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ISSN: 2056-9890

(2S,6S)-1-Methyl-2,6-trans-distyryl­piperidinium chloride

aDepartment of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536, USA, and bDepartment of Chemistry, University of Kentucky, Lexington, KY 40536, USA
*Correspondence e-mail: pcrooks@email.uky.edu

(Received 18 November 2009; accepted 19 November 2009; online 9 December 2009)

In the crystal structure of the title compound, C22H26N+·Cl, the piperidine ring is in a chair conformation and the two styryl groups are in axial and equatorial positions. The mol­ecule has a hydrogen bond between the NH group and the chloride anion.

Related literature

The title compound is a des-oxygen derivative of epimerized (−)-lobeline (Zheng et al., 2005[Zheng, G., Dwoskin, L. P., Deaciuc, A. G., Norrholm, S. D. & Crooks, P. A. (2005). J. Med. Chem. pp. 5551-5560.]).

[Scheme 1]

Experimental

Crystal data
  • C22H26N+·Cl

  • Mr = 339.89

  • Orthorhombic, P 21 21 21

  • a = 9.9355 (4) Å

  • b = 12.3075 (5) Å

  • c = 15.8299 (7) Å

  • V = 1935.70 (14) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.20 mm−1

  • T = 173 K

  • 0.38 × 0.28 × 0.08 mm

Data collection
  • Nonius KappaCCD diffractometer

  • Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]) Tmin = 0.930, Tmax = 0.984

  • 11921 measured reflections

  • 3416 independent reflections

  • 2957 reflections with I > 2σ(I)

  • Rint = 0.065

Refinement
  • R[F2 > 2σ(F2)] = 0.054

  • wR(F2) = 0.091

  • S = 1.11

  • 3416 reflections

  • 218 parameters

  • H-atom parameters constrained

  • Δρmax = 0.45 e Å−3

  • Δρmin = −0.26 e Å−3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), 1457 Friedel pairs

  • Flack parameter: 0.06 (7)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1⋯Cli 0.93 2.10 3.027 (2) 176
Symmetry code: (i) [-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}].

Data collection: COLLECT (Nonius, 1998[Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: SCALEPACK (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]); data reduction: DENZO-SMN (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: XP in Siemens SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97 and local procedures.

Supporting information


Comment top

The title compound is a des-oxygen derivative of epimerized (-)-lobeline (Zheng et al., 2005). The molecular structure is illustrated in Fig. 1. The piperidine ring of the molecule is in the chair conformation and the N-methyl group is bonded equatorially to the piperidine ring. The N atom has an axial H atom that is hydrogen bonded to the chloride anion (HN..Cl = 3.027 (2) Å). One styryl group is attached equatorially to the piperidine ring and the other styryl group is pseudo-axial, with C15—C2—N1 [111.67 (18)°] and C15—C2—C3 [113.7 (2)°] bond angles slightly different from the ideal 109.5°. The piperidine ring is not mirror symmetric, as indicated by unequal bond lengths and angles (Table 1). The double bond and phenyl ring of the styryl side chain are not coplanar, as evidenced by the C15—C16—C17—C18 and C7—C8—C9—C14 torsion angles, -165.4 (3)° and -169.0 (2)°, respectively.

Related literature top

The title compound is a des-oxygen derivative of epimerized (-)-lobeline (Zheng et al., 2005).

Experimental top

The title compound was prepared from (-)-lobeline (Zheng et al., 2005). Crystals suitable for X-ray diffraction studies were obtained by slow recrystallization from a solution in methanol and diethyl ether.

Refinement top

H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained distances of 0.98 Å (RCH3), 0.99 Å (R2CH2), 1.00 Å (R3CH), 0.95 Å (R2CH), 0.93 Å (N—H), and with Uiso(H) values set to either 1.2Ueq or 1.5Ueq (RCH3) of the attached atom.

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in Siemens SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELX97 (Sheldrick, 2008) and local procedures.

