Carbocyclic phosphonate-based nucleotide analogs related to PMEA II. Racemic cis-configured derivatives

Article abstract of DOI:10.1135/cccc19960778

Racemic N-(cis-2-phosphonomethoxycycloalkyl) derivatives of heterocyclic bases, a novel type of nucleotide analogs related to 9-(2-phosphonomethoxyethyl)adenine (PMEA), are reported. The synthesis of adenine-(6a, 6b), uracil-(6c) and cytosine-(6d) contain

Full text of DOI:10.1135/cccc19960778

778
Liboska, Masojidkova, Rosenberg:
CARBOCYCLIC PHOSPHONATE-BASED NUCLEOTIDE ANALOGS
RELATED TO PMEA II. RACEMIC cis-CONFIGURED DERIVATIVES
1
2
3
Radek LIBOSKA , Milena MASOJIDKOVA and Ivan ROSENBERG
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
166 10 Prague 6, Czech Republic; e-mail: 1 liboska@uochb.cas.cz, 2 saman@uochb.cas.cz,
3 ivan@uochb.cas.cz
Received November 29, 1995
Accepted January 19, 1996
Racemic N-(cis-2-phosphonomethoxycycloalkyl) derivatives of heterocyclic bases, a novel type of
nucleotide analogs related to 9-(2-phosphonomethoxyethyl)adenine (PMEA), are reported. The syn-
thesis of adenine- (6a, 6b), uracil- (6c) and cytosine- (6d) containing carbocyclic phosphonates is
based on the reaction of cis-2-hydroxycycloalkyl derivatives of protected nucleobases with diisopro-
pyl tosyloxymethanephosphonate. The starting purine-containing nucleoside analogs 5a–5f were pre-
pared by the Mitsunobu reaction of protected nucleobases with trans-2-benzyloxycycloalkanols,
whereas pyrimidine-containing nucleoside analogs 5g–5k were obtained by configurational inversion
at C-2′ of the corresponding 1-(trans-2-hydroxycycloalkyl)pyrimidines via ring opening of their 2,2′-
anhydro derivatives.
Key words: Carbocyclic analogs; Antivirals; Nucleoside phosphonates.
In our previous paper1 we described the preparation of racemic trans-configured N-(2-phos-
phonomethoxycycloalkyl) derivatives of nucleobases as one type of conformationally re-
stricted compounds related to N-(2-phosphonomethoxyethyl) derivatives of nucleobases
(PME-compounds). Another type of such compounds are cis-configured N-(2-phos-
phonomethoxycycloalkyl) derivatives 6a–6d, described in this communication. The im-
portance of these compounds (trans as well as cis isomers) from the viewpoint of
systematic study of antiviral effect of nucleotide phosphonate analogs has already been
explained in our preceding communication1.
Pyrimidine cis-2-hydroxycycloalkyl derivatives 5g–5k were obtained from the corre-
sponding trans-2-hydroxycycloalkylpyrimidines 3c and 3e–3h by inversion of configu-
ration at the carbon atom bearing the hydroxy group. This was accomplished by closing
and subsequent opening the ring in 2,2′-anhydro derivatives 4b and 4d–4f (for the cy-
tosine derivative 5k the 2,2′-anhydro derivative 4g was not isolated). The 2,2′-anhydro
derivatives were in turn prepared from the corresponding 2′-O-mesyl derivatives of
trans-2-hydroxycycloalkylpyrimidines by intramolecular substitution with the oxygen
atom of the 2-oxo group in the base on treatment with DBU in acetonitrile (Scheme 1).
In the mesylation of pyrimidine trans-2-hydroxycyclopentyl derivatives 3b and 3e in
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Carbocyclic Phosphonate-Based Nucleotides
779
HO
B
C H CH O
OH
6
5
2
( )
( )
n
n
3a
1
a
b
HO
B
c
( )
X
N
n
R
5
N
e
d
O
O
(HO) PCH O
B
2
2
( )
( )
n
n
6
4
n
B
B
n
n
n
B
n
R
X
1
3
4
5
6
1
2
3
1
2
3
2
1
2
3
2
1
2
2
2
a
b
c
d
e
f
a
b
c
d
e
f
a
b
c
d
e
f
A
A
A
G
G
G
T
a
b
c
d
A
A
U
C
a
b
c
1
1
2
1
2
3
1
2
3
2
1
2
3
A
T
Me O
Me O
Me O
T
H
H
H
O
O
O
3
1
2
3
2
T
U
U
U
C
H NH
g
h
g
g
h
i
2
U
U
j
U
C
k
a) (i) protected nucleobase B (2a-2c), Ph P, DIPAD, THF; (ii) concentrated aqueous
3
ammonia; (iii) H /Pd. b) (i) N,N-dibutylformamide dimethyl acetal; (ii) 4-nitrobenzoic
2
acid, Ph P, DIPAD, THF; (iii) concentrated aqueous ammonia. c) mesyl chloride,
3
pyridine (DBU). d) NaOH, pyridine, water; e) (i) N,N-dimethylformamide dimethylacetal;
(ii) TsOCH P(O)(OiPr) , DMF, NaH; (iii) concentrated aqueous ammonia; (iv) bromo-
2
2
trimethylsilane.
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

780
Liboska, Masojidkova, Rosenberg:
pyridine, the mesylates have not been detected at all, the mesyl group being instanta-
neously removed under formation of the 2,2′-anhydro derivatives 4a and 4d. To obtain
the desired cis-2-hydroxycycloalkylpyrimidines, the ring in the 2,2′-anhydro derivatives 4b
and 4d–4g was opened by reaction with 0.02 M aqueous solution of sodium hydroxide
at 100 °C. However, no cis-2-hydroxycyclopentylthymine has been obtained from com-
pound 4a under these conditions.
