A solid-phase approach to novel purine and nucleoside analogs

Article abstract of DOI:10.1016/j.bmc.2005.05.007

This paper describes a method for the preparation of purine analogs using the solid-phase approach. Nucleoside bases were constructed on Merrifield resin by sequential displacement of purine dichloride with amines, and after detachment, the purine analogs were condensed with d,l-ribofuranoside compounds by the Vorbrueggen method. Thereof, l-ribofuranoside was prepared from l-arabinose via the selective oxidation-reduction procedure of the 2-OH group. Some compounds exhibited moderate activity against HIV-1 in PBM cells.

Full text of DOI:10.1016/j.bmc.2005.05.007

Bioorganic & Medicinal Chemistry 13 (2005) 4760–4766
A solid-phase approach to novel purine and nucleoside analogs
b
b
a
a
Junbiao Chang,a,b, Chunhong Dong, Xiaohe Guo, Weidong Hu, Senxiang Cheng,
*
Qiang Wanga and Rongfeng Chena
aHenan Key Laboratory of Fine Chemicals, Zhengzhou 450002, PR China
bDepartment of Chemistry, University of Science and Technology of China, Hefei 230026, PR China
Received 7 March 2005; revised 27 April 2005; accepted 2 May 2005
Available online 8 June 2005
Abstract—This paper describes a method for the preparation of purine analogs using the solid-phase approach. Nucleoside bases
were constructed on Merrifield resin by sequential displacement of purine dichloride with amines, and after detachment, the purine
analogs were condensed with D,L-ribofuranoside compounds by the Vorbruggen method. Thereof, L-ribofuranoside was prepared
¨
from L-arabinose via the selective oxidation–reduction procedure of the 2-OH group. Some compounds exhibited moderate activity
against HIV-1 in PBM cells.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
nucleosides, could effectively interact and inhibit meta-
bolic enzymes. With the discovery of the antiviral activ-
ity of L-oxathiolane nucleosides, which eventually led to
the 3TC as a therapeutic agent and the development of
FTC and L-FMAU among others,9 this assumption has
been proven not to be true. Favorable features of L-nu-
cleosides include an antiviral activity comparable to and
sometimes even greater than that of their D-counter-
parts, a more favorable toxicological profile, and a
greater metabolic stability.
Drug discovery for antiviral chemotherapy during the
last 30 years has provided effective treatments for
numerous viral diseases. In particular, the fight against
AIDS has prompted the development of new classes of
antiviral drugs, which have provided a considerable de-
crease in HIV-associated morbidity and mortality as
well as improvement in the quality of life of AIDS pa-
tients. Although new, promising targets are being iden-
tified, nucleoside analogs remain the cornerstone of
antiviral therapy. Currently, seven of the sixteen drugs
available for the treatment of AIDS (AZT,1 ddC,2
ddI,3 d4T,4 3TC,5 abacavir,6,7 and tenofovir8) belong
to the category of nucleoside reverse transcriptase inhib-
itors (NRTIs). Among NRTIs for AIDS, 3TC is also the
drug of choice for the treatment of hepatitis B virus
infection.
This paper reports an efficient preparation of novel pur-
ine nucleoside analogs, which allows for the simulta-
neous modification of both purine and carbohydrate
units. Purine can be synthesized on solid support for
its potential inhibition of target nucleotide-binding pro-
teins, which play a significant role in many biological
processes.10–14 Novel purine analogs with 2,6-disubstitu-
ents can react with D- or L-ribofuranoside to provide the
corresponding nucleoside derivatives.
The efficacy of nucleoside analogs depends on their abil-
ity to mimic natural nucleosides, thus interacting with
viral and/or cellular enzymes and inhibiting critical
processes in the metabolism of nucleic acids. For this
reason, it had been believed that only D-enantiomer ana-
logs, which possess the same stereochemistry as natural
2. Results and discussion
The method for synthesis of novel purine analogs using
solid-phase chemistry is shown in Scheme 1. The start-
ing material for the THP linker used in Ellmanꢀs syn-
thesis to prepare 3,4-dihydro-2H-pyran-2-methanol is
no longer commercially available, but this highly versa-
tile linker can be easily prepared.15 3,4-Dihydro-2H-py-
ran-2-methanol was converted to its sodium alkoxide
Keywords: Solid-phase synthesis; Purine bases; D,L-Ribofuranoside;
Condensation; Nucleoside.
