Tricyclic etheno analogs of PMEG and PMEDAP: Synthesis and biological activity

Article abstract of DOI:10.1016/j.bmc.2006.07.036

A series of novel 9-substituted (2-(3H-imidazo[1,2-a]purin-3-yl)ethoxy)methylphosphonic and 4-substituted (2-(1H-imidazo[2,1-b]purin-1-yl)ethoxy)methylphosphonic acids as tricyclic etheno analogs of potent antivirals and cytostatics PMEG and PMEDAP was synthesized and evaluated for their biological activity. Most of the compounds showed modest activity against varicella-zoster virus (VZV) and human cytomegalovirus (HCMV) except for (2-(9-oxo-5,9-dihydro-3H-imidazo[1,2-a]purin-3-yl)ethoxy)methylphosphonic acid 8 which proved markedly active against VZV and HCMV. None of the compounds tested exhibited any significant cytostatic effect.

Full text of DOI:10.1016/j.bmc.2006.07.036

Bioorganic & Medicinal Chemistry 14 (2006) 8057–8065
Tricyclic etheno analogs of PMEG and PMEDAP:
Synthesis and biological activity
a
b
b
b
´
Katerˇina Horˇejsˇı, Graciela Andrei, Erik De Clercq, Robert Snoeck,
a
a,
*
´
´
Radek Pohl and Antonın Holy
aInstitute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2,
CZ-166 10 Praha 6, Czech Republic
bRega Institute for Medical Research, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
Received 11 June 2006; revised 13 July 2006; accepted 20 July 2006
Available online 10 August 2006
Abstract—A series of novel 9-substituted (2-(3H-imidazo[1,2-a]purin-3-yl)ethoxy)methylphosphonic and 4-substituted (2-(1H-imi-
dazo[2,1-b]purin-1-yl)ethoxy)methylphosphonic acids as tricyclic etheno analogs of potent antivirals and cytostatics PMEG and
PMEDAP was synthesized and evaluated for their biological activity. Most of the compounds showed modest activity against var-
icella-zoster virus (VZV) and human cytomegalovirus (HCMV) except for (2-(9-oxo-5,9-dihydro-3H-imidazo[1,2-a]purin-3-yl)eth-
oxy)methylphosphonic acid 8 which proved markedly active against VZV and HCMV. None of the compounds tested exhibited
any significant cytostatic effect.
ꢀ 2006 Elsevier Ltd. All rights reserved.
O
NH2
N
1. Introduction
N
N
N
N
NH
NH2
P(O)(OH)2
N
O
Acyclic nucleoside phosphonates (ANPs) represent a
key class of nucleotide analogs with broad spectrum of
biological activity, either antiviral, antineoplastic, or
antiprotozoal.1
N
O
NH2
P(O)(OH)2
1
2
PMEDAP
PMEG
The highlights of the ANP series are EMEA and FDA-
approved antiviral drugs PMEA (adefovir, formulated
as adefovir dipivoxil, HepseraTM), (S)-HPMPC (cidofo-
vir, VistideTM), and (R)-PMPA (tenofovir, formulated
as tenofovir disoproxil fumarate, VireadTM).2 Another
important member of the family of acyclic nucleoside
phosphonates, PMEDAP (1, Fig. 1), is a broad-spec-
trum antiviral agent with potent activity against DNA
viruses. Despite its excellent antiviral parameters, it
was never systemically pursued in preclinical phase of
drug development, mainly due to its cytotoxicity. Its
main importance now lies in the antitumor therapy.
Similarly, PMEG (2) is an extremely active antiviral,
but again handicapped for clinical use by its toxicity.3,4
Both PMEDAP (1) and PMEG (2) are phosphorylated
Figure 1. PMEDAP and PMEG structures.
by cellular nucleotide kinases. The corresponding
diphosphates (PMEDAPpp and PMEGpp) inhibit cellu-
lar DNA polymerases and its incorporation in the grow-
ing DNA chain leads to chain termination.5–7 In
addition, PMEG and its anabolites efficiently inhibit
purine nucleoside phosphorylases;8 this activity proba-
bly contributes to their high toxicity. PMEDAP (1) as
well as PMEG (2) exhibit potent cytostatic activity in vi-
vo in rat and mouse carcinomas and sarcomas.9–11 Some
of the N6-substituted PMEDAP derivatives show
marked cytostatic activity in vivo or in vitro.12,13
In this paper, we describe the synthesis of tricyclic ethe-
no analogs of PMEDAP and PMEG, and their antiviral
and cytostatic properties. The tricyclic etheno-bridged
purine derivatives result from the reaction of purines
bearing at least one amino group on the pyrimidine ring
with chloroacetaldehyde or its synthetic congeners.14–16
Keywords: Acyclic nucleoside phosphonates; Antiviral; Chloroacetal-
dehyde; Purines.
*
Corresponding author. Tel.: +420220183555; fax: +420220183560;
e-mail: holy@uochb.cas.cz
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.07.036

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8058
Generally, two sites of cyclization are possible, giving
rise to linear and angular isomer, respectively.14,15,17
Among the etheno-bridged purines, the most intensely
studied are the 1,N6-ethenoadenine derivatives,18–25
while there are relatively few scientific papers concerning
ethenopurines derived from 2,6-diaminopurine or 2-
aminopurine.17,26,27,32 Some time ago, an analogous
Cl
O
N
O
N
N
N
N
N
N
N
iv
v
N
N
N
N
N
N
NH2
H
H
O P(O)(OiPr)2
O P(O)(OiPr)2
O
P(O)(OH)2
4
7
8
study of biological activity of tricyclic etheno derivatives
28,29
R
of acyclovir and ganciclovir was performed.
These
R
N
R
iv
N
N
N
tricyclic derivatives were less potent antivirals, but they
showed marked selectivity toward some of the DNA
viruses, namely HSV-1 and HSV-2.30 In the view of
these results, we were interested to find out whether
the introduction of the etheno bridge to PMEDAP (1)
and PMEG (2) would lead to modulation of their activ-
ity, selectivity or cytotoxicity.
N
N
N
+
N
N
N
N
N
N
N
NH2
O P(O)(OiPr)2
O
P(O)(OiPr)2
O
P(O)(OiPr)2
5a-e
9a-e
10a-e
v
v
In compounds 5 and 9-12:
a: R = cyclopropylamino
b: R = NEt2
c: R = NMe2
d: R = pyrrolidino
e: R = NH2
R
R
N
N
N
N
N
N
N
N
N
N
2. Chemistry
O
P(O)(OH)2
11a-e
O
P(O)(OH)2
There are different synthetic approaches toward the
etheno-bridged purine analogs based on the reaction
of aminopurines with aqueous chloroacetaldehyde,14–16
anhydrous haloacetaldehydes,31 or bromoacetaldehyde
diethyl acetal.31 For the synthesis of our etheno-bridged
PMEDAP and PMEG analogs, we have decided to use
the method employing aqueous chloroacetaldehyde that
we recently optimized for the cyclization of 2-amino-9-
methylpurines affording the etheno-bridged products in
reasonable yields.32
12a-e
Scheme 2. Synthesis of etheno-bridged PMEDAP and PMEG deriv-
atives. Reagents and conditions: (iv) 1 M aq ClCH2CHO, water/
dioxane, 70 ꢁC, 8 h, for yields, see Table 1; (v) Me3SiBr, acetonitrile, rt,
24 h, for yields, see Section 5.
