Synthesis of 7-halogenated 8-aza-7-deaza-2'-deoxyguanosines and related pyrazolo[3,4-d]pyrimidine 2'-deoxyribonucleosides

Article abstract of DOI:10.1055/s-1998-4483

The synthesis of 7-bromo and 7-iodo derivatives of 8-aza-7-deaza-2'- deoxyguanosine (2, 3) as well as the halogenated 4-alkoxy derivatives 4a-c and 5a-c is described. Glycosylation of the halogenated pyrazolo[3,4- d]pyrimidine anions of 7a-c or 8a-c with 2-deoxy-3,5-di-O-(p-toluoy)-α-D- erythro-pentofuranosyl chloride (9) yields regioisomeric glycosylation products, the N(1)-isomers 10a-c and 11a-c as well sa the N(2)-compounds 12a- c. The latter isomers lose their halogen during the glycosylation in the presence of non-anhydrous KOH. Anhydrous conditions (NaH) furnished 10c, 11c together with the halogenated N(2)-isomers 13a,b. Compounds 10a-c, and 11a-c were deprotected and converted to the 4-alkoxy nucleosides 4a-c and 5a-c. The N(1)-nucleosides 4c and 5c were hydrolyzed to give the 7-bromo or 7-iodo derivatives of 8-aza-7-deaza-2'-deoxyguanosines 2 and 3. Different from regular 2'-deoxyribonucleosides the sugar moiety of pyrazolo[3,4-d]pyrimidine 2'-deoxyribonucleosides shows a preferred N-type pucker (³T₂) in solution, a conformation which is also detected in the solid state.

Full text of DOI:10.1055/s-1998-4483

207
FEATURE ARTICLE
¢
Synthesis of 7-Halogenated 8-Aza-7-deaza-2 -deoxyguanosines and Related
¢
Pyrazolo[3,4-d]pyrimidine 2 -Deoxyribonucleosides
Frank Seela,* Georg Becher
Laboratorium für Organische und Bioorganische Chemie, lnstitut für Chemie, Universität Osnabrück, Barbarastr. 7, D-49069 Osnabrück, Germany
Fax +49(541)9692370; E-mail: Fraseela@rz.uni-Osnabrueck.de
Received 24 July 1997
Abstract: The synthesis of 7-bromo and 7-iodo derivatives of 8-aza-
7-deaza-2¢-deoxyguanosine (2, 3) as well as the halogenated 4-
alkoxy derivatives 4a–c and 5a–c is described. Glycosylation of the
halogenated pyrazolo[3,4-d]pyrimidine anions of 7a–c or 8a–c with
2-deoxy-3,5-di-O-(p-toluoyl)-a-D-erythro-pentofuranosyl chloride
(9) yields regioisomeric glycosylation products, the N(1)-isomers
10a–c and 11a–c as well as the N(2)-compounds 12a–c. The latter
isomers lose their halogen during the glycosylation in the presence of
non-anhydrous KOH. Anhydrous conditions (NaH) furnished 10c,
11c together with the halogenated N(2)-isomers 13a,b. Compounds
10a–c, and 11a–c were deprotected and converted to the 4-alkoxy
nucleosides 4a–c and 5a–c. The N(1)-nucleosides 4c and 5c were
hydrolyzed to give the 7-bromo or 7-iodo derivatives of 8-aza-7-
deaza-2¢-deoxyguanosines 2 and 3. Different from regular 2¢-deoxy-
ribonucleosides the sugar moiety of pyrazolo[3,4-d]pyrimidine 2¢-
deoxyribonucleosides shows a preferred N-type pucker (3 T2) in solu-
tion, a conformation which is also detected in the solid state.
Scheme 1
Key words: pyrazolo[3,4-d]pyrimidines, nucleosides, halogenation,
glycosylation, sugar conformation
nucleobase anion glycosylation20, 21 for the synthesis of 6-
amino-4-methoxypyrazolo[3,4-d]pyrimidine (6a)4 it was
The introduction of 7-substituents into 7-deazapurine (7-
deazapurine = pyrrolo[2,3-d]pyrimidine) nucleosides re-
sults in duplex stabilization when such a residue is in-
decided to also employ the halogenated compounds 7a–c
and 8a–c for nucleoside synthesis (route iii).
corporated into an oligonuc]eotide instead of a purine
base.1–3 Within the series of various nucleobases related to
Recently, the bromination of 6-amino-4-isopropoxypyra-
zolo[3,4-d]pyrimidine (6c) was studied and the glycosyla-
tion of the brominated derivative 7c was performed.22
Originally, 6-amino-4-methoxypyrazolo[3,4-d]pyrimidi-
ne (6a) was used in the bromination reaction.22 However,
it appeared that the solubility of this base is poor in dich-
loroethane (DCE). Therefore, various 4-alkoxy-6-amino-
pyrazolo[3,4-d]pyrimidines were prepared in order to
optimize the halogenation reactions. 6-Amino-4-chloro-
pyrazolo[3,4-d]pyrimidine4 served as the starting material
which was treated with various alkali alkoxides yielding
the 4-alkoxy-6-aminopyrazolo[3,4-d]pyrimidines 6a–c.
The 4-ethoxy and the 4-isopropoxy derivatives 6b,c are
described herein, while the 4-methoxy compound 6a4 has
previously been synthesized. The alkoxy compounds 6a,b
were halogenated with a slight excess of N-bromosuccini-
mide or N-iodosuccinimide to give the halo derivatives
7a,b and 8a,b (Scheme 2).23 Changing to the more lipo-
philic isopropoxy derivatives 7c, 8c increased the yield of
halogenation.
purines the 8-aza-7-deazapurines (pyrazolo[3,4-d]pyri-
midines) represent another heterocyclic system which can
be functionalized at the same position. Pyrazolo[3,4-d]-
pyrimidine nucleosides, such as 8-aza-7-deaza-
2¢-deoxyguanosine
(1)4
and
8-aza-7-deaza-2¢-
deoxyadenosine5, 6 as well as the corresponding 2¢,3¢-
dideoxynucleosides have already been synthesized.7, 8
Also 8-aza-7-deazapurine ribonucleosides with 7-bromo
or 7-iodo substituents have been prepared.9–11 These com-
pounds exhibit interesting biological activity, in particular
antiparasitic effects and inhibitory activity against ad-
enosine kinases.9 Furthermore, pyrazolo[3,4-d]pyrim-
idine 2¢-deoxyribonucleosides have already been
incorporated into oligonucleotides12, 13 and it has already
been shown that the nonsubstituted 8-aza-7-deazaguanine
base stabilizes the DNA-duplex compared to the parent
guanine.14,15 As we wanted to combine the stabilizing ef-
fect of the pyrazolo[3,4-d]pyrimidine system with the fa-
vorable properties of the 7-substituents of 7-deazapurines,
halogenated nucleosides, such as the 8-aza-7-deaza-2¢-
deoxyguanosines 2 (Br7c7z8Gd) and 3 (I7c7z8Gd) as well as
related alkoxypyrazolo[3,4-d]pyrimidine nucleosides
4a–c and 5a–c were synthesized.
