Highly methylated purines and purinium salts as analogues of heteromines

Article abstract of DOI:10.1002/ejoc.200500154

Three new unsubstituted or N-methylated derivatives of 2-amino-6,7,9- trimethylpurinium iodides were prepared by quaternization of the corresponding 2-amino-6,7-dimethylpurines. These intermediates were synthesized either by Pd-catalysed cross-coupling of

Full text of DOI:10.1002/ejoc.200500154

FULL PAPER
Highly Methylated Purines and Purinium Salts as Analogues of Heteromines
[a]
[a]
[b]
ˇ
Michal Hocek,* Radek Pohl, and Ivana Císarová
Keywords: Purines / Natural products / Cross-coupling / Alkylation / 15N NMR spectroscopy
Three new unsubstituted or N-methylated derivatives of 2-
methylmagnesium chloride, followed by amination. Both the
amino-6,7,9-trimethylpurinium iodides were prepared by title purinium salts and the purine intermediates were
quaternization of the corresponding 2-amino-6,7-dimeth-
ylpurines. These intermediates were synthesized either by
studied by 15N NMR, and one example of the purinium salts
also by X-ray diffraction. None of the compounds exerted
Pd-catalysed cross-coupling of 2-amino-6-chloro-9-meth- significant cytostatic activity.
ylpurine with trimethylaluminium or by regioselective Fe-ca- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
talysed cross-coupling of 2,6-dichloro-9-methylpurine with
Germany, 2005)
Several types of purines bearing C-substituents in their
6-positions are biologically active. 6-Aryl-,[5] 6-trifluoro-
methyl-[6] and 6-(hydroxymethyl)purine[7] ribonucleosides
display significant cytostatic activities. 6-Methylpurine is
highly cytotoxic,[8] its liberation from 2Ј-deoxyribonucleo-
side by purine nucleoside phosphorylases being used for de-
tection of mycoplasma in cell cultures.[9] It is highly potent
and toxic both to nonproliferating and to proliferating tu-
mour cells, and the use of cytotoxic 6-methylpurine base
liberated by purine nucleoside phosphorylases from its non-
toxic deoxyribonucleoside has recently been proposed as a
novel principle in the gene therapy of cancer.[10]
Introduction
Heteromines are quaternary purinium alkaloids from
Heterostemma brownii,[1] used in Taiwanese traditional
medicine for treatment of tumours. Heteromines A, B and
C (Scheme 1) were isolated and found to exhibit significant
cytostatic activity,[2] and total syntheses of heteromines A[3]
and C[4] were developed very shortly after their isolation.
So far, however, neither have synthetic analogues of these
bioactive natural products been reported, nor has the
mechanism of action been solved.
In this paper we report on the synthesis of novel com-
pounds combining the unique structural features of cyto-
static heteromines and 6-methylpurines. In these novel het-
eromine analogues, the original methoxy or oxo groups in
the 6-positions were replaced by methyl units (Scheme 1).
This structural modification should not only test the impor-
tance of the oxygen in the 6-positions of the parent com-
pounds but it may also increase stability towards catabo-
lism, due to the presence of a stable C–C bond.
Results and Discussion
The key intermediates in the two total syntheses of heter-
omines, 2-dimethylamino- or 2-amino-6-chloro-9-methylpu-
rines, were originally prepared either in several steps from
acyclic precursors[3] or in the latter case in two steps from
guanine.[4] In the both syntheses the 6-chloropurines were
methoxylated with sodium methoxide and quaternized with
iodomethane, and the counteranion was exchanged for
chloride. In our synthesis of the corresponding 6-methyl de-
rivatives we used two approaches (Scheme 2): (i) introduc-
tion of the methyl group into 2-amino-6-chloropurine (1) by
cross-coupling, or (ii) regioselective cross-coupling of 2,6-
Scheme 1. Structures of heteromines and 6-methyl analogues under
study.