*
Corresponding author. Tel.: +86 371 65719822; fax: +86 371
65719822; e-mail: jbchang@public2.zz.ha.cn
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.05.007

J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
4761
Scheme 1. Solid-phase synthesis of purine analogs. Reagents and conditions: (a) 2,6-dichloropurine, CSA, CH2Cl2, 60 ꢁC; (b) 1-phenyl piperazine or
1-piperonylpiperazine, n-BuOH, Et3N, 80 ꢁC; (c) piperidine, 102 ꢁC; (d) TFA/CH2Cl2.
L-Ribofuranoside was prepared from L-arabinose via
using NaH in DMF at 25 ꢁC for 30 min and then was
the following steps according to Ref. 16. L-Arabinose re-
acted with benzyl alcohol (saturated with HCl (gas)) at
rt for 10 h to give compound 7 as a white solid (94%).
Compound 7 reacted with acetone in the presence of
p-TsOH Æ H2O at rt for 2 h to give compound 8 as a yel-
lowish syrup, which was used for the next reaction with-
out further purification. Compound 8 was oxidized with
PDC in dichloromethane and acetic anhydride to give
compound 9 as a syrup. Then the product was reduced
with NaBH4 at ꢀ20 ꢁC over 3 h to give compound 10.
Compound 10 was hydrolyzed with 4% CF3COOH for
ꢁ8 h to give L-ribose 11 as a yellowish syrup. The prod-
uct was dissolved in 1% HCl (gas) in methanol at rt for
2 h to produce 12 as a yellowish syrup. Compound 12
reacted with benzoyl chloride in pyridine at rt for 8 h
to give compound 13 as a yellowish syrup. Compound
13 was dissolved in acetic acid, acetic anhydride, and
catalyzed by concd H2SO4 to give the product 1-O-ace-
tyl-2,3,5-tri-O-benzoyl-b-L-ribofuranose (14) as a white
solid, which was used in the following condensations
with purines (Scheme 2).
treated with Merrifield chloride resin to give compound
1. We routinely performed this reaction with excellent
results regardless of the initial chlorine loading level.
The attachment of 2,6-dichloropurine onto DHP resin
1
was accomplished using camphorsulfonic acid
(CSA) in 1,2-dichloroethane at 60 ꢁC for 30 h. The ex-
cess 2,6-dichloropurine was removed by filtration (the
unreacted materials can be recovered simply by extrac-
tion and chromatography). Differential reactivity of the
two chlorine atoms on 2,6-dichloropurine derivative 2
with nucleophilics allows for the sequential introduc-
tion of different substituents. The more reactive, 6-
chloro position, was easily displaced with 1-phenyl
piperazine or 1-piperonyl piperazine in triethylamine
and n-butanol at 80 ꢁC for 3 h to give 3a and 3b,
respectively. The purity of the crude product was
98%. The 2-chloro substituent was less reactive and re-
quired more forcing reaction conditions. This was
accomplished using the piperidine as solvent and heat-
ing the resin to 102 ꢁC for 4 h to give 4a and 4b. The
final product was cleaved from the resin using the stan-
dard protocol of acidic hydrolysis. The treatment of
the resins 3a, 3b, 4a, and 4b with dichloromethane
and trifluoroacetic acid (8:1) at room temperature for
10 min and subsequent washing with methanol gave
compounds 5a–d (Scheme 1).
A series of nucleoside analogs was then synthesized by
coupling the disubstituted purines with 1,2,3,5-tetra-O-
acetyl-b-D-ribofuranose or 1-O-acetyl-2,3,5-tri-O-benzo-
yl-b-L-ribofuranose by the Vorbruggen method
¨

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J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
Scheme 2. Synthesis of 1-O-acetyl-2,3,5-tri-O-benzoyl-b-L-ribofuranose. Reagents and conditions: (a) HCl (g)/BnOH; (b) DMP, acetone; (c) PDC,
Ac2O, CH2Cl2, reflux; (d) NaBH4, MeOH; (e) 4% CF3COOH, reflux; (f) 1% HCl (g)/MeOH; (g) BzCl, pyridine; (h) AcOH, Ac2O, concd H2SO4.
(Schemes 3 and 4). A Lewis acid can be used for the acti-
vation of the sugar portion in the condensation with eas-
ily prepared silylated bases. This one-step procedure
produced the desired products in good yield.
