crystallization strategies
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Crystallization strategies
the quest for increased yield and chiral purity
Andrew Byrne
APC Ltd.
Technobis Crystallisation Systems
4th February 2021
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General Overview
➢ Brief Background
• Stereoisomers, chirality and Active Pharmaceutical Ingredients
• Ternary Phase Diagrams – Why are they relevant to Enantioselective Crystallization?
➢ Case Study 1: Ternary Diagrams as a tool for Process Definition
• Problem Statement
• Methodology & Development
• Outcomes, Conclusions & Recommendations
➢ Case Study 2: Enhanced Process Understanding & Yield Improvement
• Problem Statement
• Methodology & Development
• Outcomes, Conclusions & Recommendations
➢ Conclusions, Learnings & Acknowledgements
2
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APC and Our Partners
3
Material to Medicine Process Research
▪ Engineering
▪ Formulation
▪ Scale-up
▪ Containment
▪ Analytical
▪ Chemistry
▪ Bioprocessing
▪ Continuous
140+Ph.D. Chemical
Engineers & Scientists
200+Medicines
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Brief Background – Chirality & Pharmaceutical APIs
• Altered Chirality of Active Pharmaceutical Ingredients –> different physiological & pharmaceutical effects
4
• Revenue Commerical Chiral Small Molecule APIs 2019:
1. Lipitor (Atorvastatin) – Sales: ~ $ 1.9 billion
2. Plavix (Clopidogrel) – Sales: ~ $ 2.1 billion
3. Seretide (Fluticasone) – Sales: ~ $ 5.3 billion
4. Crestor (Rosuvastatin) – Sales: ~ $ 5.1 billion
• Separation & Purification
• Ideal Scenario: 100 % enantio. pure synthesis!
• Reality:
• Classical synthesis – Racemic mixtures – can be optimised
• Chiral resolution strategies
• Prochiral substrates + chiral catalysts -> improved ee%
• Chiral Chromatography – High cost
• Resolving Agents
• Crystallization – Key pharmaceutical Unit Operation
**
*
**
Mirror Plane
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Brief Background – Chirality & Pharmaceutical APIs
• Glossary of Terms (Refresher) –
• Chirality:
Geometric property of molecules. A chiral molecule is non superimposable with its mirror image
• Achiral:
The opposite of chiral is achiral. Achiral objects are superimposable with their mirror images.
• Enantiomer:
Chiral compounds that are mirror images of each other and non-superimposable.
• Diastereomer:
Chiral compounds that are not mirror images of each other and non-superimposable.
• Eutomer:
The chiral enantiomer having the desiredpharmacological activity
• Distomer:
The chiral enantiomer having the undesiredpharmacological activity
5
Enantiomers
Enantiomers are stereoisomers that are non-superimposable mirror
images
Are always in pairs
Have identical physical properties except the ability rotate plan-
polarized light
Shape of the molecules is similar
Diastereomers
Diastereomers are stereoisomers that are non-superimposable and
are not mirror images
There can be several molecules
Have distinct physical properties
Have different molecular shapes
Vs
Lactic Acid Threonine2 pairs of Enantiomers
Or2 pairs of Diasteromers
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Brief Background – Characterisation of the Solid Phase
➢Crystallization of Chiral Compounds
6
• Solubility measurement - determine the solubility of pure enantiomers (R or S) and their mixtures
• Eutectic Point – Highest solubility point obtained, Typically Symmetrical for Enantiomers!