ously for 2-amino-9-methylpurines.32 Apart from the
cyclization, hydrolysis of C–Cl bond took place leading
directly and exclusively to linear etheno-bridged PMEG
analogue 7 in a good yield (Table 1, entry 1). The exclu-
sive formation of linear regioisomer is explained by the
stabilization in the form of 5-H tautomer and corre-
sponds to our previous results from the 2-amino-9-
methylpurine series.32 The target tricyclic PMEG deriv-
In the present work, the cyclizations were performed
with diisopropyl esters of 2-amino-9-(phosphonometh-
oxyethyl)purines 4 and 5a–e. The starting compounds
4 and 5e were prepared by alkylation of 2-amino-6-chlo-
ropurine 3 and 2,6-diaminopurine 6 with the phospho-
nomethoxyethyl synthon (Scheme 1).3 Further
nucleophilic substitution of chloro intermediate 4 by
various amines led to series of N6-substituted PMEDAP
derivatives 5a–d.4
Table 1. Yields of linear and angular isomers
Entry Starting Linear
Yield of
Angular Yield of
product angular
isomer (%)
material product linear
isomer (%)
1
2
3
4
5
6
4
7
54
36
0
—
0
0
5a
5b
5c
5d
5e
9a
9b
9c
9d
9e
10a
10b
10c
10d
10e
First, we have examined the cyclization of 2-amino-6-
chloropurine derivative
(Scheme 2). The reaction was carried out at pH 6 and
70 ꢁC, in a mixture of water–dioxane as solvents, under
the same conditions as those we have described previ-
48
49
36
43
4 with chloroacetaldehyde
28
22
15
R
N
Cl
Cl
N
N
N
N
N
N
ii or iii
i
N
N
NH2
N
NH2
N
H
N
NH2
O
3
O P(O)(OiPr)2
P(O)(OiPr)2
5a-d
In compounds 5:
a: R = cyclopropylamino
b: R = NEt2
4
c: R = NMe2
d: R = pyrrolidino
e: R = NH2
NH2
N
NH2
N
N
i
N
N
N
H
N
N
NH2
NH2
6
O
P(O)(OiPr)2
5e
Scheme 1. Synthesis of starting compounds. Reagents and conditions: (i) 1—0.5 equiv Cs2CO3, DMF; 2—1.2 equiv Cl(CH2)2OCH2P(O)(O-i-Pr)2,
80 ꢁC, 8 h, 50–56%; (ii) 3 equiv (CH3)2NH(CH3)2NCOOH, acetonitrile, reflux, 3 h, 75%; (iii) 4 equiv amine RH, abs EtOH, reflux, 3 h, 65–80%.

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8059
R
3
1
R4
8
N
9
N3a
N 5
2
7
N9a
2
6
5a
3N 3aN4a N
1
N9a
N
6
N
7
5
9
4
O
P
HO
2´
1´
O
P
2´
1´
8
O3´
O3´
HO
HO
4´
4´
HO
angular
linear
Figure 2. General numbering and NOE contacts for the linear and
angular isomers.
ative 8 was obtained after cleavage of isopropyl esters of
intermediate 7 by Lewis acid (Scheme 2).
Cyclizations of PMEDAP derivatives 5a–e with chloro-
acetaldehyde were further studied (Scheme 2). Regiose-
lectivity of the reaction was strongly dependent on the
character of the amino substituent in position 6 of pur-
ine scaffold. Cyclization of 6-cyclopropylaminopurine
derivative 5a provided exclusively the linear tricyclic sys-
tem 9a (Table 1, entry 2), again probably due to the sta-
bilization in the form of 5-H tautomer. However, in the
case of cyclization of 6-diethylaminopurine 5b the angu-
lar product 10b was the only product observed (entry 3).
In all the other cases, 6-dimethylamino 5c, 6-pyrrolidino
5d, and 6-aminopurine 5e, both linear 9 and angular 10
products were isolated with some predominance of the
angular one (entries 4–6).
The overall yields of the cyclizations were good to very
good (Table 1) and higher than those of previously
reported similar cyclizations14,30,31 and even higher than
those of corresponding 9-methylpurine derivatives.32
Target-free tricyclic PMEDAP derivatives 11 and 12
were again obtained after cleavage of isopropyl esters
by Lewis acid (Scheme 2).
For structure elucidation of the new compounds, NMR
spectroscopy was used. While the complete assignment
1
of all H and 13C signals was based on a combination
1
of H, 13C APT, H,C-HSQC, and H,C-HMBC experi-
ments, a DPFGSE NOE experiment was found to be
the most efficient way to distinguish between the linear
and angular isomers (Fig. 2).32
3. Biological activity
3.1. Antiviral activity
All the free nucleotide analogs 8, 11a, 11c, 11d, 11e, 12b,
12c, 12d, and 12e were examined for their inhibitory
effect on the replication of herpes viruses, namely
varicella-zoster virus (VZV) and human cytomegalovi-
rus (HCMV), in human embryonic lung (HEL) cells
(Table 2). One of the parent compounds, PMEDAP
(1), is highly active against HSV-1 and HSV-2 within
the 50% effective concentration (EC50) range of
0.00024–0.007 lmol/mL. Against VZV and CMV it
exhibited inhibitory activity within the EC50 range of
0.0035–0.035 lmol/mL.3 The other parent compound,
PMEG (2), exhibits potent activity against all men-
tioned DNA viruses (EC50 ꢀ 0.000034–0.00007 lmol/
mL), but it is significantly toxic against the host cells.3

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8060
Compounds 12b and 11e proved to be inactive against
both VZV and HCMV. Compounds 11a, 11c, 11d,
12c, 12d, and 12e exhibited activity against both wild-
type and thymidine kinase-deficient (TKꢁ) strain of
VZV with EC50 values ranging from 0.003 to
0.053 lmol/mL. These compounds exhibited lower
activity against CMV, since EC50 values ranged from
0.004 to 0.144 lmol/mL. The best results were obtained
for the PMEG analog 8 which exhibited significant
activity against both VZV and CMV (see Table 2).
Thus, EC50 values for analog 8 against TK+ strains of
VZV were similar to those obtained for the reference
compound acyclovir. In contrast to acyclovir, com-
pound 8 proved equally active against TK+ and TKꢁ
VZV strains. Also, the PMEG analog 8 showed anti-
HCMV activity comparable to that observed for the ref-
erence compound ganciclovir. Furthermore, all the com-
pounds were subjected to cytotoxicity measurements
based on the following parameters: alteration of cell
morphology and inhibition of cell growth (see Table
2). All of the test compounds did not affect cell morphol-
ogy up to a concentration of 0.27 lmol/mL and CC50
values for cell growth were P0.12 lmol/mL.
d = 2.50 and 39.70 ppm, respectively). Chemical shifts
are in ppm and coupling constants (J) in Hz. UV spectra
were taken on a Beckman DU-65 spectrophotometer in
methanol or water solution. IR spectra were obtained
on an FT IR Bruker Equinox IFS 55 spectrometer in
KBr pellets.
5.2. Alkylation of 2-amino-6-chloropurine and 2,6-
diaminopurine
Compounds 4 and 5e were prepared by alkylation of 2-
amino-6-chloropurine (3) or 2,6-diaminopurine (6),
respectively, with diisopropyl[(2-chloroethoxy)meth-
yl]phosphonate as described in Ref. 3.
5.3. Preparation of N6-substituted 2,6-diamino-9-[2-
(phosphonomethoxy)ethyl]purines
Compounds 5a–d were prepared from 4 by heating with
the corresponding primary or secondary amine in dry
ethanol or, in case of dimethylamino derivative 7c, by
reflux with dimethylammonium N,N-dimethylcarba-
mate in dry acetonitrile, as described in Ref. 4. Products
were purified by flash chromatography and used directly
in the cyclization reaction with chloroacetaldehyde. The
following compounds were prepared by this procedure:
3.2. Cytostatic activity
Compounds 8, 11a, 11c, 11d, 11e, 12b, 12c, 12d, and 12e
were tested for cytostatic effect on the cultures of murine
leukemia L1210 cells, murine L929 cells, human cervix
carcinoma HeLa S3 cells, and human T-lymphoblastoid
CCRF-CEM cell line. None of the samples exhibited
any significant activity in these cell culture assays.
