Syntheses of 7-(2-hydroxy-1-phenylethyl)- and 7-(2-hydroxy-2-phenylethyl) guanine, DNA adducts derived from styrene 7,8-oxide

Article abstract of DOI:10.1002/ejoc.200300811

7-(2-Hydroxy-1-phenylethyl)- and 7-(2-hydroxy-2-phenylethyl)guanines are important DNA adducts which can be used as markers of exposure to styrene. Two synthetic routes leading to these compounds are presented using allyl-protected bromohydrins as synthetic equivalents of styrene oxide to alkylate 2-amino-6-chloropurine or 7-methyl-10-oxo-9,10-dihydropyrimido[1,2-a]purine as precursors to guanine. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200300811

FULL PAPER
Syntheses of 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-Hydroxy-2-
phenylethyl)guanine, DNA Adducts Derived from Styrene 7,8-Oxide
[a]
[a]
[b]
´
ˇ´
´
Jan Novak, Igor Linhart,* and Hana Dvorakova
Keywords: DNA adducts / Alkylation / Heterocycles / Protecting groups / Guanine derivatives
7-(2-Hydroxy-1-phenylethyl)- and 7-(2-hydroxy-2-phenyl-
ethyl)guanines are important DNA adducts which can be
used as markers of exposure to styrene. Two synthetic routes
ide to alkylate 2-amino-6-chloropurine or 7-methyl-10-oxo-
9,10-dihydropyrimido[1,2-a]purine as precursors to guanine.
leading to these compounds are presented using allyl-pro- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
tected bromohydrins as synthetic equivalents of styrene ox-
Germany, 2004)
Introduction
ethylene oxide followed by acidic hydrolysis leads to 7-(2-
hydroxyethyl)guanine.[9] However, alkylations of nucleos-
ides and nucleotides with less reactive alkylating agents gen-
erally proceed with low regioselectivity. In particular, oxir-
ane 1, as a weak alkylating reagent, gives low regioselectiv-
ity in alkylations.[10] To improve both reactivity and regiose-
lectivity we searched for suitable synthetic equivalents of
1 and for a possible precursor of guanine giving a better
regioselectivity of alkylation. Several precursors to guanine
with enhanced selectivity of alkylation have been reported
in the literature, such as 6,7-diacetoxy-5-acetyl-5,6,7,9-
tetrahydro-9-oxo-3H-imidazo[1,2-a]purine (3),[11] 5-acetyl-
6,7-bis(2-methylpropanoyloxy)-5,6,7,9-tetrahydro-9-oxo-3H-
imidazo[1,2-a]purine (4),[11] 7-methyl-10-oxo-9,10-dihydro-
pyrimido[1,2-a]purine (5)[12] and 2-amino-6-chloropurine
(6).[6]
In our preliminary report we described a synthetic route
to compounds 2a and 2b based on the alkylation of 2-am-
ino-6-chloropurine (6) with allyl-protected bromohydrins as
synthetic equivalents to 1.[13] In this paper we report two
possible ways to protect guanine in order to improve the
regioselectivity of the alkylation. The results are compared
with those obtained by alkylation of the purine 6.
7-[Hydroxy(phenyl)ethyl]guanines are important DNA
adducts formed as a result of exposure to styrene, a large-
scale industrial monomer.[1,2] Styrene is metabolised to styr-
ene 7,8-oxide (1) an electrophilic intermediate capable of
attacking nucleophilic centres in nucleic acids.[3] The main
site of the attack in DNA is at N-7 of guanine. When ox-
irane 1 binds to this site, two guanine adducts can be
formed — 7-(2-hydroxy-1-phenylethyl)guanine (2a) and 7-
(2-hydroxy-2-phenylethyl)guanine (2b).[4] The former is
formed by nucleophilic attack at the oxirane α-carbon atom
and is therefore often denoted as the α adduct, whereas the
latter arises from attack at the β-carbon atom and is there-
fore called the β adduct. Consequently, 7-alkylguanines are
the main types of DNA adducts excreted in urine and are
therefore important markers of DNA damage caused by
alkylating agents.[5] Therefore, 7-alkylated guanines derived
from an industrially important compound such as styrene
are needed as analytical standards for the development of
diagnostic methods to detect and quantitate specific types
of DNA damage.
Oxiranes can be used to alkylate purine derivatives
mainly at the most reactive position N-9.[6,7] However, in
guanine nucleosides, nucleotides and DNA the N-9 position
is substituted by a sugar, so the N-7 position becomes the
most reactive nucleophilic centre of the molecule. In fact,
the most reactive alkylating agents such as methyl iodide,
dimethyl sulfate and benzyl bromide can alkylate guanosine
effectively and regioselectively to give the corresponding 7-
alkylated products.[8] Similarly, reaction of guanosine with
Results and Discussion
Synthetic Equivalents of Styrene 7,8-Oxide (1)
Two isomeric bromohydrins, 2-bromo-2-phenylethanol
(7a) and 2-bromo-1-phenylethanol (7b) can be derived from
1, each giving potentially one type of alkylation product —
the α and β adduct, respectively (Scheme 1). Bromohydrin
7b reacted with purine 6 to give a 1:6 mixture of 2-amino-
6-chloro-7-(2-hydroxy-2-phenylethyl)purine (10b) and 2-
amino-6-chloro-9-(2-hydroxy-2-phenylethyl)purine (11b).[13]
In contrast, bromohydrin 7a did not alkylate 6 but under
[a]
Department of Organic Chemistry, Institute of Chemical
Technology Prague,
´
Technicka 5, 16628 Prague, Czech Republic
[b]
Central Laboratories, Institute of Chemical Technology Prague,
´
Technicka 5, 16628 Prague, Czech Republic
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Syntheses of 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-Hydroxy-2-phenyl)ethylguanines
FULL PAPER
the reaction conditions applied (dimethylformamide with
potassium carbonate as a base) underwent a base-catalysed
condensation reaction. Protection of the hydroxy group by
a suitable protective group was therefore required to pre-
vent elimination of HBr from bromohydrins 7a and 7b. Al-
lyl has proved to be an effective OH protective group not
only to prevent base-catalysed side-reactions of the bromo-
hydrins but also to enhance reactivity in the nucleophilic
substitution. This latter effect can be explained by a partici-
pation of allylic π-electrons in the nucleophilic substi-
tution.[14] Therefore, allyl-protected bromohydrins, namely
allyl 2-bromo-2-phenylethyl ether (8a) and allyl 2-bromo-1-
phenylethyl ether (8b), as well as the allyl-protected tosylate
2-allyloxy-2-phenylethyl tosylate (9b), were studied as alkyl-
ating agents. Allyl-protected bromohydrin 8a, a synthetic
equivalent of 1 affording α-adduct-type products on alky-
lation, was prepared from the corresponding alcohol, i.e.,
allyl 2-hydroxy-2-phenylethyl ether, upon reaction with
phosphorus tribromide. In contrast, an analogous reaction
of allyl 2-hydroxy-1-phenylethyl ether gave a low yield of
8b. Therefore, compound 8b was prepared from 2-allyloxy-
2-phenylethyl tosylate (9b)[15] by nucleophilic substitution
with lithium bromide. Both the bromide 8b and the tosylate
9b are synthetic equivalents of 1 giving the β adducts. All
our attempts to prepare isomeric 2-allyloxy-1-phenylethyl
tosylate (9a), which should give the corresponding α-ad-
duct-type products on alkylation, were unsuccessful. Data
summarising the results of the alkylation of 6 with synthetic
equivalents of 1 are shown in Table 1. Both reactivity and
selectivity were improved by introducing the allyl protective
group. As expected, benzylic alkyl bromide 8a showed a
better reactivity (a higher yield) than the phenethylic bro-
mide 8b. In all cases, the position N-9 in purine 6 was the
main site of alkylation.