3. Experimental
3.1. Materials
Melting points were recorded with an XT-4 melting
point apparatus and are uncorrected. H NMR spectra
were recorded on a BrukerAV-300, and are referenced
to internal tetramethylsilane (TMS) at 0.0 ppm, chemi-
cal shifts being reported in parts per million (d). IR spec-
1
All the synthesized nucleosides were evaluated for anti-
viral activity against human immunodeficiency virus
type-1 (HIV-1) (Table 1). The compounds 22 and 23
showed moderate activity against HIV-1 in PBM cells
(9.8, 3.6 lM) and no other compound showed any sig-
nificant activity or toxicity up to 100 lM concentration
against HIV-1.
tra were obtained on
a Shimadzu-8700 infrared
spectrometer (mmax in cmꢀ1). Elemental analyses were
performed with a Carlo-Erba 1106 C, H, and N ana-
Scheme 3. Synthesis of novel D-purine nucleoside analogs. Reagents and conditions: (a) HMDS, (NH4)SO4, reflux; (b) TMSOTf, DCE, rt; (c) NH3/
CH3OH.

J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
4763
Scheme 4. Synthesis of novel L-purine nucleoside analogs. Reagents and conditions: (a) HMDS, (NH4)SO4, reflux; (b) TMSOTf, DCE, rt; (c) NH3/
CH3OH.
Table 1. Anti-HIV-1 activities of L-nucleosides
the desired product 2 (22.3 g). The loading level of 2,6-
dichloropurine was determined to be 1.37 mmol/g by
gravimetric methods.
Compound
HIV-1 EC50 (lM)
Toxicity (cell count)
PBM (IC50, lM)
AZT
16
0.004
>100
>100
>100
>100
>100
9.8
>100
>100
>100
>100
>100
>100
>100
>100
>100
3.1.3. Support bound 2-chloro-6-(1-(4-phenyl)piperazine)-
purine (3a) and support bound 2-chloro-6-(1-(4-pipero-
nyl)piperazine)purine (3b). A suspension of resin 2 (5 g,
6.85 mmol), 1-phenyl piperazine (5.55 g, 34.25 mmol),
and triethylamine (5.5 ml, 35 mmol) in n-butanol
(1000 ml) was heated to 80 ꢁC for 3 h. The mixture
was cooled to rt and filtered, the resin was washed with
methanol (3 · 30 ml), CH2Cl2 (3 · 30 ml), and dried in a
vacuum oven at 60 ꢁC for overnight to give the desired
product 3a (5.9 g).
17
18
19
20
21
22
>100
3.6
23
lyzer. UV spectra were obtained on a Shimadzu-2100
spectrophotometer. LC–MS spectra were measured on
an Agilent MSD-1100 ESI-MS/MS System. TLC was
performed on silica gel GF254 precoated plates.
Using the same procedure, resin 2 was made to react
with 1-piperonyl piperazine in the presence of triethyl-
amine and n-butanol to give the desired product 3b.
3.1.4. Support bound 2-piperidine-6-(1-(4-phenyl)piper-
azine)purine (4a) and support bound 2-piperidine-6-(1-(4-
piperonyl)piperazine)purine (4b). A suspension of 3a
(2.5 g) in piperdine (10 ml) was heated to 102 ꢁC for
4 h. The mixture was then cooled and filtered, the resin
was washed with methanol (3 · 30 ml), DMF
(3 · 30 ml), methanol (3 · 30 ml), and CH2Cl2
(3 · 30 ml), and dried in a vacuum oven at 60 ꢁC for
overnight to give the desired product 4a (4.6 g).
3.1.1. ((3,4-Dihydro-2H-pyran-2-yl-methyl)oxy)-linked
Merrifield resin (1). The Merrifield resin (1) was pre-
pared (yield 92%) according to Ref. 15.
3.1.2. Support bound 2,6-dichloropurine (2). A solution of
2,6-dichloropurine (10 g, 53 mmol), resin 1 (17.7 g,
13.5 mmol), and camphorsulfonic acid (2.95 g,
12.5 mmol) in 1,2-dichloroethane (200 ml) was stirred
at 60 ꢁC for 30 h. The mixture was filtered, the resin
was collected on a Buchner funnel, washed with CH2Cl2
(3 · 50 ml), DMF (3 · 50 ml), CH2Cl2 (3 · 50 ml), and
dried in a vacuum oven at 60 ꢁC for overnight to give
A procedure similar to that used for 4a was used to get
the desired product 4b.