Purine cis-2-hydroxycycloalkyl derivatives 5a–5f were prepared by the Mitsunobu
reaction2–4 that makes use of activation of a hydroxy group by formation of alkoxytri-
phenylphosphonium salt which as a strong leaving group undergoes nucleophilic sub-
stitution with a suitably protected nucleobase, resulting in configurational inversion at
the corresponding carbon atom. We started from racemic trans-2-benzyloxycyclopenta-
nol (1a), trans-2-benzyloxycyclohexanol5 (1b) and trans-2-benzyloxycycloheptanol
(1c). The compounds 1a and 1c were prepared by reaction of cyclopentene and cyclo-
heptene oxide with benzyl alcohol in the presence of boron trifluoride etherate (in the
case of cyclopentene epoxide we isolated, in addition to the desired compound 1a, a
1
product identified by H NMR spectrum as a mixture of trans-2-(trans-2-benzyloxy-
cyclopentyloxy)cyclopentanols). The obtained partially protected diols 1a–1c reacted
with 6-chloropurine, 2-N-acetyl-6-O-diphenylcarbamoylguanine6 or N-(dibutylamino-
methylene) derivatives of adenine and 6-O-benzylguanine (2a and 2b, respectively) in
tetrahydrofuran in the presence of triphenylphosphine and diisopropyl azodicarboxylate
(DIPAD). This procedure afforded the cis derivatives in the adenine (5a–5c) and
guanine (5d–5f) series; an analogous treatment with 4-N-(dibutylaminomethylene)cyto-
sine (2c) and 3-N-benzoylthymine7 was not successful. Alternatively, we prepared
9-(cis-2-hydroxycyclopentyl)adenine (5a) by configurational inversion at the hydroxyl-
bearing carbon atom in N-protected 9-(trans-2-hydroxycyclopentyl)adenine1 (3a) using
the Mitsunobu reaction in the presence of 4-nitrobenzoic acid8. The above-mentioned
dibutylaminomethylene derivatives od adenine, 6-O-benzylguanine and cytosine (2a–2c)
were obtained in quantitative yields by sonication of free nucleobases with N,N-dibu-
tylformamide dineopentyl acetal9 in dimethylformamide at room temperature. The thus-
protected bases are much better soluble in organic solvents than other derivatives such
as dimethylaminomethylene or N-benzoyl derivatives.
The obtained protected cis derivatives 5a–5f were fully deprotected: the amidine
group was removed by heating in methanolic ammonia in an autoclave, the diphenyl-
carbamoyl group by treatment with sodium methoxide in methanol, and the O-benzyl
group by catalytic hydrogenation on palladium. The free purine (5a, 5b) and pyrimidine
(5i, 5k) cis-hydroxycycloalkyl derivatives were further converted into the correspond-
ing O-phosphonomethyl ethers 6a, 6b and 6c, 6d, respectively. The O-phosphono-
methyl group was attached by reaction of an alkoxide generated from the secondary
hydroxyl of the N,N-dimethylaminomethylene derivatives of compounds 5a and 5b, of
the uracil derivative 5i, and of the N-benzoyl derivative of compound 5k with diisopropyl
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Carbocyclic Phosphonate-Based Nucleotides
781
tosyloxymethanephosphonate1. The N-protecting groups were removed by treatment with
aqueous ammonia, the phosphonate ester groups were cleaved off with bromotrimethylsilane
in acetonitrile and the free cis-2-phosphonomethoxycycloalkyl derivatives of adenine 6a
and 6b, uracil 6c and cytosine 6d were obtained by ion exchanger chromatography.
The structure of the compounds was verified by 1H NMR and J-modulated 13C NMR
spectra (“attached proton test pulse sequence”). The observed coupling constants J(H-1′,
H-2′) of the carbocycles (4.2–4.6 Hz for five-membered, 2.4–3.4 Hz for six-membered,
and 2.7–3.0 Hz for seven-membered rings), as well as the chemical shifts of individual
carbon atoms (Table I) correspond to the cis configuration of 1,2-disubstituted cyclo-
alkanols10. The 1H NMR spectra of 2,2′-anhydro derivatives are characterized by down-
field shift of the H-1′ and H-2′ signals (about 0.8 ppm) and by change in the coupling
constant J(1′,2′) (6.8 and 9.0, respectively). The signals of the heterocyclic base protons
are influenced only negligibly (about 0.2 ppm downfield shift); however, the 13C NMR
spectra exhibit marked downfield shifts (about 8 ppm) of the C-2 and C-4 carbon sig-
nals (Table I). These shifts, together with the observed downfield shift of the C-2′
signal (about 15 ppm; Table II), indicate a 2,2′-anhydro bond10. Chemical shifts (C-2′,
3
C-P, 31P) and coupling constants (1J(P-C,P), J(P,C-2′)) of the phosphonomethoxy-
cycloalkyl derivatives are given in Table III.
The antiviral activity of all the nucleoside and nucleotide analogs prepared in this
study was determined on virus-infected host cells in cell cultures in the laboratory of
Prof. E. De Clercq, Catholic University, Leuven (Belgium). The effect on the following
herpetic viruses was systematically studied: herpes simplex virus type 1 and 2 (HSV-1,
HSV-2) and vaccinia virus (VV) as representatives of DNA viruses, vesicular stomatitis
virus (VSV), in many cases also reovirus type 1, parainfluenzavirus 3, poliovirus and
sindbisvirus as representatives of RNA viruses, and finally human immunodeficiency
virus type 1 and 2 (HIV 1, HIV 2) and Moloney sarcoma virus (MSV) as retroviruses.
None of the studied compounds approached the activity of the parent compound, 9-(2-
phosphonomethoxyethyl)adenine (PMEA).
EXPERIMENTAL
Unless stated otherwise, solvents were evaporated at 40 °C and 2 kPa. The products were dried over
phosphorus pentoxide at 50–70 °C and 13 Pa. Their purity was checked by chromatographic methods
(TLC, HPLC, GLC), paper electrophoresis (for ionic compounds), spectral methods (NMR, MS, IR,
quantitative UV determination) and elemental analysis.
All the described reactions were monitored by TLC (RF values are given in the text) on Silufol UV
254 foils (Kavalier, Votice). Detection by (i) UV irradiation at 254 nm (aromatic chromophores); (ii)
heating (mesyl and tosyl derivatives); (iii) spraying with 0.4% ethanolic solution of 4-(4-nitro-
benzyl)pyridine, followed by heating at 150 °C for 10 min and exposure to ammonia vapours (blue
coloration: mono- and diesters of phosphonic acids; pink coloration: tosyl and acyl groups; red-violet
coloration 2-amino-6-chloropurine derivatives).
Preparative flash chromatography was carried out on 20–40 µm spherical silica gel (Tessek, Czech
Republic); the amount of adsorbent was 20–40 times the weight of the separated mixture. Reversed-
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

782
Liboska, Masojidkova, Rosenberg:
phase preparative chromatography was carried out on spherical octadecylsilica gel (20–40 µm,
Tessek, Czech Republic). Elution was performed with water or a linear gradient of methanol in
water. For chromatographic solvent systems the concentrations are given in vol.%. Desalting of
aqueous and aqueous-alcoholic solutions was carried out on a column of a cation exchanger (Dowex
50W X 2, 200–400 mesh, H+ form). After washing the column with water (aqueous ethanol) to loss
of absorption, the product was eluted with 2.8% ammonia in water (aqueous ethanol). Chromato-
graphy on anion exchanger Dowex 1 X 2 (acetate form) was executed using a linear concentration
gradient of acetic acid in water (0–2 mol l–1), chromatography on DEAE-Sephadex A-25 was car-
ried out with a linear concentration gradient of triethylammonium hydrogen carbonate in water
(0–0.3 mol l–1).
