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Acta Crystallogr Sect E Struct Rep Online. 2009 September 1; 65(Pt 9): o2255–o2256.
Published online 2009 August 26. doi:  10.1107/S1600536809033364
PMCID: PMC2969859

Dimethyl 4-(4-ethoxy­phen­yl)-2,6-dimethyl-1,4-dihydro­pyridine-3,5-dicarboxyl­ate

Abstract

In the title mol­ecule, C19H23NO5, the dihedral angle formed by the benzene ring and the planar part of the dihydro­pyridine ring is 83.52 (5)°. The dihydro­pyridine ring adopts a flattened boat conformation. In the crystal, mol­ecules are linked by N—H(...)O hydrogen bonds, generating chains running parallel to [100]. The crystal structure is consolidated by C—H(...)O contacts.

Related literature

For general background to Hantzsch 1,4-dihydro­pyridines (1,4-DHPS), see: Gaudio et al. (1994 [triangle]); Bocker & Guengerich (1986 [triangle]); Gordeev et al. (1996 [triangle]); Sunkel et al. (1992 [triangle]); Vo et al. (1995 [triangle]); Cooper et al. (1992 [triangle]). For a related structure, see: Fun et al. (2009 [triangle]). For hydrogen-bond motifs, see: Bernstein et al. (1995 [triangle]). For geometric analysis, see: Cremer & Pople (1975 [triangle]). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 [triangle]).

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Object name is e-65-o2255-scheme1.jpg

Experimental

Crystal data

  • C19H23NO5
  • M r = 345.38
  • Triclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-o2255-efi2.jpg
  • a = 7.4108 (1) Å
  • b = 9.7459 (2) Å
  • c = 12.3359 (2) Å
  • α = 87.412 (1)°
  • β = 86.244 (1)°
  • γ = 76.402 (1)°
  • V = 863.72 (3) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.10 mm−1
  • T = 100 K
  • 0.39 × 0.33 × 0.19 mm

Data collection

  • Bruker SMART APEXII CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2005 [triangle]) T min = 0.963, T max = 0.982
  • 26880 measured reflections
  • 4579 independent reflections
  • 3972 reflections with I > 2σ(I)
  • R int = 0.026

Refinement

  • R[F 2 > 2σ(F 2)] = 0.036
  • wR(F 2) = 0.099
  • S = 1.05
  • 4579 reflections
  • 235 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.38 e Å−3
  • Δρmin = −0.23 e Å−3

Data collection: APEX2 (Bruker, 2005 [triangle]); cell refinement: SAINT (Bruker, 2005 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809033364/tk2529sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809033364/tk2529Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

HKF and CKQ thank Universiti Sains Malaysia (USM) for a Research University Golden Goose Grant (No. 1001/PFIZIK/811012). CKQ thanks USM for a Research Fellowship. VV is grateful to DST–India for funding through the Young Scientist Scheme (Fast Track Proposal).

supplementary crystallographic information

Comment

Hantzsch 1,4-dihydropyridines (1,4-DHPS) are biologically active compounds which include various vasodilator, anti-hypertensive, bronchodilator, hepatoprotective, anti-tumor, anti-mutagenic, geroprotective, and anti-diabetic agents (Gaudio et al., 1994). Nifedipine, Nitrendipine and Nimodipine have found commercial utility as calcium channel blockers (Bocker & Guengerich, 1986; Gordeev et al., 1996). For the treatment of congestive heart failure, a number of DHP calcium antagonists have been introduced (Sunkel et al., 1992; Vo et al., 1995). Some DHPs have been introduced as neuroprotectants and cognition enhancers. In addition, a number of DHPs with platelet anti-aggregatory activity have also been discovered (Cooper et al., 1992).

The geometric parameters in (I), Fig. 1, are comparable to those in a closely related structure (Fun et al., 2009). The benzene ring (C1—C6) and dihydropyridine ring (C7—C11/N1) are nearly perpendicular as seen in the angle of 83.52 (5)° between their least-squares planes. The dihydropyridine ring adopts a flattened boat conformation with puckering parameters (Cremer & Pople, 1975) Q = 0.2688 (10) Å; Θ = 73.7 (2)° and [var phi] = 183.6 (2)°, with atoms N1 and C7 deviating by 0.125 (1) and 0.172 (1) Å, respectively, from the mean plane of the dihydropyridine ring.

