Photooxygenation Product Research Articles

Internal and External Stereoisomers of Squaraine Rotaxane Endoperoxide: Synthesis, Chemical Differences, and Structural Revision

Photooxygenation of permanently interlocked squaraine rotaxanes with anthracene-containing macrocycles produces the corresponding squaraine rotaxane endoperoxides (SREPs) quantitatively. SREPs are stored at low temperature, and upon warming, they undergo clean cycloreversion, releasing singlet oxygen and emitting light. The structural elucidation in 2010 assigned the structure as the SREP-int stereoisomer, with the endoperoxide unit directed inside the macrocycle cavity. New experimental and computational evidence reported here proves that the initial, kinetic photooxygenation product is the less stable SREP-ext stereoisomer with the endoperoxide unit directed outside the macrocycle. The photophysical properties and subsequent reactivity of mechanically strained SREP-ext depend on the size of the end groups of the encapsulated squaraine dye. If the end groups are sufficiently large to prevent dissociation of the interlocked components, the strained SREP-ext stereoisomer undergoes clean thermal cycloreversion. However, smaller squaraine end groups allow transient dissociation, resulting in a pseudorotaxane dissociation/association process that produces SREP-int as the thermodynamic stereoisomer that does not cyclorevert. The large difference in endoperoxide reactivity for the two SREP stereoisomers illustrates the power of the mechanical bond to induce cross-component steric strain and selective enhancement of a specific reaction pathway. The new insight enabled synthetic development of triptycene-containing squaraine rotaxanes with high fluorescence quantum yields and large Stokes shifts.

Photohemolysis Sensitized by the Furocoumarin Derivative Alloimperatorin and its Hydroperoxide Photooxidation Product

The dark and photosensitized effects of alloimperatorin methyl ether 1 (hereafter simply alloimperatorin) and its photooxygenation product alloimperatorin hydroperoxide 2 were investigated on human erythrocytes. The results reveal that the furocoumarin 1 photosensitizes efficiently the hemolysis of erythrocytes. The rate of photohemolysis increases on raising the temperature of the postirradiated incubation from 4°C to 37°C. Thermal activation of the photohemolysis and inhibition by 2,6-di-tert-butyl-p-cresol (BHT) suggest that the furocoumarin 1 photosensitizes lipid peroxidation, increasing permeability in the erythrocyte membrane. The hydroperoxide 2 induces dark and photosensitized hemolysis more efficiently than the furocoumarin 1. The rate of hemolysis induced by 2 increases with the incubation temperature and decreases in the presence of tert-butanol and BHT. The hydroperoxide 2 photosensitizes the formation of lipid peroxidation products as shown by the reaction with thiobarbituric acid. This process is diminished by BHT. Our data imply that the photohemolysis sensitized by the furocoumarin 1 is caused by the in situ-formed photooxygenation product 2. Such hydroperoxides are potent hemolytic agents in the dark and especially on photosensitization.

Rubrene endoperoxide acetone monosolvate

The title acetone solvate, C42H28O2·C3H6O [systematic name: 1,3,10,12-tetra­phenyl-19,20-dioxapenta­cyclo­[10.6.2.02,11.04,9.013,18]icosa-2(11),3,5,7,9,13,15,17-octa­ene acetone monosolvate], is a photooxygenation product of rubrene (systematic name: 5,6,11,12-tetra­phenyl­tetra­cene). The mol­ecule bends at the bridgehead atoms, which are linked by the O—O transannular bond, with a dihedral angle of 49.21 (6)° between the benzene ring and the naphthalene ring system of the tetra­cene unit. In the crystal, the rubrene mol­ecules are linked by C—H⋯O hydrogen bonds into a column along the c axis. The acetone solvent mol­ecules form a dimer around a crystallographic inversion centre through a carbon­yl–carbonyl dipolar inter­action. A C—H⋯O hydrogen bond between the rubrene and acetone mol­ecules is also observed.

Benzylamine-Free, Heavy-Metal-Free Synthesis of CL-20 via Hexa(1-propenyl)hexaazaisowurtzitane

Base-catalyzed isomerization of recently reported hexaallylhexaazaisowurtzitane produced a new derivative, hexa(1-propenyl)hexaazaisowurtzitane (HPIW). Photooxygenation of this intermediate by singlet oxygen oxidized most of the 1-propenyl substituents to formyl substituents. The course of this reaction of singlet oxygen with HPIW involves peroxide intermediates, which may include relatively stable macrocyclic (tetroxocane) derivatives. The resulting nitrolyzable polyformylhexaazaisowurtzitane was found to be a promisingly efficient new precursor to CL-20 (in a single preliminary experiment without any process development). The new intermediate HPIW also underwent direct nitrolysis to form CL-20, though not as efficiently as its photooxygenation product did.

