O2 in tissues upon suitable trigger. Four aromatic substrates were synthesized and the formation of their corresponding endoperoxides was optimized in organic solvent upon selective irradiation of Methylene Blue, a low-cost photocatalyst, producing the reactive singlet oxygen species. Complexation of the hydrophobic substrates within a hydrophilic cyclodextrin (CyD) polymer allowed their photooxygenation in homogeneous aqueous environment using the same optimized protocol upon dissolution in water of the three readily accessible reagents. Notably, reaction rates were comparable in buffered D2O and organic solvent and, for the first time, the photooxygenation of highly hydrophobic substrates was achieved for millimolar solutions in non-deuterated water. Quantitative conversion of the substrates, straightforward isolation of the endoperoxides and recovery of the polymeric matrix were achieved. Cycloreversion of one ORA to the original aromatic substrate was observed upon thermolysis. These results hold great potential for the launch of CyD polymers both as reaction vessels for green, homogeneous photocatalysis and as carrier for the delivery of ORAs in tissues. [ABSTRACT FROM AUTHOR]

Oxygen atom incorporation into organic molecules is one of the most powerful strategies to increase their pharmacological activity and to obtain valuable intermediates in organic synthesis. Traditional oxidizing agents perform very well, but their environmental impact and their low selectivity constitute significant limitations. On the contrary, visible-light-promoted oxygenations represent a sustainable method for oxidizing organic compounds, since only molecular oxygen and a photocatalyst are required. Therefore, photocatalytic oxygenation reactions exhibit very high atom-economy and eco-compatibility. This mini-review collects and analyzes the most recent literature on organo-photocatalysis applications to promote the selective oxygenation of organic substrates. In particular, acridinium salts, Eosin Y, Rose Bengal, cyano-arenes, flavinium salts, and quinone-based dyes are widely used as photocatalysts in several organic transformations as the oxygenations of alkanes, alkenes, alkynes, aromatic compounds, amines, phosphines, silanes, and thioethers. In this context, organo-photocatalysts proved to be highly efficient in catalytic terms, showing similar or even superior performances with respect to their metal-based counterparts, while maintaining a low environmental impact. In addition, given the mild reaction conditions, visible-light-promoted photo-oxygenation processes often display remarkable selectivity, which is a striking feature for the late-stage functionalization of complex organic molecules. [ABSTRACT FROM AUTHOR]

