Christine Aurigemma
Pfizer Global Research & Development,
La Jolla, CA
July 24, 2006
July 24-27, 2006, San Diego, CA

I.
Stereochemistry Refresher a.
Relationships of Stereoisomers b.
Terminology
II.
Chiral Separations a.
Why do we need chiral separations?
b.
Different approaches to enantiopure products
III. Chromatographic Chiral Separations a.
What is Chiral Recognition? 3-point rule b.
SFC vs. HPLC c.
Types of CSP’s d.
Screening option e.
Problem solving
IV. Absolute Stereochemistry (Oliver McConnell)
July 24-27, 2006, San Diego, CA

Isomers: Compounds with the same molecular formula
Same atom connectivity
Different atom connectivity
Interconvert through rotation about a single bond
Stereoisomers
Not readily
Interconvertible
Constitutional (or structural) isomers
Conformational Configurational isomers or rotamers w/o chiral centers (opt. inactive) isomers
Constitutional (structural) isomers
Configurational isomers w/ chiral centers (optically active)
Conformational isomers mirror images at this carbon
Achiral
Not mirror images at this carbon
Diastereomeric
Geometric isomers
Chiral
Diastereomers Enantiomers
Not mirror images
Diastereomers Cis, Trans
(E,Z) isomers cis and trans isomers
Courtesy of Brown/Foote, Organic Chemistry, 3/e, Figure 1
Harcourt, Inc. items and derived items copyright 2002 by Harcourt, Inc. and http://www.chem.uic.edu/web1/OCOL-II/WIN/STEREO/ISOMER.HTM
mirror images
Enantiomers
July 24-27, 2006, San Diego, CA

Chiral Molecule:
• Has one stereogenic center
(typically C, but can be N, P, etc.), which is attached to 4 different substituents  asymmetric
• one that is not superimposable on its mirror image (the two are not identical)
– i.e. hands, keys, shoes
• the two mirror image forms are called enantiomers
• Optically active
Achiral Molecule:
• Has no stereogenic center; the carbon atom has less than
4 non-equivalent substituents attached
• has a plane of symmetry
• one that is superimposable on its mirror image (the two are identical)
– i.e. nail, ball, a baseball bat
• Not optically active http://wps.prenhall.com/wps/media/objects/724/741576/Instructor_Resources/Chapter_05/Text_Images/FG05_01-10UN.JPG
July 24-27, 2006, San Diego, CA

• Each enantiomer has an equal but opposite optical rotation; can be measured using optical rotation polarimeter
• One enantiomer rotates polarized light in a clockwise direction and is then designed as (+), or dextrorotatory
• The other enantiomer rotates polarized light in counter-clockwise direction and is the (-) enantiomer, or levorotatory
• Racemates (1:1 mixture of enantiomers) have no observable optical rotation; they cancel each other out
Specific Rotation = [

]
D
=
 l * c where

= observed rotation, l = cell length in dm, c = concentration in g/mL, and D is the 589nm light from a sodium lamp
July 24-27, 2006, San Diego, CA ©1999 William Reusch, All rights reserved (most recent revision 7/14/2006) whreusch@msu.edu

• Isomers: Compounds with the different chemical structures and the same molecular formula
• Stereoisomers: compounds made up of the same atoms but have different arrangement of atoms in space
• Enantiomers are the 2 mirror image forms of a chiral molecule
– can contain any number of chiral centers, as long as each center is the exact mirror image of the corresponding center in the other molecule
– Identical physical and chemical properties, but may have different biological profiles. Need chiral recognition to be separated.
– Different optical rotations (One enantiomer is (+) or dextrorotatory
(clockwise), while the other is (-) or levorotatory (counter clockwise))
• Racemate: a 1:1 mixture of enantiomers.
– Separation of enantiomers occurs when mixture is reacted with a chiral stationary phase to form 2 diastereomeric complexes that can be separated by chromatographic techniques
• Diastereomers: stereoisomers that are not enantiomers
– Have different chemical and physical characteristics, and can be separated by non-chiral methods.
– Has at least 2 chiral centers; the number of potential diastereomers for each chiral center is determined by the equation 2 n , where n=the number of chiral centers
July 24-27, 2006, San Diego, CA

