9,10-Di­methoxy-4-methyl-1,2-di­hydro-1-aza­anthracen-2-one (kalasin­amide), a new aza­anthracene alkaloid

A new aza­anthracene alkaloid, namely 9,10-di­methoxy-4-methyl-1,2-di­hydro-1-aza­anthracen-2-one (kalasin­amide), C₁₆H₁₅NO₃, has been isolated from the stems of Polyal­thia suberosa collected in the northeastern part of Thailand. Each of the aromatic rings in the mol­ecule is planar within 0.021 (2) Å. Molecules are linked to form centrosymmetric dimers by N-H...O hydrogen bonds [N...O 2.941 (4) Å].

S1. Comment

Polyalthia suberosa (Roxb.), a shrubby tree native to southeast Asia and South China, has been under wide investigation since 1985. Various parts of the tree, leaves, stems and barks have been investigated. The compounds identified are coumarin, sterols (Dan et al., 1985; Goyal et al., 1986), alkaloids (Ferdous et al., 1992; Sahai et al., 1996), triterpenes (Goyal et al., 1986; Li et al., 1993) and nitrogen heterocyclic compounds (Sahai et al., 1996, Tuchinda et al., 2000). Studies of suberosa has shown an anti-HIV principle (Li et al.,1993).

The title compound, (I), extracted from the stem of the tree from Kalasin Province in the northeastern part of Thailand was found to be a new azaanthracene alkaloid (Tuchinda et al., 2000). We therefore report the structure of the title compound as this might lead to a new anti-HIV active compound.

Bond lengths and angles within the anthracene rings system of (I) are in good agreement with literature values (Brown et al., 1964). However, the C2═O2 bond length of 1.237 (6) Å is slightly longer than that normally found in ketones. Also, the N1—C2 and N1—C91 mean distance of 1.373 (6) Å is slightly shorter than C—N bond length in heteroaromatic systems (Allen et al., 1987). Appreciable electron delocalizations therefore occur here. Noticable electron delocalizations also occur at O1 and O3; the C9—O1 and O1—C12 bond lengths are 1.373 (6) and 1.435 (1) Å, and C10—O3 and O3—C13 are 1.369 (5) and 1.430 (2) Å, respectively. Mean planes through each of the three fused six-membered rings show that they are planar within ±0.02 Å. The dihedral angles A/B 3.00, B/C 2.2 and A/C 5.15° [A = C5—C6—C7—C8—C81—C101, B = C81—C9—C91—C41—C10—C101 and C = C91—N1—C2—C3—C4—C41] indicate that the planes are not quite coplanar. Mean-plane calculation through the 14-membered fused A/B/C ring shows a total puckering amplitude of 0.166 (3) Å. The torsion angles C13—O3—C10—C41 and C12—O1—C9—C91 of 102.5 (3) and 94.8 (3)°, respectively, are as expected. The methyl group at C4 has a steric effect on the methoxy group at C10. Molecules are linked by N—H···O hydrogen bonds about inversion centres to form centrosymmetric dimers with an N···O distance of 2.941 (4) Å.

S2. Experimental

The orange title compound was crystallized from EtOH–CH₂Cl₂.

S3. Refinement

Based on a statistical analysis of intensity distribution, the space group was determined to be P21/a and has been transformed to the conventional space group of P21/c. Friedel opposites were collected and merged. The H atoms were allowed in the refinement at geometrically idealized positions.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: maXus (Mackay et al., 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

(I)

Crystal data

C16H15NO3	Dx = 1.380 Mg m^−3
Mr = 269.30	Mo Kα radiation, λ = 0.70930 Å
Monoclinic, P21/c	Cell parameters from 9 reflections
a = 10.005 (5) Å	θ = 8.8–11.7°
b = 16.449 (5) Å	µ = 0.10 mm^−1
c = 8.186 (5) Å	T = 298 K
β = 105.8 (2)°	Needle, orange
V = 1297.0 (10) Å^3	0.25 × 0.04 × 0.03 mm
Z = 4

