Literature DB >> 25995882

The crystal structure of 3-chloro-2-(4-methyl-phenyl)-2H-pyrazolo-[3,4-b]quinoline.

Haliwana B V Sowmya1, Tholappanavara H Suresha Kumara2, Jerry P Jasinski3, Sean P Millikan3, Hemmige S Yathirajan4, Christopher Glidewell5.   

Abstract

In the mol-ecule of 3-chloro-2-(4-methyl-phen-yl)-2H-pyrazolo-[3,4-b]quinoline, C17H12ClN3, (I), the dihedral angle between the planes of the pyrazole ring and the methyl-ated phenyl ring is 54.25 (9)°. The bond distances in the fused tricyclic system provide evidence for 10-π delocalization in the pyrazolo-pyridine portion of the mol-ecule, with diene character in the fused carbocyclic ring. In the crystal, mol-ecules of (I) are linked by two independent C-H⋯N hydrogen bonds, forming sheets containing centrosymmetric R 2 (2)(16) and R 6 (4)(28) rings, and these sheets are all linked together by π-π stacking inter-actions with a ring-centroid separation of 3.5891 (9) Å.

Entities:  

Keywords:  crystal structure; hydrogen bonding; pyrazolo­quinoline; π–π stacking inter­actions

Year:  2015        PMID: 25995882      PMCID: PMC4420078          DOI: 10.1107/S205698901500818X

Source DB:  PubMed          Journal:  Acta Crystallogr E Crystallogr Commun


Chemical context

Quinoline exhibits anti­malarial, anti-bacterial, anti­fungal, anthelmintic, cardiotonic, anti­convulsant, anti-inflammatory and analgesic activity (Marella et al., 2013 ▸). Quinoline and its fused heterocyclic derivatives constitute an important class of compounds for new drug development (Kumar et al., 2009 ▸), and the medicinal applications of pyrazolo­[3,4-b]quinolines have been summarized, along with an efficient synthetic method (Afghan et al., 2009 ▸). Recently, we have reported the synthesis of a number of novel pyrazolo­[3,4-b]quinoline derivatives, including that of the title compound (I), and mol­ecular docking studies of their binding affinity to the active sites of human telomerase (Sowmya et al., 2014 ▸). In a continuation of that study, we now report the crystal and mol­ecular structure of one such example, the title compound 3-chloro-2-p-tolyl-2H-pyrazolo­[3,4-b]quinoline, (I).

Structural commentary

Within the mol­ecule of compound (I) (Fig. 1 ▸), the pendent phenyl group is twisted out of the plane of the fused heterocyclic ring system, as indicated by the relevant torsional angles (Table 1 ▸): the dihedral angle between the mean planes of the pyrazole and the methyl­ated phenyl rings is 54.25 (9)°. The mol­ecules of (I) exhibit no inter­nal symmetry and thus they are conformationally chiral: however, the centrosymmetric space group accommodates equal numbers of both of the conformational enanti­omers. The non-planar character of the mol­ecular skeleton may be plausibly ascribed to the combined effects of the intra­molecular non-bonded repulsion between the Cl substituent and the nearest H atom of the methyl­ated phenyl ring, and of the direction-specific inter­molecular inter­actions, in particular the hydrogen bonds.
Figure 1

The mol­ecular structure of compound (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Table 1

Selected geometric parameters (, )

N1N21.3644(18)C7C81.358(2)
N2C31.346(2)C8C8A 1.432(2)
C3C3A 1.398(2)C8AN91.342(2)
C3AC41.388(2)N9C9A 1.346(2)
C4C4A 1.394(2)C9AN11.349(2)
C4AC51.429(2)C3AC9A 1.430(2)
C5C61.357(3)C4AC8A 1.446(2)
C6C71.419(3)C3Cl31.6993(16)
    