[a] Centre for New Antivirals and Antineoplastics, Institute of Or-
ganic Chemistry and Biochemistry, Academy of Sciences of the
Czech Republic,
Flemingovo nam. 2, 16610 Prague 6, Czech Republic
Fax: +420-220183559
E-mail: hocek@uochb.cas.cz
[b] Deptartment of Inorganic Chemistry, Faculty of Natural Sci-
ences, Charles University,
Hlavova 2030, 12840 Prague 2, Czech Republic
3026
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200500154
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Highly Methylated Purines and Purinium Salts as Analogues of Heteromines
FULL PAPER
dichloro-9-methylpurine (2) with methylmagnesium chlo- with ethanolic methylamine in a sealed tube to give the cor-
ride, followed by amination in the 2-position.
responding 6-methyl-2-methylaminopurine 6 in excellent
yield. Dimethylammonium dimethylcarbamate was success-
fully used as a convenient dimethylamine substitute[18] for
analogous nucleophilic substitution. Its reaction with 5 in
refluxing acetonitrile proceeded nearly quantitatively to
give the 2-dimethylamino derivative 7 in high preparative
yield.
The quaternization of the 2-substituted 6,9-dimethylpu-
rines 3–7 (Scheme 3) was performed analogously to the
published procedures for the syntheses of heteromines by
treatment with excess of iodomethane in acetone at ambient
temperature. The reactions were very sluggish, taking 1–2
weeks to reach nearly complete conversion. While the quat-
ernizations of the 2-aminopurines 3, 6 and 7 proceeded re-
gioselectively at the 7-positions and the desired purinium
salts 8, 9 and 10 crystallized from the reaction mixtures in
pure form in good yields, in the cases of the 2-methyl and
2-chloro derivatives 4 and 5 the quaternization occurred un-
selectively on several N-atoms in the purine rings and the
resulting mixtures were not separable and neither were any
of the components crystallizable from the reaction mixtures.
The quaternization of 4 provided an inseparable 2:1 mixture
1
of 7- and 1-quaternized products (combination of H and
1H,15N-HMBC NMR experiments with the crude mixture).
Scheme 2. Synthesis of 2-substituted 6-methylpurines.
Cross-coupling reactions are a general tool[11] for intro-
duction of C-substituents into purine moieties. Of the vari-
ety of possible organometallics, trimethylaluminium[12]
(with Pd catalysis) and methylmagnesium chloride (Fe ca-
talysis)[13] were the most efficient reagents for the methyl-
ation of 6-halopurines and so were the reagents of choice
in this study. Thus, the known 2-amino-6-chloro-9-meth-
ylpurine (1)[4] reacted smoothly with trimethylaluminium
under Pd(PPh3)4 catalysis conditions in THF to give the
corresponding 6-methyl derivative 3 in a good preparative
yield of 80%. In our previous studies we had found that
this highly reactive reagent could not be applied for regiose-
lective monomethylation of dihalopurines[13] but was very
Scheme 3. Quaternization of purines.
As we suppose that the counteranion does not influence
efficient in di- and trimethylations of di- and trihalopur- the biological activity, due to dissociation and large excesses
ines.[14] Here we applied it in the reaction with 2,6-dichloro- of chloride anions in aqueous solutions under physiological
9-methylpurine (2)[15] under the same conditions to afford conditions, we did not exchange the anions, but used the
2,6,9-trimethylpurine (4) in 74% yield.
purinium iodides 8–10 directly for cytostatic activity screen-
Fe-catalysed cross-coupling reactions[16] of dihalopurines ing. The intermediate 2-substituted 6,9-dimethylpurines 3–
with one equivalent of methylmagnesium chloride had pre- 7 were also subjected to cytostatic activity screening for
viously been shown[13,14] to be reasonably regioselective.[17] comparison. In vitro cytostatic activity tests (inhibition of
In 2,6-dichloropurines the substitution preferentially oc- cell growth) were performed with cultures of mouse leuke-
curred in the 6-position,[13] while in 6,8-dichloropurines the mia L1210 cells (ATCC CCL 219), human promyelocytic
reaction took place in the 8-position.[14] Here, treatment of leukemia HL60 cells (ATCC CCL 240), human cervix carci-
dichloropurine 2 with 1.5 equivalent of MeMgCl in the noma HeLa S3 cells (ATCC CCL 2.2) and the human T
presence of Fe(acac)3 in a THF/NMP mixture proceeded lymphoblastoid CCRF-CEM cell line (ATCC CCL 119).
regioselectively to give the desired 2-chloro-6,9-dimethylpu- None of the tested compounds showed any significant cyto-
rine (5) in 69% isolated yield accompanied by unreacted static effect in any of these assays (inhibition at 10 μm was
starting compound 2 (27%), which was recovered and re- lower than 30%, so no IC50 values were determined). The
used. The chlorine in the 2-position of the intermediate 5 absence of activity in these analogues suggests that the 6-
was substituted with a methylamino group on treatment methoxy group in heteromines is important either for inter-
Eur. J. Org. Chem. 2005, 3026–3030
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Hocek, R. Pohl, I. Císarˇová
FULL PAPER
action with the target cellular system (enzyme) or for trans-
port of heteromines through cell membranes.
