Trifluoroacetic acid-promoted ring contraction in 2,3-di-O-silylated O-galactopyranosides and hemiacetals

Synlett ◽  
2022 ◽  
Author(s):  
Polina Igorevna Abronina ◽  
Nelly Malysheva ◽  
Alexander Zinin ◽  
Maxim Y. Karpenko ◽  
Natalya G. Kolotyrkina ◽  
...  
Keyword(s):  
Trifluoroacetic Acid ◽  
Easy Access ◽  
Pyranose Ring ◽  
Ring Contraction ◽  
Protective Groups ◽  
Furanose Form ◽  
First Time

A pyranose ring contraction of 2,3-di-O-silylated O-galactopyranosides with retention of aglycone promoted by anhydrous trifluoroacetyc acid (TFA) in CH2Cl2 was demonstrated for the first time. In addition, TFA-promoted pyranose ring contraction of 2,3-bis-O-(triisopropylsilyl)-D-galactopyranose with formation of the corresponding anomeric triols in furanose form was successfully performed. A representative series of β-D-galactopyranosides with Me, Bn, allyl, or 3-(trifluoroacetamido)propyl aglycones has been investigated. TBDPS protective groups were found to be more stable than TIPS groups under conditions of TFA-promoted pyranose ring contraction. An easy access to 2,3-di-O-TBDPS substituted allyl and benzyl galactofuranosides and 2,3-bis-O-(triisopropylsilyl)-β-D-galactofuranose may present an advantage in synthesis of selectively protected monosacharide bilding blocks, useful for the synthesis of biologically important oligosaccharides.

Formation and Trapping of the Thermodynamically Unfavoured Inverted-Hemicucurbit[6]uril

2019 ◽  
Author(s):  
Elena Prigorchenko ◽  
Sandra Kaabel ◽  
Triin Narva ◽  
Anastassia Baškir ◽  
Maria Fomitšenko ◽  
...  
Keyword(s):  
Complex Formation ◽  
Combinatorial Chemistry ◽  
Trifluoroacetic Acid ◽  
Chloride Anion ◽  
Binding Affinities ◽  
Dynamic Covalent Chemistry ◽  
Reaction Selectivity ◽  
Low Concentration ◽  
Dynamic Combinatorial Chemistry ◽  
First Time

Amplification of a thermodynamically unfavoured macrocyclic product through the directed shift of the equilibrium between dynamic covalent chemistry library members is difficult to achieve. We show for the first time that during condensation of formaldehyde and <i>cis</i>-<i>N,N'</i>-cyclohexa-1,2-diylurea formation of <i>inverted-cis</i>-cyclohexanohemicucurbit[6]uril (<i>i-cis</i>-cycHC[6]) can be induced at the expense of thermodynamically favoured <i>cis</i>-cyclohexanohemicucurbit[6]uril (<i>cis</i>-cycHC[6]). The formation of <i>i-cis-</i>cycHC[6] is enhanced in low concentration of the templating chloride anion and suppressed in excess of this template. We found that reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous removal of the formed cycHC[6] macrocycles from the equilibrating solution by precipitation. Notably, the <i>i-cis</i>-cycHC[6] was isolated with 33% yield. Different binding affinities of three diastereomeric <i>i-cis</i>-, <i>cis</i>-cycHC[6] and their chiral isomer (<i>R,R</i>)-cycHC[6] for trifluoroacetic acid demonstrate the influence of macrocycle geometry on complex formation.

Oxford Handbook of Psychiatry

2009 ◽  
Author(s):  
David Semple ◽  
Roger Smyth
Keyword(s):  
Medical Students ◽  
Easy Access ◽  
First Time ◽  
Psychiatric Problems

The Oxford Handbook of Psychiatry is a new book directed at medical students, doctors coming to psychiatry for the first time, psychiatric trainees, and other professionals who may have to deal with patients with psychiatric problems. It is written by a group of experienced psychiatrists and is designed to provide easy access to the information required by psychiatry trainees on the wards or on-call.

