Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Electromagnetic field-induced protection of chick embryos against hypoxia exhibits characteristics of temporal sensing

We previously studied the response of mammalian cultured cells to weak, 60 Hz-electromagnetic (EM) fields. Two time constants, similar to those observed in chemotaxis, were found to govern the cellular response to the field. We concluded that a system of temporal sensing, similar to that employed in chemotaxis by motile bacteria, was operative. We termed the shorter time (approximately 0.1 s) the "sensing" time, and the longer time (approximately 10 s) the "memory" time. To investigate the possibility that temporal sensing was a general property of EM field-cell interaction, the temporal properties of another EM field-induced effect was studied. The EM field-induced protection against the effects of extreme hypoxia was examined in chick embryos. Embryos were exposed to 60 Hz-magnetic fields, the amplitudes of which were regularly altered throughout the 20-min exposure. Alteration was accomplished either by turning the field off and on at regular intervals (1-50 s), or by introducing brief (10 or 100 ms), zero amplitude gaps, once each second, throughout exposure. When the field was turned on and off at 0.1 s intervals, the protective effect conferred by a constant field was lost. At progressively longer on/off intervals, protection was progressively restored, maximizing at intervals of 10-30 s. Gapping the magnetic field for 10 ms, each second of exposure conferred the same protection as that observed for an uninterrupted field, but gapping the field at 100 ms each second produced a significant reduction in protection. These data exhibit remarkable consistency with those obtained in similar temporal studies of the magnetic field-induced enhancement of ornithine decarboxylase activity in L929 fibroblasts. It appears that temporal sensing is a general feature of the EM field-cell interaction.     

Spectroscopy and reactivity of a photogenerated tryptophan radical in a structurally defined protein environment

Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE.     

Kinetic and catalytic aspects of dimethylterephtalate transesterification also through the use of model molecules

Kinetic and catalytic aspects of DMT transesterification reaction, key step in the industrial production of polyethylenterephtalate (PET), have been deepened also through the use of model molecules such as CH₃COO–Ph–X. These molecules give the same reactions with ethylene glycol occurring in the DMT transesterification too. The use of model molecules in the study of this reaction seems therefore to be promising in perspective. As we observed, however, the nature of the para-substituent X has a very strong influence on the reaction rate, when salts of bivalent metals such as Zn, Cd, Co, Mg, Mn, are used as catalysts, while this influence is much smaller when a tetravalent metal, as Ti, is used. This fact suggests that the transesterification mechanism operating in the two cases is different and this suggestion has been confirmed by applying Hammett's approach to the available kinetic data. Experimental kinetic runs were all performed at 193°C, by withdrawing small samples of the reaction mixture at different reaction times. These samples were gaschromatographically analyzed. We found volcano shaped curves of the reaction rates as a function of the metal ion acidities and we obtained different trends with a maximum of activity shifted from a metal to another for different substrates. A comparison of the kinetic results obtained, respectively, with the model molecules and DMT will be reported too.     

Assay for urinary estriol during the menstrual cycle based on extraction by a graphitized carbon black cartridge followed by high-performance liquid chromatography

Summary A high-performance liquid chromatography (HPLC) assay for estriol in nonpregnancy urine is described. After Enzymic hydrolysis, the estriol is extracted from urine by the sorbent trap technique utilizing graphitized carbon black (Carbopack B). After some washing steps, estriol is desorbed by a suitable solvent system. After solvent removal, the sample is injected into an HPLC column for estriol quantification. Analytical recovery of estriol was 96.1%. The precision of the method was 2.6 and 4.9% respectively at 145 and 10.6ng/ml of urine. The limit of sensitivity was set at 0.8 ng/ml of urine. The mean contents of estriol in the follicular and luteal phases were respectively 11.3 and 38.8 ng/ml of urine.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

Theoretical study on the hydrogen migration reactions in ground state vinyl fluoride: Basis set and correlation energy effects

We performed ab initio molecular orbital (MO) calculations using Hartree—Fock SCF, and second- and fourth-order Møller—Plesset perturbation theory for hydrogen migration reactions on the singlet vinyl fluoride potential energy surface. We used different basis sets and polarization functions to obtain the stationary point geometries and activation barriers. Basis set and the polarization function extension have small effects, while the correlation energy evaluation leads to new conclusions for one of the studied reactions: the product singlet CHCH₂F is not a true local minimum on the potential energy surface.     

