Synthesis of 3′-acetamidoadenosine derivatives as potential A 3 adenosine receptor agonists

Article abstract of DOI:10.1080/15257770801944436

On the basis of high binding affinity of 3′-aminoadenosine derivatives 2b at the human A3 adenosine receptor (AR), 3′- acetamidoadenosine derivatives 3a-e were synthesized from 1,2:5,6-di-O- isopropylidene-D-glucose via stereoselective hydroboration as a key step. Although all synthesized compounds were totally devoid of binding affinity at the human A3AR, our results revealed that 3′-position of adenosine can only be tolerated with small size of a hydrogen bonding donor like hydroxyl or amino group in the binding site of human A3AR. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15257770801944436

Nucleosides, Nucleotides and Nucleic Acids, 27:408–420, 2008
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770801944436
SYNTHESIS OF 3ꢀ-ACETAMIDOADENOSINE DERIVATIVES AS
POTENTIAL A3 ADENOSINE RECEPTOR AGONISTS
Moon Woo Chun,1 Sung Wook Choi,1 Tae Kyung Kang,1 Won Jun Choi,2 Hea
Ok Kim,2 Zhan-Guo Gao,3 Kenneth A. Jacobson,3 and Lak Shin Jeong2
1College of Pharmacy, Seoul National University, Seoul, Korea
2Laboratory of Medicinal Chemistry, College of Pharmacy, Ewha Womans University,
Seoul, Korea
3Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of
Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda,
Maryland, USA
On the basis of high binding affinity of 3ꢁ-aminoadenosine derivatives 2b at the human A3
2
adenosine receptor (AR), 3ꢁ-acetamidoadenosine derivatives 3a–e were synthesized from 1,2:5,6-di-
O-isopropylidene-D-glucose via stereoselective hydroboration as a key step. Although all synthesized
compounds were totally devoid of binding affinity at the human A3AR, our results revealed that
3ꢁ-position of adenosine can only be tolerated with small size of a hydrogen bonding donor like
hydroxyl or amino group in the binding site of human A3AR.
Keywords 3ꢁ-acetamidoadenosines; human A3 adenosine receptor; hydrogen bonding
donor; hydroboration-oxidation; steric effects
INTRODUCTION
Adenosine is an endogenous chemical messenger, regulating many
physiological functions through four subtypes (A1, A2A, A2B, and A3) of
adenosine receptors (ARs).[1] Among these, A3 adenosine receptor is the
most recently identified and known to be involved in cell signaling.[2]
Activation of A3AR stimulates phospholipase C (PLC), increasing levels of
inositol triphosphate (IP3) and diacylglycerol (DAG), but inhibits adenylate
Received 30 October 2007; accepted 23 November 2007.
This work was supported by the National Core Research Center (NCRC) program (No. R15-2006-
020) of the Ministry of Science and Technology (MOST) and the Korea Science and Engineering
Foundation (KOSEF).
Address correspondence to Moon Woo Chun, College of Pharmacy, Seoul National University,
Seoul 151-742, Korea. E-mail: mwchun@snu.ac.kr
408

3ꢁ-Acetamidoadenosine Derivatives
409
FIGURE 1 The rationale for the design of the target nucloesides.
cyclase, lowering the level of cAMP.[2] Because IP3 DAG, and cAMP serve
as second messengers, A3AR is closely related to signal transduction of the
cell. Thus, control of A3AR may modulate several diseases related to cell
signaling, making it promising therapeutic target.[3] A3AR agonists have
potentials to be used for the treatment of cancer, cardiac ischemia, and
cerebral ischemia, while A3AR antagonists can be developed as anti-asthma,
anti-glaucoma, anti-inflammatory agents.[3]
Based on the structure of adenosine, a natural messenger, a number of
nucleoside derivatives have been synthesized as A3AR agonists.[3] Among
these, N 6-(3-iodobenzyl)-5-N -methylcarboxamidoadenosine (IB-MECA, 1a)
and its 2-chloro analogue (Cl-IB-MECA, 1b) are representatives of A3AR
agonists, showing high binding affinity to A3AR and high selectivity to A1,
A2A, and A2B ARs and are developed as anticancer agents (Figure 1).[4,5]
On the basis of high binding affinity and selectivity of 1a and 1b, 3ꢁ-
fluoro analogue 2a in bioisosteric relationship with 1a and 1b as a hydrogen
bonding acceptor was synthesized to determine if 3ꢁ-hydroxyl group serves as
a hydrogen bonding acceptor or donor.[6] From this study, it was concluded
that compound 2a displayed significantly decreased binding affinity to
A3AR, indicating 3ꢁ-hydroxyl group acted as a hydrogen bonding donor.
However, 3ꢁ-amino analogue 2b which are also in bioisosteric relationship
with 1a and 1b as a hydrogen bonding donor exhibited high binding affinity

