(–)-(4R,5S)-3-[2(R)-(4-Chloro­phen­yl)propion­yl]-4-methyl-5-phenyl­oxazolidin-2-one

Chavda, S.; Eames, J.; Flinn, A.; Motevalli, M.; Malatesti, N.

doi:10.1107/S1600536806031837

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 62| Part 9| September 2006| Pages o4039-o4040

https://doi.org/10.1107/S1600536806031837

(–)-(4R,5S)-3-[2(R)-(4-Chlorophenyl)propionyl]-4-methyl-5-phenyloxazolidin-2-one

Sameer Chavda,^a Jason Eames,^b ^* Anthony Flinn,^c Majid Motevalli ^a and Nela Malatesti ^d

^aDepartment of Chemistry, Queen Mary, University of London, Mile End Road, London E1 4NS, England, ^bDepartment of Chemistry, University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, England, ^cOnyx Scientific Limited, Units 97-98, Silverbriar, Sunderland Enterprise Park East, Sunderland SR5 2TQ, England, and ^dDepartment of Chemistry, J. J. Strossmayer University of Osijek, Trg. Sv. Trojstva 3, Osijek 31000, Croatia
^*Correspondence e-mail: j.eames@hull.ac.uk

(Received 27 June 2006; accepted 12 August 2006; online 23 August 2006)

The title compound, C₁₉H₁₈ClNO₃, is formed from enantiomerically pure (+)-(4R,5S)-4-methyl-5-phenyl-2-oxazolidinone and racemic 2-(4-chlorophenyl)propanoyl chloride. The crystal structure resembles closely that of the comparable (4-methylphenyl)propionyl derivative, although the two structures differ in the nature of the intermolecular contacts to the Cl atom and methyl group.

Comment

The title compound, (I), is the fourth in a series of structurally related compounds, introduced in our earlier report (Coumbarides et al., 2006 ). With R¹ = 4-(Cl)C₆H₄, the reaction shown in that report yielded the anti–syn and syn–syn diastereomers in 38 and 39% yields, respectively. The title compound, (I), is the anti–syn diastereomer (Fig. 1). In the crystal structure, the conformation of the molecule is essentially indistinguishable from that of the (4-methylphenyl)propionyl derivative (Chavda et al., 2006 ).

The crystal structure of (I) is closely related to that of the (4-methylphenyl)propionyl derivative. The two structures contain essentially identical two-dimensional layers, lying in the (010) planes for (I) and in the (100) planes for the methyl derivative (Fig. 2). In the methyl derivative, adjacent layers are related by translation along a, bringing the methyl groups of the 4-(CH₃)C₆H₄ substituent into the vicinity of O2 [H20B⋯O2 = 2.71 Å]. In (I), adjacent layers are related by 2₁ screw axes, and Cl1 forms its shortest intermolecular contacts between layers to the methyl group C19 [H19B⋯Cl1ⁱ = 3.35 Å; symmetry code: (i) − $[{1\over 2}]$ + x, $[{3\over 2}]$ + y, $[{3\over 2}]$ − z]. Thus, chloro/methyl interchange (Edwards et al., 2006 ) does not lead to isostructurality in this instance, and this can be attributed to the influence of the different charge distributions of the Cl atom and CH₃ group.

Figure 1
The molecular structure of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted.

Figure 2
Overlay of the unit-cell contents of (I)

(blue) and the (4-methylphenyl)propionyl derivative (red) (Chavda et al., 2006

), showing essentially identical layers of molecules in the (010) planes of (I) and (100) planes of the methyl derivative.