All the new compounds were fully characterized. It is
well known that 15N chemical shifts of purines are ex-
tremely sensitive to electronic changes at nitrogen,[19] so 15
N
NMR spectra of all the compounds were also measured
1
and chemical shifts were assigned with the aid of H–15N
multiple-bond chemical shift correlation experiments opti-
mized for long-range couplings of 4 Hz. Table 1 shows com-
parisons of 15N chemicals shifts of 9-methylated purines 3,
6 and 7 and the corresponding quaternized 7,9-dimethylpu-
rinium iodides 8, 9 and 10. The dramatic N-7 upfield shift
(Ϸ 87 ppm) observed upon quaternization is associated
with strong shielding of the 15N nucleus. In the 7,9-dimeth-
ylpurinium iodides 8, 9 and 10 the 15N chemicals shifts of
N-7 and N-9 are virtually the same, indicating delocaliza-
tion of the positive charge. The quaternization has also
long-range effects on the N-1 and NRRЈ chemical shifts,
which are less shielded than in the parent 9-methylated pu-
rines.
Figure 1. Molecular structure of 10 with selected bond lengths [Å]:
N(1)–C(2)
= 1.375(4), C(2)–N(3) = 1.350(4), C(2)–N(11) =
1.347(4), N(7)–C(8) = 1.325(4), C(8)–N(9) = 1.343(4), N(7)–C(15)
= 1.465(3), N(9)–C(14) = 1.463(4), C(8)···I(1) = 3.843(3), C(8)–
H(8)···I(1) = 149°. Displacement ellipsoids are drawn at the 50%
probability level.
In conclusion, 2-amino-6,9-dimethylpurines were ef-
ficiently prepared either by regioselective Fe-catalysed
cross-coupling reactions between 2,6-dichloro-9-methylpu-
rine and methylmagnesium chloride followed by (di)methyl-
amination of the intermediate 2-chloro-6-methylpurine or
by Pd-catalysed cross-coupling of 2-amino-6-chloro-9-
methylpurine with trimethylaluminium. Quaternization of
the 2-amino-6,9-dimethylpurines with iodomethane pro-
ceeded slowly but selectively and efficiently to form the de-
sired 2-amino-6,7,9-trimethylpurinium salts as analogues of
heteromines. On the other hand, quaternizations of 2-meth-
yl- or 2-chloropurine derivatives were unselective. 15N
NMR spectra and crystal structure of these novel purinium
derivatives are described for the first time, showing delocal-
ization of the positive charge on the purine moiety.
Table 1. 15N NMR chemical shifts[a] of 9-methylated purines 3, 6
and 7 and the corresponding quaternized iodides 8, 9 and 10 in
[D6]DMSO at 300 K.
R
RЈ
N-1
N-3
N-7
N-9
NRRЈ
3
H
H
H
CH3
241.9
241.1
238.7
254.4
256.1
251.8
198.3
–
196.1
195.8
190.6
194.2
241.2
241.4
237.7
153.1
153.4
152.9
146.8
147.0
145.2
152.4
153.4
152.5
80.4
74.0
68.1
88.3
83.1
76.9
[b]
6
7[c]
8
9
10
CH3 CH3
H
H
H
CH3
CH3 CH3
[a] With reference to the signal of liquid nitromethane (δ =
381.7 ppm).[19] [b] Not detected. [c] In CDCl3.
2-(Dimethylamino)-6,7,9-trimethylpurinium iodide (10)
crystallized directly from the reaction mixture as crystals
suitable for X-ray diffraction. Its molecular structure, with
selected bond lengths, is given in Figure 1. The organic part
is fairly planar, the largest distances of non-hydrogen atoms
of substituents from best least-squares plane defined by
nine atoms of the purine moiety being 0.193(5) Å for C(13).