Diastereomer Enantiomer
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢ Brief Background
• Title: Development of an optimized enantioselective crystallization process
• Processing Issues:
• Long process with Inconsistent key process output achieved post workup. Enantiomeric purity (AP%)),
yield, assay purity (wt%), variable heavy metals content (Rhodium, Iron and Zinc 1-200 ppm)
• Project Objectives:
a) To measure API solubility (conglomerate) and determine the effect of heavy metals on solubility (if any)
b) To develop an optimized enantioselective crystallization process for the purification of crude API (desired enantiomer)
c) To demonstrate this process on 10 g & 100 g scale
7
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Case Study 1: Ternary Diagrams as a tool for Process Definition
8
➢Key Findings During Tech Transfer (Part 1)
Sample Description
HPLC
Assay
HPLC
Chirality
ICP-MS
Rh
ICP-MS
Zn
ICP-MS
Fe
wt%AP% Desired
Enantiomerppm ppm ppm
Hydrogenation: crude reaction material
(Evaporated to Dryness)60.4
91.7
Range: 87 -92%1900 31000 1700
Charcoal treatment #1 – dry cake 73.5 92.1 1200 29000 1300
Post water slurry # 1 – dry cake 86.1 94.7 800 1400 1900
Post Isopropanol reslurry # 1 – dry cake 84.8 95.9 39.9 36.8 71.8
Charcoal treatment #2 – dry cake 96.1 96.2 1.5 28.1 49.6
Post Isopropanol reslurry # 2 – dry cake 97.2 97.5 1.0 38.4 35.4
➢Unit Operations: Solid phase analysis (Assay, Chirality & Heavy Metals)
With Each Unit Operation:
• Assay (wt%) increases
• Chirality (AP) increases
• Heavy Metals content…
Early indications:
Charcoal Treatments
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Case Study 1: Ternary Diagrams as a tool for Process Definition
9
➢Key Findings During Tech Transfer (Part 2)
➢Unit Operations: Liquid phase analysis – Loss to mother liquor
Process Run Sample DescriptionDesired
Enantiomer
# - mg/g
1 Post water slurry # 1 11.3
2 Post water slurry # 1 11.0
3 Post water slurry # 1 10.9
4 Post water slurry # 1 10.2
5 Post water slurry # 1 10.2
6 Post water slurry # 1 12.4
1 Post Isopropanol reslurry # 1 3.8
2 Post Isopropanol reslurry # 1 3.3
3 Post Isopropanol reslurry # 1 4.1
4 Post Isopropanol reslurry # 1 3.4
5 Post Isopropanol reslurry # 1 2.9
6 Post Isopropanol reslurry # 1 3.1
Reverse Phase - AssayDesired
EnantiomerUndesired
Enantiomer %Desired
mg/g mg/g
5.4 5.9 48.1
5.4 5.6 49.0
5.1 5.9 46.3
4.9 5.4 47.8
4.9 5.3 47.9
6.9 5.6 55.3
1.8 2.1 46.1
1.5 1.8 46.2
2.0 2.1 49.5
1.7 1.7 50.6
1.6 1.3 54.3
1.4 1.8 43.3
Normal Phase - Chirality HPLC method - Key
0
40
80
120
160
200
10 20 30 40 50 60
Solu
bili
ty (
mg/
g)
Temperature (°C)
Normal Phase - Chirality
Reverse Phase - Assay
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Crystallization Workflow – Overview Early Phase Solvent Selection
10
Commercial Benefits: accelerated screening of conditions leading to time & cost savings
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Case Study 1: Ternary Diagrams as a tool for Process Definition
11
➢Preliminary Computational Solvent Screening
• Computational Quantum Calculations using both COSMO & Dynochem Software packages
• Relative Solubility calculated based on electron density mapping & Chemical Potential
• 27 Solvents screened – Key Outputs guided Screening Process
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Rel
ativ
e So
lub
ility
25 degrees Celcius
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
Hex
(So
lvat
e P
rop
ensi
ty)
High Solvate Propensity
Low Solvate Propensity
PotentialPoor Solvents
Good Anti-Solvents
PotentialGood Solvents
Poor Anti-Solvents
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢ Solubility Design Space: the Ternary Diagram (Method 1)
• Classic Isothermal Method (Both Enantiomers & Mixtures)
• Synthesis of the Undesired Enantiomer was required
• Excess solids into known volume / mass of solvent mixture
• Allowed to equilibrate over extended hold period at fixed temperature
• Slurry was allowed to settle and filtered supernatant Liquor Concentration was measured by HPLC
• Concentration collected as mg/g and converted to wt%
• Data collected for a number of pure and binary solvent systems
• Remember – HPLC method selection here is critical
Note:
• Crystal 16 – Clear point determination was also used.