Secondary Prevention of Non-fatal Deliberate Self-harm

1993 ◽  
Vol 163 (1) ◽  
pp. 111-112 ◽  
Author(s):  
H. G. Morgan ◽  
E. M. Jones ◽  
J. H. Owen
Keyword(s):  
British Journal ◽  
Early Stage ◽  
Psychiatric Services ◽  
Easy Access ◽  
Deliberate Self Harm ◽  
Self Harm ◽  
One Year ◽  
First Time ◽  
Experimental Group

In an attempt to address the low compliance with offers of treatment shown by patients after episodes of non-fatal deliberate self-harm (DSH), patients who had harmed themselves for the first time were offered rapid, easy access to on-call trainee psychiatrists in the event of further difficulties, and they were encouraged to seek help at an early stage should such problems arise. The follow-up data obtained after one year showed a significant reduction of actual or seriously threatened DSH in the experimental group, who also made considerably less demands on medical and psychiatric services, when compared with controls.British Journal of Psychiatry (1993), 163, 111–112

Synthesis of 2', 6'-Dihydroxychalcones by Using Tetrahydropyran-2-yl and Trialkylsilyl Protective Groups; the Crystal Structure Determination of 2',6'-Dihydroxy-2,4,6-trimethoxychalcone

1989 ◽  
Vol 42 (7) ◽  
pp. 1103 ◽  
Author(s):  
CO Miles ◽  
L Main ◽  
BK Nicholson
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Silyl Ether ◽  
X Ray ◽  
Protective Groups ◽  
Intramolecular Hydrogen ◽  
First Time ◽  
Mild Acid

Two improved general routes to 2′,6′-dihydroxychalcones are described in which the final step is protective-group removal from O 2′ under mild acid conditions. The first involves base-catalysed condensation of benzaldehydes with 2′-hydroxy-6′-tetrahydropyran-2-yloxyacetophenone, the second ring-opening of 5-hydroxyflavanones with 1,8-diazabicyclo[5.4.0]undec-7-ene in the presence of a trialkylchlorosilane to trap out the chalcone as a bis silyl ether. Chalcones prepared by the first route are 2',6'-dihydroxychalcone (1), and its 4-methoxy (2), 3,4-dimethoxy (3), 3,4,5-trimethoxy (4), and 2,4,6-trimethoxy (5) derivatives. The 4-chloro derivative (6) and the chalcone from hesperetin are prepared by the second method. .The X-ray crystal structure of 2',6'-dihydroxy-2,4,6-trimethoxychalcone (5), the first for a 2',6′-dihydroxychalcone, is reported, the hydrogen involved in intramolecular hydrogen-bonding between the carbonyl and phenolic oxygens being located for the first time for any 2'-hydroxychalcone derivative. The O 6' involved in the intramolecular hydrogen-bonding is also hydrogen-bonded intermolecularly to the hydrogen of the other (2'-)hydroxy group of a neighbouring molecule in the lattice. 13C n.m.r. data are the first reported for a series of 2',6'-dihydroxychalcones.

Morphological Evolution of Fe-Oxy-Hydroxide Nanotubes During Electrodeposition

2019 ◽  
Vol 15 (6) ◽  
pp. 669-678
Author(s):  
Patrizia Bocchetta ◽  
Francesca Conciauro ◽  
Filippo Selleri
Keyword(s):  
Morphological Evolution ◽  
Ethanol Solution ◽  
Alcoholic Solution ◽  
Constant Current ◽  
Relative Mass ◽  
Easy Access ◽  
High Quality ◽  
Cathodic Electrodeposition ◽  
Kinetic Growth ◽  
First Time

Background: Ordered arrays of 1D iron(oxyhydr)oxide nanostructures have potential applications in magnetic recording mediums, lithium batteries, supercapacitors, and thermal production of α-, β-, γ-type Fe2O3. Large surface areas with three-dimensional architectures, such as nanotubes, are encouraged because the easy access of ion, gas, liquid and radiation assures high ion exchange capacity, sensing and catalytic activities. Objective: In this work, the morphological evolution of Fe-oxyhydroxide electrodeposition inside AAM pores has been followed for the first time by selecting two relevant electrochemical conditions of synthesis producing high quality morphologies of nanotubes. Methods: Iron(oxyhydr)oxide nanotubes have been synthesized by cathodic electrodeposition at a constant current in classic three-electrode cell. Two different electrolytic baths have been studied: (i) an aqueous bath consisting of 5 mM FeCl3+5 mM KF+0.1 M KCl+1 M H2O2 (H-Fe) and (ii) an ethanolic bath consisting of 0.3 M FeCl3 + 0.1 M KCl (Et-Fe). Results: XRD, Raman and SEM results on the iron(oxyhydr)oxide nanotubes suggest different mechanisms of chemical precipitation mechanisms in Et-Fe alcoholic solution (dehydration and rearrangement within the ferrihydrite aggregates) and H-Fe aqueous solution (dissolution/ reprecipitation). The morphological evolution of the growing nanostructure to nanotubes inside AAM in the two baths agrees very well with the overpotential vs. time curves, the kinetic growth of the nanotubes arrays and a growth mechanism governed by the relative mass transfer processes involving both OH- and Fe ions. Conclusion: The morphological evolution of Fe-oxyhydroxide cathodic electroprecipitation inside AAM pores in two relevant electrochemical baths containing Fe(III) (aqueous/H-Fe and alcoholic/Et- Fe) has been followed for the first time by a comprehensive SEM analysis accompanied by electrochemical, structural and kinetic growth of the nano-electrodeposits. : The detailed SEM results collected in this work allowed to recommend template electrogeneration of base in ethanol solution containing Fe(III) chloride as a relevant procedure to obtain high-quality, compact and well-ordered Fe oxy-hydroxide nanotubes.

