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Topic: Stereoisomers


In the News (Tue 20 Aug 19)

  
  Stereoisomers
Stereoisomers always require that an additional nomenclature prefix be added to the IUPAC name in order to indicate their spatial orientation, for example, cis (Latin, meaning on this side) and trans (Latin, meaning across) in the 2-butene case.
Stereoisomers are also observed in certain disubstituted (and higher substituted) cyclic compounds.
As in the case of the 2-butene stereoisomers, disubstituted cycloalkane stereoisomers may be designated by nomenclature prefixes such as cis and trans.
www.cem.msu.edu /~reusch/VirtualText/sterisom.htm   (2189 words)

  
 FDA'S POLICY STATEMENT FOR THE DEVELOPMENT OF NEW STEREOISOMERIC DRUGS
Stereoisomers are molecules that are identical in atomic constitution and bonding, but differ in the three-dimensional arrangement of the atoms.
Stereoisomers include not only the mirror image enantiomers, but also geometric (cis/trans) isomers and diastereoisomers (isomers of drugs with more than one chiral center that are not mirror images of one another).
To develop a single stereoisomer from a mixture that has already been studied non-clinically, an abbreviated, appropriate pharmacology/toxicology evaluation could be conducted to allow the existing knowledge of the racemate available to the sponsor to be applied to the pure stereoisomer.
www.fda.gov /cder/guidance/stereo.htm   (1931 words)

  
 Stereoisomers Lab
The goal of this lesson is to explore the differences in molecular structure between stereoisomers, which are compounds that have the same molecular formula and the same atoms bonded to one another, but a different spatial arrangement between the atoms.
Stereoisomers may differ with regard to chemical reactivity and with regard to physical properties, such as melting and boiling points, internal energies, enthalpies of combustion, and optical activities.
In the Isomers Student Lab, the properties of stereoisomers in which groups are bonded on opposite sides of a planar double bond, such as in cis-1,2-dichloroethene (Figure 1) and trans-1,2-dichloroethene (Figure 2) are explored.
chemviz.ncsa.uiuc.edu /content/lab-s-stereo.html   (1498 words)

  
 Enumerating Stereoisomers and Tautomers
Stereoisomers and tautomers have the same molecular graph (excluding bonds to hydrogen atoms) and the same molecular formula.
Stereoisomers refer to compounds that differ only by the spatial arrangement of their atoms whereas tautomers are interchangeable forms involving the displacement of hydrogen atoms and electrons.
Stereoisomers are important when modeling the bioselectivity of ligands to stereo-specific enzymes, optical properties of compounds, chromatographic selectivity and chemical reactions.
www.mol-net.com /software/category/enumerating.html   (146 words)

  
 Stereoisomers
One property of stereoisomers is that they rotate plane-polarized light.
This rotation can be effectively demonstrated on an overhead projector by placing a shallow dish of sugar solution between two sheets of polarizing film.
Conclude the lesson by passing out samples of caraway and spearmint, which are stereoisomers which have noticeably different odors.
www.iit.edu /~smile/ch8806.html   (260 words)

  
 Enumerating Stereoisomers and Tautomers
Stereoisomers and tautomers have the same molecular graph (excluding bonds to hydrogen atoms) and the same molecular formula.
Stereoisomers refer to compounds that differ only by the spatial arrangement of their atoms whereas tautomers are interchangeable forms involving the displacement of hydrogen atoms and electrons.
Stereoisomers are important when modeling the bioselectivity of ligands to stereo-specific enzymes, optical properties of compounds, chromatographic selectivity and chemical reactions.
www.mol-net.de /software/category/enumerating.html   (146 words)

  
 Stereoselectivity of porcine {beta}-adrenergic receptors for ractopamine stereoisomers -- Mills et al. 81 (1): 122 -- ...
Stereoselectivity of porcine ß-adrenergic receptors for ractopamine stereoisomers
The mixture of stereoisomers was less efficacious than the RR stereoisomer at activating adenylyl cyclase.
RS stereoisomer was not stimulatory, a reduced response to RR stereoisomer would be expected in the presence of the RS isomer.
jas.fass.org /cgi/content/full/81/1/122   (3683 words)

  
 Isomers
Stereoisomers have the same molecular formula, same connectivity or order of atoms but the three dimensional orientation of their atoms are different.
Stereoisomers that are nonsuperimposable mirror images of each other are called stereoisomers.
Recall that stereoisomers are isomers that have the same connectivity of atoms but with different disposition of groups in space.
www.wiu.edu /users/mftkv/CHEM330(00)/stereoisomers.htm   (525 words)

