New transformations involving squarate esters. Multi-channel rearrangement options available to 2-(dimethoxy-methyl)-1-cycloalken-1-yl adducts

The Vilsmeier-Haack reaction of cyclic ketones with PBr₃ and DMF is an effective means for generating β-bromo-α,β-unsaturated aldehydes, which are readily transformed into their dimethyl acetals. These bromides are conveniently amenable to halogen-metal exchange in the presence of tert-butyllithium. The resultant organometallic intermediates, when treated with an equimolar amount of diisopropyl squarate, undergo 1,2-addition to deliver α-hydroxy ketone adducts that have proven to be sensitive to different rearrangements when in the presence of silica gel or boron trifluoride etherate. Although both processes involve net ring expansion of the cyclobutene ring with loss of methanol, the similarity stops there. In the first instance, spirocyclic diketones are produced by 1,2-shift of either of two ring carbons. In the second, extensively conjugated lactones are generated. The behavior of the adduct originating from a lithiated quinone bisketal has also been scrutinized.     

Changes in matrix gene and protein expressions after single or repeated exposure to one minimal erythemal dose of solar-simulated radiation in human skin in vivo

Damage to the skin extracellular matrix (ECM) is the hallmark of long-term exposure to solar UV radiation. The aim of our study was to investigate the changes induced in unexposed human skin in vivo after single or repeated (five times a week for 6 weeks) exposure to 1 minimal erythemal dose (MED) of UV solar-simulated radiation. Morphological and biochemical analyses were used to evaluate the structural ECM components and the balance between the degrading enzymes and their physiologic inhibitors. A three-fold increase in matrix metalloproteinase 2 messenger RNA (mRNA) (P < 0.02, unexposed versus exposed) was observed after both single and repeated exposures. Fibrillin 1 mRNA level was increased by chronic exposure (P < 0.02) and unaltered by a single MED. On the contrary, a single MED significantly enhanced mRNA levels of interleukin-1alpha (IL-1alpha), IL-1beta (P < 0.02) and plasminogen activator inhibitor-1 (P < 0.05). Immunohistochemistry demonstrated a significant decrease in Type-I procollagen localized just below the dermal-epidermal junction in both types of exposed sites. At the same location, the immunodetected tenascin was significantly enhanced, whereas a slight increase in Type-III procollagen deposits was also observed in chronically exposed areas. Although we were unable to observe any change in elastic fibers in chronically exposed buttock skin, a significant increase in lysozyme and alpha-1 antitrypsin deposits on these fibers was observed. These results demonstrate the existence of a differential regulation, after chronic exposure compared with an acute one, of some ECM components and inflammatory mediators.     

Further insight in the photochemistry of DNA: structure of a 2-imidazolone (5-4) pyrimidone adduct derived from the mutagenic pyrimidine (6-4) pyrimidone photolesion by UV irradiation

Pyrimidine (6-4) pyrimidone photoproducts represent one of the major mutagenic and carcinogenic class of DNA damage produced by UV exposure. At present, besides their conversion to their Dewar valence isomer, (6-4) photoproducts are generally believed to be photostable, and the observed biological properties of Paterno-Büchi-derived photoproducts are, thus far, exclusively attributed to these two types of compounds. Using a model system (2) relevant to DNA photochemistry, we have observed that the 5'-base moiety of the (6-4) thymine dimer 3, under far-UV radiation, is able to undergo a ring contraction leading to a 2-oxoimidazoline, 1. This unprecedented secondary photochemical reaction constitutes the first report of a major photomodification affecting (6-4) photoproducts and strongly questions the biological stability of the (6-4) adducts under UV light with 2-imidazolone (5-4) pyrimidone adducts being possibly another source of endogenous DNA damage.     

Metal Complexes with Macrocyclic Ligands. Part XL. Syntheses and silver(I) complexes of mono- and disubstituted dithiadiazamacrocycles

A series of N₂S₂-macrocycles with ring sizes varying between 12 and 16, as well as two 12-membered N₂S₂-rings with a pendant carboxylic and amino group, respectively, were synthesized. Their complexation properties towards Ag⁺ were studied by pH titrations and by potentiometry with a silver electrode. The observation that 1:1 ([AgLH₂]³⁺, [AgLH]²⁺, [AgL]⁺) and 1:2 species ([AgL₂H₂]³⁺, [AgL₂H]²⁺, [AgL₂]⁺) were formed is interpreted by postulating that Ag⁺ can bind either to the S-donors only, or to both the N- and S-atoms. The most stable complex [AgL]⁺ in the series of the nonfunctionalized macrocycles was found for the 12-membered N₂S₂-ring 3 . The stability of it increased when an additional donor group was introduced into the side chain. The highest formation constant (logβ₁₁₀ = 14.43(1)) was obtained with the 12-membered ring 12 carrying the ethanamine side chain. In view of a radiochemical application, all Ag⁺ complexes were tested in blood serum for their stability, but were not stable enough against transmetallation.     