In the solid-state (Fig. 2), the molecules are linked via N1—H1N1···O4 hydrogen bonds (Table 1) to generate supramolecular chains running parallel to the [1 0 0] direction. The O4 atom also participates in a C19—H19B···O4 contact to generate, along with the N1—H1N1···O4 hydrogen bond, a R21(6) ring motif (Bernstein et al., 1995); Fig. 2. Molecules are further consolidated by intermolecular C—H···O interactions (Table 1).

Experimental

Compound (I) was prepared according to the Hantzsch pyridine synthesis. A mixture of 4-ethoxybenzaldehyde (10 mmol), methylacetoacetate (20 mmol) and ammonium acetate (10 mmol) were heated at 353 K for 3 h (monitored by TLC). After completion of the reaction, the mixture was cooled to room temperature and kept for 2 days to get the solid product. The solid was extracted using diethyl ether and the mother liquors kept for crystallization. The purity of the crude product was checked through TLC and recrystallized using acetone and ether; M.p. 403–405 K. IR (KBr): υ: 3361, 2985, 2948, 1682, 1652, 1485, 1235 cm-1.

Refinement

The N-bound H atom was located from a difference Fourier map and refined freely. The other H atoms were placed in calculated positions with C–H = 0.93 – 0.98 Å, and refined using a riding model with Uiso(H) = 1.2 or 1.5 Ueq(C). A rotating-group model was applied for the methyl groups.

Figures

Fig. 1.
The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme.
Fig. 2.
The crystal packing of (I), viewed along the b axis, showing the R21(6) ring motifs. The dashed lines indicate N-H···O hydrogen bonds and C-H···O contacts.

Crystal data

C19H23NO5Z = 2
Mr = 345.38F(000) = 368
Triclinic, P1Dx = 1.328 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.4108 (1) ÅCell parameters from 9914 reflections
b = 9.7459 (2) Åθ = 2.7–37.4°
c = 12.3359 (2) ŵ = 0.10 mm1
α = 87.412 (1)°T = 100 K
β = 86.244 (1)°Block, colourless
γ = 76.402 (1)°0.39 × 0.33 × 0.19 mm
V = 863.72 (3) Å3

Data collection

Bruker SMART APEXII CCD area-detector diffractometer4579 independent reflections
Radiation source: fine-focus sealed tube3972 reflections with I > 2σ(I)
graphiteRint = 0.026
[var phi] and ω scansθmax = 29.0°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2005)h = −10→9
Tmin = 0.963, Tmax = 0.982k = −13→13
26880 measured reflectionsl = −16→16

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.099H atoms treated by a mixture of independent and constrained refinement
S = 1.05w = 1/[σ2(Fo2) + (0.0475P)2 + 0.2882P] where P = (Fo2 + 2Fc2)/3
4579 reflections(Δ/σ)max = 0.001
235 parametersΔρmax = 0.38 e Å3
0 restraintsΔρmin = −0.23 e Å3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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)

