Effect of substituent structure on pyrimidine electrophilic substitution: A rebuttal

Article abstract of DOI:10.1016/j.tet.2012.01.044

The report about a series of unexpected and obscure effects influencing the electrophilic nitrosation of activated pyrimidines (Tetrahedron 2007, 63, 5394) was shown to be erroneous. Instead of electrophilic substitution at position 5 of the pyrimidine ring, N-nitrosation of the secondary amino group in the 4-position of the pyrimidine ring took place. Moreover it was shown that the synthetic sequence for the preparation of purines is also incorrect.

Full text of DOI:10.1016/j.tet.2012.01.044

Tetrahedron 68 (2012) 2294e2298
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Effect of substituent structure on pyrimidine electrophilic substitution: a rebuttal
ꢀ
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Virginija Jakubkiene, Inga Cikotiene
Department of Organic Chemistry, Faculty of Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania
a r t i c l e i n f o
a b s t r a c t
Article history:
The report about a series of unexpected and obscure effects influencing the electrophilic nitrosation of
activated pyrimidines (Tetrahedron 2007, 63, 5394) was shown to be erroneous. Instead of electrophilic
substitution at position 5 of the pyrimidine ring, N-nitrosation of the secondary amino group in the 4-
position of the pyrimidine ring took place. Moreover it was shown that the synthetic sequence for the
preparation of purines is also incorrect.
Received 11 November 2011
Received in revised form 22 December 2011
Accepted 16 January 2012
Available online 21 January 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Pyrimidine
Nitrosation
Alkyl substituted
Aryl substituted
Denitrosation
1. Introduction
N-substituted-6-chloropyrimidin-4-amines with explanation of
a
series of unexpected and obscure effects influencing the
For a long time, 5-nitrosopyrimidines remain important in-
termediates in the synthesis of diverse pyrimidine containing
heterocycles.1 It is also known that 5-nitrosopyrimidines have
unique crystal structures2 and they can act as bidentate ligands for
coordination of metal ions.3 Various alkoxy- and amino-substituted
5-nitrosopyrimidines are important as potential inhibitors of the
human DNA-repair protein O6-alkylguanine-DNA-transferase.4
Moreover it was found that 5-nitrosopyrimidine derivative
NU6027 acts as both a CDK1 and a CDK2 inhibitor with Ki values of
electrophilic substitution reactions. The results reported by the
authors in this paper were interesting as well as unusual to us.
According to the procedures reported in this paper, various
5-nitrosopyrimidines were prepared and used in the synthesis of
purines by the sequence presented in Scheme 1. As continuation of
our ongoing program aimed at the synthesis of 5-
nitrosopyrimidines with notable antitumor activity,7 we tried to
apply van der Westhuyzen’s method in our work and found that
direct nitrosation at position 5 of the pyrimidine ring is impossible.
Herein we report the results of our investigations.
2.5 and 1.3
inhibitory activity against human tumor cells with mean GI50 value
of 10
M.6 Recently, we discovered a series of N4,N6-disubstituted-
m
M, respectively.5 In addition, NU6027 showed growth
m
5-nitrosopyrimidine-4,6-diamines and some of them caused sig-
nificant growth inhibition in solid human cancer cell lines with GI50
values in the range 3.1e7.2 m
M.7
It is well known, that synthetically and biologically important 5-
nitrosopyrimidines can be prepared by the direct nitrosation re-
action of pyrimidines, bearing at least three electron-donating
groups in the 2, 4 and 6-positions.5a,6,8 On the other hand, N4,N6-
disubstituted-5-nitrosopyrimidine-4,6-diamines can be prepared
via intramolecular oxidation-reduction reaction of N-(5-
nitropyrimidin-4-yl)glycinates discovered by us recently.9 In 2007
a paper entitled ‘Effect of substituent structure on pyrimidine
electrophilic substitution’ by van der Westhuyzen et al. was pub-
lished.10 The paper dealt with direct nitrosation of several
Scheme 1. Synthesis of N,6-disubstituted-5-nitrosopyrimidin-4-amines and their
* Corresponding author. Tel.: þ370 5 219 31 95; fax: þ370 5 233 09 87; e-mail
utility for preparation of purines, proposed by van der Westhuyzen et al.10
ꢀ
_
address: inga.cikotiene@chf.vu.lt (I. Cikotiene).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.01.044

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2295
2. Results and discussions
other hand, the starting pyrimidines 2c,d were completely
unreactive toward nitrosation conditions.