Non-invasive phototherapy has been emerging as an ambitious tactic for suppression of amyloid-β (Aβ) self-assembly against Alzheimer's disease (AD). However, it remains a daunting challenge to develop efficient photosensitizers for Aβ oxygenation that are activatable in a deep brain tissue through the scalp and skull, while reducing side effects on normal tissues. Here, we report an Aβ targeted, low-dose X-ray-excitable long-afterglow scintillator (ScNPs@RB/Ab) for efficient deep-brain phototherapy. We demonstrate that the as-synthesized ScNPs@RB/Ab is capable of converting X-rays into visible light to activate the photosensitizers of rose bengal (RB) for Aβ oxygenation through the scalp and skull. We show that the ScNPs@RB/Ab persistently emitting visible luminescence can substantially minimize the risk of excessive X-ray exposure dosage. Importantly, peptide KLVFFAED-functionalized ScNPs@RB/Ab shows a blood–brain barrier permeability. In vivo experimental results validated that ScNPs@RB/Ab alleviated Aβ burden and slowed cognitive decline in triple-transgenic AD model mice at extremely low X-ray doses without side effects. Our study paves a new pathway to develop high-efficiency transcranial AD phototherapy. Non-invasive phototherapy has been emerging as an ambitious tactic for suppression of amyloid-β (Aβ) self-assembly against Alzheimer's disease (AD). However, it remains a daunting challenge to develop efficient photosensitizers for Aβ oxygenation that are activatable in a deep brain tissue through the scalp and skull, while reducing side effects on normal tissues. Herein, we report an Aβ targeted, low-dose X-ray-excitable long-afterglow scintillators (ScNPs@RB/Ab) for efficient deep-brain phototherapy. In vivo experimental results validated that ScNPs@RB/Ab alleviated Aβ burden and slowed cognitive decline in triple-transgenic AD model mice at extremely low X-ray doses without side effects. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-step diimide reduction of saturated 6-(4′-aryloxy phenyl) vinyl 1,2,4-trioxanes has been reported. • Antimalarial activities of the synthesized compounds were evaluated by oral route against multi-drug resistant Plasmodium yoelii nigeriensis. • Cyclopentane-based trioxanes provided best protection to infected mice amongst all. • Trioxane 12b1 is four-fold active than β-arteether via oral route. Novel saturated 6-(4′-aryloxy phenyl) vinyl 1,2,4-trioxanes 12a(1 – 3)–12d(1 – 3) and 13a(1 – 3)–13d(1 – 3) have been designed and synthesized, in one single step from diimide reduction of 11a(1 – 3)–11d(1 – 3). All the newly synthesized trioxanes were evaluated for their antimalarial activity against multi-drug resistant Plasmodium yoelii nigeriensis via oral route. Cyclopentane-based trioxanes 12b1, 12c1 and 12d1 , provided 100 % protection to the infected mice at 24 mg/kg × 4 days. The most active compound of the series, trioxane 12b1 , provided 100 % protection even at 12 mg/kg × 4 days and 60 % protection at 6 mg/kg × 4 days. The currently used drug, β-arteether provides only 20 % protection at 24 mg/kg × 4 days. [ABSTRACT FROM AUTHOR]

Toxic amyloid- β (A β) aggregates are closely related to neurodegenerative diseases. Photo-oxygenation of A β aggregates exhibits high efficiency in inhibiting A β fibrillation and degrading A β aggregates. However, indiscriminative photo-oxygenation will damage functional proteins, leading to a failure in anti-A β therapies. Herein, we develop a new quinolinium-based photo-oxygenation catalyst and introduce a non-radiative de-excitation pathway based on twisted intramolecular charge transfer (TICT) for the selective photo-oxygenation of A β 1–40 aggregates. The catalyst exhibits strong A β 1–40 fibrils binding affinity and activatable photo-oxygenation activity by limiting intramolecular rotation. Spectroscopic and microscopic characterizations demonstrate that the catalyst can efficiently inhibit A β 1–40 fibrillation and degrade preformed A β 1–40 fibrils even in a very low inhibitor:protein ratio (I:P = 0.05). Significantly attenuated neurotoxicity is also confirmed. These results provide new insight into the design of activatable photo-oxygenation catalysts for the selective inhibition of A β aggregation. [Display omitted] • A novel quinolinium-based photo-oxygenation catalyst is developed for the selective photo-oxygenation of Aβ 1–40 aggregates. • Photo-oxygenation of Aβ 1–40 aggregates by the catalyst under laser irradiation can efficiently suppress the aggregation of Aβ 1–40 peptides and degrade Aβ 1–40 aggregates even in a very low inhibitor: peptide ratio (e.g., 0.05). • The catalyst exhibits a significant neuroprotective effect against Aβ-mediated cytotoxicity. [ABSTRACT FROM AUTHOR]

Amyloids, proteinous aggregates with β-sheet-rich fibrils, are involved in several neurodegenerative diseases such as Alzheimer's disease; thus, their detection is critically important. The most common fluorescent dye for amyloid detection is thioflavin-T (ThT), which shows on/off fluorescence upon amyloid binding. We previously reported that an engineered globular protein with a flat β-sheet, peptide self-assembly mimic (PSAM), can be used as an amyloid binding model. In this study, we further explored the residue-specific properties of ThT-binding to the flat β-sheet by introducing systematic mutations. We found that site-specific mutations at the ThT-binding channel enhanced affinity. We also evaluated the binding of a ThT-based photocatalyst, which showed the photooxygenation activity on the amyloid fibril upon light radiation. Upon binding of the photocatalyst to the PSAM variant, singlet oxygen-generating activity was observed. The results of this study expand our understanding of the detailed binding mechanism of amyloid-specific molecules. [ABSTRACT FROM AUTHOR]