Planarity, together with the rather short C(2)–N(11) dis-
tance (see Figure 1, C(2)–N(11) = 1.347(4)), attest to the
contribution of the lone electron pair of N(11) into the pu-
rine π-system, a finding consistent with crystal structures
of other 2- or 6-(dimethylamino)purines described in the
literature.[20,21] The most closely related known structure,
though, is 6-amino-2-(dimethylamino)-7-methylpurine
(BIFFAX),[20] in which the corresponding distance was sig-
nificantly longer (C(2)–N(11) = 1.381Å). At the same time,
the N(7)–C(8) and C(8)–N(9) bond lengths in 10 are signifi-
cantly closer to each other then in BIFFAX, confirming
delocalization of electrons in the charged purine moiety
(N(7)–C(8) = 1.325(4), 1.354; C(8)–N(9) = 1.343(4),
1.311 Å for 10 and BIFFAX, respectively). The N(7)–C(15)
and N(9)–C(14) bond lengths are also virtually identical
and the methyl groups are coplanar with the purine moiety,
confirming the delocalization of the positive charge.
Experimental Section
Melting points were determined on a Kofler block and are uncor-
rected. Mass spectra were measured on a ZAB-EQ (VG Analytical)
spectrometer. NMR spectra were recorded on Bruker Avance 500
(1H at 500 MHz, 13C at 125.8 MHz) and Bruker Avance 400 (1H at
400 MHz, 13C at 100.6 MHz, 15N at 40.6 MHz) instruments. 1H
and 13C NMR spectra were with reference either to the signal of
TMS or to the residual solvent signal. H,13C-HMBC experiments
1
were performed for complete assignment of all signals. 15N NMR
chemical shifts were obtained by 1H,15N-g-HMBC measurements
with reference to the signal of liquid nitromethane[22] (a coaxial
2 mm capillary tube in a 5 mm NMR tube, 381.7 ppm). THF was
dried and distilled from sodium/benzophenone. Starting purines 1[4]
and 2[15] were prepared by known procedures.
2-Amino-6,9-dimethylpurine (3): Trimethylaluminium (2 m solution
in toluene, 3 mL, 6 mmol) was added dropwise, under argon at
20 °C through a septum, to a stirred solution of 2-amino-6-chlo-
ropurine 1 (183 mg, 1 mmol) and Pd(PPh3)4 (60 mg, 0.05 mmol) in
THF (20 mL). The mixture was then stirred at 75 °C for 8 h (TLC
analysis showed complete conversion) and after cooling to room
temp. was poured onto a mixture of crushed ice (ca. 100 mL), am-
monium chloride (1 g) and Na2EDTA (250 mg). The mixture was
then extracted with chloroform (4×100 mL). The collected organic
3028
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 3026–3030

Highly Methylated Purines and Purinium Salts as Analogues of Heteromines
FULL PAPER
layers were dried with MgSO4 and the solvent was evaporated in
vacuo. The residue was chromatographed on a column of silica gel
(100 g, ethyl acetate/hexanes 1:2 Ǟ ethyl acetate Ǟ ethyl acetate/
methanol 9:1) to give the title compound 3 as a solid, which was
crystallized from methanol/toluene/heptane. Yield 131 mg (80%),
white crystals, m.p. 222–225 °C. 1H NMR (400 MHz, [D6]DMSO):
δ = 2.46 (s, 3 H, 6-CH3), 3.60 (s, 3 H, 9-CH3), 6.37 (br.s, 2 H,
NH2), 7.92 (s, 1 H, 8-H) ppm. 13C NMR (100.6 MHz, [D6]DMSO):
δ = 19.01 (6-CH3), 29.13 (9-CH3), 125.79 (C-5), 142.05 (CH-8),
152.89 (C-4), 158.48 (C-6), 160.28 (C-2) ppm. 15N NMR
160 °C. 1H NMR (400 MHz, [D6]DMSO): δ = 2.48 (s, 3 H, 6-CH3),
2.82 (d, 3 H, JCH3,NH = 4.8, CH3–NH), 3.62 (s, 3 H, 9-CH3), 6.84
(q, 1 H, JNH,CH3 = 4.8, NH), 7.92 (s, 1 H, 8-H) ppm. 13C NMR
(100.6 MHz, [D6]DMSO): δ = 19.16 (6-CH3), 28.46 (CH3–NH),
29.07 (9-CH3), 125.55 (C-5), 141.83 (CH-8), 152.81 (C-4), 158.36
(C-6), 159.99 (C-2) ppm. 15N NMR (40.6 MHz, [D6]DMSO): δ =
74.0 (HN-CH3), 147.0 (N-9), 241.1 (N-1), 241.4 (N-7) ppm, N-3
not observed. IR: ν = 3268, 3075, 2945, 2901, 1610, 15981570,
˜
1519, 1477, 1395, 1322 cm–1. EI MS, m/z (rel.%): 177 (100) [M]+,
148 (55). Exact mass (EI HR MS): 177.1011; calcd. for C8H11N5:
(40.6 MHz, [D6]DMSO): δ = 80.4 (NH2), 146.8 (N-9), 198.3 (N-3), 177.1014. C8H11N5 (177.2): C 54.22, H 6.26, N 39.52; found C
241.2 (N-7), 241.9 (N-1) ppm. IR: ν = 3431, 3331, 3205, 1642, 1601, 53.98, H 6.28, N 39.19.
