N⁶-Furfuryladenine (kinetin) hydrochloride

In the title compound, N⁶-furfuryl­adenin-3-ium chloride, C₁₀H₁₀N₅O⁺·Cl⁻, the adenine moiety exists as the N3-protonated N7–H tautomer. The orientation of the N6 substituent (furfuryl moiety) is distal to the imidazole ring of the adenine base. The dihedral angle between the adenine plane and the furfuryl ring plane is 76.1 (2)°. Three N—H...Cl hydrogen bonds are responsible for the formation of a supramolecular chain-like pattern. These supramolecular chains are interconnected by C—H...Cl hydrogen bonds to form a hydrogen-bonded sheet and a three-dimensional hydrogen-bonded network.

S1. Comment

Kinetin (N⁶-furfuryladenine) is a highly potent growth factor or cytokinin (Skoog & Armstrong, 1970). Many N6-substituted adenine derivatives function as plant-growth stimulants (Hall, 1973). Cytokinin is the generic name used to designate plant-growth substances, and cytokinins occur in a wide range of plant tissues, being found abundantly in root tips, xylum sap, developing fruits, tumour tissues and germinating seeds. Kinetin was isolated from an autoclaved sample of herring sperm DNA (Miller et al., 1955). It was found to be very active in promoting mitosis and cell division in tobacco callus tissue in vitro and it is the reference compound for comparing the cytokinin activity of other cytokinins. Some synthetic N6-substituted adenines also show cytokinin activity depending upon their conformation (Pattabhi, 1990), for example, N⁶-benzyladenine is a synthetic cytokinin. The crystal structures of N⁶-benzyladenine hydrochloride (Umadevi, 1997), N⁶-benzyladenine hydrobromide (Umadevi et al., 2001), a cupric chloride complex of the benzyl adeninium ligand (Balasubramanian et al., 1996) and a cupric chloride complex of the N⁶-furfuryladeninium moiety (Umadevi et al., 2002) have already been reported from our laboratory.

Weak hydrogen bonds play an important role in stabilizing crystal structures (Desiraju & Steiner, 1999). Recently, Thallapally & Nangia have analysed C—H···Cl hydrogen bonds using the Cambridge Structural Database (CSD, Version?; Allen, 2002). They have suggested that C—H···Cl⁻ and C—H···Cl—M often behave as hydrogen bonds, but C—H···Cl—C is generally a van der Waals interaction (Thallapally & Nangia, 2001). The aim of the present study was to understand the conformation and hydrogen-bonding patterns of N⁶-furfuryladenine hydrochloride, (I) (FUCL). \sch

A view of the molecule of (I) is shown in Fig. 1. The compound crystallizes in space group P2₁ and the absolute crystal structure has not yet been determined. The asymmetric unit contains an N⁶-furfuryladeninium moiety and a Cl⁻ anion.

In the crystal structure of neutral N⁶-furfuryladenine (Soriano-Garcia & Parthasarathy, 1977), an H atom resides at the N9 position (N9—H tautomer). In mono-protonated adenine systems, N1 is the protonation site (Voet & Rich, 1970). However in the present crystal structure, very interestingly, the adenine moiety exists as the N7—H tautomer with the H atom at N3; N9 carries no H atom. Further evidence for the presence of the H atoms on these sites comes from the enhancement of the corresponding internal angles. The internal angles at N3 and N7 are 118.4 (3) and 106.4 (3)°, respectively. The corresponding angles in neutral N⁶-furfuryladenine are 110.9 (3) and 102.8 (3)°, respectively (Soriano-Garcia & Parthasarathy, 1977).

In the crystal structure of neutral N⁶-furfuryladenine, where the molecule exists as the N9—H tautomer, the internal angle at N9 (C4—N9—C8) is 106.9 (3)°, whereas in the present structure, the corresponding angle is significantly less, at 102.6 (3)°. This suggests that in (I), N9 carries no H atom. In both these compounds, the angles at N1 do not differ significantly [119.5 (3)° in (I) and 118.8 (3)° in the neutralcompound], suggesting that, in both crystal structures, there is no H atom at N1. Thus, it can be concluded that in (I), the base exists as the N3-protonated N7—H tautomer.