Synthetic Studies of Neoclerodane Diterpenes from Salvia divinorum: Preparation and Opioid Receptor Activity of Salvinicin Analogues

Further modification of salvinorin A (1a), the major active component of Salvia divinorum, has resulted in the synthesis of novel neoclerodane diterpenes with opioid receptor affinity and activity. We report in this study that oxadiazole 11a and salvidivin A (12a), a photooxygenation product of 1a, have been identified as the first neoclerodane diterpenes with kappa antagonist activity. This indicates that additional structural modifications of 1a may lead to analogues with higher potency and utility as drug abuse medications.

Time Resolved Surface Enhanced Raman Scattering Studies of 3-Hydroxyflavone on a Ag Electrode

Reverse proton transfer (RPT) of 3-hydroxyflavone (3-HF) from the tautomer ground state to normal ground state has been studied by time-resolved surface enhanced Raman scattering (TRSERS) in aqueous solution in the presence of oxygen. The tautomer ground state of 3-HF is formed by an exciting 337 nm nitrogen laser pulse and monitored by a 488 nm Ar+ laser with gated photodiode array detection. B3LYP DFT calculations with 3-HF bound to the apex adatom of a Ag20 cluster model show that a tilted orientation of the molecule with respect to the surface site is reasonable and is consistent with the SERS spectral characteristics. The geometry optimized structures also show that a cyclic monohyrate, 3-HF(H2O), species is stable from which biprotonic PT could take place. By studying the changes of some transient band intensities with time, the lifetime of tautomer 3-HF on a Ag electrode is determined to be 1.4 μs. Besides the photoinduced photo-oxygenation product, evidence for an additional endo-peroxide intermediate is obtained.

Identification of a photooxygenation product of chlortetracycline in hog lagoons using LC/ESI-ion trap-MS and LC/ESI-time-of-flight-MS.

In the present work, a photoproduct of chlortetracycline (CTC) was identified for the first time in hog lagoon samples from confined animal feeding operations. Screening of several samples by LC/ESI-MS indicated the presence of a potential photooxygenation product of CTC with a nominal mass that was 32 Da higher than the parent drug. Generation of this assumed photoproduct (designated M510) was achieved in a 24-h irradiation experiment of an oxygenated alkaline medium containing 50 mg L(-)(1) CTC. Accurate mass measurements with an ESI-TOF-MS of the protonated isomerization product of CTC (iCTC) and the postulated photooxygenation product, bearing two oxygen atoms more than iCTC, were m/z 479.1229 and 511.1109, respectively. These corresponded to errors of -2.8 ppm for iCTC and +1.0 ppm for M510 relative to the theoretical masses. The generation of second- and third-stage mass spectra in an ESI-ion trap-MS showed similar characteristic fragmentation patterns for iCTC and the photoproduct M510, leading to the conclusion that the M510 structure consisted of an iCTC-like skeleton bearing two additional hydroxy groups. The site and configuration of one hydroxylation was confidently assigned, while the position of the other hydroxy group was tentatively assigned. Comparison of the (+)-ESI-MS(3) spectrum and the retention time of M510 in the sample from the irradiation experiment with those from the hog lagoon samples yielded excellent agreement, suggesting that the compounds were identical. Quantitative analysis of seven hog lagoon samples showed iCTC concentrations of 1910-15 800 microg L(-)(1), while the levels of M510 were found to be between 46 and 303 microg L(-)(1).

An unexpected product in the photooxygenation of a cyclic enol ether

The photooxygenation product of a cyclic enol ether conjugated with an o-phenylene ring is a novel epoxy compound instead of a 1,2,4-trioxane analogue. The structure of the compound was elucidated by X-ray analysis.

Photooxygenolytic Degradation of the Vitamin‐B12 Derivative Heptamethyl Coα,Coβ‐Dicyanocobyrinate. Efficient Preparation of Bicyclic Fragments

AbstractThe methylene‐blue sensitized photooxygenation of heptamethyl Coα,Coβ‐dicyanocobyrinate (1, cobester) at ca. −45° and in (D3)acetonitrile solution proceeds readily to the stage of selective double cleavage of the corrin macrocycle. It furnishes the bisected heptamethyl Coα,Coβ‐dicyano‐5,6:14,15‐tetraoxo‐5,6:14,15‐disecocobyrinate (3) in 91% yield after warming the photooxygenation mixture to room temperature. Complex 3 is also obtained by photooxygenation of the secocorrinoid oxygenation products of 1, namely of heptamethyl Coα,Coβ‐dicyano‐5,6‐dioxo‐5,6‐secocobyrinate (2a) and of its isomer heptamethyl Coα,Coβ‐dicyano‐14,15‐dioxo‐14,15‐secocobyrinate (2b). When the raw photooxygenation product of 1 is kept at low temperature, 3 is not formed in a significant amount; spectral analysis reveals 4 as intermediate that is transformed into 3 quantitatively upon warm‐up and storage at r.t. Compound 4 is assigned the structure of heptamethyl Coα,Coβ‐dicyano‐5,6‐epidioxy‐5,6‐dihydro‐14,15‐dioxo‐14,15‐secocobyrinate, based on NMR‐spectral data and since 4 is also formed cleanly in the corresponding low‐temperature photooxygenation of 2b. Catalytic reduction of the Co(III) complex 3 (H2, Pt/C) in the presence of EDTA produces a colourless oil, from which the bicyclic fragments 5 (corresponding to rings A and D of 1) and 6 (corresponding to rings B and C of 1) are obtained in 99 and 91% yield, respectively, after chromatographic separation.

