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1.
The enantioselective synthesis of bicyclic sulfonium salts 8 or 9, thioanalogues of swainsonine derivatives, is described. The synthetic strategy is based on a stereo- and regiospecific transannular cyclization reaction of nine-membered cyclic sulfides, mediated by Me(3)SiI or carried out under acidic catalysis. 相似文献
2.
J. Lub Corresponding author V. Recaj L. Puig P. Forcén C. Luengo 《Liquid crystals》2013,40(12):1627-1637
The synthesis and photopolymerization of various liquid crystalline dioxetanes is described. The effects of the spacer length, structure of the mesogenic group and oxetane group on the liquid crystalline properties, polymerization behaviour and optical properties (birefringence) of the oriented and crosslinked network formed in photo-polymerization are discussed. Thermally stable films with birefringence values up to 0.13 can be formed from these materials. The dioxetanes show significantly lower polymerization shrinkage than do structurally related diacrylates. 相似文献
3.
Maria Elaine Araruna Pablo Silva Maria Almeida Renaly Rêgo Raiff Dantas Hilton Albuquerque Ingrid Cabral Nadjaele Apolinrio Francinalva Medeiros Ana Medeiros Vanda Santos 《Molecules (Basel, Switzerland)》2021,26(6)
Spondias mombin L. (Anacardiaceae) has a worldwide distribution and is present in all regions of Brazil. Its leaves, flowers and bark are used as teas in folk medicine to treat diseases of the digestive system. This study aimed to evaluate the acute non-clinical toxicity, gastroprotective activity, and the related mechanisms of action of nebulized extract and tablets based on dried Spondias mombin (SmNE). SmNE screening showed the presence of flavonoids (0.65%), polyphenols (25.50%), where the major compound is gallic acid. In the acute oral toxicity assay, a dose of 2000 mg/kg of SmNE administered orally in Swiss mice did not induce any behavioral changes. SmNE (250 or 500 mg/kg p.o) significantly reduced the ulcerative lesion area when compared to the control group in ethanol and non-steroidal anti-inflammatory drug (NSAIDs) models. Results showed that treatment with SmNE (250 mg/kg) reduced acid secretion and gastric content, accompanied with an increase in pH. Previous administration of indomethacin and glibenclamide reversed the protection provided by SmNE, confirming the participation of prostaglandins (PGs) and ATP-sensitive potassium channels (KATP) in its gastroprotective effect. The SmNE tablets met the pharmacopeial quality requirements with gastroprotective activity and similar protection in comparison to the isolated extract administrated. In conclusion, SmNe has a gastroprotective activity related to cytoprotective mechanisms, such as the participation of endogenous prostaglandins and KATP channels, having an anti-secretory effect with systemic action. The formulation obtained presented gastroprotective effects similar to the administration of the extract, the tablets showed favorable compression characteristics by the direct route and met the pharmacopeial quality requirements. 相似文献
4.
Vanda Veprek-Bilinski Krishna Narasimhan Andr S. Dreiding 《Helvetica chimica acta》1978,61(8):3018-3027
Reaction of Diphenylcyclopropenone with β-Carbonyl-enolates. I. Use of Acetylacetone, Methyl Acetoacetate, 2-Ethoxycarbonyl-cyclododecanone and Dimethyl Malonate The reaction of the sodium salts of acetylacetone ( 6 ), methyl acetoacetate (7) , 2-ethoxycarbonyl-cyclododecanone (8) , dimethyl malonate (19) and its methyl derivative 20 with diphenylcyclopropenone ( 5 ) in dimethylformamide at room temperature led to the unsaturated γ-lactones 14, 15, 17, 22 and 36 . In the case of dimethyl malonate ( 19 ), the halfester 21 , the acyl-malonic ester 24 and the indenone-malonic ester 23 were also isolated. Several intermediates and the final products were characterised by reactions and spectroscopically. A general mechanism is discussed for the addition of cyclo-propenones ( 1 ) to the enolate salts of β-dicarbonyl compounds 4 involving the bicyclic lactone-enolates 18 and 32 as intermediates. The products formed via 18 and 32 are considered to be the result of an attack of one of the oxygen atoms of the β-carbonyl-enolate anion ( 4 ), the product 24 , on the other hand, of the attack of the α-carbon atom of 4 ; in both cases the attack is on the carbonyl C-atom of 5 . 相似文献
5.