First of all, we prepared the starting materials 2aed by the re-
action of commercially available 4,6-dichloropyrimidine (1) with
an excess of methylamine (for compd 2a), benzylamine (for compd
2b), pyrrolidine (for comps 2c) or morpholine (for compd 2d) in
boiling 2-propanol. After the nitrosation reaction of 2a,b under the
van der Westhuyzen conditions we obtained yellow solids 3a and
3b in good yields, as it was stated in their manuscript.10 However,
the color of the obtained products was not common for 5-
nitrosopyrimidines (normally, solutions of 5-nitrosopyrimidines
are of deep green or deep blue colors). In the IR spectra of com-
pounds 3a,b there were no NH absorption bands. The 1H NMR
spectra showed the presence of two sharp singlets (non-ex-
changeable with D2O) at 8.06e8.11 and 8.86e8.94 ppm, re-
spectively. Moreover, protons of methyl and methylene groups
were uncoupled to NH protons, and appeared as singlets at 3.46
and 5.38 ppm, respectively. In the 13C NMR spectra of compounds
3a,b there were signals at 107.6e107.9 ppm, which cannot be
assigned to the C-5 of 5-nitrosopyrimidines, as stated by van der
Westhuyzen et al.10 (normally, C-(5) in 5-nitrosopyrimidines ap-
pear at lower fields, approx. at 140 ppm5a,6,8). And finally, in the
HSQC spectra of 3a,b cross-peaks between signals at
8.06e8.11 ppm and 107.6e107.9 ppm appeared, which is not con-
sistent with the formation of 6-chloro-5-nitrosopyrimidines. These
data together with HRMS data indicated that under the reaction
conditions the N-nitrosation reaction took place. Inevitably, com-
pounds 2c,d without free NH functionality were unreactive toward
nitrosation conditions (Scheme 2).
Moreover, we tried to introduce a 5-nitrogen moiety into the
starting compounds 2a,b by direct nitration or coupling with 4-
chlorophenyldiazonium salt.13,14 Diazotization of 2a,b did not give
any satisfactory result: after the work-up of the reaction mixtures
the initial products were recovered together with small amounts of
N-nitrosated products 3a,b and 4-chlorophenol, which formed af-
ter decomposition of 4-chlorophenyldiazonium salt in water.
6-chloro-N-methylpyrimidin-4-amine 2a was unreactive toward
classical nitration conditions (mixture of concd H2SO4 and HNO3),
on the other hand N-benzyl-6-chloropyrimidin-4-amine 2b
underwent smooth nitration on the phenyl ring (mainly at fourth
position). These results showed that there is insufficient electron
donation in the starting compounds 2, so the heterocyclic ring is
not activated enough for electrophilic substitution.
Interestingly, the utility of the obtained nitrosation products 3 in
the synthesis of purine derivatives was shown in the same manu-
script.10 So a careful check of the procedures reported by van der
Westhuyzen et al. was carried out in our laboratory.
N-substituted-6-chloro-N-nitrosopyrimidin-4-amines 3a,b were
treated with secondary amines pyrrolidine and morpholine in
dichloromethane or in dimethylformamide at room temperature,
smoothly generating yellowish products 4aed (Scheme 3, Table 1).
The structures of all compounds 4aed were substantiated by their
spectroscopic data. In the 1H NMR spectra of 4aed a singlet at
8.49e8.61 ppm due to the resonance of C(2)eH along with a singlet
at 6.85e7.18 ppm for the C(5)eH and signals of substituents in po-
sition 6 of the pyrimidine ring were observed. Signals of CH3N and
PhCH2N moieties appeared as singlets at 3.43e3.44 ppm and
5.40e5.41 ppm, respectively. The absence of NH absorption bands in
the IR spectra of 4aed and the cross-peak between signals at
5.41 ppm and 87.71 ppm in the HSQC spectra of 4d together with
HRMS data confirmed the structures of nucleophilic displacement
reaction products 4. It should be noted that the spectroscopic data of
our synthesized compounds are in agreement with the published
herein,10 so we obtained exactly the same compounds as van der
Westhuyzen group.
Scheme 2. Nitrosation reaction of N-substituted-6-chloropyrimidin-4-amines.
The spectroscopic data of our synthesized compounds 3a,b and
compounds, synthesized by van der Westhuyzen et al. were the
same, so it is evident, that the authors wrongly elucidated struc-
tures of products 3.
It is well known that electrophilic aromatic substitution at C-5 of
the pyrimidine ring is often problematic. The reason for this be-
havior was identified in the presence of two nitrogen atoms in the
structure.11 An electrophilic reagent, or a proton in the reaction
medium, added preferentially to the pyridine nitrogen, generating
a pyridinium cation, which is naturally very resistant to a further
attack by an electrophile.12 Therefore, pyrimidines normally require
the presence of activating groups or harsh reactions conditions for
successful introduction of an electrophile.13 Nitrous acid cannot be
used under vigorous conditions, so that pyrimidine substrates for
nitrosation need at least two, but preferably three electron-
donating groups to assist the process.5a,6,8 Therefore, the N-nitro-
sation reaction of compounds 2a,b took place readily and on the
Scheme 3. Nucleophilic displacement reaction of N-substituted-6-chloro-N-nitroso
pyrimidin-4-amines.