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J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
3.1.5. 2-Chloro-6-(1-(4-phenyl)piperazine)purine (5a). Re-
sin 3a (2.5 g) was suspended in CH2Cl2/TFA (8:1, 20 ml)
and stirred for 10 min at rt. The solution was filtered
and the resin was washed with methanol (2 · 10 ml).
The filtrate was concentrated at reduced pressure to give
the crude product 5a as a white solid (1.02 g). An analyt-
ical sample was purified by silica gel chromatography
(50% ethyl acetate/petroleum ether). Compound 5a:
mp 232–234 ꢁC. UV (MeOH): kmax 255.5 nm, 1H
NMR (acetone-d6) d 8.11 (s, 1H, H-8), 7.30–6.85 (m,
5H, Ar–H), 3.94 (m, 4H, CH2CH2), 3.38–3.31 (m, 4H,
CH2CH2). MS m/z = 315 [M+H]+. Anal. Calcd for
C15H15N6Cl: C, 57.32; H, 4.78; N, 26.75. Found: C,
57.24; H, 4.80; N, 26.70.
2,2-dimethoxypropane (24 ml, 0.195 mol) and p-TsOHÆ
H2O (0.4 g, 2 mmol) in acetone (200 ml) was stirred at
rt for 2 h. The reaction mixture was neutralized with tri-
ethylamine and evaporated under reduced pressure to
give compound 8 as a yellowish syrup, which was used
for the next reaction without further purification.
To a mixture of compound 8 and pyridinium dichro-
mate (PDC, 24 g, 0.063 mol) in CH2Cl2 (200 ml), Ac2O
(24 ml, 0.254 mol) was added at 0 ꢁC and then the mix-
ture was refluxed until the starting material disappeared.
The solvent was removed under reduced pressure to 1/3
of its original volume and the residue was poured into
EtOAc (150 ml) with vigorous stirring using a mechani-
cal stirrer, which was filtered through a Celite pad
(20 cm). The filter cake was thoroughly washed with
EtOAc. The blackish combined filtrate was filtered again
through a silica gel column. The silica gel was washed
with EtOAc until no more of compound 9 could be de-
tected on TLC. The combined clear filtrate was evapo-
rated to give compound 9 as a syrup.
3.1.6. 2-Chloro-6-(1-(4-piperonyl)piperazine)purine (5b).
Cleavage of resin 3b by using a procedure similar to that
used for 5a gave product 5b as a white solid. Mp 238–
240 ꢁC UV (MeOH) kmax 278.5 nm; 1H NMR (ace-
tone-d6) d 7.98 (s, 1H, H-8), 7.17–6.90 (m, 3H, Ar–H),
6.07 (s, 2H, –CH2–), 4.49 (s, 2H, –CH2–), 3.84 (m, 4H,
2· –CH2–), 3.58 (m, 4H, 2· –CH2–); MS m/z = 373
[M+H+]. Anal. Calcd for C17H17N6Cl: C, 54.84; H,
4.57; N, 22.58. Found: C, 54.77; H, 4.60; N, 22.54.
The syrup 9 was dissolved in 200 ml methanol and
cooled to ꢀ20 ꢁC. To the solution, NaBH4 (4 g,
0.106 mol) was slowly added over 3 h at ꢀ20 ꢁC. After
completion of the reaction, the solution was neutralized
with acetic acid and evaporated under reduced pressure
to a white solid residue, which was partitioned between
EtOAc (100 ml). The combined organic layer was
washed with brine (20 ml), dried with MgSO4, and then
evaporated to yield a white solid, which was recrystal-
lized from hexane to give compound 10 (13.5 g, 58%
from compound 7) as white crystals. Mp 79–80 ꢁC;
3.1.7. 2-Piperidine-6-(1-(4-phenyl)piperazine)purine (5c).