Synthesis and structural identification of a highly ordered mesoporous organosilica with large cagelike pores

Using 1,2-bis(trimethoxysilyl)ethane as organosiloxane precursor and a triblock copolymer surfactant, Pluronic F127, as template, a highly ordered mesoporous organosilica with large cagelike pores has been successfully synthesized. Its structure was resolved to be 3-D cubic Fmm by high-resolution transmission electron microscopy. The intergrowth of hexagonal close-packed and cubic close-packed phases was observed in this material. The effect of different siliceous precursors on the mesostructure was also investigated.     

UVB irradiation of normal human skin favors the development of type-2 T-cells in vivo and in primary dermal cell cultures

To determine the effect of UVB exposure on the balance of type-1 or type-2 T-cells in skin, we examined the expression of key markers interferon (IFN)-gamma and interleukin (IL)-4 in cryostat sections. IFN-gamma mRNA was clearly detectable in nonirradiated control skin, and IFN-gamma protein was found in 2% of the dermal CD3pos T-cells, whereas IL-4 mRNA was hardly detectable, and no IL-4 protein was found. In contrast, IL-4 mRNA expression increased upon irradiation, and IL-4 was found in 2% of the T-cells at day 2 after UVB-exposure. Concomitantly, IFN-gamma mRNA expression decreased, and IFN-gamma protein became absent. We also analyzed T-cells present in primary dermal cell cultures, which were used as an in vitro equivalent of the in vivo situation. As compared with T-cells from control skin, T-cells in dermal cell cultures from UVB-exposed skin displayed an increased IL-4 and decreased IFN-gamma expression. No such skewing occurred when the T-cells from irradiated skin were cloned in the absence of a dermal microenvironment. Except for an occasional positive T-cell, type-1-associated cell-surface markers (CCR5, CXCR3) or type-2 markers (CCR3, CD30, CRTH2) were undetectable in situ. But these markers were expressed on cultured dermal T-cells from UVB-exposed and control skin at a comparable level, but did not correlate with the IFN-gamma and IL-4 production. Altogether, UVB-induced changes of the dermal microenvironment favor the development of type-2 T-cells.     

CH2F2…H2O中强π型二级氢键

通过从头计算,用较大基组６－３１１＋Ｇ(２ｄ,２ｐ),在ＭＰ２水平上计算得到ＣＨ２Ｆ２…Ｈ２Ｏ体系的优化几何构型,与实验结构一致．其中∠Ｆ…Ｈ－Ｏ＝１１６．５°,偏离普通氢键之键角达到６３．５°．为探讨产生氢键巨大弯曲的原因,采用点电荷扫描的办法,探测ＣＨ２Ｆ２…Ｈ２Ｏ体系中Ｈ２Ｏ的Ｏ原子上的两对孤电子对的方向,发现了一个强的π型二级氢键相互作用．使用这种新的相互作用方式说明了产生这一巨大氢键弯曲的原因,并且在ＭＰ４水平上使用Ｃｏｕｎｔｅｒｐｏｉｓｅ技术计算了π型二级氢键的稳定化能．     

1,2-fused pyrimidines. V. Synthesis of 1-alkyl or phenyl-2H-dipyrido-[1,2-a:2′,3′-d]pyrimidine-2,5(1H)-diones

The reaction of 2-[(N-acyl, N-alkyl or phenyl)amino]-4H-pyrido[1,2-a]pyrimidin-4-ones 8a-g with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier reagent 1 (95°, 90 minutes) afforded 1-alkyl or phenyl-2H-dipyrido[1,2-a:2′,3′-d]pyrimidine-2,5(1H)^?diones, 3-alkyl substituted or not, 10a-g . The starting compounds 8 were prepared by treating 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones N-alkyl substituted 7a,b or N-phenyl substituted 4 with excess anhydrides (130°, 7 hours) when the 2-(alkylamino) derivatives 7 were used in the reaction, compounds 8 were obtained along with very small amounts of 3-acyl-2-(alkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones 9 .