In the light of our obtained results we became particularly in-
trigued by the Section 2.3 of the van der Westhuyzen’s et al.
manuscript10 dealing with reduction of 5-nitrosopyrimidines and
subsequent ring closure to the corresponding purines. Therefore
we performed the reduction of compounds 4a,b,d by van der
Westhuyzen’s conditions. Treating warm mixtures of compounds
4a,b,d in aqueous sulfuric acid with sodium dithionite afforded

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V. Jakubkiene, I. Cikotiene / Tetrahedron 68 (2012) 2294e2298
2296
Table 1
spectroscopic methods and by comparing the data with those of
authentic sample (9e). The IR spectrum of 6 showed strong ab-
sorption at 1683 cmꢀ1, which belongs to C]O bond. In the 1H NMR
spectrum, the signals corresponding to the C(2)eH, C(5)eH, and
PhCH2 protons appeared as singlets at 8.49, 6.66, and 5.18 ppm,
respectively. Besides the multiplets of aromatic protons at
7.23e7.32 ppm and morpholine ring at 3.75e3.79 and
3.57e3.61 ppm, there was a singlet of three protons at 2.25 ppm,
which can be attributed to CH3CO moiety. Interestingly, the latter
signal was not noticed in van der Westhuyzen manuscript. In the
13C NMR spectrum of 6 there were signals of 13 inequivalent car-
bons and the carbon of NCOMe group resonated at 171.4 ppm. The
cross-peaks in HSQC spectrum of 6 helped to assign all signals in
the 13C NMR spectrum to the corresponding carbons. And finally,
from HRMS we found the mass of molecular ion MþH equal to
313.1659 what is in agreement with molecular formula of 6.
N, 6-Disubstituted-N-nitrosopyrimidin-4-amines 4aed produced via Scheme 3
Starting
comp.
Amine
Product
Product number
in Tetrahedron
2007, 5394.
Yield %
3a
3b
3a
3b
HN(CH2)4
HN(CH2)4
HN(CH2)4O
HN(CH2)4O
4a
4b
4c
4d
4b
4d
n/s
4e
97
92
91
96
n/sdnot synthesized.
readily filterable solids 5aec. It should be noted, that the same
products 5aec were formed during heating mixtures of starting
compounds 4a,b,d in 10% sulfuric acid without addition of sodium
dithionite. The spectroscopic data of our synthesized compounds
and careful study of van der Westhuyzen’s spectroscopic data
showed that under these reaction conditions smooth and high-
yielding N-denitrosation reactions took place (Scheme 4, Table 2).
The IR spectra of 5aec exhibited absorption at 3209e3243 cmꢀ1
,
which can be attributed to the absorption of the NH bond. In the 1H
NMR spectra of 5aec a singlet at 8.11e8.12 ppm due to the reso-
nance of C(2)eH along with a singlet at 5.13e5.38 ppm for the
C(5)eH were observed. Signals of CH3NH and PhCH2NH moieties
appeared as doublets at 2.85 ppm and 4.42e4.43 ppm with cou-
pling constants 5.4e5.7 Hz, respectively. The van der Westhuyzen’s
and coauthors discussions about problems with compounds sta-
bility under the electrospray mass spectroscopic conditions do not
have any significance, because found masses are in good agreement
with masses of denitrosation products 5, and there is no need to
theorize about smooth fragmentation of molecular ion to MHþꢀNH
(Scheme 4).
Scheme 5. Acetylation of N-benzyl-6-morpholinopyrimidin-4-amine 5c.
Moreover, compound 5c did not undergo coupling with 4-
chlorophenyldiazonium salt and nitration of C-5 was also un-
successful. After the nitrosation reaction of 5c, N-nitrosated prod-
uct 4d formed.
It is known from the literature and also well-seen from our in-
vestigation that introduction of nitrogen containing functional
group at the 5-position of insufficiently activated pyrimidines is
hardly possible. It would be better to start the synthesis of 2-
unsubstituted purines from commercially available 4,6-dichloro-
5-nitropyrimidine by classical nucleophilic substitutiondreduction
of nitro groupdcyclization route.15
3. Conclusions
Scheme 4. Denitrosation reaction of N,6-disubstituted-N-nitrosopyrimidin-4-amines
4a,b,d.
