5-Phenyl-9H-1,3-dioxolo[4,5-h][2,3]benzodiazepin-8(7H)-one

The title compound, C₁₆H₁₂N₂O₃, is a novel potent and selective non-competitive antagonist at AMPA/kainate receptors [AMPA is 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)­propionic acid and kainate is 3-carboxy­methyl-4-isopropenyl­pyrrolidine-2-carboxylic acid]. The crystal structure has been determined at room temperature by X-ray diffraction and the seven-membered ring shows the usual boat conformation. The energy stabilization of the crystal packing of the title compound by significant hydrogen-bond inter­actions is discussed using theoretical computations.

S1. Comment

There is increasing evidence of the potential therapeutic utility of glutamate receptor antagonists in the treatment of several neurodegenerative disorders, including stroke and epilepsy. In the course of our studies on the modulation of glutamate receptor function, we identified novel potent and selective noncompetitive AMPA receptor antagonists based on the 2,3-benzodiazepine nucleus (Zappalá et al., 2001). In previous publications (De Sarro et al., 1998; Grasso et al., 1999, 2001), we reported chemical and biological studies of a new series of 1-aryl-3,5-dihydro-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-ones, and their 1,2,3,5-tetrahydro analogues and 3-N-alkylcarbamoyl derivatives, which have been shown to possess remarkable anticonvulsant properties, acting as noncompetitive antagonists at the AMPA receptor complexes. Structure-activity relationship studies revealed that several structural features, such as an amino group on the phenyl ring or a methylcarbamoyl moiety at the N3 position, are important to maintain and/or to potentiate the pharmacological properties of these molecules. This paper describes the crystal structure analysis of the title compound, (I), which represents the reference compound of this class of allosteric modulators. \sch

The results of this investigation will be used to compare the molecular geometry of (I) with those of the analogous 2,3-benzodiazepines reported in the literature (Anderson et al., 1996; Bruno et al., 2001; Harkness, 2001) and to provide better understanding of the structural characteristics necessary for AMPA receptor antagonists.

Among the various crystal structure literature reports on benzodiazepines, the 1,2 or 2,3 derivatives are uncommon, as we have already pointed out (Bruno et al., 2001). A systematic search of the Cambridge Structural Database (CSD, Version?; Allen, 2002) retrieved 11 compounds containing 2,3-benzodiazepines omnifariously substituted and six 1,2 diazepines. By considering the N—N interaction in this set of 2,3 derivatives, seven 4-substituted 1-methyl-1-H-2,3-benzodiazepines show a double bond (Gould & Gould, 1974; Blake et al., 1995), while one is a 2,3-benzodiazepine 2-oxide (Walkinshaw, 1985).

The diazepinone fragment of (I) shows geometrical features very close to those found in the 4,5-dihydro-7,8-dimethoxy-1-phenyl-3H-2,3-benzodiazepin-4-one parent compound (Bruno et al., 2001). The few significant bond differences vary up to 0.016 Å and are observed for the atoms involved in intermolecular hydrogen bonds. Due to the weaker hydrogen interactions concerning the carbonylic O atom, the C1—O1 bond distance is shorter than the corresponding one in the parent compound [1.217 (3) versus 1.231 (2) Å]. The seven-membered ring of (I) shows the usual boat conformation with a mirror pseudo symmetry. The puckering coordinates for the C1/N2/N3/C4—C7 ring are Δ_S(C7) = 0.028 (1), Q = 0.869 (2) Å, ϕ₂ = 100.0 (1)°, ϕ₃ = 152.4 (6)° and θ = 76.87 (1)° (Cremer & Pople, 1975).

The phenyl group attached at C4 appears more rotated in (I) with respect to the central fragment than in the parent compound, due to molecular packing influences, as evidenced by the C5—C4—C12—C17 torsion angles [−49.3 (2)° in the parent compound, versus 129.1 (2)° in (I)]. Are these values the right way round? The whole benzodioxole fragment is quite flat [the maximum deviation from the mean plane is 0.078 (1) Å for atom C18] and it is able to produce intermolecular stacking interactions of 3.395 (1) Å between adjacent slightly bent planes [7.63 (1)°] along the crystallographic axis c. The bond distances and angles of the benzodioxolo fragment are in good agreement with the corresponding values in recently reported compounds containing this fragment, for example 5-(2-hydroxy-3,3,3-trifluoropropanoyl)-1,3-benzodioxole (Singh et al., 2001).