˜
1525, 1467, 1397, 1331 cm–1. EI MS, m/z (rel.%): 163 (100) [M]+,
148 (16). Exact mass (EI HR MS): 163.0862; calcd. for C7H9N5:
163.0858. C7H9N5 (163.2): C 51.52, H 5.56, N 42.92; found C
51.16, H 5.49, N 42.56.
2-(Dimethylamino)-6,9-dimethylpurine (7): A mixture of 2-chloro-6-
methylpurine 5 (240 mg, 1.32 mmol) and dimethylammonium di-
methylcarbamate (1 mL, 7.8 mmol) in acetonitrile (20 mL) was
heated at reflux for 12 h (TLC analysis showed complete conver-
sion). The solvents were then evaporated and the product was iso-
lated in the same way as for compound 6. Yield of compound 7:
220 mg (87%) of yellowish crystals from CH2Cl2/heptane, m.p.
100–103 °C. 1H NMR (400 MHz, CDCl3): δ = 2.66 (s, 3 H, 6-CH3),
3.24 (s, 6 H, (CH3)2N), 3.70 (s, 3 H, 9-CH3), 7.60 (s, 1 H, 8-H) ppm.
13C NMR (100.6 MHz, CDCl3): δ = 19.58 (6-CH3), 29.06 (9-CH3),
37.43 ((CH3)2N), 125.35 (C-5), 140.54 (CH-8), 152.86 (C-4), 158.99
(C-6), 159.79 (C-2) ppm. 15N NMR (40.6 MHz, CDCl3): δ = 68.1
(N(CH3)2), 145.2 (N-9), 196.1 (N-3), 237.7 (N-7), 238.7 (N-1) ppm.
2,6,9-Trimethylpurine (4): This compound was prepared in the
same way as described for compound 3, from 2 (203 mg, 1 mmol)
and Me3Al (2 m, 3 mL, 6 mmol). Compound 4 was obtained as
colourless crystals (from CH2Cl2/heptane). Yield 120 mg (75%),
m.p. 116–118 °C. 1H NMR (400 MHz, CDCl3): δ = 2.80 (s, 3 H,
2-CH3), 2.82 (s, 3 H, 6-CH3), 3.87 (s, 3 H, 9-CH3), 7.92 (s, 1 H, 8-
H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 19.39 (6-CH3), 25.98
(2-CH3), 29.64 (9-CH3), 130.75 (C-5), 143.64 (CH-8), 151.48 (C-4),
158.74 (C-6), 161.97 (C-2) ppm. 15N NMR (40.6 MHz, CDCl3): δ
IR: ν = 1614, 1587, 1547, 1503, 1411, 1392 cm–1. EI MS, m/z
˜
= 147.6 (N-9), 238.6 (N-7), 242.0 (N-3), 276.2 (N-1) ppm. IR: ν =
˜
(rel.%): 191 (100) [M]+, 176 (76), 162 (50), 148 (43). Exact mass
(EI HR MS): 191.1164; calcd. for C9H13N5: 191.1172. C9H13N5
(191.2): C 56.53, H 6.85, N 36.62; found C 56.24, H 6.68, N 36.28.
1597, 1515, 1398, 1342 cm–1. EI MS, m/z (rel.%): 162 (100) [M]+,
147 (8). Exact mass (EI HR MS): 162.0901; calcd. for C8H10N4:
162.0905. C8H10N4 (162.1): C 59.24, H 6.21, N 34.54; found C
59.07, H 6.29, N 34.20.