Figures top
[Figure 1] Fig. 1. A view of the molecule. Displacement ellipsoids are drawn at the 50% probability level.
(2S,6S)-1-Methyl-2,6-trans-distyrylpiperidinium chloride top
Crystal data top
C22H26N+·ClF(000) = 728
Mr = 339.89Dx = 1.166 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 21849 reflections
a = 9.9355 (4) Åθ = 1.0–27.5°
b = 12.3075 (5) ŵ = 0.20 mm1
c = 15.8299 (7) ÅT = 173 K
V = 1935.70 (14) Å3Irregular plates, colourless
Z = 40.38 × 0.28 × 0.08 mm
Data collection top
Nonius KappaCCD
diffractometer
3416 independent reflections
Radiation source: fine-focus sealed tube2957 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.065
Detector resolution: 18 pixels mm-1θmax = 25.0°, θmin = 2.1°
ω scans at fixed χ = 55°h = 1111
Absorption correction: multi-scan
(SCALEPACK; Otwinowski & Minor, 1997)
k = 1414
Tmin = 0.930, Tmax = 0.984l = 1818
11921 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.054H-atom parameters constrained
wR(F2) = 0.091 w = 1/[σ2(Fo2) + (0.0332P)2 + 0.1721P]
where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max = 0.001
3416 reflectionsΔρmax = 0.45 e Å3
218 parametersΔρmin = 0.26 e Å3
0 restraintsAbsolute structure: Flack (1983), 1457 Friedel pairs
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.06 (7)
Crystal data top
C22H26N+·ClV = 1935.70 (14) Å3
Mr = 339.89Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 9.9355 (4) ŵ = 0.20 mm1
b = 12.3075 (5) ÅT = 173 K
c = 15.8299 (7) Å0.38 × 0.28 × 0.08 mm
Data collection top
Nonius KappaCCD
diffractometer
3416 independent reflections
Absorption correction: multi-scan
(SCALEPACK; Otwinowski & Minor, 1997)
2957 reflections with I > 2σ(I)
Tmin = 0.930, Tmax = 0.984Rint = 0.065
11921 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.054H-atom parameters constrained
wR(F2) = 0.091Δρmax = 0.45 e Å3
S = 1.11Δρmin = 0.26 e Å3
3416 reflectionsAbsolute structure: Flack (1983), 1457 Friedel pairs
218 parametersAbsolute structure parameter: 0.06 (7)
0 restraints
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 > σ(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
xyzUiso*/Ueq
Cl0.49125 (6)1.13417 (4)0.35616 (4)0.03556 (19)
N10.44499 (17)0.82481 (15)0.25784 (13)0.0275 (5)
H10.46610.76430.22530.033*
C10.4017 (3)0.9121 (2)0.19752 (16)0.0358 (7)
H1A0.31440.89280.17290.054*
H1B0.46870.91920.15240.054*
H1C0.39380.98120.22780.054*
C20.3304 (2)0.79138 (19)0.31510 (17)0.0305 (6)
H20.25790.76070.27830.037*
C30.3774 (3)0.7007 (2)0.37336 (17)0.0372 (7)
H3A0.30350.68120.41250.045*
H3B0.39910.63560.33920.045*
C40.5004 (3)0.7336 (2)0.42414 (16)0.0395 (7)
H4A0.47800.79580.46120.047*
H4B0.52980.67240.46020.047*