5.4. Diisopropyl (2-(2-amino-6-(cyclopropylamino)-9H-
purin-9-yl)ethoxy)methylphosphonate (5a)
Prepared from 4 (780 mg, 2 mmol) and cyclopropyl-
amine (450 mg, 8 mmol, 4 equiv). Yield: 530 mg (65%)
of 5a as brown syrupy product. MS (FAB) m/z (rel
intensity): 413 (100, M+1). HR MS (FAB): for
C17H29N6O4P calcd 413.2066, found 413.2050. 1H
NMR (400 MHz, DMSO-d6): 0.54–0.68 (m, 4H, CH2-
cycloprop); 1.15 and 1.19 (2· d, 2· 6H, Jvic = 6.2,
(CH3)2CH); 3.02 (br m, 1H, CH–N); 3.76 (d, 2H,
4. Conclusion
We have synthesized a series of novel tricyclic etheno ana-
logs of PMEDAP and PMEG by cyclization of deriva-
tives of parent compounds with chloroacetaldehyde.
Most of target compounds showed only modest activity
against DNA viruses, with the exception of 8, a tricyclic
PMEG analog, which exhibited a pronounced inhibitory
activity against VZV and HCMV. None of the com-
pounds possessed any significant cytostatic activity.
JH,P = 8.4, H-40); 3.82 (t, 2H, J2 ;1 ¼ 5:2, H-20); 4.13 (t,
0
0
2H, J1 ;2 ¼ 5:2, H-10); 4.51 (dh, 2H, JH,P = 7.7,
Jvic = 6.2, CH(CH3)2); 5.82 (br s, 2H, NH2); 7.27 (br s,
1H, NH); 7.64 (s, 1H, H-8). 13C NMR (100.6 MHz,
DMSO-d6): 6.61 (CH2-cycloprop); 23.83 and 23.96 (d,
JC,P = 4, (CH3)2CH); 42.06 (CH2-10); 64.78 (d,
JC,P = 164, CH2-40); 70.38 (d, JC,P = 6, CH(CH3)2);
70.59 (d, JC,P = 12, CH2-20); 113.47 (C-5); 137.59
(CH-8); 151.43 (C-4); 156.06 (C-6); 160.32 (C-2).
0
0
5. Experimental
5.1. General
5.5. Diisopropyl (2-(2-amino-6-(diethylamino)-9H-purin-
9-yl)ethoxy)methylphosphonate (5b)
Melting points were determined on a Kofler block and
are uncorrected. Analytical TLC was performed on sili-
ca gel pre-coated aluminum plates with fluorescent indi-
cator (Merck 5554, 60 F254). Spots were visualized with
UV light (254 nm). Column chromatography was car-
ried out on silica gel (Sigma S-0507, 40–63 lm). Mass
spectra were measured on a ZAB-EQ (Micromass,
Manchester, UK) spectrometer using the FAB (ioniza-
tion with Xe, accelerating voltage 8 kV, thioglycerol/
glycerol, 3:1 mixture or bis(2-hydroxyethyl) disulfide
Prepared from 4 (780 mg, 2 mmol) and diethylamine
(580 mg, 8 mmol, 4 equiv). Yield: 685 mg (80%) of 5b
as white crystalline product. MS (FAB) m/z (rel intensi-
1
ty): 429 (100, M+1). H NMR (400 MHz, DMSO-d6,
80 ꢁC): 1.17 (t, 6H, Jvic = 7.0, CH3CH2); 1.18 and 1.21
(2· d, 2· 6H, Jvic = 6.2, (CH3)2CH); 3.74 (d, 2H,
JH,P = 8.2, H-40); 3.85 (t, 2H, J2 ;1 ¼ 5:3, H-20); 3.88
0
0
0
0
(q, 4H, Jvic = 7.0, CH2CH3); 4.14 (t, 2H, J1 ;2 ¼ 5:3,
H-10); 4.54 (dh, 2H, JH,P = 7.7, Jvic = 6.2, CH(CH3)2);
5.43 (br s, 2H, NH2); 7.64 (s, 1H, H-8). 13C NMR
(100.6 MHz, DMSO-d6, 80 ꢁC): 13.45 (CH3CH2); 23.50
and 23.61 (d, JC,P = 4, (CH3)2CH); 41.65 (CH2CH3);
1
was used as matrix). H and 13C NMR spectra were
recorded at 500 and 125.7 MHz on a Varian Unity 500
instrument in DMSO-d6 (referenced to the solvent signal

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8061
41.95 (CH2-10); 64.98 (d, JC,P = 165, CH2-40); 70.28 (d,
JC,P = 6, CH(CH3)2); 70.34 (d, JC,P = 11, CH2-20);
114.64 (C-5); 136.78 (CH-8); 152.67 (C-4); 153.69 (C-
6); 159.47 (C-2). For C18H33O4P calcd 50.46% C,
7.76% H, 19.61% N, 7.23% P, found 50.26% C, 7.74%
H, 19.38% N, 7.01% P.
silica gel in MeOH/CHCl3 3:97 yielded 120 mg (54%) of
7 as yellow syrupy product. MS (FAB) m/z (rel intensi-
ty): 398 (100, M+1). HR MS (FAB): for C16H24N5O5P
calcd 398.1593, found 398.1605. UV (MeOH): 281
(7960), 224 (22500). FT IR (KBr): 3423, 3130, 2980,
2932, 2854, 2749, 1698, 1605, 1562, 1549, 1529, 1456,
1
1386, 1376, 1252, 1238, 1200, 1106, 991, 889. H NMR
(400 MHz, DMSO-d6): 1.11 and 1.15 (2· d, 2· 6H,
5.6. Diisopropyl (2-(2-amino-6-(dimethylamino)-9H-pur-
in-9-yl)ethoxy)methylphosphonate (5c)
Jvic = 6.2, (CH3)2CH); 3.78 (d, 2H, JH,P = 8.4, H-40);
3.89 (t, 2H, J2 ;1 ¼ 5:4, H-20); 4.26 (t, 2H, J1 ;2 ¼ 5:4,
H-10); 4.48 (dh, 2H, JH,P = 7.7, Jvic = 6.2, CH(CH3)2);
7.44 (d, 1H, J6,7 = 2.6, H-6); 7.61 (d, 1H, J7,6 = 2.6, H-
7); 7.93 (s, 1H, H-2); 12.48 (br s, 1H, NH). 13C NMR
(100.6 MHz, DMSO-d6): 23.75 and 23.90 (d, JC,P = 4,
(CH3)2CH); 42.73 (CH2-10); 64.74 (d, JC,P = 164, CH2-
40); 70.34 (d, JC,P = 6, CH(CH3)2); 71.15 (d, JC,P = 11,
CH2-20); 107.00 (CH-7); 114.73 (C-9a); 116.61 (CH-6);
139.49 (CH-2); 146.12 (C-4a); 150.48 (C-3a); 151.34
(C-9).
0
0
0
0
Prepared from 4 (780 mg, 2 mmol) and N,N-dimethy-
lammoniumdimethylcarbamate
(0.8 mL,
6 mmol,
3 equiv). Yield: 620 mg (75%) of 5c as yellow solid.
MS (FAB) m/z (rel intensity): 401 (100, M+1). 1H
NMR (400 MHz, DMSO-d6): 1.16 and 1.19 (2· d, 2·
6H, Jvic = 6.2, (CH3)2CH); 3.36 (br s, 6H, (CH3)2N);
3.76 (d, 2H, JH,P = 8.4, H-40); 3.82 (t, 2H, J2 ;1 ¼ 5:3,
0
0
H-20); 4.14 (t, 2H, J1 ;2 ¼ 5:3, H-10); 4.51 (dh, 2H,
JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 5.81 (br s, 2H, NH2);
7.66 (s, 1H, H-8). 13C NMR (100.6 MHz, DMSO-d6):
23.81 and 23.94 (d, JC,P = 4, (CH3)2CH); 37.77
((CH3)2N); 42.13 (CH2-10); 64.82 (d, JC,P = 164,
CH2-40); 70.41 (d, JC,P = 6, CH(CH3)2); 70.51 (d,
JC,P = 11, CH2-20); 113.75 (C-5); 136.93 (CH-8); 152.84
(C-4); 154.94 (C-6); 159.64 (C-2). For C16H29N6O4P
calcd 47.99% C, 7.30% H, 20.99% N, 7.74% P, found
47.68% C, 7.25% H, 20.72% N, 7.40% P.