N1N2C21C2253.7(2)C3N2C21C22125.08(17)
N1N2C21C26126.42(16)C3N2C21C2654.8(2)
The bond distances in compound (I) (Table 1 ▸) show some inter­esting features. Within the pyrazole ring, the bond distances N1—C9A and N2—C3 (Fig. 1 ▸) are identical within experimental uncertainty, although these two bonds are formally double and single bonds, respectively. In the fused carbocyclic ring, the bonds C5—C6 and C7—C8 are much shorted than any other CC bonds in the mol­ecule. However, in the central pyridine ring, within each of the pairs of corresponding bonds C3A—C4 and C4—C4A, C8A—N9 and N9—C9A, and C3A—C9A and C4A—C8A, the two distances are very similar. These observations taken together are fully consistent with a 10-π delocalized system in the pyrazolo­pyridine portion of the mol­ecule, comparable to those found in naphthalene and azulene (Glidewell & Lloyd, 1984 ▸), while the fused carbocyclic ring has more the character of an isolated diene (cf. Glidewell & Lloyd, 1986 ▸).

Supra­molecular features

The supra­molecular assembly in compound (I) is determined by two independent C—H⋯N hydrogen bonds (Table 2 ▸) and a π–π stacking inter­action, which together link the mol­ecules into a three-dimensional framework structure. The formation of this framework is readily analysed in terms of three simpler sub-structures (Ferguson et al., 1998a ▸,b ▸; Gregson et al., 2000 ▸). In the simplest sub-structure, the C—H⋯N hydrogen bond having atom C23 as the donor links an inversion-related pair of mol­ecules, forming a cyclic centrosymmetric dimer characterized by an (16) (Bernstein et al., 1995 ▸) motif (Fig. 2 ▸), and this dimeric unit can be regarded as the basic building block in the supra­molecular assembly. The second C—H⋯N hydrogen bond, having atom C26 as the donor, directly links the reference dimer, which is centred at (0, ½, ½) to four symmetry-related dimers centred at (0, 0, 0), (0 1, 0), (0, 0, 1) and (0, 1, 1), thereby leading to the formation of a hydrogen-bonded sheet lying parallel to (100), in which centrosymmetric (16) rings alternate with (28) rings (Fig. 3 ▸).
Table 2

Hydrogen-bond geometry (, )

Cg1 represents the centroid of the C21C26 ring.

DHA DHHA D A DHA
C23H23N9i 0.952.503.393(2)157
C26H26N9ii 0.952.503.449(2)174
C27H27A Cg1iii 0.982.843.653(2)140

Symmetry codes: (i) ; (ii) ; (iii) .

Figure 2

Part of the crystal structure of compound (I) showing the formation of a centrosymmetric hydrogen-bonded dimer. For the sake of clarity, the unit-cell outline and H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (−x, 1 − y, 1 − z).

Figure 3

A stereoview of part of the crystal structure of compound (I) showing the formation of a hydrogen-bonded sheet lying parallel to (100) and containing alternating (16) and (28) rings. For the sake of clarity, H atoms not involved in the motifs shown have been omitted.

Only one hydrogen-bonded sheet passes through each unit cell, but the sheets are linked by the π–π stacking inter­action which is associated with the extensive overlap between the tricyclic ring systems of inversion-related pairs of mol­ecules in adjacent sheets (Fig. 4 ▸). The pyridine rings of the mol­ecules at (x, y, z) and (1 − x, 1 − y, 1 − z), which lie in adjacent sheets, are strictly parallel with an inter­planar spacing of 3.3819 (6) Å. The ring-centroid separation is 3.5891 (9) Å, corresponding to a ring-centroid offset of ca 1.202 Å (Fig. 4 ▸). The effect of this inter­action is to link all of the hydrogen-bonded sheets into a single three-dimensional array.
Figure 4

Part of the crystal structure of compound (I) showing the overlap of an inversion-related pair of mol­ecules. For the sake of clarity, the unit-cell outline and all of the H atoms have been omitted. The mol­ecules are viewed normal to the planes of the fused heterocyclic ring system and atoms marked with an asterisk (*) are at the symmetry position (1 − x, 1 − y, 1 − z).