020406080
100120
0 10 20 30 40 50 60 70 80 90 100
Des
ired
So
lub
ility
(m
g/g)
Isopropanol (Volume %)
10 °C 20 °C 40 °C 60 °C
Simple EutecticComposition 50:50
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Method 2: Ternary Diagram Construction
➢ Solubility Design Space: the Ternary Diagram (Method 2)
• Two fold objective: a) Characterise the solid phase (binary & Ternary)
b) to generate solubility design space
• Methodology
• Crystal 16 – Clear point determination
• 100% Transmission corresponds to solubility of a given solids mixture
• Different masses of solid are typically charged to different vials to obtain the clearpoint temperatures of each vial and build up the solubility relationships.
• For our system solid wt% mixtures of Desired Diastereomer : Undesired Diastereomer
• Range of solid wt% mixtures: 100:0 Desired: Undesired -> 0:100 Desired: Undesired
• Generation of traditional solubility curves for different solids mixtures was therefore
possible at varied solvent compositions (0 to 100 % Desired)
• Convert data to wt%, isothermal cross-sections via data interpolation
• Spot checking by HPLC – For both concentration & Chirality
13
Slurry
undissolved solids
Solution
Dissolved solids
Clearpoint – 100% Transmissivity
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0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80
AP
I s
olu
bili
ty (
mg/
mL
solv
en
t)
Temperature (oC)
➢ Solubility Design Space: the Ternary Diagram (Method 2)
14
80:20
90:10
70:30
60:40
20:80
50:50
Solubility Design Space A:B MixturesIsothermal Cross Sections • Isotherm 60 oC
• Isotherm 40 oC• Isotherm 15 oC
Interpolate
Solubility
&
Convert to wt%
Simple EutecticConglomerate system
A:B
Method 2: Ternary Diagram Construction
Enantiomer A
Solvent Enantiomer B
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢Simple Eutectic Verification Experiments (HPLC tracking)
Solvent DescriptionDesired
Enantiomer
Undesired
EnantiomerSolvent
Desired
Enantiomer
Undesired
Enantiomer
Composition Solids Charged mg / g mg / g wt% wt% wt%
Slurry - Liquor Composition (in presence of excess solids)
Vial 1: 100 vol% MeOH Charge 1: Desired Enantiomer 21.34 1.31 97.73 0.13 2.13
Vial 1: 100 vol% MeOH Charge 2: Undesired Enantiomer 21.95 22.60 95.55 2.26 2.19
Vial 2: 100 vol% MeOH Charge 1: Undesired Enantiomer 0.25 21.39 97.84 2.14 0.02
Vial 2: 100 vol% MeOH Charge 2: Excess Desired Enantiomer 21.53 21.97 95.65 2.20 2.15
Vial 3: 100 vol% MeOHCharge 2:
Excess Desired Enantiomer & Excess Undesired Enantiomer20.26 21.82 95.79 2.18 2.03
20 oC isotherm
Pure materials
20 oC isotherm
&
Eutectic Investigation
Experiments
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢Does residual metal content effect API solubility?
• Historical Batch Data – Highlighted this as a significant Issue
• Using Normal Phase HPLC method – Accounts for Chirality
Solids Charged
ICP-MS
Rh
ICP-MS
Zn
ICP-MS
FeTemp.
