organic compounds
3-Methyl-2-(methylsulfanyl)-5,5-diphenyl-3,5-dihydro-4H-imidazol-4-one
aLaboratory of Medicinal Chemistry, Drug Sciences Research Center, Faculty of Medicine and Pharmacy, Mohammed V University in Rabat, Morocco, bLaboratory of Medicinal Chemistry, Faculty of Clinical Pharmacy, 21 September University, Yemen, and cDepartment of Chemistry, Tulane University, New Orleans, LA 70118, USA
*Correspondence e-mail: alsubaripharmaco@21umas.edu.ye, y.ramli@um5r.ac.ma
This article is part of a collection of articles to commemorate the founding of the African Crystallographic Association and the 75th anniversary of the IUCr.
In the title molecule, C17H16N2OS, the dihydroimidazolone ring is slightly puckered and the methylsulfanyl group is nearly coplanar with it. In the crystal, two sets of C—H⋯O hydrogen bonds form corrugated layers of molecules parallel to the ac plane. The layers pack with normal van der Waals contacts between them.
Keywords: crystal structure; hydrogen bond; dihydroimidazolone; alkylation.
CCDC reference: 2246179
Structure description
Imidazole and its derivatives display various biological effects such as insecticides, herbicides and fungicides (Tutino et al., 2009; Wu et al., 2023; Takle et al., 2006). Our team has been working on these derivatives for some years to evaluate their biological activities (e.g. Guerrab et al., 2022a,b) and corrosion inhibition activities (e.g. Nabah et al., 2020). In a continuation of our recent work focused on the synthesis and biological evaluation of phenytoin derivatives (e.g. Guerrab et al., 2023), we report here the of the title compound (Fig. 1).
The molecule adopts the conformation typical for this class of molecule with the phenyl groups projecting out above and below the plane of the dihydroimidazolone ring. The latter ring is slightly puckered [C1 and C2 deviate by −0.0122 (7) and 0.0121 (7) Å, respectively, from the mean plane] and the mean planes of the C4–C9 and C10–C15 rings are inclined to its mean plane by 72.32 (5) and 67.03 (3)°, respectively. The terminal carbon atom of the methylsulfanyl group lies close to the mean plane of the dihydroimidazolone ring, as indicated by the C17—S1—C3—N2 torsion angle of −2.75 (13)°. In the crystal, C7—H7⋯O1 hydrogen bonds (Table 1) form chains of molecules extending along the a-axis direction. These are linked by C15—H15⋯O1 hydrogen bonds, forming corrugated layers of molecules parallel to the ac plane (Table 1 and Fig. 2). The layers pack along the b-axis direction with normal van de Waals contacts (Fig. 3) between them.
Synthesis and crystallization
Thiohydantoin (1000 mg, 3.73 mmol) was placed in a flask with K2CO3 (1030 mg, 7.46 mmol) in 20 ml of absolute dimethylformamide (DMF), and two equivalents of iodomethane (0.5 ml, 1160 mg) were added. The solution was left stirring for 2 h at room temperature. The reaction mixture was filtered, and the solvent was distilled off under reduced pressure. The residue obtained was recrystallized from methanol solution to yield colorless, plate-like single crystals (Akrad et al., 2018).
Refinement
Crystal data, data collection and structure .
