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NaHSO4-SiO2 as an efficient and chemoselective catalyst, for the synthesis of acylal from aldehydes under, solvent-free conditions
Ravi Kumar Kannasani, V V Satyanarayana Peruri, Srinivasa Reddy Battula
Chemistry Central Journal , 2012, DOI: 10.1186/1752-153x-6-136
Abstract: Both aromatic and aliphatic aldehydes reacts smoothly with acetic anhydride in presence of silica supported sodium hydrogen sulphate to afford the corresponding 1,1-diacetates in good to excellent yields. We studied competitive reactions for the acylation of aldehydes in the presence of ketones using silica supported sodium hydrogen sulphate as a catalyst. Using this catalytic system, the highly selective conversion of an aldehyde in the presence of ketone was observed.NaHSO4-SiO2 is a chemoselective and highly efficient catalyst for acylal formation from aldehydes. The advantages of this methodology over the reported methods is the availability of the starting materials, simplicity of acylation procedure, a clean work-up, a short reaction time, high yields and reusability.The concept of green chemistry has been playing an important role in recent years for meeting the fundamental scientific challenges of protecting the living environment. One of the thrust areas for achieving this target is to explore alternative reaction conditions and reaction media to accomplish the desired chemical transformation with almost negligible by products and waste generation as well as elimination of the use of volatile and toxic organic solvents. It is therefore of utmost importance to evolve a simple and effective methodology for the different organic transformations that cover the concept of green chemistry.During the multi-step synthesis, the protection of the carbonyl group is widely achieved by the formation of acylal (1,1-diacetate) [1]. These substrates are important because of their application as precursors for the synthesis of 1-acetoxy dienes, valuable synthetic intermediates for Diels-Alder cycloaddition reactions [2]. The relative acid stability of acylal is another interesting feature in the field of protection and deprotection chemistry. General, acylals are prepared by treating aldehydes with acetic anhydride in the presence of protonic acids [3], Lewis acids [4], het
Synthesis of New Pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (PCU) Cyanosilylated Derivatives Using Sulphated Zirconia and Hydrotalcite as Catalysts in Microwave-Assisted Reactions under Solvent Free Conditions  [PDF]
Nahí Adriana Guerra-Navarro,Laura Nadxieli Palacios-Grijalva,Deyanira Angeles-Beltrán,Guillermo E. Negrón-Silva,Leticia Lomas-Romero,Eduardo González-Zamora,Rubén Gavi?o-Ramírez,Juan Navarrete-Bola?os
Molecules , 2011, DOI: 10.3390/molecules16086561
Abstract: A comparison was made of the effectiveness of the functionalization reactions of pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (PCU) using sulphated zirconia in protection-deprotection reactions and Mg/Al hydrotalcite in a cyanosilylation reaction, under classical thermal conditions and imposing microwave radiation; improved yields and reaction times were considered.
Bioactivity and Applications of Sulphated Polysaccharides from Marine Microalgae  [PDF]
Maria Filomena de Jesus Raposo,Rui Manuel Santos Costa de Morais,Alcina Maria Miranda Bernardo de Morais
Marine Drugs , 2013, DOI: 10.3390/md11010233
Abstract: Marine microalgae have been used for a long time as food for humans, such as Arthrospira (formerly, Spirulina), and for animals in aquaculture. The biomass of these microalgae and the compounds they produce have been shown to possess several biological applications with numerous health benefits. The present review puts up-to-date the research on the biological activities and applications of polysaccharides, active biocompounds synthesized by marine unicellular algae, which are, most of the times, released into the surrounding medium (exo- or extracellular polysaccharides, EPS). It goes through the most studied activities of sulphated polysaccharides (sPS) or their derivatives, but also highlights lesser known applications as hypolipidaemic or hypoglycaemic, or as biolubricant agents and drag-reducers. Therefore, the great potentials of sPS from marine microalgae to be used as nutraceuticals, therapeutic agents, cosmetics, or in other areas, such as engineering, are approached in this review.
Efficient deprotection of Boc group in amines and sulfamides using Dawson heteropolyacid catalyst  [cached]
Roubila Belghiche,Zinelaabidine Cheraiet,Malika Berredjem,Mostefa Abbessi
European Journal of Chemistry , 2012, DOI: 10.5155/eurjchem.3.3.305-309.610
Abstract: A series of sulfamides containing two protecting groups have been synthesized starting from N-benzoylaminoacids derivatives of (glycine, alanine, valine, leucine, phenylalanine), chlorosulfonylisocyanate and primary amines. Selective deprotection of the cyclic or linear sulfamides and amines has been achieved by treatment with heteropolyacid, which is easily recoverable and reusable. This method represents a reasonable alternative to the previous reported deprotection procedures.