TABLE I
Chemical shifts of carbon atoms in heterocyclic bases of compounds 4a–4f, 5a–5k and 6a–6d
δ, ppm
Compound
C-2
C-4
C-5
C-6
C-8 (CH3)
4a
4b
4c
4d
4e
4f
160.37
160.28
159.51
160.76
160.62
159.88
152.26
152.22
152.84
153.53
154.54
154.48
151.28
151.72
151.35
151.09
155.93
153.20
152.97
153.66
160.04
171.84
176.87
171.81
161.34
171.42
171.38
150.06
149.30
148.34
151.57
150.12
149.98
163.98
163.57
163.46
163.51
165.36
150.24
149.46
167.68
167.40
116.51
116.55
116.38
108.48
108.48
108.34
118.75
118.68
117.90
116.37
112.16
112.48
107.15
99.64
133.15
133.02
132.82
137.59
137.52
137.30
156.06
156.12
157.22
157.16
159.66
155.80
139.62
144.23
143.84
144.14
144.16
156.39
156.33
147.24
147.50
(13.86)
(13.86)
(13.87)
–
–
–
5a
5b
5c
5d
5e
5f
140.52
139.96
141.87
137.11
136.55
136.78
(12.39)
–
5g
5h
5i
99.88
–
5j
100.17
92.28
–
5k
6a
6b
6c
6d
–
119.01
118.91
101.62
96.71
143.39
143.52
–
–
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Carbocyclic Phosphonate-Based Nucleotides
783
HPLC analyses were performed on a reversed phase (C18) Separon SGX-RPS 10 µm (Laboratorni
pristroje, Prague); isocratic elution with 0.1 M triethylammonium acetate or gradient of methanol in
0.1 M triethylammonium acetate. Electrophoreses were carried out on Whatman No. 3 MM or What-
man No. 1 paper in 0.1 M triethylammonium hydrogen carbonate (pH 7.5) at 20 V cm–1. The electro-
phoretic mobilities (EUp) relate to uridine 5′-phosphate.
Mass spectra (m/z) were taken on a ZAB-EQ (VG Analytical) instrument, using EI (electron energy
70 eV), FAB (ionization with Xe, accelerating voltage 8 kV) or SIMS (ionization with Cs+, accele-
1
rating voltage 35 kV) techniques. Glycerol and thioglycerol were used as matrices. H NMR spectra
were measured on a Varian Unity 500 spectrometer (1H at 500 MHz, 13C at 125.7 MHz) in deute-
rated dimethyl sulfoxide with tetramethylsilane as internal standard. The free phosphonic acids were
TABLE II
Chemical shifts of carbon atoms in carbocycles of compounds 4a–4f, 5a–5k and 6a–6d
δ, ppm
Compound
C-1′
C-2′
C-3′
C-4′
C-5′
C-6′
C-7′
4a
4b
4c
4d
4e
4f
63.15
56.41
61.02
63.03
56.29
60.93
58.00
56.23
59.72
57.79
56.71
59.65
56.34
58.57
56.52
58.87
56.58
58.46
57.66
58.24
59.42
84.79
77.73
81.75
85.11
78.06
82.03
70.55
66.24
69.57
70.45
65.47
69.01
66.15
69.63
66.04
68.84
65.97
82.73
78.21
78.65
79.51
32.52
25.32
29.86
32.69
25.33
29.84
27.53
32.40
33.11
27.43
32.18
33.07
32.82
26.05
32.78
33.85
32.99
29.48
28.36
28.33
29.46
22.03
18.59
22.93
22.02
18.61
22.92
19.90
18.81
20.71
19.81
18.63
20.60
18.89
20.06
18.88
20.50
18.95
20.57
19.66
19.54
20.39
33.38
18.47
28.95
33.32
18.40
28.99
32.72
25.69
26.78
32.68
25.16
26.67
25.43
32.79
25.41
26.56
25.61
30.16
27.60
26.06
26.91
–
–
25.39
24.37
–
–
29.65
–
25.48
24.41
–
–
29.61
5a
5b
5c
5d
5e
5f
–
25.16
24.60
–
–
27.73
–
24.96
24.62
24.39
–
–
27.55
5g
5h
5i
–
–
24.35
25.24
24.71
–
–
5j
27.21
5k
6a
6b
6c
6d
–
–
–
–
–
25.80
25.85
26.91
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

784
Liboska, Masojidkova, Rosenberg:
measured in deuterium oxide containing sodium deuteroxide, internal standard sodium 3-(trimethylsi-
lyl)-1-propanesulfonate. The 13C NMR spectra were referenced to the solvent signal (δ((CD3)2SO) =
39.7), for aqueous solutions dioxane was used as external standard (δ(dioxane) = 66.86). 31P NMR spectra
were measured on a Varian Unity 200 spectrometer at 81 MHz in deuterium oxide with H3PO4 as
external standard.
The UV spectra (λmax, nm) were measured in 0.01 M hydrochloric acid (pH 2) or in 0.01 M NaOH
(pH 12) on a Pye Unicam SP 8000 or Beckmann DU65 spectrophotometer.
trans-2-Benzyloxycyclopentanol (1a)
Boron trifluoride etherate (0.62 ml, 5 mmol) was added at room temperature under argon to a mix-
ture of cyclopentene oxide (8.4 g, 100 mmol) and benzyl alcohol (12.4 ml, 120 mmol). The reaction
was strongly exothermic and the mixture was immediately cooled to room temperature in an ice bath.