Desired
Enantiomer
Undesired
Enantiomer
ppm ppm ppm °C mg / g mg / g
Isolated
Pure Material0.45 9.13 5.33
10 20.7 0
20 21.0 0
40 46.8 0
Water Slurry #1
Process
Midpoint
Dry cake
800 1400 1900
10 16.2 1.9
20 21.9 2.1
40 41.8 2.4
Crude reaction
Material
(dry cake)
1900 31000 1700
10 20.1 8.9
20 26.2 14.6
40 53.2 13.6
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢Proof of concept Enantioselective Crystallization runs (Part 1)
• Starting point: Liquor 70:30 (by Mass) Desired: Undesired in selected solvent system 50:50 IPA: Water
14.2
23.1
37.2
61.683.2
14.924.2
39.637.637.1
0.72
0.78
0.940.90
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
10
20
30
40
50
60
70
80
90
5101520253035404550556065
Frac
tio
n o
f D
esir
ed in
So
lid P
has
e
Co
nce
ntr
atio
n o
f En
anti
om
er in
liq
uid
p
has
e (
mg/
g)
Process Temperature (°C)
➢In-Situ PAT: Understanding the Crystallization ➢Off Line HPLC Sampling (Crystallization)
• Sampling of Solution & Solid phase – Chiral content
• Desired Enantiomer – Solution phase Concentration
• Undesired Enantiomer – Solution phase Concentration
• Desired Enantiomer – Solid phase Fraction
5 61 4
1
2
3
4
5
6
Internal Reactor Temperature (Tr)
In-Situ FBRM: Counts No Wt. 1-1000
In- Situ FTIR: Peak Height at 1439 cm-1
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Case Study 1: Ternary Diagrams as a tool for Process Definition
➢Proof of concept Enantioselective Crystallization runs (Part 2)
• Starting point: Liquor 70:30 (by Mass) Desired: Undesired in selected solvent system 50:50 IPA: Water
➢In-Situ PAT: Understanding the Crystallization ➢Off Line HPLC Sampling (Crystallization)
• Sampling of Solution – Chiral content
• Expressed as wt% & plotted on ternary1
2
3
4
5
6
Internal Reactor Temperature (Tr)
In-Situ FBRM: Counts No Wt. 1-1000
In- Situ FTIR: Peak Height at 1439 cm-1
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➢ Ternary Diagrams as a tool for Process Definition
• Tech Transferred Process Flow:
• Modified Process Flow:
• Advantages:
• IPC for Range of operation 87 AP% to 92 AP% Desired from reaction stream
• Shorter Duration & Scalable Process Developed - Removes Facile operations
Carbon Treatments x 2, Drying x 1, Filtrations x 2 & Distillations x 2
• Higher Assay & Enantio. purity >99%, Yield % increase, Heavy Metals Purge <20 ppm
Case Study 1: Conclusions
19
OperationAssay(wt%)
Chirality(AP%)
ICP-MSRh
(ppm)
ICP-MSZn
(ppm)
ICP-MSFe
(ppm)
Crystallisation 99.3 99.2 29 250 50
Recrystallisation 99.9 99.9 3.7 3.4 19
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Case Study 2: Enhanced Process Understanding for Yield Improvement
➢ Brief Background
• Title: Enhanced Process Understanding for Yield Improvement
• Processing Issues:
• Isolated yield of telescoped reaction & crystallization step 81 % at plant scale. Incomplete mass balance for
active pharmaceutical ingredient and hence fate of desired API yield was unknown.
• Tightly defined limits in Global filing
• Project Objectives:
• Enhanced process understanding to Investigate process yield improvement opportunities
• Reduce process wastes and increase productivity with initial target of 4% yield improvement (Current Yield: 81%)
20
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Data Rich Experimentation – Process Assessment
21
00
Event 1: Methanesulfonic acid addition; temperature Increase; dissolution of starting material Event 2: Effective Seeding of batch
Event 3: Desaturation during 3 h isothermal hold
Event 4: Desaturation during cooling profile
Event 5: End
Figure 1: Standard process followed by in situ PAT: PVM and FBRM
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Mass Balance – Standard Process Conditions
API mg/mL
concentration
Volume
of Liquor (mL)Description
Mass Lost
grammes% of total Yield
16.3 90 Mother Liquor 1.470 12.41
4.6 26 Wash 1 0.119 1.01
1.9 13 Wash 2 0.025 0.21
N/A N/A Isolated Solids 10.120 85.47
Total 99.10 %
• Typical Process Yield: 75 – 87 % (APC Yield 83 – 85 %)
• Mass balance: 99 – 96 % (Loss to ML – 10.8 to 12.4 % of batch)
• Proven Acceptable Ranges defined by FilingUnderstanding the Crystallisation Roadmap
• Seeded cooling crystallization – end point liquor = starting liquor composition
• C16 solubility by clear point for Standard crystallization mother liquor
• Please Note: -10 oC solubility by HPLC
Data Rich Experimentation – Process Assessment
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Solubility Design Space – Proof of Concept (Artificial Solvent Systems)
23
#
Acetone
(vol%)
Water
(vol%)
70%
Acid
(vol%)
Ratio
Acetone/Wa
ter
100%
Acid
(vol%)
100%
Water
(vol%)
1 80.9 17.0 2.1 4.59 1.47 17.63
2 78.4 17.8 3.8 4.14 2.66 18.94
3 77.8 17.7 4.5 4.08 3.15 19.05
4 71.3 17.1 11.6 3.46 8.12 20.58
5 82.7 17.3 0 4.78 0 17.30
6 80.6 19.4 0 4.15 0 19.40
• The Global filing indicated ranges of operation for the process solvents – variation of these ratios (volumes) within the filing could yield
altered solubility. This possibility was investigated.
