Disclosing the rich crystal chemistry of Lesinurad by ab-initio

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Disclosing the rich crystal chemistry of Lesinurad by ab-initio laboratory X-ray powder diffraction methods Stephanie Terruzzi, Sonja Bellomi, Giovanni Marras, Giuseppe Barreca, Giampiero Ventimiglia, Antonio Cervellino, and Norberto Masciocchi Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01083 • Publication Date (Web): 01 Oct 2018 Downloaded from http://pubs.acs.org on October 2, 2018

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Crystal Growth & Design

Disclosing the rich crystal chemistry of Lesinurad by ab-initio laboratory X-ray powder diffraction methods

Stephanie Terruzzi, Sonja Bellomi,b Giovanni Marras,b Giuseppe Barreca,b Giampiero Ventimiglia,b,* Antonio Cervellino,c and Norberto Masciocchia,* a) Dipartimento di Scienza e Alta Tecnologia and To.Sca.Lab, Università dell’Insubria, via Valleggio 11, I-22100 Como, Italy b) Chemessentia Srl, via Bovio 6, I-28100 Novara 28100, Italy c) Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland

ABSTRACT: Lesinurad, a uric acid reabsorption inhibitor which received FDA approval in 2015, is known to crystallize in three unsolvated crystal forms and in a few solvated phases. The structures of the former have been determined by state-of-the-art powder diffraction methods, highlighting significant conformational as well as supramolecular differences, resulting in hydrogen bonded centrosymmetric dimers (Form 1) or helical chains (Form 2). In the complex crystal packing in Form 3, additional 1D ribbons held together by unexpected C=O…Br interactions of the halogen-bond type are found. Thermal analyses and variable-temperature powder diffraction measurements (including hightemperature synchrotron X-ray diffraction experiments) provided evidence for the reversible formation of a new phase, Form 2hT, obtained upon heating above 100°C powders of Form 2. Structure solution and refinement of the high-temperature phase made it possible to attribute the structural change to a 60° rotation of the cyclopropyl residue, leaving unaffected the conformation of the (longer) polar branch and the supramolecular 1D helical chain arrangement found in the RT phase.

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Crystal Growth & Design 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 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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INTRODUCTION Lesinurad, C17H14BrN3O2S or [5-bromo-4-(4-cyclopropyl-1-naphthalenyl)-4H-1,2,4-triazol-3-yl]thio]acetic acid (see Chart 1), is a uric acid reabsorption inhibitor which received FDA approval in 2015, 1 followed by EU marketing authorization within the European Community in early 2016. 2 Marketed by AstraZeneca under the Zurampic® trademark, it is normally included in tablets or capsules, largely based on lactose monohydrate and magnesium stearate excipients, as a white non-hygroscopic powder. As these tablets are intended for oral dosage, the solubility of the active pharmaceutical ingredient in the gastric environment (in both thermodymamic and kinetic aspects), may then be affected by a number of physico-chemical parameters, including crystal form, morphology, crystal size, degree of crystallinity and inter-grain interactions with excipients and the environment. This is particularly relevant for molecules showing non-interconverting enantiomers (here, of the atropoisomeric type3), which, though being processed as 1:1 racemic forms, may further crystallize as a conglomerate of enantiomorphic crystals or even as unbalanced racemates.4 Thus, starting from material preparation, isolation, processing and formulation, up to chemical and thermal stability, bioavailability and pharmacokinetic issues, the strict control of the solid state molecular aggregation type becomes a fundamental question to be answered, particularly when the number of crystal forms is large, and the pertinent energy landscape is highly corrugated.

Chart 1. Schematic drawing of the molecular structure and connectivity of Lesinurad, including labeling scheme and the torsion angles (τ1…τ5), freed during the structure solution and refinement process. Hydrogens are omitted for clarity. The scientific literature and the patents on solid Lesinurad deposited in the last years witness the occurrence of several crystal forms (mostly racemates, collectively reported in Table 1), for which very limited structural knowledge is however available. Only recently, the isolation of an enantiomerically 2 ACS Paragon Plus Environment