C50.6127 (2)0.76520 (19)0.36400 (16)0.0331 (6)
H5A0.63900.70080.33040.040*
H5B0.69200.78840.39720.040*
C60.5726 (2)0.85631 (19)0.30435 (15)0.0272 (6)
H60.55450.92320.33830.033*
C70.6841 (2)0.87992 (19)0.24306 (15)0.0292 (6)
H70.70390.82830.20020.035*
C80.7558 (2)0.9709 (2)0.24688 (15)0.0283 (6)
H80.72601.02410.28610.034*
C90.8759 (2)0.9986 (2)0.19738 (15)0.0281 (6)
C100.9516 (2)1.0897 (2)0.22012 (17)0.0342 (7)
H100.92371.13270.26670.041*
C111.0659 (2)1.1182 (2)0.17623 (18)0.0391 (7)
H111.11641.18000.19320.047*
C121.1074 (3)1.0578 (2)0.10788 (17)0.0444 (8)
H121.18591.07800.07750.053*
C131.0347 (3)0.9682 (2)0.08396 (17)0.0460 (8)
H131.06290.92660.03660.055*
C140.9202 (3)0.9378 (2)0.12838 (17)0.0419 (7)
H140.87150.87500.11160.050*
C150.2714 (2)0.88730 (18)0.36100 (16)0.0278 (6)
H150.33000.93780.38750.033*
C160.1402 (2)0.90289 (19)0.36523 (17)0.0307 (6)
H160.08560.85200.33590.037*
C170.0685 (2)0.9906 (2)0.41046 (14)0.0257 (6)
C180.0696 (2)0.9803 (2)0.42416 (15)0.0312 (6)
H180.11470.91670.40540.037*
C190.1417 (3)1.0608 (2)0.46452 (16)0.0383 (7)
H190.23591.05270.47290.046*
C200.0774 (3)1.1519 (2)0.49227 (17)0.0390 (7)
H200.12691.20710.52040.047*
C210.0595 (3)1.1644 (2)0.47978 (16)0.0342 (7)
H210.10371.22780.49980.041*
C220.1322 (3)1.0848 (2)0.43814 (15)0.0290 (6)
H220.22581.09450.42840.035*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl0.0428 (4)0.0231 (3)0.0408 (4)0.0033 (3)0.0079 (3)0.0019 (3)
N10.0250 (11)0.0208 (11)0.0369 (12)0.0017 (9)0.0023 (10)0.0077 (10)
C10.0337 (16)0.0357 (15)0.0379 (16)0.0067 (13)0.0034 (13)0.0001 (14)
C20.0190 (14)0.0247 (14)0.0478 (16)0.0070 (11)0.0024 (13)0.0055 (13)
C30.0334 (16)0.0283 (15)0.0500 (18)0.0045 (12)0.0089 (14)0.0034 (14)
C40.0414 (16)0.0329 (14)0.0442 (17)0.0019 (15)0.0055 (16)0.0147 (13)
C50.0243 (14)0.0306 (15)0.0445 (17)0.0002 (12)0.0047 (13)0.0062 (14)
C60.0194 (13)0.0244 (14)0.0377 (15)0.0057 (12)0.0040 (12)0.0056 (13)
C70.0256 (13)0.0319 (15)0.0301 (15)0.0050 (13)0.0009 (12)0.0023 (13)
C80.0236 (14)0.0294 (15)0.0319 (15)0.0007 (12)0.0023 (12)0.0012 (13)
C90.0218 (14)0.0360 (16)0.0264 (14)0.0004 (12)0.0029 (12)0.0050 (13)
C100.0288 (15)0.0325 (15)0.0412 (16)0.0026 (12)0.0026 (13)0.0033 (13)
C110.0294 (15)0.0356 (17)0.0523 (19)0.0086 (13)0.0001 (14)0.0098 (16)
C120.0300 (16)0.061 (2)0.0427 (18)0.0069 (16)0.0042 (14)0.0142 (16)
C130.0379 (18)0.066 (2)0.0339 (17)0.0039 (16)0.0074 (14)0.0072 (15)
C140.0347 (16)0.0530 (18)0.0380 (18)0.0100 (14)0.0044 (14)0.0036 (16)
C150.0241 (14)0.0235 (14)0.0359 (15)0.0025 (11)0.0007 (12)0.0038 (12)
C160.0280 (15)0.0262 (14)0.0379 (15)0.0046 (11)0.0065 (13)0.0035 (13)
C170.0231 (14)0.0276 (15)0.0265 (14)0.0052 (12)0.0040 (11)0.0030 (12)
