The first total synthesis of heteromine B, and an improved synthesis of heteromine A; natural products with antitumor activities

Article abstract of DOI:10.1016/j.tet.2009.04.100

Efficient total syntheses of heteromines A and B (antitumor compounds previously isolated from the plant Heterostemma brownii Hayata) from commercially available 2-amino-6-chloropurine have been developed. The synthesis of heteromine A is considerably sho

Full text of DOI:10.1016/j.tet.2009.04.100

Tetrahedron 65 (2009) 5199–5203
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Tetrahedron
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The first total synthesis of heteromine B, and an improved synthesis
of heteromine A; natural products with antitumor activities
,
Heidi Roggen a, Colin Charnock b, Lise-Lotte Gundersen a
*
a Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway
b Faculty of Health Sciences, Oslo University College, P.O. Box 4, St. Olavs Plass, N-0130 Oslo, Norway
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient total syntheses of heteromines A and B (antitumor compounds previously isolated from the
plant Heterostemma brownii Hayata) from commercially available 2-amino-6-chloropurine have been
developed. The synthesis of heteromine A is considerably shorter than the previously reported synthesis,
only requiring four steps, whereas the iodide salt of heteromine B was prepared in five steps. Hetero-
mines A and B showed no significant antibacterial activity and therefore appear to be selective toward
cancer cell lines.
Received 27 February 2009
Received in revised form 14 April 2009
Accepted 30 April 2009
Available online 8 May 2009
Keywords:
Heteromine
Ó 2009 Elsevier Ltd. All rights reserved.
Purine
Reductive alkylation
N-methylation
Antitumor compounds
1. Introduction
The previously published synthesis of heteromine A (1a) in-
volves five or six steps, the five-step synthesis involves the use of
Heteromines A–H (1a–h, Fig. 1) have been isolated from Heter-
ostemma brownii Hayata (Asclepiadaceae),1,2 a plant used for the
treatment of tumors in Taipei folk medicine. Heteromines A and B
are shown to be cytotoxic to several cancer cell lines.2
highly toxic methyl chloride, from the malononitrile 2 (Scheme 1).3
We have synthesized heteromine C (1c) in four steps from the
commercially available purine 3.4 No total synthesis of heteromine
B has been described until now. Heteromines F, G, and H have been
prepared from heteromines A, B, and C, respectively, isolated from
the plant.2
As a continuation of our synthetic studies directed toward bio-
active purine natural products,4–11 we herein report the first total
synthesis of heteromine B, an improved synthesis of heteromine A
as well as an evaluation of antimicrobial activities of heteromines
A–C.
2. Results and discussion
We have previously developed an efficient synthesis of hetero-
mine C from 2-amino-6-chloropurine (3) (Scheme 1),4 and we now
wanted to explore the possibility of synthesizing heteromines A
Figure 1. Structures of heteromines A–H.
* Corresponding author. Tel.: þ47 22857019; fax: þ47 22855507.
E-mail address: l.l.gundersen@kjemi.uio.no (L.-L. Gundersen).
Scheme 1. Previously reported total syntheses of heteromines A and C.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.04.100

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H. Roggen et al. / Tetrahedron 65 (2009) 5199–5203
Scheme 2. (a) MeI, NaH, TBAB, THF; (b) NaOMe, MeOH,
D, see Ref. 3; (c) MeI, acetone, see Ref. 3; (d) HCHO, NaCNBH3, AcOH, MeOH, H2O.
and B from the same starting material using a similar strategy. The
most efficient route to heteromine A (as iodide, 6) was found to be
a one-step trimethylation of the 2-aminopurine 3 with methyl io-
dide in the presence of tributylammonium bromide (TBAB) and
NaH (Scheme 2) to give 57% of 4, followed by further synthetic
transformations according to the previously reported heteromine A
synthesis.3 The N-7-methylated isomer of 4 was isolated in 17%
yield as a by-product in the synthesis of 4. Alternatively, compound
5 was available by reductive amination of formaldehyde employing
2-aminopurine 7 (see also Table 1 below). The latter can be pre-
pared by N-9 methylation of purine 3 followed by nucleophilic
displacement of the chlorine,4 or the substituents may be in-
troduced in reverse order.12,13 Attempts to trimethylate 2-amino-6-
methoxypurine12 with methyl iodide in the presence of TBAB
resulted only in complex mixtures.