Various routes have been described for the synthesis of
pyrazolo[3,4-d]pyrimidine nucleosides: (i) Glycosylation
of pyrazole precursors which are later converted into the
target nucleosides by ring annulation,16, 17 (ii) Conversion
of a glycosyl hydrazide into a pyrazolo[3,4-d]pyrimidine
nucleoside,18, 19 and (iii) Glycosylation of a preformed
base.4, 7 As we have already employed the stereoselective
Scheme 2

208
Feature Article
SYNTHESIS
Next, the glycosylation reaction of the halogenated alkoxy
derivatives 7a–c and 8a–c was performed. The reactions
were carried out under standard conditions using various
bases, 2-deoxy-3,5-di-O-(4-toluoyl)-a-D-erythro-pento-
furanosyl chloride (9)24 as sugar component, MeCN as
solvent, and powdered KOH/TDA-1 to generate the nu-
cleobase anion. Only in the case of the isopropoxy com-
pounds 7c and 8c are the bases soluble in MeCN whereas
the glycosylation of the methoxy and ethoxy derivatives
(7a,b and 8a,b) was performed in suspension. For com-
parison of the glycosylation yields, the reaction was also
performed on 6-amino-4-isopropoxypyrazolo[3,4-d]pyri-
midine (6c) with the halogenose 9 yielding compounds
10d, 12c (see experimental section). After workup, the
glycosylation products were separated by column chro-
matography (CH2Cl2/acetone 98:2 ® 95:5). The color-
less amorphous N(1)-products 10a–c and 11a–c were
isolated from the fast migrating zones. The second zones
always gave the N(2)-isomers 12a–c which did not con-
tain halogen22 (Scheme 3). The dehalogenation of the
N(2)-nucleosides which occurred under aqueous alkaline
conditions has previously been discussed.22 For these rea-
sons, the nucleobase-anion glycosylation was performed
with NaH in anhydrous MeCN. Under these conditions
the desired halogenated N(2)-isomers 13a,b were isolated
(Scheme 4).
Scheme 3
The nature of the alkoxy group, as well as the presence of
a halogen substituent, influences the yield of glycosyla-
tion products only marginally (Table 1). In general, the pounds. Deblocking of the N(1)-compounds 10a–c and
glycosylation yield is about 10% higher when the more 11a–c and N(2)-isomers 13a,b with sodium alkoxides/al-
soluble isopropoxy bases 7c and 8c are employed. As the cohol furnished the alkoxy nucleosides 4a–c, 5a–c as well
N(2)-regioisomers lose their halogens the reaction yields as 14a,b which were purified by column chromatography.
given in Table 1 are shown for the halogenated N(1)-nu- It is interesting that the dehalogenation of the N(2)-isomer
cleosides as well as for the nonhalogenated N(2)-com- did not occur under these conditions. The alkoxy nucleo-
Biographica1 Sketches
Frank Seela, born in 1939 in Dresden, studied chemistry at the University of Göttingen.
There he received his Ph. D. in 1967 for synthetic work on actinomycines (H. Brockmann,
sen.). He was a post-doctoral fellow at Yale University (D. M. Crothers) and received his
habilitation in 1974. He spent 3 years as guest scientist at the Max-Planck-Institut für Ex-
perimentelle Medizin, Göttingen (F. Cramer). Then he joined the University of Pader-
born and became Professor (C2) in 1976. He was appointed as Full Professor (C4) for
Organic Chemistry at the University of Osnabrück in 1986. His research includes work
on heterocycles, carbohydrates, nucleosides and oligonucleotides. The current interest is
focused on the recognition of base pairs in synthetic DNA, on supramolecular assem-
blies, as well as oligonucleotide-hybridisation arrays. He has published more than 300
scientific papers and reviews.
Georg Becher was born in 1967 in Wissen/Sieg. He studied chemistry first at the Uni-
versity of Siegen and then at the University of Kassel and was awarded his Diploma in
1994 under the direction of Privatdozent I. Stahl. Since 1995 he has been working to-
wards his Ph. D. degree under the supervision of Prof. Dr. Frank Seela at the Laboratory
of Organic and Bioorganic Chemistry, University of Osnabrück.

February 1998
SYNTHESIS
209
Table 2. 13C NMR Chemical Shifts (d) of Pyrazolo[3,4-d]pyrimi-
dinesa
Com-
pound b,c C(7) C(5) C(6) C(2)
C(3) C(3a) C(4)d C(6)d C(7a)d OCHx CHx
C(4
6a4
6b
6c
7a
7b
7c
8a
8b
8c
131.6 95.4 163.5 162.0 158.9
131.7 95.6 163.3 162.7 159.0
131.7 95.8 162.9 162.1 159.1
118.0 95.3 163.1 162.3 159.3
118.1 95.2 162.7 162.3 159.3
118.4 95.5 162.5 162.5 159.5
99.2 89.1 163.1 161.9 159.0
99.0 89.2 162.8 162.0 159.0
99.3 89.6 162.6 162.6 159.1
53.1
61.6
68.3
53.4
61.8
68.9
53.3
61.6
68.7
14.5
21.9
14.2
21.8
14.2
22.0
a Measured in DMSO-d6.
b Systematic numbering.
c Purine numbering.
d Tentative.
The nucleosides described above as well as all synthetic
1
intermediates were characterized by H and 13C NMR
spectroscopy and elemental analyses (Tables 2 and 3 and
experimental section). An upfield shift of the C(3) signal
and a downfield shift of C(7a) is observed in the case of
the N(2)-nucleosides compared to the N(1)-regioisomers.
An additional upfield shift occurs on the C(3) signals in
the case of the halogenated derivatives compared to the
nonhalogenated counterparts. The anomeric configuration
was b-D as deduced from the chemical shift differences
1
H-C(4¢) and CH2(5¢) signals from the H NMR shift dif-
ferences of the toluoylated nucleosides.26 The UV spectra
of various compounds were also measured. Generally, the
UV maxima of the nonhalogenated N(2)-compounds are
bathochromically shifted compared to the N(1)-isomers, a
phenomenon which is also observed in the case of the re-
lated nucleosides. The halogenation results in a batho-
chromic shift (2–3 nm) in both series of isomers.
Scheme 4
Table 1. Reaction Yields and Regioisomer Distribution of Pyrazo-
lo[3,4-d]pyrimidine Nucleosides Formed by the Nucleobase Anion
Glycosylation (MeCN, KOH/TDA-1)
Next, studies on the glycosylic bond stability were per-
formed on the nucleosides 2 and 3 and on the parent nu-
cleoside 1 (0.5 M HCl at 25 °C) (Table 4). The reaction
was followed UV spectrophotometrically by the decrease
of the UV absorption. The half-life of hydrolysis of the
brominated nucleoside 2 was 44 minutes (l = 254 nm)
while the iodinated compound 3 showed a half-life of 47
minutes (l = 248 nm). These hydrolysis rates are consid-
erably slower than for the nonhalogenated 8-aza-7-deaza-
2¢-deoxyguanosine (1; t = 4 min, l = 251 nm)4, 27 and also
than that of 2¢-deoxyguanosine (t = 10.6 min). Apparent-
ly, the halogen substituents exert a -I effect on the bases
thereby reducing the basicity of the heterocycle. Thus the
electron-withdrawing halogen substituents decrease the
concentration of the protonated nucleosides and their hy-
drolyses are retarded. This explanation is supported by the
lower pKa values of compounds 2 and 3 (pKa below 0)
compared to 1 (pKa = 0.5). A similar observation has been
made in the case of 8-halogenated purine 2¢,3¢-dideoxyri-
bonucleosides.28
Base
Yields (%) of Protected Nucleosides
N(1)
N(2)
N(1) + N(2)
6aa
7ab
8ab
7bb
8bb
6c
57
35
33
33
34
42
44
41
41
13
14
18
13
16
22
18
20
18
70
49
51
46
50
64
62
61
59
7cc
7cd
8cc
8cd
39
18
57
a Ref 4.
b Performed in suspension.
c Performed in solution.
d Performed with NaH.
sides 4c, 5c were then treated with 1M NaOH (60°C, 2 h)
to give the target nucleosides 2 and 3, both isolated as
crystalline compounds.25 Hydrolysis of the alkoxy func-
tions of compounds 14a,b was not successful.
