Ag-mediated synthesis of six-membered N-heterocycles

Abstract

One of the highly emerging and an important aspect of organic chemistry is the metal catalyzed synthesis of heterocycles. The methods used earlier for the synthesis of heterocycles were significant in the organic synthesis and developing cost-effective, improved and facial methods were beneficial to construct the complex architectures. For the both stereoselective and regioselective synthesis of six-membered nitrogen containing heterocycles, cyclic reactions that are Ag-mediated have known to be very efficient. The present review covers the applications of Ag in the formation of six-membered nitrogen containing heterocycles.     

Analysis of certain mixtures ofα-Amino acids

Summary -Amino acids are determined by reaction with perinaphthindan-2,3,4-trione hydrate to form dihydroxyperinaphthindenone which is titrated with chloramine-T in the presence of acidified bromide and methyl red. The thiol group of cysteine is blocked by cyano-ethylation before determination. Some amino acids can be directly titrated with chloramine-T in the presence of bromide and methyl red, e. g., cysteine (after cyanoethylation), methionine and lanthionine, or in the presence of iodide and starch, e. g., cysteine (after tetrathionate reaction) when concomitant amino acids do not interfere. These methods are used to analyze model mixtures of cysteine with serine, methionine with glycine and cysteine with methionine.

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Analyse bestimmter Gemische von -Aminosäuren

Zusammenfassung -Aminosäuren werden mit Peri-Naphthindan-2,3,4-trion-hydrat umgesetzt, wobei sich Dihydroxyperinaphthindenon bildet, das mit Chloramin T in der Gegenwart von angesäuertem Bromid und Methylrot titriert wird. Die Thiolgruppe des Cysteins wird vor der Bestimmung durch Cyanoäthylierung blockiert. Manche Aminosäuren können unmittelbar mit Chloramin T in der Gegenwart von Bromid und Methylrot titriert werden, z. B. Cystein (nach Cyanoäthylierung), Methionin und Lanthionin, oder in Gegenwart von Jodid und Stärke Cystein (nach Umsetzung mit Tetrathionat), wenn die begleitende Aminosäure nicht stört. Diese Verfahren wurden benutzt, um Modellgemische von Cystein mit Serin, Methionin mit Glycin und Cystein mit Methionin zu analysieren.

     

Efficient and simple colorimetric fluoride ion sensor based on receptors having urea and thiourea binding sites

[structure: see text] Novel colorimetric receptors for selective fluoride ion sensing containing anthraquinone as chromogenic signaling subunit and urea (N,N' '-(9,10-dihydro-9,10-dioxo-1,2-anthracenediyl)bis[N'-phenyl])/thiourea (N,N' '-(9,10-dihydro-9,10-dihydro-9,10-dioxo-1,2-antrhacenediyl)bis[N-phenyl]) binding sites have been reported. These receptors have shown no affinity for other halide ions (Cl-, Br-, and I- ions). Well-defined color change in the visible region of the spectrum was observed upon addition of fluoride ion in DMSO/CH3CN solution of the receptors 1 and 2.     

Synthesis of 3,4-di-O-acylated glucose-derived furanoid sugar amino acids (Gaa): conformational analysis of a Leu-enkephalin analog containing di-O-myristoylated Gaa

3,4-Di-O-acylated derivatives 1-3 of a glucose-derived furanoid sugar amino acid (Gaa) were synthesized as novel peptide building blocks to study their effects on peptide conformation. Structural analysis of the di-O-myristoylated Gaa 3-containing Leu-enkephalin analog 4 by various NMR techniques and constrained molecular dynamics (MD) simulation studies established a well-defined β-turn structure in DMSO-d₆ with an intramolecular hydrogen bond between PheNH → TyrCO.     

Stereoselective synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone

A stereoselective synthesis of the pentaketide lactone (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone has been achieved.     