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resolved couple (of its ethyl ester, belonging to Class 3 atropisomers,3,5 with ∆Hrot > 30 kJ mol-1) was achieved, and the absolute structure and full stereochemical characterization was reported.6 Nonetheless, the pharmaceutically relevant racemate, in its many forms, has never been structurally characterized, probably because Lesinurad crystal forms typically appear as polycrystalline materials, not amenable to conventional single-crystal studies by diffraction methods. Table 1. A summary of known crystal forms of Lesinurad. Crystal Form

Solvation

Chirality

1st report

Ref. for structure

Form 1

Unsolvated

Racemate

WO2014/82957

This work

Form 2

Unsolvated

Racemate

WO2014/8295

This work

Form 2 hT

Unsolvated

Racemate

This work

This work

Form 3 (III o β)

Unsolvated

Racemate

US2016/2977788 This work

Form 4 (IV o α)

CH2Cl2 Solvated

Racemate

US2016/297778

n.a.

Form 5 (V)

CHCl3-THF Solvated

Racemate

US2016/297778

n.a.

Form 6 (VI)

CHCl3 Solvated

Racemate

US2016/297778

n.a.

Ethyl ester

Unsolvated

Enantiopure Wang, 20176

6

Our experience in the field on retrieving the correct geometry and packing features of molecular9 (or polymeric10) materials of moderate complexity, 11,12 as well our continuous interest in characterizing polymorphic drugs, prompted us to investigate this complex system by coupling ab-initio X-ray powder

diffraction

(XRPD)

methods

from

laboratory

and

synchrotron

sources,

with

thermodiffractometry, differential scanning calorimetry (DSC) and Fourier-transformed Infrared spectroscopy (FTIR). In this paper we will focus on the rich crystal chemistry of Lesinurad, disclosing the full crystal and molecular structures of Forms 1, 2, 2hT, and 3 and highlighting the different conformational and 5 supramolecular features. In this study we have not considered Forms 4, 5 and 6, since they are solvated forms, hence, according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines, not suitable for preparation of final dosage forms. Accordingly, our attention was not focused on their preparation and characterization due to regulatory limitations. Interestingly, the structural models here retrieved by the powder diffraction technique13 possess an intrinsic value in the field of polymorph detection and quantification, as the use of the Rietveld method in the “quantitative mode”, pioneered by dedicated shareware software codes like

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QUANTO14 and RIETQUAN,15 has recently been introduced in the pharmaceutical industry and made available to the non-expert level. EXPERIMENTAL SECTION Materials. For the aim of this work, Lesinurad (see Chart 1) was prepared in accordance to the company procedure, and isolated as crude methylene chloride (CH2Cl2) solvate (Form 4, see Table 1). Solvents and chemicals were purchased by Sigma-Aldrich Italia and used as received without further purification. Preparation of Different Crystal Phases. Preparation of Lesinurad Form 1. To a suspension of Lesinurad Form 4 (8 g) in water (13 mL), NaOH (pellets, 0.8 g) was added in order to obtain a clear solution. The solution was concentrated under reduced pressure at 35 °C up to half of the pristine volume to strip methylene chloride away from the starting solvate. The concentrated solution was warmed up to 65 °C and glacial acetic acid (20 mL) was added dropwise. When the addition was over, the suspension was cooled down to 0 °C and kept under these conditions for additional 30 minutes. The obtained solid was filtered, washed with water/acid acetic mixture 1:1 vol/vol (2 x 4 mL, previously cooled at 0 °C) and dried under reduced pressure at 40 °C to constant weight, thus obtaining 5 g of the title compound in its polymorphic Form 1. Preparation of Lesinurad Form 2. A suspension of Lesinurad Form 1 (10 g) in acetonitrile (50 mL) was heated to reflux temperature (80-82 °C), obtaining a clear solution. The mixture was then cooled down to 25 °C in order to promote the crystallization. The obtained solid was filtered, washed with acetonitrile (3 x 5 mL) and dried under reduced pressure at 40 °C to constant weight, thus obtaining 6 g of the title compound in its polymorphic Form 2. Preparation of Lesinurad Form 3. Lesinurad Form 4 (1 g) was dissolved at 25 °C in acetonitrile (100 mL). The solution was filtered and the clear filtrate was allowed to evaporate slowly under ambient conditions in a suitable open flask. The attained solid was finally isolated by scratching, thus obtaining 0.95 g of the title compound in its polymorphic Form 3. Laboratory X-ray Powder Diffraction (XRPD) Analysis. Diffraction patterns were obtained using a θ:θ vertical scan Bruker AXS D8 Advance diffractometer, equipped with a linear Lynxeye position sensitive detector, with a 300 mm radius goniometer. The (Ni-filtered) Cu Kα radiation was used, with the high-voltage generator set at 40 kV, 40 mA. Diffraction data for phase identification and indexing were typically collected in the 5-35° 2θ range, sampling at 0.02°. Diffraction data for structure solution 4 ACS Paragon Plus Environment