Oxygen atom incorporation into organic molecules is one of the most powerful strategies to increase their pharmacological activity and to obtain valuable intermediates in organic synthesis. Traditional oxidizing agents perform very well, but their environmental impact and their low selectivity constitute significant limitations. On the contrary, visible-light-promoted oxygenations represent a sustainable method for oxidizing organic compounds, since only molecular oxygen and a photocatalyst are required. Therefore, photocatalytic oxygenation reactions exhibit very high atom-economy and eco-compatibility. This mini-review collects and analyzes the most recent literature on organo-photocatalysis applications to promote the selective oxygenation of organic substrates. In particular, acridinium salts, Eosin Y, Rose Bengal, cyano-arenes, flavinium salts, and quinone-based dyes are widely used as photocatalysts in several organic transformations as the oxygenations of alkanes, alkenes, alkynes, aromatic compounds, amines, phosphines, silanes, and thioethers. In this context, organo-photocatalysts proved to be highly efficient in catalytic terms, showing similar or even superior performances with respect to their metal-based counterparts, while maintaining a low environmental impact. In addition, given the mild reaction conditions, visible-light-promoted photo-oxygenation processes often display remarkable selectivity, which is a striking feature for the late-stage functionalization of complex organic molecules.

The photooxygenation of naphthalene to the corresponding endoperoxide (EPO) under various conditions is described. Substantial conversion is only observed at −10 °C and after more than two days, indicating that the [4+2] cycloaddition of singlet oxygen to this acene proceeds much more slowly than corresponding reactions of substituted naphthalenes, a rate constant of k=5.4±0.3 M−1s−1 was determined by competition kinetics. Another problem is the thermal lability and photochemical cleavage of the naphthalene EPO. We investigated the mechanism of this radical process depending on the light source and sensitizer in comparison to known cyclohexadiene EPO. Thus, bisepoxides and keto epoxides are formed after homolysis of the O−O bond by irradiation with sodium lamps or blue LEDs and subsequent cyclization. This process is accelerated by the sensitizers methylene blue and 9,10‐dicyanoanthracene, indicating an electron transfer mechanism. Finally, the cleavage of the peroxidic bond is inhibited with red LEDs, and photooxygenation under such conditions affords 20 % EPO. Thus, we could demonstrate that contrary to literature statements singlet oxygen does indeed react with naphthalene. [ABSTRACT FROM AUTHOR]

In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly conjugated photosensitizers show increasing potential in photocatalysis since they combine both photo- and electrochemical properties which can substitute available metalloorganic photocatalysts. Batch and continuous-flow approaches are presented highlighting the relevance of enabling technologies for the renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors’ opinion.

The price of the currently best available antimalarial treatment is driven in large part by the limited availability of its base drug compound artemisinin. One approach to reduce the artemisinin cost is to efficiently integrate the partial synthesis of artemisinin starting from its biological precursor dihydroartemisinic acid (DHAA) into the production process. The optimal design of such an integrated process is a complex task that is easier to solve through simulations studies and process modelling. In this article, we present a quantitative kinetic model for the photooxygenation of DHAA to an hydroperoxide, the essential initial step of the partial synthesis to artemisinin. The photooxygenation reactions were studied in a two-phase photo-flow reactor utilizing Taylor flow for enhanced mixing and fast gas-liquid mass transfer. A good agreement of the model and the experimental data was achieved for all combinations of photosensitizer concentration, photon flux, fluid velocity and both liquid and gas phase compositions. Deviations between simulated predictions and measurements for the amount of hydroperoxide formed are 7.1 % on average. Consequently, the identified and parameterized kinetic model is exploited to investigate different behaviors of the reactor under study. In a final step, the kinetic model is utilized to suggest attractive operating windows for future applications of the photooxygenation of DHAA exploiting reaction rates that are not affected by mass transfer limitations. [ABSTRACT FROM AUTHOR]