After 5 min the mixture did not contain any starting epoxide (reversed-phase HPLC, linear gradient
50–100% of methanol in water). The crude product was purified by preparative chromatography on
octadecylsilica gel. Yield 6.15 g (32%) of trans-2-benzyloxycyclopentanol (1a). For C12H16O2 . 1/6 H2O
1
(195.3) calculated: 73.82% C, 8.43% H; found: 73.79% C, 8.44% C. H NMR spectrum ((CD3)2SO):
1.36–1.70 m, 4 H and 1.70–1.92 m, 2 H (CCH2); 3.68 m, 1 H and 4.00 m, 1 H (OCH); 4.48 s, 2 H
(CH2, benzyl); 4.69 d, 1 H, J(OH,CH) = 4.0 (OH); 7.32 m, 5 H (arom. H).
trans-2-Benzyloxycycloheptanol (1c)
The title compound was prepared from cycloheptene oxide (11.2 g, 100 mmol) as described above
for compound 1a. Yield 9.03 g (41%) of trans-2-benzyloxycycloheptanol (1c). For C14H20O2 . 1/6 H2O
1
(223.3) calculated: 75.30% C, 9.18% H; found: 75.11% C, 9.14% H. H NMR spectrum ((CD3)2SO):
1.30–1.85 m, 10 H (CCH2); 3.33 m, 1 H and 3.64 m, 1 H (OCH); 4.55 d, 1 H, J(OH, CH) = 4.3
(OH); 4.50 d, 1 H and 4.57 d, 1 H, J(gem) = 12.0 (CH2, benzyl); 7.20–7.40 m, 5 H (arom. H).
6-N-(Dibutylaminomethylene)adenine (2a)
A suspension of adenine (2.7 g, 20 mmol) and dibutylformamide dineopentyl acetal (8.8 ml, 24 mmol)
in dimethylformamide (40 ml) was sonicated at room temperature until the solid dissolved (2 h). The
mixture was concentrated in vacuo and the oily residue was sonicated in methanol–ether (1 : 9, 50 ml)
until all the oily material was converted into a white precipitate. This was collected, washed with
TABLE III
Selected chemical shifts and coupling constants for phosphonomethoxycycloalkyl derivatives 6
δ, ppm; J, Hz
Compound
C-2′
3J(P,C-2′)
C-P
1J(P-C,P)
31P
6a
6b
6c
6d
82.73
78.21
78.65
79.51
10.7
12.2
13.7
12.7
68.20
67.83
65.71
67.46
152.6
152.6
158.7
157.2
13.61
13.68
16.06
15.44
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Carbocyclic Phosphonate-Based Nucleotides
785
ether and dried. Yield 5.38 g (98%) of compound 2a, m.p. 175–176 °C. UV spectrum: 333 (pH 2),
314 (pH 12). For C14H22N6 (274.4) calculated: 61.29% C, 8.08% H, 30.63% N; found: 61.13% C,
1
8.10% H, 30.61% N. Mass spectrum (FAB): 275.6 (M+ + H). H NMR spectrum ((CD3)2SO): 0.91 t,
3 H and 0.92 t, 3 H, J(CH3,CH2) = 7.3 (CH3); 1.31 m, 4 H and 1.59 m, 4 H (CCH2); 3.43 t, 2 H,
J(CH2,CH2) = 7.2 and 3.59 t, 2 H, J(CH2,CH2) = 7.5 (NCH2); 8.28 brs, 1 H (H-8); 8.41 s, 1 H (H-2);
8.90 s, 1 H (CH=N); 12.94 brs, 1 H (NH).
6-O-Benzyl-2-N-(dibutylaminomethylene)guanine (2b)
Compound 2b was prepared from 6-O-benzylguanine (4.83 g, 20 mmol) as described for derivative
2a. Yield 7.31 g (96%), m.p. 141–143 °C. UV spectrum: 271, 232 (pH 2), 294, 248 (pH 12). For
C21H28N6O (380.5) calculated: 66.29% C, 7.41% H, 22.09% N; found: 66.10% C, 7.41% H, 21.85% N.
1
Mass spectrum (FAB): 381.6 (M+ + H). H NMR spectrum ((CD3)2SO): 0.90 t, 3 H and 0.91 t, 3 H,
J(CH3,CH2) = 7.3 (CH3); 1.29 m, 4 H and 1.54 m, 4 H (CCH2); 3.34 t, 2 H, J(CH2,CH2) = 7.1 and
3.44 t, 2 H, J(CH2, CH2) = 7.6 (NCH2); 8.07 brs, 1 H (H-8); 8.61 s, 1 H (CH=N); 12.80 brs, 1 H
(NH).
4-N-(Dibutylaminomethylene)cytosine (2c)
Compound 2c was prepared from cytosine (2.22 g, 20 mmol) in the same manner as described for the
derivative 2a; yield 4.91 g (98%), m.p. 179–181 °C. UV spectrum: 328, 260 (pH 2), 315, 267 (pH 12).
For C13H22N4O (250.3) calculated: 62.37% C, 8.86% H, 22.38% N; found: 62.41% C, 8.95% H,
22.44% N. Mass spectrum (FAB): 251.5 (M+ + H). 1H NMR spectrum ((CD3)2SO): 0.90 t, 6 H,
J(CH3,CH2) = 7.3 (CH3); 1.27 m, 4 H and 1.54 m, 4 H (CCH2); 3.40 t, 2 H, J(CH2,CH2) = 7.2 and
3.46 t, 2 H, J(CH2,CH2) = 7.4 (NCH2); 5.80 d, 1 H, J(5,6) = 6.8 (H-5); 7.51 brd, 1 H, J(6,5) = 6.8
(H-6); 8.58, s, 1 H (CH=N); 10.87 brs, 1 H (NH).
2,2′-Anhydro-1-(cis-2-hydroxycyclopentyl)thymine (4a)
A mixture of 1-(trans-2-hydroxycyclopentyl)thymine1 (3b; 0.21 g, 1 mmol), mesyl chloride (0.5 ml,
6 mmol) and pyridine (5 ml) was stirred at room temperature for 4 h. Water (10 ml) was added and
the mixture was set aside for 12 h. After evaporation of the solvent, the product was isolated by
chromatography on silica gel in a gradient of methanol in ethyl acetate (0–20%). Yield 0.18 g (94%)
1
of compound 4a, m.p. 189 °C. Mass spectrum (FAB): 193 (M+ + H), 127 (thymine + H+). H NMR
spectrum ((CD3)2SO): 1.40 m, 1 H, and 1.68–1.82 m, 3 H ((CH2)2); 1.78 d, 3 H, J(6, CH3) = 1.0
(CH3); 2.00 m, 2 H (CH2); 4.86 brt, 1 H, J = 6.4 and 6.8 (OCH); 5.36 dd, 1 H, J = 5.9 and 6.8
(NCH); 7.65 brq, 1 H, J = 1.0 (H-6).