Experimental

The experimental procedure is comparable with that reported previously (Coumbarides et al., 2006). The actual quantities used for the preparation of (I) were: n-butyllithium (15.81 ml, 2.5 M in hexanes, 39.5 mmol) and (R,S)-oxazolidinone (5.00 g, 28.2 mmol) in 60 ml tetrahydrofuran (THF), combined with a solution of (rac)-2-(4-chlorophenyl)propanoyl chloride (5.73 g, 28.2 mmol) in 10 ml THF. The crude residue was purified by flash column chromatography on silica gel, eluting with light petroleum (b.p. 313–333 K)/diethyl ether (7:3), to give a separable diastereoisomeric mixture in the approximate ratio anti–syn:syn–syn 50:50. The anti–syn diastereomer was obtained as colourless crystals {3.68 g, 38% yield, m.p. 362–364 K, R_F 0.58 [light petroleum (b.p 313–333 K)/diethyl ether, 7:3]}. Spectroscopic analysis: [α]²²_D = −60.0 (CHCl₃, 293 K, concentration 0.60 g per 100 ml); IR (CHCl₃, ν_max/cm⁻¹): 1779 (C=O), 1713 (C=O); ¹H NMR (270 MHz; CDCl₃): 7.36–7.20 (9H, m, 9 × CH; Ar and Ph), 5.62 (1H, d, J = 6.4 Hz, CHPh), 5.01 (1H, q, J = 6.9 Hz, ArCH), 4.79 (1H, m, CHN), 1.48 (3H, d, J = 6.9 Hz, CH₃CH), 0.86 (3H, d, J = 6.4 Hz, CH₃CHN); ¹³C NMR (100 MHz; CDCl₃): δ 173.9 (NC=O), 152.5 (OC=O), 138.9 (i-CCl; Ar), 133.2, 133.1 (2 × i-C; Ar and Ph), 129.5, 128.9, 128.8, 128.7, 125.6 (5 × CH; Ar and Ph), 78.7 (PhCHO), 55.4 (CHN), 42.7 (ArCH), 19.2 (CH₃CH), 14.4 (CH₃CHN); found: MNH₄⁺ 361.1307; C₁₉H₂₂ClN₂O₃ requires 361.1313.

Crystal data

C₁₉H₁₈ClNO₃
M_r = 343.79
Orthorhombic, P 2₁ 2₁ 2₁
a = 7.105 (3) Å
b = 25.662 (12) Å
c = 9.580 (8) Å
V = 1746.7 (18) Å³
Z = 4
D_x = 1.307 Mg m⁻³
Mo Kα radiation
μ = 0.24 mm⁻¹
T = 160 (2) K
Prism, colourless
0.20 × 0.10 × 0.10 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
ω/2θ scans
Absorption correction: none
2316 measured reflections
1794 independent reflections
1083 reflections with I > 2σ(I)
R_int = 0.044
θ_max = 25.0°
2 standard reflections frequency: 60 min intensity decay: 2%

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.047
wR(F²) = 0.105
S = 1.04
1794 reflections
219 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0394P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.21 e Å⁻³
Δρ_min = −0.22 e Å⁻³

H atoms were placed in geometrically idealised positions and constrained to ride on their parent atoms, with C—H = 0.95–1.00 Å and U_iso(H) = 1.2U_eq(C) or 1.5U_eq(methyl C). The methyl groups were allowed to rotate about their local threefold axes. The absolute configuration could not be established and is assigned on the basis of the known configuration of the starting material (Coumbarides et al., 2006).

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994 ); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536806031837/bi2031sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536806031837/bi2031Isup2.hkl

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

(-)-(4R,5S)-3-[2(R)-(4-Chlorophenyl)propionyl]-4-methyl- 5-phenyloxazolidin-2-one top

Crystal data top

C₁₉H₁₈ClNO₃	F(000) = 720
M_r = 343.79	D_x = 1.307 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 7.105 (3) Å	θ = 8.2–11.9°
b = 25.662 (12) Å	µ = 0.24 mm⁻¹
c = 9.580 (8) Å	T = 160 K
V = 1746.7 (18) Å³	Prism, colourless
Z = 4	0.20 × 0.10 × 0.10 mm

Data collection top

Enraf–Nonius CAD-4 diffractometer	R_int = 0.044
Radiation source: fine-focus sealed tube	θ_max = 25.0°, θ_min = 1.6°
Graphite monochromator	h = −7→8
ω/2θ scans	k = −29→30
2316 measured reflections	l = −9→11
1794 independent reflections	2 standard reflections every 60 min
1083 reflections with I > 2σ(I)	intensity decay: 2%

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.047	H-atom parameters constrained
wR(F²) = 0.105	w = 1/[σ²(F_o²) + (0.0394P)²] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max < 0.001
1794 reflections	Δρ_max = 0.21 e Å⁻³
219 parameters	Δρ_min = −0.22 e Å⁻³
0 restraints	Absolute structure: assigned on the basis of known starting material
Primary atom site location: structure-invariant direct methods