The quest for molecules able to trap, store, and release singlet oxygen is of utmost interest due to their applicability in various domains such as materials science and photomedicine. The aim of this study was to prepare and study a new family of singlet oxygen donors based on the 1,2‐dihydropyridine motif. The experiments demonstrated the influence of substituents and solvents on the photooxygenation rate constants. The process can be operated reversibly by thermolysis of the in situ formed endoperoxide leading to a release of singlet oxygen and formation of the parent 1,2‐dihydropyridine compound. A bifunctional structure based on a phenalenone photosensitizer covalently connected to a 1,2‐dihydropyridine module was synthesized via a multi‐step sequence. Upon irradiation with blue light, singlet oxygen was produced leading to the formation of the endoperoxide intermediate. In the dark cycle, the endoperoxide underwent cycloreversion reaction affording the parent 1,2‐dihydropyridine unit paving the way to a continuous production of singlet oxygen during the light/dark cycles. [ABSTRACT FROM AUTHOR]

A mild photocatalytic phenol oxygenation enabled by a continuous‐flow photoreactor using visible light and pressurized air is described herein. Products for wide‐ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p‐quinols contributes to sustainable synthesis. [ABSTRACT FROM AUTHOR]

Synthesis of angular furoquinolinone derivatives with a new skeleton structure was accomplished via Williamson reaction of hydroxyquinolinones with α‐haloketones, such as 3‐chloro‐2‐butanone and phenacyl bromide, followed by treatment with polyphosphoric acid (PPA). The synthesized angular furoquinolinones were photooxygenated in chloroform or dimethyl formamide and in the presence of tetraphenylporphyrin (TPP) as a singlet oxygen sensitizer (1O2). The photooxygenation reactions furnished the photocleaved product through the [2 + 2] cycloaddition reaction. All photoproducts were isolated and fully characterized by spectral analyses. [ABSTRACT FROM AUTHOR]

Cage‐opened bisfulleroids are one of suitable building blocks for making a large hole on fullerenes. This work focuses on the Diels‐Alder reaction of C60 with azines, among synthetic methods developed thus far, to provide bisfulleroids. Surprisingly, the computational study predicted that the reaction proceeds with normal electron demand in contrast to hitherto considered inverse‐electron‐demand pathway. The benzoannulation to the pyridazine ring, i. e. phthalazine, resulted in the remarkably shortened reaction time due to the better interaction between the HOMO of phthalazine and the LUMO of C60 as well as stronger 2,3‐diaza‐1,3‐butadiene character in the phthalazine as confirmed crystallographically. Contrary to expectations, the benzobisfulleroid was converted into corresponding orifice‐enlarged derivative via the photooxygenation slightly faster than the fulleroid derived from pyridazine. [ABSTRACT FROM AUTHOR]

[Display omitted] • Malaria persists as a challenge to world health in low-income countries. • Resistance of malaria parasites added plight to affordable antimalarial drugs. • Antimalarial activities of the synthesized compounds were evaluated by oral and intramuscular routes against multi-drug resistant Plasmodium yoelii nigeriensis. • 17a1 and 17a2 are two-fold more active than artemisinin via oral route. Following the economic and social state of humanity, Malaria is categorized as one of the life-threatening illness epidemics in under developed countries. For the eradication of the same, 1,2,4-trioxanes 17a1-a2 , 17b1-b2 , 17c1-c2 15a-c , 18 and 19 have been synthesized continuing the creation of a novel series. Additionally, these novel compounds were tested for their effectiveness against the multidrug-resistant Plasmodium yoelii nigeriensis in mice model using both oral and intramuscular (im) administration routes. The two most potent compounds of the series, 17a1 and 17a2, demonstrated 100 % protection at 48 mg/kg x 4 days via oral route, which is twice as potent as artemisinin. In this model artemisinin provided 100 % protection at a dose of 48 mg/kg × 4 days and 80 % protection at 24 mg/kg × 4 days via im route. [ABSTRACT FROM AUTHOR]