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were collected in the 5-105° 2θ range, sampling at 0.02°, in approximately 16 h in recycling mode. All samples were deposited in a 0.2 mm deep silicon monocrystal sample holder. When necessary, the samples were gently ground in an agate mortar with a pestle prior to the analysis. Figure 1 shows the raw XRPD data, which can be easily used for fingerprinting purposes; peak lists are supplied in Table S1. Synchrotron XRPD Analysis. As the in-house aluminum heating stage (in flat plate conditions) did not allow the collection of the entire diffraction dataset of Lesinurad Form 2hT, we resorted to a (Cryostream heated) capillary stage available at the X04SA-MS beamline of the SLS synchrotron facility at the Paul Scherrer Institute. The pristine powder sample of Form 2 was loaded in 0.5 mm quartz capillary, and diffraction data were measured using a Debye–Scherrer geometry and 17.5 keV radiation (λ = 0.709690 Å, calibrated with the use of a NIST Silicon 640D standard) and a Mythen detector,16 covering 120° 2θ with 0.0036° resolution. Three independent measurements were performed (in isothermal conditions), each lasting approximately 15 minutes: 298K, 413K and 298K after cooling. Heating and cooling rates were about 1K/s. Data were carefully absorption-corrected and subtracted for air and capillary scattering contributions before analysis, using a locally developed X-ray tracing protocol.17



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Figure 1. Raw XRPD patterns of the Forms 1, 2, 2 hT and 3 of Lesinurad (in the low angle region), collected with Cu-Kα radiation in the lab. Crystal Structure Determination. A general protocol, adopted in the powder diffraction structural characterization of Form 1, Form 2, Form 2 hT and Form 3 of Lesinurad, is here described. Exact peak positions of the different phases were determined using standard peak search methods followed by profile fitting methods incorporated in the program TOPAS-R,18 also used for indexing and determining approximate cell parameters for each phase. The initially derived unit cell parameters were then refined with the structureless Le Bail whole pattern profile fitting method.19 Density considerations and the analysis of systematic absences lead to the determination of the space groups and of the Z value. Structure solutions were carried out by employing a semirigid molecular fragment of the Lesinurad molecule, which was constructed using a molecular modeling optimization routine20, flexible about five torsion angles (see Chart 1). The location and orientation of the fragments were found using the simulated annealing algorithm incorporated in TOPAS-R. Each simulated annealing run yielded the correct solution in times varying from 4 hours to 3 days and was run until a reasonable structure solution (chemically and crystallographically) was repeatedly found. The structural models 6 ACS Paragon Plus Environment

