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`Grunenthal GmbH Exhibit 2035
`Rosellini v. Grunenthal GmbH
`IPR2016-00471
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`

`
`Scheme 1
`
`Synthetic route:
`
`P
`
`/*2
`
`S
`
`I ; Ph
`
`ABT-538
`
`Deprotcction
`
`O
`
`_, Ph
`HO
`N
`/KK 0 E BOC
`s
`fir’
`:-
`1:1
`0
`\
`
`Ph
`
`BOC monoacyl
`
`N \
`
`O
`
`5—Wing
`
`H2N
`
`HO
`
`;'
`\
`
`Ph
`
`{ Ph
`N BOC
`H
`
`TO
`
`2,4—Wing
`
`BOC—eore-succinatc
`
`wing acid. The 2,4-wing acid was convened by in situ
`reaction to the 2,4-wing activc ester, which underwent further
`assembly reaction to produce ritonavir. The phase II synthetic
`process differs from the phase I process as it uses 2.4-wing
`active ester as a starting material for the convergent synthesis
`of ritonavir.
`
`Polymorphism
`Polymorphism is the ability of a solid compound to exist
`in more than one crystalline form. These crystalline forms,
`although chemically identical, result from a different ordered
`arrangement of molecules within the crystalline lattice.
`Consequently, two polymorphs of the same compound can
`differ in physical properties that depend on the crystal lattice
`stability, such as melting p0i11t a11d solubility. The solubilities
`of different polymorphs of the same compound reflect the
`differences in flee energy between their respective crystalline
`states (which are different for each polymorph) and the
`solvated state. Thus, at a given temperature, different
`polymorphs may have significantly different solubility values.
`It is widely recognized that once a compound is in solution,
`any differences in solid-state structure are no longer ap-
`plicable.4 This is indicated by the decision process regarding
`polymorphism in the Proceedings of the Fourth International
`
`(4) Osol, A. Remingtonir Pharmaceutical Sciences; Mack Publishing C0,:
`Easton, PA, l980; p 1358.
`
`414
`
`-
`
`Vol. 4, No. 5, 2000 I Organic Process Research 8. Development
`
`3 C
`
`onference on Harmonization, Brussels, 1997, “for a drug
`product that is a solution, there is little scientific rationale
`for polymorph control”.5 Once the solid has been completely
`dissolved and there are no undissolved crystals present, the
`properties of the compound are unaffected by the original
`Crystal form.
`Since the discovery of ritonavir Form ll, several charac-
`terization studies have been conducted. Forms I and II have
`
`different crystal habits. When examined using polarized light
`microscopy, Form I is usually observed as lath crystals or
`rods. whereas Form II crystals appear as fine needles.
`In Form II, all of the strong hydrogen bond donors and
`acceptors have been satisfied, and the hydrogen bonds are
`strong. The difference between the solubilities of Forms I
`and II ca11 be explained i11 terms of the strength of the
`hydrogen bonds present within the crystal. Since the strength
`and completeness of the hydrogen bonding has attained the
`maximum possible in the Form II lattice, it is not thought
`possible that another undiscovered polymorph of ritonavir
`would exist with equivalent or lower solubility than that of
`Form II.
`
`Additional studies have been carried out to investigate
`the crystallization behavior using different solvent systems
`(5) Berridge, J. Physico—Chemical Characteristics of Drug Substances. D’Arcy,
`P. F., Harron, D. W'., Eds; JEFPIA Proceedings ofThe Fourth International
`Conference on Harmonization; Queen’s University of Belfast: Brussels,
`I997; p 66.
`
`4!
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`
`
`
`any:-Luamniusu
`Iaiununununn-noun:-agin-
`ii-mu-simu-
`
`.
`
`I
`
`1
`
`i
`
`I
`
`i
`
`-
`
`;
`
`Figure 1. Video micrograph of crystal Form I (left) and Form II (right).
`on
`ma.
`nun.
`IX.
`3|-.0
`mm
`mm
`ma.
`non
`flltb
`am.
`am.
`l!fl.|
`ma.
`ms.
`at.
`VUJ
`am
`nm
`
`
` Ll
`
`|.o
`
`l.I
`
`n.o
`
`10.!
`
`at:
`
`am no in lI.I
`
`II.I
`
`31.1
`
`8.0
`5..
`
`N 5..
`
`I,|
`
`in 1a.:
`
`1i.| no an an an 31.:
`
`am anin.
`
`Figure 2. X-ray powder diffraction of Form I (left) and Form II (right).
