scholarly journals High-Yield and Sustainable Synthesis of Quinoidal Compounds Assisted by Keto-Enol Tautomerism

2021 ◽  
Author(s):  
Cheng Wang ◽  
Rongjin Li ◽  
Yanfeng Dang ◽  
Haipeng Wei ◽  
Yu Jiang ◽  
...  
Keyword(s):  
High Yield ◽  
Air Oxidation ◽  
Subsequent Oxidation

The classical synthesis of quinoids, which involves Takahashi coupling and subsequent oxidation, often gives only low to medium yields. Herein, we disclose keto-enol-tautomerism-assisted spontaneous air oxidation of the coupling products...

Practical Synthesis of 2'-5'-Linked Oligoadenylates (2-5A Oligomers)

1992 ◽  
Vol 45 (1) ◽  
pp. 205 ◽  
Author(s):  
R Noyori ◽  
M Uchiyama ◽  
T Nobori ◽  
M Hirose ◽  
Y Hayakawa
Keyword(s):  
Ethyl Acetate ◽  
Second Order ◽  
High Yield ◽  
Similar Reaction ◽  
Reaction Sequence ◽  
Facile Synthesis ◽  
One Pot ◽  
Subsequent Oxidation ◽  
Practical Synthesis ◽  
Related Compounds

A general, facile synthesis of 2'-5'-linked oligonucleotides (2-5A oligomers ) has been achieved based on the second-order regioselective protection of adenosine, one-pot formation of the 2'5' internucleotide linkage, and O-selective phosphorylation of N-unblocked nucleosides. Standard t- butyldimethylsilylation of 5'-O-p-methoxytrityladenosine followed by careful recrystallization from a mixture of triethylamine , methanol, ethyl acetate and ether (4 : 4 : 5 : 100 v/v) gives the 3',5'-di-O-protected adenosine in high yield. Magnesium alkoxide -mediated condensation of the 2'-O-free adenosine with o-chlorophenyl p-nitrophenyl phosphorochloridate followed by 2',3'-di-O-t-butyldimethylsilyladenosine produces the N-free and fully O-protected adenylyl (2'-5')adenosine. The resulting adenylyl dimer, after removal of the 5'-O-trityl protector, is elongated to the protected trimeric compound through a similar reaction sequence. Deprotection of the product furnishes the 2-5A core. Condensation of the 5?-0-detritylated core and bis (2,2,2-trichloroethyl) phosphorochloridite assisted by 2,6-lutidine and subsequent oxidation with aqueous iodine produces, after deblocking, 2-5A 5'-monophosphate (p5'A2'p5'pA2'p5'A). The 2-5A 5'-monophosphate is converted into 2-5A 5'-triphosphate (ppp5'A2'p5'A2'p5'A) by reaction with N,N'-carbonyldiimidazole in the presence of triethylamine followed by tributylammonium diphosphate. This procedure allows ready synthesis of 2-5A oligomers and related compounds on a multigram scale.

A convenient synthesis of 1,4-benzoquinones

2019 ◽  
Vol 43 (3-4) ◽  
pp. 124-126
Author(s):  
Yong-Fu Qiu ◽  
Bin Lu ◽  
Yi-Yu Yan ◽  
Wan-Yue Luo ◽  
Zhen-Qiu Gao ◽  
...  
Keyword(s):  
High Yield ◽  
Subsequent Oxidation ◽  
Convenient Synthesis

A series of 1,4-benzoquinones was prepared in a high yield by a two-step reaction starting from 2,3,4,5-tetramethoxytoluene by a Blanc reaction and subsequent oxidation.

Facile separation of the subunits of ovine and bovine gonadotrophins by high-performance liquid chromatrography: microheterogeneity and biological activity

1991 ◽  
Vol 130 (3) ◽  
pp. 415-424 ◽  
Author(s):  
M. R. Sairam
Keyword(s):  
High Performance ◽  
High Yield ◽  
Complete Analysis ◽  
Dilute Acid ◽  
Air Oxidation ◽  
Preparative Scale ◽  
Α Subunit ◽  
Prolonged Incubation ◽  
Multiple Components ◽  
Yield And Quality

ABSTRACT The α and β subunits of ovine and bovine gonadotrophins which undergo instant dissociation in 0·1% (v/v) trifluoroacetic acid in water could be separated into their multiple components by reverse-phase high-performance liquid chromatography on analytical and preparative scales. Several batches of highly purified ovine LH (oLH) separated into four α components (α1 to α4) and five β components (β1 to β5). While the major α component (α3) remained the same in all, the β subunit was variable in all these prepartions of oLH of equal biological and immunoreactivity. Various manipulations, such as prolonged incubation in dilute acid or alkali or conditions prone to air oxidation, did not change elution patterns or produce interconversions among the α or β components, suggesting that microheterogeneity arose in the pituitary itself or during its collection. The subunits obtained on a preparative scale were of high yield and quality and recombined (100%) to produce fully active LH or FSH. Chemical deglycosylations in which 75–80% of the peripheral sugars were removed shifted the elution of all components (a as well as β) slightly but modifications to the protein backbone by other reagents changed the profile of the α subunit. Obtaining the various α and β components in high yield would permit a complete analysis of gonadotrophin microheterogeneity. Journal of Endocrinology (1991) 130, 415–424

scholarly journals Phosphoramidite building blocks with protected nitroxides for the synthesis of spin-labeled DNA and RNA

