Conformational polymorphism of diethyl 1-(phthalylglycyloxy)-2-phthalylaminoethenephosphonate

Journal of Molecular Structure 595 (2001) 167±174

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Conformational polymorphism of diethyl 1-(phthalylglycyloxy)-2-phthalylaminoethenephosphonate Jolanta Holband a,*, GrazÇyna WoÂjcik a, Zyta Ziora b, Paweø Kafarski b a

Institute of Physical and Theoretical Chemistry, Wrocøaw University of Technology, WybrzezÇe WyspianÂskiego 27, 50-370 Wrocøaw, Poland b Institute of Organic Chemistry, Biochemistry and Biotechnology, Wrocøaw University of Technology, WybrzezÇe WyspianÂskiego 27, 50-370 Wroclaw, Poland Received 21 November 2000; revised 25 January 2001; accepted 25 January 2001

Abstract In course of the synthesis of phosphonic derivatives of bestatine, several products have been obtained. One of them turned out to occur in two polymorphic forms. Two crystal structures correspond to two molecular conformations. The  b ˆ 12:092…2† A;  c ˆ 24:103…5† A;  bˆ crystal structures are as follows: (1a) C24H21N2O9P, P21/n, a ˆ 8:023…2† A;  b ˆ 16:378…2† A;  c ˆ 18:442…2† A;  b ˆ 101:13…1†8; 92:39…3†8; Z ˆ 4; (1b) C24H21N2O9P, P21/c, a ˆ 8:322…1† A; Z ˆ 4:The main conformational difference consists in the mutual orientation of two phthalyl rings. The conformation and packing of sterically overcrowded and conformationally ¯exible molecules seem to be stabilized by very weak C± H´ ´´O hydrogen bonds. The extremely large thermal vibration amplitudes of the phosphonic group's atoms indicate the occurrence of disorder, probably of dynamical character. This disorder becomes frozen below room temperature. The differential scanning calorimetry (DSC) revealed the occurrence of phase transitions below room temperature in both crystals. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Aminophosphonate; Polymorphism; Molecular conformation; Weak hydrogen bond

1. Introduction Aminoacid analogs, in which carboxylic groups are substituted by phosphonic ones, exhibit often various biological activities [1±3]. They are good inhibitors of enzymes due to the fact that a phosphonic group is the mimic of highenergetic, tetrahedral transition state of aminoacids during the reaction with enzymes. Bestatine [4] and its analogs [5] mimic active, nonterpenoic fragment of taxol [6], an anticancer drug isolated from yew-tree bark. Phosphonic analogs of * Corresponding author. Tel.: 148-71-320-2415; fax: 148-71320-3364. E-mail address: [email protected] (J. Holband).

bestatine are potential inhibitors of proteolitic enzymes and potential anticancer drugs. The reaction of phthalyloaminoacid chlorides with triethyl phosphite seemed to be one of the synthetic methods of phosphonic analogs of bestatine [7]. However, in course of the synthesis, the ®rst step of this reaction did not lead to the expected ketophosphonate but we obtained a mixture of products [8]. NMR and IR methods were used to analyze them. The structure of the title compound, which turned out to be the condensation product of two ketophosphonate molecules, had to be determined by X-ray analysis. Depending on synthesis and crystallization conditions we obtained two forms of the compound. They corresponded to different molecular conformations and crystal structures; hence they may be called

0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0022-286 0(01)00521-X

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Table 1 Crystal data and structure re®nement parameters for 1a and 1b

Chemical formula Chemical formula weight Temperature (K) Crystal system Space group

Ê 3) Volume (A Z Dcalc (g/cm 3) Dm (g/cm 3) Melting point (8C) Absorption coef®cient (mm 21) F(000) Crystal size (mm) u range for data collection Index ranges Re¯ections collected Independent re¯ections Data/restraints/parameters Goodness-of-®t on F 2 Final R indices [I . 2s (I)] R indices (all data) Extinction coef®cient Largest diffraction peak/hole Ê 3] [e/A