details are summarized in Table 2Structural data
CCDC reference: 2246179
https://doi.org/10.1107/S2414314623002080/vm4058sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314623002080/vm4058Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2414314623002080/vm4058Isup3.cml
Data collection: APEX4 (Bruker, 2021); cell
SAINT (Bruker, 2021); data reduction: SAINT (Bruker, 2021); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2019/1 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg & Putz, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C17H16N2OS | F(000) = 624 |
Mr = 296.38 | Dx = 1.326 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54178 Å |
a = 8.4129 (1) Å | Cell parameters from 9855 reflections |
b = 22.9217 (4) Å | θ = 3.9–72.4° |
c = 8.6719 (1) Å | µ = 1.93 mm−1 |
β = 117.417 (1)° | T = 150 K |
V = 1484.44 (4) Å3 | Plate, colourless |
Z = 4 | 0.20 × 0.06 × 0.03 mm |
Bruker D8 VENTURE PHOTON 3 CPAD diffractometer | 2930 independent reflections |
Radiation source: INCOATEC IµS micro—-focus source | 2733 reflections with I > 2σ(I) |
Mirror monochromator | Rint = 0.036 |
Detector resolution: 7.3910 pixels mm-1 | θmax = 72.4°, θmin = 3.9° |
φ and ω scans | h = −9→10 |
Absorption correction: multi-scan (SADABS; Krause et al., 2015) | k = −28→28 |
Tmin = 0.85, Tmax = 0.94 | l = −10→10 |
37955 measured reflections |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.030 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.080 | H-atom parameters constrained |
S = 1.04 | w = 1/[σ2(Fo2) + (0.040P)2 + 0.6009P] where P = (Fo2 + 2Fc2)/3 |
2930 reflections | (Δ/σ)max = 0.001 |
192 parameters | Δρmax = 0.30 e Å−3 |
0 restraints | Δρmin = −0.24 e Å−3 |
Experimental. The diffraction data were obtained from 15 sets of frames, each of width 0.5° in ω or φ, collected with scan parameters determined by the "strategy" routine in APEX4. The scan time was θ-dependent and ranged from 5 to 15 sec/frame. |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. H-atoms attached to carbon were placed in calculated positions (C—H = 0.95 - 0.98 Å). All were included as riding contributions with isotropic displacement parameters 1.2 - 1.5 times those of the attached atoms. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.72407 (4) | 0.53586 (2) | 1.16914 (4) | 0.02823 (11) | |
O1 | 0.54051 (12) | 0.71912 (4) | 0.82460 (12) | 0.0271 (2) | |
N1 | 0.61671 (14) | 0.63912 (5) | 1.00499 (13) | 0.0236 (2) | |