It has been shown in the case of 7-deazapurine 2¢-deoxyri-
bonucleosides that a 7-substituent exerts stereoelectronic
effects on the puckering of the sugar moiety: electron-

210
Feature Article
SYNTHESIS
Table 3. 13C NMR Chemical Shifts (d) of Pyrazolo[3.4-d]pyrimidine 2¢-Deoxyribonucleosidesa
Compound C(3)
C(3a)
C(7)
C(4)b
C(5)
C(6)b
C(6)
C(7a)b
C(2)
OCHx
C(4)
CHx
C(1¢)
C(2¢)
C(3¢)
C(4¢)
C ( 5 ¢ )
2
3
4a
4b
4c
5a
5b
5c
10a
10b
10c
10d
11a
11b
11c
12a
12b
12c
13a
13b
14a
14b
122.0
101.9
119.1
119.2
119.3
100.0
100.0
100.0
119.8
119.9
120.0
132.5
100.2
100.2
100.2
124.5
124.5
124.5
108.2
103.8
108.0
103.3
98.4
93.7
96.0
96.0
96.2
90.8
90.8
90.9
96.2
96.2
96.3
96.6
91.5
91.5
91.7
97.9
97.9
98.3
99.2
89.2
98.9
89.2
158.1
157.5
163.1
163.1
162.5
163.0
163.0
162.5
163.2
163.4
162.6
162.8
163.3
163.3
162.6
165.0
165.0
164.2
163.7
164.0
163.8
163.9
156.3
155.1
162.4
162.3
162.5
162.2
162.2
162.1
162.5
162.5
162.5
162.1
162.1
162.1
162.3
161.5
161.5
161.6
161.7
161.3
161.6
161.2
156.5
155.8
158.5
158.5
158.6
158.1
158.1
158.1
158.7
158.7
158.7
158.1
158.3
158.3
158.3
163.4
163.4
163.4
162.4
163.5
162.3
163.3
–
–
–
–
–
83.1
83.2
83.2
83.2
83.2
83.3
83.2
83.2
83.4
83.4
83.4
83.4
83.5
83.5
83.4
89.9
89.9
89.9
87.1
87.1
88.5
89.3
37.6
37.7
37.5
37.5
37.5
37.5
37.6
37.6
34.8
34.8
34.8
34.9
34.8
34.8
34.8
36.7
36.7
36.6
35.9
36.3
70.8
70.9
70.8
70.8
70.8
70.9
70.8
70.9
74.9
74.9
74.9
74.9
75.1
75.1
75.0
74.3
74.3
74.8
74.4
74.5
71.0
71.2
87.4
87.5
87.4
87.4
87.4
87.4
87.4
87.4
81.3
81.3
81.3
80.9
81.3
81.3
81.3
81.9
81.9
81.8
81.8
81.7
87.1
88.5
62.4
62.4
62.3
62.4
62.4
62.4
62.3
62.4
64.0
64.0
64.0
64.0
64.1
64.1
64.1
64.1
64.1
64.1
63.8
63.9
62.4
62.4
53.8
53.8
69.2
53.6
53.6
69.0
53.8
62.4
69.2
68.6
53.6
62.2
69.0
53.2
62.2
68.6
63.8
63.9
69.0
69.0
14.2
21.6
–
14.2
21.7
–
14.2
21.6
21.6
–
14.3
21.6
–
14.2
21.6
21.6
21.6
21.6
21.6
c
–
c
–
a Measured in DMSO-d6 at 298 K.
b Tentative.
c Superimposed by DMSO.
withdrawing substituents drive the N Û S equilibrium to-
wards N and the conformational equilibrium about the
C(4¢)–C(5¢) bond is biased toward g .
(+)g 29 These data were
obtained in D2O on the basis of vicinal J [1H, H] cou-
pling constants (PSEUROT 6.2).30, 31 Applying the pseu-
dorotational analysis to 8-aza-7-deaza-2¢-deoxyguanosine
(1) as well as to its 7-bromo derivative, 2N-conformer
populations of 36% and 37% were calculated.32 These
values are about 10% higher than those of 2¢-deoxygua-
nosine. This suggests that the N-8 has a similar influence
on the sugar puckering as an electron-withdrawing 7-sub-
stituent in pyrrolo[2,3-d]pyrimidine 2¢-deoxynucleo-
sides.29 The influence of the 7-halogen substituents
becomes low in the case of 8-aza-7-deazanucleosides. In-
terestingly, the single crystal X-ray analysis of 8-aza-7-
deaza-7-bromo-2¢deoxyguanosine (2) reveals also an N
(3T2)-type sugar pucker as it is preferred in solution.32
This is different to most other 2¢-deoxyribonucleosides
which favor S (2T3)-conformation.
3
1
Figure. Molecular structure of 6-amino-3-bromo-1-(2¢-deoxy-b-D-
erythro-pentofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one (2)
taken from the X-ray analysis33
Another interesting feature concerns the conformation of
the N-glycosylic bond of the base. As has been shown for
8-azapurine nucleosides, coulomb repulsion between
nonbonding electron pairs of O(4¢) and N-8 drives the
conformation into the high-anti range (c î –90°).34 The
same is true for the nucleosides 2 and 3. It will be interest-
ing to see if the incorporation of such 2¢-deoxynucleosides
into oligodeoxynucleotides will result in the formation of
the so-called “vertical” DNA which has been reported for
oligomers containing nucleotides with a covalent link be-
tween C(8) of the base and the C-2¢ position of the sugar
moiety.35
Table 4. Half-Life Values (t) of Proton-Catalyzed Hydrolysis of the
Glycosylic Bond of Halogenated Pyrazolo[3,4-d]pyrimidine 2¢-De-
oxyribonucleosidesa
Gd
c7z8Gd
Br7c7z8Gd I7c7z8Gd
k ´ 102 (min–1)
t (min)b
l (nm)
6.5
10.6
–
13.9
4
251
1.6
44
254
1.5
47
248
a Determined UV spectrophotometrically.
b In 0.5 N HCl at 20 °C.

February 1998
SYNTHESIS
211
1H NMR (DMSO-d6): d = 1.32 [d, J = 6.4 Hz, (CH3)2]; 5.41 (m,
OCH); 6.77 (s, NH2); 13.0 (s, NH).
Anal. Calcd for C8H10N5BrO (272.1): C 35.31, H 3,70, N 25.74.
Found: C 35.58, H 3.81, N 25.54.
Flash chromatography (FC): at 0.4 bar on silica gel 60 H (Merck,
Darmstadt, Germany). TLC: aluminum sheets silica gel 60 F254 (0.2
mm, Merck, Germany). TLC Scanning: CS-930 TLC scanner
(Shimadzu, Japan). Solvent systems for FC and TLC: CH2Cl2/MeOH
98:2 (A), CH2Cl2/MeOH 95:5 (B), CH2Cl2/MeOH 9:1 (C), CH2Cl2/
acetone 98:2 (D), CH2Cl2/acetone 95:5 (E).
6-Amino-3-iodo-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (8a):
Analogously to 7a, with 6a (1.0 g, 6.1 mmol) and NIS (2.0 g,
9.1 mmol, 9 h). Recrystallization (aq MeOH) yielded colorless need-
les (870 mg, 49%); mp > 230°C(d); TLC (C): Rƒ 0.7.
UV (MeOH): l (e) = 248 (5900), 276 nm (7700).
1H NMR (DMSO-d6): d = 3.98 (s, OCH3); 6.75 (s, NH2); 13.11 (s,
NH).