1a

1b

C24H21N2O9P 512.40 298(2) Monoclinic P21/n  a ˆ 8:023…2† A  b ˆ 12:092…2† A  c ˆ 24:103…5† A b ˆ 92:39…3†8 2336.3(9) 4 1.457 1.462 182±183 0.176 1064 0:6 £ 0:5 £ 0:5 27.48 210 # h # 10 0 # k # 15 0 # 1 # 31 5409 5288 5288/0/399 1.098 0.069/0.164 0.131/0.223 0.024(3) 0.698/20.656

C24H21N2O9P 512.40 298(2) Monoclinic P21/c  a ˆ 8:322…1† A  b ˆ 16:378…2† A  c ˆ 18:442…2† A b ˆ 101:13…1†8 2466.3(5) 4 1.380 1.377 172±173 0.167 1064 0:51 £ 0:26 £ 0:18 27.88 210 # h # 6 221 # k # 24 222 # 1 # 24 15392 5785 5785/4/345 0.861 0.079/0.216 0.154/0.253

conformational polymorphs [9]. Hereafter these two forms are labeled 1a and 1b. In this paper we report X-ray crystal structure analysis and some results of differential scanning calorimetry (DSC) measurements concerning the thermal stability of the two crystals. 2. Experimental The synthesis details of 1a and 1b have been described by Ziora et al. [8]. The reaction performed in benzene solution and crystallization of the product from ethyl acetate/hexane solution led to 1a. When we performed this reaction in toluene and crystallized the product from chloroform/hexane solution we obtained 1b. Crystals of both forms are colorless, transparent

0.428/20.553

lumps. Their X-ray diffraction patterns were excellent with good intensities of diffracted beams. The X-ray data of 1a were collected at room temperature, on the Kuma KM4 diffractometer equipped with a conventional detector. Graphitemonochromatized MoKa radiation was employed. Cell parameters have been determined on 32 re¯ections from the 6±178 u range. Data reductions were performed using Kuma KM4 Software [10] without absorption corrections. The X-ray data of 1b were collected at room temperature, on the Kuma KM4CCD diffractometer equipped with an area detector. The detector was positioned at 46 mm from the crystal. Number of frames was 556. The frames were measured at 0.88 v width with 10 s exposure time. The intensities were corrected for Lorentz and polarization effects. No absorption

J. Holband et al. / Journal of Molecular Structure 595 (2001) 167±174 Table 2 Atomic coordinates …£104 † and equivalent isotropic displacement  2 £ 103 † for 1a. Only more occupied (primmed) parameters …A atoms of the disordered phosphonate group are shown

P(1) 0 N(1) N(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7 0 ) O(8 0 ) O(9 0 ) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21 0 ) C(22 0 ) C(23 0 ) C(24 0 )

x

y

z

U(eq)

6517(3) 5318(3) 5884(3) 6375(3) 3909(3) 6493(2) 4403(3) 6711(3) 4949(3) 5107(5) 6545(8) 8126(5) 5949(4) 5523(3) 5703(3) 5137(3) 5206(4) 4499(4) 3748(4) 3673(3) 4382(3) 4467(3) 5635(3) 6534(4) 6023(4) 5199(3) 4953(4) 4138(5) 3601(4) 3864(4) 4681(3) 5123(4) 3390(4) 2450(3) 8327(14) 9860(3)

7949(3) 4840(2) 8029(2) 3765(2) 5373(2) 6840(2) 7952(2) 9680(2) 6705(2) 8859(3) 7605(7) 8450(4) 6803(2) 5848(2) 3825(2) 2946(2) 1806(3) 1187(3) 1683(3) 2821(3) 3444(2) 4659(2) 7433(2) 7303(3) 9180(2) 9584(2) 10648(3) 10769(4) 9872(4) 8791(4) 8670(3) 7657(3) 8670(2) 9584(15) 9324(8) 9145(18)

675(2) 1172(1) 3024(1) 478(1) 1957(1) 1685(1) 1944(1) 2649(1) 3624(1) 767(2) 97(3) 913(2) 1126(1) 894(1) 915(1) 1290(1) 1239(1) 1659(2) 2092(1) 2139(1) 1735(1) 1668(1) 2052(1) 2609(1) 3008(1) 3509(1) 3691(2) 4187(2) 4474(2) 4295(1) 3806(1) 3504(1) 600(11) 346(9) 1323(4) 1641(9)