Cleavage of resin 4a by using a procedure similar to that
used for 5a gave product 5c as a white solid. Mp 183–
185 ꢁC; UV (MeOH) kmax 277.0 nm; 1H NMR (ace-
tone-d6) d 7.94 (s, 1H, H-8), 7.30–6.83 (m, 5H, Ar–H),
4.55 (br s, 4H, 2· –CH2–), 3.84 (m, 4H, 2· –CH2–),
3.38–3.31 (4H, m, 2· –CH2), 1.69–1.72 (6H, m, 3·
–CH2–); MS m/z = 364 [M+H+]. Anal. Calcd for
C20H25N7: C, 66.11; H, 6.89; N, 27.00. Found: C,
66.23; H, 6.81; N, 26.96.
1
[a]25 +143ꢁ (c 0.7, EtOH); H NMR (CDCl3) d 7.36–
7.26 (m, 5H, Ar–H), 4.86 (d, J = 5.40 Hz, 1H, H-1),
4.56–4.28 (q, J = 11.8 Hz, 2H, PhCH2O–), 4.50 (m,
1H, H-2), 3.86–3.37 (m, 2H, H-5), 3.74 (m, 2H, H-3
and H-4), 1.55 (s, 3H), 1.37 (s, 3H).
3.1.8. 2-Piperidine-6-(1-(4-piperonyl)piperazine)purine (5d).
Cleavage of resin 4b by using a procedure similar to that
used for 5a gave product 5d as a white solid. Mp 222–
224 ꢁC. UV (MeOH): kmax 258.5 nm, 1H NMR
(acetone-d6) d 7.72 (s, 1H, H-8), 6.88–6.74 (m, 3H, Ar–
H), 6.00 (s, 2H, –CH2–), 4.64 (s, 2H, –CH2–), 4.13–
4.03 (m, 4H, 2· –CH2–), 3.64 (m, 4H, 2· –CH2–),
2.52–2.42 (m, 4H, 2· –CH2–), 1.55–1.18 (m, 6H, 3·
–CH2–). MS, m/z = 422 [M+H]+. Anal. Calcd for
C22H27N7: C, 62.71; H, 6.41; N, 23.28. Found: C,
62.69; H, 6.46; N, 23.26.
3.1.11. 1-O-Acetyl-2,3,5-tri-O-benzoyl-b-L-ribofuranose
(14). Compound 10 (20 g, 71.7 mmol) in 4% CF3COOH
(100 ml) was refluxed until the starting material and the
intermediate (1-O-benzyl derivative) disappeared. The
reaction mixture was cooled to rt and washed with
CH2Cl2 (4 · 50 ml) to remove benzyl alcohol. The aque-
ous layer was evaporated in vacuo and coevaporated
with toluene to give compound 11 as a yellowish syrup,
which was completely dried under high vacuum to re-
move a trace amount of water.
3.1.9. 1-O-Benzyl-b-L-ribofuranoside (7). Benzyl alcohol
(50 ml) was saturated with hydrogen chloride for
40 min at 0 ꢁC, to which L-arabinose (10 g, 0.067 mol)
was added and the mixture was stirred at rt for 10 h.
During this time, compound 7 precipitated. EtOAc
(75 ml) was slowly added while stirring for additional
precipitation. The precipitate was filtered and washed
with EtOAc, and dried in air, to give the product 7 as
a white solid (15.36 g, 96%). Mp 170–171 ꢁC; 1H
NMR (DMSO-d6) d 7.39–7.27 (m, 5H, Ar–H), 4.75 (d,
J = 1.8 Hz, 1H, H-1), 4.68–4.43 (q, J = 12.44 Hz, 2H,
PhCH2O–), 3.72–3.43 (m, 5H, H-2, H-3, H-4, and H-5).
Compound 11 was dissolved in 1% HCl (gas) of metha-
nol solution (200 ml), the mixture was stirred at rt for
2 h, then neutralized with pyridine (18 ml), and concen-
trated in vacuo at 30–35 ꢁC to give a yellowish syrup,
which was coevaporated with pyridine to yield com-
pound 12 as a yellowish syrup. Compound 12 was dis-
solved in pyridine (80 ml) and benzoyl chloride (22 ml)
was added dropwise to the mixture at 0 ꢁC. The mixture
was stirred at rt for 8 h. After the reaction was almost
completed, the mixture was heated at 45 ꢁC for 1.5 h.
The mixture was cooled to rt and ice was added to re-
move the remaining benzoyl chloride. Excess pyridine
was evaporated to 1/2 volume at 35–40 ꢁC and the
3.1.10. 1-O-Benzyl-3,4-O-isopropylidene-b-L-riboside (10).