An easy access to topical gels of an anti-cancer prodrug (5-fluorouracil acetic acid) for self-drug-delivery applications

2019 ◽  
Vol 55 (53) ◽  
pp. 7683-7686 ◽  
Author(s):  
Poulami Chakraborty ◽  
Parthasarathi Dastidar
Keyword(s):  
Drug Delivery ◽  
Acetic Acid ◽  
Easy Access ◽  
Salt Formation ◽  
Anti Cancer ◽  
Drug Delivery Applications ◽  
First Time ◽  
Topical Gels

An easy access to topical gels (both hydro- and organogels) derived from an anti-cancer prodrug namely 5-fluorouracil acetic acid (5-FuA) achieved by exploiting a simple salt formation strategy is reported for the first time.

Follow up after middle-ear ventilation tube insertion: what is needed and when?

2007 ◽  
Vol 122 (6) ◽  
pp. 580-583 ◽  
Author(s):  
P M Spielmann ◽  
H McKee ◽  
R M Adamson ◽  
G Thiel ◽  
D Schenk ◽  
...  
Keyword(s):  
Data Collection ◽  
Middle Ear ◽  
Hearing Threshold ◽  
Clinical Findings ◽  
Easy Access ◽  
Ventilation Tube ◽  
Tube Insertion ◽  
Middle Ear Ventilation ◽  
First Time

AbstractIntroduction:There is a paucity of evidence to guide the post-operative follow up of patients undergoing middle-ear ventilation tube insertion for the first time. This study was conceived to identify current practice at our institution (Ninewells Hospital, Dundee) and to inform subsequent change in our follow-up procedure.Methods:Two cycles of data collection and analysis were performed. All paediatric patients undergoing ventilation tube insertion for the first time were identified. Patients who had previously undergone ventilation tube insertion or additional procedures such as adenoidectomy or tonsillectomy were excluded. The first data collection period comprised all of the year 2000, and the second 18 months over 2003–2004. A minimum of 20 months' follow up was allowed for. Data regarding clinical findings and audiometry were recorded at each follow-up appointment.Results:We identified a total of 50 patients meeting our criteria for inclusion in the first cohort. There were a total of 156 appointments between surgery and data collection (a mean of 3.12 per child). A total of 113 (72 per cent) appointments lead to no medical intervention. The only statistically significant difference between patients requiring further ventilation tube insertion (n = 10) and those not requiring further treatment during the study period (n = 40) was the average hearing threshold (p < 0.01). These findings prompted a change in the post-operative regime; all patients undergoing ventilation tube insertion were subsequently seen at three months for a pure tone audiogram, and further review depended on clinical and audiometric findings. Records for 84 children were identified and collected for the second cohort, there were a total of 154 appointments (a mean of 1.83 per child). In only 18 appointments (12 per cent) were normal findings and hearing recorded and children given a further review appointment. Sixteen of 29 (55 per cent) children with abnormal clinical findings (otorrhoea, tube blockage or extrusion) required some form of intervention (p < 0.05). Twenty-six had a mean hearing threshold worse than 20 dB at first review. Nineteen (73 per cent) required further intervention of some sort (p < 0.01).Conclusions:Our study demonstrated that the vast majority of review appointments resulted in no clinical intervention. We therefore question the need for regular follow up in this patient group. Twenty per cent (10 of 50 and 18 of 84) of our patients required further ventilation tube insertion within the study periods. This is consistent with rates reported in the literature. Children with abnormal clinical findings or a mean hearing threshold greater than 20 dB were significantly more likely to require further intervention. We would recommend one post-operative review with audiometry, three months after surgery. At this initial appointment, further review should be offered to those children with poor hearing, early extrusion, blockage or infection, as they are more likely to require further ventilation tube insertion. This strategy is dependent on good links with community primary care providers and easy access to secondary care for further management, should this be required.