UV spectra were measured with a 150-20 spectrophotometer (Hita-
chi, Japan). NMR spectra: AC-250 and AMX-500 spectrometers
(Bruker, Germany); d values are in ppm downfield from internal TMS
(1H, 13C). mp: Büchi-SMP-20 apparatus (Büchi, Switzerland); uncor-
rected. Microanalyses were performed by Mikroanalytisches Labor
Beller (Göttingen, Germany).
Anal. Calcd for C6H6N5IO (291.1): C 24.76, H 2.08, N 24.06. Found:
C 24.76, H 2.16, N 24.09.
6-Amino-4-ethoxy-1H-pyrazolo[3,4-d]pyrimidine (6b):
A
solution of 6-amino-4-chloro-1H-pyrazolo[3,4-d]pyrimidine4
6-Amiuo-4-ethoxy-3-iodo-1H-pyrazolo[3,4-d]pyrimidine (8b):
As described for 7a, with 6b (1.0 g, 5.6 mmol) and NIS (1.9 g,
8.5 mmol, 9 h). Recrystallization (aq MeOH) yielded slightly yellow-
ish needles (890 mg, 52%); mp > 230°C; TLC (C): Rƒ 0.6.
UV (MeOH): l (e) = 249 (5900), 277 nm (7500).
(6.8 g, 0.04 mol) in 1 M NaOEt in EtOH (100 mL) was refluxed for
1 h. Upon cooling, NaCl was precipitated with Et2O (100 mL) and
was filtered off. The filtrate was neutralized with 96% AcOH and
evaporated to dryness. The residue was dissolved in MeOH. The re-
action product precipitated as pale yellow needles by addition of ice-
cold water. Recrystallization (aq MeOH) yielded colorless needles
(5.0 g, 70%); mp 213 °C; TLC (C): Rƒ 0.6.
1H NMR (DMSO-d6): d = 1.37 (t, J = 5.8 Hz, CH3); 4.44 (q, J =
6.4 Hz, OCH2); 6.7 (s, NH); 13.08 (s, NH).
Anal. Calcd for C7H8N5IO (305.1): C 27.56, H 2.64, N 22.96. Found:
C 27.69, H 2.76, N 22.84.
UV (MeOH): l (e) = 244 (5400), 276 nm (7100).
1H NMR (DMSO-d6): d = 2.33 (t, J = 5.8 Hz, CH3); 4.41 (q, J =
7.0 Hz, CH2); 6.55 (s, NH2); 7.76 [s, H-C(3)]; 12.82 (s, NH).
Anal. Calcd for C7H9N5O (179.2): C 46.92, H 5.06, N 39.09. Found:
C 46.80, H 5.18, N 39.11.
6-Amino-3-iodo-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine
(8c):
A mixture of 6c (1.0 g, 5.2 mmol) and NIS (1.3 g, 5.8 mmol, 2h) was
halogenated analogously to 7a. Recrystallization (aq MeOH) yielded
slightly yellowish needles (1.16 g, 70%); mp 223 °C; TLC (C): Rƒ 0.7.
UV (MeOH): l (e) = 248 (5800), 276 nm (7500).
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.4 Hz, (CH3)2]; 5.39 (m,
OCH); 6.68 (s, NH2); 13.10 (s, NH).
6-Amino-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (6c):
As described for 6b, with 6-amino-4-chloro-1H-pyrazolo[3,4-d]pyri-
midine (3.2 g, 18.9 mmol) for 1 h in 1 M i-PrONa in i-PrOH
(100 mL); Recrystallization (aq MeOH) yielded colorless needles
(2.8 g, 77%); mp 176 °C; TLC (C): Rƒ 0.6.
Anal. Calcd for C8H10N5IO (319.1): C 30.11, H 3.16, N 21.95. Found:
C 30.27, H 3.11, N 21.86.
UV (MeOH): l (e) = 244 (5600), 276 nm (7400).
1H NMR (DMSO-d6): d = 1.30 [d, J = 5.8 Hz, (CH3)2] ; 5.42–5.47 (m,
OCH); 6.52 (s, NH2); 7.73 [s, H-C(3)]; 12.78 (s, NH).
Anal. Calcd for C8H11N5O (193.2): C 49.73, H 5.74, N 36.25. Found:
C 49.73, H 5.74, N 36.48.
G1ycosylation of 4-Alkoxy-6-amino-1H-pyrazolo[3,4-d]pyrimi-
dines 7a–8c in the Presence of Powdered KOH/TDA-1; General
Procedure:
Powdered KOH (1.24g, 22 mmol) and the 4-alkoxy-6-amino-1H-py-
razolo[3,4-d]pyrimidines (7a–c or 8a–c) (5.5 mmol) were stirred in
anhyd MeCN (100 mL). The suspension was stirred for 15 min at r.t.
Then TDA-1 (tris[2-(2-methoxyethoxy)ethyl]amine; 200 mL,
0.6 mmol) was added and stirring was continued for another 15 min.
2-Deoxy-3,5-di-O-(p-toluoyl)-a-D-erythro-pentofuranosyl chloride
(9)24 (2.56 g, 6.6 mmol) was then added in portions. After 20 min in-
soluble material was filtered off and the solvent was evaporated. The
resulting foam was applied to FC (silica gel; column 15 ´ 6 cm, sol-
vent D followed by E) and separated in two zones in all cases. The fa-
ster migrating zone was always the N(1)-isomer, the slower migrating
one contained the N(2)-compound.
6-Amino-3-bromo-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine
(7a):
To a suspension of 6a (1.0 g, 6.1 mmol) in 1,2-dichloroethane
(100 mL), NBS (1.2 g, 6.7 mmol) was added. After heating under re-
flux for 2.5 h, the solvent was evaporated to yield an orange-colored
solid which was washed with water (2 ´ 100 mL), filtered, and dissol-
ved in MeOH. Decolorization with charcoal, filtration, and addition
of ice-cold water gave a yellowish precipitate. Recrystallization (aq
MeOH) yielded colorless needles (815 mg, 55%); mp >23 °C (d);
TLC (C): Rƒ 0.6.
UV (MeOH): l (e) = 248 (5900), 277 nm (7100).
1H NMR (DMSO-d6): d = 3.69 (s, OCH3); 6.82 (s, NH2); 13.1 (s, NH).
Anal. Calcd for C6H6N5BrO (244.1): C 29.53, H 2.48, N 28.70.
Found: C 29.82, H 2.48, N 28.46.
6-Amino-1-[2¢-deoxy-3¢ 5 -di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (10d):
This compound is made in analogy with the above experiment, but
starting from 6c. Colorless foam (1.3 g, 42%); TLC (D): Rƒ 0.43.
UV (MeOH): l (e) = 241 (39000), 274 nm (11500).
6-Amino-3-bromo-4-ethoxy-1H-pyrazolo[3,4-d]pyrimidine (7b):
As described for 7a, with 6b (1.0 g, 5.6 mmol) and NBS (1.1 g,
6.2 mmol, 1.5 h). Recrystallization (aq MeOH) yielded colorless
needles (780 mg, 54%); mp 221 °C (d); TLC (C): Rƒ 0.6.
UV (MeOH): l (e) = 248 (5600), 277 nm (7000).
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.2 Hz, (CH3)2], 2.36, 2.38 (2s,
2Ar-CH3); 2.68 [m, Ha-(C2¢)]; 3.21 [m, Hb-(C2¢)]; 4.45 [m, 2H-(C5¢),
H-(C4¢)]; 5.48 (m, OCH); 5.80 [m, H-(C3¢)]; 6.60 [‘t’, J = 6.2 Hz, H-
(C1¢)]; 6.68 (s, NH2); 7.28–7.92 (4d, J = 8.1 Hz, 2C6H4); 7.90 [s, H-
(C3)].
