1-Isobutyl-4-meth­oxy-1H-imidazo[4,5-c]quinoline

Fun, H.-K.; Loh, W.-S.; Dinesha; Kayarmar, R.; Nagaraja, G.K.

doi:10.1107/S1600536811031801

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 67| Part 9| September 2011| Page o2331

doi:10.1107/S1600536811031801

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1-Isobutyl-4-methoxy-1H-imidazo[4,5-c]quinoline

Hoong-Kun Fun,^a ^*‡ Wan-Sin Loh,^a § Dinesha,^b Reshma Kayarmar ^c and G. K. Nagaraja ^b

^aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, ^bDepartment of Chemistry, Mangalore University, Karnataka, India, and ^cSequent Scientific Limited, Baikampady, New Mangalore, India
^*Correspondence e-mail: hkfun@usm.my

(Received 5 August 2011; accepted 5 August 2011; online 11 August 2011)

In the title compound, C₁₅H₁₇N₃O, the 1H-imidazo[4,5-c]quinoline ring system is approximately planar, with a maximum deviation of 0.036 (1) Å. The C—N—C—C torsion angles formed between this ring system and the isobutyl unit are −99.77 (16) and 79.71 (17)°. In the crystal, intermolecular C—H⋯O hydrogen bonds link the molecules into chains along the c axis.

Related literature

For background to quinolines and their microbial activity, see: Crozat & Beutler (2004 ); Stringfellow & Glasgow (1972 ); Miller et al. (1999 ); Hemmi et al. (2002 ). For related structures, see: Loh et al. (2011a ,b ).

Experimental

Crystal data

C₁₅H₁₇N₃O
M_r = 255.32
Monoclinic, P 2₁ /c
a = 7.4196 (8) Å
b = 18.910 (2) Å
c = 10.4112 (14) Å
β = 110.568 (2)°
V = 1367.6 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 297 K
0.40 × 0.31 × 0.13 mm

Data collection

Bruker SMART APEXII DUO CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.969, T_max = 0.989
12741 measured reflections
3463 independent reflections
2386 reflections with I > 2σ(I)
R_int = 0.023

Refinement

R[F² > 2σ(F²)] = 0.042
wR(F²) = 0.127
S = 1.04
3463 reflections
175 parameters
H-atom parameters constrained
Δρ_max = 0.12 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C10—H10A⋯O1ⁱ	0.93	2.39	3.3052 (16)	169
Symmetry code: (i) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ .

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

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811031801/wn2444sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811031801/wn2444Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536811031801/wn2444Isup3.cml

checkCIF report

Comment top

The quinoline scaffold is prevalent in a variety of pharmacologically active synthetic and natural products. Long before endosomal TLR7 was discovered to serve as the primary sensor for short, single-stranded, GU-rich RNA sequences (ssRNA), mainly of viral origin (Crozat & Beutler, 2004), a number of small molecules were synthesized and evaluated in the 1970's and 1980's for antiviral activities owing to their pronounced type I interferon (IFN-R and -β) inducing properties (Stringfellow & Glasgow, 1972). Although the mechanisms of innate immune stimulation of several of these compounds (such as tilorone14 and bromopirone16) remain yet to be formally elucidated, the members of the 1H-imidazo[4,5-c]quinolines were found to be good type I IFN inducers in human cell-derived assays and FDA approval was obtained in 1997 for imiquimod for the treatment of basal cell carcinoma and actinic keratosis (Miller et al., 1999). It was not until 2002, however, that the mechanistic basis of IFN induction by the imidazoquinolines was found to be a consequence of TLR7 engagement and activation (Hemmi et al., 2002). We have earlier reported the crystal structures of 1-isobutyl-N,N-dimethyl-1H-imidazo[4,5-c]quinolin- 4-amine and 4-hydrazinyl-1-isobutyl-1H-imidazo[4,5-c]quinoline (Loh et al., 2011a,b). Following on from these, we have synthesized 1-isobutyl-4-methoxy-1H-imidazo[4,5-c]quinoline.