0
0
5.10. Diisopropyl (2-(9-(cyclopropylimino)-5,9-dihydro-
3H-imidazo[1,2-a]purin-3-yl)ethoxy)methylphosphonate
(9a)
Prepared from 5a (0.9 g, 2.2 mmol) and chloroacetalde-
hyde (20 ml, 1 M aq solution). Chromatography over
silica gel in MeOH/CHCl3 2:98 afforded 0.34 g (36%)
of 9a as brown syrupy product. MS (FAB) m/z (rel
intensity): 437 (100, M+1). HR MS (FAB): for
C19H29N6O4P calcd 437.2066, found 437.2076. UV
(MeOH): 328 (5780), 277 (4170), 239 (24630). FT IR
(KBr): 3430, 3077, 2980, 2934, 2749, 1662, 1584, 1559,
1529, 1440, 1386, 1376, 1362, 1240, 1177, 1142, 1106,
990, 889. 1H NMR (500 MHz, DMSO-d6): 0.94 and
1.03 (2· m, 2· 2H, CH2-cycloprop); 1.12 and 1.16 (2·
d, 2· 6H, Jvic = 6.2, (CH3)2CH); 3.80 (d, 2H,
JH,P = 8.3, H-40); 3.85 (tt, 1H, J = 7.1, 3.9, CH–N);
5.7. Diisopropyl (2-(2-amino-6-(pyrrolidin-1-yl)-9H-pur-
in-9-yl)ethoxy)methylphosphonate (5d)
Prepared from 4 (780 mg, 2 mmol) and pyrrolidine
(570 mg, 8 mmol, 4 equiv). Yield: 600 mg (71%) of 5d
as brown syrupy product. MS (FAB) m/z (rel intensity):
427 (100, M+1). HR MS (FAB): for C18H31N6O4P calcd
427.2222, found 427.2232. 1H NMR (400 MHz, DMSO-
d6): 1.16 and 1.20 (2· d, 2· 6H, Jvic = 6.2, (CH3)2CH);
1.89 (br m, 4H, CH2-pyrrolidine); 3.60 (br m, 2H,
CH2N-pyrrolidine); 3.75 (d, 2H, JH,P = 8.4, H-40); 3.81
3.94 (t, 2H, J2 ;1 ¼ 5:2, H-20); 4.38 (t, 2H, J1 ;2 ¼ 5:2,
H-10); 4.49 (dh, 2H, JH,P = 7.7, Jvic = 6.2, CH(CH3)2);
7.87 (d, 1H, J6,7 = 2.7, H-6); 8.32 (s, 1H, H-2); 8.80 (d,
1H, J7,6 = 2.7, H-7); 10.00 (br s, 1H, NH). 13C NMR
(125.8 MHz, DMSO-d6): 7.48 (CH2-cycloprop); 23.75
and 23.88 (d, JC,P = 4, (CH3)2CH); 27.95 (CH–N);
42.92 (CH2-10); 64.72 (d, JC,P = 164, CH2-40); 69.94 (d,
JC,P = 12, CH2-20); 70.32 (d, JC,P = 6, CH(CH3)2);
107.11 (CH-7); 112.29 (C-9a); 119.64 (CH-6); 142.98
(C-9); 143.80 (CH-2); 143.91 (C-4a); 151.21 (C-3a).
0
0
0
0
(t, 2H, J2 ;1 ¼ 5:3, H-20); 3.90 (br m, 2H, CH2N-pyrrol-
0
0
idine); 4.13 (t, 2H, J1 ;2 ¼ 5:3, H-10); 4.52 (dh, 2H,
JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 5.77 (br s, 2H, NH2);
7.63 (s, 1H, H-8). 13C NMR (100.6 MHz, DMSO-d6):
23.81 and 23.94 (d, JC,P = 4, (CH3)2CH); 24.00 and
25.40 (CH2-pyrrolidine); 42.03 (CH2-10); 47.40 (CH2N-
pyrrolidine); 64.81 (d, JC,P = 164, CH2-40);70.36 (d,
JC,P = 6, CH(CH3)2); 70.53 (d, JC,P = 12, CH2-20);
113.92 (C-5); 137.30 (CH-8); 152.39 (C-4); 153.24 (C-
6); 159.97 (C-2).
0
0
5.11. Diisopropyl (2-(9-(dimethylamino)-3H-imidazo[1,2-
a]purin-3-yl)ethoxy)methylphosphonate (9c) and diiso-
propyl (2-(4-(dimethylamino)-1H-imidazo[2,1-b]purin-1-
yl)ethoxy)methylphosphonate (10c)
5.8. Cyclization reaction with chloroacetaldehyde.
General procedure
Compounds 7, 9a–e and 10a–e were prepared by cycliza-
tion of compounds 4, 5a–e with 1 M aq solution of
2-chloroacetaldehyde in mixture of water and dioxane
under heating to 70 ꢁC for 7 h.32
Prepared from 5c (1.2 g, 3 mmol) and chloroacetalde-
hyde (20 ml, 1 M aq solution). Chromatography over
silica gel in MeOH/CHCl3 4:96 yielded 0.36 g (28%) of
9c as yellow syrupy product followed by 0.62 g (49%)
of 10c as light brown syrupy product. 9c: MS (FAB)
m/z (rel intensity): 425 (100, M+1). HR MS (FAB):
for C18H29N6O4P calcd 425.2066, found 425.2060. UV
(MeOH): 343 (3300), 284 (5980), 242 (16270). FT IR
(KBr): 3432, 2956, 2922, 2853, 1685, 1654, 1631, 1584,
1541, 1492, 1466, 1400, 1388, 1375, 1250, 1180, 1106,
5.9. Diisopropyl (2-(9-oxo-5,9-dihydro-3H-imidazo[1,2-
a]purin-3-yl)ethoxy)methylphosphonate (7)
Prepared from 4 (220 mg, 0.56 mmol) and chloroacetal-
dehyde (15 ml, 1 M aq solution). Chromatography over

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8062
1
1081, 984, 889. H NMR (500 MHz, DMSO-d6): 1.11
and 1.15 (2· d, 2· 6H, Jvic = 6.2, (CH3)2CH); 3.36 (s,
6H, (CH3)2N); 3.79 (d, 2H, JH,P = 8.3, H-40); 3.92 (t,
1647, 1583, 1454, 1386, 1375, 1349, 1233, 1178, 1142,
1106, 990, 891. H NMR (400 MHz, DMSO-d6): 1.06
1
and 1.10 (2· d, 2· 6H, Jvic = 6.2, (CH3)2CH); 1.98
(br m, 4H, CH2-pyrrolidine); 3.73 (d, 2H, JH,P = 8.0,
2H, J2 ;1 ¼ 5:2, H-20); 4.32 (t, 2H, J1 ;2 ¼ 5:2, H-10);
4.49 (dh, 2H, JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 7.51
(d, 1H, J6,7 = 1.8, H-6); 7.73 (d, 1H, J7,6 = 1.8, H-7);
8.17 (s, 1H, H-2). 13C NMR (125.8 MHz, DMSO-d6):
23.70 and 23.85 (d, JC,P = 4, (CH3)2CH); 41.78
((CH3)2N); 42.31 (CH2-10); 64.70 (d, JC,P = 164,
CH2-40); 70.01 (d, JC,P = 12, CH2-20); 70.29 (d,
JC,P = 6, CH(CH3)2); 107.83 (CH-7); 115.58 (C-9a);
132.38 (CH-6); 143.69 (C-9); 144.73 (CH-2); 149.42
(C-4a); 150.96 (C-3a). 10c: MS (FAB) m/z (rel intensity):
425 (100, M+1). HR MS (FAB): for C18H29N6O4P calcd
425.2066, found 425.2062. UV (MeOH): 287 (15200),
238 (31620). FT IR (KBr): 3423, 3086, 2979, 2932,
2878, 1649, 1634, 1584, 1467, 1421, 1407, 1387, 1237,
0
0
0
0
H-40); 3.91 (t, 2H, J2 ;1 ¼ 5:2, H-20); 3.9-4.3 (br m,
4H, CH2N-pyrrolidine); 4.38 (dh, 2H, JH,P = 7.7,
0
0
Jvic = 6.2, CH(CH3)2); 4.76 (t, 2H, J1 ;2 ¼ 5:2, H-10);
7.56 (d, 1H, J7,8 = 1.9, H-7); 8.06 (d, 1H, J8,7 = 1.9,
H-8); 8.13 (s, 1H, H-2). 13C NMR (100.6 MHz,
DMSO-d6): 23.70 and 23.81 (d, JC,P = 4, (CH3)2CH);
25.58 (CH2-pyrrolidine); 45.57 (CH2-10); 52.88
(CH2N-pyrrolidine); 64.97 (d, JC,P = 164, CH2-40);
70.21 (d, JC,P = 6, CH(CH3)2); 71.17 (d, JC,P = 11,
CH2-20); 108.32 (CH-8); 117.12 (C-3a); 122.94 (CH-
7); 134.00 (C-9a); 139.11 (CH-2); 145.61 (C-5a);
149.95 (C-4).