1H NMR (DMSO-d6): d = 1.38 (t, J = 5.9 Hz, CH3); 4.62 (q, J = 6.4
Hz, OCH2); 6.99 (s, NH2); 13.05 (s, NH).
Anal. Calcd for C7H8N5BrO (258.1): C 32.58, H 3.12, N 27.14.
Found: C 32.64, H 3.15, N 27.07.
Anal. Calcd for C29H31N5O6 (545.6): C 63.84, H 5.73, N 12.84.
Found: C 63.75, H 5.77, N 12.89.
6-Amino-3-bromo-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine
(7c):
A mixture of 6c (1.0 g, 5.2 mmol) and NBS (1.0 g, 5.6 mmol, 1.5 h)
was halogenated analogously to 7a. Recrystallization (aq MeOH)
yielded colorless needles (1.1 g, 78%); mp 231°C; TLC (C): Rƒ 0.7.
UV (MeOH): l (e) = 248 (6000), 276 nm (7100).
6-Amino-2-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (12c):
Colorless foam (680 mg, 22%); TLC (B): Rƒ 0.53.
UV (MeOH): l (e) = 240 nm (36100), 283 (8900), 296 nm (8700).
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.2 Hz, (CH3)2], 2.36, 2.38 (2s,

212
Feature Article
SYNTHESIS
From the second main zone amorphous 12b (580 mg, 16%) was iso-
lated (see above).
2Ar-CH3); 2.74 [m, Ha-(C2¢)]; 3.10 [m, Hb-(C2¢)]; 4.50 [m, 2H-(C5¢),
H-(C4¢)]; 5.47 (m, OCH); 5.83 [m, H-(C3¢)]; 6.39 [¢t`, J = 6.2 Hz, H-
(C1¢)]; 6.86 (s, NH2); 7.28–7.92 (4d, J = 8.1 Hz, 2C6H4); 7.90 [s, H-
(C3)].
Anal. Calcd for C29H31N5O6 (545.6): C 63.84, H 5.73, N 12.84.
Found: C 63.73, H 5.70, N 12.84.
6-Amino-3-bromo-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-
pentofuranosyl]-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (10c):
Colorless foam (1.5 g, 44%); TLC (D): Rƒ 0.44.
UV (MeOH): l (e) = 240 (39000), 277 nm (10100).
1H NMR (DMSO-d6): d = 1.33 (d, J = 6.2 Hz, CH3), 2.36, 2.38 (2s,
2Ar-CH3); 2.65 [m, Ha-(C2¢)]; 3.15 [m, Hb-(C2¢)]; 4.44 [m, 2H-(C5¢),
H-(C4¢)]; 5.43 (m, OCH); 5.74 [m, H-(C3¢)]; 6.52 [‘t’, J = 6.2 Hz, H-
(C1¢)]; 7.06 (s, NH2); 7.28–7.92 (4d, J = 8.1 Hz, 2C6H4).
Anal. Calcd for C29H30N5BrO6 (624.5): C 55.78, H 4.84, N 11.21,
found: C 56.01, H 4.86, N 10.93.
6-Amino-3-bromo-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-
pentofuranosyl]-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (10a):
Amorphous solid (1.15 g, 35%); TLC (D): Rƒ 0.33.
UV (MeOH): l (e) = 242 (36300), 276 nm (10000).
1H NMR (DMSO-d6): d = 2.39, 2.41 (2s, 2Ar-CH3); 2.56 [m, Ha-
(C2¢)]; 3.17 [m, Hb-(C2¢)]; 4.00 (s, OCH3); 4.45–4.49 [m, 2H-(C5);
H-(C4¢)]; 5.73 [m, H-(C3)]; 6.55 [‘t’, J = 5.7 Hz, H-(C1¢)] ; 7.12 (s,
NH2); 7.34–7.93 (4d, J = 8.1 Hz, 2C6H4).
From the second zone 12c (630 mg, 18%) was isolated as a colorless
foam (see above).
Anal. Calcd for C27H26N5BrO6 (596.4): C 54.37, H 4.39, N 11.74.
Found: C 54.24, H 4.38, N 11.55.
6-Amino-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-3-iodo-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (11c):
Colorless foam (1.4 g, 41%); TLC (D): Rƒ 0.44.
From the second zone a colorless, amorphous solid (12a, 460 mg,
14%) was isolated.
UV (MeOH): l (e) = 240 nm (34200) [Lit.4 l (e) = 239 nm (33500)].
UV (MeOH): l (e) = 239 (39600), 277 nm (9600).
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.2 Hz, (CH3)2]; 2.36, 2.38 (2s,
2Ar-CH3); 2.67 [m, Ha-(C2¢)]; 3.15 [m, Hb-(C2¢)]; 4.50 [m, 2H-
(C5¢),H-(C4¢)]; 5.43 (m, OCH); 5.73 [m, H-(C3¢)]; 6.55 [‘t’, J = 5.9
Hz, H-(C1¢)]; 7.05 (s, NH2); 7.28–7.92 (4d, J = 8.1 Hz, 2C6H4).
Anal. Calcd for C29H30N5IO6 (671.5): C 51.87, H 4.50, N 10.43.
Found: C 52.05, H 4.62, N 10.37.
6-Amino-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-3-iodo-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (11a):
Colorless, amorphous solid (1.17 g, 33%); TLC (D): Rƒ 0.33.
UV (MeOH): l (e) = 242 (36500), 276 nm (11000).
1H NMR (DMSO-d6): d = 2.39, 2.41 (2s, 2Ar-CH3); 2.68 [m, Ha-
(C2¢)] ; 3.20 [m, Hb-(C2¢)]; 4.02 (s, OCH3); 4.45–4.51 [m, H-(C5¢); H-
(C4¢)]; 5.73 [m, H-(C3¢)]; 6.55 [‘t’, J = 6.7 Hz, H-(C1¢)]; 7.01 (s,
NH2); 7.36–7.96 (4d, J = 8.1 Hz, 2C6H4).
From the second zone 12c (650 mg, 18%) was isolated (see above).
Glycosylation of Halogenated 6-Amino-4-isopropoxy-1H-pyrazo-
lo[3,4-d]pyrimidines (7c, 8c) in the Presence of NaH; General Pro-
cedure:
To a solution of 7c or 8c (5.5 mmol) in MeCN (60 mL) NaH
(97%, 150 mg, 6.1 mmol) was added. After stirring at r.t. for 10 min
the halogenose 9 (2.56 g, 6.6 mmol) was introduced and the stirring
was continued for 20 min. The mixture was filtered and the filtrate
was evaporated. The further workup was performed as described for
the glycosylation using KOH/TDA-1.
Anal. Calcd for C27H26N5IO6 (643.4): C 50.40, H 4.07, N 10.88.
Found: C 50.48, H 4.22, N 10.84.
From the second main zone amorphous 12a (640 mg, 18%) was ob-
tained (see above).
6-Amino-3-bromo-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-
pentofuranosyl]-4-ethoxy-1H-pyrazolo[3,4-d]pyrimidine (10b):
From the fast migrating zone 10b was isolated as a colorless, amorph-
ous solid (1.1 g, 33%); TLC (D): Rƒ 0.33.
UV (MeOH): l (e) = 242 (35500), 277 nm (10500).
6-Amino-3-bromo-2-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-
pentofuranosyl]-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (13a):
The fast migrating zone furnished compound 10c (1.4 g, 41%). From
the second zone a colorless foam of 13a (680 mg, 17%) was isolated;
TLC (B): Rƒ 0.5.