Data collection

Enraf-Nonius CAD-4 diffractometer	θmax = 24.9°
Radiation source: rotating anode generator	h = −11→11
ω–2θ scans	k = −19→19
9602 measured reflections	l = −9→9
2272 independent reflections	3 standard reflections every 2608 min
1785 reflections with I > 2σ(I)	intensity decay: 0.8%
Rint = 0.066

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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.163	H-atom parameters constrained
S = 1.07	Calculated w = 1/[σ^2(Fo^2) + (0.0824P)^2 + 0.7373P] where P = (Fo^2 + 2Fc^2)/3
2272 reflections	(Δ/σ)max = 0.001
184 parameters	Δρmax = 0.24 e Å^−3
0 restraints	Δρmin = −0.29 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	0.19412 (15)	0.53442 (9)	0.14924 (18)	0.0430 (4)
O2	0.66117 (17)	0.52286 (12)	0.4852 (2)	0.0579 (5)
O3	0.48398 (17)	0.70615 (9)	−0.22291 (19)	0.0487 (4)
N1	0.47139 (18)	0.55055 (11)	0.2710 (2)	0.0407 (5)
H1	0.4206	0.5260	0.3250	0.049*
C2	0.6097 (2)	0.55317 (14)	0.3438 (3)	0.0450 (5)
C3	0.6901 (2)	0.59236 (15)	0.2461 (3)	0.0496 (6)
H3	0.7860	0.5936	0.2908	0.060*
C4	0.6361 (2)	0.62745 (14)	0.0946 (3)	0.0445 (5)
C5	0.1947 (3)	0.69683 (14)	−0.3442 (3)	0.0494 (6)
H5	0.2425	0.7285	−0.4038	0.059*
C6	0.0547 (3)	0.68918 (16)	−0.4028 (3)	0.0576 (7)
H6	0.0077	0.7157	−0.5020	0.069*
C7	−0.0195 (3)	0.64184 (18)	−0.3157 (3)	0.0589 (7)
H7	−0.1149	0.6357	−0.3596	0.071*
C8	0.0469 (2)	0.60464 (15)	−0.1668 (3)	0.0489 (6)
H8	−0.0036	0.5742	−0.1086	0.059*
C9	0.2642 (2)	0.57739 (12)	0.0551 (3)	0.0374 (5)
C10	0.4140 (2)	0.66153 (12)	−0.1314 (3)	0.0393 (5)
C11	0.7350 (3)	0.6661 (2)	0.0077 (4)	0.0697 (8)
H11A	0.8264	0.6677	0.0847	0.104*
H11B	0.7047	0.7204	−0.0263	0.104*
H11C	0.7368	0.6347	−0.0905	0.104*
C12	0.1369 (3)	0.58426 (17)	0.2573 (3)	0.0548 (6)
H12A	0.2072	0.6205	0.3209	0.082*
H12B	0.1046	0.5503	0.3340	0.082*
H12C	0.0607	0.6153	0.1893	0.082*
C13	0.5062 (4)	0.66468 (17)	−0.3667 (4)	0.0671 (8)