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M. W. Chun et al.
to A3AR comparable to 1a and 1b, indicating that 3ꢁ-hydroxyl group serves
as a hydrogen bonding donor.[7] Since 3ꢁ-amino group served as a hydrogen
bonding donor, Jeong et al.[8] synthesized 3ꢁ-ureido derivatives 2c being
capable of multiple hydrogen bonding, but they were totally devoid of
binding affinities at the all subtypes of ARs, probably due to intramolecular
hydrogen bondings between 3ꢁ-ureido group and 2ꢁ-hydroxyl group. Based
on these findings, we synthesized 3ꢁ-acetamido derivatives 3a–e which can
serve as the same hydrogen bonding donor like 3ꢁ-amino group, but are
expected to possess better pharmacokinetic profiles than basic 3ꢁ-amino
derivatives 2b. Herein, we report the synthesis of 3ꢁ-acetamidoadenosine
derivatives and their binding affinities at the ARs.
RESULTS AND DISCUSSION
The synthetic strategy for the synthesis of the final nucleosides 3a–e
was first to synthesize the glycosyl donor 14 and then to condense with
2,6-dichloropurine. Synthesis of the glycosyl donor 14 from 1,2;5,6-di-
O-isopropylidene-D-glucose is shown in Scheme 1. Swern oxidation of
1,2;5,6-di-O-isopropylidene-D-glucose followed by Wittig reaction with
methyl triphenylphosphonium bromide in the presence of potassium
t-butoxide afforded 3-methylene derivative 4.[9] Hydroboration-oxidation
of 4 gave 3-C-hydroxymethyl derivative 5 as a single stereoisomer, which was
formed by the steric effect by 1,2-isopropylidene group. Benzyl protection
of 5 followed by selective hydrolysis of 5,6-isopropylidene group of the
resulting benzylated derivative 6 afforded diol 7.[10]
Oxidative cleavage of diol 7 with sodium metaperiodate followed by
reduction of the resulting aldehyde with sodium borohydride gave 8 which
was benzoylated to yield 9. Hydrolysis of 9 with 4 N HCl in MeOH
afforded methyl glycoside 10, in which 2-hydroxyl group was protected
with benzoyl group to give 11. Removal of the benzyl group of 11 using
catalytic hydrogenation gave 12. Treatment of 12 with ruthenium chloride
and sodium metaperiodate followed by treating with MeOH in the presence
of DCC gave methylester 13 which was converted to the glycosyl donor 14 by
treating with acetic acid, acetic anhydride, and sulfuric acids.
Condensation of acetate 14 with silylated 2,6-dichloropurine in the
presence of TMSOTf as Lewis acid gave the protected nucleoside 15 as
a single diastereomer due to the neighboring group effect by 2ꢁ-benzoyl
group (Scheme 2). Treatment of 15 with various alkyl, arylalkyl, or cycloalkyl
amines yielded N 6-substituted derivatives which were reacted with methyl
amine to give the final nucleosides 3a–e.
The final nucleosides 3a–e were subjected to competitive radioligand
binding assays.[11] A3AR experiments were performed using adherent
CHO cells stably transfected with cDNA encoding the human A3AR using

3ꢁ-Acetamidoadenosine Derivatives
411
SCHEME 1 Reagents and conditions: (a) DMSO, Oxalyl Chloride, MC; (b) Ph3PCH3Br, t-BuOK,THF;
(c) i. Borane Methyl Sulfide, THF, ii. H2O, 2N NaOH, H2O2; (d) NaH, TBAI, BnBr, THF; (e) 4N
HCl, THF/H2O; (f) i. NaIO4 THF/H2O, ii. NaBH4; (g) BzCl, MC; (h) 0.1% AcCl, MeOH; (i) BzCl,
pyridine; (j) H2 Pd-C; (k) i. NaIO4, RuCl3, MeCN/CCl4/H2O, ii. DCC, MeOH, 4-aminopyridine, MC;
(1) AcOH/Ac2O/c-H2SO4.
SCHEME 2 Reagents and conditions: (a) silylated 2,6-dichloropurine, TMSOTf, DCE; (b) various
amines; (c) MeNH2.
[
125I]I-AB-MECA (1.0 nM) as radioligand, while binding experiments at
A1 and A2A ARs were carried out using [3H]CPX (0.5 nM, recombinant
human A1 AR) or [3H]ZM241385 CPX (2 nM, recombinant human A2A
AR) as radioligand.[9] All tested compounds were totally devoid of binding