The enhancement of internal bond angles on protonation sites is already well established (Taylor & Kennard, 1982). It is very interesting to note that the N1 position remains unprotonated, even under acidic conditions, in (I), and in a copper complex of N⁶-benzyladenine (Balasubramanian et al., 1996), in a copper complex of N⁶-furfuryladenine (Umadevi et al., 2002) and in a copper complex of N⁶-benzyladenine (Trávníček et al., 2001). The above copper complexes of adenine derivatives were also prepared under slightly acidic conditions; the adenine moieties exist as the N7—H tautomer, with protonation at N3 and coordination at N9.

The orientation of the N6 substituent in (I) is distal to the imidazole ring of the adenine base. The dihedral angle between the adenine plane and the furfuryl ring plane is 76.1 (2)°. This is in agreement with the range of values (63–108°) proposed for cytokinin activity (Raghunathan & Pattabhi, 1981; Raghunathan et al., 1983; Soriano-Garcia & Parthasarathy, 1977; Balasubramanian et al., 1996; Umadevi et al., 2002). The N6 substituent is also distal to the imidazole ring, as in other cytokinins (Soriano-Garcia & Parthasarathy, 1977; Raghunathan & Pattabhi, 1981; Bugg & Thewalt, 1972; McMullan & Sundaralingam, 1971; Walker & Tollin, 1982). Selected bond lengths and angles are listed in Table 1.

The N7 and N6 H atoms of the same adeninium moiety in (I) are hydrogen bonded to a Cl⁻ anion via N—H···Cl hydrogen bonds, to form a seven-membered ring with graph-set R₂¹(7) (Bernstein et al., 1995). The N3 H atom of the neighbouring adeninium moiety is also hydrogen bonded to this Cl⁻ anion, leading to a hydrogen-bonded supramolecular chain, made up of Cl⁻ anions and furfuryladeninium cations arranged in an alternating manner, which runs parallel to the b axis. A view of this supramolecular chain is shown in Fig. 2.

Two such chains are further interconnected by C—H···Cl hydrogen bonds involving the C8 H atom of the adeninium moieties, generating a hydrogen-bonded sheet-like pattern. Two such sheets are further cross-linked by C—H···Cl hydrogen bonds involving a methylene H atom of the furfuryladeninium moiety, to form a three-dimensional network. In the crystal structure of N⁶-benzyladenine hydrobromide (Umadevi et al., 2001), a base pair is formed via N3—H···N9 hydrogen bonds. In the structure of (I), there is no base pairing and the crystal structure is dominated by N—H···Cl and C—H···Cl hydrogen bonds and π–π stacking. The centroid-to-centroid distance between the overlapping phenyl and imidazole planes is 3.494 (3) Å. Details of the hydrogen bonds are given in Table 2.

S2. Experimental

N⁶-Furfuryladenine (Loba Chemie, India) was dissolved in the minimum amount of dilute hydrochloric acid and recrystallized from methanol.

S3. Refinement

All H atoms were located from the difference Fourier map and were refined isotropically.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: PLATON (Spek, 1997).

Figures

Fig. 1. A view of the molecular structure of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small psheres of arbitrary radii. Fig. 2. A view of the hydrogen-bonded supramolecular chains in (I).

N⁶-furfuryladenin-3-ium chloride

Crystal data

C10H10N5O^+·Cl^−	F(000) = 260
Mr = 251.68	Dx = 1.520 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 4.5610 (8) Å	Cell parameters from 1010 reflections
b = 8.8980 (17) Å	θ = 2.7–30.0°
c = 13.562 (3) Å	µ = 0.34 mm^−1
β = 92.138 (5)°	T = 100 K
V = 550.02 (19) Å^3	Plate, colourless
Z = 2	0.26 × 0.24 × 0.04 mm

Data collection

Bruker SMART Apex CCD area-detector diffractometer	1704 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.035
Graphite monochromator	θmax = 30.7°, θmin = 1.5°
ω scans	h = −4→4
2063 measured reflections	k = −12→11
1957 independent reflections	l = −8→18

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: located from difmap
R[F^2 > 2σ(F^2)] = 0.048	All H-atom parameters refined
wR(F^2) = 0.125	w = 1/[σ^2(Fo^2) + (0.0782P)^2 + 0.032P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
1957 reflections	Δρmax = 0.59 e Å^−3
194 parameters	Δρmin = −0.37 e Å^−3
1 restraint	Absolute structure: (Flack, 1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.60 (10)