xyzUiso*/Ueq
O10.19861 (10)0.60173 (8)0.03818 (6)0.01954 (16)
O20.44712 (10)−0.06125 (8)0.22047 (7)0.02351 (17)
O30.75904 (10)−0.12488 (7)0.20146 (6)0.01800 (15)
O40.12920 (9)0.26642 (8)0.49547 (6)0.01857 (16)
O50.28689 (10)0.36872 (8)0.60451 (6)0.01980 (16)
N10.78173 (11)0.17632 (9)0.43091 (7)0.01522 (17)
C10.47641 (14)0.38112 (11)0.24725 (8)0.0186 (2)
H1A0.58110.37800.28580.022*
C20.42251 (14)0.49057 (11)0.17125 (9)0.0205 (2)
H2A0.49050.55930.15940.025*
C30.26590 (13)0.49643 (10)0.11306 (8)0.01547 (19)
C40.16801 (13)0.39106 (10)0.12993 (8)0.01699 (19)
H4A0.06460.39340.09040.020*
C50.22500 (13)0.28219 (10)0.20605 (8)0.01653 (19)
H5A0.15930.21180.21630.020*
C60.37885 (12)0.27631 (10)0.26738 (7)0.01368 (18)
C70.43800 (12)0.16185 (10)0.35541 (7)0.01319 (17)
H7A0.34100.10870.36660.016*
C80.61931 (12)0.05947 (10)0.32117 (7)0.01377 (18)
C90.78381 (13)0.07461 (10)0.35543 (8)0.01377 (18)
C100.62373 (13)0.24334 (10)0.49089 (8)0.01427 (18)
C110.45520 (12)0.22955 (10)0.46159 (7)0.01390 (18)
C120.28242 (15)0.72105 (11)0.03018 (9)0.0222 (2)
H12A0.41250.69160.00590.027*
H12B0.27440.76360.10040.027*
C130.17764 (17)0.82565 (13)−0.05091 (10)0.0293 (3)
H13A0.23060.9067−0.05850.044*
H13B0.04940.8544−0.02580.044*
H13C0.18630.7823−0.12000.044*
C140.59716 (13)−0.04608 (10)0.24493 (8)0.01548 (18)
C150.73788 (15)−0.22168 (12)0.12099 (9)0.0234 (2)
H15A0.8579−0.27770.09800.035*
H15B0.6800−0.16950.05960.035*
H15C0.6617−0.28240.15170.035*
C160.27731 (13)0.28733 (10)0.52057 (8)0.01461 (18)
C170.11161 (14)0.43650 (12)0.65823 (9)0.0214 (2)
H17A0.13360.49300.71550.032*
H17B0.05000.36590.68820.032*
H17C0.03480.49570.60670.032*
C180.97650 (13)−0.00902 (10)0.32325 (8)0.01687 (19)
H18A1.00100.00340.24650.025*
H18B0.9854−0.10730.34080.025*
H18C1.06590.02350.36190.025*
C190.66430 (13)0.32411 (11)0.58374 (8)0.01801 (19)
H19A0.59040.41920.58010.027*
H19B0.79370.32540.57920.027*
H19C0.63470.27930.65130.027*
H1N10.886 (2)0.1880 (15)0.4495 (12)0.027 (3)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O10.0198 (4)0.0181 (3)0.0215 (4)−0.0055 (3)−0.0063 (3)0.0054 (3)
O20.0157 (3)0.0248 (4)0.0319 (4)−0.0066 (3)−0.0035 (3)−0.0084 (3)
O30.0157 (3)0.0167 (3)0.0220 (4)−0.0044 (3)0.0005 (3)−0.0051 (3)
O40.0112 (3)0.0236 (4)0.0213 (4)−0.0047 (3)−0.0010 (3)−0.0018 (3)
O50.0128 (3)0.0258 (4)0.0209 (4)−0.0040 (3)0.0011 (3)−0.0073 (3)
N10.0099 (4)0.0184 (4)0.0181 (4)−0.0042 (3)−0.0022 (3)−0.0015 (3)
C10.0154 (4)0.0212 (5)0.0214 (5)−0.0075 (4)−0.0074 (4)0.0029 (4)
C20.0202 (5)0.0200 (5)0.0244 (5)−0.0104 (4)−0.0067 (4)0.0040 (4)
C30.0153 (4)0.0158 (4)0.0144 (4)−0.0017 (3)−0.0015 (3)−0.0002 (3)
C40.0142 (4)0.0197 (5)0.0178 (4)−0.0043 (3)−0.0046 (3)−0.0001 (4)
C50.0149 (4)0.0169 (4)0.0194 (5)−0.0066 (3)−0.0033 (3)0.0003 (4)
C60.0120 (4)0.0144 (4)0.0143 (4)−0.0021 (3)−0.0012 (3)−0.0013 (3)
C70.0100 (4)0.0144 (4)0.0158 (4)−0.0038 (3)−0.0021 (3)0.0000 (3)
C80.0120 (4)0.0135 (4)0.0159 (4)−0.0034 (3)−0.0009 (3)0.0008 (3)
C90.0128 (4)0.0130 (4)0.0154 (4)−0.0033 (3)−0.0008 (3)0.0019 (3)
C100.0132 (4)0.0149 (4)0.0147 (4)−0.0033 (3)−0.0016 (3)0.0013 (3)
C110.0115 (4)0.0152 (4)0.0151 (4)−0.0034 (3)−0.0009 (3)0.0004 (3)
C120.0249 (5)0.0192 (5)0.0238 (5)−0.0078 (4)−0.0035 (4)0.0042 (4)
C130.0284 (6)0.0243 (5)0.0333 (6)−0.0047 (4)−0.0020 (5)0.0120 (5)
C140.0149 (4)0.0138 (4)0.0178 (4)−0.0040 (3)−0.0009 (3)0.0012 (3)
C150.0231 (5)0.0214 (5)0.0270 (5)−0.0065 (4)0.0003 (4)−0.0093 (4)
C160.0130 (4)0.0157 (4)0.0147 (4)−0.0028 (3)−0.0011 (3)0.0023 (3)
C170.0153 (5)0.0247 (5)0.0229 (5)−0.0019 (4)0.0026 (4)−0.0055 (4)
C180.0112 (4)0.0172 (4)0.0221 (5)−0.0029 (3)−0.0012 (3)−0.0005 (4)
C190.0135 (4)0.0222 (5)0.0192 (5)−0.0050 (3)−0.0033 (3)−0.0033 (4)