I.
Stereochemistry Refresher a.
Relationships of Stereoisomers b.
Terminology
II.
Chiral Separations a.
Why do we need chiral separations?
b.
Different approaches to enantiopure products
III. Chromatographic Chiral Separations a.
What is Chiral Recognition? 3-point rule b.
HPLC vs. SFC c.
Types of CSP’s d.
Screening option e.
Problem solving
July 24-27, 2006, San Diego, CA

• Single enantiomers of chiral active pharmaceutical ingredients (APIs) may have different:
– Pharmacokinetic properties in animal models
• Absorption, distribution, metabolism and excretion
– Pharmacological or toxicological effects
• Biologically “active” isomer may have desirable effects
• Biologically “inactive” isomer may have undesirable side effects (i.e. increased toxicity)
• Increased pressures by regulatory authorities to switch from racemic to single enantiomer APIs
• Development of chiral APIs raises issues regarding:
– acceptable manufacturing control of synthesis and impurities
– pharmacological and toxicological assessment of both enantiomers
– proper assessment of metabolism and distribution
– proper clinical evaluation of these drugs http://www.fda.gov/cder/guidance/stereo.htm;
C&EN, May 5, 2003, pg. 56
July 24-27, 2006, San Diego, CA

Nine of the top 10 drugs have chiral active ingredients
Note: Sales figures from IMS Health
Courtesy of C&EN, September 5, 2005, Volume 83, Number 36, pp. 49-53
July 24-27, 2006, San Diego, CA

• Albuterol (anti-asthmatic inhalant)
– D-albuterol may actually cause airway constriction
– Levalbuterol (L-albuterol) avoids side effects
• Allegra (allergy medication)
– Single enantiomer of Seldane that avoids lifethreatening heart disorders of Seldane
• Fluoxetine (generic name for Prozac, depression medication)
– R-Fluoxetine – improved efficacy; minimizes side effects, i.e. anxiety and sexual dysfunction. Other indications
(eating disorders)
– S-Fluoxetine – use for treatment of migraines
July 24-27, 2006, San Diego, CA

• Chiral Synthetic Approach
– Stereoselective or asymmetric syntheses
– Biotransformation or Enzymatic resolution
– Catalytic enantioselective processes
• Racemic Approach
– Crystallization
– Chiral salt resolution
– CE (capillary electrophoresis)
– SMB (simulated moving bed technology)
– Chromatography (HPLC, SFC)
Many Samples
Small Scale
Few Samples
Large Scale
July 24-27, 2006, San Diego, CA
Courtesy of Christina Kraml, Wyeth

I.
Stereochemistry Refresher a.
Relationships of Stereoisomers b.
Terminology
II.
Chiral Separations a.
Why do we need chiral separations?
b.
Different approaches to enantiopure products
III. Chromatographic Chiral Separations a.
What is Chiral Recognition? 3-point rule b.
HPLC vs. SFC c.
Types of CSP’s d.
Screening option e.
Problem solving
July 24-27, 2006, San Diego, CA

• Chiral Recognition: Ability of chiral stationary phase, CSP, to interact differently with each enantiomer to form transientdiastereomeric complexes; requires a minimum of 3 interactions through:
– H-bonding
– π-π interactions
– Dipole stacking
– Inclusion complexing
– Steric bulk CSP Biphenyl derivative
• Five general types of CSPs used in chromatography:
1.
Polymer-based carbohydrates
2.
Pirkle or brush-type phases
3.
Cyclodextrins
4.
Chirobiotic phases
5.
Protein-based
July 24-27, 2006, San Diego, CA http://www.chemhelper.com/enantiomersep.html

