scholarly journals Part I Bioinspired reactions in the synthesis of complex molecules Part II New generation of In(III)-pybox complex in asymmetric synthesis

2010 ◽  
Author(s):  
Junfeng Zhao
Keyword(s):  
Asymmetric Synthesis ◽  
Complex Molecules ◽  
New Generation

Synthesis of (R)-2-(1-hydroxycyclohexyl)-2-(4-methoxyphenyl)ethyl 4-Methylbenzenesulfonate

2014 ◽  
Vol 881-883 ◽  
pp. 465-468
Author(s):  
Dong Wang Liu ◽  
Lin Jun Tang ◽  
Li Ping Wang ◽  
Fei Fei Huang ◽  
Shuang Ping Huang ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Antidepressant Drug ◽  
Synthetic Route ◽  
New Generation

Venlafaxine (Figure 1) is the new generation antidepressant drug. A synthetic route to the asymmetric synthesis of (R)-venlafaxine through Evans Aldol protocol was designed. The key intermediate, (R)-2-(1-hydroxycyclohexyl)-2-(4-methoxyphenyl) ethyl4-methylbenzenesulfonate was prepared from cyclohexanone.

Asymmetric synthesis of (1R,2S)-2-fluorocyclopropylamine, the key intermediate of the new generation of quinolonecarboxylic acid, DU-6859

1992 ◽  
Vol 33 (24) ◽  
pp. 3487-3490 ◽  
Author(s):  
Osamu Tamura ◽  
Masaru Hashimoto ◽  
Yuko Kobayashi ◽  
Tadashi Katoh ◽  
Kazuhiko Nakatani ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
New Generation

The need for a new generation of substructure searching software

2021 ◽  
Vol 77 (5) ◽  
Author(s):  
Paul R. Raithby ◽  
Robin Taylor
Keyword(s):  
Three Dimensional ◽  
Molecular Fragments ◽  
Complex Molecules ◽  
Substructure Search ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structural Database ◽  
Mechanical Bonds ◽  
New Generation ◽  
Chemistry Community

Advances in synthetic chemistry mean that the molecules now synthesized include increasingly complex entities with mechanical bonds or extensive frameworks. For these complex molecular and supramolecular species, single-crystal X-ray crystallography has proved to be the optimal technique for determining full three-dimensional structures in the solid state. These structures are curated and placed in structural databases, the most comprehensive of which (for organic and metallo–organic structures) is the Cambridge Structural Database. A question of increasing importance is how users can search such databases effectively for these structures. Here some of the classes of complex molecules and supramolecules and the challenges associated with searching for them are highlighted. The idea of substructure searches that involve topological searches as well as searches for molecular fragments is developed, and significant enhancements are proposed to substructure search programs that are both achievable and highly beneficial for both the database user community and the broader chemistry community.

ChemInform Abstract: Asymmetric Synthesis of (1R,2S)-2-Fluorocyclopropylamine, the Key Intermediate of the New Generation of Quinolonecarboxylic Acid, DU- 6859.

ChemInform ◽  
2010 ◽  
Vol 23 (48) ◽  
pp. no-no
Author(s):  
O. TAMURA ◽  
M. HASHIMOTO ◽  
Y. KOBAYASHI ◽  
T. KATOH ◽  
K. NAKATANI ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
New Generation

scholarly journals Static to inducibly dynamic stereocontrol: The convergent use of racemic β-substituted ketones

Science ◽  
2020 ◽  
Vol 369 (6507) ◽  
pp. 1113-1118 ◽  
Author(s):  
Jacob S. DeHovitz ◽  
Yong Yao Loh ◽  
Jacob A. Kautzky ◽  
Kazunori Nagao ◽  
Andrew J. Meichan ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Photoredox Catalysis ◽  
Radical Species ◽  
Complex Molecules ◽  
Precise Control ◽  
Narrow Scope ◽  
Synthetic Routes

The synthesis of stereochemically complex molecules in the pharmaceutical and agrochemical industries requires precise control over each distinct stereocenter, a feat that can be challenging and time consuming using traditional asymmetric synthesis. Although stereoconvergent processes have the potential to streamline and simplify synthetic routes, they are currently limited by a narrow scope of inducibly dynamic stereocenters that can be readily epimerized. Here, we report the use of photoredox catalysis to enable the racemization of traditionally static, unreactive stereocenters through the intermediacy of prochiral radical species. This technology was applied in conjunction with biocatalysts such as ketoreductases and aminotransferases to realize stereoconvergent syntheses of stereodefined γ-substituted alcohols and amines from β-substituted ketones.