2,2′-Anhydro-1-(cis-2-hydroxycyclohexyl)thymine (4b)
1
A solution of 1-(trans-2-hydroxycyclohexyl)thymine (3c; 0.23 g, 1 mmol) and mesyl chloride (0.5 ml,
6 mmol) in pyridine (5 ml) was stirred at room temperature for 4 h. After addition of water (10 ml)
the reaction mixture deposited the O-mesyl derivative (0.15 g). This compound was stirred with DBU
(0.082 ml, 0.55 mmol) in acetonitrile (5 ml) for 12 h and the product was isolated by chromato-
graphy on silica gel as described for compound 4a. Yield 0.09 g (44% related to the trans derivative)
1
of compound 4b, m.p. 227 °C. Mass spectrum (FAB): 207 (M+ + H), 127 (thymine + H+). H NMR
spectrum ((CD3)2SO): 1.30–1.50 m, 4 H, and 1.63 m, 1 H, and 1.86 m, 2 H, and 1.96 m, 1 H
((CH2)4); 1.79 d, 3 H, J(6,CH3) = 1.2 (CH3); 4.46 td, 1 H, J = 5.9, 6.6 and 6.6 (OCH); 4.96 dt, 1 H,
J = 4.9, 4.9 and 6.8 (NCH); 7.71 brq, 1 H, J = 1.2 (H-6).
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2,2′-Anhydro-1-(cis-2-hydroxycycloheptyl)thymine (4c)
1-(trans-2-Hydroxycycloheptyl)thymine1 (3d; 0.12 g, 0.5 mmol) was treated with mesyl chloride
(0.25 ml, 3 mmol) in pyridine (2.5 ml) as described for the preparation of 4b. Freeze-drying from
water afforded 0.08 g (73%) of compound 4c. For C12H16N2O2 (220.3) calculated: 65.43% C, 7.32% H,
1
12.72% N; found: 65.18% C, 7.36% H, 12.60% N. H NMR spectrum ((CD3)2SO): 1.30–1.75 m, 6 H
((CH2)3); 1.78 d, 3 H, J(6,CH3) = 1.0 (CH3); 1.80–2.10 m, 4 H ((CH2)2); 4.62 m, 1 H (OCH); 5.14 m,
1 H (NCH); 7.68 brq, 1 H, J = 1.0 (H-6).
2,2′-Anhydro-1-(cis-2-hydroxycyclopentyl)uracil (4d)
Compound 4d was prepared from 1-(trans-2-hydroxycyclopentyl)uracil1 (3e; 0.13 g, 0.65 mmol) as
described for the thymine derivative 4a. Chromatography on octadecylsilica gel gave 0.10 g (86%) of
1
compound 4d, m.p. 203 °C. Mass spectrum (FAB): 179 (M+ + H), 113 (uracil + H+). H NMR spec-
trum ((CD3)2SO): 1.43 m, 1 H, 1.70–1.83 m, 4 H, and 2.00 m, 1 H ((CH2)3); 4.87 brt, 1 H, J = 6.4
and 6.8 (OCH); 5.38 dd, 1 H, J = 5.9 and 6.8 (NCH); 5.81 d, 1 H, J(5,6) = 7.3 (H-5); 7.75 d, 1 H,
J(6,5) = 7.3 (H-6).
2,2′-Anhydro-1-(cis-2-hydroxycyclohexyl)uracil (4e)
Compound 4e was prepared from 1-(trans-2-hydroxycyclohexyl)uracil1 (3f; 0.21 g, 1 mmol) as de-
scribed for the preparation of compound 4b. Yield 0.17 g (90%) of product 4e, m.p. 233 °C. Mass
1
spectrum (FAB): 193 (M+ + H), 113 (uracil + H+). H NMR spectrum ((CD3)2SO): 1.30–1.50 m, 4 H,
1.60 m, 1 H, 1.88 m, 2 H, and 1.98 m, 1 H ((CH2)4); 4.48 td, 1 H, J = 5.9, 6.8 and 6.8 (OCH); 4.99 dt,
1 H, J = 4.6, 4.6 and 7.0 (NCH); 5.82 d, 1 H, J(5,6) = 7.3 (H-5); 7.80 d, 1 H, J(6,5) = 7.3 (H-6).
2,2′-Anhydro-1-(cis-2-hydroxycycloheptyl)uracil (4f)
Compound 4f was prepared from 1-(trans-2-hydroxycycloheptyl)uracil1 (3g; 0.67 g, 3 mmol) as de-
scribed for the preparation of compound 4b. Yield 0.57 g (92%) of product 4f, m.p. 214 °C. For
C11H14N2O2 (206.2) calculated: 64.06% C, 6.84% H, 13.58% N; found: 64.18% C, 6.92% H, 13.77% N.
1
Mass spectrum (FAB): 207 (M+ + H). H NMR spectrum ((CD3)2SO): 1.35–1.65 m, 6 H, and 1.90–
2.05 m, 4 H ((CH2)5); 4.62 td, 1 H, J = 3.9, 9.0 and 9.0 (OCH); 5.16 td, 1 H, J = 3.9, 9.0 and 9.0
(NCH); 5.81 d, 1 H, J(5,6) = 7.3 (H-5); 7.77 d, 1 H, J(6,5) = 7.3 (H-6).
9-(cis-2-Hydroxycyclopentyl)adenine (5a)
Method A. A mixture of 6-chloropurine (0.77 g, 5 mmol), trans-2-benzyloxycyclopentanol (1a;
0.96 g, 5 mmol) and triphenylphosphine (3.93 g, 15 mmol) was dried by codistillation with toluene
and dissolved in anhydrous THF (30 ml). Diisopropyl azodicarboxylate (2.95 ml, 15 mmol) was
added with stirring at –70 °C. The reaction mixture was stirred at room temperature for 3 days,
stripped of the solvent and the residue was chromatographed on silica gel (0–20% ethyl acetate in
toluene). The obtained intermediate was heated at 100 °C for 8 h with methanolic ammonia (50 ml,
saturated at –10 °C) in an autoclave. After evaporation of the solvent, the product was hydrogenated
for 16 h over palladium (200 mg, 10% Pd/C) in a mixture of acetic acid (200 ml) and 1 M aqueous
HCl (10 ml) at room temperature. The crude product 5a was deionized and then chromatographed on
Dowex 50W X 2. Crystallization from water afforded 0.28 g (26%) of product 5a, m.p. 225 °C.