In the title compound (Fig. 1), the 1H-imidazo[4,5-c]quinoline ring system (C1–C7/N3/C10/N2/C8/C9/N1) is approximately planar with a maximum deviation of 0.036 (1) Å at atom C8. The torsion angle, C10—N3—C11—C12, formed between this ring system and the isobutyl unit is -99.77 (16)°; the torsion angle C7—N3—C11—C12 is 79.71 (17)°. Bond lengths and angles are within the normal ranges and are comparable to those in the related crystal structures (Loh et al., 2011a,b).

In the crystal packing (Fig. 2), the intermolecular C10—H10A···O1 hydrogen bonds (Table 1) link the molecules into chains along the c axis.

Related literature top

For background to quinolines and their microbial activity, see: Crozat & Beutler (2004); Stringfellow & Glasgow (1972); Miller et al. (1999); Hemmi et al. (2002). For related structures, see: Loh et al. (2011a,b).

Experimental top

To a solution of 4-chloro-1-(2-methylpropyl)-1H-imidazo[4,5-c] quinoline (0.1 mol) in methanol (30 ml) was added a solution of sodium methoxide (0.01 mol) in methanol (10 ml) and the mixture was stirred for 1 h. The reaction mixture was heated under reflux for 12 h, concentrated and poured into crushed ice. The resultant solid was filtered, dried and recrystallized using a mixture of DMF and water (1:1). M. p. = 493–495 K.

Computing details top

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

Figures top

	Fig. 1. The molecular structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen atoms are shown as spheres of arbitrary radius.
	Fig. 2. The crystal packing of the title compound, viewed along the a axis, showing the chains along the c axis. Hydrogen bonds are indicated by dashed lines.

1-Isobutyl-4-methoxy-1H-imidazo[4,5-c]quinoline top

Crystal data top

C₁₅H₁₇N₃O	F(000) = 544
M_r = 255.32	D_x = 1.240 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3364 reflections
a = 7.4196 (8) Å	θ = 2.9–28.4°
b = 18.910 (2) Å	µ = 0.08 mm⁻¹
c = 10.4112 (14) Å	T = 297 K
β = 110.568 (2)°	Plate, colourless
V = 1367.6 (3) Å³	0.40 × 0.31 × 0.13 mm
Z = 4

Data collection top

Bruker SMART APEXII DUO CCD area-detector diffractometer	3463 independent reflections
Radiation source: fine-focus sealed tube	2386 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.023
ϕ and ω scans	θ_max = 28.6°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −7→9
T_min = 0.969, T_max = 0.989	k = −25→25
12741 measured reflections	l = −13→10

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.127	H-atom parameters constrained
S = 1.04	w = 1/[σ²(F_o²) + (0.0619P)² + 0.131P] where P = (F_o² + 2F_c²)/3
3463 reflections	(Δ/σ)_max < 0.001
175 parameters	Δρ_max = 0.12 e Å⁻³
0 restraints	Δρ_min = −0.18 e Å⁻³

Crystal data top

C₁₅H₁₇N₃O	V = 1367.6 (3) Å³
M_r = 255.32	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 7.4196 (8) Å	µ = 0.08 mm⁻¹
b = 18.910 (2) Å	T = 297 K
c = 10.4112 (14) Å	0.40 × 0.31 × 0.13 mm
β = 110.568 (2)°

Data collection top

Bruker SMART APEXII DUO CCD area-detector diffractometer	3463 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	2386 reflections with I > 2σ(I)
T_min = 0.969, T_max = 0.989	R_int = 0.023
12741 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.042	0 restraints
wR(F²) = 0.127	H-atom parameters constrained
S = 1.04	Δρ_max = 0.12 e Å⁻³
3463 reflections	Δρ_min = −0.18 e Å⁻³
175 parameters