The molecular packing of (I) is also determined by two pairs of weak N—H···N and Csp²—H···O intermolecular hydrogen interactions, bonding each molecule to two different centrosymmetric units in a `head-to-tail' arrangement. The resulting packing is characterized by flat polymeric ribbons parallel to the crystallographic a axis. Conventional `strong' hydrogen bonds (e.g. O—H···O, N—H···O, N—H···N, etc) are often the key in supramolecular organization (Desiraju & Steiner, 1999). Recently, `weak' C—H···O hydrogen bonds have been studied and many of their properties are well understood (Taylor & Kennard, 1982; Berkovitch-Yellin & Leiserowitz, 1984; Steiner, 2000).

In order to understand the role played by these hydrogen bonds in determining the molecular packing observed in (I), a series of ab initio calculations were carried out using GAUSSIAN98 (Frisch et al., 1998). The single-point energy (SPE) was computed on the molecular geometries obtained directly from the X-ray diffraction analysis. The SPE calculations, at the HF/6–31+G(d,p) level, were performed on the trimeric hydrogen-bonded aggregate and on both different types of dimer (N—H···N and C═O···H—C interconnected), as well as on the monomer. The complexation energy was obtained as the difference between the energy of the corresponding dimer and the doubled energy of the isolated monomer. The stabilization energies due to the intermolecular hydrogen bonds are 8.62 and 25.94 kJ mol⁻¹ for the N—H···N and C═O···H—C dimer aggregates, respectively, while the corresponding value for the combined trimer is 34.56 kJ mol⁻¹. The largest stabilization energy of 17.32 kJ mol⁻¹, calculated for the C═O···H—C dimer with respect to the N—H···N dimer, is essentially due to the geometrical features of the hydrogen bonds involved.

The same level of calculation was performed on 3,5-dihydrobenzo[d][2,3]diazepin-4-one, considered as a model of (I), and on its two dimeric models, created to simulate the corresponding dimers of (I) in the solid state. Their geometries were optimized without symmetry restrictions. The complexation energies were computed as before, by considering the isolated monomer geometry as appearing in the corresponding dimer. Since we are interested only in the relative energies, the basis set superposition errors and zero-point energy were not taken into account in all calculations. The bond distances and angles of the optimized geometries, as well as of the seven-membered ring conformation, are in good agreement with the X-ray diffraction data, except for the bond distances of atoms involved in the hydrogen bonds.

In the gas phase, the computed complexation energies of the N—H···N and C═O···H—C dimers are 26.11 and 31.30 kJ mol⁻¹, respectively. Hence, the value of the trimer aggregate must be assumed to be 57.41 kJ mol⁻¹. In the gas phase, we obtain the greatest possible value of the interaction energy for the same hydrogen bonds as were observed in the solid state. The value computed for the X-ray trimeric fragment in the solid state is about 40% less than the corresponding value in the gas phase and this confirms the expected stabilization of the hydrogen bonds on the crystal packing.

S2. Experimental

The title compound was obtained as described previously by De Sarro et al. (1995). Suitable single crystals of (I) were obtained by recrystallization from ethanol solution.

S3. Refinement

Reflection intensities were evaluated by profile fitting of a 96-step peak scan using the 2θ shells procedure (Diamond, 1969) and then corrected for Lorentz polarization effects. Standard deviations σ(I) were estimated from counting statistics. H atoms were located in idealized positions, with N—H = 0.86 Å and C—H distances in the range 0.93–0.97 Å Is this added text OK? and allowed to ride on their parent C atoms, with isotropic displacement parameters related to the refined values of their corresponding parent atoms.

Computing details

Data collection: P3/V (Siemens, 1989); cell refinement: P3/V; data reduction: SHELXTL-Plus (Siemens, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XPW in SHELXTL (Siemens, 1996); software used to prepare material for publication: PARST97 (Nardelli, 1995; locally modified) and SHELXL97.

Figures

Fig. 1. A perspective view of the molecule of (I), showing the atomic numbering scheme for the asymmetric unit. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Dotted lines represent hydrogen bonds to symmetry-related molecules, drawn with dashed bonds and empty ellipsoids. Primes and double primes indicate molecules at symmetry positions (1 − x, 2 − y, 1 − z) and (2 − x, 2 − y, 1 − z), respectively.