`and different crystallization techniqucs. Results from these
`Optical Microscopy. As shown in Figure I the crystal
`studies indicated that ritonavir (Form I or Form II) recrystal-
`habits of Forms I and II differ when examined using a
`lized predominantly as Form I or amorphous material. These
`polarized light microscope. Forml is usually observed as
`findings are consistent with the Ostwaldt rule which states
`lath crystals or rods, while form 11 is almost always fine
`needles.
`that the less stable form precipitates first and crystallizes
`more easily and preferably.
`Solid-state characterization by means of ‘H and “C
`nuclear magnetic resonance (NMR) spectroscopy as well as
`NIR (near infi-ared spectroscopy) and mid-IR confirmed that
`ritonavir can exist
`in two polymorphic forms. Similar
`spectroscopic studies using both NMR and IR on solutions
`of both Forms I and II ritonavir confirm that once in solution
`
`As shown in Figure 2, the two polymorphic forms have
`very different and distinctive patterns. Fonn I has a char-
`acteristic combination of peaks at 3.32 and 6.75 26, while
`Form 11 is missing these peaks and has characteristic peaks
`at 9.51, 9.88, and 22.2 26'.
`Solid-State Near Infrared Spectroscopy. The primary
`peaks for Forms I and II differ by approximately 19
`wavenumbers: 6085.6 wavenumbers (1.653 pm) for Form
`I and 6066.7 wavenumbers (1.648 pm) for Form 11.
`Solid-State “C Nuclear Magnetic Resonance (NMR).
`The solid state NMR spectra for the two forms differ
`significantly in the ranges of 150-180 ppm and 190-215
`
`the ritonavir is identical regardless of the original polymorph
`dissolved. Solutions prepared using Form I and solutions
`prepared using Form I1 gave identical NMR and IR spectra.
`Therefore, Form I or Form 11 ritonavir drug substance
`are both considered suitable for use in production of Norvir
`soft gelatin capsules as long as the manufacturing conditions
`ensure complete dissolution of the drug.
`
`Fonn I and Form II characterization and Analytical
`lnfonnation
`
`The Form 11 crystals were analyzed by using several
`established techniques for characterizing polymorphic fonns.
`The results of the comparison of Forms I and II are detailed
`below.
`
`Melting Points. There is an approximately 2-3 °C higher
`melting point for Form II (approximately 125 °C) versus
`Form I (approximately 122 °C). The heat of fusion for Form
`11 (82.8 Jig) is greater than for Form I (?8.2 Jig).
`
`Forms I and II Soliiiilities
`
`A comparison of the solubility profiles of the two forms
`in a series of cthanolnvatcr solvent mixtures at 5 °C is
`
`Vol. 4, No. 5. EEIJI1 I Organic Process Research 8: DEIrElnpI'I'lerfl
`
`u
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`115
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`
`Table 1. Solubility profile in various hydroalcoholic solvent
`systems at 5 °C
`etha;n01/
`100/1
`water
`(mg/mL)
`
`95/5
`
`90/10
`
`85/15
`
`80/20
`
`75/25
`
`individual impurities, largest unknown impurities, pH of the
`bulk drug, and amorphous content. All of the studies
`indicated no correlation between these factors and the
`
`presence of Form II.
`Impact of Form II on the Manufacturing of Bulk
`Drug. Manufacturing lots that generated Form 11 during final
`crystallization had a 50% failure rate. Failures were mainly
`for three reasons: solvent front impurities, residual solvents,
`and ethyl carbamate impurity. Extended drying time was
`needed to remove the residual solvents. It was found that
`
`early eluting impurities could be removed by an additional
`potassium carbonate wash prior to final crystallization. The
`carbamate impurity was linked to the source of the starting
`material (5-win g I-ICl containing the precursor impurity ethyl-
`p-nitrophenyl carbonate). This impurity was always formed
`whenever the source contained the precursor impurity. If the
`final product crystallized out as Form 1,
`the carbamate
`impurity was washed away with the mother liquors; on the
`other hand, it cocrystallized with Form II. Thus, this impurity
`could be eliminated either by controlling the impurity profile
`of the starting material (5-wing HCl) or by controlling the
`final crystallization process to give Form I. In conclusion,
`even though a new formulation was developed to accom-
`modate Form II solubility and no specification on the
`crystalline form of the bulk drug was required, it was still
`desirable from the manufacturing point of View to target
`Form I as the final crystal form. This also reduced processing
`time during formulation since Form I dissolves much faster
`than Form 11.