Special details top

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) top

	x	y	z	U_iso*/U_eq
O1	0.48715 (15)	0.63510 (5)	0.85500 (9)	0.0586 (3)
N1	0.37002 (15)	0.53191 (5)	0.73822 (10)	0.0447 (3)
N2	0.44565 (18)	0.70399 (5)	0.59706 (12)	0.0563 (3)
N3	0.33493 (16)	0.64771 (5)	0.39424 (11)	0.0486 (3)
C1	0.29597 (16)	0.49624 (6)	0.61429 (12)	0.0400 (3)
C2	0.24489 (19)	0.42505 (6)	0.61944 (13)	0.0483 (3)
H2A	0.2608	0.4045	0.7039	0.058*
C3	0.1725 (2)	0.38552 (7)	0.50312 (15)	0.0549 (3)
H3A	0.1400	0.3384	0.5089	0.066*
C4	0.1472 (2)	0.41521 (7)	0.37579 (14)	0.0563 (4)
H4A	0.0976	0.3879	0.2968	0.068*
C5	0.19492 (19)	0.48452 (7)	0.36623 (13)	0.0491 (3)
H5A	0.1776	0.5039	0.2806	0.059*
C6	0.26991 (16)	0.52691 (6)	0.48450 (12)	0.0397 (3)
C7	0.32629 (17)	0.59928 (6)	0.49100 (12)	0.0407 (3)
C8	0.39572 (18)	0.63518 (6)	0.61455 (13)	0.0445 (3)
C9	0.41477 (18)	0.59803 (6)	0.73647 (12)	0.0441 (3)
C10	0.4073 (2)	0.70816 (7)	0.46497 (16)	0.0587 (4)
H10A	0.4276	0.7491	0.4225	0.070*
C11	0.2801 (2)	0.64045 (8)	0.24607 (13)	0.0545 (3)
H11A	0.3224	0.5946	0.2258	0.065*
H11B	0.3465	0.6763	0.2129	0.065*
C12	0.0645 (2)	0.64739 (9)	0.16888 (15)	0.0639 (4)
H12A	−0.0010	0.6097	0.2001	0.077*
C13	−0.0102 (3)	0.71824 (10)	0.1988 (2)	0.0988 (7)
H13A	−0.1452	0.7221	0.1466	0.148*
H13B	0.0578	0.7559	0.1737	0.148*
H13C	0.0098	0.7214	0.2948	0.148*
C14	0.0257 (3)	0.63667 (16)	0.01661 (19)	0.1156 (9)
H14A	−0.1083	0.6447	−0.0342	0.173*
H14B	0.0591	0.5892	0.0012	0.173*
H14C	0.1018	0.6694	−0.0132	0.173*
C15	0.5158 (3)	0.59705 (9)	0.97911 (15)	0.0718 (5)
H15A	0.5586	0.6290	1.0555	0.108*
H15B	0.6111	0.5610	0.9900	0.108*
H15C	0.3968	0.5756	0.9753	0.108*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0849 (7)	0.0443 (5)	0.0409 (5)	−0.0024 (4)	0.0151 (5)	−0.0067 (4)
N1	0.0532 (6)	0.0404 (5)	0.0403 (5)	−0.0004 (4)	0.0162 (4)	−0.0010 (4)
N2	0.0727 (8)	0.0350 (6)	0.0589 (7)	0.0006 (5)	0.0202 (6)	0.0013 (5)
N3	0.0575 (6)	0.0416 (6)	0.0460 (6)	0.0052 (5)	0.0174 (5)	0.0094 (4)
C1	0.0401 (6)	0.0382 (6)	0.0419 (6)	0.0013 (4)	0.0147 (5)	−0.0012 (5)
C2	0.0547 (7)	0.0422 (7)	0.0496 (7)	−0.0038 (5)	0.0205 (6)	0.0020 (5)
C3	0.0614 (8)	0.0403 (7)	0.0622 (9)	−0.0084 (6)	0.0209 (6)	−0.0056 (6)
C4	0.0642 (9)	0.0483 (7)	0.0514 (8)	−0.0045 (6)	0.0140 (6)	−0.0134 (6)
C5	0.0561 (7)	0.0476 (7)	0.0405 (6)	0.0040 (6)	0.0130 (5)	−0.0014 (5)
C6	0.0392 (6)	0.0380 (6)	0.0407 (6)	0.0046 (5)	0.0126 (5)	0.0005 (5)
C7	0.0434 (6)	0.0377 (6)	0.0405 (6)	0.0068 (5)	0.0140 (5)	0.0054 (5)
C8	0.0517 (7)	0.0339 (6)	0.0465 (7)	0.0051 (5)	0.0154 (5)	0.0002 (5)
C9	0.0504 (7)	0.0402 (6)	0.0402 (6)	0.0041 (5)	0.0139 (5)	−0.0038 (5)
C10	0.0725 (9)	0.0381 (7)	0.0644 (9)	0.0021 (6)	0.0229 (7)	0.0091 (6)
C11	0.0586 (8)	0.0614 (8)	0.0447 (7)	0.0030 (6)	0.0196 (6)	0.0128 (6)
C12	0.0580 (8)	0.0774 (10)	0.0539 (8)	0.0034 (7)	0.0167 (7)	0.0247 (7)
C13	0.0755 (12)	0.0790 (12)	0.1277 (18)	0.0253 (9)	0.0180 (11)	0.0352 (12)
C14	0.0779 (13)	0.207 (3)	0.0512 (10)	−0.0164 (14)	0.0093 (9)	0.0234 (13)
C15	0.1055 (13)	0.0641 (10)	0.0429 (8)	−0.0088 (8)	0.0223 (8)	−0.0056 (7)