  
 AllRefer.com - isomer : Stereoisomers (Chemistry) - Encyclopedia
Molecular disymmetry in optical isomers may come from some source other than an asymmetrical carbon atom, e.g., structural rigidity resulting from double bonds or ring structures within a molecule.
Stereoisomers are important in metabolism; in many cases only one of several isomeric forms of a compound can take part in biochemical reactions.
For example, there are 16 stereoisomers of a simple sugar whose molecular formula is C
reference.allrefer.com /encyclopedia/I/isomer-stereoisomers.html   (589 words)

  
 Technical Overview of Ecological Risk Assessment / EFED INTERIM POLICY FOR STEREOISOMERIC PESTICIDES | Pesticides: ...
The pesticide-inactive stereoisomer may or may not be toxic to non-target organisms.
One class of stereoisomers originates from the presence of an atom containing four different substituents (that is, the presence of an asymmetric atom, mostly referred to as a "chiral atom").
The other class of stereoisomers arises from the presence of a carbon-to-carbon double bond (-C=C-) and are known as geometric isomers.
www.epa.gov /oppefed1/ecorisk_ders/stereoisomer_policy.htm   (2501 words)

  
 Stereoisomerism - Wikipedia, the free encyclopedia
Stereoisomers are isomeric molecules whose atomic connectivity is the same but whose atomic arrangement in space is different.
Enantiomers are two stereoisomers that are related to each other by a reflection: they are mirror images of each other.
Diastereomers are stereoisomers not related through a reflection operation, they are not mirror images of each other.
en.wikipedia.org /wiki/Stereoisomer   (567 words)

  
 Isomerism - History, Nomenclature, Stereoisomerism, Stereoisomers, Conformers, Rotamers, Regioisomers
Because there is an empirical component to these terms, a universally unambiguous distinction between configurational stereoisomers (sometimes simply referred to as stereoisomers) and conformational stereoisomers (sometimes simply referred to as conformations or conformers) has not emerged.
There is a general understanding, however, that stereoisomers are geometrical forms that are distinct enough to be isolated under normal conditions, whereas conformers are geometrical forms that interconvert under the same conditions.
With two such centers, there are four stereoisomers possible (2 geometries at the one center × 2 at the second = 4), and with three such centers there are eight stereoisomers (2 × 2 × 2 = 8).
www.chemistryexplained.com /Hy-Kr/Isomerism.html   (1863 words)

  
 Stereoisomers
There are eight stereoisomers of 2,3,4,5-tetrahydroxypentanal, a group of compounds referred to as the aldopentoses.
As a result, two of the four possible stereoisomers of this compound are identical due to a plane of symmetry, so there are only three stereoisomeric tartaric acids.
The nomenclature terminology and classification of stereoisomers is examined in the next two problems, followed by a question concerning the relationship of isomeric pairs.
www.cem.msu.edu /~reusch/VirtualText/sterism3.htm   (4196 words)

  
 Effects of sphingosine stereoisomers on P-glycoprotein phosphorylation and vinblastine accumulation in ...
To investigate the role of protein kinase C (PKC) in the regulation of multidrug resistance and P-glycoprotein (P-gp) phosphorylation, the natural isomer of sphingosine (SPH), D-erythro sphingosine (De SPH), and its three unnatural stereoisomers were synthesized.
Treatment of MCF-7(ADR) cells with SPH stereoisomers decreased basal phosphorylation of the P-gp, suggesting inhibition of PKC-mediated phosphorylation of P-gp.
SPH stereoisomers did not inhibit specific binding of [H-3] VLB to MCF-7(ADR) cell membranes or [3H]azidopine photoaffinity labeling of P-gp or alter P-gp ATPase activity.
www.rti.org /abstract.cfm?pubid=5541   (315 words)

  
 Stereochemistry   (Site not responding. Last check: )
A chiral molecule and its mirror image molecule are called stereoisomers or enantiomers.
Pairs of stereoisomers are sometimes indistinguishable in chemical reactions, but can be distinguished by examining a physical property of the molecule.
For this reason, stereoisomers are also called optical isomers.
web.mit.edu /course/other/esgbio/www/chem/stereo.html   (594 words)

