N-Heterocyclic Carbenes: Organocatalysts Displaying Diverse Modes of Action

2008 ◽  
pp. 158-180 ◽  
Author(s):  
K. Zeitler
Keyword(s):  
Heterocyclic Carbenes ◽  
Modes Of Action

Therapeutic options in male osteoporosis

2013 ◽  
Vol 22 (04) ◽  
pp. 271-276 ◽  
Author(s):  
P. Farahmand ◽  
J. D. Ringe
Keyword(s):  
Risk Factors ◽  
Vitamin D ◽  
Public Health Problem ◽  
Male Osteoporosis ◽  
Individual Risk ◽  
Modes Of Action ◽  
Increased Risk ◽  
Study Results ◽  
Long Term Treatment ◽  
Male Patients

SummaryOsteoporosis in men is increasingly recognized as an important public health problem but affected patients are still under-diagnosed and -treated. As in women the diagnostic and therapeutic strategy has to be adapted to the individual case. In the practical management it is very important to detect possible causes of secondary osteoporosis, to explain the possibilities of basic therapy counteracting individual risk factors and communicate that osteoporosis is a chronic disease and adherence to a long-term treatment is crucial. In established severe osteoporosis a careful analgesic therapy is important to avoid further bone loss related to immobility. In elderly men with increased risk of falling insufficient Vitamin D supply or impaired activation of Vitamin D due to renal insufficiency must be taken into consideration. Specific medications available today for the treatment of male osteoporosis comprise among antiresorptive drugs the bis phosphonates alendronate, risedronate and zoledronic acid. Denosumab, the first biological therapy is approved for men with androgen deprivation therapy for prostate cancer. An important advantage of this potent antiresorptive drug is the increased adherence due to the comfortable application by sixmonthly subcutaneous injections. Study results from the 2-year multi-center randomized controlled ADAMO-Study will very soon allow the use of denosumab in all types of male osteoporosis. Teriparatide, the 34 N-terminal amino acid sequence of parathyroid hormone was approved for men with osteoporosis as an anabolic agent based on proven efficacy by different studies. Among drugs with other modes of action the D-hormone pro-drug alfacalcidol can be used in men alone or in combination with the advantage of pleiotropic effects on calcium absorption, parathyroids, bone and muscle. Recently also Strontium-ranelate was approved for male patients with the limitation to exclude men with clinical relevant cardiovascular risk factors. In general the possibilities to treat male osteoporosis have considerably improved during recent years. Today there is a choice of a spectrum of drugs from mild to strong potency with different modes of action on bone turnover to design strategies for individual male patients.

Pesticides Modes of Action and Resistance: A Perspective from the 2019 IUPAC Congress

2019 ◽  
Vol 30 (4) ◽  
pp. 157-163 ◽  
Author(s):  
Franck E. Dayan ◽  
Geert Haesaert ◽  
Thomas Van Leeuwen ◽  
Lindy Holden-Dye ◽  
Andrew Crossthwaite ◽  
...  
Keyword(s):  
Modes Of Action

Aryl-substituted Triarsiranes: Synthesis and Reactivity

2020 ◽  
Author(s):  
André Schumann ◽  
Jonas Bresien ◽  
Malte Fischer ◽  
Christian Hering-Junghans
Keyword(s):  
Organic Chemistry ◽  
Electronic Structure ◽  
Heterocyclic Carbenes ◽  
Synthetic Approaches ◽  
Inorganic And Organic

Cyclotriarsanes are rare and limited synthetic approaches have hampered reactivity studies on these systems. Described in here is a scalable synthetic protocol towards (AsAr)<sub>3</sub> (Ar = Dip, 2,6-<sup>i</sup>Pr<sub>2</sub>-C<sub>6</sub>H<sub>3</sub>; Tip, 2,4,6-<sup>i</sup>Pr<sub>3</sub>-C<sub>6</sub>H<sub>2</sub>), which allowed to study their reactivity towards [Cp<sub>2</sub>Ti(C<sub>2</sub>(SiMe<sub>3</sub>)<sub>2</sub>], affording titanocene diarsene complexes and towards N-heterocyclic carbenes (NHCs) to give straightforward access to a variety of NHC-arsinidene adducts. The electronic structure of the titanium diarsene complxes has been studied and they are best described as Ti(IV) species with a doubly reduced As<sub>2</sub>Ar<sub>2</sub> ligand. These findings will make (AsAr)<sub>3</sub> valuable precursors in the synthetic inorganic and organic chemistry.

Application of Nitrogen Heterocyclic Carbenes in Organocatalysis

2020 ◽  
Vol 09 ◽  
Author(s):  
Minita Ojha ◽  
R. K. Bansal
Keyword(s):  
Asymmetric Catalysis ◽  
Building Blocks ◽  
Structural Features ◽  
Heterocyclic Carbenes ◽  
Stetter Reaction ◽  
Metal Pollutants ◽  
Synthetic Strategy ◽  
Wide Range ◽  
Benzoin Condensation ◽  
Nitrogen Heterocyclic

Background: During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes (NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods: By manipulating structural features and selecting appropriate substituent groups, it has been possible to control the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of Nalkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction. Results: The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions, isomerization, etc. The present review includes all these examples published during the last 10 years, i.e. from 2010 till date. Conclusion: The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They provide the synthetic strategy which does not burden the environment with metal pollutants and thus fit in the Green Chemistry.

Multi-chain action of exo-D-galacturonanase from carrot

1983 ◽  
Vol 48 (12) ◽  
pp. 3579-3588
Author(s):  
Kveta Heinrichová ◽  
Jana Perečková
Keyword(s):  
Optimal Condition ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Hydrolytic Cleavage ◽  
Chain Mechanism ◽  
Modes Of Action ◽  
Enzyme Degradation ◽  
Good Agreement

Two possible modes of action of exo-D-galacturonanase from carrot (E.C. 3.2.1.67) were investigated; this enzyme catalyses the sequential hydrolytic cleavage of pectants and oligogalacturonans by a terminal action from the nonreducing end of the molecule. The experiments indicate that the investigated exo-D-galacturonanase degrades these substrates by a predominantly multi-chain mechanism. Distribution of degradation products of oligomeric substrates (hexa- and pentagalacturonide) under an optimal condition for the action of the enzyme (pH and temperature) indicates that a multi-chain enzyme attack with a prevalent simple collision is involved. Results of the enzyme degradation kinetics are in a good agreement with the above-mentioned presumption.

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