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were then refined with the Rietveld method. Figure 2 shows the final Rietveld refinement plots for all four crystal structures solved herein. In order to minimize evident preferred orientation effects, the samples of Form 1 and Form 3 were gently ground prior to the analysis, and the relative XRPD was used for the final refinement. For each XRPD data set, the background was modeled using a Chebyshev polynomial (values reported in the SI file), and peak profiles were described by the fundamental parameters approach,21 and an average isotropic thermal factor was attributed to all atoms. Profile agreement factors for structureless (LeBail19) and Rietveld refinements are compared in the Supporting Information. Note that the RBragg values quoted below approach (but are not equal to) the conventional single-crystal R-factor based on F2. Indeed, since “observed” integrated intensities are not directly available, RBragg is biased toward the model (i.e. information from the model is used to apportion intensity between overlapped reflections). The CIF files for the final structural models have been deposited (CCDC codes 1855787-1855790). Crystal Data of Form 1. C17H14BrN3O2S, fw = 404.28 g mol-1, 298 K, λ (Å) = 1.5418, triclinic space group P-1, a = 7.3525(4) Å, b = 9.2100(7) Å, c = 13.7104(8) Å, α = 96.635(5)°, β = 104.646(4)°, γ = 108.110(4)°, V = 834.51(9) Å3, Z = 2, ρcalc = 1.6089(2) g cm-1, µ(Cu Kα) = 46.74 mm-1, Rp = 0.058, Rwp = 0.079, Rexp = 0.006, RBragg = 0.043. Crystal Data of Form 2. C17H14BrN3O2S, fw = 404.28 g mol-1, 298 K, λ (Å) = 1.5418, orthorhombic, space group Pbca, a = 22.1219(5) Å, b = 8.7073(3) Å, c = 18.2781(4) Å, V = 3520.8(6) Å3, Z = 8, ρcalc = 1.52543(7) g cm-1, µ(Cu Kα) = 44.32 mm-1, Rp = 0.075, Rwp = 0.102, Rexp = 0.0061, RBragg = 0.082. Crystal Data of Form 2 (hT). C17H14BrN3O2S, fw = 404.28 g mol-1, 418 K, λ (Å) = 1.5418, orthorhombic, space group Pbca, a = 21.942(4) Å, b = 9.266(1) Å, c = 17.497(3) Å, V = 3557(1) Å3, Z = 8, ρcalc = 1.5097(4) g cm-1, µ(Cu Kα) = 43.86 mm-1, Rp = 0.144, Rwp = 0.192, Rexp = 0.022, RBragg = 0.125. Crystal Data of Form 3. C17H14BrN3O2S, fw = 404.28 g mol-1, 298 K, λ (Å) = 1.5418, triclinic, space group P-1, a = 7.8966(4) Å, b = 10.0456(6) Å, c = 23.9934(9) Å, α = 91.433(3)°, β = 112.150(3)°, γ = 77.637(3)°, V = 1718.6(2) Å3, Z = 2, ρcalc = 1.5624(2) g cm-1, µ(Cu Kα) = 45.39 mm-1, Rp = 0.066, Rwp = 0.096, Rexp = 0.0063, RBragg =0.065.



a)

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b)

c) d) Figure 2. Final Rietveld refinement plots for (a) Form 1, (b) Form 2, (c) Form 2 hT and (d) Form 3 with difference plot and peak markers at the bottom. Panel c) shows the synchrotron X-ray diffraction pattern of Form 2 hT collected with λ = 0.709690 Å, with the high background attributed to the glass-capillary scattering. The Rietveld plot from (high temperature) laboratory data and a synoptic collection of the final refinement plots in Q-space are supplied in the Supporting Information.

Simultaneous Thermal Analysis (STA). Differential scanning calorimetric measurements and thermogravimetric analysis were carried out on a NETZSCH STA 409 PC/PG. About 10 mg of each sample, weighed exactly to the fifth decimal digit, were placed on alumina pans and heated under a nitrogen flow (60 mL/min). The heating ramp used, aimed at the identification of the thermal behavior of crystalline phases, was 10 K min-1, from 303 to 473 K. Transition temperatures were determined using the onset method, that is, the temperature at which the tangent segment taken in the first inflection point of the curve crosses the baseline. Complete plots are included in Supporting Information. Thermodiffractometric Analysis. For the variable temperature X-ray diffraction (VTXRD) measurements, a heating-stage equipped with an aluminum sample holder was used (supplied by Officine Elettrotecniche di Tenno, Ponte Arche, Italy). Scans were performed under isothermal 8 ACS Paragon Plus Environment

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conditions in the 6–33° 2θ range, typically from room temperature to sample decomposition, in 10°C steps, each measurement lasting ca. 15 min. The analysis of thermal strain was performed through the STRAIN applet available at the Bilbao Crystallographic Server22 (based on Ohashi’s approach

23

),

24

followed by graphical representation by WINPLOTR. . Melting Point determination. A melting point apparatus Stuart SMP30 equipped with a temperaturecontrolled heating system was used to monitor the formation of the liquid phase. Heating rate: 6 K/min. Infrared Spectroscopy (FTIR). FTIR spectra were recorded on a Thermo Scientific Nicolet iS5 spectrometer using KBr disks. Each spectrum was obtained as the average of 8 scans from 4000 to 400 cm-1 at 2 cm-1 of resolution. For the background correction, the spectrum of a reference blank KBr disk was used. See plots in the Supporting Information file.