Table 1. 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-hydroxy-2-phenyl-
ethyl)guanines by alkylation of 2-amino-6-chloropurine (6)
Reagent
Yield of compound
Alkylation Hydrolysis Deallylation Overall yield
7b
8b
8a
9b
48% 11b
8% 10b
51% 13a
13% 12a
62% 13b
22% 12b
62% 13b
21% 12b
95% 2b
7.6% 2b
11% 2b
20% 2a
18% 2b
95% 14b
97% 14a
90% 2b
92% 2a
90% 2b
converted into a guanine moiety by simple hydrolysis of
chlorine in the 6-position.[16] This approach allowed us to
prepare 7-[hydroxy(phenyl)ethyl]guanines 2a and 2b[13] but
the yields of the N-7 isomer required in the alkylation step
were rather low (Scheme 2, Table 1). The main problem was
the regioselectivity of the alkylation step. Position N-7 in
purine 6 is less reactive than N-9, so that the required 7-
alkylated product was always the minor one. Bromohydrin
7b, but not its isomer 7a, yielded a mixture of alkylated
purines 10b and 11b which could be converted into corre-
sponding guanine derivatives by hydrolysis with aqueous
NaOH. Allyl-protected alkylating agents 8a, 8b and 9b gave
better yields of the alkylated products, which were then con-
verted into 2a and 2b by a two-step procedure (Scheme 2).
The overall yields of 2a and 2b for allyl-protected alkylating
agents are, however, better than those for unprotected
bromohydrins.
The reactivity of the N-7 position can be increased when
modified guanine derivatives (guanine precursors) are used
which can be easily converted into the corresponding guan-
ine derivatives after alkylation.
Imidazopurine Derivatives
Imidazopurines, namely 6,7-diacetoxy-5-acetyl-5,6,7,9-
tetrahydro-9-oxo-3H-imidazo[1,2-a]purine (4) and 5-acetyl-
6,7-bis(2-methylpropanoyloxy)-5,6,7,9-tetrahydro-9-oxo-3H-
imidazo[1,2-a]purine (5), were introduced by Kjellberg and
Johansson as precursors to guanine for regioselective alky-
lations.[11] Although the original aim of the application of
these compounds was to prepare N-9 guanine derivatives
such as buciclovir selectively, the regioselectivity of alky-
lation was strongly dependent on the reaction conditions,
mainly on the base used. When sodium hydride in DMF
was used, the N-7 derivative predominated (e.g., with 4-
bromobutyl acetate as the alkylating reagent the N-7/N-9
isomer ratio was 18:1).[11a] However, we were not able to
alkylate compounds 3 or 4 with either of the three allyl-
protected synthetic equivalents of styrene oxide 8a, 8b or
9b. In all cases the reaction proceeded slowly yielding a mix-
ture of degradation products rather than the expected prod-
ucts of alkylation. On the other hand, alkylation of both 3
Scheme 1. Synthetic equivalents of styrene 7,8-oxide: i) NuϪ, for
allyl-protected compounds 7b and 8b followed by deallylation[18]
Precursors of Guanine and Their Alkylation
2-Amino-6-chloropurine (6)
Guanine itself is not a suitable substrate for alkylation and 4 with benzyl bromide yielded a nearly 3.5:1 mixture
reactions due to its low reactivity and solubility. Purine 6 of 1-/3-alkylated products. This product ratio did not
was therefore used as a precursor to guanine that can be change when potassium carbonate was used as a base in-
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Scheme 2. Alkylation of 2-amino-6-chloropurine: i) K2CO3/DMF, 60 °C; ii) aqueous NaOH; iii) [Pd(PPh3)4], PMHS, ZnCl2, DMF[18]
stead of sodium hydride. Acetyl derivative 3 gave 53% of synthetic equivalents of 1 and to the degradation of the
6,7-diacetoxy-5-acetyl-1-benzyl-5,6,7,9-tetrahydro-9-oxo-1H- starting material under these reaction conditions.
imidazo[1,2-a]purine (15) and 15% of 6,7-diacetoxy-5-acetyl-
3-benzyl-5,6,7-tetrahydro-9-oxo-1H-imidazo[1,2-a]purine (16).
The former is a precursor of the desired N-7 guanine de-
Methylmalondialdehyde Condensate of Guanine
rivative while the latter is a precursor of the N-9 isomer. A
very similar product ratio was obtained when diisobutyryl
Pyrimidopurine 5 was introduced by Kjellberg et al.[12] as
derivative 4 was alkylated (Scheme 3). In this case, however, a more stable, if not more reactive, guanine precursor for
the two isomers obtained could not be separated by column alkylation at N-7 and N-9 positions than both imidazopur-
chromatography and their ratio was determined by integrat- ines 3 and 4. It can be prepared by condensation of guanine
1
ing signals in the H NMR spectrum of their mixture. Al- with methylmalondialdehyde as described by Moschel and
though imidazopurine derivatives 3 and 4 showed a much Leonard.[17] To prepare compound 5 we used this procedure
better selectivity for desired positional isomers in the alky- with the following modification: methylmalondialdehyde
lation than purine 6, they could not be used to prepare was liberated in situ by aqueous HCl from its tetraethyl
guanine derivatives 2a and 2b due to low reactivity with diacetal, so that its isolation and purification is avoided.