Finding the Right Problems: Some HREM Applications to Interfaces

1984 ◽  
Vol 42 ◽  
pp. 376-379
Author(s):  
D. Cherns
Keyword(s):  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Atomic Structures ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Point To Point ◽  
The Right ◽  
New Generation ◽  
Better Than

The use of high resolution electron microscopy (HREM) to determine the atomic structure of grain boundaries and interfaces is a topic of great current interest. Grain boundary structure has been considered for many years as central to an understanding of the mechanical and transport properties of materials. Some more recent attention has focussed on the atomic structures of metalsemiconductor interfaces which are believed to control electrical properties of contacts. The atomic structures of interfaces in semiconductor or metal multilayers is an area of growing interest for understanding the unusual electrical or mechanical properties which these new materials possess. However, although the point-to-point resolutions of currently available HREMs, ∼2-3Å, appear sufficient to solve many of these problems, few atomic models of grain boundaries and interfaces have been derived. Moreover, with a new generation of 300-400kV instruments promising resolutions in the 1.6-2.0 Å range, and resolutions better than 1.5Å expected from specialist instruments, it is an appropriate time to consider the usefulness of HREM for interface studies.

Alkaline Dissociation Products of Lumbricus Terrestris Hemoglobin Viewed with the STEM

1981 ◽  
Vol 39 ◽  
pp. 434-435
Author(s):  
O. H. Kapp ◽  
M. Ohtsuki ◽  
N. Robin ◽  
S. N. Vinogradov ◽  
A. V. Crewe
Keyword(s):  
Carbon Film ◽  
Lumbricus Terrestris ◽  
Uranyl Acetate ◽  
Acetate Solution ◽  
Oxygen Carriers ◽  
Complex Molecules ◽  
Thin Carbon ◽  
Thin Carbon Film ◽  
Multiple Copies ◽  
Hill Coefficients

Annelid extracellular hemoglobins are among the largest known proteins (M.W = 3.9 x 106), and together with the hemocyanins are the largest known oxygen carriers. They display oxygen affinities generally higher than those o vertebrate hemoglobins with Hill coefficients ranging from slightly higher than unity to values as high as 5-6. These complex molecules are composed of multiple copies of as many as six different polypeptides and posse: approximately 150 hemes per molecule.The samples were diluted to 100-200 μg/ml with distilled water just before application to a thin carbon film (∽15 Å thick). One percent (w/v) uranyl acetate solution was used for negative staining for 2 minutes and dried in air. The specimens were examined with the high resolution STEM. Their general appearance is that of a hexagonal bilayer (Fig. 1), each layer consisting of six spheroidal subunits. The corner to corner hexagonal dimensic is approximately 300 Å and the bilayer thickness approximately 200 Å.

Total etch dentin bonding systems: scanning electron microscopy of the resin-dentin hybrid layer

1992 ◽  
Vol 50 (2) ◽  
pp. 1092-1093
Author(s):  
Jorge Perdigao
Keyword(s):  
Composite Resin ◽  
Mechanical Interlocking ◽  
Hybrid Layer ◽  
Agent Based ◽  
Dentin Bonding ◽  
Acid Agent ◽  
Bond Strengths ◽  
Main Component ◽  
Bonding Systems ◽  
New Generation

In 1955, Buonocore introduced the etching of enamel with phosphoric acid. Bonding to enamel was created by mechanical interlocking of resin tags with enamel prisms. Enamel is an inert tissue whose main component is hydroxyapatite (98% by weight). Conversely, dentin is a wet living tissue crossed by tubules containing cellular extensions of the dental pulp. Dentin consists of 18% of organic material, primarily collagen. Several generations of dentin bonding systems (DBS) have been studied in the last 20 years. The dentin bond strengths associated with these DBS have been constantly lower than the enamel bond strengths. Recently, a new generation of DBS has been described. They are applied in three steps: an acid agent on enamel and dentin (total etch technique), two mixed primers and a bonding agent based on a methacrylate resin. They are supposed to bond composite resin to wet dentin through dentin organic component, forming a peculiar blended structure that is part tooth and part resin: the hybrid layer.

Low-voltage, high-resolution scanning electron microscopy of polymers

1987 ◽  
Vol 45 ◽  
pp. 466-467 ◽  
Author(s):  
S. J. Krause ◽  
W.W. Adams ◽  
S. Kumar ◽  
T. Reilly ◽  
T. Suziki
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Low Voltage ◽  
Chromatic Aberration ◽  
Image Resolution ◽  
Resolution Limit ◽  
Crossover Point ◽  
New Generation ◽  
Beam Damage ◽  
Scanning Electron

Scanning electron microscopy (SEM) of polymers at routine operating voltages of 15 to 25 keV can lead to beam damage and sample image distortion due to charging. Imaging polymer samples with low accelerating voltages (0.1 to 2.0 keV), at or near the “crossover point”, can reduce beam damage, eliminate charging, and improve contrast of surface detail. However, at low voltage, beam brightness is reduced and image resolution is degraded due to chromatic aberration. A new generation of instruments has improved brightness at low voltages, but a typical SEM with a tungsten hairpin filament will have a resolution limit of about 100nm at 1keV. Recently, a new field emission gun (FEG) SEM, the Hitachi S900, was introduced with a reported resolution of 0.8nm at 30keV and 5nm at 1keV. In this research we are reporting the results of imaging coated and uncoated polymer samples at accelerating voltages between 1keV and 30keV in a tungsten hairpin SEM and in the Hitachi S900 FEG SEM.

Sign in / Sign up

Export Citation Format

Share Document