Method B. 9-(trans-2-Hydroxycyclopentyl)adenine (3a; 2.33 g, 10 mmol) was treated with dibutyl-
formamide dimethyl acetal (5.5 ml, 15 mmol) in DMF (10 ml) to give the dibutylaminomethylene
derivative as described for the preparation of 6-N-(dibutylaminomethylene)adenine (2a). The obtained
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787
protected nucleoside derivative was mixed with triphenylphosphine (10.5 g, 40 mmol) and 4-nitro-
benzoic acid (6.68 g, 40 mmol) in tetrahydrofuran (80 ml). Diisopropyl azodicarboxylate (7.9 ml, 40 mmol)
was added at 10 °C to the stirred mixture under argon and the mixture was allowed to stand at room
temperature for 2 days. The obtained solution was diluted with 28% aqueous ammonia (500 ml),
saturated at 0 °C with gaseous ammonia, and the resulting suspension was stirred for 4 days at room
temperature. After concentration, the solution was extracted with ether and the aqueous layer desalted
on Dowex 50W X 2 (H+ form). Crystallization from water gave 0.36 g (15%) of cis derivative 5a,
identical with the compound obtained according to method A. UV spectrum: 261 (pH 2), 262 (pH 12).
For C10H13N5O (219.3) calculated: 54.78% C, 5.98% H, 31.94% N; found: 54.41% C, 6.01% H,
1
31.05% N. Mass spectrum (FAB): 220 (M+ + H). H NMR spectrum ((CD3)2SO): 1.59–1.75 m, 2 H,
1.85–2.00 m, 2 H, 2.07 m, 1 H, and 2.24 m, 1 H ((CH2)3); 4.15 m, 1 H (OCH); 4.68 ddd, 1 H, J = 4.6,
7.8 and 11.5 (NCH); 4.97 brs, 1 H (OH); 7.22 brs, 2 H (NH2); 8.14 s, 1 H and 8.16 s, 1 H (H-2, H-8).
9-(cis-2-Hydroxycyclohexyl)adenine (5b)
Compound 5b was prepared from 6-N-(dibutylaminomethylene)adenine (2a; 1.37 g, 5 mmol) and
trans-2-benzyloxycyclohexanol5 (1b; 1.03 g, 5 mmol) as described for the preparation of derivative
5a (method A). After stirring for 48 h, the mixture was concentrated, the residue mixed with methanol–
water–triethylamine mixture (5 : 5 : 1; 50 ml) and heated at 80 °C for 4 h. The mixture was
deionized and the obtained O-benzyl derivative of compound 5b was chromatographed on octa-
decylsilica gel (methanol in water, 0–50%). Hydrogenolysis on palladium (200 mg, 10% Pd/C) under
conditions described for 5a (method A), deionization, and crystallization from water afforded 0.35 g
(30%) of product 5b, m.p. 234 °C. UV spectrum: 261 (pH 2), 262 (pH 12). For C11H15N5O (233.3)
calculated: 56.64% C, 6.48% H, 30.02% N; found: 56.25% C, 6.64% H, 29.72% N. Mass spectrum
1
(FAB): 234 (M+ + H). H NMR spectrum ((CD3)2SO): 1.39–1.49 m, 2 H, 1.57–1.72 m, 3 H; 1.75–
1.84 m, 2 H, and 2.25 m, 1 H ((CH2)4); 3.97 m, 1 H (OCH); 4.45 ddd, 1 H, J = 3.4, 2.7 and 12.9
(NCH); 5.02 d, 1 H, J(OH,CH) = 4.6 (OH); 7.20 brs, 2 H (NH2); 8.12 s, 1 H and 8.13 s, 1 H (H-2,
H-8).
9-(cis-2-Hydroxycycloheptyl)adenine (5c)
Compound 5c was prepared from 6-N-(dibutylaminomethylene)adenine (2a; 0.27 g, 1 mmol) and
trans-2-benzyloxycycloheptanol (1c; 0.22 g, 1 mmol) as described for the preparation of derivative
5a (method A). After 48 h, the triphenylphosphine oxide was removed on Dowex 50W X 2 (H+ form)
by elution with ethanol–water mixture (75 : 25, v/v) and the fully protected product was liberated by
addition of 2.8% solution of ammonia in the same mixture. After evaporation, the residue was heated
with methanolic ammonia (saturated at –10 °C) at 110 °C for 8 h in an autoclave. Hydrogenolysis on
palladium (200 mg, 10% Pd/C) under conditions described for the preparation of compound 5a
(method A) and crystallization from acetone–diethyl ether afforded 80 mg (32%) of product 5c, m.p.
263 °C. UV spectrum: 261 (pH 2), 262 (pH 12). For C12H17N5O (247.3) calculated: 58.28% C,
6.93% H, 28.32% N; found: 58.25% C, 6.94% H, 28.23% N. Mass spectrum (FAB): 248 (M+ + H).
1H NMR spectrum ((CD3)2SO): 1.10–1.80 m, 9 H, and 2.40 m, 1 H ((CH2)5); 3.97 m, 1 H (OCH);
4.59 ddd, 1 H, J = 1.5, 2.7 and 11.5 (NCH); 5.10 brs, 1 H (OH); 8.30 brs, 2 H (NH2); 8.31 s, 1 H
and 8.33 s, 1 H (H-2, H-8).
9-(cis-2-Hydroxycyclopentyl)guanine (5d)
Compound 5d was prepared from 2-N-acetyl-6-O-diphenylcarbamoylguanine6 (1.94 g, 5 mmol) and
trans-2-benzyloxycyclopentanol (1a; 0.96 g, 5 mmol) as described for the adenine derivative 5a.
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Liboska, Masojidkova, Rosenberg:
After 4 days, the reaction mixture was concentrated and the residue allowed to stand with 2 M metha-
nolic sodium methoxide (50 ml) at room temperature for 12 h. Deionization with Dowex 50W X 2
(H+ form), chromatography on silica gel in chloroform–ethanol (95 : 5) and crystallization from the
same solvent mixture gave 0.60 g (38%) of 9-(cis-2-benzyloxycyclopentyl)guanine which was de-
benzylated on palladium (1 g, 10% Pd/C) under conditions described for compound 5a (method A).
Crystallization from water gave 0.27 g (90%) of compound 5d, m.p. >335 °C (decomp.). UV spec-
trum: 254 (pH 2), 267 (pH 12). For C10H13N5O2 (235.3) calculated: 51.06% C, 5.57% H, 29.77% N;
found: 50.96% C, 5.42% H, 29.75% N. Mass spectrum (FAB): 236 (M+ + H), 152 (guanine + H+).
1H NMR spectrum ((CD3)2SO): 1.40–2.30 m, 6 H ((CH2)3); 4.07 m, 1 H, (OCH); 4.40 m, 1 H (NCH);
4.94 brs, 1 H (OH); 6.41 brs, 2 H, (NH2); 7.72 s, 1 H (H-8); 10.59 brs, 1 H (NH).