1) Polymer-based Carbohydrates
– Chiral polysaccharide derivatives, i.e. amylose and cellulose, coated on a silica support
– Enantiomers form H-bonds with carbamate links between side chains and polysaccharide backbone
– Steric restrictions at polysaccharide backbone may prevent access of one of enantiomers to H-bonding site
– Can be used with normal phase HPLC, SFC, RP-HPLC
– Limitations: Not compatible with a wide range of solvents other than alcohols
• Available columns:
– i.e. Chiralpak AD, AD-RH, AS, AS-RH, and Chiralcel OD, OD-RH, OJ, OJ-RH, etc. from Chiral Technologies, Inc.
– Chiralpak IA and IB…same chiral selectors as AD and OD, respectively, but these are immobilized on the silica; more robust and has much greater solvent compatibilities
July 24-27, 2006, San Diego, CA
Courtesy of Chiral Technologies, Inc.

MeO
CH
3
O
OH
Conditions:
Chiralpak AD-H
Hexane/IPA/TFA, 80:20:0.1
Flow: 1.0 mL/min
Conditions:
Chiralpak AS-RH aq. H
3
PO
4
(pH2)/ACN, 60:40
Flow: 0.7mL/min
Conditions:
Chiralpak AD-H, 100x4.6mm
Courtesy of Chiral Technologies, Inc.
CO
2
/MeOH, 80:20
Flow: 5.0 mL/min
Conditions:
Chiralpak AD-H, 100x4.6mm
CO
2
/MeOH, 90/10
Flow: 2.0 mL/min
July 24-27, 2006, San Diego, CA

2) Pirkle or Brush-type Phases: (Donor-Acceptor)
–
–
–
–
–
–
•
•
Small chiral molecules bonded to silica
More specific applications; strong 3-point interactions through 3 classes:
πdonor phases
πacceptor phases
• Mixed donor-acceptor phases
Binding sites are πbasic or πacidic aromatic rings (π-π interactions), acidic and basic sites (H-bonding), and steric interaction
Separation occurs through preferential binding of one enantiomer to CSP
Mostly used with normal phase HPLC, SFC. May get less resolution with RP-
HPLC; compatible with a broad range of solvents
Limitations: only works with aromatic compounds
• Available columns:
• Whelk-O 1, Whelk-O 2, ULMO, DACH-DNB (mixed phases),  -Burke 2,
β -Gem 1 ( πacceptor phases), Naphthylleucine ( πdonor phases), from
Regis Technologies, Inc.
• Phenomenex Chirex phases
Courtesy of Regis Technologies, Inc.
July 24-27, 2006, San Diego, CA

(Normal phase) (Reversed phase)
July 24-27, 2006, San Diego, CA
Courtesy of Regis Technologies, Inc.

3) Cyclodextrin CSPs
– Alpha, beta and gamma-cyclodextrins bond to silica and form chiral cavities
– 3-point interactions by:
• Opening of cyclodextrin cavity contains hydroxyls for H-bonding with polar groups of analyte
• Hydrophobic portion of analyte fits into non-polar cavity
(inclusion complexes)
– One enantiomer will be able to better fit in the cavity than the other
– Used in RP-HPLC and polar organic mode
– Limitations: analyte must have hydrophobic or aromatic group to “fit” into cavity
• Available columns:
– Cyclobond (  -,  -, and  -cyclodextrins) from Astec, Inc.
– ORpak CDA (  ), ORpak CDB (  ), ORpak CDC (  ) from JM
Sciences http://www.raell.demon.co.uk/chem/CHIbook/chiral.htm#Brush
July 24-27, 2006, San Diego, CA