In conclusion, since various 5-nitrosopyrimidines are versatile
intermediates in organic synthesis, have unique crystal structures
and posses notable biological activities; it was our duty to inform
the scientific community that direct electrophilic nitrosation re-
action of N-substituted-6-chloropyrimidin-4-amines is impossible.
Instead of electrophilic substitution reaction at the position 5 of the
pyrimidine ring, the N-nitrosation of secondary amino group in the
4-position of the pyrimidine ring took place. Moreover we have
shown that the synthetic sequence for preparation of purines
presented in Tetrahedron 2007, 63, 5394 by van der Westhuyzen is
erroneous.16
Table 2
Denitrosation of N,6-disubstituted-N-nitrosopyrimidin-4-amines 4a,b,d
Starting
comp.
R
NR1
Prod.
Prod. nr.
in Tetrahedron
2007, 5394.
Yield %
2
4a
4b
4d
CH3
PhCH2
PhCH2
N(CH2)4
N(CH2)4
N(CH2)4O
5a
5b
5c
8b
8d
8e
81
82
92
And finally, compound 5c was treated with an excess of acetic
anhydride and triethylformiate under reflux (Scheme 5). The for-
mation of N-benzyl-(6-morpholino-4-pyrimidinyl)acetamide
It may be emphasized that we have conducted all the experi-
ments several times precisely under the reported conditions and
found that our results as outlined above are consistently
reproducible.
6
took place readily. The product 6 was characterized by the usual

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4. Experimental section
4.1. General
(KBr): 2974 (CeH), 2866 (CeH), 1598 (C]N),1550, 1509,1475,1439,
1333, 1319, 1219, 1099, 1078, 1051, 1007, 900, 822, 749, 722,
703 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d
¼8.57 (1H, s, C(2)eH), 7.28
(5H, br s, ArH), 6.92 (1H, s, C(5)eH), 5.40 (2H, s, PhCH2), 3.70 (2H, br
IR spectra were run in KBr discs on a PerkineElmer FT spec-
trophotometer Spectrum BX II. 1H and 13C NMR spectra were
recorded with a Varian Unity INOVA spectrometer (300 MHz) using
residual solvents signals as internal standard. HRMS spectra were
obtained on a mass spectrometer Dual-ESI Q-TOF 6520 (Agilent
Technologies). All reactions and the purity of the synthesized
compounds monitored by TLC using Silica gel 60 F254 aluminum
plates (Merck). Visualization was accomplished by UV light.
s, NCH2), 3.41 (2H, br s, NCH2), 2.05 (4H, br s, (CH2)2). 13C NMR
(75 MHz, CDCl3):
d
¼161.2 (C(4) or C(6)), 159.7 (C(4) or C(6)), 158.1
(C(2)), 135.3 (quaternary aryl C), 128.7, 128.4, 127.7 (aryl C), 88.8
(C(5)), 46.9 ((NCH2)2), 43.9 (PhCH2), 25.4 ((CH2)2). HRMS (ES): MHþ,
found 284.1511. C15H18N5O requires 284.1512.
4.3.3. N-Methyl-6-morpholino-N-nitrosopyrimidin-4-amine
(4c). Yield 0.15 g; 91%; yellowish powder; mp 123e125 ꢁC. IR
(KBr): 2980 (CeH), 2877 (CeH), 1596 (C]N), 1550, 1491, 1464, 1447,
1254, 1200, 1176, 1120, 1108, 997, 976, 948, 865, 826, 728 cmꢀ1. 1H
4.2. General method for the N-nitrosation of pyrimidines
NMR (300 MHz, CDCl3):
3.76e3.79 (4H, m, O(CH2)2), 3.66e3.69 (4H, m, N(CH2)2), 3.43 (3H,
s, CH3). 13C NMR (75 MHz, CDCl3):
(C(4) or C(6)), 157.6 (C(2)), 87.8 (C(5)), 66.4 ((OCH2)2), 44.4,
((NCH2)2), 27.9 (CH3). HRMS (ES): MHþ, found 224.1109. C9H14N5O2
requires 224.1148.
d
¼8.52 (1H, s, C(2)eH), 7.11 (1H, s, C(5)eH),
A
solution of the corresponding 4-aminosubstituted-6-
chloropyrimidine (2a,b) in either acetic acid or hydrochloric acid
(2 M) was treated drop-wise with a solution of sodium nitrite
(1.8 equiv) in water (6.3 M). The reaction mixture was stirred at
room temperature for 2e3 h and a solid precipitate forms over time.
