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Homochiral

A particular point of interest included in these hehcal complexes concerns the chirality. The heUcates obtained from the achiral strands are a racemic mixture of left- and right-handed double heUces (Fig. 34) (202). This special mode of recognition where homochiral supramolecular entities, as a consequence of homochiral self-recognition, result from racemic components is known as optical self-resolution (203). It appears in certain cases from racemic solutions or melts (spontaneous resolution) and is often quoted as one of the possible sources of optical resolution in the biological world. On the other hand, the more commonly found process of heterochiral self-recognition gives rise to a racemic supramolecular assembly of enantio pairs (204). [Pg.194]

One of the homochiral starting materials (45) for the acetylcholinesterase (ACE) inhibitor captopril [62571 -86-2] (47) is produced by a Hpase enzyme-catalyzed resolution of racemic 3-methyl-4-acetylthiobutyric acid (44) and L-proline (46) (65). [Pg.242]

Fig. 7. Preparation of Alpine-borane (93) and use in the synthesis of homochiral butyrolactones and arylhydroxytetronic acids. Rg and denote small and... Fig. 7. Preparation of Alpine-borane (93) and use in the synthesis of homochiral butyrolactones and arylhydroxytetronic acids. Rg and denote small and...
Over 50% of clinically available dmgs have chiral centers and only about 10% of synthetic chiral dmgs are marketed in homochiral (enantiomerically pure) form (33). In contrast, dmgs that are naturally occurring substances, obtained from or related to naturally occurring molecules, are frequendy homochiral. [Pg.273]

There is increasing pressure to develop homochiral dmgs (34). Growing demands are faced by the pharmaceutical industry in dmg development to consider chiral issues in the eady preclinical phases of dmg design and synthesis. [Pg.273]

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). [Pg.359]

Derivatization with Optically Active Reagents and Separation on Achiral Columns. This method has been reviewed (65) a great number of homochiral derivatizing agents (HD A) are described together with many appHcations. An important group is the chloroformate HD As. The reaction of chloroformate HD As with racemic, amino-containing compounds yields carbamates, which are easily separated on conventional hplc columns, eg (66),... [Pg.279]

Preparation of enantiomerically enriched materials by use of chiral catalysts is also based on differences in transition-state energies. While the reactant is part of a complex or intermediate containing a chiral catalyst, it is in a chiral environment. The intermediates and complexes containing each enantiomeric reactant and a homochiral catalyst are diastereomeric and differ in energy. This energy difference can then control selection between the stereoisomeric products of the reaction. If the reaction creates a new stereogenic center in the reactant molecule, there can be a preference for formation of one enantiomer over the other. [Pg.92]

The reaction products are the same for both direct irradiation and acetophenone sensitization. When the reactant B is used in homochiral form, the product D is nearly racemic (6% e.e.). Relate the formation of the cyclobutanones to the more normal products of type E and E Why does the 5-aryl substituent favor formation of the cyclobutanones Give a complete mechanism for formation of D which is consistent with the stereochemical result. [Pg.786]

Homochiral thiiranium and aziridinium ion intermediates formed by Lewis acid-induced rearrangement of l-hetero-2, 3-epoxides 97SL11. [Pg.243]

In recent years, enantioselective variants of the above transannular C-H insertions have been extensively stiidied. The enantiodetermining step involves discrimination between the enantiotopic protons of a meso-epoxide by a homochiral base, typically an organolithium in combination with a chiral diamine ligand, to generate a chiral nonracemic lithiated epoxide (e.g., 26 Scheme 5.8). Hodgson... [Pg.148]

Different optical enantiomers of amino acids also have different properties. L-asparagine, for example, tastes bitter while D-asparagine tastes sweet (see Figure 8.3). L-Phenylalanine is a constituent of the artificial sweetener aspartame (Figure 8.3). When one uses D-phenylalanine the same compound tastes bitter. These examples clearly demonstrate the importance of the use of homochiral compounds. [Pg.239]

This review is not comprehensive but emphasizes the more recent literature through 1985 into early 1986. References to earlier work are included in an affort to make the subject understandable to those unfamiliar with past research and also to cover topics not touched upon in recent publications. The term optically active is used here in the sense that the chiral molecule under discussion is nonracemic but not necessarily enantiomerically pure. The terms homochiral and optically pure are used synonymously with enantiomerically pure. [Pg.56]