RESULTS AND DISCUSSION Crystal and molecular structures for the different polymorphs of Lesinurad. As powder diffraction methods of molecular materials of moderate complexity do not have the same “resolving power” of conventional single crystal analyses, the structural models which can be refined need to rely on known, or easily assessable, preconceived units; 25 additionally, mathematical restraints limiting the number of free parameters and providing a stable convergence to the least squares (Rietveld-like) refinement, are also typically added. 26 Accordingly, a single isotropic thermal factor was employed for all atoms (disregarding the differential connectivities) and, above all, fixing intramolecular distances and angles (much stiffer than torsions) to known values (see Experimental section). Nevertheless, even if using a rigid-body approach (with 6 rotational and translational parameters defining the molecular center of mass and orientation), the torsion angles τn, shown in Chart 1 and collectively gathered in Table 2, were derived by best-matching procedures. These values show that, in Forms 1, 2 and 2hT, the polymorphic versatility is primarily attributable to the orientation of the cyclopropyl residue with respect to the naphthalene core (τ1 in Table 2) and to the torsion angle sequence within the branched 2thyoacetic arm (τ3-τ5). As expected, in all crystal phases, the two aromatic rings are nearly perpendicular one to the other, avoiding unfavorable H…Br and H…S intramolecular contacts. The refined molecular conformations are pictorially collected in Figure 3. At a supramolecular level, in all these crystal phases the carboxylic residues interact, by H-bonding, with N-atoms of neighboring molecules (O1…N3 2.48 Å in Form 1, where centrosymmetric dimers can



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be envisaged (see Figure 4a); O1…N3 2.56 Å in Form 2, where infinite chains (catamers) winding up along a 21 axis parallel to b are present – [2.56 Å in Form 2 hT measured at 140°C] (as in Figure 4b). The structure of Lesinurad Form 3 needs, however, a special comment. First of all, two crystallographically independent molecules (A and B, in the following, see Figure 3d,e), crystallizing as a racemate in triclinic P-1 with Z=4, are present. Molecule B shows torsional angles similar to those found in Form 1 and, accordingly, through an inversion center, it generates dimers with O1…N3 distance of 2.51 Å, very much as shown in Figure 4a. Molecule A, at variance, shows a rather peculiar intramolecular arrangement in infinite ribbons running along the [1-10] direction, which are formed by H-bonded O1…N2 distances of 2.49 Å and short attractive interactions of the halogen-bond type between O2 and Br (2.69 Å) (see Figure 4c). Such a short distance was already detected in a number of cases,27 and beautifully explained by accurate theoretical computations.28 Altogether, the crystal packing of Form 3 shows the aforementioned supramolecular ribbons, intercalated by Molecule B dimers nearly perpendicular to them (see Figure 4d).

Table 2. Melting Points (m.p.), Molar Volumes (V/Z) and Relevant Conformational Features of the Lesinurad Molecule in the Different Solid Forms. Form 1

m.p.,

3

τ2, °

τ3, °

τ4, °

τ5, °

Å

C2-C4-C11-C12

C1-C3-N1-C14

N1-C15-S-C16

C15-S-C16-C17

S-C16-C17-O1

158

417

107.3

103.7

-167.0

-85.6

-156.4

440

73.4

92.6

-123.6

59.8

163.2

444

134.6

85.6

-125.7

58.9

164.3

165.8

90.0

-180.0

-168.1

122.2

123.0

87.2

139.4

99.4

-176.1

169

3, A 3, B

τ1, °

°C

2 2 hT

V/Z,

157

429


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a) Form 1

b) Form 2

c) Form 2hT

d) Form 3, Molecule A

e) Form 3, Molecule B

Figure 3. Sketch of the molecular geometries of the Lesinurad molecules in Form 1 (a), Form 2 (b), Form 2hT (c) and Form 3 [molecule A in d), and molecule B in e)]. Drawn by SCHAKAL.29



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a) Form 1

b) Form 2

c) Form 3, Molecule B

d)