5-Phenyl-9H-1,3-dioxolo[4,5-h][2,3]benzodiazepin-8(7H)-one

Crystal data

C16H12N2O3	F(000) = 584
Mr = 280.28	Dx = 1.409 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 35 reflections
a = 10.638 (2) Å	θ = 6.7–17.5°
b = 17.857 (4) Å	µ = 0.10 mm^−1
c = 6.958 (1) Å	T = 293 K
β = 91.42 (3)°	Irregular, colourless
V = 1321.4 (4) Å^3	0.50 × 0.25 × 0.12 mm
Z = 4

Data collection

Siemens P4 diffractometer	Rint = 0.048
Radiation source: sealed tube	θmax = 25.1°, θmin = 2.2°
Graphite monochromator	h = −12→12
ω scans	k = −21→0
2770 measured reflections	l = 0→8
2315 independent reflections	3 standard reflections every 197 reflections
1727 reflections with I > 2σ(I)	intensity decay: 0.0%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.151	H-atom parameters constrained
S = 0.94	w = 1/[σ^2(Fo^2) + (0.1078P)^2 + 0.2546P] where P = (Fo^2 + 2Fc^2)/3
2315 reflections	(Δ/σ)max = 0.018
190 parameters	Δρmax = 0.22 e Å^−3
0 restraints	Δρmin = −0.27 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
O1	0.83248 (17)	1.02643 (11)	0.5866 (3)	0.0707 (6)
C1	0.7766 (2)	0.99557 (13)	0.4539 (4)	0.0468 (6)
N2	0.65277 (16)	0.97698 (10)	0.4695 (3)	0.0432 (5)
H2	0.6235	0.9792	0.5835	0.052*
N3	0.56779 (16)	0.95489 (10)	0.3256 (3)	0.0394 (5)
C4	0.59639 (18)	0.90301 (11)	0.2061 (3)	0.0344 (5)
C5	0.71459 (17)	0.85936 (11)	0.2066 (3)	0.0323 (5)
C6	0.83115 (18)	0.89331 (12)	0.2380 (3)	0.0359 (5)
C7	0.8362 (2)	0.97615 (13)	0.2666 (4)	0.0479 (6)
H7A	0.7917	1.0011	0.1615	0.057*
H7B	0.9230	0.9930	0.2683	0.057*
C8	0.94203 (18)	0.84994 (13)	0.2507 (3)	0.0399 (5)
H8	1.0206	0.8719	0.2700	0.048*
C9	0.92836 (18)	0.77428 (12)	0.2334 (3)	0.0382 (5)
C10	0.81311 (19)	0.74100 (12)	0.2009 (3)	0.0363 (5)
C11	0.70492 (18)	0.78136 (11)	0.1827 (3)	0.0349 (5)
H11	0.6281	0.7584	0.1557	0.042*
O2	1.02026 (15)	0.72068 (10)	0.2437 (3)	0.0585 (5)
C18	0.9559 (2)	0.65025 (14)	0.2327 (4)	0.0516 (6)
H18A	0.9912	0.6194	0.1328	0.062*
H18B	0.9649	0.6238	0.3541	0.062*
O3	0.82705 (15)	0.66462 (9)	0.1904 (3)	0.0516 (4)
C12	0.49645 (18)	0.88151 (11)	0.0639 (3)	0.0358 (5)
