Search results for "stereo"
showing 10 items of 6147 documents
Nortriptyline hydrochloride skin absorption: development of a transdermal patch.
2007
The influence of propylen glycol (PG), ethanol, and oleic acid (OA) on nortriptyline hydrochloride (NTH) penetration through human epidermis was studied in vitro at two different pH values (5.5 and 7.4). The influence of lactic acid and polysorbate 80 was studied for a pH of 5.5. Permeation studies through Heat Separated Epidermis, as well as the enhancing effect of the different vehicles, showed a pH dependency. A pH value of 5.5 in the donor solution decreases significantly the permeability coefficient (Kp) with respect to a pH value of 7.4 (0.011+/-0.004 x 10(-6) versus 0.36+/-0.04 x 10(-6)cm/s). The vehicles showed an increasing enhancement effect in the order: polysorbate 80>ethanol/PG…
Penetration enhancer containing vesicles as carriers for dermal delivery of tretinoin.
2011
The ability of a recently developed novel class of liposomes to promote dermal delivery of tretinoin (TRA) was evaluated. New penetration enhancer-containing vesicles (PEVs) were prepared adding to conventional phosphatidylcholine vesicles (control liposomes) different hydrophilic penetration enhancers: Oramix® NS10 (OrNS10), Labrasol® (Lab), Transcutol® P (Trc), and propylene glycol (PG). Vesicles were characterized by morphology, size distribution, zeta potential, incorporation efficiency, stability, rheological behaviour, and deformability. Small, negatively charged, non-deformable, multilamellar vesicles were obtained. Rheological studies showed that PEVs had fluidity higher than conven…
A new monomeric interpretation of intrinsic optical bistability observed in Yb3+-doped bromide materials
2003
We present a mechanism able to show intrinsic bistable behaviour involving single Yb3+ ions embedded into bromide lattices, in which intrinsic optical bistability (IOB) has been observed. The mechanism is based on the experimentally found coupling between the Yb3+ ion and the totally symmetric local mode of vibration of the [YbBr6]3- coordination unit. The model reproduces the IOB observed in CsCdBr3:1% Yb3+ and allows to understand the experimentally found presence of the phenomenon in the other bromides, but its absence in Cs3Lu2Cl9:Yb3+.
Decision support towards agile eco-design of microreaction processes by accompanying (simplified) life cycle assessment
2011
Continuously running syntheses in microstructured reactors offers novel ways to intensify conventional chemical processes. An outstanding advantage of microreaction technology is the high surface-to-volume-ratio which enables intensive mixing phenomena as well as high mass and heat transfer rates. Thus, microstructured reactors may be a suitable means to improve multiphase reactions by increasing the interfacial area and the intensification of internal mixing. This improvement in reaction performances may lead to reduced environmental burdens of the process under consideration. The method of simplified life cycle assessment (SLCA) is a suitable tool to evaluate the environmental burdens cau…
The yellow toxins produced by Cercospora Beticola. Part VIII : Chemical equilibrium between beticolins ; structures of minor compounds : beticolin 6 …
1994
Abstract a general chemical transformation of the “linear” beticolin skeleton (beticolin 2 and 4) into a “bent” beticolin skeleton (cebetin A and beticolin 3 respectively) is described. Beticolins 6 and 8, minor components of mycelial extract are also characterized as minor compounds resulting from these transformations.
Sesquiterpene Lactones fromCentaurea paui
1994
Abstract A new elemanolide and two new heliangolides as well as (2R,3R)-(+)-3-hydroxy-2-methyl-butyrolactone have been isolated from Centaurea paui. The structures were elucidated by high field NMR techniques and chemical transformation.
1,3-Dipolar cycloaddition of diaryldiazomethanes across N-ethoxy-carbonyl-N-(2,2,2-trichloroethylidene)amine and reactivity of the resulting 2-azabut…
2016
Abstract 1,3-dipolar cycloaddition of diaryldiazomethanes Ar2C N2 across Cl3C–CH N–CO2Et 1 yields Δ3-1,2,4-triazolines 2. Thermolysis of 2 leads, via transient azomethine ylides 3, to diaryldichloroazabutadienes [Ar(Ar')C N–CH CCl2] 4. Treatment of 4a (Ar = Ar' = C6H5) and 4c (Ar = Ar' = p-ClC6H4) with NaSR in DMF yields 2-azabutadienes [Ar2C N–C(H) C(SR)2] 5. In contrast, nucleophilic attack of NaStBu on 4 affords azadienic dithioethers [Ar2C N–C(StBu) C(H)(StBu)] (7a Ar = C6H5; 7b Ar' = p-ClC6H4). The reaction of 4a with NaSEt conducted in neat EtSH produces [Ph2C N–C(H)(SEt)–CCl2H] 8, which after dehydrochloration by NaOMe and subsequent addition of NaSEt is converted to [Ph2C N–C(SEt) C…
Synthesis and antimicrobial screening of tetra Schiff bases of 1,2,4,5-tetra (5-amino-1,3,4-thiadiazole-2-yl)benzene
2014
Abstract In the present study, novel tetra Schiff bases were synthesized by condensation of 1,2,4,5-tetra (5-amino-1,3,4-thiadiazole-2-yl)benzene with different aromatic aldehydes. The chemical structures were confirmed by means of IR, 1 H NMR, 13 C NMR, and elemental analysis. All compounds were screened for antibacterial ( Staphylococcus aureus ATCC-9144, Staphylococcus epidermidis ATCC-155, Micrococcus luteus ATCC-4698, Bacillus cereus ATCC-11778, Escherichia coli ATCC-25922, and Pseudomonas aeruginosa ATCC-2853) and antifungal ( Aspergillus niger ATCC-9029 and Aspergillus fumigatus ATCC-46645) activities by paper disc diffusion technique. The minimum inhibitory concentrations (MICs) of …
Stereoselective syntheses of piperidinones and their modification by organometallic coupling reactions
2007
Dehydropiperidinones stereoselectively obtained from N-arabinosyl imines were iodinated at the enaminone structure. Knochel iodine-magnesium exchange afforded Grignard compounds of these piperidinone derivatives which reacted, either directly or after transmetalation to zinc or copper intermediates, with alkyl-, aryl- or acylhalides to give correspondingly substituted piperidinones. Stereoselective conjugate allyl cuprate addition to a thus obtained 5-allyl dehydropiperidinone and ring-closing metathesis of the product gave a hydroquinolinone containing three stereogenic centers.
Synthesis and Isolation of Enantiomerically Enriched Cyclopenta[b]benzofurans Based on Products from Anodic Oxidation of 2,4-Dimethylphenol
2015
The anodic treatment of 2,4-dimethylphenol offers a powerful and direct method for the construction of a dehydrotetramer with four contiguous stereocentres on a multigram scale. The installation of propellanes on this scaffold using enantiomerically pure carbonyl compounds leads to a mixture of diastereomers. This mixture is easily separable using standard chromatography and gives rise to optically pure cyclopenta[b]benzofurans which are important scaffolds in a variety of natural products. The synthesis is easy to perform and allows a reliable access to chiral compounds with very high enantiomeric excess. It was possible to determine the absolute configuration of these compounds by compari…