  
 Equal inhibition of HIV replication by stereoisomers of phosphatidyl-azidothymidine. Lack of stereospecificity of ...
Equal inhibition of HIV replication by stereoisomers of phosphatidyl-azidothymidine.
Glycerol-1-P and glycerol-3-P stereoisomers of dipalmitoylphosphatidylazidothymidine were synthesized and found to have equal antiretroviral activity in HIV-infected HT4-6C cells.
It was anticipated that the glycerol-1-P isomer would be less active because of slow metabolic conversion by cellular phospholipases A and C, but the antiretroviral results suggested that the human cell line (HT4-6C) may have phospholipases capable of hydrolyzing 2,3-dipalmitoyl-sn-glycerol-1-phospho-5'-azidothymidine (AZT).
www.aegis.com /aidsline/1993/jan/M9310738.html   (428 words)

  
 Ohmefentanyl and its stereoisomers: Chemistry and pharmacology - Publications - RTI International
This review summarizes both the initial studies on mixtures of ohmefentanyl stereoisomers and some more recent studies on the eight individual stereoisomers, in particular those in which the 3-methyl and 4-propionanilide substituents on the piperidine ring have a cis relationship to each other.
Analog studies, also on stereoisomer mixtures, have revealed that structural changes in the beta-hydroxy-beta-phenethyl portion of the molecule have considerable impact on the biological activity in the cis series while changes in the 4-propionanilide portion have smaller effects.
Since these stereoisomers differ from each other in their absolute stereochemistries, which focuses the analysis on asymmetric structural factors and avoids confounding changes in physiochemical characteristics, they constitute a unique set of molecular probes for investigation of mu receptor mediated phenomena.
www.rti.org /abstract.cfm?pubid=1069   (444 words)

  
 Introduction To Stereoisomers
If the two Chlorines had been attached to the same sp2 carbon, then that geminal isomer (See Fig 1-c) would be a constitutional isomer to both the cis and trans isomers since the Chlorine atoms on the Geminal isomer are connected to the same carbon as opposed to be connected to different carbons.
A second type of diastereoisomer is a stereoisomer that is called a meso isomer.
These stereoisomers come in "left handed" and "right handed" form and nature tends to favor one over the other.
members.aol.com /logan20/sterintr.html   (518 words)

  
 Stereoselective excision of thymine glycol from oxidatively damaged DNA -- Miller et al. 32 (1): 338 -- Nucleic Acids ...
The efficiencies are normalized with the most efficiently cleaved stereoisomer set to 1.0 to illustrate the selectivity of some of the enzymes studied.
Excision of Tg stereoisomers by mNTH as a function of time at 37°C. Oligonucleotide duplexes containing (5R,6S) or (5S,6R) stereoisomers of Tg (concentrations indicated) were incubated with 5 nM mNTH for 0–30 min under standard reaction conditions (Materials and Methods).
The (5S,6R) Tg stereoisomer is a competitive inhibitor of the (5R,6S) isomer.
nar.oxfordjournals.org /cgi/content/full/32/1/338   (4587 words)

  
 Drawing Stereoisomers
Enantiomers are just one class of "stereoisomers," i.e., molecules in which the atoms are connected to one another in the same order (same "connectivity") but have different spatial arrangement.
In the context of organic chemistry, the most common structural feature for a chiral molecule to have is a carbon atom bearing four different substituents, as shown in the diagram to the right.
For any given stereoisomer, only one of the other stereoisomers will be its enantiomer; these two are an "enantiomeric pair." Stereoisomers that are not enantiomers of one another are referred to as "diastereomers." Interestingly, the presence of multiple chiral centers within a molecule does not guarantee that the molecule itself will be chiral.
www.personal.psu.edu /faculty/t/h/the1/drawing.htm   (752 words)

  
 Inositol Stereoisomers Stabilize an Oligomeric Aggregate of Alzheimer Amyloid beta Peptide and Inhibit Abeta -induced ...
Inositol Stereoisomers Stabilize an Oligomeric Aggregate of Alzheimer Amyloid beta Peptide and Inhibit Abeta -induced Toxicity -- McLaurin et al.
Inositol has 8 stereoisomers, four of which are physiologically active.
stereoisomers were able to induce a structural transition in A
www.jbc.org /cgi/content/abstract/275/24/18495   (461 words)