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M. W. Chun et al.
affinities at the all subtypes of ARs, indicating that 3ꢁ-acetamido group,
could alter ring puckering of sugar moiety by lack of Gauche effect between
3ꢁ-OH and ring oxygen or might cause steric repulsion at the binding site of
the A3AR, instead of forming strong hydrogen bonding with A3AR, despite
of its hydrogen bonding donor ability.
In conclusion, we have accomplished the synthesis of 3ꢁ-acetami-
doadenosine derivatives, starting from 1,2:5,6-di-O-isopropylidene-D-
glucose via stereoselective hydroboration as a key step. Unfortunately, all
synthesized compounds did not show any significant binding affinity at
the human A3AR, probably due to the steric effects of 3ꢁ-acetamido group.
Our findings indicate that 3ꢁ-position of adenosine can only be tolerated
with small size of a hydrogen bonding donor like hydroxyl or amino group
in the binding site of human A3AR. Molecular modeling study of these
synthesized compounds at human A3AR is in progress and will be reported
elsewhere.
EXPERIMENTAL SECTION
General Methods
NMR data were recorded on a 300 MHz NMR spectrometer using
tetramethylsilane (TMS) as an internal standard, and the chemical shifts
are reported in ppm (δ). Coupling constants are reported in hertz. The
abbreviations used are as follows: s (singlet), d (doublet), m (multiplet),
dd (doublet of doublet), br s (broad singlet). TLC and preparative TLC
were carried out on Merck precoated plates (Kieselgel 60F254). Silica gel
for chromatography was Merck Kieselgel 60. All anhydrous solvents were
distilled over CaH2 or Na/benzophenone prior to use.
3-Deoxy-1,2;5,6-di-O-isopropylidene-3-methylene-α-D-glucofuranose (4).
To a solution of DMSO (3.4 mL, 48.0 mmol) in anhydrous CH2Cl2 (150
mL), was added oxalyl chloride (2.18 mL, 25.0 mmol) dropwise carefully
at −78◦C. After 10 minutes of stirring, to the reaction mixture was added
a solution of di-acetone-D-glucose (5 g, 19.2 mmol) in anhydrous CH2Cl2
(50 mL) with cannula at −78◦C. The mixture was stirred for 10 minutes
at the same temperature followed by treatment of TEA (17 mL), and the
yellow slurry was formed immediately and the mixture was stirred for 30
minutes at room temperature. The reaction mixture was poured into water
and extracted with methylene chloride. The organic layer was washed with
brine, dried (MgSO4), filtered, and evaporated under reduced pressure to
give the ketone (4.6 g, 93%).
To a solution of methyl triphenyl phosphonium bromide (12.7 g,
35.7 mmol) in anhydrous THF (150 mL) was added 2M solution of potas-
sium tertiary butoxide (17.9 mL) in THF at 0◦C and the mixture was stirred
at room temperature for 20 minutes and then cooled to 0◦C. To the reaction