Scheme 3. Alkylation of imidazopurines 3 and 4 by reaction with benzyl bromide: i) K2CO3/DMF, room temperature
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Syntheses of 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-Hydroxy-2-phenyl)ethylguanines
FULL PAPER
Scheme 4. Alkylation of pyrimidopurine: i) NaH or K2CO3 in DMF, 60 °C, overnight; ii) aqueous NaOH, reflux, 4Ϫ6 h; iii) PMHS,
[Pd(PPh3)4], ZnCl2 in DMF[18]
Alkylation of compound 5 with allyl-protected synthetic Identification of Products and Determination of the Site of
equivalents of 1 gave two products — the N-1 and N-3 de- Substitution
rivatives — in a ratio of nearly 1:1. This ratio did not signif-
All products and intermediates were characterised by
icantly change upon changing the base used (sodium hy-
usual spectral methods such as 1H and 13C NMR spec-
troscopy, mass spectrometry and elemental analysis. UV
spectra at neutral, acidic and alkaline pH were also re-
corded. Positional isomers such as 7- and 9-substituted
dride or potassium carbonate). A similar observation was
reported earlier for alkylation of 5 with 4-bromobutyl acet-
ate in the presence of different bases such as sodium hy-
dride, potassium carbonate, triethylamine, thallium()
guanines and their precursors show little or no differences
in the mass and UV spectra. Based on consideration of
NMR spectroscopic data for a series of purine derivatives,
including substituted pyrimidopurines (derivatives of 5) and
imidazopurines (derivatives of 3 and 4), Kjellberg and
ethoxide and lithium diisopropylamide.[12] The three alkyl-
ating agents used (8a, 8b and 9b) showed a similar reactivity
but compound 8a gave somewhat lower yields with benzylic
bromide (Scheme 4, Table 2). The products of alkylation
were separated and pure N-1 isomers 19a or 19b were de-
protected by hydrolytic cleavage followed by palladium-cat-
alysed deallylation[18] to yield the N-7 guanine derivatives
2a and 2b, respectively.
1
Johansson formulated general rules for H and 13C NMR
chemical shifts to distinguish between N-7 and N-9 deriva-
tives.[19] They observed that 8-H signals for the N-9 isomer
are shifted upfield relative to the corresponding signals for
the N-7 isomer. Similarly, the peaks for C-8 and C-1Ј of the
N-9 isomer are shifted upfield relative to the corresponding
values for the N-7 isomer. On the contrary, the signals of
C-5 are deshielded relative to those of the N-7 isomers.[13]
The ring numbering relates to the purine moiety, and may
differ from the systematic numbering of the compounds
concerned. These empirical rules can be applied also to
compounds prepared in this study. However, recent devel-
opment in 2D NMR techniques and instrumentation, na-
mely HMQC and HMBC experiments, allowed us to obtain
unequivocal and much more direct evidence of the site of
substitution. HMQC and HMBC spectra were recorded for
compounds 12a,b, 13a,b, 15, 16, 19a,b and 20a,b. Examples
of the HMBC spectrum of purine derivatives 19b and 20b
Table 2. 7-(2-Hydroxy-1-phenylethyl)- and 2-hydroxy-2-phenyl-
ethyl)guanines by alkylation of pyrimidopurine (5)
Reagent
Yield of compound
Alkylation Hydrolysis Deallylation Overall yield
8b
8a
9b
43% 20b
37% 19b
37% 20a
35% 19a
41% 20b
39% 19b
91% 14b
81% 14a
91% 14b
90% 2b
68% 2a
90% 2b
30% 2b
19% 2a
32% 2b
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Figure 1. HMBC spectrum of 19b; cross-peaks between NCH2 signals and both C-2 and C-10a are highlighted, indicating that the
corresponding atoms are separated by three bonds
are shown in Figures 1 and 2; cross-peaks indicating the
position of the substituent — the 2-hydroxy-2-phenylethyl
moiety — are highlighted. Once the site of substitution was
unequivocally determined, subsequent steps converting an
alkylation product to the target guanine derivatives could
be accomplished without the need to measure an HMBC
spectrum at each stage. It is reasonable to expect that no
isomerisation (transalkylation from one nitrogen atom to
another) will occur in the course of reactions such as hy-
drolysis and deallylation.
Comparison of Synthetic Approaches Leading to 7-(2-
Hydroxy-1- or -2-phenylethyl)guanines 2a and 2b
The most straightforward way of preparing compounds
2a and 2b appears to be an alkylation of guanosine or 2Ј-
deoxyguanosine with 1. In fact, this approach has been used
by several groups to obtain small quantities of a whole
range of 2-hydroxy-1-phenylethyl- and 2-hydroxy-2-phenyl-
ethyl derivatives of guanosine, 2Ј-deoxyguanosine and 2Ј-
deoxyguanosine phosphates.[4,10] Although guanosine and
deoxyguanosine show good selectivity of alkylation at N-7
for some reactive alkylating agents,[8,9] both the reactivity
and selectivity of their reaction with 1 was rather low, so
that only small amounts of samples could be obtained after
HPLC separation.[10] Compounds 5 and 6 as precursors of
guanine showed much greater reactivity with the synthetic
equivalents of 1 used in this study. This is achieved by de-
protonation of the imidazole ring of 5 and 6 which is not
possible when the N-9 position of the guanine moiety is
occupied by a ribosyl or 2-deoxyribosyl substituent.
For the benzyl derivatives 17 and 18 of diisobutyrylimid-
azopurine, which were not separated from each other, 2D
spectra were not measured. In this special case, the position
of the benzyl group was determined from the 1H NMR
spectrum by analogy with corresponding diacetyl deriva-
1
tives. There are characteristic differences in the H NMR
spectra between 1-benzyl and 3-benzyl derivatives. The sig-
nals of 8-H follow the rule of Kjellberg and Johansson.[19]
Moreover, the benzyl CH2 protons of the N-1 derivatives
are magnetically non-equivalent and appear as an AB sys-
tem, whereas the corresponding protons of the N-3 deriva-
A major limitation of the proposed synthetic methods
tives are magnetically equivalent and appear as a singlet. lies in the regioselectivity. In the case of compound 6, the
The singlet of the latter protons is shifted upfield by nearly N-9 position is the major site of electrophilic attack, the N-
0.2 ppm. These effects can be explained by a hindered ro- 7 position being the minor one. For compound 5 the reac-
tation in the N-1 derivatives due to the proximity of the tivity of positions N-1 and N-3 is nearly equal, leading
benzyl and carbonyl group and by shielding of the carbonyl eventually to the formation of 7- and 9-substituted guanine
π-electrons, respectively.
derivatives in a 1:1 ratio. The major advantage of purine 6
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Syntheses of 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-Hydroxy-2-phenyl)ethylguanines
FULL PAPER
Figure 2. HMBC spectrum of 20b; cross-peaks between NCH2 signals and both C-2 and C-3a are highlighted, indicating that the
corresponding atoms are separated by three bonds
as a precursor to guanine is the relative simplicity of the Experimental Section
reaction pathway. Compound 6 is commercially available
General: Column chromatography was performed on silica gel 60
obtained from Fluka, particle size 0.063Ϫ0.200 mm or
and its alkylation products can be easily separated by col-
umn chromatography and converted into the final products
0.035Ϫ0.070 (flash chromatography). For thin-layer chromatogra-
in two simple steps — hydrolysis and deallylation. On the
phy Merck Silica gel 60 F254 plates were used. Dimethylformamide
other hand, pyrimidopurine 5, which has a better regiose-
was dried by azeotropic distillation with benzene, followed by dis-
lectivity for 7-substituted guanines, is not commercially
tillation from phosphorus pentoxide under vacuum, and stored
available. In both cases the alkylation of guanine precursor
over molecular sieves. Other chemicals obtained from commercial
with synthetic equivalents of 1 is the key reaction step.
sources were of analytical or synthetic grade and were used as re-
1
ceived. H and 13C NMR spectra were recorded with a Bruker Av-
ance DRX500 (500 MHz for 1H) or with a Varian Mercury 300
1
(300 MHz for H) Fourier transform NMR spectrometer. HMQC
Conclusion
and HMBC experiments were used to facilitate the assignment of
carbon atoms and to determine the site of substitution in the alkyl-
ated products. In HMBC, the parameters were set to show cross-
peaks for nuclei interacting with a JH,C coupling constant of 7 Hz.