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.0521 (7)	0.99165 (16)	0.6453 (5)	0.0297 (11)
H1	0.1699	1.0054	0.6015	0.036*
C2	−0.1152 (6)	0.99826 (18)	0.5432 (5)	0.0313 (12)
H2	−0.0641	0.9989	0.4459	0.038*
C3	−0.1139 (7)	0.9124 (2)	0.6137 (6)	0.0431 (15)
C4	0.0255 (7)	1.01583 (19)	0.7868 (5)	0.0392 (14)
H4A	−0.0933	1.0036	0.8273	0.059*
H4B	0.0221	1.0539	0.7777	0.059*
H4C	0.1302	1.0058	0.8478	0.059*
C5	−0.2390 (7)	1.04543 (19)	0.5625 (5)	0.0316 (12)
C6	−0.1982 (7)	1.0901 (2)	0.4914 (5)	0.0438 (14)
H6	−0.0943	1.0908	0.4291	0.053*
C7	−0.3074 (9)	1.1346 (2)	0.5092 (7)	0.0571 (17)
H7	−0.2767	1.1657	0.4602	0.069*
C8	−0.4585 (9)	1.1337 (2)	0.5972 (6)	0.0546 (17)
H8	−0.5331	1.1641	0.6094	0.065*
C9	−0.5026 (7)	1.0886 (2)	0.6681 (5)	0.0504 (15)
H9	−0.6070	1.0882	0.7300	0.061*
C10	−0.3963 (7)	1.0440 (2)	0.6502 (5)	0.0399 (13)
H10	−0.4298	1.0127	0.6969	0.048*
C11	0.2150 (7)	0.9084 (2)	0.7053 (5)	0.0382 (13)
C12	0.2189 (7)	0.84953 (18)	0.6971 (5)	0.0371 (13)
H12	0.0913	0.8361	0.7222	0.045*
C13	0.2654 (7)	0.83165 (18)	0.5505 (5)	0.0346 (13)
C14	0.4216 (7)	0.85110 (19)	0.4812 (5)	0.0389 (13)
H14	0.4948	0.8777	0.5240	0.047*
C15	0.4732 (8)	0.83257 (19)	0.3506 (5)	0.0438 (14)
H15	0.5781	0.8470	0.3029	0.053*
C16	0.3700 (9)	0.79294 (19)	0.2913 (5)	0.0459 (15)
C17	0.2146 (9)	0.7732 (2)	0.3574 (6)	0.0539 (17)
H17	0.1434	0.7462	0.3148	0.065*
C18	0.1616 (9)	0.7925 (2)	0.4861 (6)	0.0513 (16)
H18	0.0530	0.7789	0.5311	0.062*
C19	0.3609 (8)	0.8280 (2)	0.8017 (5)	0.0443 (14)
H19A	0.4877	0.8396	0.7760	0.066*
H19B	0.3560	0.7898	0.8009	0.066*
H19C	0.3302	0.8407	0.8954	0.066*
Cl1	0.4415 (3)	0.76689 (5)	0.13160 (15)	0.0697 (6)
N1	0.0589 (6)	0.93434 (14)	0.6506 (4)	0.0346 (10)
O1	−0.2233 (5)	0.95084 (13)	0.5604 (4)	0.0455 (10)
O2	−0.1685 (5)	0.86858 (14)	0.6235 (5)	0.0629 (13)
O3	0.3457 (5)	0.93430 (12)	0.7494 (4)	0.0425 (9)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.021 (3)	0.032 (3)	0.036 (3)	0.000 (2)	−0.003 (3)	0.007 (2)
C2	0.026 (3)	0.038 (3)	0.030 (3)	0.003 (2)	0.001 (2)	0.000 (2)
C3	0.033 (3)	0.034 (3)	0.063 (4)	−0.002 (3)	−0.019 (3)	0.009 (3)
C4	0.030 (3)	0.052 (3)	0.036 (3)	0.008 (3)	−0.006 (3)	−0.002 (3)
C5	0.026 (3)	0.040 (3)	0.029 (3)	0.009 (2)	−0.001 (3)	0.004 (2)
C6	0.031 (3)	0.048 (3)	0.053 (4)	0.003 (3)	0.008 (3)	0.010 (3)
C7	0.047 (4)	0.052 (4)	0.072 (4)	0.014 (3)	0.008 (4)	0.007 (3)
C8	0.044 (4)	0.056 (4)	0.064 (4)	0.023 (3)	0.005 (4)	−0.001 (3)
C9	0.029 (3)	0.072 (4)	0.050 (4)	0.010 (3)	0.008 (3)	−0.003 (3)
C10	0.034 (3)	0.046 (3)	0.040 (3)	−0.003 (3)	−0.003 (3)	0.010 (3)
C11	0.032 (3)	0.041 (3)	0.041 (3)	0.002 (3)	−0.001 (3)	0.006 (3)
C12	0.028 (3)	0.033 (3)	0.050 (3)	−0.002 (2)	−0.008 (3)	0.008 (3)
C13	0.029 (3)	0.031 (3)	0.044 (3)	−0.005 (2)	−0.013 (3)	0.007 (2)
C14	0.034 (3)	0.034 (3)	0.049 (3)	−0.008 (3)	−0.011 (3)	−0.005 (3)
C15	0.040 (3)	0.044 (3)	0.046 (3)	−0.002 (3)	−0.011 (3)	0.004 (3)
C16	0.069 (4)	0.024 (3)	0.045 (3)	0.004 (3)	−0.021 (4)	0.006 (3)
C17	0.073 (5)	0.033 (3)	0.055 (4)	−0.018 (3)	−0.028 (4)	0.004 (3)
C18	0.052 (4)	0.046 (3)	0.056 (4)	−0.016 (3)	−0.017 (3)	0.012 (3)
C19	0.041 (3)	0.048 (3)	0.044 (3)	0.003 (3)	−0.010 (3)	0.012 (3)
Cl1	0.1206 (16)	0.0473 (9)	0.0412 (8)	0.0003 (10)	−0.0178 (11)	−0.0029 (7)
N1	0.022 (2)	0.038 (2)	0.044 (3)	0.000 (2)	−0.009 (2)	0.006 (2)
O1	0.034 (2)	0.036 (2)	0.067 (3)	0.0029 (18)	−0.023 (2)	0.0009 (19)
O2	0.036 (2)	0.039 (2)	0.114 (4)	−0.0045 (19)	−0.028 (3)	0.004 (2)
O3	0.026 (2)	0.040 (2)	0.061 (2)	−0.0048 (17)	−0.012 (2)	0.0033 (18)