0
0
1
1178, 1165, 1142, 1107, 987, 890. H NMR (500 MHz,
DMSO-d6): 1.06 and 1.10 (2· d, 2· 6H, Jvic = 6.2,
(CH3)2CH); 3.46 (br s, 6H, (CH3)2N); 3.75 (d, 2H,
JH,P = 7.9, H-40); 3.92 (t, 2H, J2 ;1 ¼ 5:1, H-20); 4.39
(dh, 2H, JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 4.71 (t, 2H,
5.13. Diisopropyl (2-(9-amino-3H-imidazo[1,2-a]purin-3-
yl)ethoxy)methoxyphosphonate (9e) and Diisopropyl (2-
(4-amino-1H-imidazo[2,1-b]purin-1-yl)ethoxy)meth-
ylphosphonate (10e)
0
0
J1 ;2 ¼ 5:2, H-10); 7.35 (d, 1H, J7,8 = 1.9, H-7); 7.92 (d,
1H, J8,7 = 1.9, H-8); 8.01 (s, 1H, H-2). 13C NMR
(125.8 MHz, DMSO-d6): 23.66 and 23.78 (d, JC,P = 4,
(CH3)2CH); 38.71 ((CH3)2N); 45.39 (CH2-10); 64.96 (d,
JC,P = 163, CH2-40); 70.23 (d, JC,P = 6, CH(CH3)2);
71.12 (d, JC,P = 10, CH2-20); 106.89 (CH-8); 116.44
(C-3a); 128.33 (CH-7); 134.25 (C-9a); 137.65 (CH-2);
147.47 (C-5a); 150.93 (C-4).
Prepared from 5e (370 mg, 1 mmol) and chloroacetal-
dehyde (15 ml, 1 M aq solution). Chromatography
over silica gel in MeOH/CHCl3 5:95 afforded 60 mg
(15%) of 9e as yellow syrupy product followed by
170 mg (43%) of 10e as light brown syrupy product.
9e: MS (FAB) m/z (rel intensity): 397 (100, M+1).
HR MS (FAB): for C16H25N6O4P calcd 397.1753,
found 397.1757. UV (MeOH): 278 (7800), 218
(18160). FT IR (KBr): 3429, 2960, 2920, 2852, 1654,
1637, 1559, 1491, 1468, 1399, 1388, 1362, 1213,
1196, 1082, 991, 854. 1H NMR (400 MHz, DMSO-
d6): 1.11 and 1.16 (2· d, 2· 6H, Jvic = 6.2, (CH3)2CH);
0
0
5.12. Diisopropyl (2-(9-(pyrrolidin-1-yl)-3H-imidazo[1,2-
a]purin-3-yl)ethoxy)methylphosphonate (9d) and Diiso-
propyl (2-(4-(pyrrolidin-1-yl)-1H-imidazo[2,1-b]purin-1-
yl)ethoxy)methylphosphonate (10d)
3.78 (d, 2H, JH,P = 8.4, H-40); 3.90 (t, 2H, J2 ;1 ¼ 5:2,
0
0
H-20); 4.30 (t, 2H, J1 ;2 ¼ 5:2, H-10); 4.49 (dh, 2H,
JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 7.41 (d, 1H,
J6,7 = 1.6, H-6); 7.55 (br s, 2H, NH2); 7.85 (s, 1H,
H-2); 7.94 (d, 1H, J7,6 = 1.6, H-7). 13C NMR
(100.6 MHz, DMSO-d6): 23.76 and 23.90 (d, JC,P = 4,
(CH3)2CH); 42.77 (CH2-10); 64.79 (d, JC,P = 164,
CH2-40); 70.35 (d, JC,P = 6, CH(CH3)2); 70.68 (d,
JC,P = 12, CH2-20); 109.65 (CH-7); 115.58 (C-9a);
131.26 (CH-6); 137.75 (CH-2); 141.26 (C-3a); 142.25
(C-4a); 145.06 (C-9). 10e: MS (FAB) m/z (rel intensi-
ty): 397 (100, M+1). HR MS (FAB): for
C16H25N6O4P calcd 397.1753, found 397.1743. UV
(MeOH): 324 (4470), 274 (3700), 237 (25900). FT IR
(KBr): 3429, 3104, 2980, 2925, 2854, 1665, 1633,
1584, 1546, 1524, 1451, 1409, 1387, 1375, 1227,
1179, 1143, 1106, 999. 1H NMR (500 MHz, DMSO-
d6): 1.10 and 1.15 (2· d, 2· 6H, Jvic = 6.2, (CH3)2CH);
0
0
Prepared from 5d (1.1 g, 2.6 mmol) and chloroacetalde-
hyde (20 ml, 1 M aq solution). Chromatography over
silica gel in MeOH/CHCl3 5:95 afforded 0.25 g (22%)
of 9d followed by 0.42 g (36%) of 10d as light brown
syrupy products. 9d: MS (FAB) m/z (rel intensity):
451 (100, M+1). HR MS (FAB): for C20H31N6O4P
calcd 451.2222, found 451.2202. UV (MeOH): 332
(3700), 281 (7660), 238 (16820). FT IR (KBr): 3422,
2978, 2933, 2876, 1648, 1596, 1554, 1540, 1458, 1686,
1375, 1353, 1243, 1178, 1106, 990, 890. 1H NMR
(400 MHz, DMSO-d6): 1.12 and 1.16 (2· d, 2· 6H,
Jvic = 6.2, (CH3)2CH); 1.98 (m, 4H, CH2-pyrrolidine);
3.79 (d, 2H, JH,P = 8.4, H-40); 3.89 (t, 2H, J2 ;1 ¼ 5:2,
0
0
H-20); 4.20 (m, 4H, CH2N-pyrrolidine); 4.27 (t, 2H,
J1 ;2 ¼ 5:2, H-10); 4.50 (dh, 2H, JH,P = 7.7, Jvic = 6.2,
CH(CH3)2); 7.39 (d, 1H, J6,7 = 1.9, H-6); 7.96 (d, 1H,
J7,6 = 1.9, H-7); 8.02 (s, 1H, H-2). 13C NMR
(100.6 MHz, DMSO-d6): 23.77 and 23.91 (d, JC,P = 4,
(CH3)2CH); 25.60 (CH2-pyrrolidine); 42.20 (CH2-10);
52.34 (CH2N-pyrrolidine); 64.71 (d, JC,P = 164, CH2-
40); 70.10 (d, JC,P = 12, CH2-20); 70.34 (d, JC,P = 6,
CH(CH3)2); 108.56 (CH-7); 112.98 (C-9a); 130.81
(CH-6); 142.32 (C-9); 142.44 (CH-2); 150.11 (C-4a);
150.59 (C-3a). 10d: MS (FAB) m/z (rel intensity): 451
(100, M+1). HR MS (FAB): for C20H31N6O4P calcd
451.2222, found 451.2224. UV (MeOH): 288 (7360),
238 (13600). FT IR (KBr): 3430, 2987, 2933, 2877,
0
0
3.79 (d, 2H, JH,P = 8.0, H-40); 3.91 (t, 2H, J2 ;1 ¼ 5:1,
0
0
H-20); 4.30 (t, 2H, J1 ;2 ¼ 5:1, H-10); 4.49 (dh, 2H,
JH,P = 7.6, Jvic = 6.2, CH(CH3)2); 7.51 (d, 1H,
J7,8 = 1.9, H-7); 8.00 (d, 1H, J8,7 = 1.9, H-8); 8.09 (s,
1H, H-2); 8.63 (br s, 2H, NH2). 13C NMR
(125.8 MHz, DMSO-d6): 23.77 and 23.92 (d, JC,P = 4,
(CH3)2CH); 42.40 (CH2-10); 64.69 (d, JC,P = 164,
CH2-40); 71.23 (d, JC,P = 12, CH2-20); 70.35 (d,
JC,P = 6, CH(CH3)2); 105.74 (CH-8); 109.87 (C-3a);
129.54 (CH-7); 141.92 (C-9a); 142.96 (CH-2); 148.11
(C-5a); 149.86 (C-4).