`
`Back to the lab. First, we decided to address memory
`retention of Form II in solution form. We found that,
`although Form II was much less soluble than Form I, it could
`be sonieated to form a highly supersaturated solution with
`respect to Form 11 and this solution could be maintained
`under a closed system to prevent any external contamination
`of Form II. This solution was then seeded with Form I to
`
`cause crystallization. The powder X—ray results showed only
`Form I as the product. This clearly suggested that the crystal
`form memory was not retained in the solution (Note:
`it is
`known that in the case of ritonavir if there is any contamina-
`tion of Form 11, the product is always Form II even if it is
`seeded with Form 1).
`Encouraged by this observation we moved on to pursue
`the process to selectively generate Form 1. Super seeding is
`a common approach used to achieve the formation of the
`less thermodynamically stable, yet desired, polymorph. As
`high as 50% seeding was considered for this purpose. By
`adding such a high amount of seed the throughput was
`reduced by 50% which was a huge drawback. We developed
`a very interesting idea to simulate super seeding without
`actually using large amounts of seeds, by using a reverse
`addition technique. The reverse addition technique was as
`follows: a small amount of seeds was stirred i11 the required
`amount of antisolvent. To this, the solution of product, in a
`crystallizing solvent, was slowly added. Since a very small
`amount of solution was added to the small amount of seeds
`
`originally present, this created the same effect as super-
`seeding, and as the addition progressed, the product that
`
`Forml
`Form II
`
`90
`19
`
`188
`41
`
`234
`60
`
`294
`61
`
`236
`45
`
`170
`30
`
`Table 2. Ritonavir polymorph I and II solubility
`
`solvent
`
`ratio
`
`mg/mL
`(Form I)
`
`mg/mL
`(Form II)
`
`Temperature = 70 °C
`NA
`1250
`ethy acetate
`2:1
`266
`ethy acetate:hcptancs
`1:1
`62.5
`ethy acetate:heptanes
`1:2
`11
`ethy acetate:heptanes
`Temperature = 50 °C
`NA
`ND”
`ethy acetate
`2:1
`9.26
`ethy acetate:hepta;nes
`1:1
`ND
`ethy aeetatezlieptanes
`1:2
`ND
`ethy acetatezheptanes
`Temperature = 25 °C
`NA
`14.87
`2:1
`4.43
`1:1
`ND
`1:2
`0.33
`
`ethy acetate
`ethy acetatezheptanes
`ethy acetatezheptanes
`ethy acetatezheptanes
`"’ ND = Not Deterniiried.
`
`825
`125
`31
`6
`
`26.85
`6.67
`2.38
`0.51
`
`5.45
`1.85
`0.66
`0.21
`
`presented in Table 1. As shown by these data the solubility
`profiles parallel each other, with Form II having significantly
`lower solubility throughout the series.
`The solubilities of ritonavir polymorphs I a11d II i11 the
`bulk drug manufacturing process crystallization system are
`shown in Table 2. The solubility of polymorph I
`is
`significantly higher than that of polymorph II.
`
`Evaluation of Bulk Drug Manufacturing for a Correlation
`to Form ll Found in the Semisolid Formulation
`
`After Form II was found in the semisolid formulation,
`an investigation was done to correlate manufacturing changes
`and the presence of Form II. The only significant process
`change implemented in manufacturing was during the final
`washing as described below.
`aqueous
`Normal wash sequence was the following:
`potassium carbonate, aqueous citric acid, aqueous potassium
`carbonate, aqueous citric acid, and water followed by
`crystallization .
`Modified wash sequence was the following: aqueous
`potassium carbonate, aqueous citric acid, aqueous potassium
`carbonate, aqueous citric acid, dilute aqueous potassium
`carbonate, and water followed by crystallization.
`The modified wash sequence was implemented to mini-
`mize early eluting impurities in the bulk drug. After the
`modification, at least 12 lots were used in the formulation
`without any failure for dissolution; therefore, this modifica-
`tion could not be directly responsible for the generation of
`Form Il. Graphs were plotted to find the correlation of Form
`11 appearance with bulk drug potency,
`total impurities,
`416
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`Vol. 4, No. 5, 2000 I Organic Process Research 8. Development
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`
`Table 3
`
`ethyl
`acetate
`
`heptanes
`
`results
`
`2
`1
`
`1
`0
`
`1
`1
`
`2
`I
`
`> 90% polymorph II
`50-50 polymorph I and II
`(solvent volume was 1/3 higher than normal)
`mostly polymorph I
`mostly polymorph I
`
`crystallized in turn acted as seeds, giving the effect of an
`extreme case of super-seeding.