Racemic mixtures of sulfoxides have often been separated completely or partially into the enantiomers. Various resolution techniques have been used, but the most important method has been via diastereomeric salt formation. Recently, resolution via complex formation between sulfoxides and homochiral compounds has been demonstrated and will likely prove of increasing importance as a method of separating enantiomers. Preparative liquid chromatography on chiral columns may also prove increasingly important it already is very useful on an analytical scale for the determination of enantiomeric purity. [Pg.56]

Preparation of the appropriate optically active sulfmate ester is initially required for reaction with a Grignard or other organometallic reagent. If the method is to produce homochiral sulfoxides, the precursor sulfmate ester must be optically pure. An exception to this statement occurs if the reaction yields a partially racemic sulfoxide which can be recrystallized to complete optical purity. [Pg.60]


See other pages where Homochiral is mentioned: [Pg.171]    [Pg.482]    [Pg.237]    [Pg.238]    [Pg.238]    [Pg.239]    [Pg.241]    [Pg.241]    [Pg.242]    [Pg.242]    [Pg.243]    [Pg.244]    [Pg.249]    [Pg.249]    [Pg.263]    [Pg.263]    [Pg.29]    [Pg.61]    [Pg.69]    [Pg.336]    [Pg.348]    [Pg.75]    [Pg.92]    [Pg.157]    [Pg.161]    [Pg.135]    [Pg.261]    [Pg.264]    [Pg.265]    [Pg.266]    [Pg.266]    [Pg.267]    [Pg.74]    [Pg.139]    [Pg.164]    [Pg.56]   
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See also in sourсe #XX -- [ Pg.30 ]

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Achirality homochirality classes

Aldol reactions homochiral

Alkenyloxydialkylboranes homochiral

Bases homochiral

Biochemical Homochirality

Biological homochirality

Biomolecular homochirality

Borane, alkenyloxydialkylaldol reactions homochiral

Borane, alkenyloxydirected aldol reactions homochiral

Boyer and Lallemand homochiral -calystegines

Chiral separation homochiral

Enantiomers homochirality classes

Enantiomorphs homochirality classes

Epoxides homochiral

Erythronolides via reactions of organocuprates and homochiral

Helices homochiral

Homochiral -branched

Homochiral -calystegines

Homochiral -calystegines synthesis

Homochiral Amine Racemization Processes

Homochiral MOCPs

Homochiral Metal-Organic Coordination Polymers for Heterogeneous Enantioselective Catalysis Self-Supporting Strategy

Homochiral amines

Homochiral auxiliary

Homochiral boronate

Homochiral chairs

Homochiral compound

Homochiral dendrimer

Homochiral derivatizing agent

Homochiral dimers

Homochiral dimers enantiomers

Homochiral diol auxiliaries

Homochiral enone

Homochiral epoxide

Homochiral interaction

Homochiral ions

Homochiral ketone auxiliaries

Homochiral lattice

Homochiral ligand complexes

Homochiral ligands

Homochiral lithium

Homochiral lithium amides

Homochiral macrocycles

Homochiral molecules

Homochiral nucleophiles

Homochiral nucleophiles oxide

Homochiral reactions

Homochiral recognition

Homochiral segments

Homochiral selection

Homochiral self-organization

Homochiral side chains

Homochiral supramolecular architecture

Homochiral synthesis

Homochiral triple helicate

Homochiral, definition

Homochirality

Homochirality asymmetric amplification

Homochirality asymmetric autocatalysis

Homochirality biomolecules

Homochirality classes

Homochirality definition

Homochirality importance

Homochirality in chains

Homochirality in nature

Homochirality mirror symmetry breaking

Homochirality of biomolecules

Homochirality origin

Homochirality peptide

Homochirality problem

Homochirality spontaneous asymmetric synthesis

Homochirality, living systems

Ligands, homochirality classes

Mandelic acid homochiral

Nucleophiles homochiral, reaction with

Organic molecules homochirality

Origin of homochirality

Oxazoline homochiral

Oxazolines homochiral

P-Lactams homochiral

P-Lactams, 3-aminosynthesis via homochiral ketenes

Racemization homochiral amines

Self-replication, homochiral peptides

Some notes on homochirality

Spontaneous formation, homochiral

Steroids, 11-keto homochiral

Sulfoxides homochiral

The Homochirality Problem

The Origin of Homochirality in Living Systems

Topological chirality homochirality classes

Type I Homochiral MOCP Catalysts in Heterogeneous Asymmetric Reactions

Type II Homochiral MOCP Catalysts in Heterogeneous Asymmetric Reactions

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