6-Sulphated Chondroitins Have a Positive Influence on Axonal Regeneration  [PDF]
Rachel Lin,Thomas W. Rosahl,Paul J. Whiting,James W. Fawcett,Jessica C. F. Kwok
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021499
Abstract: Chondroitin sulphate proteoglycans (CSPGs) upregulated in the glial scar inhibit axon regeneration via their sulphated glycosaminoglycans (GAGs). Chondroitin 6-sulphotransferase-1 (C6ST-1) is upregulated after injury leading to an increase in 6-sulphated GAG. In this study, we ask if this increase in 6-sulphated GAG is responsible for the increased inhibition within the glial scar, or whether it represents a partial reversion to the permissive embryonic state dominated by 6-sulphated glycosaminoglycans (GAGs). Using C6ST-1 knockout mice (KO), we studied post-injury changes in chondroitin sulphotransferase (CSST) expression and the effect of chondroitin 6-sulphates on both central and peripheral axon regeneration. After CNS injury, wild-type animals (WT) showed an increase in mRNA for C6ST-1, C6ST-2 and C4ST-1, but KO did not upregulate any CSSTs. After PNS injury, while WT upregulated C6ST-1, KO showed an upregulation of C6ST-2. We examined regeneration of nigrostriatal axons, which demonstrate mild spontaneous axon regeneration in the WT. KO showed many fewer regenerating axons and more axonal retraction than WT. However, in the PNS, repair of the median and ulnar nerves led to similar and normal levels of axon regeneration in both WT and KO. Functional tests on plasticity after the repair also showed no evidence of enhanced plasticity in the KO. Our results suggest that the upregulation of 6-sulphated GAG after injury makes the extracellular matrix more permissive for axon regeneration, and that the balance of different CSs in the microenvironment around the lesion site is an important factor in determining the outcome of nervous system injury.
A Straightforward Diphenylmethyl Protection Method and Deprotection of Some Pyrimidine Nucleosides  [PDF]
Milind Saudi,Arthur van Aerschot
Molecules , 2013, DOI: 10.3390/molecules18078524
Abstract: Benzhydryl protection of primary and secondary alcohols has been reported previously via reaction with metal alcoholates. Our aim was to find generally useful and very mild conditions for the alcoholic protection and deprotection of nucleosides with the diphenylmethyl group. This was accomplished for some pyrimidine nucleosides using PdCl 2 as the transition metal catalyst, and with optimization yields of 70–90% have been achieved. A lack of solubility of other nucleosides hampers its more general use.
Role of sulphated polysaccharides from Sargassum Wightii in Cyclosporine A-induced oxidative liver injury in rats
Josephine Anthony,Nithya Kalaiselvam,Amudha Ganapathy,Veena Coothan
BMC Pharmacology , 2008, DOI: 10.1186/1471-2210-8-4
Abstract: Background Seaweeds or marine algae have long been made up a key part of the Asian diet, and as an antioxidant, sulphated polysaccharides have piqued the interest of many researchers as one of the ocean's greatest treasures. The present investigation suggests the therapeutic potential of sulphated polysaccharides from marine brown algae "Sargassum wightii" in Cyclosporine A (CsA)- induced liver injury. CsA is a potent immunosuppressive agent used in the field of organ transplantations and various autoimmune disorders. However, hepatotoxicity due to CsA remains to be one of the major clinical challenges. Methods The effect of sulphated polysaccharides on CsA-induced hepatotoxicity was studied in adult male albino rats of Wistar strain, and the animals were randomized into four groups with six rats in each. Group I served as vehicle control. Group II rats were given CsA at a dosage of 25 mg/kg body weight, orally for 21 days. Group III rats were given sulphated polysaccharides at a dosage of 5 mg/kg body weight, subcutaneously for 21 days. Group IV rats were given sulphated polysaccharides simultaneously along with CsA, as mentioned in Group II for 21 days. Results CsA provoked hepatotoxicity was evident from the decreased activities of hepatic marker enzymes. A significant rise in the level of oxidants, along with a striking decline in both the enzymic and non-enzymic antioxidants, marks the severity of oxidative stress in CsA-induced rats. This in turn led to enhanced levels of lipid peroxidation, 8-hydroxy-2-deoxy guanosine and protein carbonyls, along with a decrease in ATPase activities and alterations in lipid profile. Histopathological changes also strongly support the above aberrations. However, concomitant treatment with sulphated polysaccharides restored the above deformities to near control and prevented the morphological alterations significantly. Conclusion Thus, the present study highlights that sulphated polysaccharides can act therapeutically against CsA-induced hepatotoxicity. Key Words Cyclosporine A; hepatic markers; antioxidants; hyperlipidemia; macromolecules; sulphated polysaccharides.