9-(cis-2-Hydroxycyclohexyl)guanine (5e)
Compound 5e was prepared from 6-O-benzyl-2-N-(dibutylaminomethylene)guanine (2b; 1.91 g, 5 mmol)
and trans-2-benzyloxycyclohexanol5 (1b; 1.03 g, 5 mmol) as described for the adenine derivative 5a
(method A). After hydrogenation, the crude product was purified by reversed-phase chromatography.
Yield 0.35 g (28%) of compound 5e, m.p. >310 °C (decomp.). UV spectrum: 254 (pH 2), 267 (pH
12). For C11H15N5O2 (249.3) calculated: 53.00% C, 6.07% H, 28.10% N; found: 52.81% C, 5.93% H,
1
27.83% N. Mass spectrum (FAB): 250 (M+ + H). H NMR spectrum ((CD3)2SO): 1.34–1.70 m, 5 H,
1.80 m, 2 H, and 2.16 m, 1 H ((CH2)4); 3.90 brs, 1 H (OCH); 4.26 ddd, 1 H, J = 2.5, 3.5 and 12.5
(NCH); 5.08 brs, 1 H (OH); 6.88 brs, 2 H (NH2); 8.36 s, 1 H (H-8); 11.13 brs, 1 H (NH).
9-(cis-2-Hydroxycycloheptyl)guanine (5f)
Compound 5f was prepared from 6-O-benzyl-2-N-(dibutylaminomethylene)guanine (2b; 0.38 g, 1 mmol)
and trans-2-benzyloxycycloheptanol (1c; 1.03 g, 5 mmol) as described for the adenine derivative 5a
(method A). Hydrogenolysis on palladium (48 h, method A), chromatography on octadecylsilica gel
(methanol in 0.1 M triethylammonium acetate, pH 7.1; gradient 0–50%), and desalting on the same
carrier (gradient of methanol 0–50%) afforded 0.23 g (85%) of compound 5f, m.p. >310 °C (de-
comp.) UV spectrum: 254 (pH 2), 267 (pH 12). For C12H17N5O2 (263.3) calculated: 54.74% C,
6.51% H, 26.60% N; found: 54.41% C, 6.36% H, 26.49% N. Mass spectrum (FAB): 264 (M+ + H),
152 (guanine + H+). 1H NMR spectrum ((CD3)2SO): 1.40–1.80 m, 9 H, and 2.28 m, 1 H ((CH2)5);
3.95 m, 1 H (OCH); 4.35 dt, 1 H, J = 3.0, 3.0 and 11.5 (NCH); 5.40 brs, 1 H (OH); 6.87 brs, 2 H
(NH2); 8.26 s, 1 H (H-8); 11.18 brs, 1 H (NH).
1-(cis-2-Hydroxycyclohexyl)thymine (5g)
Anhydro derivative 4b (0.10 g, 0.5 mmol) was heated with 0.2 M aqueous sodium hydroxide (10 ml)
at 60 °C for 1 h. Deionization on Dowex 50W X 2 (H+ form; elution with 50% aqueous methanol),
followed by freeze-drying, afforded the product 5g in quantitative yield. For C11H16N2O3 (224.3) cal-
culated: 58.91% C, 7.19% H, 12.49% N; found: 58.97% C, 7.25% H, 12.37% N. Mass spectrum
1
(FAB): 225 (M+ + H), 127 (thymine + H+). H NMR spectrum ((CD3)2SO): 1.30–1.58 m, 5 H, and
1.75 m, 2 H, and 2.03 m, 1 H ((CH2)4); 1.76 d, 3 H, J(6,CH3) = 1.0 (CH3); 3.82 m, 1 H (OCH); 4.27 ddd,
1 H, J = 2.4, 3.5 and 12.9 (NCH); 4.92 d, 1 H, J(OH,CH) = 4.6 (OH); 7.48 brq, 1 H, J = 1.0 (H-6);
11.17 brs, 1 H (NH).
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1-(cis-2-Hydroxycyclopentyl)uracil (5h)
Compound 5h was prepared in quantitative yield from the anhydro derivative 4d (0.18 g, 1 mmol) by
the same procedure as compound 5g; m.p. 177 °C. UV spectrum: 267 (pH 2), 268 (pH 12). For
C9H12N2O3 (196.2) calculated: 55.09% C, 6.16% H, 14.28% N; found: 54.94% C, 6.17% H, 14.14% N.
1
Mass spectrum (FAB): 197 (M+ + H), 113 (uracil + H+). H NMR spectrum ((CD3)2SO): 1.48–1.62 m,
2 H, 1.74–1.84 m, 2 H, and 1.84–1.96 m, 2 H ((CH2)3); 4.02 m, 1 H, J = 2.1, 4.2, 4.6 and 5.6
(OCH); 4.50 ddd, 1 H, J = 4.6, 7.6 and 11.2 (NCH); 4.94 d, 1 H, J(OH,CH) = 4.2 (OH); 5.47 d, 1 H,
J(5,6) = 8.0 (H-5); 7.60 d, 1 H, J(6,5) = 8.0 (H-6); 11.71 brs, 1 H (NH).
1-(cis-2-Hydroxycyclohexyl)uracil (5i)
Compound 5i was prepared in quantitative yield from the anhydro derivative 4e (0.17 g, 0.9 mmol)
by the same procedure as described for compound 5g; m.p. 248 °C. UV spectrum: 267 (pH 2), 268
(pH 12). For C10H14N2O3 (210.23) calculated: 57.13% C, 6.71% H, 13.32% N; found: 57.33% C,
6.78% H, 13.25% N. Mass spectrum (FAB): 211 (M+ + H), 113 (uracil + H+). 1H NMR spectrum
((CD3)2SO): 1.30–1.60 m, 5 H, 1.70–1.80 m, 2 H, and 1.97 m, 1 H ((CH2)4); 3.83 m, 1 H (OCH);
4.28 ddd, 1 H, J = 2.4, 3.4 and 13.2 (NCH); 4.94 d, 1 H, J(OH,CH) = 4.6 (OH); 5.48 d, 1 H, J(5, 6) = 8.0
(H-5); 7.60 d, 1 H, J(6,5) = 8.0 (H-6); 11.18 brs, 1 H (NH).
1-(cis-2-Hydroxycycloheptyl)uracil (5j)
Compound 5j was prepared in quantitative yield from the anhydro derivative 4f (0.41 g, 2 mmol) by
the same procedure as described for compound 5g; m.p. 221 °C. UV spectrum: 267 (pH 2), 268 (pH 12).