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl1	0.6593 (2)	0.79597 (9)	0.33495 (5)	0.0244 (3)
O1	0.3562 (7)	0.6559 (3)	0.04593 (19)	0.0278 (9)
N1	0.1427 (8)	0.2833 (4)	0.2418 (2)	0.0238 (9)
N3	0.4215 (9)	0.1138 (3)	0.3402 (2)	0.0246 (12)
N6	0.2169 (9)	0.5412 (4)	0.2502 (2)	0.0236 (12)
N7	0.6880 (9)	0.4628 (3)	0.4165 (2)	0.0206 (9)
N9	0.7897 (9)	0.2213 (4)	0.4548 (2)	0.0231 (12)
C2	0.2133 (11)	0.1467 (4)	0.2720 (3)	0.0247 (13)
C4	0.5704 (10)	0.2298 (4)	0.3858 (3)	0.0222 (13)
C5	0.5004 (10)	0.3765 (4)	0.3594 (2)	0.0184 (13)
C6	0.2841 (10)	0.4042 (4)	0.2832 (3)	0.0203 (13)
C8	0.8528 (11)	0.3663 (5)	0.4722 (3)	0.0236 (13)
C10	0.0119 (11)	0.5663 (4)	0.1661 (3)	0.0224 (13)
C11	0.1522 (10)	0.5482 (4)	0.0698 (3)	0.0218 (13)
C12	0.1224 (12)	0.4492 (5)	−0.0053 (3)	0.0288 (16)
C13	0.3112 (12)	0.4956 (5)	−0.0803 (3)	0.0300 (16)
C14	0.4486 (13)	0.6196 (5)	−0.0463 (3)	0.0300 (16)
H2	0.126 (11)	0.063 (6)	0.238 (3)	0.027 (12)*
H3	0.488 (13)	0.022 (8)	0.349 (3)	0.051 (17)*
H6	0.312 (10)	0.609 (5)	0.277 (3)	0.019 (11)*
H7	0.713 (11)	0.567 (6)	0.409 (3)	0.034 (13)*
H8	0.995 (10)	0.407 (4)	0.517 (3)	0.010 (9)*
H10A	−0.162 (11)	0.511 (6)	0.172 (3)	0.021 (12)*
H10B	−0.079 (11)	0.669 (6)	0.176 (3)	0.025 (12)*
H12	−0.004 (12)	0.378 (5)	−0.002 (3)	0.022 (11)*
H13	0.353 (12)	0.447 (6)	−0.134 (3)	0.036 (14)*
H14	0.578 (13)	0.671 (6)	−0.068 (4)	0.035 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0366 (7)	0.0110 (3)	0.0254 (4)	0.0019 (4)	−0.0012 (3)	−0.0014 (3)
O1	0.040 (2)	0.0151 (12)	0.0284 (13)	0.0024 (12)	0.0029 (13)	0.0006 (10)
N1	0.032 (2)	0.0155 (15)	0.0238 (12)	−0.0010 (16)	0.0010 (12)	−0.0012 (12)
N3	0.039 (3)	0.0082 (14)	0.0266 (15)	0.0003 (15)	0.0017 (15)	−0.0005 (10)
N6	0.032 (3)	0.0152 (16)	0.0233 (15)	0.0021 (15)	−0.0042 (14)	0.0002 (12)
N7	0.028 (2)	0.0133 (14)	0.0202 (13)	0.0013 (13)	−0.0012 (13)	0.0011 (10)
N9	0.031 (3)	0.0160 (16)	0.0225 (15)	0.0051 (14)	0.0029 (15)	−0.0007 (11)
C2	0.037 (3)	0.0114 (17)	0.0261 (17)	−0.0028 (17)	0.0066 (18)	−0.0026 (14)
C4	0.025 (3)	0.0172 (18)	0.0247 (17)	−0.0002 (17)	0.0058 (17)	0.0004 (13)
C5	0.020 (3)	0.0154 (18)	0.0204 (15)	−0.0006 (16)	0.0069 (15)	−0.0005 (12)
C6	0.025 (3)	0.0112 (16)	0.0254 (16)	0.0026 (16)	0.0086 (16)	0.0009 (13)
C8	0.029 (3)	0.021 (2)	0.0209 (16)	0.0061 (18)	0.0010 (17)	0.0024 (14)
C10	0.020 (3)	0.0188 (19)	0.0281 (18)	0.0022 (17)	−0.0024 (16)	0.0002 (13)
C11	0.025 (3)	0.0159 (16)	0.0243 (16)	0.0064 (16)	−0.0006 (16)	−0.0001 (13)
C12	0.032 (4)	0.022 (2)	0.032 (2)	−0.0016 (19)	−0.0055 (19)	−0.0059 (15)
C13	0.035 (4)	0.028 (2)	0.0267 (18)	0.0057 (19)	−0.0017 (18)	−0.0039 (15)
C14	0.042 (4)	0.023 (2)	0.0255 (18)	0.001 (2)	0.0066 (19)	0.0054 (14)