The solid is filtered off, washed with water, and dried under suction.
d¼162.9 (C(4) or C(6)), 160.7
4.3.4. N-Benzyl-6-morpholino-N-nitrosopyrimidin-4-amine
(4d). Yield 0.215 g; 96%; yellowish solid; mp 128e130 ꢁC. IR (KBr):
2868; (CeH), 1594 (C]N), 1549, 1494, 1472, 1445, 1338, 1113, 982,
4.2.1. 6-Chloro-N-methyl-N-nitrosopyrimidin-4-amine (3a). Yield
0.15 g; 88%; yellow powder; mp 78e79 ꢁC. IR (KBr): 3095 (CeH),
1568 (C]N), 1490, 1457, 1166, 1146, 1080, 959, 781 cmꢀ1. 1H NMR
903, 744, 696 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d
¼8.61 (1H, s, C(2)e
(300 MHz, CDCl3):
d
¼8.86 (1H, s, C(2)eH), 8.06 (1H, s, C(5)eH), 3.46
H), 7.29 (5H, br s, ArH), 7.18 (1H, s, C(5)eH), 5.41 (2H, s, PhCH2),
(3H, s, CH3). 13C NMR (75 MHz, CDCl3):
d
¼161.9 (C(4) or C(6)), 161.6
3.82e3.85 (4H, m, O(CH2)2), 3.71e3.74 (4H, m, N(CH2)2). 13C NMR
(C(4) or C(6)),158.1 (C(2)),107.6 (C(5)), 27.3 (CH3). HRMS (ES): MHþ,
found 173.0244. C5H365ClN4O requires 173.0230.
(75 MHz, CDCl3):
d
¼162.8 (C(4) or C(6)), 160.2 (C(4) or C(6)), 157.5
(C(2)), 134.6 (quaternary aryl C), 128.2, 127.9, 127.2 (aryl C), 87.7
(C(5)), 66.1 ((OCH2)2), 44.1, ((NCH2)2), 43.3 (PhCH2). HRMS (ES):
MHþ, found 300.1459. C15H18N5O2 requires 300.1461.
4.2.2. N-Benzyl-6-chloro-N-nitrosopyrimidin-4-amine
(3b). Yield
0.22 g; 89%; yellow solid; mp 55e57 ꢁC. IR (KBr): 3092 (CeH), 1568
(C]N),1568,1487,1459,1392,1128,1070,1059, 984, 927, 888, 777, 728,
4.4. General method for denitrosation of N,6-disubstituted-
N-nitrosopyrimidin-4-amines
711 cmꢀ1.1H NMR (300 MHz, CDCl3):
d
¼8.94 (1H, s, C(2)eH), 8.11 (1H,
s, C(5)eH), 7.28 (5H, br s, ArH), 5.38 (2H, s, CH2). 13C NMR (75 MHz,
CDCl3):
¼161.9 (C(4) or C(6)), 161.8 (C(4) or C(6)), 158.3 (C(2)), 133.9
(quaternaryaryl C),128.4,128.1,127.7 (aryl C),107.8(C(5)), 43.4.3 (CH2).
d
To the 3 mL of aqueous sulfuric acid (10%), the corresponding 6,-
N-disubstituted-N-nitrosopyrimidin-4-amine (4) was added. The
resulting mixture was stirred at 120 ꢁC for 5 min. After cooling to
room temperature, the pH of mixture was adjusted to >10 with 2 M
aqueous sodium hydroxide. The precipitated solid was filtered off
to give pure products 5aec. Addition amounts of product were
obtained by extraction of mother liquid with dichloromethane. It
should be noted that the same products were obtained during
treatment of reaction mixture with sodium dithionite, as stated in
original paper.10
35
HRMS (ES): MHþ, found 249.0581. C11
H ClN4O requires 249.0543.
10
4.3. General method for the preparation of N,6-disubstituted-
N-nitrosopyrimidin-4-amines (4aed)
Method A. A mixture of the corresponding 6-chloro-N-nitro-
sopyrimidin-4-amine (3a,b) in dichloromethane (2 M) was treated
drop-wise with 2.2 equiv of the corresponding amine. The mixture
was stirred for 18 h at room temperature. Then the resulting solution
was washed with water, dried over sodium sulfate, filtered, and
concentrated under the reduced pressure affording products 4aed.
Method B. A mixture of the corresponding 6-chloro-N-nitro-
sopyrimidin-4-amine (3a,b) in DMF (2 M) was treated drop-wise
with 2.2 equiv of the corresponding amine. The mixture was stirred
for 10 min at room temperature. After addition of water, precipitated
product was filtered, washed with water, and dried overnight.