Conditions Results
Column:
Dimensions (mm):
Catalog Number:
Mobile Phase:
Flow Rate (mL/min):
Temp ( o C):
CYCLOBOND I 2000
250x4.6mm
20024
10/90: CH3CN/1% TEAA, pH 4.1
1.0 mL/min.
23°C
Chart Speed (cm/min): 0.4cm/min.
Detection (nm): 254nm
Injection Volume (µL): 2.0µL
Sample Concentration (mg/mL): 5.0mg/mL chlorpheniramine
Peak1 16.1
Peak2 18.1
July 24-27, 2006, San Diego, CA http://www.astecusa.com/applications/result_Mod.asp

4) Chirobiotic Phases
– Macrocyclic glycopeptides linked to silica
– Contain a large number of chiral centers together with cavities for analytes to enter and interact
– Potential interactions:
• π-π complexes, H-bonding, ionic interactions
• Inclusion complexation, steric interactions
– Capable of running in RP-HPLC, normal phase, polar organic, and polar ionic modes
• Available columns:
– Chirobiotic V and V2 (Vancomycin), Chirobiotic T and T2
(Teicoplanin), Chirobiotic R (Ristocetin A) from Astec
July 24-27, 2006, San Diego, CA http://www.raell.demon.co.uk/chem/CHIbook/chiral.htm#Macrocyclic

Conditions Results
Column:
Dimensions (mm):
Catalog Number:
Mobile Phase:
Flow Rate (mL/min):
Temp ( o C):
CHIROBIOTIC V
250x4.6
11024
10/90:THF/0.1% TEAA, pH7
1.0 mL/min.
25°C
Chart Speed (cm/min): 0.5
Detection (nm): 254
Injection Volume (µL): 2
Sample Concentration (mg/mL): 5
Naproxen
Peak1 8.78
Peak2 10.48
July 24-27, 2006, San Diego, CA http://www.astecusa.com/applications/result_Mod.asp

– Natural proteins bonded to a silica matrix
– Proteins contain large numbers of chiral centers and interact strongly with small chiral analytes through:
• Hydrophobic and electrostatic interactions, H-bonding
– Limitations:
• Requires aqueous based conditions in RP-HPLC
• Analyte must have ionizable groups such as amine or acid.
• Not suited for preparative applications due to low sample capacity
• Available columns:
– Chiral AGP (  -glycoprotein) from ChromTech
– HSA (human serum albumin) from ChromTech
– BSA (bovine serum albumin) from Regis Technologies
July 24-27, 2006, San Diego, CA

Human Serum Albumin CSP Acid glycoprotein CSP http://www.chromtech.se/nap-2x.htm
July 24-27, 2006, San Diego, CA

• General use column with no solubility issues
Polymer-based phases
• Specific applications; solubility issues
Pirkle-type
Chirobiotic phases
• SFC only
Polymer-based, Pirkle-type, Chirobiotic
• Biological Samples
Protein-based phases
July 24-27, 2006, San Diego, CA

β -Lactams
Compiled from Snyder, et. al, “Practical HPLC Method Development”, 2 nd ed., John Wiley and Sons, Inc. 1997, p. 549
July 24-27, 2006, San Diego, CA

• Advantages
– Reduced solvent
• Amounts (CO
2
– Reduced toxicity reduces liquid waste)
• Solvent types (alkanes, chlorinated, etc)
• CO
2 has a net zero environmental impact
– Safety
• Reduce flammability
– Separation speed/efficiency
• Disadvantages
– Equipment costs
– Maintenance/robustness
– Solubility
July 24-27, 2006, San Diego, CA

SFC (normal phase) HPLC (normal phase)

= 1.76
Run time = 20.5 minutes
Flow rate = 1.5 mL/min http://www.registech.com/chiral/sfcappguide2006.pdf

= 1.35
Run time = 10 minutes
Flow rate = 0.4 mL/min
July 24-27, 2006, San Diego, CA

SFC
Column 1
Column 2
Column 3
Column 4
Column 5
Solvent selector valve
Column selector valve
Solvents
• Mobile phases: CO isopropanol
• Columns:
2
+ methanol or
– Chiralpak AD-H, AS-H
– Chiralcel OD-H, OJ-H
– Chiralpak IA (immobilized AD)
Detector
July 24-27, 2006, San Diego, CA