C180.0238 (15)0.0347 (16)0.0350 (15)0.0033 (13)0.0051 (12)0.0003 (13)
C190.0237 (15)0.0502 (19)0.0410 (18)0.0055 (14)0.0035 (13)0.0038 (15)
C200.0382 (18)0.0449 (19)0.0338 (16)0.0115 (15)0.0034 (13)0.0065 (15)
C210.0378 (17)0.0297 (17)0.0352 (16)0.0010 (13)0.0011 (13)0.0052 (13)
C220.0224 (14)0.0335 (15)0.0311 (15)0.0016 (12)0.0019 (12)0.0009 (13)
Geometric parameters (Å, º) top
N1—C11.500 (3)C9—C101.397 (3)
N1—C21.512 (3)C10—C111.377 (3)
N1—C61.517 (3)C10—H100.9500
N1—H10.9300C11—C121.376 (3)
C1—H1A0.9800C11—H110.9500
C1—H1B0.9800C12—C131.371 (4)
C1—H1C0.9800C12—H120.9500
C2—C151.505 (3)C13—C141.389 (3)
C2—C31.522 (3)C13—H130.9500
C2—H21.0000C14—H140.9500
C3—C41.518 (3)C15—C161.320 (3)
C3—H3A0.9900C15—H150.9500
C3—H3B0.9900C16—C171.478 (3)
C4—C51.517 (3)C16—H160.9500
C4—H4A0.9900C17—C221.392 (3)
C4—H4B0.9900C17—C181.394 (3)
C5—C61.519 (3)C18—C191.380 (3)
C5—H5A0.9900C18—H180.9500
C5—H5B0.9900C19—C201.363 (4)
C6—C71.501 (3)C19—H190.9500
C6—H61.0000C20—C211.383 (3)
C7—C81.329 (3)C20—H200.9500
C7—H70.9500C21—C221.384 (3)
C8—C91.468 (3)C21—H210.9500
C8—H80.9500C22—H220.9500
C9—C141.395 (3)
C1—N1—C2111.13 (18)C7—C8—C9127.4 (2)
C1—N1—C6111.45 (18)C7—C8—H8116.3
C2—N1—C6114.09 (19)C9—C8—H8116.3
C1—N1—H1106.5C14—C9—C10117.5 (2)
C2—N1—H1106.5C14—C9—C8123.4 (2)
C6—N1—H1106.5C10—C9—C8119.1 (2)
N1—C1—H1A109.5C11—C10—C9121.2 (3)
N1—C1—H1B109.5C11—C10—H10119.4
H1A—C1—H1B109.5C9—C10—H10119.4
N1—C1—H1C109.5C12—C11—C10120.4 (3)
H1A—C1—H1C109.5C12—C11—H11119.8
H1B—C1—H1C109.5C10—C11—H11119.8
C15—C2—N1111.67 (18)C13—C12—C11119.6 (3)
C15—C2—C3113.7 (2)C13—C12—H12120.2
N1—C2—C3109.39 (19)C11—C12—H12120.2
C15—C2—H2107.2C12—C13—C14120.6 (3)
N1—C2—H2107.2C12—C13—H13119.7
C3—C2—H2107.2C14—C13—H13119.7
C4—C3—C2111.81 (19)C13—C14—C9120.7 (3)
C4—C3—H3A109.3C13—C14—H14119.7
C2—C3—H3A109.3C9—C14—H14119.7
C4—C3—H3B109.3C16—C15—C2121.6 (2)
C2—C3—H3B109.3C16—C15—H15119.2
H3A—C3—H3B107.9C2—C15—H15119.2
C5—C4—C3109.2 (2)C15—C16—C17127.4 (2)
C5—C4—H4A109.8C15—C16—H16116.3
C3—C4—H4A109.8C17—C16—H16116.3
C5—C4—H4B109.8C22—C17—C18118.3 (2)
C3—C4—H4B109.8C22—C17—C16122.8 (2)
H4A—C4—H4B108.3C18—C17—C16118.9 (2)
C4—C5—C6112.74 (19)C19—C18—C17121.2 (3)
C4—C5—H5A109.0C19—C18—H18119.4
C6—C5—H5A109.0C17—C18—H18119.4
C4—C5—H5B109.0C20—C19—C18119.7 (2)
C6—C5—H5B109.0C20—C19—H19120.1
H5A—C5—H5B107.8C18—C19—H19120.1
C7—C6—N1110.65 (18)C19—C20—C21120.5 (3)
C7—C6—C5110.60 (19)C19—C20—H20119.8
N1—C6—C5109.39 (19)C21—C20—H20119.8
C7—C6—H6108.7C20—C21—C22120.2 (3)
N1—C6—H6108.7C20—C21—H21119.9
C5—C6—H6108.7C22—C21—H21119.9
C8—C7—C6122.0 (2)C21—C22—C17120.1 (2)
C8—C7—H7119.0C21—C22—H22119.9
C6—C7—H7119.0C17—C22—H22119.9
C1—N1—C2—C1554.9 (3)C8—C9—C10—C11179.3 (2)