4.4.1. N-Methyl-6-pyrrolidinopyrimidin-4-amine (5a). Yield 0.07 g;
81%; white solid; mp 190e192 ꢁC. IR (KBr): 3243 (NH), 3098 (CeH),
2976 (CeH), 2861 (CeH), 1592 (C]N), 1573, 1539, 1503, 1483, 1439,
1417, 1333, 1301, 1288, 1145, 1099, 973, 795 cmꢀ1 1H NMR
.
(300 MHz, CDCl3):
(1H, br s, NH), 3.44 (4H, br s, N(CH2)2), 2.85 (3H, d, J¼5.4 Hz,
NHCH3), 1.98 (4H, br s, (CH2)2). 13C NMR (75 MHz, CDCl3):
d
¼8.11 (1H, s, C(2)eH), 5.13 (1H, s, C(5)eH), 5.03
d
¼162.5
(C(4) or C(6)), 160.5 (C(4) or C(6)), 156.8 (C(2)), 79.4 (C(5)), 46.3
(NCH2)2, 28.5 (CH3), 25.3 ((CH2)2). HRMS (ES): MHþ, found
179.1294. C9H15N4 requires 179.1297.
4.3.1. N-Methyl-N-nitroso-6-pyrrolidinopyrimidin-4-amine
(4a). Yield 0.15 g; 97%; yellowish solid; mp 96e98 ꢁC. IR (KBr): 2973
(CeH), 2868 (CeH), 1598 (C]N), 1552, 1510, 1442, 1442, 1312, 1300,
1183,1153,1099,1021, 960, 819, 729 cmꢀ1.1H NMR (300 MHz, CDCl3):
4.4.2. N-Benzyl-6-pyrrolidinopyrimidin-4-amine (5b). Yield 0.105 g;
82%; white powder; mp 169e171 ꢁC. IR (KBr): 3209 (NH), 3071
(CeH), 2962 (CeH), 2858 (CeH), 1591 (C]N), 1530, 1502, 1482,
1444, 1353, 1337, 1279, 1222, 1104, 978, 796, 748, 697 cmꢀ1. 1H NMR
d
¼8.49 (1H, s, C(2)eH), 6.85 (1H, s, C(5)eH), 3.67 (2H, br s, NCH2),
3.44 (3H, s, CH3), 3.37 (2H, br s, NCH2), 2.02 (4H, br s, (CH2)2).13C NMR
(75 MHz, CDCl3):
d
¼160.6 (C(4) or C(6)), 159.6 (C(4) or C(6)), 157.6
(C(2)), 88.3 (C(5)), 46.7 ((NCH2)2), 27.9 (CH3), 25.2 ((CH2)2). HRMS
(300 MHz, CDCl3):
d
¼8.12 (1H, s, C(2)eH), 7.33 (5H, br s, ArH), 5.55
(ES): MHþ, found 208.1195. C9H14N5O requires 208.1199.
(1H, br s, NH), 5.15 (1H, s, C(5)eH), 5.42 (2H, br s, PhCH2), 3.36 (4H,
br s, N(CH2)2), 1.94 (4H, br s, (CH2)2). 13C NMR (75 MHz, CDCl3):
4.3.2. N-Benzyl-N-nitroso-6-pyrrolidinopyrimidin-4-amine
(4b). Yield 0.185 g; 92%; yellowish needles; mp 105e107 ꢁC. IR
d
¼161.9 (C(4) or C(6)), 160.5 (C(4) or C(6)), 157.2 (C(2)), 138.2
(quaternary aryl C), 128.6, 127.3, 127.2 (aryl C), 80.4 (C(5)), 46.2

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V. Jakubkiene, I. Cikotiene / Tetrahedron 68 (2012) 2294e2298
2298
(NCH2)2, 45.8 (PhCH2), 25.2 ((CH2)2). HRMS (ES): MHþ, found
References and notes
255.1607. C15H19N4 requires 255.1611.
1. (a) Cobo, J.; Nogueras, M.; Low, J. N.; Rodríguez, R. Tetrahedron Lett. 2008, 49,
7271; (b) Del Carmen Ruiz, M.; Vasella, A. Helv. Chim. Acta 2011, 94, 785; (c)
Steinlin, T.; Vasella, A. Helv. Chim. Acta 2009, 92, 588; (d) Xu, M.; Vasella, A. Helv.
Chim. Acta 2006, 89, 1140; (e) George, T. G.; Szolcsanyi, P.; Koenig, S. G.;
Paterson, D. E.; Isshiki, Y.; Vasella, A. Helv. Chim. Acta 2004, 87, 1287; (f) Murata,
S.; Kiguchi, K.; Sugimoto, T. Heterocycles 1993, 35, 639; (g) Soyka, R.; Pfleiderer,
W.; Prewo, R. Helv. Chim. Acta 1990, 73, 808; (h) Boyle, P. H.; Lockhart, R. J. J. Org.