1H NMR (CDCl3): d = 1.36 (t, J = 7.1 Hz, CH3); 2.36, 2.38 (2s, 2Ar-
CH3); 2.66 [m, Ha-(C2¢)] ; 3.17 [m, Hb-(C2¢)]; 4.35–4.49 [m, OCH2,
2H-(C5¢); H-(C4¢)]; 5.73 [m, H-(C3¢)]; 6.53 [‘t’, J = 6.7 Hz, H-(C1¢)];
6.80 (s, NH2); 7.23–7.91 (4d, J = 8.1 Hz, 2C6H4).
Anal. Calcd for C28H28N5BrO6 (610.5): C 55.09, H 4.62, N 11.47.
Found: C 54.93, H 4.77, N 11.34.
UV (MeOH): l (e) = 240 (37500), 285 (7900), 302 nm (7500).
1H NMR (DMSO-d6): d = 1.38 [d, J = 5.7 Hz, (CH3)2], 2.36, 2.39 (2s,
2Ar-CH3); 2.77 [m, Ha-(C2¢)]; 3.29 [m, Hb-(C2¢)]; 4.39, 4.50 [m, 2H-
(C5¢)]; 4.57 [m, H-(C4¢)]; 5.46 (m, OCH); 5.91 [m, H-(C3¢)]; 6.53
[‘t’, J = 6.2 Hz, H-(C1¢)]; 6.61 (s, NH2); 7.28–7.92 (4d, J = 8.1 Hz,
2C6H4).
6-Amino-2-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-4-ethoxy-1H-pyrazolo[3,4-d]pyrimidine (12b):
From the slower migrating zone a colorless foam of 12b (440 mg,
13%) was isolated; TLC (B): Rƒ 0.36.
Anal. Calcd for C29H30N5BrO6 (624.5): C 55.78, H 4.84, N 11.21,
found: C 55.89, H 4.80, N 11.24.
UV (MeOH): l (e) = 283 (7700), 296 nm (8200).
1H NMR (DMSO-d6): d = 1.33 (t, J = 7.0 Hz, CH3); 2.34, 2.38 (2s,
2Ar-CH3); 2.73 [m, Ha-(C2¢)]; 3.09 [m, Hb-(C2¢)]; 4.39–4.56 [m,
OCH2, 2H-(C5¢); H-(C4¢)] ; 5.82 [m, H-(C3¢)]; 6.39 [‘t’, J = 5.6 Hz,
H-(C1¢)]; 6.58 (s, NH2); 7.25–7.91 (4d, J = 8.1 Hz, 2C6H4); 8.65 [s,
H-(C3)].
6-Amino-2-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-3-iodo-4-isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (13b):
The fast migrating zone furnished compound 11c (1.44 g, 39%); from
the second zone 13b (610 mg, 18%) was isolated both as colorless
foams; TLC (B): Rƒ 0.5.
UV (MeOH): l (e) = 240 (37000), 285 (7900), 302 nm (7800).
1H NMR (DMSO-d6): d = 1.34 [d, J = 6.2 Hz, (CH3)2]; 2.34, 2.38 (2s,
2Ar-CH3); 2.75 [m, Ha-(C2¢)]; 3.25 [m, Hb-(C2¢)]; 4.32–4.56 [m, 2H-
(C5¢),H-(C4¢)]; 5.41 (m, OCH); 5.92 [m, H-(C3¢)]; 6.47 [‘t’, J = 5.9
Hz, H-(C1¢)]; 6.79 (s, NH2); 7.26–7.92 (4d, J = 8.1 Hz, 2C6H4).
Anal. Calcd for C29H30N5IO6 (671.5): C 51.87, H 4.50, N 10.43.
Found: C 51.96, H 4.53, N 10.54.
Anal. Calcd for C28H29N5O6 (531.6): C 63.27, H 5.50, N 13.17.
Found: C 63.43, H 5.66, N 13.06.
6-Amino-1-[2¢-deoxy-3¢,5¢-di-O-(p-toluoyl)-b-D-erythro-pentofura-
nosyl]-4-ethoxy-3-iodo-1H-pyrazolo[3,4-d]pyrimidine (11b):
Compound 11b was isolated as a colorless amorphous solid (1.23 g,
34%); TLC (D): Rƒ 0.33.
UV (MeOH): l (e) = 241 (35500) 277 nm (9800).
1H NMR (CDCl3): d = 1.43 (t, J = 7.2 Hz, CH3); 2.38, 2.41 (2s, 2Ar-
CH3); 2.55 [m, Ha-(C2¢)]; 3.49 [m, Hb-(C2¢)]; 4.43–4.57 [m, OCH2,
2H-(C5¢); H-(C4¢)]; 5.76 [m, H-(C3¢)]; 6.63 [‘t’, J = 7.2 Hz, H-(C1¢)];
6.80 (s, NH2); 7.23–7.91 (4d, J = 8.1 Hz, 2C6H4).
6-Amino-3-bromo-1-[2
¢-deoxy-b-D-erythro-pentofuranosyl]-4-
methoxy-1H-pyrazolo[3,4-d]pyrimidine (4a); Typical Procedure:
A solution of 10a (500 mg, 0.84 mmol) in 0.1 M NaOMe in MeOH
(50 mL) was stirred for 30 min at 40°C. Then, the solution was ad-
sorbed on silica gel, loaded onto the top of a silica gel column (10 ´
Anal. Calcd for C28H28N5IO6 (657.5): C 51.15, H 4.29, N 10.65.
Found: C 50.99, H 4.26, N 10.51.

February 1998
SYNTHESIS
213
1H NMR (DMSO-d6): d = 1.36 [d, J = 5.2 Hz, (CH3)2]; 2.29 [m, Ha-
C(2¢)]; 2.82 [m, Hb-C(2¢)]; 3.51, 355 [m, CH2(5¢)]; 3.87 [m, H-C(4¢)];
4.48 [m, H-C(3¢)]; 4.79 [t, J = 5.7 Hz, OH-C(5¢)] ; 5.30 [d, J = 3.9 Hz,
OH-C(3¢)]; 5.45 (m, OCH); 6.34 [‘t’, J = 6.5 Hz, H-C(1¢)], 6.53 (s,
NH2).
4 cm) and chromatographed; elution with A followed by B gave a
main zone which yielded a colorless solid after evaporation. Crystal-
lization (water) gave 4a as colorless needles (200 mg, 66%); mp
173 °C; TLC (B): Rƒ 0.2.
UV (MeOH): l (e) = 277 nm (8500).
1H NMR (DMSO-d6): d = 2.16 [m, Ha-C(2¢)]; 2.67 [m, Hb-C(2¢)] ;
3.35, 3.48 [m, CH2(5¢)] ; 3.75 [m, H-C(4¢)]; 3.97 (s, OCH3); 4.34 [m,
H-C(3¢)]; 4.69 [t, J = 5.4 Hz, OH-C(5¢)]; 5.22 [d, J = 4.1 Hz, OH-
C(3¢)]; 6.59 [‘t’, J = 6.4 Hz, H-C(1¢)], 7.06 (s, NH2).
Anal. Calcd for C11H14N5BrO4 (360.2): C 36.70, H 3.92, N 19.44.
Found: C 36.82, H 3.90, N 19.55.
Anal Calcd for C13H18N5BrO4 (388.2): C 40.22, H 4.67, N 18.04.
Found: C 40.41, H 4.81, N 17.96
6-Amino-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-3-iodo-4-iso-
propoxy-1H-pyrazolo[3,4-d]pyrimidine (5c):
Compound 11c (5 g, 7.4 mmol) in 0.1 M i-PrONa in i-PrOH (200 mL,
3 h, 40°C) was deprotected analogously to 4a. Crystallization (water)
gave 5c as solid (2.4 g, 75%); mp 190°C; TLC (B): Rƒ 0.2.