0
0

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8063
5.14. Diisopropyl (2-(4-(diethylamino)-1H-imidazo[2,1-
b]purin-1-yl)ethoxy)methylphosphonate (10b)
of the corresponding sodium salt. MS (FAB) m/z (rel
intensity): 314 (72, M+1). UV (H2O): 282 (4320), 224
(12350). FT IR (KBr): 3425, 3103, 2924, 2854, 2759,
1685, 1600, 1572, 1549, 1533, 1454, 1391, 1293, 1218,
Prepared from 5b (2 g, 4.7 mmol) and chloroacetalde-
hyde (30 ml, 1 M aq solution). Chromatography over
silica gel in MeOH/CHCl3 5:95 afforded 1 g (48%) of
10b as yellow syrupy product. MS (FAB) m/z (rel inten-
sity): 453 (100, M+1). HR MS (FAB): for C20H33N6O4P
calcd 453.2379, found 453.2396. UV (MeOH): 283
(12600), 236 (18600). FT IR (KBr): 3428, 2979, 2932,
2875, 1647, 1594, 1579, 1507, 1465, 1438, 1386, 1377,
1329, 1254, 1233, 1178, 1105, 994, 891. 1H NMR
(400 MHz, DMSO-d6): 1.06 and 1.08 (2· d, 2· 6H,
Jvic = 6.2, (CH3)2CH); 1.23 (t, 6H, Jvic = 6.9, CH3CH2);
1
1107, 1067, 912. H NMR (400 MHz, D2O + NaOD,
ref(dioxane) = 3.75 ppm): 3.51 (d, 2H, JH,P = 8.5,
H-40); 3.96 (t, 2H, J2 ;1 ¼ 5:0, H-20); 4.32 (t, 2H,
0
0
J1 ;2 ¼ 5:0, H-10); 7.26 (d, 1H, J6,7 = 1.7, H-6); 7.59 (d,
1H, J7,6 = 1.7, H-7); 7.98 (s, 1H, H-2). 13C NMR
(100.6 MHz, D2O + NaOD, ref(dioxane) = 69.3 ppm):
45.60 (CH2-10); 71.70 (d, JC,P = 150, CH2-40); 72.88 (d,
JC,P = 10, CH2-20); 108.72 (CH-7); 115.31 (C-9a);
131.29 (CH-6); 144.09 (CH-2); 153.72 (C-3a); 154.16
(C-4a); 157.11 (C-9). For C10H10N5Na2O5P calcd
33.63% C, 2.82% H, 19.61% N, 12.87% Na, 8.67% P,
found 33.31% C, 2.88% H, 19.43% N, 8.51% P.
0
0
3.74 (d, 2H, JH,P = 8.0, H-40); 3.91 (t, 2H, J2 ;1 ¼ 5:3,
H-20); 3.99 (br m, 4H, CH2CH3); 4.36 (dh, 2H,
JH,P = 7.7, Jvic = 6.2, CH(CH3)2); 4.73 (t, 2H,
0
0
J1 ;2 ¼ 5:3, H-10); 7.48 (d, 1H, J7,8 = 2.1, H-7); 7.99 (d,
1H, J8,7 = 2.1, H-8); 8.09 (s, 1H, H-2). 13C NMR
(100.6 MHz, DMSO-d6): 13.63 (CH3CH2); 23.67 and
23.79 (d, JC,P = 4, (CH3)2CH); 43.21 (CH2CH3); 45.53
(CH2-10); 64.94 (d, JC,P = 163, CH2-40); 70.20 (d,
JC,P = 6, CH(CH3)2); 71.12 (d, JC,P = 11, CH2-20);
107.80 (CH-8); 116.33 (C-3a); 124.94 (CH-7); 134.38
(C-9a); 138.58 (CH-2); 146.27 (C-5a); 150.15 (C-4).
5.17. (2-(9-(Cyclopropylimino)-5,9-dihydro-3H-imi-
dazo[1,2-a]purin-3-yl)ethoxy)methylphosphonic acid (11a)
0
0
Prepared from 9a (340 mg, 0.8 mmol), afforded 60 mg
(22%) of 11a as light brown powder, mp >300 ꢁC. MS
(FAB) m/z (rel intensity): 353 (90, M+1). UV (H2O):
325 (4830), 285 sh (2700), 277 (2730 sh), 239 (17300).
FT IR (KBr): 3412, 3146, 3050, 2836, 1663, 1589,
1535, 1514, 1407, 1286, 1172, 1121, 1053, 971. 1H
NMR (500 MHz, D2O, ref(dioxane) = 3.75 ppm): 0.83
and 1.03 (2· m, 2· 2H, CH2-cycloprop); 3.32 (tt, 1H,
J = 7.1, 3.7, CH-N); 3.63 (d, 2H, JH,P = 8.8, H-40);
5.15. Cleavage of protecting isopropyl esters. General
procedure
0
0
0
0
Compounds 7, 9a–e, and 10a–e were dissolved in dry
acetonitrile (70 ml). Bromotrimethylsilane (2 ml) was
added and the reaction mixture was stirred at ambient
temperature for 24 h. The solvent was removed by evap-
oration in vacuo, the residue was treated with water, and
neutralized with ammonia solution. The mixture was
evaporated in vacuo, the residue dissolved in minimum
amount of water, and applied on a Dowex 50 · 8
column in H+ cycle. The column was washed with water
followed by a solution of ammonia/water 1:10 and the
fractions with UV absorption were collected, evaporated
in vacuo, the residue was dissolved in minimum amount
of water and alkalized with ammonia. Then it was ap-
plied on a Dowex 1 · 2 column in AcOꢁ cycle and
washed with water followed by linear gradient of acetic
acid solution (0.01–0.5 M). Fractions containing prod-
uct were collected, the solvent was removed in vacuo,
and the residue was codistilled with methanol. Then it
was dissolved in minimum amount of methanol and
the product crystallized upon addition of excessive
amount of diethyl ether. The product was filtered off
and dried. This procedure was used for the following
compounds.