Our first strategy for the synthesis of heteromine B involved at-
tempts to monomethylate the amino group in compound 84
employing the same set of reaction conditions used in trimethylation
of compound 3 (Scheme 3) only witha reduced amountofall reagents
[MeI (1.1 equiv), NaH (1.2 equiv), TBAB (1.2 equiv)], but compound 4
was the only isolated product, in 24% yield. Reduction in temperature
or reaction time, or a combination of the two, gave either the same
product or no conversion of starting material. Alkylation of 8 by the
Mitsunobu reaction, usingtriphenylphosphine, diethylazodicarboxy-
late (DEAD), and methanol was also unsuccessful.
Scheme 3. (a) RCHO, NaCNBH3, AcOH, 50 ꢀC, for further details see Table 1.
made to adjust the reaction conditions in the reductive alkylation of
7 to obtain the monomethylated product 9, instead of the dime-
thylated compound 5. We found the aminopurines to be essentially
unreactive toward formaldehyde unless acetic acid (AcOH) was
present, and that using only a small excess of AcOH (1.3 equiv),
resulted in a rather complex mixture. In addition to 5, compound 13
was the only compound isolated from the mixture. The latter com-
pound is probably formed by nucleophilic attack by methanol on an
iminium ion intermediate in the reductive alkylation. Similar re-
actions are known in the literature.16 Interestingly, acetaldehyde
gave a mixture of the monoethylated and diethylated purines 10 and
12, with the former as the major product and without complete
conversion, under the same set of reaction conditions. Removal of
methanol as a solvent in the reaction with formaldehyde, resulted in
the formation of 5 and a range of by-products. No reaction was ob-
served when the hydride reagent was changed to NaBH4. The highest
isolated yield of 5 was achieved using 35 equiv of formaldehyde. The
amount could be reduced to 12 equiv, but still only the dimethylated
product was observed. Lowering the reaction time to only 1.25 or 3 h
showed full conversion by 1H NMR spectroscopy of the crude, but
only 62 and 81% yield of 5 was isolated. Employing the latter reaction
Next, we turned to reductive amination using purines 7 and 8
(Scheme 3 and Table 1). Guanosine derivatives have been mono-
alkylated on N2 when reacted with the desired aldehyde and
NaCNBH3.14 However, dimethylation has been achieved when the
aldehyde employed was formaldehyde.15 Several attempts were
Table 1
Reductive alkylation of 2-aminopurines 7 and 8
X
R (equiv HCHO or MeCHO)
Equiv AcOH
Equiv NaCNBH3
Time (h)
Solventa
Yield (%) 9–11
Yield (%) 4, 5 or 12
Yield (%) 13
Cl
Me (35)
Me (35)
Me (35)
Me (12)
Me (35)
Me (12)
Me (12)
Me (12)
Me (12)
Et (35)
1.6
1.3
1.3
2.4
23
23
23
23
23
1.3
23
6.0
6.3
6.0
6.3
6.3
6.3
6.3f
6.3
6.3
6.3
6.3
71
69
70
70
70
70
70
1.25
3
MeOH/H2O
MeOH/H2O
H2O
db
db
db
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
dc
dc
37 (13)
dc
dc
dc
MeOH/H2O
MeOH/H2O
MeOH/H2O
MeOH/H2O
MeOH/H2O
MeOH/H2O
MeOH/H2O
MeOH/H2O
<12 (9)
dc
45 (5)
97d (5)
92 (5)
dc
62d (5)
81 (5)
<10 (12)
51d,e (12)
4 (13)
dc
dc
dc
dc
dc
dc
dc
dc
dc
70
3
ca. 55 (10)
49d,e (10)
dc
Et (12)
dc
a
MeOH/H2O was used in a ratio of 3:2.
b
c
d
e
f
A complex mixture was formed, no products were identified.