A mixture of 1-O-benzyl-b-L-riboside 7 (20 g, 0.083 mol),

J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
4765
residue was dissolved in EtOAc (150 ml), which was
washed with cold H2O (50 ml), cold H2SO4 (3 N,
58 ml), satd NaHCO3 (2 · 50 ml), and brine
(2 · 50 ml). The organic layer was dried, filtered, and
evaporated to afford compound 12 as a yellowish syrup.
2· –CH2–), 2.12 (s, 6H, 2· Ac), 2.07 (s, 3H, Ac); ESI-
MS/MS at m/z 622 [M+H+].
3.1.14. 9-(b-D-Ribofuranosyl)-2-chloro-6-(1-(4-phenyl)pi-
perazine)purine (18). To a solution of 16 (0.15 g,
0.252 mmol) in MeOH (3 ml) was added saturated
MeOH/NH3 (5 ml), and the reaction mixture was stirred
at rt for 24 h. After the solvent was removed under re-
duced pressure, the residue was purified by thin column
chromatography to get the desired product 18 (99.1 mg,
88%) as a white solid. Mp 236–238 ꢁC; UV(MeOH) kmax
To a solution of 12 in acetic acid (14.5 ml, 253 mol) and
acetic anhydride (33 ml, 354 mmol), concd H2SO4 (5 ml,
90 mmol) was slowly added dropwise at 0 ꢁC, during
which crystallization occurred. The mixture was brought
to rt and kept in a refrigerator overnight. The mixture
was poured into ice water (70 ml) mixture and filtered,
and the filter cake was washed twice with cold water.
The solid was dissolved in EtOAc (200 ml), which was
washed with water (50 ml), satd NaHCO3 (50 ml), and
brine (50 ml), respectively. The organic layer was dried
and filtered, with the removal of the solvent and recrys-
tallization of the residue from methanol to give com-
pound 14 as a white solid (15 g, 41.5% from compound
10). Mp 124–125 ꢁC; 1H NMR (CDCl3) d 8.09–7.32
(m, 15H, 3· Ar–H), 6.43 (s, 1H, H-1), 5.91 (dd, J = 4
and 8 Hz, 1H, H-3), 5.79 (d, J = 8 Hz, 1H, H-2), 4.49–
4.81 (m, 3H, H-4 and H-5), 2.00 (s, 3H, CH3COO).
1
279.5 and 207.5 nm; H NMR(CDCl3) d: 7.81 (s, 1H,
H-8), 6.95–6.89 (m, 5H, Ar–H), 6.32 (d, J = 6.6 Hz,
1H, 10-H), 5.76 (t, J = 6.3 Hz, 1H, 20-H), 5.02 (m, 1H,
30-H), 4.37–4.28 (m, 4H, 2· –CH2–), 4.15-4.03 (m, 1H,
40-H), 3.76–3.69 (m, 2H, 50-H), 3.27–3.22 (m, 4H, 2·
–CH2–); ESI-MS/MS at m/z 447 [M+H]+; Anal. Calcd
for C20H23O4N6Cl: C, 53.81; H, 5.16; N, 18.83. Found:
C, 53.92; H, 5.25; N, 18.89.