Geometric parameters (Å, º) top

O1—C9	1.3553 (14)	C6—C7	1.4257 (16)
O1—C15	1.4281 (17)	C7—C8	1.3839 (16)
N1—C9	1.2955 (15)	C8—C9	1.4137 (17)
N1—C1	1.3870 (15)	C10—H10A	0.9300
N2—C10	1.3051 (19)	C11—C12	1.523 (2)
N2—C8	1.3825 (15)	C11—H11A	0.9700
N3—C10	1.3635 (17)	C11—H11B	0.9700
N3—C7	1.3796 (15)	C12—C14	1.522 (2)
N3—C11	1.4571 (17)	C12—C13	1.523 (3)
C1—C2	1.4046 (17)	C12—H12A	0.9800
C1—C6	1.4199 (16)	C13—H13A	0.9600
C2—C3	1.3626 (18)	C13—H13B	0.9600
C2—H2A	0.9300	C13—H13C	0.9600
C3—C4	1.3902 (19)	C14—H14A	0.9600
C3—H3A	0.9300	C14—H14B	0.9600
C4—C5	1.3705 (18)	C14—H14C	0.9600
C4—H4A	0.9300	C15—H15A	0.9600
C5—C6	1.4095 (16)	C15—H15B	0.9600
C5—H5A	0.9300	C15—H15C	0.9600

C9—O1—C15	116.66 (10)	N2—C10—N3	114.66 (12)
C9—N1—C1	118.43 (10)	N2—C10—H10A	122.7
C10—N2—C8	103.07 (11)	N3—C10—H10A	122.7
C10—N3—C7	105.82 (11)	N3—C11—C12	113.66 (11)
C10—N3—C11	124.15 (11)	N3—C11—H11A	108.8
C7—N3—C11	130.03 (11)	C12—C11—H11A	108.8
N1—C1—C2	117.04 (11)	N3—C11—H11B	108.8
N1—C1—C6	124.31 (11)	C12—C11—H11B	108.8
C2—C1—C6	118.65 (11)	H11A—C11—H11B	107.7
C3—C2—C1	121.28 (12)	C14—C12—C11	108.51 (14)
C3—C2—H2A	119.4	C14—C12—C13	112.37 (17)
C1—C2—H2A	119.4	C11—C12—C13	110.99 (14)
C2—C3—C4	120.33 (12)	C14—C12—H12A	108.3
C2—C3—H3A	119.8	C11—C12—H12A	108.3
C4—C3—H3A	119.8	C13—C12—H12A	108.3
C5—C4—C3	120.24 (12)	C12—C13—H13A	109.5
C5—C4—H4A	119.9	C12—C13—H13B	109.5
C3—C4—H4A	119.9	H13A—C13—H13B	109.5
C4—C5—C6	120.88 (12)	C12—C13—H13C	109.5
C4—C5—H5A	119.6	H13A—C13—H13C	109.5
C6—C5—H5A	119.6	H13B—C13—H13C	109.5
C5—C6—C1	118.63 (11)	C12—C14—H14A	109.5
C5—C6—C7	127.34 (11)	C12—C14—H14B	109.5
C1—C6—C7	114.03 (10)	H14A—C14—H14B	109.5
N3—C7—C8	104.80 (10)	C12—C14—H14C	109.5
N3—C7—C6	133.69 (11)	H14A—C14—H14C	109.5
C8—C7—C6	121.49 (11)	H14B—C14—H14C	109.5
N2—C8—C7	111.65 (11)	O1—C15—H15A	109.5
N2—C8—C9	129.72 (11)	O1—C15—H15B	109.5
C7—C8—C9	118.55 (11)	H15A—C15—H15B	109.5
N1—C9—O1	120.52 (11)	O1—C15—H15C	109.5
N1—C9—C8	123.15 (11)	H15A—C15—H15C	109.5
O1—C9—C8	116.31 (11)	H15B—C15—H15C	109.5