3.98 (t, 2H, J2 ;1 ¼ 4:9, H-20); 4.35 (t, 2H, J1 ;2 ¼ 4:9,
H-10); 7.50 (d, 1H, J6,7 = 2.5, H-6); 7.64 (d, 1H,
J7,6 = 2.5, H-7); 8.17 (s, 1H, H-2). 13C NMR
(125.8 MHz, D2O, ref(dioxane) = 69.3 ppm): 10.58
(CH2-cycloprop); 29.55 (CH–N); 46.00 (CH2-10); 70.71
(d, JC,P = 153, CH2-40); 72.69 (d, JC,P = 12, CH2-20);
109.48 (CH-7); 113.39 (C-9a); 125.59 (CH-6); 145.26
(C-9); 147.24 (CH-2); 147.36 (C-4a); 153.36 (C-3a).
For C13H17N6O4P calcd 44.32% C, 4.86% H, 23.86%
N, 8.79% P, found 44.05% C, 4.54%H, 23.48% N,
8.60% P.
5.18. (2-(9-(Dimethylamino)-3H-imidazo[1,2-a]purin-3-
yl)ethoxy)methylphosphonic acid (11c)
Prepared from 9c (360 mg, 0.8 mmol), afforded 120 mg
(41%) of 11c as white powder, mp 250–254 ꢁC. MS
(FAB) m/z (rel intensity): 341 (40, M+1), 316 (20),
288 (53). UV (H2O): 345 (6600), 294 (5720), 289
(5700), 244 (24350). FT IR (KBr): 3141, 3046, 2806,
1656, 1578, 1442, 1404, 0089, 1128, 997. 1H NMR
(500 MHz, D2O + NaOD, ref(dioxane) = 3.75 ppm):
3.35 (s, 6H, (CH3)2N); 3.48 (d, 2H, JH,P = 8.5, H-40);
3.92 (t, 2H, J2 ;1 ¼ 5:1, H-20); 4.29 (t, 2H,
0
0
0
0
5.16. Sodium (2-(9-oxo-5,9-dihydro-3H-imidazo[1,2-
a]purin-3-yl)ethoxy)methylphosphonate (8)
J1 ;2 ¼ 5:1, H-10); 7.39 (d, 1H, J6,7 = 2.0, H-6); 7.58
(d, 1H, J7,6 = 2.0, H-7); 8.12 (s, 1H, H-2). 13C NMR
(125.8 MHz, D2O + NaOD, ref(dioxane) = 69.3 ppm):
44.29 ((CH3)2N); 45.71 (CH2-10); 71.76 (d,
JC,P = 150, CH2-40); 72.52 (d, JC,P = 10, CH2-20);
111.93 (CH-7); 116.88 (C-9a); 133.46 (CH-6); 147.34
(C-9); 147.38 (CH-2); 152.22 (C-4a); 153.11 (C-3a).
For C12H17N6O4P calcd 42.36% C, 5.04% H, 24.70%
N, 9.10% P, found 42.02% C, 5.36% H, 24.32% N,
8.84% P.
Prepared from 7 (120 mg, 0.3 mmol), afforded 40 mg
(42%) of 8 as slightly colored powder, mp >300 ꢁC. In-
stead of Dowex 1 column, DEAE Sephadex column
was used and the product was eluted with gradient of
tetrabutylammoniumbicarbonate (0.0–0.6 M). Then it
was treated with Dowex 50 in Na+ cycle, filtered off,
and evaporated in vacuo to give product in the form

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K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8064
5.19. (2-(9-(Pyrrolidin-1-yl)-3H-imidazo[1,2-a]purin-3-
yl)ethoxy)methylphosphonic acid (11d)
145.96 (C-5a); 153.99 (C-4). For C14H21N6O4P calcd
45.65% C, 5.75% H, 22.82% N, 8.41% P, found 45.28%
C, 6.09% H, 22.65% N, 8.13% P.
Prepared from 9d (250 mg, 0.5 mmol), afforded 65 mg
(32%) of 11d as white amorphous powder. MS (FAB)
m/z (rel intensity): 367 (100, M+1), 343 (37). UV
(H2O): 342 (5850), 283 (5550), 245 (21600). FT IR
(KBr): 3113, 2924, 2883, 2747, 1654, 1579, 1556, 1453,
5.22. (2-(4-(Dimethylamino)-1-H-imidazo[2,1-b]purin-1-
yl)ethoxy)methylphosphonic acid (12c)
Prepared from 10c (500 mg, 1.2 mmol), afforded 130 mg
(32%) of 12c as white powder, mp 180–185 ꢁC. MS
(FAB) m/z (rel intensity): 341 (60, M+1). UV (H2O):
284 (12500), 251 (12700 sh), 236 (23100). FT IR
(KBr): 3145, 3050, 2815, 1654, 1588, 1549, 1509, 1407,
1
1407, 1347, 1219, 1119, 990, 927. H NMR (500 MHz,
D2O, ref(dioxane) = 3.75 ppm): 2.10 (m, 4H, CH2-pyr-
rolidine); 3.56 (d, 2H, JH,P = 8.7, H-40); 3.95 (t, 2H,
J2 ;1 ¼ 4:9, H-20); 4.22 (m, 4H, CH2N-pyrrolidine);
0
0
1
4.32 (t, 2H, J1 ;2 ¼ 4:9, H-10); 7.45 (d, 1H, J6,7 = 2.7,
H-6); 8.03 (d, 1H, J7,6 = 2.7, H-7); 8.11 (s, 1H, H-2).
13C NMR (125.8 MHz, D2O, ref(dioxane) = 69.3 ppm):
28.10 (CH2-pyrrolidine); 45.89 (CH2-10); 56.62 (CH2N-
pyrrolidine); 70.87 (d, JC,P = 153, CH2-40); 72.72 (d,
JC,P = 11, CH2-20); 113.45 (CH-7); 115.98 (C-9a);
123.57 (CH-6); 145.74 (CH-2); 145.93 (C-9); 149.37 (C-
4a); 152.63 (C-3a). For C14H19N6O4P calcd 45.90% C,
5.23% H, 22.94% N, 8.46% P, found 45.55% C, 5.48%
H, 22.61% N, 8.10% P.
1232, 1113, 977. H NMR (400 MHz, D2O, ref(diox-
ane) = 3.75 ppm): 3.32 (br s, 6H, (CH3)2N); 3.44 (d,
0
0
2H, JH,P = 8.4, H-40); 3.96 (t, 2H, J2 ;1 ¼ 5:2, H-20);
0
0
4.55 (t, 2H, J1 ;2 ¼ 5:2, H-10); 7.25 (d, 1H, J7,8 = 1.9,
H-7); 7.63 (d, 1H, J8,7 = 1.9, H-8); 7.91 (s, 1H, H-2).
13C NMR (125.8 MHz, D2O+NaOD, ref(diox-
ane) = 69.3 ppm): 41.72 ((CH3)2N); 48.43 (CH2-10);
71.87 (d, JC,P = 150, CH2-40); 72.78 (d, JC,P = 10, CH2-
20); 109.24 (CH-8); 118.13 (C-3a); 132.18 (CH-7);
136.48 (C-9a); 140.36 (CH-2); 151.08 (C-5a); 153.55
(C-4). For C12H17N6O4P calcd 42.36% C, 5.04% H,
24.70% N, 9.10% P, found 42.20% C, 5.28% H,
24.52% N, 8.90% P.