  
 ChemCases: Nutrasweet - 1c. Stereoisomers
The spatial difference is a consequence of carbon’s hybridization and, in the case of Pair 4, restricted rotation.
To distinguish isomers without drawing the structures, terminology is used in the naming of compounds (nomenclature) to describe stereoisomers.
The importance of the concept of stereoisomers, particularly enantiomers, is dramatically evident in most biological processes that occur in the natural world, including something as routine and as pleasing as taste sensation.
www.chemcases.com /nutra/nutra1c.htm   (960 words)

  
 Valine Stereoisomers   (Site not responding. Last check: )
The next structure uses the wedge/dash system to attempt a 3-D representation of one enantiomer; by switching the positions of two ligands on the stereogenic center we obtain the other enantiomer, shown at right.
The orientation of the two is not quite the same, but they are placed in approximately mirror image positions.
The structure on the left is the "naturally"-occurring stereoisomer.
chemistry.umeche.maine.edu /CHY132/Valine.html   (304 words)

  
 Combined HPLC-MS and HPLC-NMR On-Line Coupling for the Separation and Determination of Lutein and Zeaxanthin ...
The determination and unambiguous identification of carotenoid stereoisomers from biological tissues, avoiding isomerization and oxidation due to the extraction process, is still a major challenge.
Particularly, the analysis of lutein and zeaxanthin stereoisomers is of great importance, as these are the main constituents of the macula lutea, the central part of the human retina, and act as possible agents in the prevention and treatment of age-related macular degeneration (AMD).
By using HPLC-MS with atmospheric pressure chemical ionization, the lutein stereoisomers can be distinguished from the zeaxanthin stereoisomers within one chromatographic run in the upper picogram range, whereas HPLC-NMR coupling allows the unequivocal identification of each stereoisomer with a concentration in the upper nanogram range.
pubs.acs.org /cgi-bin/jtext?ancham/73/i03/abs/ac000635g   (323 words)

  
 SparkNotes: Stereoisomers
Home : Math & Science : Chemistry Study Guides : Organic III : Stereoisomers
Ask a question or start a discussion on the SparkNotes community boards.
Study right for the SAT II Chemistry test with the experts at SparkNotes.
www.sparknotes.com /chemistry/organic3/stereoisomers   (51 words)

  
 CHEM 331, Organic Chemistry I   (Site not responding. Last check: )
In that case the number of stereoisomers will be reduced because of the presence of meso stereoisomers (see part i below).
However, molecule with more than one stereogenic carbons may have meso stereoisomers that are not chiral.
Arrangement of groups around a chiral atom characteristic of a stereoisomer.
www.towson.edu /~ryzhkov/handouts/stereo.html   (826 words)

  
 JCE 2005 (82) 1048 [Jul] Menthol Stereoisomers
The JCE Featured Molecules for July come from the paper by Edward M. Treadwell and T. Howard Black on the use of commercially available stereoisomers of menthol to illustrate properties of enantiomers and diastereomers.
Structures of all eight stereoisomers are included in this month’s molecule collection, labeled by the chirality of the three chiral atoms.
In addition to the exercises described in the paper, students can be asked to match the appropriate structures to those shown in the paper, or to generate structures for the isomers that are not discussed.
jchemed.chem.wisc.edu:8000 /journal/Issues/2005/Jul/abs1048.html   (331 words)

  
 Wiley::Basic Organic Stereochemistry
Stereoisomers are compounds with the same chemical formula and connectivity but with different arrangements of their atoms in 3-dimensional space.
Stereochemistry encompasses the study of stereoisomers and their properties.
Despite having an identical chemical formula, stereoisomers can have drastically different biological, medicinal, and chemical properties.
www.wiley.com /WileyCDA/WileyTitle/productCd-0471374997.html   (201 words)

  
 Determination of muscle-specific glucose flux using radioactive stereoisomers and microdialysis -- MacLean et al. 280 ...
Determination of muscle-specific glucose flux using radioactive stereoisomers and microdialysis -- MacLean et al.
Determination of muscle-specific glucose flux using radioactive stereoisomers and microdialysis
uptake; thus the use of radioactive stereoisomers in conjunction
ajpendo.physiology.org /cgi/content/abstract/280/1/E187   (355 words)

  
 Stereoisomers
Each model shown is one of 4 stereoisomers of the general formula:
Each pair of models, top and bottom, represents enantiomers; all other pairwise combinations represent diastereomers.
The four models shown represent 3 stereoisomers of the general formula:
classweb.gmu.edu /sslayden/graphics/stereo-pics.htm   (169 words)

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