Studies on the chemical synthesis of oligodeoxynucleotides containing the s5T(6-4)T photoproduct: side reactions derived from the methylsulfenyl thiol protection elucidated by MALDI mass spectrometry

Attempts to incorporate the phosphoramidite of the thymine-thymine (6-4) photoproduct C5 thiol analogue (s(5)T(6-4)T PP), whose sulfur atom was protected with the methylsulfenyl group, into oligodeoxynucleotides (ODNs), are reported. Using matrix-assisted laser desorption-ionisation mass spectrometry (MALDI-MS) coupled to enzymatic digestion, accurate mass measurements and tandem mass spectrometry experiments, we demonstrated that ODNs containing the (2-cyanoethylthio)(5)T(6-4)T PP were obtained. Supported by model reactions, these results were explained 1) by the incorporation, during oligonucleotide synthesis, of the sulfur deprotected phosphoramidite that arose from a Michaelis-Arbusov-type rearrangement, and 2) the Michael addition to the thiol of acrylonitrile released upon the cyanoethyl phosphotriester deprotection. To avoid the formation of the cyanoethyl adduct, the phosphotriester deprotection was carried out in the presence of a thiol in excess. This afforded the ODN containing the h(5)T(6-4)T PP.     

Unexpected formation of new chiral 3-amino-5-alkyl-2,5-dihydro-1H-pyrrolin-2-ones from N-Boc-α-amino esters

We describe a one-pot process involving the DiBAl-H reduction of the ester moiety of N-protected α-amino esters, followed by Horner-Wadsworth-Emmons olefination in the presence of the trimethyl ester phosphonoglycinate carbanion allowing the formation of new chiral 3-amino-5-alkyl-2,5-dihydro-1H pyrrolin-2-one 5. The Z-enoate 4b, which is formed during this reaction, could be converted into the corresponding lactam 5b under UV irradiation with the presence of BuLi.     

(EDT-TTF-CONH2)6[Re6Se8(CN)6], a metallic Kagome-type organic-inorganic hybrid compound: electronic instability, molecular motion, and charge localization

(EDT-TTF-CONH2)6[Re6Se8(CN)6], space group R, was prepared by electrocrystallization from the primary amide-functionalized ethylenedithiotetrathiafulvalene, EDT-TTF-CONH2 (E(1/2)1 = 0.49 V vs SCE in CH3CN), and the molecular cluster tetraanion, [Re6Se8(CN)6]4- (E(1/2) = 0.33 V vs SCE in CH3CN), equipped with hydrogen bond donor and hydrogen bond acceptor functionalities, respectively. Its Kagome topology is unprecedented for any TTF-based materials. The metallic state observed at room temperature has a strong two-dimensional character, in coherence with the Kagome lattice symmetry, and the presence of minute amounts of [Re6Se8(CN)6](3-)* identified by electron spin spectroscopy. A structural instability toward a distorted form of the Kagome topology of lesser symmetry is observed at ca. 180 K. The low-temperature structure is associated with a localized, electrically insulating electronic ground state and its magnetic susceptibility accounted for by a model of uniform chains of localized S = 1/2 spins in agreement with the 100 K triclinic crystal structure and band structure calculations. A sliding motion, within one out of the three (EDT-TTF-CONH2)2 dimers coupled to the [Re6Se8(CN6)(3-)*]/[Re6Se8(CN6)4-] proportion at any temperature, and the electronic ground state of the organic-inorganic hybrid material are analyzed on the basis of ESR, dc conductivity, 1H spin-lattice relaxation, and static susceptibility data which qualify a Mott localization in [EDT-TTF-CONH2]6[Re6Se8(CN)6]. The coupling between the metal-insulator transition and a structural transition allows for the lifting of a degeneracy due to the ternary axis in the high temperature, strongly correlated metallic phase which, in turn, leads to Heisenberg chains at low temperature.     