Not observed.
From 1H NMR.
Isolated yields were 11% of 10 and 19% of 12.
NaBH4 used instead of NaCNBH3.

H. Roggen et al. / Tetrahedron 65 (2009) 5199–5203
5201
Scheme 4. (a) PhCOCl, pyridine; (b) K2CO3, MeI, acetone; (c) NaOMe, MeOH; (d) MeI, acetone.
conditions only using acetaldehyde, resulted in equivalent amounts
of monoalkylated and dialkylated products. Attempts to employ 2-
amino-6-methoxypurine6 or the 2-aminopurine 3 in reductive
aminations, resulted only in complex mixtures.
125 or 75 MHz using the instruments mentioned above. Assign-
ments of 1H and 13C resonances are inferred from 1D 1H NMR, 1D
13C NMR, as well as relevant 2D NMR spectral data. Mass spectra
under electron impact conditions were recorded with a VG Prospec
instrument at 70 eV ionizing voltage, and are presented as m/z (%
rel int.). Electrospray MS spectra were recorded with a Micromass
Q-Tof-2 mass spectrometer. Elemental analyses were carried out at
the Centre for Chemical and Biochemical Analysis, School of
Chemistry, University of Birmingham, UK. Melting points were
determined with a Bu¨chi Melting Point B-545 apparatus and are
uncorrected. THF was purified by a solvent purification system, MB
SPS-800 from MBraun. Pyridine was distilled from CaH2 and stored
over molecular sieves (4 Å). Acetone was distilled from potassium
carbonate and stored over molecular sieves (4 Å). Methanol used as
solvent in reactions was distilled from Mg and stored over molec-
ular sieves (4 Å). Silica gel for flash chromatography was purchased
from Merck, Darmstadt, Germany (Merck No. 09385) and flash
chromatography were performed manually or with an Isco Inc.
CombiFlash Companion instrument. Compounds available by lit-
erature methods: 5,3 6,3 7,4,21 and 8.21 All other reagents were
commercially available and used as received. Antimicrobial activi-
ties were determined as described before.7
Since none of the 2-methylaminopurines 9 or 11 were available
by direct monomethylation, the N2 amino function was protected by
a benzoyl group before methylation to give compound 15 (Scheme
4). Introduction of the methoxy group and removal of the protecting
group was achieved in one step, by treatment with sodium meth-
oxide. Compound 9 was finally reacted with methyl iodide to give
the iodide salt of heteromine B (16). Since heteromines F (1f) and G
(1g) earlier have been synthesized from heteromines A and B iso-
lated from plant material,2 the work described herein may also be
regarded as a formal synthesis of heteromines F and G.
Heteromines A and B are reported to show cytotoxicity toward
cancer cell lines; esophageal carcinoma, hepatoma, lymphoma, and
leukemia cells.2 Agelasines (cationic purinium salts isolated from
marine sponges) and derivatives often display cytotoxicity both
toward cancer cells and microorganisms.6,7,9,11,17–19 Hence we also
evaluated iodide salts of heteromines A–B, as well as the previously
synthesized heteromine C,4 as antimicrobial compounds. As also
argued in a study of heteromine analogs, the identity of the counter
ion is not expected to influence bioactivity since chloride anions
will be present in a large excess in the bioassays used.20 However
the cytotoxicity displayed by these compounds appears to be se-
lective toward cancer cell lines, with none of the heteromines ex-
amined exhibiting any significant inhibitory activity against
a variety of microorganisms [MIC Staphylococcus aureus (Gram
positive bacterium) and Escherichia coli (Gram negative bacterium)
4.1.1. 6-Chloro-N,N,9-trimethyl-9H-purin-2-amine (4)
2-Amino-6-chloropurine 3 (0.848 g, 5.00 mmol) in dry THF
(50 mL) was cooled to 0 ꢀC under an argon atmosphere and NaH
(0.86 g, 36 mmol) was added. The cooling bath was removed, TBAB
(5.80 g, 18.0 mmol) followed by methyl iodide (1.1 mL, 18 mmol)
was added at ambient temperature, and the resulting reaction
mixture stirred for 21 h and filtered. The filtrate was evaporated in
vacuo and the residue was purified twice by flash chromatography
(CombiFlash, 0–5% MeOH in CH2Cl2) to give 4 (0.604 g, 2.85 mmol)
in 57% yield and 6-chloro-N,N,7-trimethyl-7H-purin-2-amine
(0.179 g, 0.846 mmol) in 17% yield, both as colorless solids.