49(1) 43(1) 48(1) 63(1) 59(1) 46(1) 55(1) 68(1) 73(1) 57(1) 62(2) 72(1) 46(1) 45(1) 44(1) 45(1) 59(1) 65(1) 61(1) 52(1) 43(1) 44(1) 42(1) 53(1) 48(1) 50(1) 67(1) 81(1) 82(1) 65(1) 48(1) 48(1) 137(11) 154(8) 69(2) 119(8)

correction was applied. The data reduction was performed with the Kuma KM4CCD Software [11]. Unit cell parameters were determined by least-squares re®nement using 1532 re¯ections from the 6±378 u range. The structures were solved by direct (1a) and Patterson (1b) methods using the shelxs program and re®ned on F 2 values by full-matrix least squares using the shelxl program from the shelxl-97 package [12] with anisotropic displacement parameters for non-hydrogen atoms. Positions of

169

Table 3 Atomic coordinates …£104 † and equivalent isotropic displacement Ê 2 £ 10 3) for 1b. Only more occupied (primmed) atoms parameters (A of the disordered phosphonate group are shown

P(1) N(1) N(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21 0 ) C(22 0 ) C(23) C(24)

x

y

z

U(eq)

6690(1) 3816(3) 2507(3) 2781(4) 4518(4) 5364(2) 2630(3) 2337(4) 2060(6) 8471(3) 6510(3) 6295(3) 5447(4) 4780(4) 2896(4) 2219(4) 1236(5) 811(6) 1363(6) 2304(5) 2729(4) 3785(4) 3870(4) 4059(4) 1736(4) 129(4) 2 1160(5) 2 2499(6) 2 2510(8) 2 1216(8) 73(5) 1621(6) 9180(16) 10340(2) 4814(6) 4734(9)

9059(1) 9821(2) 6595(2) 11026(2) 8751(2) 8218(1) 8202(1) 6300(2) 6603(4) 8882(2) 9838(2) 8279(2) 9014(2) 9682(2) 10538(2) 10546(2) 11125(3) 10943(5) 10257(5) 9701(3) 9857(3) 9381(2) 7869(2) 7001(2) 6290(2) 5977(2) 5646(3) 5397(3) 5445(4) 5750(5) 6048(3) 6427(3) 8113(12) 7769(14) 8239(3) 7480(4)

8169(1) 6252(1) 6413(2) 6598(2) 5536(2) 6966(1) 6842(2) 7608(2) 5157(2) 8046(2) 8525(1) 8566(2) 7264(2) 6952(2) 6122(2) 5316(2) 4909(3) 4138(3) 3838(3) 4264(2) 5008(2) 5589(2) 6799(2) 6558(2) 6959(2) 6574(2) 6835(3) 6340(4) 5601(5) 5329(3) 5829(2) 5713(2) 7911(10) 8474(14) 8860(3) 9237(4)

73(1) 61(1) 69(1) 91(1) 102(1) 68(1) 77(1) 100(1) 203(3) 108(1) 85(1) 96(1) 60(1) 61(1) 68(1) 73(1) 104(2) 118(2) 115(2) 97(1) 74(1) 70(1) 60(1) 72(1) 68(1) 68(1) 91(1) 115(2) 156(3) 157(3) 95(1) 107(2) 130(6) 204(12) 108(2) 169(3)

hydrogen atoms were calculated geometrically (except the H(2) atoms, which were located by differential Fourier map) using the riding model and re®ned isotropically. Conformational restraints were applied to disordered atoms to improve bond distances. We performed diffraction measurements at lower temperatures (by 110 K) using Oxford Cryosystem cooling unit. Calorimetric measurements of both forms 1a and 1b were undertaken by means of differential scanning