Despite the large number of aromatic C—H bonds in the mol­ecule of compound (I), the only short C—H⋯π contact involves one of the C—H bonds of the methyl group. Not only are such bonds of low acidity but, perhaps more important, such a methyl group will be undergoing very rapid rotation about the adjacent CC bond. When a group having local C 3 symmetry, such as a methyl group, is directly bonded to another group having local C 2 symmetry, such as a phenyl group, as in (I), the rotational barrier about the bond between them is very low, generally of the order of J mol−1 rather than the usual kJ mol−1 (Naylor & Wilson, 1957 ▸; Tannenbaum et al., 1956 ▸). Moreover, it has been shown that simple hydro­carbyl substituents undergo rapid rotation about CC bonds in the solid state, even at reduced temperatures (Riddell & Rogerson, 1996 ▸, 1997 ▸). Therefore, while such a C—H⋯π inter­molecular inter­action may not be regarded as structurally significant, we report it here for completeness (Table 2 ▸).

Database survey

Structural information on un-reduced pyrazolo­[3,4-b]quinolines carrying a substituent at the N2 position but not at N1, is sparse. In a series of pyrazolo­[3,4-b]quinolin-5-ones, each carrying a substituent at N2, the central heterocyclic ring is in reduced form, carrying H atoms at positions 4 and 8 (Cannon et al., 2001a ▸,b ▸,c ▸,d ▸). By contrast, in a series of less highly reduced pyrazolo­[3,4-b]quinolin-5-ones which each carry a substituent at N1 but not at N2, the central fused ring is fully aromatic (Mera et al., 2005 ▸; Cruz et al., 2006 ▸; Portilla et al., 2007 ▸). Similarly, in a series of benzo[f]pyrazolo­[3,4-b]quinolines, in each of which there is a substituent at position 1, but not at position 2, the pyridine ring is fully aromatic (Portilla, Quiroga et al., 2005 ▸; Portilla, Serrano et al., 2005 ▸; Portilla et al., 2008 ▸).

Synthesis and crystallization

A sample of the title compound was prepared using the recently published procedure (Sowmya et al., 2014 ▸). Crystals suitable for single-crystal X-ray diffraction were obtained by slow evaporation, at ambient temperature and in the presence of air, of a solution in hexa­ne–ethyl acetate (19:1, v/v).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. All H atoms were located in difference maps, and then treated as riding atoms in geometrically idealized positions with C—H distances 0.95 Å (aromatic) or 0.98 Å (meth­yl) and with U iso(H) = kU eq(C), where k = 1.5 for the methyl group, which was permitted to rotate but not to tilt, and 1.2 for all other H atoms.
Table 3

Experimental details

Crystal data
Chemical formulaC17H12ClN3
M r 293.75
Crystal system, space groupMonoclinic, P21/c
Temperature (K)173
a, b, c ()10.2194(4), 13.4661(5), 10.4600(4)
()102.780(4)
V (3)1403.80(10)
Z 4
Radiation typeCu K
(mm1)2.36
Crystal size (mm)0.42 0.28 0.12
 
Data collection
DiffractometerAgilent Eos Gemini
Absorption correctionMulti-scan (CrysAlis RED; Agilent, 2012)
T min, T max 0.554, 0.753
No. of measured, independent and observed [I > 2(I)] reflections8443, 2738, 2479
R int 0.032
(sin /)max (1)0.619
 
Refinement
R[F 2 > 2(F 2)], wR(F 2), S 0.040, 0.114, 1.05
No. of reflections2738
No. of parameters191
H-atom treatmentH-atom parameters constrained
max, min (e 3)0.36, 0.22