2018 ◽  
Vol 14 ◽  
pp. 1563-1569 ◽  
Author(s):  
Timo Weinrich ◽  
Eva A Jaumann ◽  
Ute M Scheffer ◽  
Thomas F Prisner ◽  
Michael W Göbel
Keyword(s):  
Building Blocks ◽  
High Yield ◽  
Spin Labels ◽  
Molecular Models ◽  
Protective Group ◽  
Air Oxidation ◽  
Nitroxide Radicals ◽  
Complementary Dna ◽  
Dna And Rna ◽  
Standard Procedures

TEMPO spin labels protected with 2-nitrobenzyloxymethyl groups were attached to the amino residues of three different nucleosides: deoxycytidine, deoxyadenosine, and adenosine. The corresponding phosphoramidites could be incorporated by unmodified standard procedures into four different self-complementary DNA and two RNA oligonucleotides. After photochemical removal of the protective group, elimination of formic aldehyde and spontaneous air oxidation, the nitroxide radicals were regenerated in high yield. The resulting spin-labeled palindromic duplexes could be directly investigated by PELDOR spectroscopy without further purification steps. Spin–spin distances measured by PELDOR correspond well to the values obtained from molecular models.

Quality films from carbon fiber evaporation for thorough coverage of TEM grids

1988 ◽  
Vol 46 ◽  
pp. 418-419
Author(s):  
N. Tempel ◽  
M. C. Ledbetter
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Carbon Films ◽  
Low Noise ◽  
Vacuum Evaporation ◽  
High Yield ◽  
Good Adhesion ◽  
Noise Structure ◽  
Resolution Electron ◽  
Carbon Foils

Carbon films have been a support of choice for high resolution electron microscopy since the introduction of vacuum evaporation of carbon. The desirable qualities of carbon films and methods of producing them has been extensively reviewed. It is difficult to get a high yield of grids by many of these methods, especially if virtually all of the windows must be covered with a tightly bonded, quality film of predictable thickness. We report here a method for producing carbon foils designed to maximize these attributes: 1) coverage of virtually all grid windows, 2) freedom from holes, wrinkles or folds, 3) good adhesion between film and grid, 4) uniformity of film and low noise structure, 5) predictability of film thickness, and 6) reproducibility.Our method utilizes vacuum evaporation of carbon from a fiber onto celloidin film and grid bars, adhesion of the film complex to the grid by carbon-carbon contact, and removal of the celloidin by acetone dissolution. Materials must be of high purity, and cleanliness must be rigorously maintained.

Effects of high pressure on the crystallization of carbon fiber reinforced polyetheretherketone (CF/PEEK) laminate composites

1990 ◽  
Vol 48 (4) ◽  
pp. 876-877
Author(s):  
Hong-Ming Lin ◽  
C. H. Liu ◽  
R. F. Lee
Keyword(s):  
High Pressure ◽  
Carbon Fiber ◽  
Sample Surface ◽  
High Yield ◽  
Fiber Reinforced ◽  
Laminate Composites ◽  
Peek Composite ◽  
Continuous Carbon Fiber ◽  
Carbon Fiber Reinforced

Polyetheretherketone (PEEK) is a crystallizable thermoplastic used as composite matrix materials in application which requires high yield stress, high toughness, long term high temperature service, and resistance to solvent and radiation. There have been several reports on the crystallization behavior of neat PEEK and of CF/PEEK composite. Other reports discussed the effects of crystallization on the mechanical properties of PEEK and CF/PEEK composites. However, these reports were all concerned with the crystallization or melting processes at or close to atmospheric pressure. Thus, the effects of high pressure on the crystallization of CF/PEEK will be examined in this study.The continuous carbon fiber reinforced PEEK (CF/PEEK) laminate composite with 68 wt.% of fibers was obtained from Imperial Chemical Industry (ICI). For the high pressure experiments, HIP was used to keep these samples under 1000, 1500 or 2000 atm. Then the samples were slowly cooled from 420 °C to 60 °C in the cooling rate about 1 - 2 degree per minute to induce high pressure crystallization. After the high pressure treatment, the samples were scanned in regular DSC to study the crystallinity and the melting temperature. Following the regular polishing, etching, and gold coating of the sample surface, the scanning electron microscope (SEM) was used to image the microstructure of the crystals. Also the samples about 25mmx5mmx3mm were prepared for the 3-point bending tests.

Catalytic enantioselective synthesis of indolizino[8,7-b]indole alkaloid derivatives based on the tandem reaction of tertiary enamides

2021 ◽  
Author(s):  
Xin-Ming Xu ◽  
Ming Xie ◽  
Jiazhu Li ◽  
Mei-Xiang Wang
Keyword(s):  
Indole Alkaloid ◽  
Enantioselective Synthesis ◽  
High Yield ◽  
Tandem Reaction ◽  
Indole Derivatives

An exquisite Pybox/Cu(OTf)2-catalyzed asymmetric tandem reaction of tertiary enamides was developed, which enabled the expeditious synthesis of indolizino[8,7-b]indole derivatives in high yield, excellent enantioselectivity and diastereoselectivity.

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