Compound 4. Mp 151.1–151.4 ꢀC (from MeOH–CH2Cl2), (lit. 152–
>32 mg/mL, MIC Candida albicans (yeast) >16 mg/mL, 0% inhibition
of Mycobacterium tuberculosis (mycobacterium) at 6.25 mg/mL].
3. Conclusion
We have shown the first total synthesis of the iodide salt of
heteromine B, in five steps from commercially available 2-amino-6-
chloropurine (3). All steps were completed in good to very good
yields. Direct trimethylation of 2-amino-6-chloropurine (3) greatly
improved the synthesis of heteromine A. Reductive alkylation of 2-
amino-6-methoxy-9-methyl-9H-purine (7) resulted in dimethyla-
tion of the amino group and thus opens up an alternative pathway
to heteromine A. Heteromines A and B are previously reported to be
active against cancer cell lines and were now evaluated as anti-
microbials. Neither of the two displayed any significant growth
inhibition of the different microorganisms examined, and therefore
appear to display a selective activity against (certain) cancer cell
lines. The narrow spectrum of toxicity and the efficient syntheses
reported herein, makes heteromines A and B more interesting as
potential anticancer drugs or drug leads.
153 ꢀC).3 1H NMR (300 MHz, DMSO-d6)
(s, 3H, N9CH3), 8.07 (s,1H, H-8); 13C NMR (75 MHz, DMSO-d6)
d
3.11 [s, 6H, N(CH3)2], 3.63
29.3
d
(N9CH3), 37.1 [N(CH3)2], 122.5 (C-5), 144.0 (C-8), 148.8 (C-6), 154.2
(C-4), 158.3 (C-2); MS EI m/z (rel %) 213/211 (Mþ, 33/100), 198/196
(18/50), 184/182 (15/45), 170/168 (7/20), 133 (31); HRMS (EI) calcd
for C8H10ClN5 211.0625, found 211.0632. More spectral data can be
found in Ref. 3.
4.1.2. 6-Chloro-N,N,7-trimethyl-7H-purin-2-amine
Mp 172–173 ꢀC (from MeOH–CH2Cl2, decomp.). 1H NMR
(300 MHz, DMSO-d6)
d
3.09 [s, 6H, N(CH3)2], 3.90 (s, 3H, NCH3), 8.31
33.5 (NCH3), 37.2
(s, 1H, H-8); 13C NMR (75 MHz, DMSO-d6)
d
[N(CH3)2], 115.1 (C-5), 142.3 (C-6), 150.0 (C-8), 158.7 (C-2), 163.9 (C-
4); MS EI m/z (rel %) 213/211 (Mþ, 32/100), 198/196 (20/62), 184/182
(23/70), 170/168 (10/28), 133 (25); HRMS (EI) calcd for C8H10ClN5
211.0625, found 211.0621.