Quaternization of 2,6-Disubstituted 9-Methylpurines – General Pro-
cedure: A solution of 9-methylpurine 3–7 (0.5–0.7 mmol) in acetone
(20 mL) was stirred at 20 °C while iodomethane (1 mL, 16 mmol)
was added dropwise. The stirring was continued for several days
until the product had crystallized from the reaction mixture. In the
cases of the unsubstituted or substituted 2-aminopurine com-
pounds 3, 6 and 7 the desired products 8, 9 and 10 crystallized in
pure form and were just filtered off and washed with diethyl ether
and dried. In the cases of 2-methyl- and 2-chloropurines 4 and
5, the quaternization/methylation occurred unselectively in several
positions of the purine ring (NMR analysis of crude mixtures of
products), the resulting mixtures were not separable, and neither
did any of the components crystallize in pure form.
2-Chloro-6,9-dimethylpurine (5): Methylmagnesium chloride (3 m
solution in THF, 2 mL, 6 mmol) was added dropwise under argon
at 20 °C to a stirred solution of dichloropurine 2 (820 mg, 4 mmol)
and Fe(acac)3 (400 mg, 1.1 mmol) in NMP (1 mL) and THF
(20 mL). The mixture was stirred for 2 h and allowed to stand over-
night at ambient temperature. It was then poured onto a mixture of
crushed ice (ca. 300 mL), ammonium chloride (2 g) and Na2EDTA
(500 mg). The mixture was then extracted with chloroform
(4×200 mL). The collected organic layers were dried with MgSO4
and the solvent was evaporated in vacuo. The residue was chro-
matographed on a column of silica gel (200 g, ethyl acetate/hexanes
1:2 Ǟ ethyl acetate). Unreacted compound 2 (220 mg, 27%) was
eluted first, followed by the desired 6-methyl derivative 5, which
was crystallized from CH2Cl2/heptane to provide colourless crystals
2-Amino-6,7,9-trimethylpurinium Iodide (8): This compound was
prepared from compound 3 (80 mg, 0.49 mmol) in 14 days. Yield
106 mg (71%) of yellowish crystals, m.p. 279–281 °C. 1H NMR
(400 MHz, [D6]DMSO): δ = 2.73 (s, 3 H, 6-CH3), 3.77 (s, 3 H, 9-
CH3), 4.13 (s, 3 H, 7-CH3), 7.32 (s, 2 H, NH2), 9.39 (s, 1 H, 8-
H) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ = 21.22 (6-CH3),
31.09 (9-CH3), 36.38 (7-CH3), 115.52 (C-5), 141.86 (CH-8), 150.70
(C-4), 157.39 (C-6), 161.87 (C-2) ppm. 15N NMR (40.6 MHz, [D6]-
DMSO): δ = 88.3 (NH2), 152.4 (N-9), 153.1 (N-7), 195.8 (N-3),
1
(504 mg, 69%), m.p. 153–156 °C. H NMR (400 MHz, CDCl3): δ
= 2.85 (s, 3 H, 6-CH3), 3.89 (s, 3 H, 9-CH3), 8.00 (s, 1 H, 8-H) ppm.
13C NMR (100.6 MHz, CDCl3): δ = 19.42 (CH3-6), 30.00 (CH3-9),
132.03 (C-5), 144.89 (CH-8), 152.54 (C-4), 153.91 (C-2), 161.67 (C-
6) ppm. 15N NMR (40.6 MHz, CDCl3): δ = 149.4 (N-9), 240.8 (N-
7), 274.2 (N-1), N-3 not observed. IR: ν = 1598, 1589, 1511, 1397,
˜
1364, 1330, 1303 cm–1. EI MS, m/z (rel.%): 182 (100) [M]+, 147
(14). Exact mass (EI HR MS): 182.0366; calcd. for C7H7ClN4:
182.0359. C7H7ClN4 (182.6): C 46.04, H 3.86, N 30.68; found C
45.88, H 3.82, N 30.35.
254.4 (N-1) ppm. IR: ν = 3402, 3313, 3189, 3055, 2986, 1639, 1621,
˜
1599, 1574, 1502, 1455, 1403, 1384, 1374, 1324 cm–1. FAB MS,
m/z (rel.%): 178 (100) [M]+ (cation). Exact mass (FAB HR MS):
178.1096; calcd. for C8H12N5: 178.1093. C8H12IN5 (305.1): C 31.49,
H 3.96, N 22.95; found C 31.43, H 3.91, N 22.67.