The development of robust and cheap photocatalyst systems for visible-light induced organic substrate transformations is a significant uprising research topic at the crossroads of green chemistry and modern synthetic methodology. Atom economy, efficiency and selectivity are key parameters for the future practical applicability of the specific processes catalyzed. In this context, we report a simple and sustainable oxygen-dependent route for oxidizing various aromatic and aliphatic aldehydes to the corresponding carboxylic acids at room temperature under visible light and sunlight irradiation mediated by cobalt phthalocyanine tetrasulfonic acid (CoPcS) supported on reduced graphene oxide (RGO). Remarkably, products are obtained with (81–100)% conversion and 100% selectivity. [ABSTRACT FROM AUTHOR]

Syntheses of novel fused furo, dioxolo and dioxino derivatives of coumarin are carried out through the reaction of 7,8‐dihydroxycoumarin derivative 1 with α‐halocarbonyl compounds (α‐haloketone, α‐haloester and chloroacetyl chloride) and 1,2‐dichloroethane. The photooxygenation of synthesized furocoumarin derivative was performed and the affinity of furocoumarin derivative towards DNA was evaluated and compared with 8‐methoxypsoralen (8‐MOP), which extensively used in photochemotherapy. [ABSTRACT FROM AUTHOR]

Substrate selectivity by means of synthetic catalysts remains a challenging topic in chemistry. Here, a catalytic system combining an iodo-BODIPY photosensitizer and quinine was evaluated in the competitive photooxygenation of non-hydrogen and hydrogen-bond-donor substrates. The ability of quinine to activate hydrogen-bond-donor substrates towards photooxygenation was reported and the results were benchmarked with photooxygenation experiments in the absence of quinine. [ABSTRACT FROM AUTHOR]

Lavender oil, obtained from the flowers of Lavandula angustifolia (Family: Lamiaceae) by steam distillation, The major component of lavender oil is linalyl acetate was isolated and subjected to oxidation thermally and photochemically using (mcpba and H 2 O 2) respectively to produce mixture of 6,7-epoxy-3,7-dimethyl-1-octene-3-yl acetate (3) and 1,2-epoxy-3,7-dimethyl-6-octene-3-yl acetate (4) photochemically, while produced epoxide 4 only thermally. On the other hand, photooxygenation of 1 using different singlet oxygen sensitizers gave two hydroperoxide derivatives of 6-hydroperoxy-3,7-dimethylocta-1,7-diene-3-yl acetate (5) and 7-hydroperoxy-3,7-dimethylocta-1,5-diene-3-yl acetate (6) in the presence of tetraphenyl porphin (TPP), whereas gave hydroperoxide 6 only using hematoporphyrin (HP). Studies on the antimicrobial especially Microsporum canis and Microsprum gallinna showed that linalyl acetate and its epoxide and hydroperoxide derivatives have a good antibacterial action. [ABSTRACT FROM AUTHOR]

The synthesis of glycosides and modified nucleosides represents a wide research field in organic chemistry. The classical methodology is based on coupling reactions between a glycosyl donor and an acceptor. An alternative strategy for new C-nucleosides is used in this approach, which consists of modifying a pre-existent furyl aglycone. This approach is applied to obtain novel pyridazine C-nucleosides starting with 2- and 3-(ribofuranosyl)furans. It is based on singlet oxygen [4+2] cycloaddition followed by reduction and hydrazine cyclization under neutral conditions. The mild three-step one-pot procedure leads stereoselectively to novel pyridazine C-nucleosides of pharmacological interest. The use of acetyls as protecting groups provides an elegant direct route to a deprotected new pyridazine C-nucleoside.

Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.

We have studied the efficiency of the C=C double bond cleavage on open‐cage fullerene C60 derivatives by singlet oxygen using four different LED lamps including UV, blue, green, and red radiation. The results indicate that red radiation is the most efficient for this photochemical oxidation owing to the sufficient penetration of the longer‐wavelength light. By applying this method to a 2‐methoxyethoxymethyl‐substituted azafulleroid derivative, we demonstrated the sequential double photooxygenation which provides a symmetric diketo imide derivative having a 15‐membered‐ring opening via stepwise cleavage of two C=C double bonds. Using a H2‐encapsulating derivative, we further examined the size of the opening by comparison with the structural isomer, based on H2‐release experiments and theoretical calculations. Open up: The self‐photooxygenation of a fullerene C60 derivative with red light resulted in a symmetric open‐cage compound that encapsulates a hydrogen molecule. Using the H2 molecule as an indicator, it was found that the opening is smaller than that of a structural isomer having a 15‐membered‐ring opening. [ABSTRACT FROM AUTHOR]

The singlet oxygen reaction with trisubstituted E‐allylic alcohols resulted in the unselective formation of regioisomeric secondary and tertiary allylic hydroperoxides. Increasing the steric demand at the allylic hydroxymethyl group leads to a moderate large‐group effect that can be strongly enhanced by deprotonation of a dimethylated allylic alcohol and even more pronounced by cation complexation. The presence of alkoxide groups did additionally alter the diastereoselectivity of the singlet oxygen ene reactions with chiral allylic alcohols. The molecular combination of Michael ester and enol ether in α‐alkoxy ester substrates made possible the design of chemoselective substrates for singlet oxygen ene versus [2+2] cycloaddition, e. g. a 3,3‐dimethylated Michael ester as a selective substrate for the ene reaction and an adamantyl analogue as a selective 2+2 substrate. The Z/E‐monomethylated substrates as probes for cis regioselectivity revealed that there is no site preference for Z‐alkoxy hydrogen transfer on the way to the corresponding ene product. Pick and choose: Increasing the steric demand at the allylic hydroxymethyl group in trisubstituted E‐allylic alcohols in reaction with 1O2 leads to a moderate large‐group effect that can be strongly enhanced by deprotonation of a dimethylated allylic alcohol and cation complexation. The molecular combination of a Michael ester and enol ether in α‐alkoxy ester substrates made possible the design of chemoselective substrates for 1O2 ene versus [2+2] cycloaddition reactions. [ABSTRACT FROM AUTHOR]

Continuous flow photochemistry relying on photosensitizers faces two main challenges: 1) Photodegradation (bleaching) and 2) the downstream removal of the photosensitizer. Rose bengal (RB) is a common photosensitizer utilized for photooxygenation reactions with singlet oxygen (1O2), but is notoriously sensitive to photobleaching and difficult to remove from reactor effluents. The heterogenization of photosensitizers on mesoporous silica nanoparticles (MSNs) is arguably a viable option for such applications. Herein, we report on the use of RB covalently incorporated into MSNs (RB@MSNs) for photooxygenation reactions under continuous flow conditions. RB@MSNs enable the 1O2 photooxygenation of various organic substrates upon irradiation with 540 nm LEDs. A series of organic substrates were evaluated including methionine, α‐terpinene, 2‐furoic acid, triphenylphosphine, citronellol and cyclopentadiene. These results emphasize an improved resistance to photobleaching, and the possibility to use RB@MSNs as an easily recoverable catalyst, which could be removed from the reactor effluent either a) by centrifugation or b) by in‐line membrane filtration. Get in line! The immobilization of Rose Bengal (RB) onto mesoporous silica nanoparticles (MSNs) enabled the 1O2 photooxygenation of various organic substrates under microfluidic conditions upon irradiation with 540 nm LEDs. An improved resistance to photobleaching was obtained and the heterogenized photosensitizer could be easily recovered from the reactor effluent by in‐line membrane separation. [ABSTRACT FROM AUTHOR]