4. Experimental
4.1. General
4.1.3. 6-Methoxy-N,9-dimethyl-9H-purin-2-amine (9)
Sodium methoxide (0.95 M, 4.0 mL, 3.8 mmol) in methanol was
added to N-(6-chloro-9-methyl-9H-purin-2-yl)-N-methylbenzamide
14 (0.227 g, 0.752 mmol) and the resulting mixture was stirred at
ambient temperature under an argon atmosphere for 22 h. The
1H NMR spectra were recorded at 500 MHz with a Bruker
Avance DRX 500 instrument or at 300 MHz with a Bruker Avance
DPX 300 instrument. Decoupled 13C NMR spectra were recorded at

5202
H. Roggen et al. / Tetrahedron 65 (2009) 5199–5203
reaction was quenched by addition of ammonium chloride (0.041 g,
0.77 mmol) and water (ca. 2 mL) and evaporated in vacuo. The residue
was purified by flash chromatography (CombiFlash, 40 g column, 0–5%
MeOH in CH2Cl2) to give 9 (0.134 g, 0.695 mmol) in 92% yield as
a colorless solid. Mp 173.6–175.6 ꢀC (from MeOH–CH2Cl2). 1H NMR
1.66 mmol) in pyridine (13.4 mL) at 0 ꢀC, and the resulting mixture
was stirred at ambient temperature under an argon atmosphere for
2.5 h. The solution was evaporated in vacuo and the residue was
purified by column flash chromatography (3ꢁ12 cm column, 3%
MeOH in CH2Cl2) to give 14 (0.314 g, 1.09 mmol) in 66% yield as
a colorless solid. Mp 213.7–215.1 ꢀC (from MeOH–CH2Cl2, decomp.).
(300 MHz, CD2Cl2)
d
3.01 (d, J¼5.1 Hz, 3H, N2CH3), 3.66 (s, 3H, N9CH3),
4.05 (s, 3H, OCH3), 5.03 (br s, 1H, NH), 7.50 (s, 1H, H-8); 13C NMR
1H NMR (300 MHz, CD2Cl2)
7.57–7.60 (m, 1H, Ph), 7.93 (m, 2H, Ph), 8.01 (s, 1H, H-8), 8.88 (s, 1H,
NH); 13C NMR (75 MHz, CD2Cl2)
d 3.85 (s, 3H, CH3), 7.49–7.54 (m, 2H, Ph),
(75 MHz, CD2Cl2) d
28.9 (N2CH3), 29.6 (N9CH3), 53.8 (OCH3), 115.0 (C-
5),139.7 (C-8),155.0 (C-4),160.3 (C-2),161.5 (C-6); MS EI m/z (rel %) 193
(Mþ, 100), 164 (28), 149 (28); HRMS (EI) calcd for C8H11N5O 193.0964,
found 193.0958. Anal. Calcd C, 49.73; H, 5.74; N, 36.25. Found C, 49.65;
H, 5.65; N, 36.18%.
d
30.5 (CH3), 127.8 (2ꢁCH in Ph),
128.7 (C-5), 129.1 (2ꢁCH in Ph), 132.7 (Ph), 134.6 (Ph), 146.0 (C-8),
150.9 (C-2 or C-6),152.5 (C-2 or C-6),153.7 (C-4),164.8 (C]O); MS EI
m/z (rel %) 289/287 (Mþ, 8/23), 260/258 (12/29), 105 (100), 77 (49);
HRMS (EI) calcd for C13H10ClN5O 287.0574, found 287.0577. Anal.
Calcd C, 54.27; H, 3.50; N, 24.34. Found C, 54.08; H, 3.30; N, 24.01%.
4.1.4. N-Ethyl-6-methoxy-9-methyl-9H-purin-2-amine (10) and
N,N-diethyl-6-methoxy-9-methyl-9H-purin-2-amine (12)
Methanol (3 mL), water (2 mL), formaldehyde (0.34 mL,
6.0 mmol), and NaBH3CN (0.20 g, 3.2 mmol) were added to 6-
methoxy-9-methyl-9H-purin-2-amine 7 (0.091 g, 0.51 mmol) and
the resulting reaction mixture was stirred at ambient temperature
for ca. 3 min. Glacial acetic acid (0.67 mL, 12 mmol) was added and
the reaction mixture was stirred at 50 ꢀC in a sealed container for
3 h. The solvents were evaporated in vacuo and the crude product
was purified twice by flash chromatography (CombiFlash, 0–6%
MeOH in CH2Cl2) to give 10 (0.012 g, 0.058 mmol) in 11% yield and
12 (0.023 g, 0.098 mmol) in 19% yield, both as colorless solids.