Mass spectra were measured with a triple quadrupole HPLC-MS
system Varian 1200 equipped with electrospray ionization or on an
ion-trap GC-MS system Varian Saturn 2000.
Allyl-protected bromohydrins 8a and 8b as well as tosyl-
ate 9b are suitable synthetic equivalents of styrene oxide for
synthesis of 7-[hydroxy(phenyl)ethyl]guanines, namely 7-(2-
hydroxy-1-phenylethyl)guanine (2a) and 7-(2-hydroxy-2-
phenylethyl)guanine (2b), which are important markers of
DNA damage. Two guanine precursors, pyrimidopurine 5
and chloropurine 6 can be used as starting material. In both
cases the 7-[hydroxy(phenyl)ethyl]guanines required are ob-
tained by a two-step process including alkaline hydrolysis
and palladium-catalysed deallylation. Alkylation of purine
6 by 8a is the process of choice for the preparation of 2a
whereas the alkylation of 5 by 9b is the best choice for the
preparation of 2b.
Allyl 2-Bromo-1-phenylethyl Ether (8b): This compound was pre-
pared by reaction of 2-(allyloxy)-2-phenylethyl tosylate (9b)[15] with
LiBr in analogy with Dickman et. al.[20] and identified by compari-
son of its NMR spectra with published data.[15] A mixture of tosyl-
ate 9b (3 g, 9.42 mmol) and LiBr (4.1 g, 47.2 mmol) was refluxed
in acetone for 20 h. The solvent was removed by evaporation under
vacuum and the residue was diluted with 50 mL of water and
washed twice with dichloromethane. The organic layer was dried
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with MgSO4. The crude product (2.17 g, 96%) obtained by evapo-
and 129.1 (phenyl-CH), 135.0 (phenyl-C), 143.4 (C-2), 147.6 (C-
ration of the solvent was purified by column chromatography on 3a), 151.5 (C-4a), 158.0 (C-9), 167.6, 168.2 and 168.7 (CO) ppm;
silica gel. A yellowish liquid (2.0 g, 88%) was obtained.
HMBC shows cross-peaks between CH2Ph (δH ϭ 5.46 and 5.67
ppm) and both C-9a (δC ϭ 111.4 ppm) and C-2 (δC ϭ 143.4 ppm).
C20H19N5O6·1/2H2O (434.42): calcd. C 55.3, H 4.6, N 16.1; found
C 55.0, H,4.7, N 16.1. 6,7-Diacetoxy-5-acetyl-3-benzyl-5,6,7-tetra-
hydro-9-oxo-3H-imidazo[1,2-a]purine (16), white powder (107 mg,
Allyl 2-Bromo-2-phenylethyl Ether (8a): Allyl 2-hydroxy-2-phenyl-
ethyl ether[21] (6 g, 33.7 mmol) was added dropwise to phosphorus
tribromide (3.84 g, 14.2 mmol, 26% excess) under dry nitrogen
whilst stirring and with external cooling by an ice/water mixture.
The reaction mixture was then stirred for 1 h, left overnight at
room temperature and thereafter diluted with 60 mL of diethyl
ether, washed twice with cold water, dried with anhydrous MgSO4
and filtered. Evaporation of ether yielded 8.1 g (99%) of the crude
product. Its vacuum distillation yielded 5.2 g (64%) of colourless
liquid, b.p. 88Ϫ92 °C at 0.4 mbar. 1H NMR (300 MHz, CDCl3),
δ ϭ 3.92 (dd, J ϭ 10.8, 6.7 Hz, 1 H, OCH2CHBr), 3.97 (dd, 1 H,
J ϭ 10.8 and 8 Hz, OCH2CHBr), 4.05 (m, 2 H, OCH2CHϭCH2);
5.07 (t, J ϭ 7 Hz, 1 H, CHBr), 5.19 (dd, J ϭ 10.3, 1.3 Hz, 1 H,
CH2ϭCH), 5.27 (dq, J ϭ 17.2, 1.3 Hz, 1 H, CH2ϭCH), 5.87 (m,
1
15%). H NMR (500 MHz, CDCl3): δ ϭ 2.12 (s, 6 H, CH3COO),
2.70 (s, 3 H, CH3CON), 5.27 (s, 2 H, CH2Ph), 6.85 (s, 1 H, CHO),
6.86 (s, 1 H, CHO), 7.28 (m, 2 H, Ph), 7.39 (m, 3 H, Ph), 7.74 (s,
1 H, 2-H) ppm. 13C NMR (125.8 MHz, CDCl3): δ ϭ 20.4
(CH3COO), 25.0 (CH3CON), 47.9 (CH2Ph), 78.0 and 81.0
(CHOAc), 120.5 (C-9a), 127.6, 128.7 and 129.1 (Ph), 134.9 (Ph),
139.2 (C-2), 148.4 and 148.6 (C-3a and C-4a), 153.5 (-C9), 167.8,
167.9 and 168.0 (CO) ppm; HMBC shows cross-peaks between
CH2Ph (δH ϭ 5.27 ppm) and both C-3a (δC ϭ 148.4 ppm) and C-
2 (δC ϭ 139.3 ppm). UV: λmax ϭ 262 nm (pH ϭ 6.5), 260 nm (pH
1) 260 nm (pH ϭ 12). C20H19N5O6·1/2H2O (434.42): calcd. C 55.3,
H 4.6, N 16.1; found C 55.5, H 4.8, N 16.4.
1 H, CH2ϭCH), 7.35 (m, 3 H, Ph) and 7.43 (m, 2 H, Ph) ppm. 13
C
NMR (75 MHz, CDCl3): δC ϭ 51.9 (CHBr), 72.2 and 74.3 (CH2O),
117.5 (CH2ϭCH), 127.9, 128.6 and 128.7 (Ph), 134.2 (CH2ϭCH),
139.2 (Ph) ppm. EI-MS: m/z (%) ϭ 183 and 185 (25) [M Ϫ CH2ϭ
CHCH2O]ϩ, 169 and 171 (50) [M Ϫ CH2ϭCHCH2OCH2]ϩ, 161
(65) [M Ϫ Br]ϩ, 143 (80) [M Ϫ Br Ϫ H2O]ϩ, 104 (100) [M Ϫ Br
Ϫ CH2ϭCHCH2O]ϩ, 91 (85). C11H13BrO (231.13): calcd. C 54.8,
H 5.4 Br 33.1; found C 54.9, H 5.7, Br 32.7.