3.1.15. 9-(b-D-Ribofuranosyl)-2-piperidine-6-(1-(4-phen-
yl)piperazine)purine (19). Using a procedure similar to
that used for 18, to get the product 19 (91%) as a white
solid. Mp 245–248 ꢁC; UV(MeOH) kmax 297.0, 251.5
1
3.1.12. 9-(20,30,50-Tri-O-acetyl-b-D-ribofuranosyl)-2-chlo-
ro-6-(1-(4-phenyl)piperazine)purine (16). A suspension of
5a (0.16 g, 0.5 mmol) and ammonium sulfate (0.01 g) in
hexamethyldisilazane (HMDS, 10 ml) was heated at re-
flux until a clear solution was obtained. The reaction
mixture was cooled to room temperature, and the
HMDS was removed under reduced pressure and
anhydrous conditions. To the residue under nitrogen
was added the 1,2,3,5-tetra-O-acetyl-D-ribofuranosyl
(0.11 g, 0.35 mmol) in dry 1,2-dichloroethane. The reac-
tion mixture was cooled to 0 ꢁC, treated with trimethyl-
silyl triflate (TMSOTf) (0.2 ml, 1.03 mmol), and allowed
to stir at 0 ꢁC for 10 min and then 10 min at room tem-
perature. The reaction mixture was poured into EtOAc
and the organic layer was washed once with satd NaH-
CO3 (3 · 20 ml), water (3 · 20 ml), and brine (3 · 20 ml),
dried (MgSO4), filtered, and concentrated. The residue
was chromatographed over silica gel eluting with hex-
anes and hexanes/ethyl acetate (6:1 to 4:1) to give 16
(0.17 g, 82%) as a white solid. Mp 228–231 ꢁC; UV
and 205.5 nm; H NMR(CDCl3) d 7.56 (s, 1H, H-8),
7.29–6.85 (m, 5H, Ar), 5.70 (d, J = 6.6 Hz, 1H, 10-H),
4.86 (t, J = 6.3 Hz, 1H, 20-H), 4.37 (m, 1H, 30-H),
4.26–4.21 (m, 5H, 2· –CH2–, 40-H), 3.83–3.65 (m, 2H,
50-H), 3.61 (m, 4H, 2· –CH2–), 3.23 (m, 4H, 2·
–CH2–), 1.58 (m, 6H, 3· –CH2–); ESI-MS/MS at m/z
496 [M+H+]. Anal.Calcd for C25H33O4N7: C, 60.61;
H, 6.67; N, 19.80. Found: C, 60.58; H, 6.62; N, 19.86.
3.1.16. 9-(20,30,50-Tri-O-benzoyl-b-2-chloro-L-ribofurano-
syl)-6-(1-(4-piperonyl)piperazine)purine (20). A suspen-
sion of 5b (0.17 g, 0.5 mmol) and (NH4)2SO4(0.01 g) in
hexamethyldisilazane (HMDS, 10 ml) was heated at re-
flux until a clear solution was obtained. The reaction
mixture was cooled to rt, and the HMDS was removed
under reduced pressure and anhydrous conditions. To
the residue under nitrogen was added the 1-O-acetyl-
2,3,5-tri-O-benzoyl-b-L-ribofuranose 14 (0.177 g, 0.35
mmol) in dry 1,2-dichloroethane (DCE) (5 ml). The reac-
tion mixture was cooled to 0 ꢁC, treated with trimethyl-
silyl triflate (TMSOTf) (0.2 ml, 1.03 mmol), allowed to
stir at 0 ꢁC for 10 min, and then the mixture was brought
to rt until the starting material (14) disappeared. The
reaction mixture was poured into EtOAc and satd NaH-
CO3 with stirring. The organic layer was washed once
with satd NaHCO3 (2 · 5 ml), water (2 · 5 ml), bri-
ne(2 · 5 ml), and then dried (MgSO4), and concentrated.
The residue was purified by TLC to give 20 (0.25 g, 88%)
as a white syrup. UV (CH3OH), kmax 200.0, 225.0,
1
(MeOH) kmax 204.5 nm; H NMR (CDCl3) d 7.89 (s,
1H, H-8), 7.33–6.90 (m, 5H, Ar–H), 6.20 (d,
J = 5.7 Hz, 1H, 10-H), 5.77 (t, J = 5.7 Hz, 1H, 20-H),
5.58 (dd, 1H, J = 5.1 and 5.4 Hz, 30-H), 4.48–4.23 (m,
7H, 40-H, 50-H, 2· –CH2–), 3.30 (m, 4H, 2· –CH2–),
2.16 (s, 6H, 2· Ac), 2.08 (s, 3H, Ac); ESI-MS/MS at
m/z 595 [M+Na+].
3.1.13. 9-(20,30,50-Tri-O-acetyl-b-D-ribofuranosyl)-2-piper-
idine-6-(1-(4-phenyl)piperazine)purine (17). Using a pro-
cedure similar to that used for 16, the silylation of 5c
(0.18 g, 0.5 mmol) reacted with 1,2,3,5-tetra-O-acetyl-
D-ribofuranosyl (0.11 g, 0.35 mmol) to give 17 (0.19 g,
86%) as a white solid. Mp 221–224 ꢁC; UV(MeOH) kmax
1
281.0 nm; H NMR(CDCl3) d 8.08–7.85 (m, 16H, H-8,
and 3· Ar–H), 6.87–6.75 (m, 3H, Ar–H), 6.47 (d,
J = 6.6 Hz, 1H, H-10), 6.13 (m, 2H, H-20, and H-30),
5.94 (s, 2H, –OCH2O–), 4.88–4.70 (m, 3H, H-40, and
H-50), 4.25 (br s, 4H, 2· –CH2–), 3.48 (s, 2H, –CH2–),
2.56 (m, 4H, 2· –CH2–), 2.00–1.56 (m, 6H, 3· –CH2–);
ESI-MS/MS m/z = 817 [M+H+].