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calorimeter Perkin±Elmer DSC-7 in the 118±340 K temperature range with the aim to check the thermodynamic stability of both forms. Densities of crystals were measured by ¯otation method in CCl4/heptane solution. 3. Results and discussion Crystal data and structure re®nement parameters as well as some experimental details are shown in Table 1. Positional and isotropic thermal vibration parameters of 1a are shown in Table 2. Table 3 shows the above-mentioned parameters of 1b. The overall view and labeling of atoms in 1a and 1b molecules are displayed in Fig. 1a and b, respectively [13]. Molecular packing in the 1a and 1b polymorphic crystals is shown in Fig. 2a and b, respectively [14,15]. Tables 4 and 5 report bond distances in 1a and 1b molecules, respectively. Selected torsion angles are presented in Table 6 (1a) and Table 7 (1b). Both conformers 1a and 1b differ from each other considerably. Two phthalyl rings in form 1a are nearly coplanar (interplanar angle is 1.358), while in form 1b two rings are almost perpendicular (inter-

(a)

planar angle is 85.088). The molecules exhibit large thermal vibration amplitudes in the crystals. The values of atomic thermal displacements indicated the occurrence of some structural disorder in both forms. This disorder relates mainly to the phosphonic groups atoms. We had to model the disorder within these fragments of the molecules. The whole phosphonic group of molecule 1a is disordered over two positions, with occupancy factor of about 0.40 and 0.60. Such a partition of the phosphonic group resulted in more rational values of bond lengths. Nevertheless the bond lengths between the carbon atoms in the ethoxy `wires' (C(21)±C(22) and C(23)±C(24)) remain very short indicating the large amplitudes of the librational motion in which the atoms are involved. The same relates to 1b. In the 1b polymorph we modelled the disordered occupancy over two positions only within the ±C(21)H2 ± C(22)H3 group. However, the bond lengths are only slightly better and the thermal motion amplitudes remain still large. The occupancy of both positions of the disordered group were re®ned and converged to 0.548 for C(21 0 ) and C(22 0 ). The other ethoxy group has not been divided because the O(9)±C(23) and C(23)±C(24) bonds do not exhibit large deviations from the ideal values.

(b)

Fig. 1. (a) Molecular conformation of 1a form. Ellipsoids were drawn at the 25% probability level. Only one position (more occupied) of the disordered phosphonic group is shown. (b) Molecular conformation of 1b form. Ellipsoids were drawn at the 25% probability level. Only one position (more occupied) of the disordered ethyl group is shown.

J. Holband et al. / Journal of Molecular Structure 595 (2001) 167±174

171

Fig. 2. (a) Molecular packing in 1a crystal viewed along the a axis. (b) Molecular packing in 1b crystal viewed along the a axis.

Table 4 Ê ) in 1a molecule. Only more occupied (primmed) Bond distances (A atoms of the disordered phosphonate group are shown

Table 5 Ê ) in 1b molecule. Only more occupied (primmed) Bond distances (A atoms of the disordered phosphonate group are shown

P(1 0 )±O(7 0 ) P(1 0 )±O(8 0 ) P(1 0 )±O(9 0 ) P(1 0 )±C(1) N(1)±C(2) N(1)±C(10) N(1)±C(3) N(2)±C(13) N(2)±C(12) N(2)±C(20) O(1)±C(3) O(2)±C(10) O(3)±C(1) O(3)±C(11) O(4)±C(11) O(5)±C(13) O(6)±C(20) O(7 0 )±C(21 0 ) O(9 0 )±C(23 0 ) C(1)±C(2)

P(1)±O(8) P(1)±O(9) P(1)±O(7) P(1)±C(1) N(1)±C(3) N(1)±C(2) N(1)±C(10) N(2)±C(20) N(2)±C(13) N(2)±C(12) O(1)±C(3) O(2)±C(10) O(3)±C(11) O(3)±C(1) O(4)±C(11) O(5)±C(13) O(6)±C(20) O(7)±C(21 0 ) O(9)±C(23) C(1)±C(2)

1.601(4) 1.455(8) 1.517(5) 1.831(5) 1.403(3) 1.418(3) 1.415(3) 1.397(4) 1.443(3) 1.404(4) 1.204(3) 1.207(3) 1.399(3) 1.350(3) 1.190(3) 1.207(4) 1.196(4) 1.44(3) 1.452(9) 1.322(4)