3ꢁ-Acetamidoadenosine Derivatives
413
mixture was added a solution of ketone (4.6 g, 17.8 mmol) in anhydrous
THF (30 mL). After 1 hour of stirring at room temperature, the mixture
was partitioned between EtOAc and water. The aqueous layer was washed 3
times by EtOAc, the combined organic layer was dried over MgSO4, filtered
and evaporated. The resulting residue was purified by silica gel column
chromatography (hexane : ethyl acetate = 2:1) to give compound 4 (3.92 g,
86%) as a colorless oil, whose spectral data were identical with those of
authentic sample.[9]
3-Deoxy-C-hydroxymethyl-O-1,2;5,6-di-O-isopropylidene-α-D-allofura-
nose (5). To a solution of 1 (323 mg, 1.26 mmol) in anhydrous THF (10
mL), 2M solution of BH3-SMe2 complex in THF (3.78 mL) was dropped at
0◦C. The mixture was stirred for 3 hours at room temperature followed by
consecutive addition of THF : H2O (1:1, 1.8 mL), 2N NaOH (5.3 mL), 30%
H2O2 (3.2 mL) at 0◦C and then stirred for 2 hours at room temperature.
The mixture was extracted with EtOAc, and the organic layer was washed
with brine, dried, filtered, and evaporated. Column chromatography
(hexane : ethyl acetate = 1:1) afforded 5 (283 mg, 82%) as a colorless oil,
whose spectral data were identical with those of authentic sample.[9]
3-C-Benzyloxymethyl-3-deoxy-1,2;5,6-di-O-isopropylidene-α-D-allofura-
nose (6).[10] To a solution of 5 (601 mg, 2.19 mmol) in anhydrous THF (22
mL) were added 60% suspension of NaH in mineral oil (80 mg, 3.29 mmol)
and n-Bu4NI (catalytic amount). The mixture was stirred for 20 minutes at
room temperature, and then BnBr (0.4 mL, 3.29 mmol) was added at 0◦C.
The reaction mixture was stirred for 18 hours at room temperature and
quenched with H2O, poured into EtOAc. The organic layer was washed with
brine, dried (MgSO4), filtered, and evaporated under reduced pressure.
The residue was purified by silica gel column chromatography (hexane :
ethyl acetate = 10:1) to give 6 (596 mg, 75%): [α]25D 56.81◦ (c 1.0, CHCl3);
1H NMR (CDCl3, 300 MHz) δ 7.36∼7.26 (m, 5H), 5.78 (d, 1H, J = 3.7
Hz), 4.77 (dd, 1H), 4.56 (s, 2H) 4.17∼3.71 (m, 6H), 2.27∼2.18 (m, 1H),
1.50 (s, 3H), 1.36 (s, 3H), 1.34 (s, 3H), 1.33 (s, 3H); MS (FAB) m/z 363
(M-H).
3-C-Benzyloxymethyl-3-deoxy-1,2-O-isopropylidene-α-D-allofuranose
(7).[10] To a solution of 6 (2.02 g, 5.54 mmol) in a 1:1 mixture of THF
and H2O (25 mL) was added 4N HCl (0.5 mL). After being stirred at
50◦C for 24 hours, the reaction mixture was neutralized by addition of
triethylamine. The mixture was poured into EtOAc, and the organic layer
was washed with brine, dried (MgSO4), filtered, and evaporated. The
residue was purified by silica gel column chromatography (hexane : ethyl
acetate = 1:2) to give diol 7 (1.17 g, 65%): [α]25 25.44◦ (c 1.0, CHCl3);
D
1H NMR (CDCl3, 300 MHz) δ 7.41∼7.31 (m, 5H), 5.79 (d, 1H, J = 3.7 Hz),
4.71∼4.52 (m, 4H), 4.05∼3.55 (m, 6H), 2.32∼2.28 (m, 1H), 2.22∼2.13 (m,
1H), 1.50 (s, 3H), 1.29 (s, 3H); IR (neat) 3397 cm−1; MS (FAB) m/z 325
(M+H).