Compound 10. Mp 129.9–131.2 ꢀC (MeOH–CH2Cl2). 1H NMR
4.1.7. N-(6-Chloro-9-methyl-9H-purin-2-yl)-N-methyl
benzamide (15)
K2CO3 (0.282 g, 2.04 mmol) and methyl iodide (0.60 mL,
9.6 mmol) were added to N-(6-chloro-9-methyl-9H-purin-2-
yl)benzamide 14 (0.279 g, 0.970 mmol) in acetone (24 mL), and the
resulting mixture was stirred at ambient temperature under an
argon atmosphere for 21 h. The reaction mixture was evaporated in
vacuo and the resulting residue was purified by flash chromatog-
raphy to give 15 (0.254 g, 0.842 mmol) in 87% yield as a yellow
solid. Mp 119.3–120.8 ꢀC (from MeOH–CH2Cl2, decomp.). 1H NMR
(300 MHz, CD2Cl2)
d
3.46 (s, 3H, N9CH3), 3.67 (s, 3H, N2CH3), 7.19–
29.9
(300 MHz, DMSO-d6)
CH2), 3.59 (s, 3H, NCH3), 3.95 (s, 3H, OCH3), 6.86 (t, J¼5.4 Hz, 1H,
NH), 7.79 (s,1H, H-8); 13C NMR (75 MHz, DMSO-d6)
14.7 (CH2CH3),
d
1.13 (t, J¼7.1 Hz, 3H, CH2CH3), 3.31 (m, 2H,
7.34 (m, 5H, Ph), 7.92 (s, 1H, H-8); 13C NMR (75 MHz, CD2Cl2)
d
(N9CH3), 35.1 (N2CH3), 128.0 (2ꢁCH in Ph), 128.2 (2ꢁCH in Ph),
128.4 (C-5), 130.2 (Ph), 138.0 (Ph), 146.2 (C-8), 150.2 (C-6), 152.9 (C-
4), 156.7 (C-2), 172.5 (C]O); MS EI m/z (rel %) 303/301 (Mþ, 14/40),
274/272 (11/29), 105 (100), 77 (57); HRMS (EI) calcd for
C14H12ClN5O 301.0730, found 301.0735. Anal. Calcd C, 57.73; H,
4.01; N, 23.21. Found C, 57.34; H, 3.65; N, 23.26%.
d
29.1 (NCH3), 35.8 (CH2), 52.9 (OCH3), 113.4 (C-5), 140.1 (C-8), ca. 152
(br, C-4), 158.7 (C-2), 160.4 (C-6); MS EI m/z (rel %) 207 (Mþ, 89), 192
(100), 164 (25), 163 (27), 149 (25); HRMS (EI) calcd for C9H13N5O
207.1120, found 207.1115.
Compound 12. Mp 89.8–91.0 ꢀC (from MeOH–CH2Cl2). 1H NMR
(300 MHz, DMSO-d6)
NCH3), 3.61 (q, J¼7.0 Hz, 4H, 2ꢁCH2), 3.97 (s, 3H, OCH3), 7.81 (s, 1H,
H-8); 13C NMR (75 MHz, DMSO-d6)
41.6 (2ꢁCH2), 52.8 (OCH3), 112.9 (C-5), 140.3 (C-8), 154.6 (C-4), 157.2
(C-2), 160.0 (C-6); MS EI m/z (rel %) 235 (Mþ, 78), 220 (100), 206
(66), 192 (150); HRMS (EI) calcd for C11H17N5O 235.1433, found
235.1433. Anal. Calcd C, 56.15; H, 7.28; N, 29.77. Found C, 56.33; H,
7.29; N, 29.78%.