Geometric parameters (Å, º)

O1—C11	1.383 (5)	N7—H7	0.94 (5)
O1—C14	1.373 (5)	C4—C5	1.388 (5)
N1—C2	1.319 (5)	C5—C6	1.423 (6)
N1—C6	1.364 (5)	C10—C11	1.484 (6)
N3—C2	1.333 (6)	C11—C12	1.350 (6)
N3—C4	1.370 (5)	C12—C13	1.418 (7)
N6—C6	1.330 (5)	C13—C14	1.342 (7)
N6—C10	1.465 (6)	C2—H2	0.96 (5)
N7—C5	1.368 (5)	C8—H8	0.94 (4)
N7—C8	1.353 (6)	C10—H10A	0.94 (5)
N9—C4	1.346 (6)	C10—H10B	1.01 (5)
N9—C8	1.341 (6)	C12—H12	0.86 (5)
N3—H3	0.88 (7)	C13—H13	0.87 (4)
N6—H6	0.82 (5)	C14—H14	0.81 (6)
Cl1···N3^i	3.031 (3)	C6···N7^vii	3.361 (6)
Cl1···N6	3.218 (4)	C6···C8^vii	3.306 (6)
Cl1···N7	3.165 (3)	C8···C6^ii	3.306 (6)
Cl1···C10^ii	3.504 (4)	C8···C5^ii	3.378 (6)
Cl1···C8^iii	3.625 (5)	C8···Cl1^x	3.625 (5)
Cl1···C8^iv	3.428 (5)	C8···Cl1^xi	3.428 (5)
Cl1···H3^i	2.17 (7)	C10···Cl1^vii	3.504 (4)
Cl1···H10B^ii	2.75 (5)	C11···N1	3.318 (5)
Cl1···H6	2.41 (4)	C11···C14^vii	3.578 (7)
Cl1···H7	2.28 (5)	C12···C14^ix	3.580 (7)
Cl1···H8^iv	2.69 (4)	C12···C14^vii	3.453 (8)
Cl1···H13^v	3.04 (4)	C13···O1^ix	3.406 (5)
O1···N6	3.042 (4)	C14···C12^v	3.580 (7)
O1···C13^v	3.406 (5)	C14···C11^ii	3.578 (7)
O1···H12^vi	2.60 (5)	C14···C2^v	3.487 (6)
N1···C4^vii	3.352 (6)	C14···C12^ii	3.453 (8)
N1···C11	3.318 (5)	C2···H14^ix	2.97 (6)
N3···Cl1^viii	3.031 (3)	C12···H14^ix	2.98 (6)
N6···Cl1	3.218 (4)	C13···H2^vi	2.93 (5)
N6···O1	3.042 (4)	H2···C13^xii	2.93 (5)
N6···N7	3.135 (5)	H3···Cl1^viii	2.17 (7)
N7···N6	3.135 (5)	H6···Cl1	2.41 (4)
N7···C6^ii	3.361 (6)	H6···N7	2.82 (4)
N7···Cl1	3.165 (3)	H6···H7	2.54 (6)
N9···C2^ii	3.268 (6)	H7···Cl1	2.28 (5)
N1···H14^ix	2.90 (6)	H7···H6	2.54 (6)
N1···H10A	2.61 (5)	H8···Cl1^xi	2.69 (4)
N7···H6	2.82 (4)	H10A···N1	2.61 (5)
C2···N9^vii	3.268 (6)	H10B···Cl1^vii	2.75 (5)
C2···C4^vii	3.444 (7)	H12···O1^xii	2.60 (5)
C2···C14^ix	3.487 (6)	H13···Cl1^ix	3.04 (4)
C4···N1^ii	3.352 (6)	H14···N1^v	2.90 (6)
C4···C2^ii	3.444 (7)	H14···C2^v	2.97 (5)
C5···C8^vii	3.378 (6)	H14···C12^v	2.98 (5)
C11—O1—C14	106.4 (3)	N6—C10—C11	112.6 (4)
C2—N1—C6	119.5 (3)	O1—C11—C12	109.0 (4)
C2—N3—C4	118.4 (3)	O1—C11—C10	116.5 (3)
C6—N6—C10	122.3 (3)	C10—C11—C12	134.4 (4)