2-(Methylamino)-6,9-dimethylpurine (6): A mixture of 2-chloro-6-
methylpurine 5 (225 mg, 1.24 mmol) and ethanolic CH3NH2 (33%,
20 mL) was stirred in a sealed 35 mL Ace® pressure tube at 80 °C
for 8 h. The solvent was then evaporated and the residue was chro-
matographed on a column of silica gel (100 g, ethyl acetate/hexanes
1:1 Ǟ ethyl acetate Ǟ ethyl acetate/methanol 9:1) to give the title
compound 6 as a solid, which was crystallized from methanol/tolu-
ene/heptane. Yield 195 mg (89%) of colourless crystals, m.p. 157–
2-(Methylamino)-6,7,9-trimethylpurinium Iodide (9): This com-
pound was prepared from compound 6 (119 mg, 0.67 mmol) in 10
days. Yield 184 mg (86%) of yellowish crystals, m.p. 249–252 °C.
1H NMR (500 MHz, [D6]DMSO): δ = 2.73 (s, 3 H, 6-CH3), 2.87
(bd, JCH3,NH = 4.3 Hz, 3 H, CH3–NH), 3.80 (br.s, 3 H, 9-CH3),
4.14 (s, 3 H, 7-CH3), 7.84 (br.s, 1 H, NH), 9.39 (s, 1 H, 8-H) ppm.
Eur. J. Org. Chem. 2005, 3026–3030
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3029

M. Hocek, R. Pohl, I. Císarˇová
FULL PAPER
13C NMR (125.8 MHz, [D6]DMSO): δ = 21.17 (6-CH3), 28.11
(CH3–NH), 30.98 (9-CH3), 36.38 (7-CH3), 115.18 (C-5), 141.40
(CH-8), 150.60 (C-4), 157.15 (C-6), 161.27 (C-2) ppm. 15N NMR
(40.6 MHz, [D6]DMSO): δ = 83.1 (NHCH3), 153.4 (N-7 and N-9),
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53, 8269–8272.
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190.6 (N-3), 256.1 (N-1) ppm. IR: ν = 3249, 3006, 2986, 2793, 1627,
˜
[5] a) M. Hocek, A. Holý, I. Votruba, H. Dvoráková, J. Med.
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1592, 1558, 1483, 1463, 1411, 1386, 1376, 1322 cm–1. FAB MS,
m/z (rel.%): 192 (100) [M]+ (cation). Exact mass (FAB HR MS):
192.1250; calcd. for C9H14N5: 192.1249. C9H14IN5 (319.1): C 33.87,
H 4.42, N 21.94; found C 33.78, H 4.41, N 21.65.
Chem. 2000, 43, 1817–1825; b) M. Hocek, A. Holý, I. Votruba,
H. Dvorˇáková, Collect. Czech. Chem. Commun. 2001, 66, 483–
499.
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dron 1999, 55, 11109–11118.
2-(Dimethylamino)-6,7,9-trimethylpurinium Iodide (10): This com-
pound was prepared from compound 7 (113 mg, 0.59 mmol) in 7
days. Yield 155 mg (79%) of yellowish crystals, m.p. 268–270 °C.
1H NMR (500 MHz, [D6]DMSO): δ = 2.78 (s, 3 H 6-CH3), 3.21
(br.s, 6 H, (CH3)2N), 3.81 (s, 3 H, 9-CH3), 4.15 (s, 3 H, 7-CH3),
9.42 (s, 1 H, 8-H) ppm. 13C NMR (125.8 MHz, [D6]DMSO): δ =
21.65 (6-CH3), 30.91 (9-CH3), 36.39 (7-CH3), 37.23 ((CH3)2N),
114.99 (C-5), 142.16 (CH-8), 150.61 (C-4), 156.78 (C-6), 159.97 (C-
2) ppm. 15N NMR (40.6 MHz, [D6]DMSO): δ = 76.9 (N(CH3)2),
ˇ
[7] P. S ilhár, R. Pohl, I. Votruba, M. Hocek, Org. Lett. 2004, 6,
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152.5 (N-9), 152.9 (N-7), 194.2 (N-3), 251.8 (N-1) ppm. IR: ν =
˜
3027, 2990, 1629, 1581, 1560, 1462, 1415, 1402, 1386, 1368,
1332 cm–1. FAB MS, m/z (rel.%): 206 (100) [M]+ (cation). Exact
mass (FAB HR MS): 206.1407; calcd. for C10H16N5: 206.1406.
C10H16IN5 (333.2): C 36.05, H 4.84, N 21.02; found C 36.03, H
4.93, N 20.76.