Geometric parameters (Å, º) top

C1—N1	1.472 (5)	C9—H9	0.950
C1—C4	1.503 (6)	C10—H10	0.950
C1—C2	1.548 (6)	C11—O3	1.217 (6)
C1—H1	1.000	C11—N1	1.396 (6)
C2—O1	1.449 (5)	C11—C12	1.513 (7)
C2—C5	1.508 (6)	C12—C13	1.514 (7)
C2—H2	1.000	C12—C19	1.526 (6)
C3—O2	1.194 (6)	C12—H12	1.000
C3—O1	1.355 (6)	C13—C14	1.387 (7)
C3—N1	1.396 (6)	C13—C18	1.391 (7)
C4—H4A	0.980	C14—C15	1.388 (6)
C4—H4B	0.980	C14—H14	0.950
C4—H4C	0.980	C15—C16	1.377 (7)
C5—C6	1.364 (7)	C15—H15	0.950
C5—C10	1.399 (7)	C16—C17	1.370 (8)
C6—C7	1.392 (7)	C16—Cl1	1.745 (6)
C6—H6	0.950	C17—C18	1.381 (8)
C7—C8	1.365 (8)	C17—H17	0.950
C7—H7	0.950	C18—H18	0.950
C8—C9	1.378 (7)	C19—H19A	0.980
C8—H8	0.950	C19—H19B	0.980
C9—C10	1.383 (7)	C19—H19C	0.980

