Chiral resolution and deracemization through
co-crystallization
Crystallization workshop
Barcelona, 11th March 2019
Tom Leyssens
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3
Personal Expertise!
�2.5y, Automation Team Leader UCB Pharma (2007-2009)
�Process optimization (Crystallization process)
�Polymorphism issues, optimization, purity, crystal
form, PSD, …
4
…
??Citric acid
Mandelic acid
Caffeine
Isonicotinamide
??
�UCL Professor in Physical chemistry (2009-…)
Personal Expertise!
60% of all drug compounds contain
at least one chiral center
Enantiomers � ≠ biological
properties
5/1
1
� Regulatory instances push
towards the development of
enantiopure drugs
Chirality and drug compounds
6
Diastereomeric salt formationLess costly process
But only for compounds that can form salts
Chiral chromatography
Used for many compounds
Expensive technique
Resolution by entrainment
Chirality and drug compounds
Less costly process
Only for conglomerates
7
Chirality and drug compounds
Entrainment
Enantiospecific
Deracemizat.
Resolution by entrainment/
preferential crystallization
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1. Resolution by entrainment
CaCl2, MgCl2, ZnCl2
� Selectracetam, Brivaracetam, Piracetam, …. CrystEngComm 2014, 5887.
*O. Shemshuk, L. Song, Chem. Comm., 2018.
� Entrainment
Enantiospecific
Deracemizat.
10
� ETI and LEV co-crystals have different stoichiometry!!
� No other forms identified
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
11
� Simulated and experimental XRPD match
Lev.ZnCl2 Eti2.ZnCl2
5 10 15 20 25 30 35 40 45 50
Lev·ZnCl2 calc.
Lev·ZnCl2 exp.
2θ / deg
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
12
LEV + ZnCl2
1:1
2LEV.ZnCl2
2LEV.ZnCl2
+ ZnCl2
ZnCl2ZnCl2
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
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ETI + ZnCl2
2:1
2 2ETI2.ZnCl2
2LEV(S).ZnCl2
+ 1 eq. ZnCl2
2DEV(S).ZnCl2
+ 1 eq. ETI
Thermodynamically stable
racemic compound
Thermodynamically stable
conglomerate
!!Reversible stoichiometric switch!!
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
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Understand the solid state thermodynamics (Phase Diagram)
Single Phases
ZnCl2
S-ETIR-ETI
(1:1)-S(1:1)-R
(2:1)
RS-ETI+ S-ETIRS-ETI+ R-ETI RS-ETI
RS
-ET
I + 2:1
1:1 (R) + 1:1 (S)
Mixture of 2 phases
2:1+ RS-ETI
+S-ETI
2:1+ RS-ETI
+R-ETI
2:1+ 1:1 (S) +
S-ETI
2:1+ 1:1 (R) +
R-ETI
2:1+ 1:1 (S) +
1:1 (R)
1:1 (S) + 1:1 (R)
+ ZnCl2
Mixture of 3 phases
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
15
Solvent included
� Importance of this PD: when adding solvent, one can only get one of the
combinations shown above in suspension eg.
� 2:1 + 1:1 (R) + 1:1 (S)
� 2:1 + ZnCl2
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
16
Solvent included
� Importance of this PD: when adding solvent, one can only get one of the
combinations shown above in suspension eg.
� 1:1 (R) + 1:1 (S)
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
� Stoichiometric switch also holds in suspension
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� Based on reasoning only
Solvent
ETI ZnCl2
ETI +2:1
ETI
2:1
2:1
ZnCl2
1:1 (S)
+2:1
+ 1:1 (R)
1:1 (S)
+ 1:1 (R)
1:1 (S)
+ 1:1 (R)
+ ZnCl2
Stable racemic compound
Stable conglomerate
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
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� Theory and experiment allign !!!
� In zone V, resolution by entrainment becomes possible!!
Solvent
ETI ZnCl2
ETI +2:1
ETI
2:1
2:1
ZnCl2
1:1 (S)
+2:1
+ 1:1 (R)
1:1 (S)
+ 1:1 (R)
1:1 (S)
+ 1:1 (R)
+ ZnCl2
Stable racemic compound
Stable conglomerate
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
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Make ternary phase diagrams.
X X X X X X X X X
1. Resolution by entrainment
� Entrainment
Enantiospecific
Deracemizat.
Resolution by
Diasteriomeric/enantiospecific
co-crystal formation
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Diastereomeric salt formationLess costly process
But only for compounds that can form salts
Chiral chromatography
Used for many compounds
Expensive technique
Resolution by entrainment
Chirality and drug compounds
Less costly process
Only for conglomerates
Entrainment
� Enantiospec.
Deracemizat.
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Just make some co-crystals, get some structures
and this will get us a publication ….
…
??Citric acid
Mandelic acid
Caffeine
Isonicotinamide
Levetiracetam
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
23
….
TRIAL AND ERROR APPROACH!!!
∆G of a few kcal.mol-1 , while for salts this goes up to 50 kcal.mol-1.
� Only 10% succesrate for cocrystals
� Difficult to become predictive
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
*G. Springuel, T. Leyssens, CrystGrowth Des. 2012-2015.