On the role of singlet oxygen in the self-sensitized photo-oxygenation of bilirubin and its pyrromethenone models

4-Ethyl-3-methyl-5-(4-ethyl-3,5-dimethylpyrrolyl-2-methylidene)-3-pyrrolin-2-one ( 1), 3,4- diethyl-5-(4-ethyl-3,5-dimethylpyrrolyl-2-methylidene)-3-pyrrolin-2-one ( 2) and xanthobilirubinic acid (XBR) undergo self-sensitized photo-oxygenation, as does bilirubin. The reaction products of 1 consist of methylethylmaleimide, kryptopyrrole aldehyde and its photo-oxygenation product and oxygenated dipyrroles. The same products are formed from 2, except xeronimide is found instead of methylethyl-maleimide. Kinetic studies indicate that singlet oxygen is not necessarily involved in the photo-oxygenation reactions. Geometric photoisomerization ( Z →2 E) of 1 and 2, and XBR proceeds at an even faster rate than photosensitized oxygenation.

ChemInform Abstract: PHOTOOXYGENATION OF FLAVANONOL‐RED RELATED COMPOUNDS

AbstractDurch Photooxidation von (I) und anschließende Umkristallisation aus Ethanol oder Methanol erhält man die Verbindungen (II), von denen (IIa) mit Methanol zu (III) austauscht.

ChemInform Abstract: PHOTOOXYGENATION PRODUCT OF DIBENZO(A,J)PERYLENE

AbstractDie Photooxidation der nach bekannter Methode synthetisierten Titelverbindung (I) wird spektroskopisch untersucht.

PHOTOOXYGENATION OF FLAVANONOL-RED RELATED COMPOUNDS

Abstract Photooxygenation of 6-phenyl-5,7-dioxa-benz[a]anthracene in ethanol followed by recrystallization from ethanol resulted in the formation of a diethoxy compound by unusual addition of two ethoxyl groups to a C–C double bond. While, recrystallization of the photooxygenation product from methanol afforded a monoethoxy monomethoxy compound.

Photooxygenation Product of Dibenzo[a,j]perylene

Abstract The photooxygenation of dibenzo[a,j]perylene by visible light irradiation was studied spectroscopically. The structure of unstable photooxygenation product was deduced from spectroscopic data and results of MO calculations to be as 8,12b-endoperoxide of dibenzo[a,j]perylene. This endoperoxide released oxygen gradually at room temperature, recovering the original hydrocarbon. The activation energy for this dark reaction was determined to be 21.4±0.5 kcal/mol in benzene and 22.6±0.5 kcal/mol in ethanol.

The thermal and photochemical rearrangement of 1,2(4H)-diazepine derivatives

Thermolysis of 3,5,7-triphenyl-1,2(4H)-diazepine (1) gives, besides the known 2,4,6-triphenyl-pyridine (2), 3,5,6-triphenyl-1,2(4H)-diazepine (3) and 3,5,6-triphenyl-1,2(1H)-diazepine (4) whose structures are deduced on the basis of spectroscopic and chemical evidence. Neat thermolysis of 1 and the related 5-(p-methoxyphenyl)-3,7-diphenyl-1,2(4H)-diazepine (24a) and 5-(p-chlorophenyl)-3,7-diphenyl-1,2(4H)-diazepine (24c) gives only the corresponding pyridine derivatives 2, 26a, and 26c in low yields. Photolysis of 1 in ethanol affords the somewhat unstable 3,5,7-triphenyl-1,2-diazabicyclo[3.2.0]hepta-2,6-diene (21) which upon thermolysis undergoes cycloreversion to 1 and upon hydrolysis provides 3,5-diphenylpyrazole (23) and aceto-phenone. In contrast, photolysis of 1 as well as of 24a and 24c in acetone results in the formation of the pyridine (26a, 26c) and pyrazole (25a, 25c) derivatives respectively in low yields. Irradiation of 5-(P-dimethylaminophenyl)-3,7-diphenyl-1,2(4H)-diazepine (24d) under these conditions gives the photo-oxygenation product 24e. The observed thermolysis and photolysis results of 1 are compared and contrasted with those reported for the closely related 4,4-dimethyl-3,7-diphenyl-1,2(4H)-diazepine (16).