N2 | 0.70761 (14) | 0.57313 (4) | 0.86599 (13) | 0.0217 (2) | |
C1 | 0.64968 (16) | 0.62639 (5) | 0.75658 (15) | 0.0202 (2) | |
C2 | 0.59464 (16) | 0.66941 (5) | 0.86029 (16) | 0.0216 (2) | |
C3 | 0.68352 (15) | 0.58379 (5) | 0.99846 (15) | 0.0216 (2) | |
C4 | 0.80769 (16) | 0.64949 (5) | 0.73319 (16) | 0.0219 (3) | |
C5 | 0.92075 (18) | 0.69236 (6) | 0.84133 (18) | 0.0305 (3) | |
H5 | 0.896928 | 0.709387 | 0.928442 | 0.037* | |
C6 | 1.0688 (2) | 0.71050 (7) | 0.8226 (2) | 0.0369 (3) | |
H6 | 1.145882 | 0.739664 | 0.897666 | 0.044* | |
C7 | 1.10450 (18) | 0.68648 (7) | 0.69606 (19) | 0.0346 (3) | |
H7 | 1.205289 | 0.699222 | 0.683353 | 0.041* | |
C8 | 0.99264 (19) | 0.64370 (6) | 0.58764 (18) | 0.0321 (3) | |
H8 | 1.016772 | 0.626991 | 0.500337 | 0.039* | |
C9 | 0.84503 (17) | 0.62513 (6) | 0.60624 (17) | 0.0260 (3) | |
H9 | 0.769091 | 0.595615 | 0.531833 | 0.031* | |
C10 | 0.48418 (16) | 0.61446 (5) | 0.58351 (15) | 0.0209 (2) | |
C11 | 0.39872 (18) | 0.56066 (6) | 0.54725 (17) | 0.0273 (3) | |
H11 | 0.443592 | 0.530142 | 0.630553 | 0.033* | |
C12 | 0.24745 (19) | 0.55132 (6) | 0.38914 (19) | 0.0337 (3) | |
H12 | 0.190002 | 0.514342 | 0.364685 | 0.040* | |
C13 | 0.18031 (17) | 0.59563 (6) | 0.26740 (17) | 0.0301 (3) | |
H13 | 0.076931 | 0.589203 | 0.159682 | 0.036* | |
C14 | 0.26501 (17) | 0.64947 (6) | 0.30376 (17) | 0.0277 (3) | |
H14 | 0.218962 | 0.680058 | 0.220802 | 0.033* | |
C15 | 0.41649 (17) | 0.65893 (6) | 0.46046 (16) | 0.0249 (3) | |
H15 | 0.474305 | 0.695842 | 0.484019 | 0.030* | |
C16 | 0.5778 (2) | 0.66282 (7) | 1.13960 (19) | 0.0364 (3) | |
H16A | 0.690265 | 0.671538 | 1.243296 | 0.055* | |
H16B | 0.509363 | 0.634189 | 1.168803 | 0.055* | |
H16C | 0.507500 | 0.698691 | 1.097364 | 0.055* | |
C17 | 0.7916 (2) | 0.47276 (6) | 1.0905 (2) | 0.0348 (3) | |
H17A | 0.700908 | 0.464056 | 0.971597 | 0.052* | |
H17B | 0.804208 | 0.439295 | 1.165589 | 0.052* | |
H17C | 0.906603 | 0.480549 | 1.091373 | 0.052* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.03234 (19) | 0.03103 (18) | 0.02251 (17) | 0.00075 (12) | 0.01364 (14) | 0.00651 (12) |
O1 | 0.0333 (5) | 0.0212 (4) | 0.0296 (5) | 0.0024 (4) | 0.0169 (4) | −0.0003 (4) |
N1 | 0.0283 (5) | 0.0254 (5) | 0.0210 (5) | 0.0013 (4) | 0.0146 (4) | −0.0003 (4) |
N2 | 0.0236 (5) | 0.0217 (5) | 0.0209 (5) | 0.0003 (4) | 0.0112 (4) | 0.0020 (4) |
C1 | 0.0232 (6) | 0.0197 (5) | 0.0202 (6) | 0.0001 (4) | 0.0120 (5) | 0.0006 (4) |
C2 | 0.0207 (6) | 0.0239 (6) | 0.0210 (6) | −0.0026 (5) | 0.0102 (5) | −0.0018 (5) |
