2. GOAL
• Develop a robust process to isolate and purify a pharmaceutical
intermediate.
3. Problems to Address
• Impurity Purging
• Three main impurities were identified (referred to here as Impurity I – III)
• Impurity I was known to have negative effects downstream
• Vendor lacked the equipment to carry out a controlled cooling crystallization
• Cooling crystallization was not sufficient to fully purge impurities
• Liquid-Liquid Phase Separation
• A phase separation was sometimes observed during the antisolvent crystallization
leading to a loss of control
• The exact cause of this phenomenon was not known
• Yield of Intermediate
• Maximize yield while maintaining adequate impurity purging
• The extent to which water content decreased yield was not known
4. Developing an Antisolvent Crystallization
• The Pharmaceutical Intermediate :
• A small polar organic molecule capable of hydrogen bonding
• Reaction stream was made up of the intermediate and a polar Solvent A
• Water was a bi-product of the synthesis and present in the reaction stream
• Three major impurities were also bi-products of the reaction
• Chosen Antisolvent (Antisolvent B):
• A nonpolar solvent selected from a solvent screen
• The intermediate was highly insoluble in Antisolvent B
• Degree of supersaturation could be very well controlled by addition rate
5. Effect of Aging on Purity Profile
• Antisolvent B could be added upfront or over time
• Crystallization could be carried out at different temperatures
• Impurities can crash out on aging the slurry o/n depending on the
conditions
• Kinetic effects had to be minimized to develop a scalable process
• At 25°C and in a 50/50 Solvent A to Antisolvent B solution some
purging was observed, but not within the specifications
Aging @ 25 C HPLC Purity Solids – wt% Impurity I
Name st.m 40°C 25°C o/n Age
Impurity I 2.50 0.04 0.04 1.11
Intermediate 99.27 99.99 99.99 99.69
6. Aging @ 35 C HPLC Purity Solids – wt% Impurity I
Name st.m 40°C 35°C o/n Age
Impurity I 2.50 0.04 0.04 0.04
Intermediate 99.27 99.99 99.99 99.99
Temperature Played a Key Role
• At 35°C very good purging of Impurity I was observed in 50
volume% Antisolvent B
• No change was observed on aging overnight
• 61% of Intermediate was isolated compared to 78% at 25°C
• Better purging could be achieved at the expense of yield
• At 35°C the purity of the isolated solids was within specification
7. Liquid-Liquid Phase Separation
A liquid-liquid phase separation was sometimes observed during the antisolvent
addition, leading to a loss of control. This phase separation was not well
understood. Additional work was required to make this process feasible.
• Concentration of the intermediate could be monitored by FTIR
• The phase separation appeared to be dependent on the concentration of the
intermediate and temperature
• Effect of antisolvent amount on the phase separation had to be investigated
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0 5 10 15 20 25 30 35 40
Intermediate
Concentration(g/ml)
Temperature (°C)
Solubility and LLPS
Solubility
LLPS
LLPS Region
Single Phase
Supersaturated
Solution
8. In Situ FTIR Probe
A Mettler Toledo ReactIR 15 FTIR probe was used to track the concentration of the
intermediate in real-time as well as to monitor for oiling.
Seeded
Addition
Started
LLPS
A spike in peak height
was observed by FTIR
that was representative
of a liquid-liquid phase
separation.