Prompt and delayed nonsteroidal anti-inflammatory drug-photoinduced DNA damage in peripheral blood mononuclear cells measured with the comet assays

Nonsteroidal anti-inflammatory drug (NSAID)-photoinduced DNA damage in human peripheral blood mononuclear cells measured using the alkaline comet assay is presented. Whereas Tiaprofenic Acid-photoinduced DNA damage was promptly induced (i.e. observed at relatively low radiation doses), Ketoprofen-photoinduced DNA damage was delayed. This prompt and delayed effect is observed with UVA (320-400 nm), UVB (290-320 nm) and solar-simulated radiation and is attributed to the different photochemical properties of NSAID. The results from these experiments, carried out in living cells, confirm the speculations of NSAID-photoinduced DNA damage brought up by the many experiments conducted in solution.     

Ruthenium(II) and ruthenium(IV) complexes containing kappa1-P-, kappa2-P,O-, and kappa3-P,N,O-iminophosphorane-phosphine ligands Ph2PCH2P[=NP(=O)(OR)2]Ph2 (R = Et,Ph): synthesis,reactivity, theoretical studies,and catalytic activity in transfer hydrogenation of cyclohexanone

[(Ru(eta(6)-p-cymene)(mu-Cl)Cl)(2)] and [(Ru(eta(3):eta(3)-C(10)H(16))(mu-Cl)Cl)(2)] react with Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2) (R = Et (1a), Ph (1b)) affording complexes [Ru(eta(6)-p-cymene)Cl(2)(kappa(1)-P-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))] (R = Et (2a), Ph (2b)) and [Ru(eta(3):eta(3)-C(10)H(16))Cl(2)(kappa(1)-P-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))] (R = Et (6a), Ph (6b)). While treatment of 2a with 1 equiv of AgSbF(6) yields a mixture of [Ru(eta(6)-p-cymene)Cl(kappa(2)-P,O-Ph(2)PCH(2)P[=NP(=O)(OEt)(2)]Ph(2))][SbF(6)] (3a) and [Ru(eta(6)-p-cymene)Cl(kappa(2)-P,N-Ph(2)PCH(2)P[=NP(=O)(OEt)(2)]Ph(2))][SbF(6)] (4a), [Ru(eta(6)-p-cymene)Cl(kappa(2)-P,O-Ph(2)PCH(2)P[=NP(=O)(OPh)(2)]Ph(2))][SbF(6)] (3b) and [Ru(eta(3):eta(3)-C(10)H(16))Cl(kappa(2)-P,O-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))][SbF(6)] (R = Et (7a), Ph (7b)) are selectively formed from 2b and 6a,b. Complexes [Ru(eta(6)-p-cymene)(kappa(3)-P,N,O-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))][SbF(6)](2) (R = Et (5a), Ph (5b)) and [Ru(eta(3):eta(3)-C(10)H(16))(kappa(3)-P,N,O-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))][SbF(6)](2) (R = Et (8a), Ph (8b)) have been prepared using 2 equiv of AgSbF(6). The reactivity of 3-5a,b has been explored allowing the synthesis of [Ru(eta(6)-p-cymene)X(2)(kappa(1)-P-Ph(2)PCH(2)P[=NP(=O)(OR)(2)]Ph(2))] (R = Et, Ph; X = Br, I, N(3), NCO (9-12a,b)). The catalytic activity of 2-8a,b in transfer hydrogenation of cyclohexanone, as well as theoretical calculations on the models [Ru(eta(6)-C(6)H(6))Cl(kappa(2)-P,N-H(2)PCH(2)P[=NP(=O)(OH)(2)]H(2))]+ and [Ru(eta(6)-C(6)H(6))Cl(kappa(2)-P,O-H(2)PCH(2)P[=NP(=O)(OH)(2)]H(2))]+, has been also studied.     

Determination of T-2 toxin in cereal grains by liquid chromatography with fluorescence detection after immunoaffinity column clean-up and derivatization with 1-anthroylnitrile

1-Anthroylnitrile (1-AN) has been shown to be an efficient labelling reagent for the determination of T-2 toxin (T-2) by high-performance liquid chromatography (HPLC)-fluorescence detection. This reaction has been used to develop a sensitive, reproducible and accurate method for the determination of T-2 in wheat, corn, barley, oats, rice and sorghum. The method uses immunoaffinity columns containing antibodies specific for T-2 for extract clean-up, pre-column derivatization with 1-AN and HPLC with fluorescence detection for toxin determination. Ground cereal samples were extracted with methanol-water (80:20, v/v), the extracts were purified by immunoaffinity columns and the toxin was quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 381 nm, emission wavelength 470 nm) after derivatization with 1-AN. Recoveries from the different cereals spiked with T-2 at levels ranging from 0.05 to 1.5 microg/g were from 80 to 99%, with relative standard deviations of less than 6%. The limit of detection was 0.005 microg/g, based on a signal-to-noise ratio of 3:1.