Computer programs: CrysAlis PRO and CrysAlis RED (Agilent, 2012 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S205698901500818X/sj5454sup1.cif Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901500818X/sj5454Isup2.hkl Click here for additional data file. Supporting information file. DOI: 10.1107/S205698901500818X/sj5454Isup3.cml CCDC reference: 1012361 Additional supporting information: crystallographic information; 3D view; checkCIF report
C17H12ClN3F(000) = 608
Mr = 293.75Dx = 1.390 Mg m3
Monoclinic, P21/cCu Kα radiation, λ = 1.54184 Å
a = 10.2194 (4) ÅCell parameters from 2738 reflections
b = 13.4661 (5) Åθ = 4.4–72.6°
c = 10.4600 (4) ŵ = 2.36 mm1
β = 102.780 (4)°T = 173 K
V = 1403.80 (10) Å3Block, yellow
Z = 40.42 × 0.28 × 0.12 mm
Agilent Eos Gemini diffractometer2479 reflections with I > 2σ(I)
Radiation source: Enhance (Cu) X-ray SourceRint = 0.032
ω scansθmax = 72.6°, θmin = 4.4°
Absorption correction: multi-scan (CrysAlis RED; Agilent, 2012)h = −12→12
Tmin = 0.554, Tmax = 0.753k = −12→16
8443 measured reflectionsl = −12→11
2738 independent reflections
Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.040H-atom parameters constrained
wR(F2) = 0.114w = 1/[σ2(Fo2) + (0.0702P)2 + 0.2814P] where P = (Fo2 + 2Fc2)/3
S = 1.05(Δ/σ)max < 0.001
2738 reflectionsΔρmax = 0.36 e Å3
191 parametersΔρmin = −0.21 e Å3
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.
xyzUiso*/Ueq
N10.18699 (13)0.38247 (10)0.54035 (13)0.0290 (3)
N20.21652 (13)0.38697 (10)0.67397 (13)0.0269 (3)
C30.34907 (16)0.38742 (11)0.72750 (16)0.0271 (3)
Cl30.41552 (4)0.39736 (3)0.89093 (3)0.03435 (15)
C3A0.41587 (16)0.38246 (11)0.62459 (15)0.0257 (3)
C40.54815 (16)0.37944 (11)0.61183 (15)0.0280 (3)
H40.62100.38250.68600.034*
C4A0.56909 (16)0.37163 (11)0.48495 (16)0.0287 (3)
C50.70051 (17)0.36552 (13)0.45927 (18)0.0356 (4)
H50.77670.36800.53020.043*
C60.71795 (19)0.35618 (14)0.33496 (19)0.0401 (4)
H60.80600.35160.31970.048*
C70.60533 (19)0.35325 (13)0.22768 (18)0.0390 (4)
H70.61910.34720.14110.047*
C80.47823 (19)0.35900 (12)0.24644 (16)0.0352 (4)
H80.40450.35690.17300.042*
C8A0.45426 (17)0.36816 (11)0.37577 (15)0.0282 (3)
N90.32609 (13)0.37210 (10)0.38697 (13)0.0283 (3)
C9A0.30883 (16)0.37944 (11)0.51055 (15)0.0264 (3)
C210.10959 (16)0.39242 (12)0.74232 (16)0.0283 (3)
C220.01295 (16)0.46631 (12)0.70896 (16)0.0318 (3)
H220.01470.51090.63900.038*