9. Eliminating Water as a Variable
• The intermediate was dissolved in Solvent A and distilled under nitrogen
• A sample of the solution was acquired and analyzed by Karl Fischer titration for water content
• Known amounts of water were spiked in using an automated dosing unit
• Cooling until nucleation was observed, the reactor was heated at a set rate until dissolution was
observed by FTIR
• A 3°C difference was observed in dissolution below 0.7 wt% water
• The effect of water content on the phase separation had to be investigated as well
34.5
35
35.5
36
36.5
37
37.5
38
38.5
0.0% 0.1% 0.2% 0.3% 0.4% 0.5% 0.6% 0.7%
DissolutionTemperature(°C)
Water Content (wt%)
10. Designing an Experiment to Map out the LLPS Region
• Three separate experiments (starting in 2.1 vol, 4.2 vol and 12.5 vol Solvent A)
• Dissolution and LLPS were observed by FTIR, as well as nucleation (not shown here)
• Serial dilution with Antisolvent B while measuring dissolution and/or LLPS temperature at a
given solvent/antisolvent ratio and intermediate concentration
• Demonstrated potential of using more Antisolvent B to drive up yield
Solvent A Starting (vol):
2.1 vol (RED)
4.2 vol (GREEN)
12.5 vol (BLUE)
20
25
30
35
40
45
50
55
60
0% 10% 20% 30% 40% 50% 60% 70% 80%
Temperature(°C)
Antisolvent B (volume%)
11. Additional Problems to Address
• A large quantity of crude Intermediate produced on scale could not be carried
forward due to very poor purity
• Impurity II purged fully, Impurity III did not purge in this step
• Only about 2 wt% of Impurity I was shown to purge
• An additional step was needed to fully purge Impurity I
HPLC Solids – wt%
RRT Name Crude 4.2 vol Final 6.2 vol Final
0.72 Impurity I 4.61 3.14 2.53
0.81 Impurity II 1.05 0.00 0.00
1.00 Intermediate 94.06 96.62 97.22
2.59 Impurity III 0.28 0.24 0.25
Impurity I Concentration (g/ml): 0.0057 0.0050
Intermediate Concentration (g/ml): 0.061 0.059
Percent Yield: 70.8% 61.0%
12. Procedure Modification
• A large amount of crude Intermediate could not be carried forward on scale due to
poor purity, most notably 4.5 wt% Impurity I and 1 wt% Impurity II
• Impurity I was highly insoluble in Solvent B, a very good solvent for the
Intermediate
• By taking crude intermediate and dissolving in Solvent B, Impurity I could be
purged to less than 0.8 wt% upon filtering prior to the crystallization
• Without any understanding of performing a crystallization from this solvent
system, a solvent swap to Solvent A was necessary
• Both the filtration from Solvent B and the subsequent solvent swap had to be
defined
• The effect of residual Solvent B on the recrystallization was unknown
13. Filtration from Solvent B
• Filtration of solids from Solvent B purged Impurity I to less than 0.8 wt% in the
filtrate
• Impurity II and Impurity III did not purge
• Impurity III was shown to purge in a latter step in the process
• Filtrate was carried forward into the solvent swap
HPLC Purity – wt% known impurities (area% for unknown impurities)
Name RRT Crude 57 ml Filtration 340 ml Filtration
Impurity I 0.68 5.18 0.79 0.64
Impurity II 0.76 1.21 1.21 1.11
Intermediate 1.00 97.78 92.29 92.59
1.91 0.04 0.04 0.05
2.36 0.18 0.16 0.15
Impurity III 2.53 0.28 0.26 0.26
2.55 0.11 0.10 0.11
2.93 0.00 6.77 6.51
14. Solvent Swap
• Following the initial filtration, a distillation was carried out on the filtrate using an
equivalent volume of Solvent A as chase
• Intermediate in 5.7 vol Solvent B starting w/ Solvent A charged as chase
• Distilled down to 2.1 vol final solution
• Initial results demonstrated that 0.5 vol% Solvent B was achievable
• Final solvent composition was characterized by NMR (results shown below)
NMR
Single
5.7 vol
Solvent A Chase
Three
4.8 vol
Solvent A Chases
Vol% Solvent B
Resulting
0.5% 0.2%
15. Recrystallization with Residual Solvent B
• Intermediate in 2.1 vol solution starting (0.5 vol% Solvent B in Solvent A)
• 2.1 vol Antisolvent B was dosed over 14 h to avoid a liquid-liquid phase separation
during the addition
• Very good purging of Impurity I and II was observed by HPLC
• Aging step demonstrated that purging was independent of kinetics
HPLC Purity Solids - wt% known impurities
Name Post-
Solvent B
Filtration
7 h Age 2 day Age Wet Cake Dry Cake
Impurity I 0.68 0.04 0.04 0.07 0.07
Impurity II 1.21 0.00 0.00 0.16 0.16
Intermediate 94.70 99.81 99.82 99.69 98.83
Impurity III 0.29 0.25 0.24 0.33 0.29
Unknown 4.16 0.00 0.00 0.00 0.00
Percent Yield Intermediate: 75.6%
16. Next Steps
• Define the Solvent B Filtration
– Optimize filter aid
• Define the Solvent B to Solvent A Solvent Swap
– Perform solvent swap using OptiMax reactor
• Optimize Recrystallization for Purging and Intermediate Yield
– Determine effect of residual solvent B on the recrystallization
– Develop a model to predict Intermediate yield and purging capacity for a given amount
of Antisolvent B, temperature and volume of Solvent A starting
– Choose a 10°C temperature window to operate the recrystallization