For C11H16N2O3 (224.3) calculated: 58.91% C, 7.19% H, 12.49% N; found: 58.82% C, 7.09% H,
1
12.40% N. Mass spectrum (FAB): 225 (M+ + H), 113 (uracil + H+). H NMR spectrum ((CD3)2SO):
1.32–1.78 m, 9 H, and 2.02–2.11 m, 1 H ((CH2)5); 3.85 m, 1 H (OCH); 4.37 dt, 1 H, J = 2.5, 2.5
and 11.5 (NCH); 4.98 d, 1 H, J(OH,CH) = 5.1 (OH); 5.49 d, 1 H, J(5,6) = 8.0 (H-5); 7.52 d, 1 H,
J(6,5) = 8.0 (H-6); 11.14 brs, 1 H (NH).
1-(cis-2-Hydroxycyclohexyl)cytosine (5k)
1
A solution of 1-(trans-2-hydroxycyclohexyl)cytosine (3h; 1.04 g, 5 mmol) and mesyl chloride (1.2 ml,
15 mmol) in pyridine (25 ml) was set aside at room temperature for 24 h. The mixture was diluted
with 1 M aqueous sodium hydroxide (100 ml) and heated at 100 °C for 3 h. Desalting on Dowex
50W X 2 (H+ form) afforded 0.8 g (77%) of compound 5k, m.p. 278 °C. UV spectrum: 286 (pH 2),
275 (pH 12). For C10H15N3O2 (209.3) calculated: 57.40% C, 7.23% H, 20.08% N; found: 57.64% C,
7.38% H, 19.89% N. Mass spectrum (FAB): 210 (M+ + H), 112 (uracil + H+). 1H NMR spectrum
((CD3)2SO): 1.35 m, 3 H, 1.40–1.60 m, 2 H, 1.73 m, 2 H, and 1.95 m, 1 H ((CH2)4); 3.80 m, 1 H
(OCH); 4.37 ddd, 1 H, J = 2.4, 4.4 and 13.4 (NCH); 4.81 d, 1 H, J(OH,CH) = 4.6 (OH); 5.61 d, 1 H,
J(5,6) = 7.3 (C-5); 6.84 brs, 1 H and 6.95 brs, 1 H (NH2); 7.53 d, 1 H, J(6,5) = 7.3 (C-6).
9-(cis-2-Phosphonomethoxycyclopentyl)adenine (6a)
Nucleoside derivative 5a (0.11 g, 0.5 mmol) was converted into the title compound as described for
the trans isomer1. Freeze-drying afforded 0.12 g (67%) of sodium salt of compound 6a. UV spectrum:
261 (pH 2), 262 (pH 12). Mass spectrum (FAB): 358 (M+ + H). 1H NMR spectrum (D2O, NaOD):
1.80 m, 1 H, 2.05 m, 3 H, and 2.28 m, 2 H ((CH2)3); 3.04 dd, 1 H, J(P,CH) = 8.5, J(gem) = 12.7
and 3.27 dd, 1 H, J(P,CH) = 9.3, J(gem) = 12.7 (PCH2); 4.17 brq, 1 H, J = 4.2 (OCH); 4.80 dt, 1 H,
J = 4.2, 4.2 and 8.0 (NCH); 8.16 s, 1 H and 8.39 s, 1 H (H-2, H-8).
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9-(cis-2-Phosphonomethoxycyclohexyl)adenine (6b)
Nucleoside derivative 5b (0.12 g, 0.5 mmol) was converted into the title compound as described for
the trans isomer1. Freeze-drying afforded 0.14 g (75%) of sodium salt of compound 6b. UV spectrum:
261 (pH 2), 262 (pH 12). Mass spectrum (FAB): 372 (M+ + H). 1H NMR spectrum (D2O, NaOD):
1.55 m, 3 H, 1.68 m, 1 H, 1.82 m, 1 H, 1.92 m, 1 H, and 2.30 m, 2 H ((CH2)4); 3.06 dd, 1 H,
J(P,CH) = 9.5, J(gem) = 12.2 and 3.44 dd, 1 H, J(P,CH) = 9.8, J(gem) = 12.2 (PCH2); 3.77 brs, 1 H
(OCH); 4.48 ddd, 1 H, J = 2.7, 3.8 and 12.9 (NCH); 8.13 s, 1 H and 8.56 s, 1 H (H-2, H-8).
1-(cis-2-Phosphonomethoxycyclohexyl)uracil (6c)
Compound 6c was prepared from compound 5i (0.21 g, 1 mmol) as described for the trans deriva-
tive1. Freeze-drying afforded 0.12 g (39%) of sodium salt of compound 6c. UV spectrum: 268 (pH 2),
1
268 (pH 12). Mass spectrum (FAB): 305 (M+ + H), 327 (M + Na). H NMR spectrum (D2O): 1.42–
1.63 m, 5 H, 1.90 m, 1 H, and 2.07–2.20 m, 2 H ((CH2)4); 3.32 dd, 1 H, J(P,CH) = 9.8, J(gem) =
12.9 and 3.67 dd, 1 H, J(P,CH) = 9.5, J(gem) = 12.9 (PCH2); 3.71 brs, 1 H (OCH); 4.52 ddd, 1 H,
J = 2.7, 3.9 and 13.2 (NCH); 5.82 d, 1 H, J(5,6) = 8.2 (H-5); 7.99 d, 1 H, J(6,5) = 8.2 (H-6).
1-(cis-2-Phosphonomethoxycyclohexyl)cytosine (6d)
Nucleoside derivative 5k (0.48 g, 2 mmol) was converted into the title compound as described for
the trans derivative1. Freeze-drying afforded 0.21 g (35%) of compound 6d. Mass spectrum (FAB):
1
304 (M+ + H). H NMR spectrum (D2O, NaOD): 1.35–1.65 m, 5 H, and 1.80–2.23 m, 3 H ((CH2)4);
3.24 dd, 1 H, J(P,CH) = 9.5, J(gem) = 12.5 and 3.58 dd, 1 H, J(P,CH) = 9.5, J(gem) = 12.5 (PCH2);
3.66 m, 1 H (OCH); 4.53 ddd, 1 H, J = 2.4, 3.4 and 13.1 (NCH); 6.01 d, 1 H, J(5,6) = 7.6 (H-5);
7.96 d, 1 H, J(6,5) = 7.6 (H-6).
The authors are indebted to Professor Eric De Clercq, Rega Institute, Leuven, Belgium, for the anti-
viral screening, Dr V. Pechanec of this Institute for elemental analyses, and Dr K. Ubik, also of this
Institute, for mass spectra (FAB) measurements. This work was supported by Grant No. 203/93/2352 of
the Grant Agency of the Czech Republic.
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