Transcript Fischer Projections and the DL Nomenclature System

Chirality and Chiral Separations
Fischer Projections and the DL Nomenclature System:
This was invented by Fischer in 1891. It works by having horizontal bonds in
front of the plane and vertical bonds behind the plane.
Still used for sugars, but generally discouraged.
Definitions
Isomers: different compounds that have the same molecular formula.
Stereochemistry: the science that deals with structure in three dimensions.
Stereoisomers: isomers that are different from each other only in the way
atoms are oriented in space. However. they are similar to one another in
that the atom of each are joined in an identical order. There two types of
stereoisomers: (1)enantiomers and (2)diastereomers.
Enantiomer: an isomeric compound that cannot be superimposed on its
mirror image. In an isotropic environment, enantiomers have identical
physical and chemical properties.
Diastereomers: stereoisomers that are not mirror images of each other.
Diastereomers can have similar chemical properties since they have the
same functional groups and are members of the same family. However.
their chemical properties are not identical and they have different
physical properties.
There are two basic types of diastereomers. One containsno
chiral center and is not optically active (e. g., geometrical isomers: cistrans. syn- anti. etc.) The other type is optically active and often
contains two or more chiral centers.
Epimer : two diastereomers that differ in configuration at only one
chiral center. Carbohydrates. steroids. etc. exist as epimers. Epimcrs
are optically active.
Meso Compound: a compound whose molecules are superimposable cn
their mirror images even though they contain chiral centers . It is
optically inactive.
Racemate or Racemic Mixture: a mixture composed of
equal amounts of enantiomers (50/50). This mixture is
not optically active. Frequently, the properties of the
mixture arc slightly different than those of the pure
enantiomers.
The 2n rule: The maximum number of stereoisomer
that can exist for a compound containing more than
one chital center is 2n. where n is the number of chital
centers.
D-, L-: In the system invented by Fisher. These are the letters used to
designate opposite enantiomers (relates back to glyceraldehydes).
Amino acids, sugars and related compounds often use this system
These letters have nothing to do with the direction of rotation of
plane polarized light. This system actually is inconsistent and is
considered archaic. Many feel this system will be disgarded soon.
d -, l - and (+) and (-): d is the abbreviation for dextrorotatory and l is
for levorotatory. If plane polarized light (sodium D - line, 589.3 nm)
is rotated to the right (clockwise) it is “d” or (+). If it is rotated to the
left (counter clockwise) it is designated “l” or (-),
NOTE: the degree and direction of rotation of plane polarized
light varies with the wavelength of the light used in the measurement.
Sometimes (+) and (-) is used to refer to the direction of the
Cotton effect in a circular dichroism measurement.
R-and S-: “R” is the abbreviation for rectus (Latin) right (clockwise).
“S” is the abbreviation for sinister (Latin) left (counter clockwise).
These are the terms coined by Cahn.
Ingold and Prolog and are used to described the absolute
conformation of a chiral compound according to their sequence rules.
Specific rotation: the number of degrees of rotation, , observed if a l
- decimeter tube is used, and the compound being examined is present
to the extent of l g/cc. This is usually calculated from observations
with tubes of other lengths and at different concentrations by means of

the equation.
[ ] 
1 d
specific rotation=
observcdro tation(deg rees )
length( dm)

g / cc
where d represents density for a pure liquid or concentration for
solution
% Optical Purity
or
=
Enantiomeric Excess
100
Example: If the specific rotation of enantiomers “A” was +60° and a
partially racemized mixture was +30°, what was the % optical
purity of the enantiomeric excess? What are the relative amounts
of ( + ) and ( - ) enantiomers in the mixture?
(a) % optical purity=
(b) In the mixture there is 75% of the ( + ) enantiomer and 25% of
the ( - )enantiomer.
This can be calculated via two simultaneous equations:
X + Y = 100%
X – Y =50%
Let X = % of ( + ) enantiomer
Let Y = % of ( - ) enantiomer
Enantiomeric Excess (%e.e.):
Enantiopurity is usually reported in terms of “enantiomeric excess”
(e.e.). %e.e. = Major - minor x 100
major + minor
Pirkle型 :
又名brush型（brush type）、π-錯合物
型（π-complex type）或電荷轉移型
（charge transfer type）。其中影響分
離的作用力形式有：
π-π作用力（π-π interactions）
氫鍵（hydrogen bonds）
立體障礙（steric interactions）
靜電作用力（electrostatic interactions）
表一常見之蛋白質靜相的種類及其適用的分析物特性
蛋白質種類
適用之分析物的特性
α1-Acid glycoprotein
適用於具芳香環的環狀二級胺，
以及某些酸性或中性化合物
Bovine serum albumin
適用於某些芳香羥酸和離子型化合物
Human serum albumin
適用於某些芳香羥酸和離子型化合
Ovomucoid
適用於具芳香環的環狀二級胺，以及
某些中性化合物
Cellobiohydrolase
一級胺和其他二級胺及胺基化合物
The structure of (R,R) P-CAP chiral stationary phase
Hydrogen bond interaction
Dipolar interaction
Solvophobic-driven attraction
Steric repulsive
J. Chromatogr. A 2005,1066 55
Proposed Structure of Vancomycin
amine
hydrogen bonding &
dipole stacking sites
H3C
NH
HO
H
 Multiple use
O
O
NH
 Covalent bonding
 Broad applicability
NH
O
COOH
O
C
NH
O
A
B
O
Cl
p-acceptor
NH
NH
O
H
HO
O
Cl
O
O
HO
O
HO
HO
sugar moieties
OH
NH 2
NH
HO
HO
O
O
CH 3 OH
NH 2
CH 3
A, B, C are inclusion pockets (weak)
ionic
site
Proposed Structures of Glycopeptide
CSPs
Teicoplanin
HO
OH
NHR
CH 2OH O
Cl
O
CH 2OH O
O
O
HO
HNCOCH
OH
H
O
O
C
B
O H H
N
N
H H A
HN
H
3
Cl
O
N
H
O H
N
O H H H
D
HOOC
HO
O
H H
N
NH 2
Teicoplanin Aglycone
O
O
HO
OH
CH 2OH
OH
O
OH
OH
H
O
Cl
HO
O
HO
O
H
O
C
B
O H H
N
N
H H A
HN
H
Cl
O
N
H
H
O
N
O H H H
D
HOOC
Key sites
HO
O
H H
N
O
O
H
OH
HO
HO
NH 2
Proposed Structures of Glycopeptide
CSPs
HO
OH
OH
HO
OH
HO
OH
HO
OH
O
O
O
O
O
OH
O
H2N
CH 3
Ristocetin A
O
O
O
O
O
B
C
O HH H
N
H
N
H
COOCH
HN
3
O
O
N
H
H
H H
N
O
D
A
CH 3
O OH
HO
HO
OH
O
OH
OH
H
N O
H
NH 2
O
HO
OH
CH 3
O
O
OH
OH
OH