C9—N1—C1—C2	−178.62 (11)	C10—N2—C8—C7	−0.46 (15)
C9—N1—C1—C6	1.65 (18)	C10—N2—C8—C9	176.13 (14)
N1—C1—C2—C3	−179.42 (12)	N3—C7—C8—N2	0.34 (14)
C6—C1—C2—C3	0.32 (18)	C6—C7—C8—N2	178.58 (11)
C1—C2—C3—C4	−0.2 (2)	N3—C7—C8—C9	−176.68 (11)
C2—C3—C4—C5	0.1 (2)	C6—C7—C8—C9	1.57 (18)
C3—C4—C5—C6	−0.1 (2)	C1—N1—C9—O1	179.84 (11)
C4—C5—C6—C1	0.29 (19)	C1—N1—C9—C8	−1.44 (18)
C4—C5—C6—C7	179.85 (12)	C15—O1—C9—N1	1.81 (19)
N1—C1—C6—C5	179.35 (11)	C15—O1—C9—C8	−177.00 (13)
C2—C1—C6—C5	−0.37 (17)	N2—C8—C9—N1	−176.51 (13)
N1—C1—C6—C7	−0.27 (16)	C7—C8—C9—N1	−0.11 (19)
C2—C1—C6—C7	−179.99 (11)	N2—C8—C9—O1	2.3 (2)
C10—N3—C7—C8	−0.08 (14)	C7—C8—C9—O1	178.66 (11)
C11—N3—C7—C8	−179.63 (12)	C8—N2—C10—N3	0.41 (16)
C10—N3—C7—C6	−178.01 (13)	C7—N3—C10—N2	−0.22 (17)
C11—N3—C7—C6	2.4 (2)	C11—N3—C10—N2	179.36 (12)
C5—C6—C7—N3	−3.3 (2)	C10—N3—C11—C12	−99.77 (16)
C1—C6—C7—N3	176.32 (12)	C7—N3—C11—C12	79.71 (17)
C5—C6—C7—C8	179.09 (12)	N3—C11—C12—C14	−178.33 (15)
C1—C6—C7—C8	−1.33 (16)	N3—C11—C12—C13	57.73 (17)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10A···O1ⁱ	0.93	2.39	3.3052 (16)	169

Symmetry code: (i) x, −y+3/2, z−1/2.

Experimental details

Crystal data
Chemical formula	C₁₅H₁₇N₃O
M_r	255.32
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	297
a, b, c (Å)	7.4196 (8), 18.910 (2), 10.4112 (14)
β (°)	110.568 (2)
V (Å³)	1367.6 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.08
Crystal size (mm)	0.40 × 0.31 × 0.13

Data collection
Diffractometer	Bruker SMART APEXII DUO CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.969, 0.989
No. of measured, independent and observed [I > 2σ(I)] reflections	12741, 3463, 2386
R_int	0.023
(sin θ/λ)_max (Å⁻¹)	0.673

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.127, 1.04
No. of reflections	3463
No. of parameters	175
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.12, −0.18

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10A···O1ⁱ	0.93	2.39	3.3052 (16)	168.8

Symmetry code: (i) x, −y+3/2, z−1/2.

Footnotes

‡Thomson Reuters ResearcherID: A-3561-2009.

§Thomson Reuters ResearcherID: C-7581-2009.

Acknowledgements

HKF and WSL thank Universiti Sains Malaysia (USM) for the Research University Grant (1001/PFIZIK/811160). WSL thanks the Malaysian Government and USM for the award of a Research Fellowship.

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