UV (MeOH): l (e) = 277 nm (8700).
6-Amino-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-3-iodo-4-meth-
oxy-1H-pyrazolo[3,4-d]pyrimidine (5a):
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.5 Hz, (CH3)2]; 2.14 [m,
HaC(2¢)]; 2.69 [m, Hb-C(2¢)]; 3.35, 3.44 [m, CH2(5¢)]; 3.74 [m, H-
C(4¢)]; 4.34 [m, H-C(3¢)]; 4.7 [t, J = 5.7 Hz, OH-C(5¢)]; 5.21 [d, J =
4.3 Hz, OH-C(3¢)]; 5.68 (m, OCH); 6.33 [‘t’ J = 6.5 Hz, H-C(1¢)],
7.26 (s, NH2).
Analogously to 4a, with 11a (500 mg, 0.78 mmol) in 0.1 M NaOMe
in MeOH (50 mL, 30 min, 40°C). Crystallization (water) gave 5a as
colorless needles (220 mg, 69%); mp 161 °C; TLC (B): Rƒ 0.2.
UV (MeOH): l (e) = 277 nm (8400).
1H NMR (DMSO-d6): d = 2.16 [m, Ha-C(2¢)] ; 2.67 [m, Hb-C(2¢)];
3.35, 3.48 [m, CH2(5¢)] ; 3.75 [m, H-C(4¢)]; 3.97 (s, OCH3); 4.34 [m,
H-C(3¢)]; 4.69 [t, J = 5.4 Hz, OH-C(5¢)]; 5.22 [d, J = 4.1 Hz, OH-
C(3¢)]; 6.59 [‘t’, J = 6.4 Hz, H-C(1¢)], 7.06 (s, NH2).
Anal. Calcd for C13H18N5IO4 (435.2): C 35.88, H 4.17, N 16.09.
Found: C 35.69, H 4.17, N 1602.
Anal. Calcd for C11H14N5IO4 (407.2): C 32.45, H 3.47, N 17.20.
Found: C 32.61, H 3.55, N 17.17.
6-Amino-2-[2¢-deoxy-b-D-erythro-pentofuranosyl]-3-iodo-4-iso-
propoxy-2H-pyrazolo[3,4-d]pyrimidine (14b):
As described for 4a, with 13b (200 mg, 0.3 mmol) in 0.1 M i-PrONa
in i-PrOH (20 mL, 30 min, 40°C). A colorless solid (79 mg, 61%) was
isolated; mp 168 °C; TLC (C) Rƒ 0.44.
6-Amino-3-bromo-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-4-
ethoxy-1H-pyrazolo[3,4-d]pyrimidine (4b):
1H NMR (DMSO-d6): d = 1.37 [d, J = 6.2 Hz, (CH3)2]; 2.29 [m, Ha-
C(2¢)]; 2.80 [m, Hb-C(2¢)] ; 3.51, 355 [m, CH2(5¢)] ; 3.87 [m, H-C(4¢)];
4.48 [m, H-C(3¢)]; 4.79 [t, J = 5.9 Hz, OH-C(5¢)] ; 5.29 [d, J = 4.5 Hz,
OH-C(3¢)]; 5.45 (m, OCH); 6.33 [‘t’, J = 6.5 Hz, H-C(1¢)], 6.45 (s,
NH2).
Compound 10b (250 mg, 0.41 mmol) in 0.1 M NaOEt in EtOH (30 mL,
30 min, 40°C) was deprotected analogously to 4a.Acolorless solid (80
mg, 52%) was isolated; mp 171°C; TLC (B): Rƒ 0.2. (MeOH)
UV: l (e) = 276 nm (8600).
1H NMR (DMSO-d6): d = 1.33 (t, J = 7.0 Hz, CH3); 2.16 [m, Ha-
(C2¢)] ; 2.67 [m, Hb-(C2¢)]; 3.35, 3.47 [m, CH2(5¢)] ; 3.74 [m, H-C(4¢)];
4.34 [m, H-C(3¢)] ; 4.62 (q, J = 6.4 Hz, OCH2); 4.69 [t, J = 5.6 Hz, OH-
C(5¢)]; 5.22 [d, J = 4.2 Hz, OH-C(3¢)]; 6.55 [‘t’, J = 6.7 Hz, H-(C1¢)] ;
6.80 (s, NH2).
Anal. Calcd for C13H18N5IO4 (435.2): C 35.88, H 4.17, N 16.09.
Found: C 35.74, H 4.07, N 15.92.
6-Amino-3-bromo-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-1H-
pyrazolo[3,4-d]pyrimidin-4(5H)-one (2):
Anal. Calcd for C12H16N5BrO4 (374.2): C 38.52, H 4.31, N 18.72.
Found: C 38.58, H 4.47, N 18.66.
A solution of 4c (1.8 g, 4.6 mmol) in 1 M NaOH (80 mL) was stirred
for 2 h at 60°C and then neutralized with 96% AcOH under cooling.
The resulting precipitate was filtered off and recrystallized (water)
yielding colorless needles (1.4 g, 89%); mp 221 °C; TLC (C): Rƒ 0.18.
UV (MeOH): l (e) = 257 nm (10600).
1H NMR (DMSO-d6): d = 2.12 [m, Hb-C(2¢)]; 2.62 [m, Ha-C(2¢)];
3.35, 3.44 [m, CH2(5¢)]; 3.73 [m, H-C(4¢)]; 4.31 [m, H-C(3¢)] ; 4.71 [t,
J = 5.7 Hz, OH-C(5¢)]; 5.19 (d, J = 4.3 Hz, OH-C(3¢)] ; 6.23 [‘t’, J =
6.5 Hz, H-C(1¢)], 7.01 (s, NH2); 10.79 (s; NH).
Anal. Calcd for C10H12N5BrO4 (346.1): C 34.70, H 3.49, N 20.23.
Found: C 34.50, H 3.56, N 20.12.
6-Amino-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-4-ethoxy-3-
iodo-1H-pyrazolo[3,4d]pyrimidine (5b):
As described for 4a, with 11b (200 mg, 0.3 mmol) in 0.1 M NaOEt in
EtOH (20 mL, 30 min, 40°C). A colorless solid (65 mg, 51%) was
isolated; mp 164°C; TLC (B): Rƒ 0.2.
UV (MeOH): l (e) = 276 nm (8400).
1H NMR (DMSO-d6): d = 1.33 (t, J = 7.0 Hz, CH3); 2.15 [m, Ha-
(C2¢)]; 2.68 [m, Hb-(C2¢)] ; 3.35, 346 [m, CH2(5¢)] ; 3.76 [m, H-C(4¢)] ;
4.34 [m, H-C(3¢)] ; 4.62 (q, J = 6.4 Hz, OCH2); 4.69 [t, J = 5.6 Hz, OH-
C(5¢)]; 5.22 [d, J = 4.2 Hz, OH-C(3¢)]; 6.57 [‘t’, J = 6.7 Hz, H-(C1¢)] ;
6.80 (s, NH2).
6-Amino-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-3-iodo-1H-py-
razolo[3,4-d]pyrimidin-4(5H)-one (3):
As described for 2, with 5c (1.7 g, 3.9 mmol) in 1 M NaOH (80 mL,
2 h, 60°C). The resulting precipitate was filtered off and recrystalli-
zed (water) yielding colorless needles (1.3 g, 87%); mp 221 °C; TLC
(C): Rƒ 0.18.