C23−0.08594 (16)0.47332 (13)0.78014 (17)0.0356 (4)
H23−0.15200.52390.75880.043*
C24−0.09102 (16)0.40803 (14)0.88226 (17)0.0353 (4)
C250.00467 (17)0.33313 (14)0.90984 (18)0.0393 (4)
H250.00160.28700.97790.047*
C260.10438 (17)0.32453 (13)0.83996 (17)0.0360 (4)
H260.16850.27250.85900.043*
C27−0.19679 (19)0.41851 (18)0.9614 (2)0.0476 (5)
H27A−0.15450.43871.05100.071*
H27B−0.24240.35470.96360.071*
H27C−0.26230.46890.92120.071*
U11U22U33U12U13U23
N10.0265 (7)0.0343 (7)0.0250 (7)−0.0008 (5)0.0028 (5)−0.0009 (5)
N20.0244 (7)0.0303 (7)0.0251 (7)0.0004 (5)0.0035 (5)−0.0002 (5)
C30.0251 (8)0.0298 (8)0.0251 (8)0.0001 (6)0.0026 (6)−0.0006 (6)
Cl30.0305 (2)0.0482 (3)0.0228 (2)0.00019 (15)0.00256 (16)−0.00138 (14)
C3A0.0272 (8)0.0244 (7)0.0243 (8)−0.0007 (5)0.0034 (6)−0.0001 (6)
C40.0261 (8)0.0288 (7)0.0278 (8)−0.0013 (6)0.0033 (6)−0.0009 (6)
C4A0.0298 (8)0.0243 (7)0.0322 (8)−0.0025 (6)0.0074 (7)−0.0008 (6)
C50.0304 (9)0.0361 (9)0.0411 (9)−0.0026 (7)0.0093 (7)−0.0028 (7)
C60.0366 (9)0.0391 (9)0.0503 (11)−0.0026 (7)0.0220 (8)−0.0036 (8)
C70.0500 (11)0.0363 (9)0.0359 (9)−0.0041 (8)0.0204 (8)−0.0028 (7)
C80.0445 (10)0.0335 (9)0.0288 (8)−0.0032 (7)0.0109 (7)−0.0009 (7)
C8A0.0336 (8)0.0226 (7)0.0287 (8)−0.0014 (6)0.0078 (6)0.0003 (6)
N90.0306 (7)0.0293 (7)0.0243 (7)−0.0020 (5)0.0042 (5)−0.0003 (5)
C9A0.0270 (8)0.0246 (7)0.0267 (8)−0.0008 (6)0.0038 (6)−0.0002 (6)
C210.0230 (7)0.0330 (8)0.0283 (8)0.0005 (6)0.0045 (6)−0.0020 (6)
C220.0266 (8)0.0352 (8)0.0305 (8)0.0015 (6)−0.0003 (6)0.0016 (7)
C230.0230 (8)0.0413 (9)0.0397 (9)0.0047 (6)0.0005 (7)−0.0042 (7)
C240.0236 (8)0.0463 (10)0.0355 (9)−0.0018 (6)0.0053 (7)−0.0075 (7)
C250.0320 (9)0.0486 (10)0.0388 (9)0.0009 (7)0.0111 (7)0.0095 (8)
C260.0300 (8)0.0378 (9)0.0418 (10)0.0067 (7)0.0114 (7)0.0084 (7)
C270.0302 (9)0.0671 (13)0.0483 (11)−0.0017 (8)0.0145 (8)−0.0121 (10)
N1—N21.3644 (18)C7—H70.9500
N2—C31.346 (2)C8—H80.9500
C3—C3A1.398 (2)N2—C211.434 (2)
C3A—C41.388 (2)C3—Cl31.6993 (16)
C4—C4A1.394 (2)C21—C261.380 (2)
C4A—C51.429 (2)C21—C221.391 (2)
C5—C61.357 (3)C22—C231.385 (2)
C6—C71.419 (3)C22—H220.9500
C7—C81.358 (2)C23—C241.393 (3)
C8—C8A1.432 (2)C23—H230.9500
C8A—N91.342 (2)C24—C251.390 (3)
N9—C9A1.346 (2)C24—C271.507 (2)
C9A—N11.349 (2)C25—C261.384 (2)
C3A—C9A1.430 (2)C25—H250.9500
C4A—C8A1.446 (2)C26—H260.9500
C4—H40.9500C27—H27A0.9800
C5—H50.9500C27—H27B0.9800
C6—H60.9500C27—H27C0.9800
C9A—N1—N2103.40 (12)C8—C8A—C4A118.05 (15)