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X-ray Crystallographic Study for 10: The diffraction data were col-
lected on NoniusKappaCCD diffractometer at 150 K, Mo-Kα radi-
ation, λ = 0.71073, graphite monochromator, ω-scans. Data were
corrected for LP factor and absorption by Gaussian methods.[23]
The structure was solved by direct methods (SIR)[24] and refined by
full-matrix, least-squares methods based on F2 with all measured
reflections, all non-hydrogen atoms are refined anisotropically
(SHELXL).[25] The positions of the hydrogen atoms were calcu-
lated into idealized positions and refined as riding on their pivot
atom with assigned temperature factors Hiso(H) = 1.2 Ueq(C(8)
atom) and Hiso(H) = 1.5 Ueq(pivot atom) for methyl moieties.
ˇ
1992, 57, 5268–5270; b) M. Cesnek, M. Hocek, A. Holý, Col-
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[17] Other examples of regioselective cross-couplings of dihalopur-
ines: a) G. Langli, L.-L. Gundersen, F. Rise, Tetrahedron 1996,
52, 5625–5638; b) J. M. J. Nolsoe, L.-L. Gundersen, F. Rise,
Acta Chem. Scand. 1999, 53, 366–372; c) M. Havelková, D.
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I. Votruba, H. Dvorˇáková, Tetrahedron 2003, 59, 607–611; e)
Crystal Data for 10: The colourless crystal of C10H16N5I
(0.27×0.25×0.025 mm) was triclinic, space group P-1 (No.2), a =
6.5390(2), b = 7.7630(2), c = 13.4670(5) Å, α = 94.066(2), β =
99.003(2), γ = 99.418(2)°, V = 662.82(4) Å3, Z = 2, M = 333.18,
dcalc = 1.669 g·cm–3, μ = 2.400 mm–1, Tmin = 0.563, Tmax = 0.908,
11048 reflections (θmax = 27.5°) were collected, of which 3025 were
unique [Rint = 0.033]. No of parameters = 150, R1 = 0.024 for
ˇ
M. Hocek, D. Hocková, J. Stambaský, Collect. Czech. Chem.
Commun. 2003, 68, 837–848. For a general review on regiose-
lective cross-coupling reactions of dihaloheterocycles, see: f) S.
Schöter, C. Stock, T. Bach, Tetrahedron 2005, 61, 2245–2267.
[18] Krecˇmerová, M. Masojídková, A. Holý, Collect. Czech. Chem.
Commun. 2004, 69, 1889–1913.
2825 reflections [I Ͼ 2σ(I)), wR2 = 0.067 (all, 3025 refl), Δρmax
=
0.609 e·Å–3, Δρmin = –0.679 e·Å–3.
CCDC-265258 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[19] R. Marek, V. Sklenárˇ, Annu. Rep. NMR Spectrosc. 2004, 54,
201–242.
[20] N. VasilЈchenko, V. V. Mitkevich, A. A. Moiseenko, V. G. Kho-
menko, V. A. Chernov, J. Struct. Chem. 1982, 23, 257–263.
[21] a) T. Dahl, Acta Chem. Scand. B. 1987, 41, 379–382; b) M.
Kubicki, P. W. Codding, Acta Crystallogr., Sect. E: Struct. Rep.
Online 2001, 57, o332–o334.
Acknowledgments
[22] S. Wishart, C. G. Bigam, J. Yao, F. Abildgaard, H. J. Dyson,
E. Oldfield, J. L. Markley, B. D. Sykes, J. Biomol. NMR 1995,
6, 135–140.
[23] P. Coppens, Acta Crystallogr., Sect. A 1970, 26, 71–83.
[24] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr.
1994, 27, 435–436.
This work was supported by the “Centre for New Antivirals and
Antineoplastics” (1M6138896301) of the programme of Ministry
of Education, Youth and Sport of the Czech Republic and by Sum-
itomo Chemical Inc., Osaka, Japan. It is also a part of the Insti-
tute’s research project Z4 055 0506. The authors thank Dr. Ivan
Votruba for cytostatic activity screening.
[25] M. Sheldrick, SHELXL97, University of Göttingen, Germany,
1997.
[1] Y.-L. Lin, H.-P. Lee, J.-C. Ou, K.-H. Kuo, Heterocycles 1996,
43, 115–122.
Received: March 3, 2005
Published Online: June 2, 2005
3030
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3026–3030