Anal. Calcd for C12H16N5IO4 (421.2): C 34.22, H 3.83, N 16.63.
Found: C 34.30, H 3.95, N 16.64.
6-Amino-3-bromo-1-[2¢-deoxy-b-D-erythro-pentofuranosyl]-4-
isopropoxy-1H-pyrazolo[3,4-d]pyrimidine (4c):
Analogously to 4a, with 10c (5 g, 8 mmol) in 0.1 M i-PrONa in
i-PrOH (200 mL, 3 h, 40°C). Crystallization (water) gave colorless
needles (2.15 g, 69%); mp 181 °C; TLC (B): Rƒ 0.2.
UV (MeOH): l (e) = 258 nm (10800).
1H NMR (DMSO-d6): d = 2.15 [m, Ha-C(2)]; 2.66 [m, Hb-C(2¢)];
3.35, 3.47 [m, CH2(5¢)] ; 3.77 [m, H-C(4¢)]; 4.36 [m, H-C(3¢)]; 4.7 [t,
J = 5.7 Hz, OH-C(5¢)]; 5.2 [d, J = 4.3 Hz, OH-C(3¢)]; 6.24 [‘t’, J = 6.5
Hz, H-C(1¢)], 6.81 (s, NH2); 10.79 (s, NH).
UV (MeOH): l (e) = 277 nm (8700).
1H NMR (DMSO-d6): d = 1.33 [d, J = 6.8 Hz, (CH3) 2]; 2.18 [m, Ha-
C(2¢)]; 2.67 [m, Hb-C(2¢)]; 3.35, 347 [m, CH2(5¢)]; 3.74 [m, H-C(4¢)];
4.34 [m, H-C(3¢)]; 4.69 [t, J = 5.7 Hz, OH-C(5¢)]; 5.22 [d, J = 4.3 Hz, OH-
C(3¢)]; 5.39 (m, OCH); 6.33 [‘t’, J = 6.5 Hz, H-C(1¢)], 6.99 (s, NH2).
Anal Calcd for C13H18N5BrO4 (388.2): C 40.22, H 4.67, N 18.04.
Found: C 40. 17, H 4.63, N 18.01.
Anal. Calcd for C10H12N5IO4 (393.1): C 30.55, H 3.10, N 17.52.
Found: C 30.50, H 3.21, N 17.21
6-Amino-3-bromo-2-[2¢-deoxy-b-D-erythro-pentofuranosyl]-4-
isopropoxy-2H-pyrazolo[3,4-d]pyrimidine (14a):
As described for 4a, with 13a (200 mg, 0.32 mmol) in 0.1 M i-PrONa
in i-PrOH (20 mL, 30 min, 40°C). A colorless solid (71 mg, 57%) was
isolated; mp 171°C; TLC (C): Rƒ 0.44.
We thank Drs. H. Rosemeyer and N. Ramzaeva for helpful discus-
sion. Compounds 6c, 10d and 12c have been described in the Thesis
of Dr. H. Steker, Paderborn. Financial support by the Bundesministe-
rium für Bildung, Wissenschaft, Forschung und Technologie (BMBF)
is gratefully acknowledged.

214
Feature Article
SYNTHESIS
(1) Seela, F.; Thomas, H. Helv. Chim. Acta 1995, 78, 94.
(2) Ramzaeva, N.; Seela, F. Helv. Chim. Acta 1996, 79, 1549.
(3) Seela, F.; Chen, Y. J. Chem. Soc., Chem Commun. 1996, 2263.
(4) Seela, F.; Steker, H. Helv. Chim. Acta 1986, 69, 1602.
(5) Seela, F.; Steker, H. Helv. Chim. Acta 1985, 68, 563.
(6) Seela, F.; Kaiser, K. Helv. Chim. Acta 1988, 71, 1813.
(7) Seela, F.; Kaiser, K. Chem. Pharm. Bull. 1988, 36, 4153.
(8) Seela, F.; Driller, H. Helv. Chim. Acta 1988, 71, 757.
(9) Cottam, H. B.; Wasson, D. B.; Shih, H. C; Raychaudhuri, A.; Di
Pasquale, G.; Carson, D. A. J. Med. Chem. 1993, 36, 3424.
(10) Cottam, H. B.; Petrie, C. R.; McKernan, P. A.; Goebel, R. J.;
Dalley, N. K.; Davidson, R. B.; Robins, R. R.; Revankar, G. R.
J. Med. Chem. 1984, 27, 1119.
(20) Seela, F.; Westermann, B.; Bindig, U. J. Chem. Soc., Perkin
Trans. 1 1988, 697.
(21) Winkeler, H.- D.; Seela, F. J. Org. Chem. 1983, 48, 3119.
(22) Seela, F.; Zulauf, M.; Becher, G. Nucleosides, Nucleotides
1997, 16, 305.
(23) Taylor, E. C.; Patel, H. H. Tetrahedron 1992, 48, 8089.
(24) Hoffer, M. Chem. Ber. 1960, 93, 2777.
(25) Seela, F.; Ramzaeva, N.; Becher, G. Collect. Czech. Chem.
Commun. 1996, 61, S258.
(26) Nuhn, P.; Zschunke, A.; Heller, D.; Wagner, G. Tetrahedron
1969, 25, 2139.
(27) Seela, F.; Steker, H. J. Chem. Soc., Perkin Trans. 1 1985, 2573.
(28) Nair, V.; Buenger, G. S. J. Org. Chem .1990, 55, 3695.
(29) Rosemeyer, H.; Seela, F. J. Chem. Soc., Perkin Trans. 2 1997,
2341.
(11) Petrie, C. R. III; Cottam, B. C.; McKernan, P. A.; Robins, R. K.;
Revankar, G. R. J. Med. Chem. 1985, 28, 1010.
(12) Seela, F.; Driller, H. Nucleic Acids Res. 1989, 17, 901.
(13) Seela, F.; Kaiser, K. Nucleic Acids Res. 1986, 14, 1825.
(14) Seela, F.; Driller, H.; Kaiser, K.; Rosemeyer, H.; Steker, H. Nu-
cleosides, Nucleotides 1989, 8, 789.
(15) Seela, F.; Driller, H. Helv. Chim. Acta 1988, 71, 1191.
(16) Earl, R. A.; Panzica, R. P.; Townsend, L. B. J. Chem. Soc. Per-
kin Trans. 1 1972, 2672.
(17) Tanaka, H.; Hayashi, T.; Nakayama, K. Agric. Biol. Chem.
1973, 37, 1731.
(18) Schmidt, R. R.; Guilliard, W.; Karg, J. Chem. Ber. 1977, 110,
2445.
(30) van Wijk, J.; Altona, C. “PSEUROT 6.2 – A program for the
conformational analysis of five membered rings”, University of
Leiden, July 1993.
(31) Haasnoot, C. A. G.; de Leeuw, F. A. A. M.; Altona, C. Tetrahe-
dron 1980, 86, 2783.
(32) Rosemeyer, H.; Zulauf, M.; Ramzaeva, N.; Becher, G.; Feiling,
E.; Mühlegger, K.; Münster, I.; Lohmann, A.; Seela, F. Nucleo-
sides, Nucleotides 1997, 16, 821.
(33) Seela, F.; Reuter H.; Becher G.; 1997, unpublished results.
(34) Saenger, W. Principles ofNucleic Structure; Springer-Verlag:
New York, 1984; p 189.
(19) Schmidt, R. R.; Guilliard, W.; Heermann, D. Liebigs Ann.
Chem. 1981, 2309.
(35) Saenger, W. Principles ofNucleic Structure; Springer-Verlag:
New York, 1984; pp 329, 330.