Alkylation of 5-Acetyl-6,7-bis(2-methylpropanoyloxy)-5,6,7,9-tetra-
hydro-9-oxo-3H-imidazo[1,2-a]purine (5) with Benzyl Bromide: Pot-
assium carbonate (0.71 g, 0.51 mmol) was added to a solution of 5
(0.200 g, 0.51 mmol) in 3 mL of dry DMF followed, after 15 min,
by benzyl bromide (288 mg, 1.68 mmol) and the reaction mixture
was stirred for 3Ϫ4 h. The solvent was evaporated under vacuum
and the oily residue was purified by column chromatography on
silica gel. The product obtained (150 mg, 61%) was a mixture of
two compounds, 5-acetyl-1-benzyl-6,7-bis(2-methylpropanoyloxy)-
5,6,7,9-tetrahydro-9-oxo-1H-imidazo[1,2-a]purine (regioisomer a)
and 5-acetyl-3-benzyl-6,7-bis(2-methylpropanoyloxy)-5,6,7,9-tetra-
hydro-9-oxo-3H-imidazo[1,2-a]purine (regioisomer b), which were
not separated (a/b ϭ 3.5:1). 1H NMR (300 MHz, CDCl3): δ ϭ
1.10aϩb (m, 12 H, CH3CHCO), 2.48aϩb (sept, J ϭ 6.9 Hz, 2 H,
CH3CHCO), 2.50a (s, 3 H, CH3CON) 2.52b (s, 3 H, CH3CON),
5.41a (d, J ϭ 14.9 Hz, 1 H, CH2Ph), 5.45a (d, J ϭ 14.9 Hz, 1 H,
CH2Ph), 5.18b (s, 2 H, CH2Ph), 6.70a (s, 1 H, CHO), 6.75a (s, 1 H,
CHO), 6.71b (s, 1 H, CHO), 6.72b (s, 1 H, CHO), 7.22aϩb (m, 5 H,
Ph), 7.77a (s, 1 H, 2-H), 7.65b (s, 1 H, 2-H) ppm.
7-Methyl-10-oxo-9,10-dihydropyrimido[1,2-a]purine (5): Compound
5 was prepared by a modified reaction described by Moschel and
Leonard[17] and identified by comparison of its NMR spectra with
published data.[12] Methylmalondialdehyde tetraethyldiacetal[22,23]
was used instead of free methylmalondialdehyde. Methylmalondial-
dehyde tetraethyldiacetal (3.5 equiv.) was added to a solution of
guanine hydrochloride (4.6 g, 23 mmol) in 288 mL of 1  HCl and
the resulting solution was stirred at 45 °C for 24 h. The product was
obtained as a hydrochloride. Free base was recovered by cautious
neutralization of a hot acid solution of the hydrochloride. After
cooling, the yellow precipitate was collected by filtration to give 2 g
(43%) of 5.
6,7-Diacetoxy-5-acetyl-5,6,7,9-tetrahydro-9-oxo-3H-imidazo[1,2-
a]purine (3) and 5-Acetyl-6,7-bis(2-methylpropanoyloxy)-5,6,7,9-
tetrahydro-9-oxo-3H-imidazo[1,2-a]purine (4): These compounds
were prepared by a previously described procedure from guan-
ine.[11,12] Compound 3, m.p. 212Ϫ214 °C; compound 4, m.p.
Alkylation of 7-Methyl-10-oxo-9,10-dihydropyrimido[1,2-a]purine
(5): Potassium carbonate (206 mg, 1.49 mmol) was added to a solu-
tion of pyrimidopurine 5 (300 mg, 1.49 mmol) in 15 mL of dry
DMF and the mixture was stirred for 15Ϫ30 min. An excess of
alkylating reagent (3.94 mmol) was then added and the reaction
mixture was stirred under dry nitrogen at 60 °C overnight. The
solvent was evaporated under vacuum and the oily residue was
separated by column chromatography on silica gel (eluent Me2CO/
EtOAc, 1:1).
1
177Ϫ179 (ref.[11b] m.p. 169Ϫ170 °C). H NMR spectra of both 3
and 4 are in agreement with published data.[6c]
Alkylation of 6,7-Diacetoxy-5-acetyl-5,6,7,9-tetrahydro-9-oxo-3H-
imidazo[1,2-a]purine with Benzyl Bromide: Sodium hydride (0.390 g,
1.64 mmol) or K2CO3 (0.227 g, 1.64 mmol) was added to a solution
of imidazopurine 3 (0.550 g, 1.64 mmol) in 10 mL of dry DMF.
After 15 min, benzyl bromide (1.27 g, 7.45 mmol) was added and
the reaction mixture was stirred at room temperature for 3Ϫ4 h.