Geometric parameters (Å, °)

O1—C31.3745 (11)C8—C91.3580 (13)
O1—C121.4384 (13)C8—C141.4686 (13)
O2—C141.2143 (12)C9—C181.5062 (13)
O3—C141.3551 (11)C10—C111.3605 (12)
O3—C151.4403 (12)C10—C191.5033 (13)
O4—C161.2237 (11)C11—C161.4651 (13)
O5—C161.3479 (12)C12—C131.5100 (15)
O5—C171.4443 (12)C12—H12A0.9700
N1—C101.3841 (12)C12—H12B0.9700
N1—C91.3872 (12)C13—H13A0.9600
N1—H1N10.852 (15)C13—H13B0.9600
C1—C61.3888 (13)C13—H13C0.9600
C1—C21.3909 (14)C15—H15A0.9600
C1—H1A0.9300C15—H15B0.9600
C2—C31.3928 (13)C15—H15C0.9600
C2—H2A0.9300C17—H17A0.9600
C3—C41.3912 (14)C17—H17B0.9600
C4—C51.3919 (13)C17—H17C0.9600
C4—H4A0.9300C18—H18A0.9600
C5—C61.3978 (12)C18—H18B0.9600
C5—H5A0.9300C18—H18C0.9600
C6—C71.5293 (12)C19—H19A0.9600
C7—C111.5188 (13)C19—H19B0.9600
C7—C81.5207 (12)C19—H19C0.9600
C7—H7A0.9800
C3—O1—C12117.11 (8)O1—C12—C13107.30 (9)
C14—O3—C15114.71 (8)O1—C12—H12A110.3
C16—O5—C17116.10 (8)C13—C12—H12A110.3
C10—N1—C9123.78 (8)O1—C12—H12B110.3
C10—N1—H1N1117.3 (10)C13—C12—H12B110.3
C9—N1—H1N1118.0 (10)H12A—C12—H12B108.5
C6—C1—C2122.08 (9)C12—C13—H13A109.5
C6—C1—H1A119.0C12—C13—H13B109.5
C2—C1—H1A119.0H13A—C13—H13B109.5
C1—C2—C3119.51 (9)C12—C13—H13C109.5
C1—C2—H2A120.2H13A—C13—H13C109.5
C3—C2—H2A120.2H13B—C13—H13C109.5
O1—C3—C4116.37 (8)O2—C14—O3121.92 (9)
O1—C3—C2124.04 (9)O2—C14—C8123.53 (9)
C4—C3—C2119.58 (9)O3—C14—C8114.53 (8)
C3—C4—C5119.90 (9)O3—C15—H15A109.5
C3—C4—H4A120.1O3—C15—H15B109.5
C5—C4—H4A120.1H15A—C15—H15B109.5
C4—C5—C6121.45 (9)O3—C15—H15C109.5
C4—C5—H5A119.3H15A—C15—H15C109.5
C6—C5—H5A119.3H15B—C15—H15C109.5
C1—C6—C5117.45 (9)O4—C16—O5121.62 (9)
C1—C6—C7120.24 (8)O4—C16—C11123.31 (9)
C5—C6—C7122.30 (8)O5—C16—C11115.06 (8)
C11—C7—C8110.84 (7)O5—C17—H17A109.5
C11—C7—C6109.88 (7)O5—C17—H17B109.5
C8—C7—C6111.28 (7)H17A—C17—H17B109.5
C11—C7—H7A108.2O5—C17—H17C109.5
C8—C7—H7A108.2H17A—C17—H17C109.5
C6—C7—H7A108.2H17B—C17—H17C109.5
C9—C8—C14125.40 (9)C9—C18—H18A109.5
C9—C8—C7120.71 (8)C9—C18—H18B109.5
C14—C8—C7113.77 (8)H18A—C18—H18B109.5
C8—C9—N1118.66 (8)C9—C18—H18C109.5
C8—C9—C18127.97 (9)H18A—C18—H18C109.5
N1—C9—C18113.36 (8)H18B—C18—H18C109.5
C11—C10—N1118.71 (8)C10—C19—H19A109.5
C11—C10—C19127.90 (9)C10—C19—H19B109.5
N1—C10—C19113.39 (8)H19A—C19—H19B109.5
C10—C11—C16124.96 (9)C10—C19—H19C109.5
C10—C11—C7120.47 (8)H19A—C19—H19C109.5
C16—C11—C7114.33 (8)H19B—C19—H19C109.5
C6—C1—C2—C30.06 (16)C10—N1—C9—C18−164.68 (8)
C12—O1—C3—C4171.89 (9)C9—N1—C10—C11−12.56 (14)
C12—O1—C3—C2−7.98 (14)C9—N1—C10—C19167.12 (9)
C1—C2—C3—O1178.41 (9)N1—C10—C11—C16176.37 (8)
C1—C2—C3—C4−1.46 (15)C19—C10—C11—C16−3.25 (16)
O1—C3—C4—C5−178.70 (9)N1—C10—C11—C7−9.52 (13)
C2—C3—C4—C51.18 (15)C19—C10—C11—C7170.86 (9)
C3—C4—C5—C60.51 (15)C8—C7—C11—C1026.43 (12)
C2—C1—C6—C51.58 (15)C6—C7—C11—C10−96.98 (10)
C2—C1—C6—C7−177.17 (9)C8—C7—C11—C16−158.87 (8)
C4—C5—C6—C1−1.86 (15)C6—C7—C11—C1677.72 (10)
C4—C5—C6—C7176.86 (9)C3—O1—C12—C13−176.21 (9)
C1—C6—C7—C1151.88 (11)C15—O3—C14—O22.92 (14)
C5—C6—C7—C11−126.81 (9)C15—O3—C14—C8−175.86 (8)
C1—C6—C7—C8−71.27 (11)C9—C8—C14—O2176.04 (10)
C5—C6—C7—C8110.05 (10)C7—C8—C14—O2−7.83 (14)
C11—C7—C8—C9−24.86 (12)C9—C8—C14—O3−5.20 (14)
C6—C7—C8—C997.74 (10)C7—C8—C14—O3170.92 (8)
C11—C7—C8—C14158.81 (8)C17—O5—C16—O4−3.79 (13)
C6—C7—C8—C14−78.58 (10)C17—O5—C16—C11175.00 (8)
C14—C8—C9—N1−177.70 (8)C10—C11—C16—O4−175.82 (9)
C7—C8—C9—N16.43 (13)C7—C11—C16—O49.75 (13)
C14—C8—C9—C180.95 (16)C10—C11—C16—O55.42 (14)
C7—C8—C9—C18−174.92 (9)C7—C11—C16—O5−169.02 (8)
C10—N1—C9—C814.15 (14)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
N1—H1N1···O4i0.854 (15)2.230 (15)3.0710 (11)168.0 (13)
C4—H4A···O1ii0.932.583.5104 (12)174
C15—H15A···O1iii0.962.603.5500 (14)172
C19—H19B···O4i0.962.573.4677 (12)155