Chem. 1985, 50, 5127; (i) Brown, D. J.; Lan, S.-B.; Mori, K. Aust. J. Chem. 1984, 37,
2093; (j) Rohm Pharma GmbH. U.S. Patent 4,252,809, 1981; (k) Marchal, A.;
4.4.3. N-Benzyl-6-morpholino-N-nitrosopyrimidin-4-amine
(5c). Yield 0.125 g; 92%; beige solid; mp 173e175 ꢁC. IR (KBr): 3218
(NH), 2993 (CeH), 2964 (CeH), 1587 (C]N), 1447, 1441, 1333, 1319,
1233, 1204, 1115, 1011, 978, 904, 803, 702 cmꢀ1. 1H NMR (300 MHz,
CDCl3):
d
¼8.12 (1H, s, C(2)eH), 7.32 (5H, br s, ArH), 5.54 (1H, br s,
NH), 5.38 (1H, s, C(5)eH), 4.44 (2H, d, J¼5.7 Hz, PhCH2), 3.71e3.74
ꢁ
Nogueras, M.; Sanchez, A.; Low, J. N.; Naesens, L.; De Clercq, E.; Melguizo, M.
Eur. J. Org. Chem. 2010, 3823.
(4H, m, O(CH2)2), 3.45e3.48 (4H, m, N(CH2)2). 13C NMR (75 MHz,
CDCl3):
d
¼163.0 (C(4) or C(6)), 162.9 (C(4) or C(6)), 157.4 (C(2)),
2. (a) Glidewell, C.; Low, J. N.; Marchal, A.; Melguizo, M.; Quesada, A. Acta Crys-
tallogr. 2002, C58, 655; (b) Low, J. N.; Quesada, A.; Marchal, A.; Nogueras, M.;
138.0 (quaternary aryl C),127.7,127.5,127.2 (aryl C), 80.8 (C(5)), 66.4
((OCH2)2), 45.7 (PhCH2), 44.3, (NCH2)2. HRMS (ES): MHþ, found
271.1558. C15H19N4O requires 271.15597.
ꢁ
Sanchez, A.; Glidewell, C. Acta Crystallogr. 2002, C58, 284; (c) Urbelis, G.;
Susvilo, I.; Tumkevicius, S. J. Mol. Model. 2007, 13, 219.
3. (a) Gaballa, A. S. Spectrochim. Acta, Part A 2010, 75, 146; (b) Lopez-Garzon, R.; Ar-
ranz-Mascaro, P.; Godino-Salido, M. L.; Gutierrez-Valero, M. D.; Cuesta, R.; Mor-
eno, J. M. Inorg. Chim. Acta 2003, 355, 41; (c) Lopez-Garzon, R.; Arranz-Mascaro, P.;
Godino-Salido, M. L.; Gutierrez-Valero, M. D.; Perez-Cadenas, A.; Cobo-Domingo,
J.; Moreno, J. M. Inorg. Chim. Acta 2000, 308, 59.
4.5. Preparation of N-benzyl-(6-morpholino-4-pyrimidinyl)-
acetamide 6
4. (a) Marchal, A.; Melguizo, M.; Nogueras, M.; Sanchez, A.; Low, J. N. Synlett 2002,
255; (b) Chae, M. Y.; McDougall, M. G.; Dolan, M. E.; Swenn, K.; Pegg, A. E.;
Moschel, R. C. J. Med. Chem. 1995, 38, 359.
5. (a) Mesguiche, V.; Parsons, R. J.; Arris, C. E.; Bentley, J.; Boyle, F. T.; Curtin, N. J.;
Davies, T. G.; Endicott, J. A.; Gibson, A. E.; Golding, B. T.; Griffin, R. J.; Jewsbury,
P.; Johnson, L. N.; Newell, D. R.; Noble, M. E.; Wang, L. Z.; Hardcastle, I. R. Bioorg.
Med. Chem. Lett. 2003, 13, 217; (b) Marchetti, F.; Cano, C.; Curtin, N. J.; Golding,
B. T.; Griffin, R. J.; Haggerty, K.; Newell, D. R.; Parsons, R. J.; Payne, S. L.; Wang, L.
Z.; Hardcastle, I. R. Org. Biomol. Chem. 2010, 8, 2397.
N-Benzyl-6-morpholino-N-nitrosopyrimidin-4-amine
(5c)
(0.07 g, 0.26 mmol) was suspended in a mixture of acetic anhydride
(0.35 g) and triethyl orthoformate (0.35 g) and heated to reflux
with stirring. After 4 h at reflux, the mixture was evaporated under
reduced pressure. The crude residue was purified by flash chro-
matography using chloroform/ethyl acetate mixture.
