This document discusses methods for separating enantiomers and for performing stereo-selective synthesis. It describes 7 common methods for separating enantiomers from a racemic mixture: 1) mechanical separation, 2) preferential crystallization, 3) biochemical separation using microorganisms, 4) chromatographic separation, 5) kinetic resolution, 6) precipitation, and 7) forming diastereomers. It also defines enantioselective synthesis as a chemical reaction that produces unequal amounts of stereoisomeric products with new chiral elements. Examples of these separation methods and stereo-selective synthesis are provided.

1. ENATIOPURE SEPARATION AND STEREO
SELECTIVE SYNTHESIS
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2. CONTENTS
■ Introduction
■ Method of separation of enantiopure
■ Stereo selective synthesis
■ References
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3. What is enantiopure?
■ Enantiomerically pure (containing a single enantiomer).
■ Most of the molecules of important to living system are enantiopure and it also known
as enantioenriched.
■ An enantiopure drug is a pharmaceutical that is available in one specific enantiomeric
form. Most biological molecules (proteins, sugars, etc.) are present in only one of
many chiral forms, so different enantiomers of a chiral drug molecule bind differently
(or not at all) to target receptors.
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4. Method of separation of enantiopure
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Method of
separation
Mechanical
separation
Preferential
crystallization
method
Biochemical
separation
Chromatograp
hic separation
Kinetic
method
Precipitation
method
Diastereomers
method

5. 1.MECHANICAL SEPARATION OR SPONTANEOUS
RESOLUTION:
■ This involved mechanical separation of the crystal of one enantiomers from the
other. In racemic mixture based on difference in their shapes.
■ Crystal of the two forms have different shapes separated by magnifying lens and
forceps.
■ This method first used by Pasteur for he resolution of sodium ammonium tartarate
which crystallise out in the form of racemic mixture below 27 degree.
■ Disadvantage:- This methods is time consuming and every compound can not be
crystallized at room temperature
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6. 2.PREFERENTIAL CRYSTALIZATION BY INOCULATION:
■ This method involve seeding of a saturated solution of the racemic mixture with a
pure crystal of one the two enantiomers.
■ The solution now become supersaturated with respect to the added enantiomers
■ It begins to crystallise out.
■ Eg. Harda obtained free from amino acid by adding corresponding d/l isomers of
amino acid.
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7. 3.BIOCHEMICAL SEPARATION:
■ It was introduced by Pasteur in 1858.
■ This method is based on fact that when certain micro organisms like bacteria,
fungi, yeast, etc are grown in dilute solution of racemic mixture, they eat up
one enantiomer rapidly than other.
■ Example: The mould penicillium glaucum preferentially destroys the (+) isomer
of racemic ammonium tartarate leaving (-) ammonium tartarate in solution.
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8. 4.CHROMATOGRAPHIC SEPERATION:
■ The racemic mixture can be separated by chromatography on an optically
active support.
■ The diastereomeric adsorbates which are formed have different stabilities.
■ Thus one enantiomer will be held more tightly than the other and would be
eluted first.
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9. 5.KINETIC METHOD :
■ This method is based on the fact that one of the enantiomer of racemic mixture
reacts faster than other with optically active compound.
■ Menthol reacts faster with (+) mandelic acid than with (-) mandelic acid.
■ Thus with difference in kinetics of reaction so racemic mixture can be separated.
6.PRECIPITATION:
■ This method is based on formation of precipitate by reaction between any reagent
and racemic mixture.
■ Example: (+) & (-) narcotine when dissolved in HCL, precipitates (+) narcotine.
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10. 7.BY DIASTEREOMERS:
■ When racemic mixture is allowed to interact with optically active material, it
give a diastereomeric derivatives.
■ Diastereomer have different physical properties and hence can easily separated
into two component by fractional crystallisation
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11. Stereo selective synthesis
■ Enantioselective synthesis, also called asymmetric synthesis.
■ It is a form of chemical synthesis.
■ It is defined by IUPAC as: a chemical reaction (or reaction sequence) in which one or
more new elements of chirality are formed in a substrate molecule and which
produces the stereo isomeric (enantiomeric or diastereoisomeric) products in unequal
amounts.
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Hydrogenation of ketone

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