C13	0.5259 (2)	0.87213 (13)	−0.1269 (3)	0.0444 (6)
H13	0.6075	0.8811	−0.1659	0.053*
C14	0.4353 (2)	0.84962 (14)	−0.2606 (3)	0.0514 (6)
H14	0.4561	0.8439	−0.3888	0.062*
C15	0.3147 (2)	0.83570 (15)	−0.2047 (4)	0.0539 (6)
H15	0.2540	0.8201	−0.2946	0.065*
C16	0.2839 (2)	0.84485 (15)	−0.0152 (4)	0.0570 (7)
H16	0.2024	0.8349	0.0230	0.068*
C17	0.3733 (2)	0.86866 (14)	0.1188 (4)	0.0483 (6)
H17	0.3512	0.8761	0.2459	0.058*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0431 (10)	0.0771 (13)	0.0914 (14)	−0.0062 (9)	−0.0057 (9)	−0.0431 (11)
C1	0.0328 (12)	0.0391 (12)	0.0684 (16)	0.0009 (9)	−0.0025 (10)	−0.0166 (11)
N2	0.0311 (10)	0.0483 (11)	0.0502 (11)	0.0014 (8)	−0.0008 (8)	−0.0143 (9)
N3	0.0287 (9)	0.0400 (10)	0.0494 (11)	0.0007 (7)	−0.0012 (7)	−0.0073 (8)
C4	0.0282 (10)	0.0322 (11)	0.0427 (11)	0.0004 (8)	0.0008 (8)	−0.0004 (9)
C5	0.0275 (10)	0.0337 (11)	0.0358 (10)	0.0011 (8)	0.0009 (8)	0.0001 (8)
C6	0.0307 (10)	0.0389 (12)	0.0383 (11)	−0.0006 (8)	0.0032 (8)	−0.0042 (9)
C7	0.0360 (12)	0.0416 (13)	0.0664 (16)	−0.0080 (10)	0.0061 (10)	−0.0044 (11)
C8	0.0236 (10)	0.0540 (14)	0.0420 (12)	−0.0011 (9)	0.0021 (8)	−0.0075 (10)
C9	0.0289 (10)	0.0496 (13)	0.0362 (11)	0.0119 (9)	0.0013 (8)	−0.0028 (9)
C10	0.0387 (11)	0.0359 (11)	0.0344 (11)	0.0061 (9)	0.0013 (8)	−0.0010 (9)
C11	0.0289 (10)	0.0376 (11)	0.0382 (11)	−0.0010 (8)	−0.0003 (8)	−0.0030 (8)
O2	0.0362 (9)	0.0599 (11)	0.0791 (12)	0.0202 (8)	−0.0021 (8)	−0.0045 (9)
C18	0.0517 (14)	0.0549 (15)	0.0479 (13)	0.0239 (12)	−0.0032 (10)	−0.0013 (11)
O3	0.0477 (10)	0.0393 (9)	0.0677 (11)	0.0129 (7)	−0.0002 (7)	−0.0039 (8)
C12	0.0272 (10)	0.0334 (11)	0.0467 (12)	0.0044 (8)	−0.0021 (8)	−0.0005 (9)
C13	0.0320 (11)	0.0527 (14)	0.0483 (13)	0.0034 (9)	0.0005 (9)	0.0002 (10)
C14	0.0482 (14)	0.0601 (15)	0.0453 (13)	0.0093 (11)	−0.0076 (10)	−0.0041 (11)
C15	0.0400 (13)	0.0577 (15)	0.0631 (16)	0.0030 (11)	−0.0171 (11)	−0.0081 (12)
C16	0.0284 (12)	0.0687 (17)	0.0737 (17)	−0.0047 (11)	−0.0030 (11)	−0.0079 (14)
C17	0.0315 (11)	0.0612 (15)	0.0523 (14)	−0.0003 (10)	0.0017 (9)	−0.0058 (11)