S-Fluorenylmethyl protection of the cysteine side chain upon Nα-Fmoc deprotection
Johannes W. Wehner,Thisbe K. Lindhorst
Beilstein Journal of Organic Chemistry , 2012, DOI: 10.3762/bjoc.8.242
Abstract: Deprotection of an Nα-Fmoc-protected glycocysteine derivative 7 with an excess of morpholine unexpectedly led to the fluorenylmethyl-protected thioether 8 in high yield. The suggested mechanism for this reaction comprises the addition of the cysteine thiolate on the exocyclic double bond of dibenzofulvene, which is formed during Fmoc deprotection. The influence of base concentration on this transprotection reaction was studied.
Fast two-dimensional GC-MS with thermal extraction for anhydro-sugars in fine aerosols  [PDF]
Y. Ma,M. D. Hays,C. D. Geron,J. T. Walker
Atmospheric Chemistry and Physics Discussions , 2010,
Abstract: A fast two-dimensional gas chromatography (GC-MS) method that uses heart-cutting and thermal extraction (TE) and requires no chemical derivatization was developed for the determination of anhydro-sugars in fine aerosols. Evaluation of the TE-GC-GC-MS method shows high average relative accuracy (≥90%), reproducibility (≤10% relative standard deviation), detection limits of less than 3 ng/μL, and negligible carryover for levoglucosan, mannosan, and galactosan markers. TE-GC-GC-MS- and solvent extraction (SE)-GC-MS-measured levoglucosan concentrations correlate across several diverse types of biomass burning aerosols. Because the SE-GC-MS measurements were taken 8 years prior to the TE-GC-GC-MS ones, the stability of levoglucosan is established for quartz filter-collected biomass burning aerosol samples stored at ultra-low temperature (–45°C). Levoglucosan concentrations (w/w) in aerosols collected following atmospheric dilution near open fires of varying intensity are similar to those in biomass burning aerosols produced in a laboratory enclosure. An average levoglucosan-mannosan-galactosan ratio of 15:2:1 is observed for these two aerosol sets. TE-GC-GC-MS analysis of atmospheric aerosols from the US and Africa produced levoglucosan concentrations (0.01–1.6 μg/m3) well within those reported for aerosols collected globally and examined using different analytical techniques (0.004–7.6 μg/m3). Further comparisons among techniques suggest that fast TE-GC-GC-MS is among the most sensitive, accurate, and precise methods for compound-specific quantification of anhydro-sugars. In addition, an approximately twofold increase in aerosol sample throughput may be realized when combining TE with fast chromatography for anhydro-sugar determination.
Technical Note: Fast two-dimensional GC-MS with thermal extraction for anhydro-sugars in fine aerosols  [PDF]
Y. Ma,M. D. Hays,C. D. Geron,J. T. Walker
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010, DOI: 10.5194/acp-10-4331-2010
Abstract: A fast two-dimensional gas chromatography (GC-MS) method that uses heart-cutting and thermal extraction (TE) and requires no chemical derivatization was developed for the determination of anhydro-sugars in fine aerosols. Evaluation of the TE-GC-GC-MS method shows high average relative accuracy (≥90%), reproducibility (≤10% relative standard deviation), detection limits of less than 3 ng/μL, and negligible carryover for levoglucosan, mannosan, and galactosan markers. TE-GC-GC-MS- and solvent extraction (SE)-GC-MS-measured levoglucosan concentrations correlate across several diverse types of biomass burning aerosols. Because the SE-GC-MS measurements were taken 8 years prior to the TE-GC-GC-MS ones, the stability of levoglucosan is established for quartz filter-collected biomass burning aerosol samples stored at ultra-low temperature ( 50 °C). Levoglucosan concentrations (w/w) in aerosols collected following atmospheric dilution near open fires of varying intensity are similar to those in biomass burning aerosols produced in a laboratory enclosure. An average levoglucosan-mannosan-galactosan ratio of 15:2:1 is observed for these two aerosol sets. TE-GC-GC-MS analysis of atmospheric aerosols from the US and Africa produced levoglucosan concentrations (0.01–1.6 μg/m3) well within those reported for aerosols collected globally and examined using different analytical techniques (0.004–7.6 μg/m3). Further comparisons among techniques suggest that fast TE-GC-GC-MS is among the most sensitive, accurate, and precise methods for compound-specific quantification of anhydro-sugars. In addition, an approximately twofold increase in anhydro-sugar determination may be realized when combining TE with fast chromatography.
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