The abnormal aggregation of β-amyloid protein (Aβ) is one of the main pathological hallmarks of Alzheimer's disease (AD), and thus development of potent scavengers targeting Aβ is considered an effective strategy for AD treatment. Herein, photosensitizer-doped carbonized polymer dots (PS-CPDs) were synthesized by a one-step hydrothermal method using photosensitizer (PS) and o -phenylenediamine ( o PD) as precursors, and furtherly applied to inhibit Aβ aggregation via photooxygenation. The inhibition efficiency of such PS-CPDs can be adjusted by varying the type of photosensitizer, and among them, methylene blue-doped carbonized polymer dots (MB-CPDs) showed the strongest photooxygenation inhibition capability. The results demonstrated that under 650 nm NIR light irradiation, MB-CPDs (2 μg/mL) produced reactive oxygen species (ROS) to efficiently inhibit Aβ fibrillization and disaggregate mature Aβ fibrils and increased the cultured cell viability from 50% to 83%. In vivo studies confirmed that MB-CPDs extended the lifespan of AD nematodes by 4 days. Notably, the inhibitory capability of MB-CPDs is much stronger than that of MB and previously reported carbonized polymer dots. This work indicated that potent photooxygenation carbon dots can be obtained by using a photosensitizer as one of the precursors, and the results have provided new insights into the design of potent photooxygenation carbon nanomaterials targeting Aβ in AD treatment.

The photooxygenation of α-terpinene was investigated in a falling film microreactor. The formation of microfilms and the flow operation allowed for a safe and controllable production of the bioactive endoperoxide ascaridole. Stepwise investigation of the process parameters resulted in the selective formation of ascaridole of up to 89% and a productivity of 2.5–3.2 mol L −1 h −1 , respectively. [ABSTRACT FROM AUTHOR]

Singlet oxygen-based photocatalytic oxygenation reactions have emerged as an efficient technology to synthesize value-added organic molecules. Among organic substrates, bio-sourced molecules such as amino acids or terpenes have a promising forecast as synthetic building blocks. A pseudo first-order kinetic study for the photocatalytic oxygenation of natural amino acid (L)-methionine was carried out in a macroscopic batch reactor. Various parameters were studied, including the effect of the photosensitizer (Rose Bengal, RB) concentration, the intensity of the light and the O 2 flow in terms of apparent kinetic constants and space-time yields. The identification of important limiting parameters as pressure, gas flow or light efficiency during the photocatalytic oxygenation of methionine allowed its transition from macroscopic batch reactor to continuous-flow microreactor. [ABSTRACT FROM AUTHOR]

Photooxygenation of Δ 8 tetrahydrocannabinol (Δ 8 -THC), Δ 9 tetrahydrocannabinol (Δ 9 -THC), Δ 9 tetrahydrocannabinolic acid (Δ 9 -THCA) and some derivatives (acetate, tosylate and methyl ether) yielded 24 oxygenated derivatives, 18 of which were new and 6 were previously reported, including allyl alcohols, ethers, quinones, hydroperoxides, and epoxides. Testing these compounds for their modulatory effect on cannabinoid receptors CB 1 and CB 2 led to the identification of 7 and 21 as CB 1 partial agonists with Ki values of 0.043 μM and 0.048 μM, respectively and 23 as a cannabinoid with high binding affinity for CB 2 with Ki value of 0.0095 μM, but much less affinity towards CB 1 (Ki 0.467 μM). The synthesized compounds showed cytotoxic activity against cancer cell lines (SK-MEL, KB, BT-549, and SK-OV-3) with IC 50 values ranging from 4.2 to 8.5 μg/mL. Several of those compounds showed antimicrobial, antimalarial and antileishmanial activities, with compound 14 being the most potent against various pathogens. [ABSTRACT FROM AUTHOR]