C5—N7—C8	106.4 (3)	C11—C12—C13	107.7 (4)
C4—N9—C8	102.6 (3)	C12—C13—C14	106.3 (4)
C2—N3—H3	122 (3)	O1—C14—C13	110.6 (4)
C4—N3—H3	118 (4)	N1—C2—H2	118 (3)
C6—N6—H6	114 (3)	N3—C2—H2	116 (3)
C10—N6—H6	123 (3)	N7—C8—H8	118 (2)
C8—N7—H7	128 (3)	N9—C8—H8	128 (2)
C5—N7—H7	125 (3)	N6—C10—H10A	112 (3)
N1—C2—N3	125.3 (4)	N6—C10—H10B	107 (2)
N3—C4—C5	119.1 (4)	C11—C10—H10A	114 (3)
N3—C4—N9	127.9 (3)	C11—C10—H10B	114 (2)
N9—C4—C5	113.0 (3)	H10A—C10—H10B	96 (4)
N7—C5—C4	104.4 (3)	C11—C12—H12	119 (3)
N7—C5—C6	135.7 (3)	C13—C12—H12	133 (3)
C4—C5—C6	119.8 (3)	C12—C13—H13	128 (4)
N6—C6—C5	123.2 (4)	C14—C13—H13	125 (4)
N1—C6—C5	117.8 (3)	O1—C14—H14	117 (4)
N1—C6—N6	119.0 (4)	C13—C14—H14	133 (4)
N7—C8—N9	113.7 (4)
C11—O1—C14—C13	0.2 (5)	C4—N9—C8—N7	−1.1 (5)
C14—O1—C11—C12	0.3 (5)	C8—N9—C4—N3	179.6 (4)
C14—O1—C11—C10	−178.1 (4)	N9—C4—C5—N7	−0.4 (5)
C2—N1—C6—C5	−1.2 (6)	N3—C4—C5—C6	−2.4 (6)
C2—N1—C6—N6	178.1 (4)	N9—C4—C5—C6	176.5 (4)
C6—N1—C2—N3	−1.5 (7)	N3—C4—C5—N7	−179.2 (4)
C4—N3—C2—N1	2.2 (7)	C4—C5—C6—N1	3.0 (6)
C2—N3—C4—C5	−0.2 (6)	N7—C5—C6—N6	−0.6 (8)
C2—N3—C4—N9	−178.8 (4)	C4—C5—C6—N6	−176.2 (4)
C6—N6—C10—C11	−81.9 (5)	N7—C5—C6—N1	178.7 (4)
C10—N6—C6—C5	174.7 (4)	N6—C10—C11—O1	−68.7 (4)
C10—N6—C6—N1	−4.6 (6)	N6—C10—C11—C12	113.4 (6)
C5—N7—C8—N9	0.9 (5)	C10—C11—C12—C13	177.4 (5)
C8—N7—C5—C4	−0.3 (4)	O1—C11—C12—C13	−0.6 (5)
C8—N7—C5—C6	−176.4 (5)	C11—C12—C13—C14	0.7 (6)
C8—N9—C4—C5	0.9 (5)	C12—C13—C14—O1	−0.5 (6)

Symmetry codes: (i) x, y+1, z; (ii) x+1, y, z; (iii) −x+1, y+1/2, −z+1; (iv) −x+2, y+1/2, −z+1; (v) −x+1, y+1/2, −z; (vi) −x, y+1/2, −z; (vii) x−1, y, z; (viii) x, y−1, z; (ix) −x+1, y−1/2, −z; (x) −x+1, y−1/2, −z+1; (xi) −x+2, y−1/2, −z+1; (xii) −x, y−1/2, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···Cl1^viii	0.88 (7)	2.17 (7)	3.031 (3)	167 (4)
N6—H6···Cl1	0.82 (5)	2.41 (4)	3.218 (4)	170 (4)
N7—H7···Cl1	0.94 (5)	2.28 (5)	3.165 (3)	157 (4)
C8—H8···Cl1^xi	0.94 (4)	2.69 (4)	3.428 (5)	135 (3)
C10—H10B···Cl1^vii	1.01 (5)	2.75 (5)	3.504 (4)	132 (3)

Symmetry codes: (vii) x−1, y, z; (viii) x, y−1, z; (xi) −x+2, y−1/2, −z+1.