d
1.15 (t, J¼7.0 Hz, 6H, 2ꢁCH2CH3), 3.59 (s, 3H,
4.1.8. 6-Methoxy-7,9-dimethyl-2-(methylamino)-9H-purin-7-ium
iodide (16)
d
13.1 (2ꢁCH2CH3), 29.0 (NCH3),
Methyl iodide (0.64 mL,10 mmol) was added to 6-methoxy-N,9-
dimethyl-9H-purin-2-amine 9 (0.142 g, 0.735 mmol) in acetone
(5.5 mL) and the resulting mixture was stirred at ambient tem-
perature under an argon atmosphere for four days and filtered. The
solid was washed with acetone (5 mL) and dried in vacuo to give 1b
(0.178 g, 0.531 mmol) in 78% as a pinkish solid. Mp 293–294 ꢀC
(decomp.) 1H NMR (500 MHz, DMSO-d6, 50 ꢀC)
d
2.87 (d, J¼4.8 Hz,
4.1.5. 6-Methoxy-N-(methoxymethyl)-9-methyl-9H-
purin-2-amine (13)
NaBH3CN (0.105 g, 1.67 mmol), aq formaldehyde (36%, 0.75 mL,
9.7 mmol), methanol (1.5 mL), water (1.0 mL), and finally glacial
acetic acid (0.02 mL, 0.4 mmol) were added to 2-amino-6-
3H, NHCH3), 3.78 (s, 3H, N9CH3), 4.00 (s, 3H, N7CH3), 4.08 (s, 3H,
OCH3), 7.65 (br d, J¼4.8 Hz, 1H, NH), 9.32 (s, 1H, H-8); 13C NMR
(125 MHz, DMSO-d6, 50 ꢀC) 27.8 (NHCH3), 30.7 (N9CH3), 35.7
d
(N7CH3), 54.3 (OCH3), 104.5 (C-5), 139.9 (C-8), 151.7 (C-4), 157.8 (C-
6), 160.6 (C-2); MS ESI m/z (rel %) 208 (Mþ, 100%); HRMS (ESI) calcd
for C9H14N5O 208.1198, found 208.1199. Anal. Calcd C, 32.25; H,
4.21; N, 20.90. Found C, 32.66; H, 3.97; N, 20.57%. More spectral
data (of the chloride salt) can be found in Ref. 1.
methoxy-9-methyl-9H-purine
7 (0.050 g, 0.28 mmol) and the
resulting mixture was stirred at 50 ꢀC in a sealed container for three
days. The reaction mixture was allowed to cool to ambient tem-
perature and the solvents were evaporated in vacuo. The residue
was purified by manual flash chromatography (3ꢁ12 cm column,
2–10% MeOH in CH2Cl2) to give 13 (0.029 g, ca. 80% purity) as an off-
Acknowledgements
white wax. 1H NMR (300 MHz, DMSO-d6)
d 3.22 (s, 3H, CH3,
The Norwegian Research Council is greatly acknowledged for
a scholarship to H.R. (grant 171323/V30), and for financing of the
Bruker Avance instruments used in this study. Antimycobacterial
data were provided by the Tuberculosis Antimicrobial Acquisition
and Coordinating Facility (TAACF) through a research and de-
velopment contract with the U.S. National Institute of Allergy and
Infectious Diseases.
CH2OCH3), 3.61 (s, 3H, NCH3), 3.98 (s, 3H, O6CH3), 4.76 (d, J¼7.0 Hz,
2H, CH2), 7.79 (t, J¼7.0 Hz, 1H, NH), 7.87 (s, 1H, H-8); 13C NMR
(75 MHz, DMSO-d6)
d
29.0 (NCH3), 53.2 (O6CH3), 54.7 (CH2OCH3),
73.5 (CH2), 114.4 (C-5), 141.0 (C-8), 154.2 (C-4), 158.2 (C-2), 160.5 (C-
6); MS EI m/z (rel %) 223 (Mþ, 54), 208 (100), 192 (100), 191 (77), 180
(48), 164 (82), 163 (53), 149 (75); HRMS (EI) calcd for C9H13N5O2
223.1069, found 223.1072.
References and notes
4.1.6. N-(6-Chloro-9-methyl-9H-purin-2-yl)benzamide (14)
Distilled benzoyl chloride (0.39 mL, 3.3 mmol) was added to
a suspension of 2-amino-6-chloro-9-methyl-9H-purine 8 (0.305 g,
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