C3 | 0.0201 (6) | 0.0240 (6) | 0.0206 (6) | −0.0016 (4) | 0.0092 (5) | 0.0011 (5) |
C4 | 0.0213 (6) | 0.0249 (6) | 0.0199 (6) | 0.0016 (4) | 0.0098 (5) | 0.0046 (5) |
C5 | 0.0308 (7) | 0.0374 (7) | 0.0256 (6) | −0.0069 (6) | 0.0150 (6) | −0.0020 (5) |
C6 | 0.0305 (7) | 0.0444 (8) | 0.0340 (8) | −0.0126 (6) | 0.0132 (6) | 0.0001 (6) |
C7 | 0.0235 (6) | 0.0466 (8) | 0.0359 (8) | 0.0009 (6) | 0.0157 (6) | 0.0139 (6) |
C8 | 0.0300 (7) | 0.0418 (8) | 0.0312 (7) | 0.0081 (6) | 0.0199 (6) | 0.0080 (6) |
C9 | 0.0262 (6) | 0.0292 (6) | 0.0250 (6) | 0.0030 (5) | 0.0137 (5) | 0.0022 (5) |
C10 | 0.0216 (6) | 0.0239 (6) | 0.0208 (6) | 0.0007 (4) | 0.0130 (5) | −0.0014 (4) |
C11 | 0.0279 (6) | 0.0237 (6) | 0.0297 (7) | −0.0007 (5) | 0.0129 (5) | 0.0006 (5) |
C12 | 0.0295 (7) | 0.0294 (7) | 0.0371 (8) | −0.0057 (5) | 0.0111 (6) | −0.0065 (6) |
C13 | 0.0231 (6) | 0.0398 (7) | 0.0250 (6) | 0.0013 (5) | 0.0090 (5) | −0.0068 (5) |
C14 | 0.0274 (7) | 0.0334 (7) | 0.0229 (6) | 0.0056 (5) | 0.0122 (5) | 0.0030 (5) |
C15 | 0.0280 (6) | 0.0246 (6) | 0.0245 (6) | −0.0005 (5) | 0.0141 (5) | 0.0003 (5) |
C16 | 0.0501 (9) | 0.0395 (8) | 0.0285 (7) | 0.0082 (6) | 0.0257 (7) | −0.0008 (6) |
C17 | 0.0381 (8) | 0.0278 (7) | 0.0356 (8) | 0.0051 (6) | 0.0145 (6) | 0.0074 (6) |
S1—C3 | 1.7461 (12) | C8—H8 | 0.9500 |
S1—C17 | 1.7995 (15) | C9—H9 | 0.9500 |
O1—C2 | 1.2130 (15) | C10—C11 | 1.3887 (17) |
N1—C2 | 1.3699 (16) | C10—C15 | 1.3937 (17) |
N1—C3 | 1.3991 (16) | C11—C12 | 1.3922 (19) |
N1—C16 | 1.4550 (16) | C11—H11 | 0.9500 |
N2—C3 | 1.2786 (16) | C12—C13 | 1.384 (2) |
N2—C1 | 1.4840 (15) | C12—H12 | 0.9500 |
C1—C4 | 1.5287 (16) | C13—C14 | 1.387 (2) |
C1—C10 | 1.5302 (16) | C13—H13 | 0.9500 |
C1—C2 | 1.5426 (16) | C14—C15 | 1.3867 (19) |
C4—C5 | 1.3888 (18) | C14—H14 | 0.9500 |
C4—C9 | 1.3932 (18) | C15—H15 | 0.9500 |
C5—C6 | 1.391 (2) | C16—H16A | 0.9800 |
C5—H5 | 0.9500 | C16—H16B | 0.9800 |
C6—C7 | 1.379 (2) | C16—H16C | 0.9800 |
C6—H6 | 0.9500 | C17—H17A | 0.9800 |
C7—C8 | 1.384 (2) | C17—H17B | 0.9800 |
C7—H7 | 0.9500 | C17—H17C | 0.9800 |
C8—C9 | 1.3907 (19) | ||
C3—S1—C17 | 99.02 (6) | C8—C9—H9 | 119.8 |
C2—N1—C3 | 108.05 (10) | C4—C9—H9 | 119.8 |
C2—N1—C16 | 124.06 (11) | C11—C10—C15 | 119.33 (12) |
C3—N1—C16 | 127.88 (11) | C11—C10—C1 | 121.54 (11) |
C3—N2—C1 | 106.02 (10) | C15—C10—C1 | 119.12 (11) |
N2—C1—C4 | 108.67 (9) | C10—C11—C12 | 120.18 (12) |
N2—C1—C10 | 111.27 (9) | C10—C11—H11 | 119.9 |
C4—C1—C10 | 112.70 (10) | C12—C11—H11 | 119.9 |
