Julia-Kocienski reaction-based 1,3-diene synthesis: aldehyde-dependent (E,E/E,Z)-selectivity

A new modification of Julia-Kocienski olefination reaction based on the use of cation-specific chelating agents that yields 1,3-dienes with predictable (E/Z)-selectivity on newly created double bond was developed. The influence of the aldehyde structure on reaction (E/Z) selectivity is discussed and rationalized.     

Cucurbitacin E: some preliminary observations

Evidence presented indicates that the functional groupings of cucurbitacin E (-elaterin) are as follows: an β-unsaturated ketone, a 1:2-diketone (enolised), three hydroxyl groups, one of which is acetylated, and probably a further carbonyl group.     

(E,E)-1,5-Cyclooctadiene: a small and fast click-chemistry multitalent

Two in one--We show here that the highly strained trans,trans-diolefin (E,E)-1,5-cyclooctadiene can perform efficiently two different click reactions at fast reaction rates. It is capable of first undergoing [3+2] cycloadditions with 1,3-dipoles at a reaction rate comparable to that of strained cyclooctynes. The resulting cycloadduct can then perform a much faster inverse-electron-demand Diels-Alder reaction with tetrazines, effectively linking an azide to a tetrazine. Thus, (E,E)-1,5-cyclooctadiene could have many applications in chemical biology and polymer chemistry.     

Studies toward the total synthesis of popolohuanone E: enantioselective synthesis of 8-O-methylpopolohuanone E

[structure: see text]. 8-O-methylpopolohuanone E (2) was synthesized in a highly convergent manner starting from the cis-fused decalin derivative accessible from the (-)-Wieland-Miescher ketone analogue. The synthetic method features a biogenetic-type annulation of the phenolic and quinone segments to regioselectively construct the central tricyclic ring system as the key step.     

Resolvin E2: identification and anti-inflammatory actions: pivotal role of human 5-lipoxygenase in resolvin E series biosynthesis

The family of resolvins consists of omega-3 fatty acid-derived mediators, including E series resolvins generated from eicosapentaenoic acid (EPA), and carry potent anti-inflammatory properties. Here, we report the isolation, identification, and bioactions of resolvin E2 (RvE2), which is 5S,18-dihydroxy-eicosapentaenoic acid. RvE2 stopped zymosan-induced polymorphonuclear (PMN) leukocyte infiltration and displayed potent anti-inflammatory properties in murine peritonitis. We also demonstrate that human recombinant 5-lipoxygenase generates RvE2 from a common precursor of E series resolvins, namely, 18-hydroxyeicosapentaenoate (18-HEPE). Furthermore, the initial 5-hydroperoxide intermediate was also converted to a 5(6)-epoxide intermediate in RvE1 formation. These results demonstrate that RvE2, together with RvE1, may contribute to the beneficial actions of omega-3 fatty acids in human diseases. Moreover, they indicate that the 5-lipoxygenase in human leukocytes is a pivotal enzyme that can produce both pro- and anti-inflammatory chemical mediators.     

A CIDEP and fluorescence study of the oxidation of vitamin E: The vitamin E radical cation

The photochemical and thermal oxidations of vitamin E in trifluoroacetic acid were investigated by the combination of electron spin resonance, chemically induced dynamic electron polarization, and fluorescence techniques. Two independent thermal pathways led to the formation of the vitamin E radical cation in which one of the paths involved the intermediate neutral semiquinone radical. Photo-oxidation, however, did not involve the neutral radicals. The fluorescence spectra of both the neutral and the charged forms of the vitamin E radicals are reported here for the first time. Some model charge transfer reactions involving the vitamin E radical cation were reported.     

The photochemical reaction of (E,E)-dibenzylidenesuccinic thioanhydride: A spectroscopic and structural study

The first photochromic thioanhydride, (E,E)-2,3-dibenzylidenesuccinic thioanhydride ( 1b ), was synthesized. Irradiation of ( 1b ) in benzene, dichloromethane, or chloroform gives isomerization and cyclization products similar to those obtained for the anhydride analogue ( 1a ). The crystal structure of ( 1b ) was determined (X-rays) and compared to the structures of the anhydridge ( 1a ) and N-phenylimide ( 1c ). ¹H and ¹³C NMR spectra were recorded, and the electron charge densities of the carbon atoms were calculated with AM1. These results are discussed and compared with those for the compounds 1a–1c . The thioanhydride ( 1b ) ring is much more twisted than either the anhydridge ( 1a ) or the imide ( 1c ) rings. The linear relationship between the ¹³C NMR chemical shifts and the electron charge density on the given atom has been investigated. The C(carbonyl) and C(α) carbon atoms of 1b were found to be greatly deshielded relative to the corresponding atoms in 1a and 1b . The increase in corresponding atoms in 1a and 1b . The increase in sensitivity toward cyclization of the thioanhydridge ( 1b ) is attributed to the marked change in the charge distribution. Crystal data. Thioanhydride ( 1b ): space group P2_1/c with a = 12.956(3) Å, b = 14.843(6) Å, c = 7.512(6) Å, β = 98.05(2)°, Rw = 0.085 and R = 0.089.     