The solvent was evaporated to dryness and the resulting oily resi-
due purifed by column chromatography on silica gel. Two products
3-[2-(Allyloxy)-2-phenylethyl]-7-methyl-10-oxo-9,10-dihydro-
pyrimido[1,2-a]purine (20b): Yellow powder obtained by alkylation
of 5 (above procedure) with bromide 8b (yield 230 mg, 43%) or
with tosylate 9 (yield 219 mg, 41%), m.p. 185Ϫ187 °C, RF (Me2CO/
EtOAc, 1:1) ϭ 0.56. UV: λmax ϭ 258, 320 and 356 nm (pH ϭ 6.5),
250, 314 and 344 nm (pH ϭ 1), 258, 320 and inflex at 356 nm
were obtained: 6,7-Diacetoxy-5-acetyl-1-benzyl-5,6,7-tetrahydro-9- (pH ϭ 11). 1H NMR (500 MHz, CDCl3): δ ϭ 2.47 (s, 3 H, 7-CH3),
oxo-1H-imidazo[1,2-a]purine (15), white powder (374 mg, 54%). 3.74 (dd, J ϭ 6, 12.7 Hz, 1 H, OCH2CHCH2), 3.98 (dd, J ϭ 4.9,
UV: λmax ϭ 264 nm (pH ϭ 6.5), 260 nm (pH ϭ 1) 264 nm (pH ϭ
12). 1H NMR (500 MHz, CDCl3): δ ϭ 2.10 (s, 3 H, CH3COO), NCH2), 4.59 (dd, J ϭ 3.6, 14.3 Hz, 1 H, NCH2), 4.72 (dd, J ϭ 3.6,
2.14 (s, 3 H, CH3COO), 2.80 (s, 3 H, CH3CON), 5.46 (d, J ϭ 8.7 Hz, 1 H, NCH2CHPh), 5.08 (d, J ϭ 10.3 Hz, 1 H,
15 Hz, CH2Ph), 5.67 (d, J ϭ 15 Hz, CH2Ph), 6.82 (s, 1 H, CHO), OCH2CHCH2), 5.13 (d, J ϭ 17.3 Hz, 1 H, OCH2CHCH2), 5.74
6.86 (s, 1 H, CHO), 7.34 (m, 5 H, Ph), 7.82 (s, 1 H, 2-H) ppm. 13
(m, 1 H, OCH2CHCH2), 7.34 (m, 5 H, Ph), 8.00 (s, 1 H, 2-H), 8.85
NMR (125.8 MHz, CDCl3): δ ϭ 20.5 (CH3COO), 25.2 (CH3CON), (d, J ϭ 2.4 Hz, 1 H, 6-H), 9.27 (s, 1 H, 8-H) ppm. 13C NMR
12.7 Hz, 1 H, OCH2CHCH2), 4.37 (dd, J ϭ 8.7, 14.3 Hz, 1 H,
C
50.7 (CH2Ph), 77.3 and 80.9 (CHOAc), 111.4 (C-9a), 128.1, 128.7 (125.8 MHz, CDCl3):
δ
ϭ
15.3 (CH3) 49.5 (NCH2), 69.8
2744  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjoc.org
Eur. J. Org. Chem. 2004, 2738Ϫ2746

Syntheses of 7-(2-Hydroxy-1-phenylethyl)- and 7-(2-Hydroxy-2-phenyl)ethylguanines
FULL PAPER
(OCH2CHCH2), 79.2 (NCH2CHPh), 117.4 (OCH2CHCH2), 118.0 OCH2CHN), 4.26 (dd, J ϭ 7.3, 10.9 Hz, 1 H, OCH2CHN), 5.18
(C-10a), 119.2 (C-7), 126.5, 126.7, 128.6, 128.8 and 137.9 (Ph), (dd, J ϭ 1.3, 9.1 Hz, 1 H, OCH2CHCH2), 5.22 (dd, J ϭ 1.3, 17.3
133.9 (OCH2CHCH2), 134.3 (C-8), 143.2 (C-2), 148.3 (C-3a), 149.9 Hz, 1 H, OCH2CHCH2), 5.82 (m, 1 H, OCH2CHCH2), 6.42 (dd,
(-C4a), 152.5 (C-10), 162.8 (C-6) ppm; HMBC shows cross-peaks
between NCH2 (δH ϭ 4.37 and 4.59 ppm) and both C-3a (δC
J ϭ 4.1, 7.3 Hz, 1 H, NCH), 7.53 (m, 5 H, Ph), 8.42 (s, 1 H, 2-H),
ϭ
9.80 (d, J ϭ 1.3 Hz, 1 H, 6-H), 9.00 (m, 1 H, 8-H) ppm. 13C NMR
148.3 ppm) and C-2 (δC ϭ 143.2 ppm). ESI-MS: m/z ϭ 400 [M ϩ (75 MHz, CDCl3): δ ϭ 15.3 (CH3) 60.9 (NCHPh), 71.1 and 72.6
K]ϩ, 384 [M ϩ Na]ϩ, 362, 340, 242, 130 [M ϩ H]ϩ. C20H19N5O2·
1/4H2O (365.91): calcd. C 65.6, H 5.4, N 19.1; found C 65.6, H
5.3, N 18.9.
(OCH2), 110.3 (C-10a), 118.3 (OCH2CHCH2), 119.3 (C-7), 127.4,
128.8, 129.1 and 137.2 (Ph), 132.7 (OCH2CHCH2), 133.9 (C-8),
146.2 (C-2), 147.9 (C-3a), 150.4 (C-4a), 158.8 (C-10), 162.6 (C-6)
ppm; HMBC shows cross-peaks between between NCHPh (δH
6.42 ppm) and both C-10a (δC ϭ 110.3 ppm) and C-2 (δC
ϭ
1-[2-(Allyloxy)-2-phenylethyl]-7-methyl-10-oxo-9,10-dihydro-
pyrimido[1,2-a]purine (19b): Yellow needles obtained by alkylation
of 5 with bromide 8b (yield 198 mg, 37%), or tosylate 9 (yield
219 mg, 41%), m.p. 213Ϫ215 °C, RF (Silica gel Merck; Me2CO/
ϭ
146.2 ppm). ESI-MS: m/z ϭ 384 [M ϩ Na]ϩ, 362 [M ϩ H]ϩ.
C20H19N5O2·3/4H2O (374.92): calcd. C 64.1, H 5.5, N 18.7; found
C 64.0, H 5.2, N 18.5.
1
EtOAc, 1:1) ϭ 0.24. H NMR (500 MHz, CDCl3): δ ϭ 2.47 (s, 3
H, 7-CH3); 3.68 (dd, J ϭ 6, 12.8 Hz, 1 H, OCH2CHCH2), 3.97 (dd,
J ϭ 4.9, 12.7 Hz, 1 H, OCH2CHCH2), 4.46 (dd, J ϭ 8.9, 14.0 Hz,
1 H, NCH2), 4.78 (dd, J ϭ 3.0, 8.9 Hz, 1 H, NCH2), 4.84 (dd, J ϭ
3.0, 14.0 Hz, 1 H, CHPh), 5.03 (d, J ϭ 10.2 Hz, 1 H,
OCH2CHCH2), 5.07 (d, J ϭ 17.3 Hz, 1 H, OCH2CHCH2), 5.66
(m, 1 H, OCH2CHCH2), 7.38 (m, 5 H, Ph), 8.14 (s, 1 H, 2-H), 8.86
(d, J ϭ 2.5 Hz, 1 H, 6-H), 9.08 (s, 1 H, 8-H) ppm. 13C NMR
Hydrolytic Cleavage of the Alkylated Pyrimidopurines: Pyrimidopu-
rine derivative 19a or 19b (0.170 g, 0.47 mmol) was refluxed in 47
mL of 0.1  NaOH for 4Ϫ6 h. After neutralization with 2  hydro-
chloric acid, the white precipitate formed was collected by fil-
tration.
7-[2-(Allyloxy)-2-phenylethyl]-2-aminopurin-6-one (14b): A white
powder (0.134 g, 91%), obtained by hydrolytic cleavage of 19b, m.p.