Seco-porphyrazines with eight (p-tolyl) and (o-tolyl) units

2008 ◽  
Vol 12 (02) ◽  
pp. 116-122 ◽  
Author(s):  
Ergün Gonca ◽  
Ümmü Gülsüm Baklaci ◽  
Hatice Akin Dinçer
Keyword(s):  
Spectral Data ◽  
Elemental Analysis ◽  
Trifluoroacetic Acid ◽  
Mass Spectral Data ◽  
Mass Spectral ◽  
H Nmr ◽  
Ft Ir ◽  
First Time ◽  
Oxidized Products

Magnesium porphyrazinates substituted with eight (p-tolyl) and (o-tolyl) units on the peripheral positions have been synthesized for the first time by cyclotetramerization of 1,2-bis(p-tolyl)maleonitrile and 1,2-bis(o-tolyl)maleonitrile in the presence of magnesium butanolate. Their demetalation by the treatment with trifluoroacetic acid resulted in partially oxidized products, namely, octakis(p-tolyl)-2-seco-porphyrazine-2,3-dione and octakis(o-tolyl)-2-seco-porphyrazine-2,3-dione. Further reactions of these products with copper(II) acetate, zinc(II) acetate and cobalt(II) acetate have led to the metallo derivatives, [octakis(p-tolyl)-2-seco-2,3-dioxoporphyrazinato] M(II) and [octakis(o-tolyl)-2-seco-2,3-dioxoporphyrazinato] M(II) ( M = Cu , Zn , Co ). These novel compounds have been characterized by elemental analysis, together with FT-IR, 1H NMR, UV-vis and mass spectral data.

Synthetic Studies Concerning the Crinine Alkaloid Haemultine

2013 ◽  
Vol 66 (1) ◽  
pp. 30 ◽  
Author(s):  
Nadia (Yuqian) Gao ◽  
Xinghua Ma ◽  
Laurent Petit ◽  
Brett D. Schwartz ◽  
Martin G. Banwell ◽  
...  
Keyword(s):  
Double Bond ◽  
Natural Product ◽  
Trifluoroacetic Acid ◽  
Spectroscopic Data ◽  
Ene Reaction ◽  
Enantiomerically Pure ◽  
Racemic Form ◽  
Pure Compounds ◽  
First Time ◽  
Bond Isomer

The racemic form, (±)-1, of the structure originally assigned to the crinine alkaloid haemultine has been prepared for the first time. A key step involved the conversion of compound (±)-4 into the isomeric cis-C3a-arylhexahydroindole (±)-3 using a Pd0-catalysed intramolecular Alder-ene reaction. The amino-alcohol (±)-2 derived from the latter compound reacted with paraformaldehyde in the presence of trifluoroacetic acid to give, via a Pictet–Spengler reaction, the target (±)-1. The diastereoisomeric Mosher esters 15 and 16 obtained by coupling the racemate (±)-1 with the R-form, 14, of the Mosher acid could be separated chromatographically and then reductively cleaved to give the enantiomerically pure compounds (+)-1 and (–)-1, respectively. The physical and spectroscopic data derived from the former enantiomer are consistent with the proposition that the title natural product is, in fact, a mixture of (+)-1 and its Δ2,3-double bond isomer.

Formation and Trapping of the Thermodynamically Unfavoured Inverted-Hemicucurbit[6]uril

2019 ◽  
Author(s):  
Elena Prigorchenko ◽  
Sandra Kaabel ◽  
Triin Narva ◽  
Anastassia Baškir ◽  
Maria Fomitšenko ◽  
...  
Keyword(s):  
Complex Formation ◽  
Combinatorial Chemistry ◽  
Trifluoroacetic Acid ◽  
Chloride Anion ◽  
Binding Affinities ◽  
Dynamic Covalent Chemistry ◽  
Reaction Selectivity ◽  
Low Concentration ◽  
Dynamic Combinatorial Chemistry ◽  
First Time

Amplification of a thermodynamically unfavoured macrocyclic product through the directed shift of the equilibrium between dynamic covalent chemistry library members is difficult to achieve. We show for the first time that during condensation of formaldehyde and <i>cis</i>-<i>N,N'</i>-cyclohexa-1,2-diylurea formation of <i>inverted-cis</i>-cyclohexanohemicucurbit[6]uril (<i>i-cis</i>-cycHC[6]) can be induced at the expense of thermodynamically favoured <i>cis</i>-cyclohexanohemicucurbit[6]uril (<i>cis</i>-cycHC[6]). The formation of <i>i-cis-</i>cycHC[6] is enhanced in low concentration of the templating chloride anion and suppressed in excess of this template. We found that reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous removal of the formed cycHC[6] macrocycles from the equilibrating solution by precipitation. Notably, the <i>i-cis</i>-cycHC[6] was isolated with 33% yield. Different binding affinities of three diastereomeric <i>i-cis</i>-, <i>cis</i>-cycHC[6] and their chiral isomer (<i>R,R</i>)-cycHC[6] for trifluoroacetic acid demonstrate the influence of macrocycle geometry on complex formation.

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