Figure 4. Sketch of the supramolecular arrangements of the Lesinurad molecules in the different crystal forms: centrosymmetric dimers in Form 1 (a), 1D chains in Forms 2 (b) and 2hT (not shown here), and 1D ribbons for molecule B in Form 3 (c). The complex crystal packing of Form 3 viewed down b (c, horizontal), is shown in panel (d), where the two differently bonded molecules (A, as dimers in the blue circle; B halogen-bonded ribbons in the red one) are highlighted. The supplied CIF files should help the interested reader in designing its proper view(s). Drawn by SCHAKAL.29

Spectroscopic Analysis In the IR spectra recorded at ambient conditions, the main absorption bands for the Lesinurad molecule can be seen (Figure 5). Above 1000 cm-1, i.e. in the “simplified” stretching region, all spectra show a C-O band at ca. 1290 cm-1, a strong resonance for the C=O stretching near 1730 cm-1, and a broad OH signal above 3000 cm-1. Additional bands for the C=C and C=N stretching modes are seen at 1600 cm-1 or below. It is important to note that every crystal form has its characteristic set of absorption bands in the fingerprint region; thus, IR spectroscopy, in addition to XRPD, can be easily used to distinguish the different forms. This is particularly significant for fast production control in the industrial field, and, to this goal, the sharp bands falling near 1700 cm-1 or slightly above, with their peculiar, and different, shapes in the three forms (see Figure 5), can be straightforwardly used. 12 ACS Paragon Plus Environment

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Figure 5. IR spectra of Form 1, Form 2 and Form 3. Note the difference in the shape of the intense νC=O band near 1730 cm-1, which can be taken as a fingerprint for fast polymorph identification. Thermal Behaviour Unsolvated Forms 1, 2 and 3 melt at rather different temperatures (see Table 2); in their DSC traces, shown in Figure 6, endothermal events with onsets above 150°C (up to ca. 177°C for Form 2) and latent heats near 20 kJ mol-1, or slightly above, can be seen. Among these forms, only Form 2 shows an additional solid-to-solid transformation (a weak endotherm near 92°C, with ∆H = 0.5 kJ mol-1), assigned by thermodiffractometric methods to the formation of the new 2hT Lesinurad phase. With reference to the molar volumes reported in Table 2, apparently there is no evident trend correlating crystal densities (hence, packing fractions) with melting points. Variable-temperature X-ray diffraction measurements (shown below in Figure 7) clearly indicated the absence of phase changes of Forms 1 and 3 before melting. Worthy of note, visual inspection of the melting process of Form 3 indicated that 13 ACS Paragon Plus Environment


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the endothermic event occurring near 160°C is a complex one, as it occurs over a large temperature interval. Thorough (though manual) grinding of Form 3 partially narrows such range, but inhomogeneities (not seen while melting Forms 1 and 2hT) do not disappear. Whether this is due to particle size effects, incongruent melting or incipient solid-solid phase transformation before melting occurs, cannot be assessed on the basis of our available data.

Figure 6. DSC traces for Form 1, Form 2, and Form 3, obtained at a 10 K min-1 heating rate. The analysis of the lattice parameters variation, in oblique crystal systems, requires the determination of the full strain tensor, and of the linear thermal expansion coefficients (∂lnx/∂T, for x = a,b,c) and their angular analogues (∂lnφ/∂T, for φ =α,β,γ). For simplicity, ∂lnx/∂T and ∂lnφ/∂T values and the full 3D tensors are shown, respectively, in Table 3 and in Figure 8. For Forms 1 and 3, the graphically depicted tensors show only positive lobes (in green), manifesting a gradual expansion, which is significantly more anisotropic in Form1 than in Form 3; In both cases, the presence of a complex and 14 ACS Paragon Plus Environment