414
M. W. Chun et al.
3-C-Benzyloxymethyl-3-deoxy-1,2-O-isopropylidene-α-D-ribofuranose
(8). To a solution of 7 (178 mg, 0.60 mmol) in MeOH (3 mL) was added
NaIO4 (140 mg, 0.66 mmol) in H2O (3 mL) at 0◦C. After 30 minutes of
stirring, NaBH4 (32 mg, 0.89 mmol) was added at 0◦C, and the resulting
mixture was stirred for 30 minutes at room temperature. After evaporating
to remove MeOH, the mixture was poured into EtOAc. The organic layer
was washed with brine, dried over MgSO4, filtered and evaporated. Column
chromatography (hexane: ethyl acetate = 1:1) afforded 8 (137 mg, 85%):
[α]25 35.36◦ (c 1.0, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 7.38∼7.26 (m,
D
5H), 5.81 (d, 1H, J = 3.5 Hz), 4.71 (m, 1H), 4.55 (s, 2H), 2.68∼2.63 (m,
1H), 4.10∼3.57 (m, 5H), 2.68∼2.64 (m, 1H), 2.31∼2.22 (m, 1H), 1.5 (s,
3H), 1.3 (s, 3H); IR (neat) 3460 cm−1; MS (FAB) m/z 293 (M-H).
5-O-Bezoyl-3-C-benzyloxymethyl-3-deoxy-1,2-O-isopropylidene-α-D-ribo-
furanose (9). To a solution of 8 (1.18 g, 4.00 mmol) in anhydrous pyridine
(20 mL) was added benzoyl chloride (1.65 mL, 12 mmol) at 0◦C. The
mixture was stirred at room temperature for 2 hours, quenched with a cold
saturated NaHCO3 solution, and extracted with CH2Cl2 three times. The
combined extracts were dried over MgSO4, and evaporated to dryness in
vacuo. The residue was dissolved in 5 mL of toluene and the evaporation
was repeated to remove pyridine. The residue was purified by silica gel
column chromatography (hexane: ethyl acetate = 8:1) to give 9 (1.48
1
g, 93%): [α]25 35.62◦ (c 1.0, CHCl3); H NMR (CDCl3, 300 MHz) δ
D
8.10∼7.28 (m, 10H), 5.86 (d, 1H, J = 30.0 Hz), 5.87 (d, 1H, J = 3.7 Hz),
4.69∼4.77 (m, 2H), 4.54 (s, 2H), 4.22∼4.39 (m,2H), 3.82∼3.88 (dd, 1H,
J = 7.0 and 6.8 Hz), 2.30∼2.40 (m, 1H), 1.64 (s, 3H), 1.38 (s, 3H); IR
(neat) 1721 cm−1; MS (FAB) m/z 399 (M+H).
Methyl-5-O-bezoyl-3ꢁ-C-benzyloxymethyl-3-deoxy-α-D-ribofuranoside
(10). To a solution of 9 (535 mg, 1.34 mmol) in MeOH (13 mL) was
added AcCl (0.1 mL) dropwise at 0◦C. The reaction mixture was stirred
for 30 hours, quenched with TEA until being basic condition, and then
evaporated to remove MeOH. The mixture was partitioned between EtOAc
and water. The organic layer was dried over MgSO4, filtered and evaporated
under reduced pressure. Column chromatography (hexane : ethyl acetate
= 3:1) afforded 10 (432 mg, 86%): [α]25D −13.40◦ (c 1.0, CHCl3); 1H NMR
(CDCl3, 300 MHz) δ 8.07∼8.04 (m 2H), 7.60∼7.53 (m, 1H), 7.46∼7.41 (m,
2H), 7.47∼7.32 (m, 7H), 4.83 (s, 1H), 4.61∼4.46 (m, 4H), 4.37∼4.28 (m,
2H), 3.86∼3.77 (m, 2H), 3.26 (s, 3H), 3.02∼3.00 (d, 1H, J = 21.6 Hz),
2.63∼2.55 (m, 1H); IR (neat) 3440, 1720 cm−1; MS (FAB) m/z 373 (M+H).
Methyl-2,5-di-O-benzoyl-3-C-benzyloxymethyl-3-deoxy-β-D-ribofu rano-
side (11). To a solution of 10 (1.11 g, 3.10 mmol) in anhydrous pyridine
(15 mL) was added benzoyl chloride (0.58 mL, 4.7 mmol) at 0◦C. The
mixture was stirred at room temperature for 5 hours, quenched with a
cold saturated NaHCO3 solution. The mixture was poured into CH2Cl2,
and then organic layer was dried, filtered and evaporated. The residue was