Hydroxymethylation and cyanoethylation of nitroimidazoles

A series of nitroimidazoles were subjected to hydroxymethylations under a variety of conditions. Hydroxymethylation of 1-(2-hydroxyethyl), 1-(2-acetoxyethyl), and 1-(2-chloroethyl) substituted 5-nitroimidazoles with paraformaldehyde in dimethyl sulfoxide yielded the respective 2-hydroxymethyl analogs (5–7). However, attempts to hydroxymethylate 1-(2-hydroxyethyl), 1-(2-acetoxyethyl), 1-(2-cyanoethyl) substituted 4-nitroimidazoles and 1-(2-hydroxyethyl)-2-nitroimidazole were unsuccessful. Treatment of 1-(2-acetoxyethyl)-5-nitro-2-imidazolecar-baldehyde(10) with hydroxylamine-O-sulfonic acid afforded a mixture of corresponding 2-carbonitrile (12) and 2-(N-hydroxy)carboximidamide (13). Hydrolysis of 10 with ethanolic hydrochloric acid yielded 8-ethoxy-5,6-dihydro-3-nitro-8H-imidazo[2,1-c] [1,4]oxazine (11) which, on subsequent reaction with hydroxylamine-O-sulfonic acid, afforded 1-(2-hydroxyethyl)-5-nitroimidazole-2-(N-hydroxy)carboximidamide (15). Reaction of 4(5)-nitroimidazole with chloropropionitrile produced a mixture of the isomeric 1-(2-cyanoethyl) substituted 4- and 5-nitroimidazoles. Treatment of 2,4(5)-dinitroímidazole with chloropropionitrile afforded a mixture of 4(5)-chloro-5(4)-nitroimidazole and 1-(2-cyanoethyl)-4-nitro-5-chloroimidazoIe. Reaction of nitroimidazoles with acrylonitrile in the presence of Triton B yielded the corresponding 1-(2-cyanoethyl) substituted derivatives.     

A novel tetracyclic ring system. 10H-tetrazolo[5′,1′:3,4][1,2,4]triazino[5,6-b]indole

The reaction of 3-hydrazino-1,2,4-triazino[5,6-b]indole with nitrous acid affords a novel tetracyclic ring system: 10H-tetrazolo[5′,1′:3,4][1,2,4]triazino[5,6-b]indole. The mode of cyclization has been discussed.     

A new sphingolipid from the gorgonian Junceella juncea of the Indian Ocean

A new sphingolipid, (2S,3R,4E)-1,3-dihydroxy-2-[(nonadecanoyl) amino]-octadec-4-ene (1) along with ubiquitous batyl alcohol is isolated from the gorgonian, Junceella juncea Pallas (Gorgonaceae) of the Indian Ocean. The structure of 1 is determined on the basis of 1H- and 13C-NMR, COSY, FABMS, and GC-EIMS experiments.     

Novel Synthesis of Mafenide and Other Amino Sulfonamides by Electrochemical Reduction of Cyano Sulfonamides

Both aliphatic and aromatic amino sulfonamides such as mafenide ( 1a ) were synthesized in good yields (80–86%) by direct electrochemical hydrogenation of the corresponding nitriles in an undivided cell containing a Ni cathode, a Pt anode, and Raney Ni as catalyst (Table 1). The reaction can be performed without external supply of pressurized gas by in situ generation of H₂. Slightly elevated temperatures (45°) and low current densities (10 mA/cm²) are favorable conditions for this type of electrochemical nitrile hydrogenation. Our synthetic protocol does not require high‐pressure equipment or chemical hazards, is environmentally very friendly, and more economical than traditional methods. The concentration of adsorbed H^. radicals on the catalyst surface can be easily controlled by adjusting the electric potential, which may lead to improved product selectivity and, at the same time, reduces the risk of explosion and fire.     

Laboratory investigation of biodegradability of a polyurethane foam under anaerobic conditions

Polyurethane (PU) foams can be used in many remediation applications as an isolation material to prevent the release of hazardous materials into the environment. The integrity of a PU foam was investigated in this study using short-term accelerated laboratory experiments including bioavailability assays, soil burial experiments, and accelerated bioreactors to determine the fate of PU foam in the soil where anaerobic processes are dominant. The experimental results have shown that the studied PU foam is likely not biodegradable under anaerobic conditions. Neither weight loss nor a change in the tensile strength of the PU material after biological exposure was observed. The FT-IR chemical signature of the PU foams was also nearly identical before and after biological exposure. The composition of the PU material (aromatic polyester and polyether PU) used in this study could have played a significant role in its resistance to microbial attack during the short-term accelerated experiments.