0
0
5.20. (2-(9-Amino-3H-imidazo[1,2-a]purin-3-yl)eth-
oxy)methylphosphonic acid (11e)
Prepared from 9e (120 mg, 0.3 mmol), afforded 35 mg
(37%) of 11e as slightly colored powder, mp 185–190 ꢁC.
MS (FAB) m/z (rel intensity): 313 (67, M+1), 289 (100).
UV (H2O): 308 (2400 sh), 280 (7700), 254 (5300), 215
(17630). FT IR (KBr): 3407, 3142, 3049, 2925, 1692,
5.23. (2-(4-(Pyrrolidin-1-yl)-1-H-imidazo[2,1-b]purin-1-
yl)ethoxy)methylphosphonic acid (12d)
Prepared from 10d (420 mg, 0.9 mmol), afforded 105 mg
(31%) of 12d as slightly colored powder, mp 175–
180 ꢁC. MS (FAB) m/z (rel intensity): 367 (100, M+1).
UV (H2O): 283 (10160), 251 (12700 sh), 16350. FT IR
(KBr): 3417, 3143, 3051, 2880, 2742, 1651, 1584, 1506,
1
1650, 1581, 1531, 1407, 1192, 1110, 990, 932. H NMR
(400 MHz, D2O + NaOD, ref(dioxane) = 3.75 ppm):
3.50 (d, 2H, JH,P = 8.5, H-40); 3.29 (t, 2H, J2 ;1 ¼ 5:3, H-
0
0
1
20); 4.23 (t, 2H, J1 ;2 ¼ 5:3, H-10); 7.30 (d, 1H, J6,7 = 1.7,
1454, 1409, 1349, 1227, 1212, 1114, 994, 933. H NMR
0
0
H-6); 7.46 (d, 1H, J7,6 = 1.7, H-7); 7.88 (s, 1H, H-2). 13
C
(400 MHz, DMSO-d6): 1.95 and 2.09 (2· p, 2· 2H,
Jvic = 7.0, CH2-pyrrolidine); 3.45 (t, 2H, Jvic = 7.0,
CH2N-pyrrolidine); 3.62 (d, 2H, JH,P = 8.7, H-40); 3.97
(t, 2H, Jvic = 7.0, CH2N-pyrrolidine); 4.04 (t, 2H,
NMR (100.6 MHz, D2O + NaOD, ref(dioxane) =
69.3 ppm): 46.01 (CH2-10); 71.66 (d, JC,P = 150,
CH2-40); 72.97 (d, JC,P = 10, CH2-20); 112.39 (CH-7);
116.99 (C-9a); 133.41 (CH-6); 141.63 (CH-2); 142.92
(C-3a); 144.14 (C-4a); 147.70 (C-9). For C10H13N6O4P
calcd 38.47% C, 4.20% H, 26.92% N, 9.92% P, found
38.20% C, 4.52% H, 26.58% N, 9.68% P.
J2 ;1 ¼ 5:0, H-20); 4.70 (t, 2H, J1 ;2 ¼ 5:0, H-10); 7.40 (d,
1H, J7,8 = 2.7, H-7); 7.92 (d, 1H, J8,7 = 2.7, H-8); 8.12
(s, 1H, H-2). 13C NMR (100.6 MHz, DMSO-d6): 26.12
and 28.52 (CH2-pyrrolidine); 49.22 (CH2-10); 51.51 and
52.39 (CH2N-pyrrolidine); 69.99 (d, JC,P = 157, CH2-
40); 73.53 (d, JC,P = 11, CH2-20); 111.57 (CH-8); 119.71
(C-3a); 120.11 (CH-7); 136.27 (C-9a); 142.57 (CH-2);
145.96 (C-5a); 152.91 (C-4). For C14H19N6O4P calcd
45.90% C, 5.23% H, 22.94% N, 8.46% P, found 45.60%
C, 5.56% H, 22.72% N, 8.25% P.
0
0
0
0
5.21. (2-(4-(Diethylamino)-1-H-imidazo[2,1-b]purin-1-
yl)ethoxy)methylphosphonic acid (12b)
Prepared from 10b (1 g, 2 mmol), afforded 240 mg (28%)
of 12b as white amorphous powder. MS (FAB) m/z (rel
intensity): 369 (100, M+1). UV (H2O): 287 (16300), 251
(16700, sh), 237 (29100). FT IR (KBr): 3420, 2975, 2935,
2894, 2361, 1653, 1577, 1507, 1464, 1438, 1381, 1363,
5.24. (2-(4-Amino-1H-imidazo[2,1-b]purin-1-yl)eth-
oxy)methylphosphonic acid (12e)
1
1329, 1254, 1235, 1176, 1114, 1079, 989, 932. H NMR
(400 MHz, D2O, ref(dioxane) = 3.75 ppm): 1.23 (br t,
6H, Jvic = 6.7, CH3CH2); 3.56–3.79 and 3.91–4.16 (2·
vb, 2· 2H, CH2CH3); 3.68 (d, 2H, JH,P = 8.8, H-40);
Prepared from 10e (170 mg, 0.4 mmol), afforded 35 mg
(27%) of 12e as slightly colored powder, mp 270–
280 ꢁC. MS (FAB) m/z (rel intensity): 313 (52, M+1).
UV (H2O): 324 (3500), 308 (3250), 274 (3030), 237
(19500). FT IR (KBr): 3397, 3132, 3050, 1688, 1583,
1560, 1526, 1446, 1408, 1324, 1227, 1145, 1117, 1054,
916. 1H NMR (400 MHz, D2O + NaOD, ref(diox-
ane) = 3.75 ppm): 3.50 (d, 2H, JH,P = 8.5, H-40); 3.93
4.04 (t, 2H, J2 ;1 ¼ 5:0, H-20); 4.73 (t, 2H, J1 ;2 ¼ 5:0, H-
10); 7.43 (d, 1H, J7,8 = 2.7, H-7); 7.91 (d, 1H, J8,7 = 2.7,
H-8); 8.09 (s, 1H, H-2). 13C NMR (100.6 MHz, D2O,
ref(dioxane) = 69.3 ppm): 16.12 (CH3CH2); 47.20
(CH2CH3); 49.11 (CH2-10); 69.02 (d, JC,P = 159, CH2-
40); 73.79 (d, JC,P = 12, CH2-20); 111.56 (CH-8); 119.43
(C-3a); 120.16 (CH-7); 136.74 (C-9a); 142.23 (CH-2);
0
0
0
0
(t, 2H, J2 ;1 ¼ 5:3, H-20); 4.26 (t, 2H, J1 ;2 ¼ 5:3, H-10);
0
0
0
0
7.25 (d, 1H, J7,8 = 1.9, H-7); 7.50 (d, 1H, J8,7 = 1.9,

ˇ ˇ´
K. Horejsı et al. / Bioorg. Med. Chem. 14 (2006) 8057–8065
8065
H-8); 7.90 (s, 1H, H-2). 13C NMR (100.6
MHz, D2O+NaOD, ref(dioxane) = 69.3 ppm): 45.55
(CH2-10); 71.71 (d, JC,P = 150, CH2-40); 72.87 (d,
JC,P = 10, CH2-20); 108.85 (CH-8); 113.15 (C-3a);
131.62 (CH-7); 143.09 (CH-2); 150.11 (C-9a); 152.14
(C-4); 153.35 (C-5a). For C10H13N6O4P calcd 38.47%
C, 4.20% H, 26.92% N, 9.92% P, found 38.05%
C, 4.61% H, 26.64% N, 9.75% P.
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Acknowledgments
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This work was supported by the Centre for New Antiv-
irals and Antineoplastics (1M0508) of the Ministry of
Education, Youth and Sport of the Czech Republic
and it is also part of the Institute research project Z4
055 0506. The authors are indebted to Dr. Ivan Votruba
and Ing. Eva Tloustova for cytostatic activity screening
and Anita Camps, Lies Van Den Heurck and Steven
Carmans for excellent technical support.
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