C3—N2—N1113.60 (13)C8A—N9—C9A115.12 (14)
C3—N2—C21126.87 (14)N9—C9A—N1123.20 (14)
N1—N2—C21119.52 (12)N9—C9A—C3A124.38 (14)
N2—C3—C3A107.30 (14)N1—C9A—C3A112.41 (14)
N2—C3—Cl3124.06 (12)C26—C21—C22121.19 (15)
C3A—C3—Cl3128.59 (13)C26—C21—N2119.56 (14)
C4—C3A—C3136.66 (15)C22—C21—N2119.25 (14)
C4—C3A—C9A120.04 (14)C23—C22—C21118.42 (16)
C3—C3A—C9A103.30 (14)C23—C22—H22120.8
C3A—C4—C4A116.84 (15)C21—C22—H22120.8
C3A—C4—H4121.6C22—C23—C24121.64 (15)
C4A—C4—H4121.6C22—C23—H23119.2
C4—C4A—C5122.13 (16)C24—C23—H23119.2
C4—C4A—C8A119.06 (15)C25—C24—C23118.24 (15)
C5—C4A—C8A118.81 (15)C25—C24—C27120.74 (17)
C6—C5—C4A120.91 (17)C23—C24—C27121.02 (17)
C6—C5—H5119.5C26—C25—C24121.16 (16)
C4A—C5—H5119.5C26—C25—H25119.4
C5—C6—C7120.32 (17)C24—C25—H25119.4
C5—C6—H6119.8C21—C26—C25119.26 (16)
C7—C6—H6119.8C21—C26—H26120.4
C8—C7—C6121.22 (16)C25—C26—H26120.4
C8—C7—H7119.4C24—C27—H27A109.5
C6—C7—H7119.4C24—C27—H27B109.5
C7—C8—C8A120.68 (17)H27A—C27—H27B109.5
C7—C8—H8119.7C24—C27—H27C109.5
C8A—C8—H8119.7H27A—C27—H27C109.5
N9—C8A—C8117.40 (15)H27B—C27—H27C109.5
N9—C8A—C4A124.55 (14)
C9A—N1—N2—C30.34 (16)C8—C8A—N9—C9A179.20 (14)
C9A—N1—N2—C21179.24 (13)C4A—C8A—N9—C9A−0.2 (2)
N1—N2—C3—C3A−0.29 (17)C8A—N9—C9A—N1−178.78 (14)
C21—N2—C3—C3A−179.08 (14)C8A—N9—C9A—C3A−0.4 (2)
N1—N2—C3—Cl3177.38 (11)N2—N1—C9A—N9178.30 (14)
C21—N2—C3—Cl3−1.4 (2)N2—N1—C9A—C3A−0.27 (16)
N2—C3—C3A—C4−179.33 (17)C4—C3A—C9A—N91.1 (2)
Cl3—C3—C3A—C43.1 (3)C3—C3A—C9A—N9−178.44 (14)
N2—C3—C3A—C9A0.10 (16)C4—C3A—C9A—N1179.66 (14)
Cl3—C3—C3A—C9A−177.43 (12)C3—C3A—C9A—N10.11 (17)
C3—C3A—C4—C4A178.21 (17)N1—N2—C21—C22−53.7 (2)
C9A—C3A—C4—C4A−1.1 (2)N1—N2—C21—C26126.42 (16)
C3A—C4—C4A—C5−178.51 (14)C3—N2—C21—C22125.08 (17)
C3A—C4—C4A—C8A0.6 (2)C3—N2—C21—C26−54.8 (2)
C4—C4A—C5—C6178.81 (16)C26—C21—C22—C232.9 (2)
C8A—C4A—C5—C6−0.3 (2)N2—C21—C22—C23−177.01 (14)
C4A—C5—C6—C70.6 (3)C21—C22—C23—C24−0.6 (3)
C5—C6—C7—C8−0.4 (3)C22—C23—C24—C25−1.5 (3)
C6—C7—C8—C8A0.0 (3)C22—C23—C24—C27178.15 (16)
C7—C8—C8A—N9−179.12 (15)C23—C24—C25—C261.4 (3)
C7—C8—C8A—C4A0.3 (2)C27—C24—C25—C26−178.25 (17)
C4—C4A—C8A—N90.1 (2)C22—C21—C26—C25−3.0 (3)
C5—C4A—C8A—N9179.25 (14)N2—C21—C26—C25176.89 (16)
C4—C4A—C8A—C8−179.31 (14)C24—C25—C26—C210.8 (3)
C5—C4A—C8A—C8−0.2 (2)
D—H···AD—HH···AD···AD—H···A
C23—H23···N9i0.952.503.393 (2)157
C26—H26···N9ii0.952.503.449 (2)174
C27—H27A···Cg1iii0.982.843.653 (2)140
  12 in total