Yield 58 mg, 72%; yellowish solid; mp 105e106 ꢁC. IR (KBr):
3034 (CeH), 2965 (CeH), 2857 (CeH), 1683 (C]O), 1577 (C]N),
6. Arris, C. E.; Boyle, F. T.; Calvert, A. H.; Curtin, N. J.; Endicott, J. A.; Garman, E. F.;
Gibson, A. E.; Golding, B. T.; Grant, S.; Griffin, R. J.; Jewsbury, P.; Johnson, L. N.;
Lawrie, A. M.; Newell, D. R.; Noble, M. E.; Sausville, E. A.; Schultz, R.; Yu, W. J.
Med. Chem. 2000, 43, 2797.
1482, 1446, 1211, 984, 968 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d
¼8.49
ꢁ
7. Ríos-Luci, C.; Domínguez-Kelly, R.; Leon, L. G.; Díaz-Rodríguez, E.; Freire, R.;
(1H, s, C(2)eH), 7.22e7.32 (5H, m, ArH), 6.66 (1H, s, C(5)eH), 5.18
(2H, s, PhCH2), 3.75e3.78 (4H, m, O(CH2)2), 3.57e3.61 (4H, m,
ꢁ
Pandiella, A.; Cikotiene, I.; Padron, J. M. Bioorg. Med. Chem. Lett. 2011, 21, 6641.
8. (a) ASTRAZENECA AB, ASTRAZENECA UK LIMITED. Patent WO2009/34386,
2009; (b) Breault, G. A.; Comita-Prevoir, J.; Eyermann, C. J.; Geng, B.; Petrichko,
R.; Doig, P.; Gorseth, E.; Noonan, B. Bioorg. Med. Chem. Lett. 2008, 18, 6100; (c)
Roth, B.; Smith, J. M., Jr.; Hultquist, M. E. J. Am. Chem. Soc. 1950, 72, 1914.
9. (a) Susvilo, I.; Brukstus, A.; Tumkevicius, S. J. Heterocycl. Chem. 2006, 43, 267;
(b) Susvilo, I.; Brukstus, A.; Tumkevicius, S. Tetrahedron Lett. 2005, 46, 1841.
10. van der Westhuyzen, C. W.; Rousseau, A. L.; Parkinson, C. J. Tetrahedron 2007,
63, 5394.
N(CH2)2), 2.25 (3H, s, COCH3). 13C NMR (75 MHz, CDCl3):
d
¼171.4
(C]O), 163.0 (C(4) or C(6)), 160.8 (C(4) or C(6)), 157.5 (C(2)), 137.5
(quaternary aryl C), 128.6, 127.3, 127.1 (aryl C), 96.6 (C(5)), 66.3
((OCH2)2), 50.2 (PhCH2), 44.3, (NCH2)2, 24.2 (COCH3). HRMS (ES):
MHþ, found 313.1659. C17H21N4O2 requires 313.1666.
11. D’Auria, M. Tetrahedron Lett. 2005, 46, 6333.
Acknowledgements
12. Mills, K. Heterocyclic Chemistry; Blackwell Science: Oxford, UK, 2000.
13. Brown, D. J. with a chapter by Evans, R. F. and sections by Cowden, W. B. and
Fenn, M. D. The Pyrimidines; John Wiley & Sons: New York, 1994.
14. (a) Elion, G. B.; Hitchings, G. H. J. Am. Chem. Soc. 1952, 74, 3877; (b) Gaffney, B.
L.; Kung, P.-P.; Jones, R. A. J. Am. Chem. Soc. 1990, 112, 6748.
The research was funded by the European Social Fund under the
Global Grant measure (Grant No. VP1-3.1-SMM-07-K-01-002).
ꢀ
15. (a) Daly, J. W.; Christensen, B. E. J. Org. Chem. 1956, 21, 177; (b) Robins, R. K.; Lin,
H. H. J. Am. Chem. Soc. 1957, 79, 490; (c) Young, R. C.; Jones, M.; Milliner, K. J.;
Supplementary data
ꢁ
Rana, K. K.; Ward, J. G. J. Med. Chem. 1990, 33, 2073; (d) Desaubry, L.; Georges
Wermuth, C.; Bourguignon, J.-J. Tetrahedron Lett. 1995, 36, 4249.
16. The corresponding author of the original manuscript was contacted by us on
26th of November, 2011; however we did not receive any comments from him
about this new evidence.
Supplementary data contains copies of 1H, 13C NMR and HSQC
spectra. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tet.2012.01.044.