Symmetry codes: (i) x+1, y, z; (ii) −x, −y+1, −z; (iii) x+1, y−1, z.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2529).

References

  • Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl.34, 1555–1573.
  • Bocker, R. H. & Guengerich, F. P. (1986). J. Med. Chem.28, 1596–1603. [PubMed]
  • Bruker (2005). APEX2, SAINT and SADABS Bruker AXS Inc., Madison, Wisconsin, USA.
  • Cooper, K., Fray, M. J., Parry, M. J., Richardson, K. & Steele, J. (1992). J. Med. Chem.35, 3115–3129. [PubMed]
  • Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst.19, 105–107.
  • Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc.97, 1354–1358.
  • Fun, H.-K., Goh, J. H., Reddy, B. P., Sarveswari, S. & Vijayakumar, V. (2009). Acta Cryst. E65, o2247–o2248. [PMC free article] [PubMed]
  • Gaudio, A. C., Korolkovas, A. & Takahata, Y. J. (1994). Pharm. Sci.83, 1110–1115. [PubMed]
  • Gordeev, M. F., Patel, D. V. & Gordon, E. M. (1996). J. Org. Chem.61, 924–928.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]
  • Sunkel, C. E., Fau de Casa-Juana, M., Santos, L., Garcia, A. G., Artalejo, C. R., Villarroya, M., Gonzalez-Morales, M. A., Lopez, M. G. & Cillero, J. (1992). J. Med. Chem.35, 2407–2414. [PubMed]
  • Vo, D., Matowe, W. C., Ramesh, M., Iqbal, N., Wolowyk, M. W., Howlett, S. E. & Knaus, E. E. (1995). J. Med. Chem.38, 2851–2859. [PubMed]

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