Ͼ250 °C, RF (CHCl3/MeOH, 20:1) ϭ 0.20. UV: λmax ϭ 286 nm
(pH ϭ 6.5), 252 nm (pH ϭ 1), 282 nm (pH ϭ 12). 1H NMR
(500 MHz, [D6]DMSO ϩ CF3COOH): δ ϭ 3.71 (dd, J ϭ 5.1, 13.4
Hz, 1 H, OCH2CHCH2), 3.86 (dd, J ϭ 4.0, 13.4 Hz, 1 H,
OCH2CHCH2), 4.50 (d, J ϭ 6.2 Hz, 2 H, NCH2CHPh), 4.80 (t,
J ϭ 6.2 Hz, 1 H, NCH2CHPh), 5.03 (d, J ϭ 10.4 Hz, 1 H,
OCH2CHCH2), 5.07 (d, J ϭ 17.3 Hz, 1 H, OCH2CHCH2), 5.66
(m, 1 H, OCH2CHCH2), 7.41 (m, 5 H, Ph), 8.77 (s, 1 H, 8-H)
ppm. 13C NMR (125.8 MHz, [D6]DMSO ϩ CF3COOH): δ ϭ 53.0
(NCH2CHPh), 69.2 (OCH2CHCH2), 78.6 (NCH2CHPh), 114.1 (C-
5), 116.5 (OCH2CHCH2), 126.6, 128.6, 128.8 and 137.9 (Ph), 134.5
(OCH2CHCH2), 140.2 (C-8), 149.7 (C-2), 153.4 (C-4), 154.3 (C-6)
ppm. ESI-MS: m/z ϭ 350 [M ϩ K]ϩ, 334 [M ϩ Na]ϩ, 312 [M ϩ
H]ϩ, 242 [M ϩ H Ϫ CH2CHCH2OCH2]ϩ. C16H17N5O2 (311.35):
calcd. C 61.7, H 5.5, N 22.5; found C 61.7, H 5.5, N 22.4.
(125.8 MHz, CDCl3):
(OCH2CHCH2), 80.0
δ
ϭ
15.4 (CH3), 53.3 (NCH2), 70.0
(CHPh), 110.3 (C-10a), 117.3
(OCH2CHCH2), 119.1 (C-7), 126.5, 128.5, 128.8 and 138.0 (Ph),
132.3 (OCH2CHCH2), 133.8 (C-8), 147.6 (C-3a), 148.0 (C-2), 150.3
(C-4a), 158.7 (C-10), 162.3 (C-6) ppm; HMBC showed cross-peaks
between NCH2 (δH ϭ 4.46 and 4.78 ppm) and both C-10a (δC
ϭ
110.3 ppm) and C-2 (δC ϭ 148.0 ppm). ESI-MS: m/z ϭ 400 [M ϩ
K]ϩ, 384 [M ϩ Na]ϩ, 362 [M ϩ H]ϩ. UV: λmax ϭ 260 and inflex
at 322 nm (pH ϭ 6.5), 250, 314 and 342 nm (pH ϭ 1), 260 and
320 nm (pH ϭ 11). C20H19N5O2·1/4H2O (365.91): calcd. C 65.6, H
5.37, N 19.14; found C 65.8; H 5.4, N 19.1. Reaction of 5 with
tosylate 9b under the same conditions yielded 41% of 20b and 39%
of 19b.
3-[2-(Allyloxy)-1-phenylethyl]-7-methyl-10-oxo-9,10-dihydro-
pyrimido[1,2-a]purine (20a): A yellow foam (186 mg, 35%), ob-
tained by alkylation of 5 by bromide 8a, RF (Me2CO/EtOAc, 1:1) ϭ
0.60, UV: λmax ϭ 258 and 356 nm (pH ϭ 6.5), 250, 312 and 344 nm
(pH ϭ 1), 258 and 320 nm (pH ϭ 12). 1H NMR (300 MHz,
CDCl3): δ ϭ 2.38 (s, 3 H, 7-CH3), 3.96 (dd, J ϭ 0.9, 5.6 Hz, 2 H,
OCH2CHCH2); 4.00 (dd, J ϭ 4.4, 10.6 Hz, 1 H, OCH2CHN), 4.25
(dd, J ϭ 6.4, 10.6 Hz, 1 H, NCHCH2), 5.09 (dd, J ϭ 0.9, 10.3 Hz,
7-[2-(Allyloxy)-1-phenylethyl]-2-aminopurin-6-one (14a): A white
powder (0.158 g, 81%) obtained by hydrolytic cleavage of 19a, m.p.
Ͼ250 °C, RF (CHCl3/MeOH, 20:1) ϭ 0.18. UV: λmax ϭ 286 nm
(pH ϭ 6.5), 250 nm (pH ϭ 1), 282 nm (pH ϭ 12). 1H NMR
(300 MHz, [D6]DMSO):
δ ϭ 4.00 (m, 3 H, NCHPhCH2,
OCH2CHCH2), 4.37 (t, J ϭ 9.7 Hz, 1 H, NCHPhCH2), 5.10 (dd,
J ϭ 1.5, 10.3 Hz, 1 H, OCH2CHCH2), 5.16 (dd, J ϭ 1.7, 17.3 Hz,
1 H, OCH2CHCH2), 5.82 (m, 1 H, OCH2CHCH2), 6.10 (dd, J ϭ
4.7, 9.7 Hz, 1 H, NCHPhCH2), 6.20 (s, 2 H, NH2), 7.30 (m, 5 H,
Ph), 8.28 (s, 1 H, 8-H), 10.76 (s, 1 H, 6-OH) ppm. 13C NMR
1
H, OCH2CHCH2), 5.12 (dd, J ϭ 0.9, 17.9 Hz, 1 H,
OCH2CHCH2), 5.72 (m, 1 H, OCH2CHCH2), 6.08 (dd, J ϭ 4.4,
6.4 Hz, 1 H, NCHPh), 7.23 (m, 5 H, Ph), 8.04 (s, 1 H, 2-H), 8.78
(d, J ϭ 2.6 Hz, 1 H, 6-H), 9.10 (s, 1 H, 8-H) ppm. 13C NMR
(75 MHz, CDCl3):
δ ϭ 15.5 (CH3), 57.8 (PhCHN), 70.8
(75 MHz, [D6]DMSO):
δ
ϭ
59.1 (NCHPhCH2), 69.9
(OCH2CHN) and 72.5 (OCH2), 118.1 (OCH2CHCH2), 118.4 (C-
10a), 119.5 (C-7), 127.5, 128.7, 129.1, and 136.9 (Ph), 134.0 (C-8),
136.9 (OCH2CHCH2), 141.7 (C-2), 148.5 (C-4a), 150.1 (C-3a),
152.7 (C-10), 163.0 (C-6) ppm; HMBC shows cross-peaks between
(OCH2CHCH2), 70.7 (NCHPhCH2), 107.7 (C-5), 116.6
(OCH2CHCH2), 126.3, 127.5, 128.1 and 137.7 (Ph), 134.3
(OCH2CHCH2), 141.6 (C-8), 152.3 (C-2), 154.2 (C-4), 159.2 (C-6)
ppm. ESI-MS: m/z ϭ 334 [M ϩ Na]ϩ, 312 [M ϩ H]ϩ, 152 [M
ϩ H Ϫ CH2CHCH2OCHCHPh]ϩ. C16H17N5O2·1/2H2O (320.36):
calcd. C 60.0, H 5.7, N 21.9; found C 59.8, H 5.4, N 21.4.
between NCHPh (δH
ϭ 6.08 ppm) and both C-3a (δC ϭ
150.1 ppm) and C-2 (δC ϭ 141.7 ppm). ESI-MS: m/z ϭ 384 [M ϩ
Na]ϩ, 362 [M ϩ H]ϩ. C20H19N5O2·3/4H2O (374.92): calcd. C 64.1,
H 5.5, N 18.7; found C 64.0, H 5.2, N 18.5.