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difficult-to-quantify network of intermolecular interactions does not allow to easily correlate the soft direction with the structural models. However, Forms 1 and 3, in the studied range, do not show transformation into new crystal phases, and their lattice variations are caused by increased atomic/molecular mobility, rather than by structural changes. At variance, variable temperature XRPD plots clearly indicated that Form 2, through a (reversible) solid-solid phase transformation, generates the Form 2hT crystal phase, from which it differs by a significant rotation of the cyclopropyl residue about the exocyclic C-C bond, larger than 60° (see also the τ1 values in Table 2); at variance, the conformations of the remaining torsions are only marginally affected. The strain tensor calculated from comparison of the RT and 145°C lattice parameters shown in the insert of Figure 7b, evidences the high anisotropy of the thermal expansion coefficients, also confirmed by the large discontinuities in the VTXRD plot. Figure S4 in the Supporting Information file shows the overlaid XRPD patterns, collected in the laboratory, for the RT and 145°C (Forms 2 and 2hT, respectively), highlighting, the anisotropy of the cell parameter changes, which can be easily visually traced by the (often countercorrelated) peak shifts.

Table 3. The thermal expansion coefficients, ∂lnx/∂ ∂T (x = a,b,c) and ∂lnφ φ/∂ ∂T (φ φ = α,β β,γγ), in MK-1, for the different crystal forms of Lesinurad, together with the direction of null expansion. Form

∂lna/∂T

∂lnb/∂T

∂lnc/∂T

∂lnα/∂T

∂lnβ/∂T

∂lnγ/∂T

Direction of null expansion

1 2a 3

+48 −63 +61

+20 +493 +62

+65 −328 +58

−40 0 +54

−54 0 +4

−19 0 −31

none ca. [021] none

a

Across the phase transition from Form 2 to Form 2ht.



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Figure 7. 2D VTXRD plots for Form 1, Form 2, and Form 3 (top to bottom). In the insert, the thermal strain tensor relative to the Form 2 – Form 2hT phase transformation, highlights the negative thermal expansion coefficient along c. 16 ACS Paragon Plus Environment

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a)

b)

c)

Figure 8 – Thermal strain tensors derived for a) Form 1 (RT - 155 °C), b) Form 2 (RT - 145 °C hT) and c) Form 3 (RT - 155 °C) (not to scale). CONCLUSIONS In this paper we have presented the isolation of three unsolvated forms of the recently marketed Lesinurad molecular crystals, together with their full structural characterization by ab-initio powder diffraction methods. Comparison of their crystal packing manifested different supramolecular arrangements, ranging from centrosymmetric dimers, helical catemers and even 1D ribbons held together by halogen bonds of the C=O…Br type, strong enough to compete, in Form 3, with conventional hydrogen bond interactions. Additionally, Form 2 was shown to reversibly generate a high-temperature phase, by the coherent rotation of the cyclopropyl residue about the C-C exocyclic bond. A thorough thermal characterization by DSC and variable temperature powder diffraction methods provided additional structural information and the thermal expansion tensors. Work can be anticipated in the direction of i) characterizing the many Lesinurad solvates reported in the literature, for which scarce structural data are available, and ii) possibly isolating polycrystalline conglomerates, rather than racemates, widening the spectrum of its polymorphic versatility and opening the way to alternative pharmaceutical processing routes and, whenever possible, biochemical benefits.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publication website at DOI://***



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Crystal information files (CIFs) of Forms 1, 2, 2hT and 3. Supplementary Table S1 (list of most relevant XRPD peak positions for fingerprinting purposes), S2 (Chebyshev polynomial coefficients), S3 (comparison of profile agreement factors in the LeBail and Rietveld modes, and refined isotropic Debye-Waller parameters, Biso) and Figures S1-S5 (XRPD, FTIR and STA plots) (pdf).

Accession Codes CCDC 1855787-1855790 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Website: toscalab.uninsubria.it Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS We thank Cristina Corti, University of Insubria, for technical assistance.


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For Table of Contents Use Only

Disclosing the rich crystal chemistry of Lesinurad by ab-initio laboratory X-ray powder diffraction methods Stephanie Terruzzi, Sonja Bellomi, Giovanni Marras, Giuseppe Barreca, Giampiero Ventimiglia,* Antonio Cervellino, and Norberto Masciocchi*

The structure and thermal evolution of three polymorphic crystal phases of unsolvated Lesinurad, studied by powder diffraction methods, showed the occurrence of centrosymmetric dimers, 1D helical catemers of homochiral molecules and 1D ribbons, the latter built upon unusual halogen-bond interactions of the C=O…Br type.


Disclosing the rich crystal chemistry of Lesinurad by ab-initio

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