N2—C1—C2 | 104.57 (9) | C13—C12—C11 | 120.34 (13) |
C4—C1—C2 | 111.64 (10) | C13—C12—H12 | 119.8 |
C10—C1—C2 | 107.71 (9) | C11—C12—H12 | 119.8 |
O1—C2—N1 | 125.90 (11) | C12—C13—C14 | 119.54 (12) |
O1—C2—C1 | 129.05 (11) | C12—C13—H13 | 120.2 |
N1—C2—C1 | 105.04 (10) | C14—C13—H13 | 120.2 |
N2—C3—N1 | 116.26 (11) | C15—C14—C13 | 120.41 (12) |
N2—C3—S1 | 126.26 (10) | C15—C14—H14 | 119.8 |
N1—C3—S1 | 117.47 (9) | C13—C14—H14 | 119.8 |
C5—C4—C9 | 118.93 (12) | C14—C15—C10 | 120.20 (12) |
C5—C4—C1 | 121.51 (11) | C14—C15—H15 | 119.9 |
C9—C4—C1 | 119.49 (11) | C10—C15—H15 | 119.9 |
C4—C5—C6 | 120.28 (13) | N1—C16—H16A | 109.5 |
C4—C5—H5 | 119.9 | N1—C16—H16B | 109.5 |
C6—C5—H5 | 119.9 | H16A—C16—H16B | 109.5 |
C7—C6—C5 | 120.55 (14) | N1—C16—H16C | 109.5 |
C7—C6—H6 | 119.7 | H16A—C16—H16C | 109.5 |
C5—C6—H6 | 119.7 | H16B—C16—H16C | 109.5 |
C6—C7—C8 | 119.62 (13) | S1—C17—H17A | 109.5 |
C6—C7—H7 | 120.2 | S1—C17—H17B | 109.5 |
C8—C7—H7 | 120.2 | H17A—C17—H17B | 109.5 |
C7—C8—C9 | 120.14 (13) | S1—C17—H17C | 109.5 |
C7—C8—H8 | 119.9 | H17A—C17—H17C | 109.5 |
C9—C8—H8 | 119.9 | H17B—C17—H17C | 109.5 |
C8—C9—C4 | 120.49 (13) | ||
C3—N2—C1—C4 | 121.22 (11) | C10—C1—C4—C9 | −41.41 (15) |
C3—N2—C1—C10 | −114.13 (11) | C2—C1—C4—C9 | −162.79 (11) |
C3—N2—C1—C2 | 1.88 (12) | C9—C4—C5—C6 | 0.0 (2) |
C3—N1—C2—O1 | −179.29 (12) | C1—C4—C5—C6 | 176.77 (12) |
C16—N1—C2—O1 | −0.1 (2) | C4—C5—C6—C7 | 0.4 (2) |
C3—N1—C2—C1 | 1.68 (12) | C5—C6—C7—C8 | −0.4 (2) |
C16—N1—C2—C1 | −179.13 (12) | C6—C7—C8—C9 | 0.1 (2) |
N2—C1—C2—O1 | 178.84 (12) | C7—C8—C9—C4 | 0.3 (2) |
C4—C1—C2—O1 | 61.52 (16) | C5—C4—C9—C8 | −0.33 (19) |
C10—C1—C2—O1 | −62.70 (16) | C1—C4—C9—C8 | −177.20 (12) |
N2—C1—C2—N1 | −2.18 (12) | N2—C1—C10—C11 | 4.07 (15) |
C4—C1—C2—N1 | −119.50 (11) | C4—C1—C10—C11 | 126.43 (12) |
C10—C1—C2—N1 | 116.28 (10) | C2—C1—C10—C11 | −109.99 (12) |
C1—N2—C3—N1 | −0.95 (14) | N2—C1—C10—C15 | −176.77 (10) |
C1—N2—C3—S1 | 178.44 (9) | C4—C1—C10—C15 | −54.41 (14) |
C2—N1—C3—N2 | −0.54 (15) | C2—C1—C10—C15 | 69.17 (13) |
C16—N1—C3—N2 | −179.68 (13) | C15—C10—C11—C12 | 0.28 (19) |
C2—N1—C3—S1 | −179.98 (8) | C1—C10—C11—C12 | 179.44 (12) |
C16—N1—C3—S1 | 0.87 (18) | C10—C11—C12—C13 | −0.4 (2) |
C17—S1—C3—N2 | −2.75 (13) | C11—C12—C13—C14 | 0.1 (2) |
C17—S1—C3—N1 | 176.63 (10) | C12—C13—C14—C15 | 0.3 (2) |
N2—C1—C4—C5 | −94.40 (14) | C13—C14—C15—C10 | −0.50 (19) |
C10—C1—C4—C5 | 141.79 (12) | C11—C10—C15—C14 | 0.19 (18) |
C2—C1—C4—C5 | 20.42 (16) | C1—C10—C15—C14 | −178.99 (11) |