Deallylation: The reaction conditions were analogous to those de-
scribed by Chandrasekhar et al.[18] Poly(methylhydrosiloxane)
(PMHS) (162 mg), tetrakis(triphenylphosphane)palladium (14 mg)
and ZnCl2 (34 mg) were added to a stirred solution of the allyl-
protected purine derivative (1.35 mmol) in 9 mL of DMF under
1-[2-(Allyloxy)-1-phenylethyl]-7-methyl-10-oxo-9,10-dihydro-
pyrimido[1,2-a]purine (19a): A yellow foam (0.180 g, 34%) obtained
by alkylation of 5 by bromide 8a, RF (Me2CO/EtOAc, 1:1) ϭ 0.25.
UV: λmax ϭ 258, 356 and 320 nm (pH ϭ 6.5), 250, 314 and 342 nm
(pH ϭ 1), 260 and 322 nm (pH ϭ 12). 1H NMR (300 MHz, argon. The reaction mixture was stirred at 60 °C for 2Ϫ3 h. After
CDCl3): δ ϭ 2.40 (d, J ϭ 0.9 Hz, 3 H, 7-CH3), 4.02 (dm, J ϭ
4.2 Hz, 2 H, OCH2CHCH2), 4.12 (dd, J ϭ 4.1, 10.9 Hz, 1 H,
evaporation of the solvent under vacuum, the crude product was
purified by column chromatography on silica gel (chloroform/
Eur. J. Org. Chem. 2004, 2738Ϫ2746
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2745

´
ˇ´
´
J. Novak, I. Linhart, H. Dvorakova
FULL PAPER
methanol, 6:1) and crystallized from iPrOH/H2O (4:1) with the ad-
[3]
K. C. Leibman, E. Ortiz, J. Pharmacol. Exp. Therap. 1970,
173, 242Ϫ246.
P. Vodicka, K. Hemminki, Carcinogenesis 1988, 9, 1657Ϫ1660.
D. E. G. Shuker, P. B. Farmer, Chem. Res. Toxicol. 1992, 5,
450Ϫ460.
dition of charcoal as a decolourising agent.
[4]
[5]
2-Amino-7-(2-hydroxy-2-phenylethyl)purin-6-one (2b): Obtained as a
greyish powder (80%) by deallylation of 14b. Crystallisation from
iPrOH/H2O (8:2) with the addition of charcoal as a decolourising
agent yielded a white powder (36%), m.p. Ͼ 250 °C, RF (Silica gel
Merck; CHCl3/MeOH, 6:1) ϭ 0.21. UV: λmax ϭ 286 nm (pH ϭ
[6] [6a]
ˇ
ˇ´
´
´
J. Jindrich, H. Dvorakova, A. Holy, Coll. Czech. Chem.
[6b]
´
A. Holy, Coll. Czech.
Commun. 1992, 57, 1466Ϫ1482.
Chem. Commun. 1993, 58, 649Ϫ674. [6c] M. Spassova, H. Dvo-
ˇ´ ˇ´
´
´
´
´
´
rakova, A. Holy, M. Budesınsky, M. Masojıdkova, Coll. Czech.
1
[6d]
6.5), 252 nm (pH ϭ 1), 282 nm (pH ϭ 12). H NMR (500 MHz,
Chem. Commun. 1994, 59, 1153Ϫ1174.
S. Andrews, Tetrahedron Lett. 1996, 37, 3931Ϫ3934.
O. L. Aceveda, R.
[D6]DMSO): δ ϭ 4.15 (dd, J ϭ 7, 13.5 Hz, 1 H, NCH2), 4.37 (dd,
J ϭ 3.5, 13.5 Hz, 1 H, NCH2), 4.93 (m, 1 H, CHOH), 5.68 (d, J ϭ
5.0 Hz, 1 H, OH), 6.14 (s, 2 H, NH2), 7.34 (m, 5 H, Ph), 7.73 (s, 1
H, 8-H), 10.78 (s, 1 H, 6-OH) ppm. 13C NMR (125.8 Hz,
[D6]DMSO): δ ϭ 53.7 (NCH2), 71.6 (CHO), 108.0 (C-5), 125.8,
127.3, 128.2 and 142.5 (Ph), 143.7 (C-8), 152.7 (C-2), 154.8 (C-4),
160.0 (C-6) ppm. ESI-MS: m/z ϭ 310 [M ϩ K]ϩ, 294 [M ϩ Na]ϩ,
272 [M ϩ H]ϩ, 152 [M ϩ H Ϫ CH2CHOHPh]ϩ, 135 [M ϩ H Ϫ
CH2CHOHPh Ϫ OH]ϩ. C13H13N5O2·1/5 H2O (274.89): calcd. C
56.8, H 4.90, N 25.5; found C 57.1, H 5.0, N 25.2.
[7]
ˇ´
´
´
H. Dvorakova, A. Holy, I. Rosenberg, Coll. Czech. Chem.
Commun. 1994, 59, 2069Ϫ2094.
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[8b]
193Ϫ201.
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[9]
J. L. Sessler, D. Magda, H. Furuta, J. Org. Chem. 1992, 57,
818Ϫ826.
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[10b]
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1
(pH ϭ 1), 282 nm (pH ϭ 12). H NMR (300 MHz, [D6]DMSO):
[12]
[13]
δ ϭ 3.97 (m, 1 H, CH2OH), 5.30 (t, J ϭ 5.5 Hz, 1 H, CH2OH),
5.90 (dd, J ϭ 3.85, 4.95 Hz, 1 H, PhCH), 6.26 (s, 2 H, NH2), 7.27
(m, 5 H, Ph), 8.23 (s, 1 H, 8-H), 10.82 (s, 1 H, 6-OH) ppm. 13C
NMR (75 MHz, [D6]DMSO): δ ϭ 62.2 (PhCH), 62.4 (CH2OH),
108.0 (C-5), 126.7, 127.6, 128.4 and 138.6 (Ph), 141.5 (C-8), 152.6
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´
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Acknowledgments
The authors are grateful to Dr. A. Holy for valuable advice given
at the initial stage of this study. The financial support by grants
No. 310/03/0437 from the Grant Agency of the Czech Republic
and No. 1553/2003 from the Ministry of Education of the Czech
Republic is gratefully acknowledged.
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Received December 30, 2003
2746
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2738Ϫ2746