`We put this idea into practice and developed a very
`reliable crystallization process on a laboratory scale to
`generate desired meta-stable polymorph I, using less than
`5% seeds (as little as 0.5% was also demonstrated in the
`lab). This process not only assured generation of Form I
`(even in the area contaminated with Form II) during
`recrystallization, but it was also used to generate Form I,
`starting with 100% Form II. We also discovered that by
`choosing an appropriate ratio of solvent to antisolvent the
`equilibrium leading to conversion of Form I to Form II could
`also be controlled with time.
`
`The typical process is described as follows:
`Charge 1 kg of ritonavir to reactor A. Then charge 4 L
`of ethyl acetate to the reactor and reflux until all the solids
`dissolve. Charge 0.005 kg of seed crystals (of Form I) to
`reactor B. Charge 4 L of heptanes to reactor B and agitate
`at ambient temperature.
`Slowly filter, using 0.2 mm filter cartridge, the hot solution
`(ritonavir in ethyl acetate) from reactor A to reactor B
`(containing seed crystals of Form 1 as a slurry in heptanes)
`over NLT 2 h. (It is not critical to maintain any particular
`temperature).
`Note: An initial slower addition will increase the chance
`
`of success. Cool the slurry in reactor B to an ambient
`temperature, agitate for NLT 3 h, filter, wash with heptanes,
`and dry. Following this process we were consistently
`successful in obtaining Form I.
`Solvent Ratio Effects on Rates of Equilibration. To
`reduce the propagation of polymorph 1 to polymorph 11, an
`equilibration study was carried out with different solvent
`ratios (ethyl acetate:heptanes) at room temperature.
`The results are as follows (Table 3):
`Isolated polymorph I was contaminated with 1% poly-
`morph II and stirred at room temperature for 21 h.
`Conclusion: Equilibration from polymorph I to poly-
`morph II is reduced as the percentage of heptanes increases.
`Manufacturing Process to Control Form 1. From lab
`studies it was clear that Form I could be generated during
`
`crystallization as long as the solution and the reactor were
`free of any Form II contamination. Form I, being the kinetic
`form, will always crystallize out first, and seeding with Form
`I crystals free of Form II could further control this. The
`following process was successfully developed and imple-
`mented in the manufacturing of the bulk drug to consistently
`obtain the crystalline product with less than 3% Form II
`contamination:
`
`A solution of ritonavir in ethyl acetate was refluxed for
`at least 1 h. To this heptanes were charged at the rate to
`control reflux. After the addition of heptanes was over, reflux
`was continued for at least 2 h. The solution was cooled to
`
`45 °C and seeded with crystalline ritonavir (Form I) and then
`stirred for not less than 3 h at that temperature. This was
`then cooled to 22 °C at the rate of not more than 8 °C/h.
`The solids were filtered at 22 °C.
`
`Manufacturing Process to Control Form 11. We also
`have designed a manufacturing process to produce exclu-
`sively the thermodynamically stable Form 11, which is
`described below.
`
`A solution of ritonavir in ethyl acetate was heated to 70
`°C. It was filtered and cooled to 52 °C (rate 2-10 °C/h)
`and seeded with Form II crystals of ritonavir and agitated
`for not less than 1 h at 52 °C. It was then cooled to 40 °C
`
`(rate 10 °C/h) and heptanes was charged and the mixture
`cooled to 25 °C and stirred for 12 h and filtered. It was dried
`
`at 55 °C for 18 11 to give exclusively Form II.
`
`Summary
`Although the polymorphism phenomenon is not new to
`the pharmaceutical and chemical
`field, Mother Nature
`continues to surprise the scientific community. One cannot
`be too careful in dealing with crystalline pharmaceutical bulk
`drug substances.‘ It
`is highly advisable to put enough
`resources to carry on exhaustive research to identify the most
`stable and all possible polymorphs. Moral of the story is:
`Dealing with Polymorphs is Potentially Precarious Practice
`and the Proper way to Play this game is with Patience and
`Perseverance.
`
`Acknowledgment
`We thank Dr. Wayne Genck, Genck International, and
`Dr. S. R. Byrn, SSCI, Inc./Purdue University, for their
`valuable advice in this work.
`
`Received for review March 3, 2000.
`OP000023Y
`
`(6) Dunitz, J. D.; Bernstein, J. Acc. Chem. Res. 1995, 28, 193 —200.
`
`Vol. 4, No. 5, 2000 I Organic Process Research & Development
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