Asymmetric reactions. XVI. Utilization of the asymmetric transformation to determine the absolute configuration of acids bearing as asymmetric carbon atom at the α-position in respect to the carbonyl group

1967 ◽  
Vol 32 (6) ◽  
pp. 2295-2300 ◽  
Author(s):  
O. Červinka ◽  
L. Hub
Keyword(s):  
Carbon Atom ◽  
Carbonyl Group ◽  
Absolute Configuration ◽  
Asymmetric Reactions ◽  
Asymmetric Carbon Atom ◽  
The Absolute ◽  
Asymmetric Transformation ◽  
Asymmetric Carbon

The Decomposition of Lasiocarpic and Echimidinic Acids in Hydrochloric Acid

1960 ◽  
Vol 13 (2) ◽  
pp. 269 ◽  
Author(s):  
HC Crowley ◽  
CCJ Culvenor
Keyword(s):  
Carbon Atom ◽  
Hydrochloric Acid ◽  
Absolute Configuration ◽  
Dilute Hydrochloric Acid ◽  
Methoxyl Group ◽  
Asymmetric Carbon Atom ◽  
Asymmetric Carbon

In concentrated hydrochloric acid at 100 �C, lasiocarpic acid is readily decomposed with formation principally of acetaldehyde, dimethylpyruvic acid, and α-keto-ββ-dimethyl-γ-valerolactone. Echimidinic acid is similarly and more rapidly decomposed while trachelanthic and heliotric acids are stable at 100 �C. In dilute hydrochloric acid, lasiocarpic acid is slowly converted into acetaldehyde, acetone, dimethylpyruvic acid, (+)-2-methoxy-4-methylpentan-3-one (IX), 2-methylpent-1-en-3-one (XI), and an unidentified compound. The isolation of IX shows that lasiocarpic and heliotric acids have the same absolute, configuration at the asymmetric carbon atom which bears the methoxyl group.

Anomalous scattering and absolute configuration

2010 ◽  
Author(s):  
Jenny Pickworth Glusker ◽  
Kenneth N. Trueblood
Keyword(s):  
Carbon Atom ◽  
Absolute Configuration ◽  
Three Dimensional ◽  
Polarized Light ◽  
Mirror Image ◽  
Dimensional Structure ◽  
X Ray ◽  
Three Dimensional Structure ◽  
The Absolute ◽  
Asymmetric Carbon

The concept of the carbon atom with four bonds extending in a tetrahedral fashion was put forward by van’t Hoff and Le Bel in 1874. It coincided with the realization that such an arrangement could be asymmetric if the four substituents were different, as shown in Figure 10.1a (van’t Hoff, 1874; Le Bel, 1874). Thus, for any compound containing one such asymmetric carbon atom, there are two isomers of opposite chirality (individually called enantiomers), for which threedimensional representations of their structural formulas are related by a mirror plane. Aqueous solutions of these enantiomers rotate the plane of polarized light in opposite directions. As discussed in Chapter 7, Pasteur showed that crystals of sodium ammonium tartrate had small asymmetrically located faces and that crystals with these so-called “hemihedral faces” rotated the plane of polarization of light clockwise, while crystals with similar faces in mirror-image positions rotated this plane of polarization counterclockwise. Thus the external form (that is, the morphology) of the crystals illustrated in Figure 10.1b was used to separate enantiomers (see Patterson and Buchanan, 1945). Pure enantiomers can only crystallize in noncentrosymmetric space groups unless both isomers are present. But even if the chemical formula and the three-dimensional structure of a molecule such as tartaric acid have been determined by standard X-ray diffraction methods, there is an ambiguity about the absolute configuration. Information about the absolute configuration is not contained in the diffraction pattern of the crystal as it is normally measured. Thus, although the substituents on the asymmetric carbon atoms have been identified, and even the detailed three-dimensional geometry of the molecule has been determined, it is not known which of the two enantiomers (mirror-image forms, analogous to those shown in Figure 10.1a) represents the three-dimensional structure of a particular individual molecule that has some distinguishing chiral property, such as the ability to rotate the plane of polarized light to the right. In other words, what is the absolute structure of the dextrorotatory form of the compound under study? A means of determining the absolute configurations of molecules was, however, provided by X-ray crystallographic studies.

Studies on the biosynthesis of cholesterol XVIII. The stereospecificity of mevaldate reductase and the biosynthesis of asymmetrically labelled farnesyl pyrophosphate

1966 ◽  
Vol 163 (993) ◽  
pp. 465-491 ◽  
Keyword(s):  
Carbon Atom ◽  
Absolute Configuration ◽  
Farnesyl Pyrophosphate ◽  
Asymmetric Carbon Atom ◽  
Isotopic Label ◽  
Asymmetric Carbon

It is demonstrated that mevaldate reductase transfers hydrogen stereospecifically from the ‘Aʼ-side of NADH or NADPH to substrate. When 4 R -[ 3 H 1 ]NADH, or NADPH, is used for the reduction of mevaldate the resulting [5. 3 H 1 ]mevalonate is stereospecifically labelled at C-5 with an absolute configuration of R . Mevaldate reductase shows no stereospecificity for the asymmetric carbon atom, C-3, in mevaldate: the product of the reduction of 3 RS -mevaldate is 3 RS -mevalonate. 5 R -[5. 3 H 1 ]- and 5 R -[5-D 1 ]mevalonate have been prepared and used for the synthesis of 1 R -[1,5,9. 3 H 3 ]- and 1 R -[1,5,9-D 3 ]farnesyl pyrophosphate and squalene. It is shown that when squalene is synthesized from such farnesyl pyrophosphate all the isotopic label appears in the squalene without loss. The implications of the last observations are discussed in the light of previous results.

scholarly journals The symmetrical spiro -heptanediamine and its resolution into optically active components

1936 ◽  
Vol 154 (881) ◽  
pp. 53-60 ◽  
Keyword(s):  
Carbon Atom ◽  
Optical Activity ◽  
Optically Active ◽  
Active Components ◽  
Asymmetric Carbon Atom ◽  
Molecular Configuration ◽  
Experimental Realization ◽  
Asymmetric Carbon ◽  
Acetic Acids

The experimental realization of the simplest possible types of molecular configuration which can show optical activity in the amorphous con­dition is important in connexion with stereochemical theory. Among optically active spiranes containing no asymmetric carbon atom such simple types are found in the d - and l -1-methyl- cyclo -hexylidene-4-acetic acids and the d - and 1-spiro- 5:5-dihydantoins, but no satisfactory case has hitherto been described of optical activity in substances of the constitution H —C—( CH 2 ) n —C—(CH 2 ) n —X X —C—( CH 2 ) n —C—(CH 2 ) n —H. One of the simplest conceivable examples of the latter kind should be found in the previously unknown symmetrical spiro -heptanediamine of the constitution— NH 2 —C—CH 2 —C—CH 2 —C—H H—C—CH 2 —C—CH 2 —C—NH 2 .

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