C(3)±C(4) C(4)±C(5) C(4)±C(9) C(5)±C(6) C(6)±C(7) C(7)±C(8) C(8)±C(9) C(9)±C(10) C(11)±C(12) C(13)±C(14) C(14)±C(15) C(14)±C(19) C(15)±C(16) C(16)±C(17) C(17)±C(18) C(18)±C(19) C(19)±C(20) C(21 0 )±C(22 0 ) C(23 0 )±C(24 0 )

1.479(4) 1.384(4) 1.392(4) 1.398(5) 1.365(5) 1.382(5) 1.374(4) 1.480(4) 1.506(4) 1.484(4) 1.375(4) 1.390(4) 1.394(5) 1.367(6) 1.395(6) 1.381(4) 1.476(4) 1.46(3) 1.44(3)

1.454(3) 1.539(3) 1.569(3) 1.788(3) 1.398(4) 1.400(4) 1.415(4) 1.384(5) 1.388(4) 1.431(4) 1.203(4) 1.212(4) 1.348(4) 1.411(4) 1.184(4) 1.204(4) 1.189(5) 1.433(16) 1.440(5) 1.309(4)

C(3)±C(4) C(4)±C(9) C(4)±C(5) C(5)±C(6) C(6)±C(7) C(7)±C(8) C(8)±C(9) C(9)±C(10) C(11)±C(12) C(13)±C(14) C(15)±C(16) C(15)±C(14) C(14)±C(19) C(16)±C(17) C(17)±C(18) C(18)±C(19) C(19)±C(20) C(21 0 )±C(22 0 ) C(23)±C(24)

1.484(5) 1.368(5) 1.376(6) 1.429(8) 1.370(8) 1.350(7) 1.373(5) 1.471(5) 1.508(4) 1.479(5) 1.360(7) 1.370(5) 1.370(5) 1.362(8) 1.368(9) 1.363(6) 1.482(6) 1.39(2) 1.432(7)

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Table 6 Selected torsion angles (8) for 1a O(9 0 )±P(1 0 )±O(7 0 )±C(21 0 ) C(1)±P(1 0 )±O(7 0 )±C(21 0 ) O(7 0 )±P(1 0 )±O(9 0 )±C(23 0 ) C(1)±P(1 0 )±O(9 0 )±C(23 0 ) C(11)±O(3)±C(1)±P(1 0 ) O(9 0 )±P(1 0 )±C(1)±O(3) O(7 0 )±P(1 0 )±C(1)±O(3) P(1 0 )±C(1)±C(2)±N(1) C(3)±N(1)±C(2)±C(1) C(2)±N(1)±C(3)±O(1) C(1)±O(3)±C(11)±O(4) C(13)±N(2)±C(12)±C(11) O(3)±C(11)±C(12)±N(2) C(12)±N(2)±C(13)±O(5) P(1 0 )±O(7 0 )±C(21 0 )±C(22 0 ) P(1 0 )±O(9 0 )±C(23 0 )±C(24 0 )

Table 7 Selected torsion angles (8) for 1b 54.8(12) 265.6(12) 22.2(8) 288.5(7) 82.2(3) 26.9(3) 284.8(3) 168.9(2) 45.0(4) 7.9(4) 0.1(4) 266.7(4) 171.4(2) 20.6(5) 2139.6(16) 149.0(11)

The amplitudes of thermal vibrations were so large that we decided to perform the diffraction experiment at low temperature. However, the lower temperature was, the weaker re¯ections became. Together with lowering temperature, the errors of the lattice parameters determined became bigger. At certain temperature we did not manage to ®nd the cell. We made a hypothesis that the crystals studied undergo some transitions at lower temperatures. DSC measurements con®rmed our suppositions. Fig. 3a and b show the DSC curves of 1a and 1b, respectively. Some anomalies on the curves indicate the occurrence of phase and, probably, glass transitions. They are described in Table 8. The disorder seems to have a dynamical character. The atomic positions are frozen with lowering of temperature and the species studied turn out to be an orientational glass, at least to some extend. The analysis of non-bonded, short interatomic contacts reveals several interactions that may be classi®ed as weak, C±H´ ´ ´O hydrogen bonds. Such bonds can play a structure-determining role even at long distances [16,17]. Selected C±H´ ´ ´O interactions in 1a and 1b are shown in Table 9. Due to the weak H bonds two ethoxy groups in both conformers are not equivalent. One of them, involved in these interactions, has smaller atomic thermal displacement values and smaller deviations from the ideal values of chemical bonds. The C±H´ ´ ´O hydrogen bond makes the dynamical ethoxy groups more rigid.