H13A	0.5741	0.6227	−0.3289	0.101*
H13B	0.5388	0.7026	−0.4362	0.101*
H13C	0.4205	0.6410	−0.4314	0.101*
C41	0.4869 (2)	0.62533 (12)	0.0213 (3)	0.0377 (5)
C81	0.1926 (2)	0.61220 (13)	−0.1007 (3)	0.0396 (5)
C91	0.4058 (2)	0.58486 (12)	0.1147 (2)	0.0360 (5)
C101	0.2686 (2)	0.65706 (12)	−0.1931 (3)	0.0404 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0419 (8)	0.0495 (8)	0.0414 (8)	−0.0065 (6)	0.0178 (7)	0.0028 (6)
O2	0.0444 (9)	0.0837 (13)	0.0440 (9)	0.0057 (8)	0.0092 (7)	0.0177 (9)
O3	0.0615 (10)	0.0490 (9)	0.0432 (9)	−0.0067 (7)	0.0274 (8)	0.0038 (7)
N1	0.0371 (10)	0.0512 (10)	0.0361 (9)	0.0001 (8)	0.0136 (8)	0.0078 (8)
C2	0.0392 (12)	0.0562 (13)	0.0405 (12)	0.0033 (10)	0.0121 (10)	0.0025 (10)
C3	0.0339 (11)	0.0658 (15)	0.0498 (13)	−0.0012 (10)	0.0125 (10)	0.0021 (11)
C4	0.0405 (12)	0.0513 (12)	0.0465 (13)	−0.0001 (10)	0.0202 (10)	0.0024 (10)
C5	0.0629 (15)	0.0504 (13)	0.0355 (11)	0.0038 (11)	0.0146 (11)	0.0018 (10)
C6	0.0631 (16)	0.0673 (16)	0.0375 (12)	0.0133 (13)	0.0052 (11)	0.0063 (11)
C7	0.0458 (13)	0.0809 (17)	0.0437 (13)	0.0043 (12)	0.0013 (11)	−0.0008 (12)
C8	0.0435 (12)	0.0611 (14)	0.0417 (12)	−0.0025 (11)	0.0105 (10)	−0.0038 (10)
C9	0.0390 (11)	0.0413 (10)	0.0345 (10)	−0.0031 (9)	0.0145 (9)	0.0001 (8)
C10	0.0484 (12)	0.0397 (11)	0.0347 (11)	−0.0018 (9)	0.0198 (9)	−0.0005 (8)
C11	0.0439 (14)	0.096 (2)	0.0766 (19)	−0.0019 (14)	0.0284 (13)	0.0244 (16)
C12	0.0500 (14)	0.0719 (16)	0.0491 (14)	0.0083 (12)	0.0249 (11)	0.0060 (12)
C13	0.095 (2)	0.0667 (16)	0.0551 (16)	−0.0054 (15)	0.0461 (15)	0.0016 (13)
C41	0.0406 (11)	0.0396 (11)	0.0370 (11)	−0.0009 (9)	0.0173 (9)	−0.0032 (8)
C81	0.0417 (11)	0.0445 (11)	0.0331 (11)	−0.0014 (9)	0.0110 (9)	−0.0052 (9)
C91	0.0405 (11)	0.0387 (10)	0.0301 (10)	0.0012 (9)	0.0120 (8)	−0.0015 (8)
C101	0.0501 (13)	0.0405 (11)	0.0319 (11)	0.0007 (9)	0.0130 (9)	−0.0021 (8)