Vitamin E: Or Why We Don't Go Rancid

The authors' chemical studies on vitamin E are summarized. These studies provide very strong support for the view that vitamin E owes its biological activity solely to the fact that it acts as a general purpose, lipid-soluble, peroxyl-radical-trapping antioxidant.     

A2E: a component of ocular lipofuscin

The presence of lipofuscin in postmitotic cells is considered a hallmark of the aging process. In the retinal pigment epithelium (RPE), lipofuscin is found as micrometer-sized spherical particles and characterized by its yellow autofluorescence when exposed to blue light. This exposure to light is also known to produce reactive oxygen intermediates (ROI), but the particular molecular constituent(s) responsible for this phototoxicity have yet to be completely identified. Resulting mostly from the autophagocytosis of intracellular organelles, the composition of lipofuscin is poorly defined but known to contain protein, lipids and several fluorophores. The subsequent identification of one of the fluorophores in lipofuscin, A2E, generated much interest and resulted in a variety of studies to understand its potential role in the phototoxicity of lipofuscin. Several modes of toxicity have been suggested through which A2E can affect the health of RPE cells. These modes include photoinduced production of ROI, which places additional oxidative stress on RPE cells, the disruption of membrane integrity through its natural role as an amphiphilic detergent and inhibition of key cellular functions. This article presents the current understanding of the photochemistry of A2E and its involvement as a phototoxic agent in RPE cells.     

PHOTOPEROXIDATION OF LENS LIPIDS: PREVENTION BY VITAMIN E

Abstract— Light of visible frequency was observed to initiate peroxidative degradation of lipids of rat lenses when the latter were maintained in organ culture. The extent of degradation was monitored by measurement of malanaldehyde. This photodegradative process, which we believe is triggered by light catalyzed generation of superoxide and its subsequent transformation to other potent oxidants. was observed to be thwarted substantially if the medium of organ culture was fortified with 10⁻³ and 10⁷ M vitamin E (α-tochopherol). These studies suggest that vitamin E may be metabolically beneficial by protecting light exposed tissues, such as those in the eye against photoperoxidativc damage concomitant to light-catalyzed generation of oxygen-free radicals. The findings appear relevant to age-associated pathogenesisof cataracts and their possible attenuation. In addition, they provide a basis of pathogenesis in other ocular tissues such as the macula known to undergo age-dependent degeneration.     

Superacid cyclization of (2E,6E,10E,14E)-8-phenylsulfonylgeranylfarnesol tetrahydropyranyl ether

A mixture of (13E,17E)-12-phenylsulfonylbicyclogeranylfarnesol tetrahydropyranyl ether (8) and (13E,17E)-12-phenylsulfonylbicyclogeranylfarnesol (9) was formed by superacid low-temperature cyclization of exclusively trans-8-phenylsulfonylgeranylfarnesol tetrahydropyranyl ether (1). The structures of 8 and 9 were established using spectral data. The optically active form of 9 was also confirmed by retrosynthesis from (+)-sclareolide (10). __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 224–228, May–June, 2007.     

Vitamin E

Ohne Zusammenfassung     

Stereochemistry of nitrogen E lone pair in NH3E,NOFE, N2O3E2, AgNO2E,and NCl3E

We revisit nitrogen based simple fundamental molecules in their solid state structures, with the purpose of casting new light on the stereoactivity of valence lone pairs (LPs)—formally N(2s²)—in different crystal geometries. Based on coupled investigations of crystal chemistry and ab initio DFT calculations providing the electron localization function (ELF), LP behavior is analyzed precisely by finding its position E, orientation and “volume of influence” which consists in an electronic cloud generated around the so-called ‘centroïd’ Ec of the electronic doublet. The results show the paramount importance of the role of N(2s²) LP in the crystal network architecture through the different case studies pertaining to ammonia (NH₃), nitrosyl fluoride (NOF), nitrosyl nitrite (N₂O₃), silver nitrite (AgNO₂), and nitrogen trichloride (NCl₃). An unexpected direct ionic interaction between [NO]⁺ or Ag⁺ and the centroïd Ec of the [NO₂Ec]⁻ nitrite group has been evidenced in N₂O₃E₂ and AgNO₂, respectively.