C6—N1—C2—C1572.2 (2)C9—C10—C11—C120.7 (4)
C1—N1—C2—C3178.35 (18)C10—C11—C12—C130.4 (4)
C6—N1—C2—C354.6 (3)C11—C12—C13—C140.4 (4)
C15—C2—C3—C469.2 (3)C12—C13—C14—C90.9 (4)
N1—C2—C3—C456.4 (3)C10—C9—C14—C130.6 (4)
C2—C3—C4—C558.0 (3)C8—C9—C14—C13180.0 (2)
C3—C4—C5—C657.4 (3)N1—C2—C15—C16133.2 (3)
C1—N1—C6—C757.5 (2)C3—C2—C15—C16102.5 (3)
C2—N1—C6—C7175.62 (18)C2—C15—C16—C17177.6 (2)
C1—N1—C6—C5179.60 (19)C15—C16—C17—C2216.4 (4)
C2—N1—C6—C553.5 (2)C15—C16—C17—C18165.4 (3)
C4—C5—C6—C7176.7 (2)C22—C17—C18—C190.4 (4)
C4—C5—C6—N154.6 (3)C16—C17—C18—C19178.7 (2)
N1—C6—C7—C8129.0 (2)C17—C18—C19—C200.5 (4)
C5—C6—C7—C8109.6 (3)C18—C19—C20—C210.4 (4)
C6—C7—C8—C9172.7 (2)C19—C20—C21—C220.6 (4)
C7—C8—C9—C1410.4 (4)C20—C21—C22—C171.5 (4)
C7—C8—C9—C10169.0 (2)C18—C17—C22—C211.4 (4)
C14—C9—C10—C110.2 (3)C16—C17—C22—C21179.7 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Cli0.932.103.027 (2)176
Symmetry code: (i) x+1, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC22H26N+·Cl
Mr339.89
Crystal system, space groupOrthorhombic, P212121
Temperature (K)173
a, b, c (Å)9.9355 (4), 12.3075 (5), 15.8299 (7)
V3)1935.70 (14)
Z4
Radiation typeMo Kα
µ (mm1)0.20
Crystal size (mm)0.38 × 0.28 × 0.08
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correctionMulti-scan
(SCALEPACK; Otwinowski & Minor, 1997)
Tmin, Tmax0.930, 0.984
No. of measured, independent and
observed [I > 2σ(I)] reflections
11921, 3416, 2957
Rint0.065
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.054, 0.091, 1.11
No. of reflections3416
No. of parameters218
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.45, 0.26
Absolute structureFlack (1983), 1457 Friedel pairs
Absolute structure parameter0.06 (7)

Computer programs: COLLECT (Nonius, 1998), SCALEPACK (Otwinowski & Minor, 1997), DENZO-SMN (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP in Siemens SHELXTL (Sheldrick, 2008), SHELX97 (Sheldrick, 2008) and local procedures.

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Cli0.932.103.027 (2)175.7
Symmetry code: (i) x+1, y1/2, z+1/2.
 

Acknowledgements

This research was supported by National Institute of Health grants DA13519 and DA00399.

References

First citationFlack, H. D. (1983). Acta Cryst. A39, 876–881.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationNonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.  Google Scholar
First citationOtwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationZheng, G., Dwoskin, L. P., Deaciuc, A. G., Norrholm, S. D. & Crooks, P. A. (2005). J. Med. Chem. pp. 5551–5560.  Web of Science CrossRef Google Scholar

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