Geometric parameters (Å, º)

O1—C9	1.371 (3)	C7—H7	0.9300
O1—C12	1.435 (3)	C8—C81	1.416 (4)
O2—C2	1.237 (3)	C8—H8	0.9300
O3—C10	1.371 (3)	C9—C91	1.374 (3)
O3—C13	1.429 (3)	C9—C81	1.404 (4)
N1—C2	1.351 (4)	C10—C41	1.398 (4)
N1—C91	1.389 (3)	C10—C101	1.406 (4)
N1—H1	0.8600	C11—H11A	0.9600
C2—C3	1.433 (4)	C11—H11B	0.9600
C3—C4	1.342 (4)	C11—H11C	0.9600
C3—H3	0.9300	C12—H12A	0.9600
C4—C41	1.451 (4)	C12—H12B	0.9600
C4—C11	1.508 (4)	C12—H12C	0.9600
C5—C6	1.357 (4)	C13—H13A	0.9600
C5—C101	1.417 (4)	C13—H13B	0.9600
C5—H5	0.9300	C13—H13C	0.9600
C6—C7	1.398 (4)	C41—C91	1.423 (3)
C6—H6	0.9300	C81—C101	1.417 (3)
C7—C8	1.365 (4)
C9—O1—C12	113.78 (18)	C41—C10—C101	122.4 (2)
C10—O3—C13	114.35 (19)	C4—C11—H11A	109.5
C2—N1—C91	124.3 (2)	C4—C11—H11B	109.5
C2—N1—H1	117.8	H11A—C11—H11B	109.5
C91—N1—H1	117.8	C4—C11—H11C	109.5
O2—C2—N1	121.1 (3)	H11A—C11—H11C	109.5
O2—C2—C3	123.4 (2)	H11B—C11—H11C	109.5
N1—C2—C3	115.6 (2)	O1—C12—H12A	109.5
C4—C3—C2	124.3 (2)	O1—C12—H12B	109.5
C4—C3—H3	117.8	H12A—C12—H12B	109.5
C2—C3—H3	117.8	O1—C12—H12C	109.5
C3—C4—C41	118.8 (3)	H12A—C12—H12C	109.5
C3—C4—C11	117.8 (2)	H12B—C12—H12C	109.5
C41—C4—C11	123.3 (2)	O3—C13—H13A	109.5
C6—C5—C101	120.6 (3)	O3—C13—H13B	109.5
C6—C5—H5	119.7	H13A—C13—H13B	109.5
C101—C5—H5	119.7	O3—C13—H13C	109.5
C5—C6—C7	120.8 (2)	H13A—C13—H13C	109.5
C5—C6—H6	119.6	H13B—C13—H13C	109.5
C7—C6—H6	119.6	C10—C41—C91	116.4 (2)
C8—C7—C6	120.6 (2)	C10—C41—C4	126.0 (2)
C8—C7—H7	119.7	C91—C41—C4	117.5 (2)
C6—C7—H7	119.7	C9—C81—C8	122.0 (3)
C7—C8—C81	120.2 (3)	C9—C81—C101	118.8 (2)
C7—C8—H8	119.9	C8—C81—C101	119.2 (2)
C81—C8—H8	119.9	C9—C91—N1	118.3 (2)
O1—C9—C91	118.9 (2)	C9—C91—C41	122.3 (2)
O1—C9—C81	120.6 (2)	N1—C91—C41	119.3 (2)
C91—C9—C81	120.6 (2)	C10—C101—C5	122.2 (3)
O3—C10—C41	119.8 (2)	C10—C101—C81	119.2 (2)
O3—C10—C101	117.7 (2)	C5—C101—C81	118.6 (2)
C91—N1—C2—O2	178.4 (2)	C91—C9—C81—C101	−1.7 (3)
C91—N1—C2—C3	−2.0 (3)	C7—C8—C81—C9	177.6 (2)
O2—C2—C3—C4	−178.2 (2)	C7—C8—C81—C101	−1.6 (3)
N1—C2—C3—C4	2.2 (4)	O1—C9—C91—N1	−2.0 (3)
C2—C3—C4—C41	−0.9 (4)	C81—C9—C91—N1	178.85 (18)
C2—C3—C4—C11	−179.9 (2)	O1—C9—C91—C41	177.16 (17)
C101—C5—C6—C7	−0.1 (4)	C81—C9—C91—C41	−2.0 (3)
C5—C6—C7—C8	2.2 (4)	C2—N1—C91—C9	179.7 (2)
C6—C7—C8—C81	−1.4 (4)	C2—N1—C91—C41	0.5 (3)
C12—O1—C9—C91	95.8 (2)	C10—C41—C91—C9	3.5 (3)
C12—O1—C9—C81	−85.0 (2)	C4—C41—C91—C9	−178.24 (19)
C13—O3—C10—C41	102.3 (3)	C10—C41—C91—N1	−177.30 (17)
C13—O3—C10—C101	−80.4 (3)	C4—C41—C91—N1	0.9 (3)
O3—C10—C41—C91	175.73 (17)	O3—C10—C101—C5	−0.1 (3)
C101—C10—C41—C91	−1.5 (3)	C41—C10—C101—C5	177.21 (19)
O3—C10—C41—C4	−2.3 (3)	O3—C10—C101—C81	−179.29 (17)
C101—C10—C41—C4	−179.5 (2)	C41—C10—C101—C81	−2.0 (3)
C3—C4—C41—C10	177.3 (2)	C6—C5—C101—C10	178.0 (2)
C11—C4—C41—C10	−3.7 (4)	C6—C5—C101—C81	−2.8 (3)
C3—C4—C41—C91	−0.7 (3)	C9—C81—C101—C10	3.6 (3)
C11—C4—C41—C91	178.2 (2)	C8—C81—C101—C10	−177.1 (2)
O1—C9—C81—C8	0.0 (3)	C9—C81—C101—C5	−175.63 (19)
C91—C9—C81—C8	179.1 (2)	C8—C81—C101—C5	3.6 (3)
O1—C9—C81—C101	179.19 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2^i	0.86	2.10	2.941 (4)	164

Symmetry code: (i) −x+1, −y+1, −z+1.