• The solubility of the target product in these solvent mixtures was studied using clearpoint by Crystal 16.
• HPLC was utilised for the solubility at -10°C .
87.7
11.0
82.3
9.4
82.0
8.5
56.6
4.5
85.3
36.2
85.3
37.1
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65A
PI s
olu
bili
ty (
mg/
g)
Temperature (°C)
API (Artificial Solvent Systems)
Solvent Mix 1
Solvent Mix 2
Solvent Mix 3
Solvent Mix 4
Solvent Mix 5
Solvent Mix 6
• Variation of the solvent ratios within accepted PAR leads to altered solubility in artificial solvent systems.
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Solubility Design Space – Proof of Concept (True Process)
24
Process Liquor Composition 1
35.3
104.1
11.3
54.7
19.0
92.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65
AP
I so
lub
ility
(m
g/g)
Temperature (°C)
API solubility: Varied liquor compositions within PAR• Working within PAR defined by Filing
• C16 solubility by clear point for Standard crystallization mother liquor. • Please Note: -10 oC solubility by HPLC
• Variation of the solvent ratios within accepted PAR leads to altered solubility
• Can be harnessed to increase process yield!
Process Liquor Composition 2
Process Liquor Composition 3
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Solubility Design Space – Proof of Concept (True Process)
25
Process Liquor Composition 1
35.3
104.1
11.3
54.7
19.0
92.5
0.010.020.030.040.050.060.070.080.090.0
100.0110.0
-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65
AP
I so
lub
ility
(m
g/g)
Temperature (°C)
API solubility: Varied liquor compositions within PAR• Working within PAR defined by Filing
Process Liquor Composition 2
Process Liquor Composition 3
Process Run IDIsolated
Yield
Loss
Mother Liquor
Loss
Cake wash 1
Loss
Cake wash 2
Mass
Balance
– (%) (%) (%) (%) (%)
Process Liquor Composition 1 85.4 12.4 1.0 0.2 99.1
Process Liquor Composition 2 90.1 8.1 0.7 0.2 99.3
Process Liquor Composition 3 74.7 23.4 0.6 0.1 98.9
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Process Development – Defining the Future State (in-situ FBRM & FT-IR)
26
Isolated yield: 90.8%
Mass Balance – Modified Process (High acid/water; low acetone; median MS Acid)
mg/mL concentration
Volumeof Liquor (mL)
DescriptionMass Lostgrammes
% of total Yield
8.58 565 Mother Liquor 4.84 5.84
2.89 158 Wash 1 0.45 0.55
1.05 138 Wash 2 0.14 0.18
N/A N/A Isolated Solids 75.36 90.76
Total 97.32
• Crystal 16 solubility by clear point for standard, modified process & PAR limits crystallization mother liquors.
• New setpoint established within PAR limits
• From process development work, the concentration of the API lost to the mother liquor has been decreased from:
16.33 mg/mL → 8.58 mg/mL
• Results in a ~7% isolated yield increase.equivalent physical and chemical properties (purity, form & PSD)
In- Situ FTIR
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Conclusion – How it performed on plant?
27
~7% isolated yield increase.
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Overall Conclusions
28
➢ Brief Background
• Stereoisomers, chirality and Active Pharmaceutical Ingredients
• Ternary Phase Diagrams & Enantioselective Crystallization
➢ Case Study 1: Ternary Diagrams as a tool for Process Definition
• Methodology & Development: End-to-end process definition & Enantioselective Crystallization
• Development of solubility design space (‘Roadmap’)
• Shorter Duration & Scalable Process Developed - Removed Facile operations
• More Robust & Cleaner - Higher Assay & Enantio. purity >99%, Yield increase, Heavy Metals Purge <20 ppm
➢ Case Study 2: Enhanced Process Understanding - Yield Improvement
• Methodology & Development: data rich experimentation
• Development of solubility design space (‘Roadmap’) & models to describe the unit operations
• Enhanced process knowledge leading to increased yield
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