N2—C1—C4—C9 | 82.39 (13) |
D—H···A | D—H | H···A | D···A | D—H···A |
C7—H7···O1i | 0.95 | 2.55 | 3.390 (2) | 148 |
C15—H15···O1ii | 0.95 | 2.59 | 3.3797 (17) | 140 |
Symmetry codes: (i) x+1, y, z; (ii) x, −y+3/2, z−1/2. |
Acknowledgements
Author contributions are as follows. Conceptualization, YR; methodology, AEMAA and AA; investigation, AEMAA and WG; writing (original draft), JMT and YR; writing (review and editing of the manuscript), YR; formal analysis, AA and YR; supervision, YR;
determination and validation, JTM.Funding information
The support of NSF–MRI grant No. 1228232 for the purchase of the diffractometer and Tulane University for support of the Tulane Crystallography Laboratory are gratefully acknowledged.
References
Akrad, R., Guerrab, W., Lazrak, F., Ansar, M., Taoufik, J., Mague, J. T. & Ramli, Y. (2018). IUCrData, 3, x180934. Google Scholar
Brandenburg, K. & Putz, H. (2012). DIAMOND, Crystal Impact GbR, Bonn, Germany. Google Scholar
Bruker (2021). APEX4 and SAINT. Bruker AXS LLC, Madison, Wisconsin, USA. Google Scholar
Guerrab, W., Akachar, J., Jemli, M. E., Abudunia, A. M., Ouaabou, R., Alaoui, K., Ibrahimi, A. & Ramli, Y. (2022a). J. Biomol. Struct. Dyn. pp. 1–9. Web of Science CrossRef Google Scholar
Guerrab, W., El Jemli, M., Akachar, J., Demirtaş, G., Mague, J. T., Taoufik, J., Ibrahimi, A., Ansar, M., Alaoui, K. & Ramli, Y. (2022b). J. Biomol. Struct. Dyn. 40, 8765–8782. Web of Science CSD CrossRef CAS PubMed Google Scholar
Guerrab, W., El Moutaouakil Ala Allah, A., Alsubari, A., Mague, J. T. & Ramli, Y. (2023). IUCrData, 8, x230125. Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
Nabah, R., Benhiba, F., Laabaissi, T., Zarrok, H., Cherkaoui, M., Oudda, H., Ramli, Y., Warad, I. & Zarrouk, A. (2020). Surf. Rev. Lett. 27, 2050005. Web of Science CrossRef Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Takle, A. K., Brown, M. J., Davies, S., Dean, D. K., Francis, G., Gaiba, A., Hird, A. W., King, F. D., Lovell, P. J., Naylor, A., Reith, A. D., Steadman, J. G. & Wilson, D. M. (2006). Bioorg. Med. Chem. Lett. 16, 378–381. Web of Science CrossRef PubMed CAS Google Scholar
Tutino, F., Posteri, H., Borghi, D., Quartieri, F., Mongelli, N. & Papeo, G. (2009). Tetrahedron, 65, 2372–2376. Web of Science CrossRef CAS Google Scholar
Wu, Y., Wang, P., Zheng, L., Guo, H. & Yang, F. (2023). Sens. Actuators B Chem. 380, 133330. CrossRef Google Scholar
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