1.  8-tert-Butyl-7-(4-chlorophenyl)-10-phenyl-5,6-dihydro-10H-benzo[h]pyrazolo[3,4-b]quinoline.

Authors:  Jaime Portilla; Jairo Quiroga; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr C       Date:  2007-09-01       Impact factor: 1.172

2.  3-(4-Methoxyphenyl)-7,7-dimethyl-1,6,7,8-tetrahydropyrazolo[3,4-b]quinolin-5-one: a chain of centrosymmetric rings built from N-H...N and C-H...pi(arene) hydrogen bonds.

Authors:  Silvia Cruz; Jairo Quiroga; José M de la Torre; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr C       Date:  2006-07-29       Impact factor: 1.172

3.  A monoclinic polymorph of 3,7,7-trimethyl-1-phenyl-5,6,7,8-tetrahydro-1H-pyrazolo[3,4-b]quinolin-5-one.

Authors:  Jaime Mera; Jairo Quiroga; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr C       Date:  2005-06-22       Impact factor: 1.172

4.  Two isomeric 10-methyl-8-phenyl-11-pyridyl-6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinolines: cyclic hydrogen-bonded tetramers versus isolated molecules.

Authors:  Jaime Portilla; Hugo Serrano; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr C       Date:  2005-07-23       Impact factor: 1.172

5.  Effect of substitution on the dimensionality of supramolecular aggregation in dihydrobenzopyrazoloquinolines.

Authors:  Jaime Portilla; Jairo Quiroga; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr C       Date:  2005-07-23       Impact factor: 1.172

6.  meso-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane as a building block in supramolecular chemistry; salts formed with 2,2-biphenol, 4,4-thiodiphenol, 4,4-sulfonyldiphenol, 3-and 4-hydroxybenzoic acids, 3,5-dihydroxybenzoic acid and phenylphosphonic acid; supramolecular structures in zero, one, two and three dimensions

Authors: 
Journal:  Acta Crystallogr B       Date:  2000-02

Review 7.  Biological activities of quinoline derivatives.

Authors:  Suresh Kumar; Sandhya Bawa; Himanshu Gupta
Journal:  Mini Rev Med Chem       Date:  2009-12       Impact factor: 3.862

8.  Structural comparisons of isomeric series of 7-aryl-benzo[h]pyrazolo[3,4-b]quinolines and 11-aryl-benzo[f]pyrazolo[3,4-b]quinolines.

Authors:  Jaime Portilla; Jairo Quiroga; Manuel Nogueras; Jose M de la Torre; Justo Cobo; John N Low; Christopher Glidewell
Journal:  Acta Crystallogr B       Date:  2008-01-17

9.  Crystal structure refinement with SHELXL.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr C Struct Chem       Date:  2015-01-01       Impact factor: 1.172

10.  Structure validation in chemical crystallography.

Authors:  Anthony L Spek
Journal:  Acta Crystallogr D Biol Crystallogr       Date:  2009-01-20
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