1
251.5 and 203.5 nm; H NMR(CDCl3) d 7.54 (s, 1H,
8-H), 7.32–6.91 (m, 5H, Ar–H), 6.13 (dd, 1H, J = 3.3,
and 5.4 Hz, 20-H), 5.95 (d, J = 3.3 Hz, 1H, 10-H), 5.79
(t, J = 5.7 Hz, 1H, 30-H), 4.48–4.23 (m, 7H, 40-H, 50-H,
and 2· –CH2–), 3.76 (m, 4H, 2· –CH2–), 3.30 (m, 4H,
3.1.17. 9-(20,30,50-Tri-O-benzoyl-b-L-ribofuranosyl)-2-pi-
peridine-6-(1-(4-phenyl)piperazine)purine (21). Using a

4766
J. Chang et al. / Bioorg. Med. Chem. 13 (2005) 4760–4766
procedure similar to that used for 20, the silylation of 5c
(0.182 g, 0.5 mmol) reacted with 1-O-acetyl-2,3,5-tri-O-
benzoyl-b-L-ribofuranose (0.177 g, 0.35 mmol) to give
21 (0.231 g, 82%) as a white syrup. UV (CH3OH), kmax
201.0, 230.0 nm; 1H NMR (CDCl3) d 7.99–6.85 (m,
21H, 4 · Ar–H and H-8), 6.54 (d, J = 6.3 Hz, 1H, H-
10), 6.39 (m, 1H, H-20), 6.21 (m, 1H, H-30), 4.81-4.64
(m, 3H, H-40, and H-50), 4.39 (m, 4H, 2· –CH2–), 3.79
(m, 4H, 2· –CH2–), 3.32 (m, 4H, 2· –CH2–), 1.68–1.61
(m, 6H, 3· –CH2–); ESI/MS/MS m/z = 808 [M+H+].
Province and National Natural Science Foundation of
China (29972009, 200342005).
References and notes
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piperazine)purine (22). To a solution of 20 (0.25 g,
0.306 mmol) in methanol (5 ml), which was saturated
with ammonia at 0 ꢁC, was added and stirred at rt for
48 h. After the reaction was completed, the solvent
was removed under reduced pressure, the residue was
purified by TLC to give the desired product 22
(139 mg, 90%) as a white solid. Mp 203–205 ꢁC; UV
(CH3OH), kmax 200.0, 218.0, 282.0 nm; 1H NMR
(CDCl3) d 7.74 (s, 1H, H-8), 6.87–6.75 (m, 3H, Ar–H),
5.96 (s, 2H, –OCH2O–), 5.74 (d, J = 7.2 Hz, 1H, H-10),
5.03 (m, 1H, H-20), 4.37–4.22 (m, 6H, H-30, H-40, and
2· –CH2–), 3.95–3.71 (m, 2H, H-50), 3.48 (s, 2H,
–CH2–), 2.62 (br s, 4H, 2· –CH2–); ESI-MS /MS
m/z = 504.8 [M+H+].
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piperazine)purine (23). Using a procedure similar to that
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solid. Mp 245–247 ꢁC; UV (CH3OH), kmax 201.0, 251.0,
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1
295.0 nm; H NMR (DMSO-d6) d 8.03 (s, 1H, H-8),
7.26–6.81 (m, 5H, Ar–H), 5.80 (d, J = 6.6 Hz, 1H, H-
10), 4.56 (m, 1H, H-20), 4.27 (m, 4H, 2· –CH2–), 4.14–
3.87 (m, 2H, H-30, and H-40), 3.70 (m, 4H, 2· –CH2–),
3.60–3.41 (m, 2H, H-50), 3.24 (m, 4H, 2· –CH2–),
1.59–1.52 (m, 6H, 3· –CH2–); ESI-MS/MS m/z = 496
[M+H+].
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¨
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Acknowledgments
J.B.C. is grateful for the financial support from the out-
standing Scholar Innovation Foundation of Henan