O(9)±P(1)±O(7)±C(21 0 ) C(1)±P(1)±O(7)±C(21 0 ) O(7)±P(1)±O(9)±C(23) C(1)±P(1)±O(9)±C(23) C(11)±O(3)±C(1)±P(1) O(9)±P(1)±C(1)±O(3) O(7)±P(1)±C(1)±O(3) P(1)±C(1)±C(2)±N(1) C(3)±N(1)±C(2)±C(1) C(2)±N(1)±C(3)±O(1) C(1)±O(3)±C(11)±O(4) C(13)±N(2)±C(12)±C(11) O(3)±C(11)±C(12)±N(2) C(12)±N(2)±C(13)±O(5) P(1)±O(7)±C(21 0 )±C(22 0 ) P(1)±O(9)±C(23)±C(24)

33.0(9) 277.0(9) 172.5(3) 278.5(4) 119.0(2) 239.9(3) 67.4(3) 177.6(3) 162.9(4) 25.8(5) 5.0(5) 278.1(4) 177.0(3) 23.9(5) 2107.6(19) 2177.0(4)

In the crystal 1b the O6 atom has a very large displacement parameters and seems to be bended out of the phthalyl ring plane. The similar large amplitudes of carbonyl oxygen atoms have been found, for example by Søowikowska et al. [18] and Antony et al. [19]. Such oxygen atoms are often simultaneously engaged in numerous hydrogen bonds. In our case they are the C±H´ ´ ´O interactions. The O6 atom behaves as a bifurcated acceptor involved in an intermolecular hydrogen bond with C(24)_4 and an intramolecular one with C(12). Crystal density of form 1b is signi®cantly smaller than the density of form 1a. It results in considerably larger values of thermal motion amplitudes of the conformer 1b. What is more, its melting point is lower than 1a. All this indicates that 1b is a less stable polymorph than 1a.

Table 8 Temperatures and entalpies of the phase transitions in 1a and 1b crystals Conformer

T (K)

DH (J/g)

Comments

1a

136 159 213

1.28 0.33

First order First order Glass transition (?)

1b

132 156

0.128 0.072

First order First order

J. Holband et al. / Journal of Molecular Structure 595 (2001) 167±174

173

Fig. 3. (a) DSC heating curve of 1a species. (b) DSC heating and cooling curves of 1b species. Table 9 Selected C±H´´´O interactions in 1a and 1b crystals (1a: (1) x, y, z; (2) 2x 1 1/2, y 1 1/2, 2z 1 1/2; (3) 2x, 2y, 2z; (4) x 1 1/2, 2y 1 1/2, z 1 1/2. 1b: (1) x, y, z; (2) 2x, y 1 1/2, 2z 1 1/2; (3) 2x, 2y, 2z; (4) x, 2y 1 1/2, z 1 1/2) D

H

A

Ê) H´´´A (A

Ê) D´´ ´A (A

D±H´´´A (8)

Comments

1a

C23 0 _2 C18_3 C2_1 C12_1

H23c_1 H18_3 H2_1 H12a_1

O6_1 O8 0 _2 O1_1 O6_1

2.486 2.385 2.449 2.507

3.194 3.217 2.806 2.894

129.75 148.91 101.70 103.67

Inter Inter Intra Intra

1b

C24_4 C6_3 C12_1 C2_1 C2_1

H24a_4 H6_3 H12a_1 H2_1 H2_1

O6_1 O4_1 O6_1 O8_1 O1_1

2.615 2.528 2.517 2.559 2.300

3.395 3.382 2.863 2.990 2.760

138.61 152.84 100.87 102.66 103.34

Inter Inter Intra Intra Intra

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