We consider complex-valued functions f ∈ L 1 (R+2),where R +:= [0,∞),and prove sufficient conditions under which the double sine Fourier transform f ss and the double cosine Fourier transform f cc belong to one of the two-dimensional Lipschitz classes Lip(α,β) for some 0 α,β≤ 1;or to one of the Zygmund classes Zyg(α,β) for some 0 α,β≤ 2.These sufficient conditions are best possible in the sense that they are also necessary for nonnegative-valued functions f ∈ L 1 (R+2). 相似文献
6.
Cláudia Simões Vanda Simões Ana Reis Pedro Domingues M. Rosário M. Domingues 《Analytical and bioanalytical chemistry》2010,397(6):2417-2427
Phosphatidylethanolamine glycation occurs in diabetic patients and was found to be related with oxidative stress and with
diabetic complications. Glycated phosphatidylethanolamines seem to increase oxidation of other molecules; however, the reason
why is not understood. In this work, we have studied the oxidation of glycated phosphatidylethanolamines (1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphatidylethanolamine (PLPE) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (dPPE)) using a Fenton system. Liquid chromatography–electrospray ionization (ESI)–mass
spectrometry and ESI–tandem mass spectrometry in both positive and negative modes were used for detecting and identifying
the oxidation products. We were able to identify several oxidation products with oxidation in unsaturated sn-2 acyl chain of PLPE, as long- and short-chain products with main oxidation sites on C-7, C-8, C-9, and C-12 carbons. Other
products were identified in both glycated PLPE and glycated dPPE, revealing that oxidation also occurs in the glycated polar
head. This fact has not been reported before. These products may be generated from oxidation of glycated phosphatidylethanolamines
(PE) as Schiff base, leading to short-chain product without the amine moiety, due to cleavage of glycated polar head and long-chain
product with two keto groups linked to the glycated polar head or from glycated PE as Amadori product, short-chain products
with –NHCHO and –NHCHOHCHO terminal in polar head. Oxidation of glycated phosphatidylethanolamines occurred more quickly than
the oxidation of non-glycated phosphatidylethanolamines probably because of the existence of more oxidation sites derived
from glycation of polar head group. Monitoring glycated polar head oxidation could be important to evaluate oxidative stress
modifications that occur in diabetic patients. 相似文献
7.
P. Saavedra C. N. Hernández I. Luengo J. Artiles A. Santana 《Computational Statistics》2008,23(1):79-98
A set of time series generated by stationary linear processes with an absolutely continuous spectral distribution is analysed.
The time series can then be considered realizations of a linear process of random coefficients. Likewise, each spectral density
function is a realization of a stochastic process whose function of means is called a population spectrum. We propose a kernel
estimator for the population spectrum and give conditions for its consistency. We then illustrate the properties of this estimator
in a simulation study and compare its performance with an alternative parametric estimator that can be found in the literature.
相似文献
8.
Oblatum 28-XII-1988 & 26-III-1990 & 10-X-1990 & 13-VI-1991 & 30-IX-1991 相似文献
9.
10.
Cerè V Minzoni M Pollicino S Ricci A Gasparrini F Ciogli A D'Acquarica I 《Journal of combinatorial chemistry》2006,8(1):74-78
A straightforward synthetic protocol apt to synthesize a library constituted by all conduritol stereoisomers in solution phase is described and successfully applied to some polymer-supported substrates. During the solid-phase sequence, an unprecedented rearrangement of a resin-bound sulfone performed under the Ramberg-B?cklund conditions appears of particular interest. Upon treatment with Me(3)Si-I, thiepanes supported on resin are found to undergo regio- and stereospecific ring contraction to a six-membered ring system with traceless cleavage from the solid support. 相似文献