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4 co-crystals
40% Succesrate
D-tartaric acid 1:1
citric acid 1:1
citric acid 3:2
Mandelic acid (racemic) 2:1
R-mandelic acid 2:1
p-hydroxy-benzoic acid 1:1
2,3-dihydroxy-benzoic acid 1:1
2,4-dihydroxy-benzoic acid 1:1
2,5-dihydroxy-benzoic acid 1:1
3,4-dihydroxy-benzoic acid 1:1
3,5-dihydroxy-benzoic acid 1:1
D-tartaric acid 1:1
Mandelic acid (racemic) 1:1
S-mandelic acid 1:1
2,4-dihydroxy-benzoic acid 1:1
11 co-crystals with 10
different acids
Piracetam
Co-crystals
Levetiracetam
Co-crystals
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
NO
NH2
O
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D-tartaric acid 1:1
citric acid 1:1
citric acid 3:2
Mandelic acid (racemic) 2:1
R-mandelic acid 2:1
p-hydroxy-benzoic acid 1:1
2,3-dihydroxy-benzoic acid 1:1
2,4-dihydroxy-benzoic acid 1:1
2,5-dihydroxy-benzoic acid 1:1
3,4-dihydroxy-benzoic acid 1:1
3,5-dihydroxy-benzoic acid 1:1
D-tartaric acid 1:1
Mandelic acid (racemic) 1:1
S-mandelic acid 1:1
2,4-dihydroxy-benzoic acid 1:1
Piracetam
Co-crystals
Levetiracetam
Co-crystals
NO
NH2
O
(S,S)
(S,R)
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
26 26
Piracetam Co-crystals:
S-tartaric acid R-tartaric acid
S-Mandelic acid R-Mandelic acid
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
27 27
Levetiracetam Co-crystals:
S-tartaric acid R-tartaric acid
S-mandelic R-mandelic
NO
NH2
O
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
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AND NOW WHAT???
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
29 29
Separate two enantiomers in solution:
� No diastereomeric salts formation
� No column chromatography
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
30 30
Variables:� S enantiomer of API
� R enantiomer of API
� Enantiopure chiral acid (coformer)
� Solvent
� Temperature
5 variables !!!
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
31 31
4 variables !
For a fixed temperature
RS-API
Cocrystal
Variables:� S enantiomer of API
� R enantiomer of API
� Chiral acid (coformer)
� Solvent
� Temperature
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
32 32
RS-API
Cocrystal
Solvent
R-API S-APIRS-API
RS-API
+ liq.
R-API
+ liq.
S-API
+ liq.
R-API +
RS-API +
liq.
S-API +
RS-API +
liq.
At racemic composition
both enantiomers of API
crystallize in the same
crystal lattice
For a fixed temperature
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
RS-API
Cocrystal
33 33
Solvent
S-API S-coformerCocrystal
S-API
+ liq.
S-API
+ CC
+ liq.
CC +
liq.
CC +
S-cof.
+ liq.
S-cof.
+ liq.
Cocrystal formation of S-API
and S-coformer
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
34 34
4 variables !
RS-API
Cocrystal
Variables:� S enantiomer of API
� R enantiomer of API
� Chiral acid (coformer)
� Solvent
� Temperature
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
35 35
3 variables
Solvent
S-coformer
S-API
R-
API
S-coformer
S-API
R-
API
Solvent
S-API
R-
API
For a fixed temperature and
a fixed molar% of solvent
S-coformerVariables:� S enantiomer of API
� R enantiomer of API
� Chiral acid (coformer)
� Solvent
� Temperature
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
36 36
Conditions for an effective chiral resolution:
S-coformer
S-APIR-API
S-coformer
S-coformer +
cocrystal
RS-API
cocrystal
+ RS-API
Liq.
RS-API
Cocrystal
1. Enantiospecific cocrystallization between one enantiomer
of an API and a chiral coformer in solution.
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
37 37
Conditions for an effective chiral resolution:
S-coformer
S-APIR-API
S-coformer
S-coformer +
cocrystal
RS-API
cocrystal
+ RS-API
Liq.
RS-API
Cocrystal
1. Enantiospecific cocrystallization between one enantiomer of an API and a
chiral coformer in solution.
2. Area in which cocrystal solid phase is stable in suspension
need to cross the racemic composition line.
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
38 38
Phase diagram of Etiracetam –
S-mandelic acid in 89%mol of
acetonitril at 9°C
S-2
S-1R-2
I. S-2
II. LSMA co-crystal
II+IV. RS-1 + LSMA
I+II. S-2 + LSMA
Liquid
IV. RS-1
IV+V. RS-1 + R-1
Phase diagram of Etiracetam –
S-mandelic acid in 89%mol of
acetonitril at -10°C
At 9°C At -10°C
Etiracetam – S-mandelic acid in acetonitrile
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
39 39
Seeding
Chiral resolution through enantiospecific co-crystallization in solution
Works on compounds which do not or not easily form salts !!!
High yield (83%) in a single resolution step with 100% of ee
Solvent
Racemic compound
Chiral coformer
Diagram at crystallization
temperature
T� until complete
dissolutionT� to cyst. Temp.
Filtration
and
washing
Mother liquor enriched
in one enantiomer
Cocrystal of one enantiomer
and coformer
100% ee
2. Enantiospecific/diasteriomeric resolution
Entrainment
� Enantiospec.
Deracemizat.
DE-racemization
40
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AND BEYOND????
MeOH, MeONa
3. Deracemization
Entrainment
Enantiospec.
� Deracemizat.
42
3. Deracemization
Entrainment
Enantiospec.
� Deracemizat.
43
Chirality
Resolution
� Deracem.
3. Deracemization
96% ee, 34% yield
*B. Harmsen, Cryst. Growth Des., 2018, 18, 441-448.
44
Diasteriomeric dynamic deracemizationDuloxetine
FOR SALTS ONLY????
3. Deracemization
Entrainment
Enantiospec.
� Deracemizat.
�Development of a co-crystallization based
one pot deracemization
Addition of racemizing agent
R
R
R
S
S
S
RR
R
SS
SR S
RRSS
SS SS
R S
S RSS
SS SS SS SS SS
R
S
SS SS SS SS
SS SS
R
SS
Addition of
racemic mixture
Addition of
chiral co-former
3. Deracemization
Thank you for your attention!