N1—C1—C4	112.7 (4)	C5—C10—H10	120.4
N1—C1—C2	99.0 (4)	O3—C11—N1	118.4 (5)
C4—C1—C2	115.3 (4)	O3—C11—C12	123.3 (5)
N1—C1—H1	109.8	N1—C11—C12	118.1 (5)
C4—C1—H1	109.8	C13—C12—C11	110.8 (4)
C2—C1—H1	109.8	C13—C12—C19	110.8 (4)
O1—C2—C5	110.5 (4)	C11—C12—C19	109.9 (4)
O1—C2—C1	104.1 (3)	C13—C12—H12	108.4
C5—C2—C1	117.3 (4)	C11—C12—H12	108.4
O1—C2—H2	108.2	C19—C12—H12	108.4
C5—C2—H2	108.2	C14—C13—C18	118.2 (5)
C1—C2—H2	108.2	C14—C13—C12	120.6 (5)
O2—C3—O1	121.9 (5)	C18—C13—C12	121.0 (5)
O2—C3—N1	130.2 (5)	C13—C14—C15	121.3 (5)
O1—C3—N1	107.9 (4)	C13—C14—H14	119.3
C1—C4—H4A	109.5	C15—C14—H14	119.3
C1—C4—H4B	109.5	C16—C15—C14	119.0 (5)
H4A—C4—H4B	109.5	C16—C15—H15	120.5
C1—C4—H4C	109.5	C14—C15—H15	120.5
H4A—C4—H4C	109.5	C17—C16—C15	120.7 (5)
H4B—C4—H4C	109.5	C17—C16—Cl1	119.9 (4)
C6—C5—C10	119.5 (5)	C15—C16—Cl1	119.4 (5)
C6—C5—C2	119.3 (5)	C16—C17—C18	120.0 (5)
C10—C5—C2	121.2 (4)	C16—C17—H17	120.0
C5—C6—C7	120.7 (5)	C18—C17—H17	120.0
C5—C6—H6	119.7	C17—C18—C13	120.7 (6)
C7—C6—H6	119.7	C17—C18—H18	119.6
C8—C7—C6	120.0 (6)	C13—C18—H18	119.6
C8—C7—H7	120.0	C12—C19—H19A	109.5
C6—C7—H7	120.0	C12—C19—H19B	109.5
C7—C8—C9	119.8 (5)	H19A—C19—H19B	109.5
C7—C8—H8	120.1	C12—C19—H19C	109.5
C9—C8—H8	120.1	H19A—C19—H19C	109.5
C8—C9—C10	120.7 (5)	H19B—C19—H19C	109.5
C8—C9—H9	119.7	C11—N1—C3	127.0 (4)
C10—C9—H9	119.7	C11—N1—C1	121.0 (4)
C9—C10—C5	119.3 (5)	C3—N1—C1	111.4 (4)
C9—C10—H10	120.4	C3—O1—C2	110.4 (4)

N1—C1—C2—O1	25.6 (4)	C12—C13—C14—C15	175.7 (5)
C4—C1—C2—O1	−94.8 (5)	C13—C14—C15—C16	−2.1 (7)
N1—C1—C2—C5	148.1 (4)	C14—C15—C16—C17	2.3 (8)
C4—C1—C2—C5	27.7 (6)	C14—C15—C16—Cl1	−176.4 (4)
O1—C2—C5—C6	−149.4 (4)	C15—C16—C17—C18	−1.0 (8)
C1—C2—C5—C6	91.5 (6)	Cl1—C16—C17—C18	177.7 (4)
O1—C2—C5—C10	29.6 (6)	C16—C17—C18—C13	−0.6 (8)
C1—C2—C5—C10	−89.5 (5)	C14—C13—C18—C17	0.8 (8)
C10—C5—C6—C7	2.4 (8)	C12—C13—C18—C17	−174.3 (5)
C2—C5—C6—C7	−178.6 (5)	O3—C11—N1—C3	−170.2 (5)
C5—C6—C7—C8	−0.9 (9)	C12—C11—N1—C3	14.2 (8)
C6—C7—C8—C9	0.0 (9)	O3—C11—N1—C1	0.4 (7)
C7—C8—C9—C10	−0.7 (8)	C12—C11—N1—C1	−175.3 (4)
C8—C9—C10—C5	2.2 (8)	O2—C3—N1—C11	2.3 (10)
C6—C5—C10—C9	−3.0 (7)	O1—C3—N1—C11	−177.8 (4)
C2—C5—C10—C9	178.0 (4)	O2—C3—N1—C1	−169.0 (6)
O3—C11—C12—C13	−99.3 (6)	O1—C3—N1—C1	10.9 (6)
N1—C11—C12—C13	76.1 (6)	C4—C1—N1—C11	−72.3 (6)
O3—C11—C12—C19	23.4 (7)	C2—C1—N1—C11	165.3 (4)
N1—C11—C12—C19	−161.1 (4)	C4—C1—N1—C3	99.6 (5)
C11—C12—C13—C14	51.5 (6)	C2—C1—N1—C3	−22.8 (5)
C19—C12—C13—C14	−70.7 (6)	O2—C3—O1—C2	−172.4 (5)
C11—C12—C13—C18	−133.5 (5)	N1—C3—O1—C2	7.7 (6)
C19—C12—C13—C18	104.3 (6)	C5—C2—O1—C3	−148.7 (4)
C18—C13—C14—C15	0.5 (7)	C1—C2—O1—C3	−21.9 (5)

Acknowledgements

We are grateful to the Royal Society and the University of London Central Research Fund for their financial support to JE, and the EPSRC National Mass Spectrometry Service (Swansea) for accurate mass determination.

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