Daicel Chiralcel OD-H
25% MeOH, 140 bar
Daicel Chiralpak AD-H
30% MeOH, 140 bar
> LOADABILITY
July 24-27, 2006, San Diego, CA

• Derivatization of final products and intermediates
– Use of protecting groups such as t-BOC and CBZ (carbobenzyloxy)
– CBZ derivatization of chiral primary and secondary amines
(common intermediates or final products of enantioselective synthesis)
– Adding CBZ can improve compound solubility, enables high efficiency purifications through repetitive, stacked injections
– Enhances chiral recognition and improves 3-point interactions; improves baseline separation ability by either HPLC or SFC
– CBZ protecting group easily attached and removed during synthetic processes
H
N
PhCH
2
OCOCl iPr
2
NEt
O
N
O Pd/C
H
2
H
N
+ CO2 + toluene
•
•
•
Acylation of amine with benzyl chloroformate
Amine is regenerated by catalytic hydrogenolysis using palladium on carbon
Product is isolated by simple filtration and evaporation of the solvent
Kraml, Christina et. al ,“Enhanced chromatographic resolution of amine enantiomers as carbobenzyloxy derivatives in high-performance liquid chromatography and supercritical fluid chromato
Graphy”, J. of Chrom A, 1100 (2005) 108-115..
July 24-27, 2006, San Diego, CA

• 47.5 g per day
• Isolated 70 g
• 35.4 hrs. purification time
Low S/N ratio
Poor separation
0 0
0 0 2 2 1 1 underivatized
3 3
Aurigemma, C., BSAT 2005, Boston, MA
Purify: ~2g/hr
July 24-27, 2006, San Diego, CA

• Addition of strong acid additives to mobile phase
– Especially useful for separation of chiral amines
– 0.1% ethanesulfonic acid (ESA) added to ethanol, or
0.1% methanesulfonic acid (MSA) added to methanol will cause formation of ion pairs with the amine to increase chances of successful enantioseparation
July 24-27, 2006, San Diego, CA
Courtesy of Roger Stringham, Chiral Technologies, Inc

•Use of Basic Additives to Mobile Phase and
Sample solvent
Analytical
SFC
Isopropylamine in
Mobile phase only
H
2
N *
(S,S) Whelk-O 1,
250x4.6mm, 10u i.d.
(Regis Technologies, Inc.)
40% IPA w/ 0.1% IPAm
2.5 mL/min @ 140 bar
110
100
90
80
70
60
50
190
180
170
160
150
140
130
120
40
30
20
10
0
-10
260
250
240
230
220
210
200
350
340
330
320
310
300
290
280
270
0
360
350
340
330
320
310
300
260
250
240
230
220
210 sample solvent
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
0 5 10 15
1 2 3 4 5 6
20
7
25
8
30
9
Preparative
35
10
40
11
45
140
130
120
110
100
90
230
220
210
200
190
180
170
160
150
50
40
30
20
80
70
60
340
330
320
310
300
290
280
270
260
250
240
0
-10
0
IPAm in sample solvent
55
1
60
2
65
3
70
4
75
5
80
6
85
7
90 95
8 9
Result: better peak shapes, allowing for high throughput purifications through stacked injections and yielding pure enantiomers
*Trans(

)-2-Phenylcyclopropanamine•HCl, CAS No. 1986-47-6
Aurigemma, C., BSAT 2005, Boston, MA July 24-27, 2006, San Diego, CA

•Use of Basic Additives to Sample Solvent only
No IPAm in sample solvent
IPAm added to sample solvent

NO residual base in collected sample
IPAm
Aurigemma, C., BSAT 2005, Boston, MA July 24-27, 2006, San Diego, CA

July 24-27, 2006, San Diego, CA

July 24-27, 2006, San Diego, CA