Geometric parameters (Å, º)

O1—C1	1.217 (3)	C10—C11	1.361 (3)
C1—N2	1.366 (3)	C10—O3	1.374 (3)
C1—C7	1.504 (3)	C11—H11	0.9300
N2—N3	1.390 (2)	O2—C18	1.433 (3)
N2—H2	0.8600	C18—O3	1.418 (3)
N3—C4	1.286 (3)	C18—H18A	0.9700
C4—C5	1.479 (3)	C18—H18B	0.9700
C4—C12	1.485 (3)	C12—C13	1.382 (3)
C5—C6	1.393 (3)	C12—C17	1.393 (3)
C5—C11	1.406 (3)	C13—C14	1.383 (3)
C6—C8	1.412 (3)	C13—H13	0.9300
C6—C7	1.494 (3)	C14—C15	1.372 (3)
C7—H7A	0.9700	C14—H14	0.9300
C7—H7B	0.9700	C15—C16	1.377 (4)
C8—C9	1.364 (3)	C15—H15	0.9300
C8—H8	0.9300	C16—C17	1.382 (3)
C9—O2	1.369 (2)	C16—H16	0.9300
C9—C10	1.376 (3)	C17—H17	0.9300
O1—C1—N2	120.2 (2)	C9—C10—O3	109.9 (2)
O1—C1—C7	123.6 (2)	C10—C11—C5	117.01 (18)
N2—C1—C7	116.2 (2)	C10—C11—H11	121.5
C1—N2—N3	128.6 (2)	C5—C11—H11	121.5
C1—N2—H2	115.7	C9—O2—C18	105.7 (2)
N3—N2—H2	115.7	O3—C18—O2	108.1 (2)
C4—N3—N2	120.7 (2)	O3—C18—H18A	110.1
N3—C4—C5	126.4 (2)	O2—C18—H18A	110.1
N3—C4—C12	116.1 (2)	O3—C18—H18B	110.1
C5—C4—C12	117.4 (2)	O2—C18—H18B	110.1
C6—C5—C11	120.79 (18)	H18A—C18—H18B	108.4
C6—C5—C4	121.6 (2)	C10—O3—C18	105.9 (2)
C11—C5—C4	117.51 (17)	C13—C12—C17	118.7 (2)
C5—C6—C8	120.68 (19)	C13—C12—C4	119.76 (18)
C5—C6—C7	118.76 (18)	C17—C12—C4	121.49 (19)
C8—C6—C7	120.50 (19)	C14—C13—C12	120.7 (2)
C6—C7—C1	109.2 (2)	C14—C13—H13	119.6
C6—C7—H7A	109.8	C12—C13—H13	119.6
C1—C7—H7A	109.8	C15—C14—C13	120.2 (2)
C6—C7—H7B	109.8	C15—C14—H14	119.9
C1—C7—H7B	109.8	C13—C14—H14	119.9
H7A—C7—H7B	108.3	C14—C15—C16	119.8 (2)
C9—C8—C6	116.79 (18)	C14—C15—H15	120.1
C9—C8—H8	121.6	C16—C15—H15	120.1
C6—C8—H8	121.6	C17—C16—C15	120.4 (2)
C8—C9—O2	127.85 (19)	C17—C16—H16	119.8
C8—C9—C10	122.33 (18)	C15—C16—H16	119.8
O2—C9—C10	109.8 (2)	C16—C17—C12	120.1 (2)
C11—C10—C9	122.3 (2)	C16—C17—H17	119.9
C11—C10—O3	127.78 (19)	C12—C17—H17	119.9
O1—C1—N2—N3	166.8 (2)	O2—C9—C10—O3	0.4 (2)
C7—C1—N2—N3	−12.8 (3)	C9—C10—C11—C5	−2.6 (3)
C1—N2—N3—C4	49.3 (3)	O3—C10—C11—C5	177.63 (19)
N2—N3—C4—C5	2.2 (3)	C6—C5—C11—C10	3.1 (3)
N2—N3—C4—C12	177.33 (18)	C4—C5—C11—C10	−174.16 (17)
N3—C4—C5—C6	−43.0 (3)	C8—C9—O2—C18	175.2 (2)
C12—C4—C5—C6	141.99 (19)	C10—C9—O2—C18	−5.0 (2)
N3—C4—C5—C11	134.2 (2)	C9—O2—C18—O3	7.7 (2)
C12—C4—C5—C11	−40.8 (3)	C11—C10—O3—C18	−175.8 (2)
C11—C5—C6—C8	−1.4 (3)	C9—C10—O3—C18	4.4 (2)
C4—C5—C6—C8	175.69 (18)	O2—C18—O3—C10	−7.4 (2)
C11—C5—C6—C7	−178.71 (19)	N3—C4—C12—C13	135.1 (2)
C4—C5—C6—C7	−1.6 (3)	C5—C4—C12—C13	−49.3 (3)
C5—C6—C7—C1	67.6 (3)	N3—C4—C12—C17	−46.4 (3)
C8—C6—C7—C1	−109.7 (2)	C5—C4—C12—C17	129.1 (2)
O1—C1—C7—C6	119.1 (3)	C17—C12—C13—C14	−0.7 (3)
N2—C1—C7—C6	−61.3 (3)	C4—C12—C13—C14	177.8 (2)
C5—C6—C8—C9	−0.8 (3)	C12—C13—C14—C15	−0.5 (4)
C7—C6—C8—C9	176.4 (2)	C13—C14—C15—C16	0.6 (4)
C6—C8—C9—O2	−178.87 (19)	C14—C15—C16—C17	0.6 (4)
C6—C8—C9—C10	1.3 (3)	C15—C16—C17—C12	−1.9 (4)
C8—C9—C10—C11	0.4 (3)	C13—C12—C17—C16	1.9 (4)
O2—C9—C10—C11	−179.42 (18)	C4—C12—C17—C16	−176.5 (2)
C8—C9—C10—O3	−179.79 (19)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···N3^i	0.86	2.45	3.030 (3)	126
C8—H8···O1^ii	0.93	2.58	3.431 (3)	152

Symmetry codes: (i) −x+1, −y+2, −z+1; (ii) −x+2, −y+2, −z+1.