3ꢁ-Acetamidoadenosine Derivatives
415
dissolved in toluene and evaporated repeatedly to remove pyridine. Column
chromatography (hexane : ethyl acetate = 10:1) afforded 11 (1.16 g, 82%):
[α]25 40.89◦ (c 1.0, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 8.13∼8.10 (m,
D
2H), 7.99∼7.95 (m, 2H), 7.61∼7.55 (m, 2H), 7.48∼7.41 (m, 4H), 7.28∼7.18
(m, 3H), 5.49 (d, 1H, J = 4.7 Hz), 4.98 (s, 1H), 4.68∼4.63 (dd, 1H, J = 8.6
and 14.3 Hz), 4.52∼4.36 (m, 4H), 3.83∼3.78 (m, 1H), 3.68∼3.60 (m, 1H),
3.36 (s, 3H), 3.03∼2.94 (m, 1H); IR (neat) 1722 cm−1; MS (FAB) m/z 499
(M+Na).
Methyl-2,5-di-O-benzoyl-3-deoxy-3-C-hydroxymethyl-β-D-ribofuranose
(12). To a solution of 11 (1.26 g, 2.64 mmol) in EtOAc (25 mL) was added
Pd/C. After stirring for 5 hours with hydrogenation, the solution was
filtered through a pad of Celite, concentrated in vacuo. The residue was
purified by silica gel column chromatography (hexane : ethyl acetate = 2:1)
1
to give 12 (970 mg, 95%): [α]25 −2.47◦ (c 1.0, CHCl3); H NMR(CDCl3,
D
300 MHz) δ 8.12∼8.04 (m, 4H), 7.65∼7.56 (m, 2H), 7.55∼7.43 (m, 4H),
5.47 (d, 2H, J = 4.4 Hz), 5.06 (s, 1H), 4.63∼4.56 (m, 1H), 4.50∼4.32 (m,
2H), 3.85∼3.71 (m, 2H), 3.39 (s, 3H), 2.95∼2.86 (m, 1H), 2.56∼2.51 (m,
1H), 2.17 (s, 1H); IR (neat) 3497, 1721 cm−1; MS (FAB) m/z 409 (M+Na).
Methyl-2,5-di-O-benzoyl-3-deoxy-3-C-methoxycarbonyl-β-D-ribofuran-
oate (13). A mixture of 12 (1.23 g, 3.19 mmol), NaIO4 (2.73 g,
12.75 mmol) and RuCl3 (0.189 g, 0.701 mL) in CCl4/CH3CN/H2O
(1:1:1, 9 mL) was stirred at room temperature for 2 hours. The reaction
mixture was evaporated to give the residue, which was dissolved in 5 mL of
toluene. The evaporation was repeated to remove water. The residue was
dissolved in anhydrous CH2Cl2 and to this solution were added DMAP (78
mg, 0.64 mmol), DCC (1M in CH2Cl2, 4.15 mL, 4.15 mmol) and MeOH
(0.17 mL, 4.15 mmol). The mixture was stirred at room temperature for
12 hours, evaporated, and the residue was purified by silica gel column
chromatograph (hexane : ethyl acetate = 5:1) to give 13 (837 mg, 64%):
[α]25 28.17◦ (c 1.0, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 8.11∼8.08 (m,
D
2H), 8.00∼7.98 (m, 2H), 7.62∼7.56 (m, 2H), 7.49∼7.43 (m, 4H), 5.60 (d,
1H, J = 4.8 Hz), 5.14∼5.08 (m, 1H), 5.03 (s, 1H), 4.66∼4.44 (m, 2H),
3.69∼3.59 (m, 4H), 3.36 (s, 3H); IR (neat) 1723 cm−1; MS (FAB) m/z 415
(M+H).
1-O-Acetyl-2,5-di-O-benzoyl-3-deoxy-3-C-methoxycarbonyl-α,β-D-ribofu-
ranoate (14). To a stirred solution of 13 (430 mg, 1.04 mmol) in AcOH
(5 mL) and Ac2O (1.2 mL) was added conc. H2SO4 dropwise at room
temperature. The reaction mixture was stirred for 30 minutes, poured
into a cold saturated NaHCO3 solution, and extracted with CH2Cl2 three
times. The combined extracts were dried over MgSO4, filtered, and
evaporated. The residue was purified by column chromatography (hexane
: ethyl acetate = 8:1) to afford 14, which was used directly for the next
step.

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M. W. Chun et al.
2,6-Dichloro-9-(2,5-di-O-benzoyl-3-deoxy-3-C-methyl-O-carbonyl-β-D-
ribofuranosyl)purine (15). To a solution of silylated 2,6-dichloropurine,
prepared by refluxing 2,6-dichloropurine (125 mg, 0.613 mmol) and
ammonium sulfate (catalytic amount) in HMDS (2 mL), in anhydrous
ClCH2CH2Cl (2 mL) was added a solution of 14 (208 mg, 0.472 mmol)
in anhydrous ClCH2CH2Cl (3 mL) followed by addition of TMSOTf (0.11
mL, 0.613 mmol) at 0◦C, and the mixture was stirred at room temperature
for 20 minutes and then at 50◦C for 12 hours. The mixture was quenched
with saturated NaHCO3 solution, filtered through a Celite pad, and poured
into CH2Cl2. The organic layer was washed with brine, dried, filtered,
and evaporated. Column chromatography (hexane : ethyl acetate = 4:1)
afforded 12 (228 mg, 85%): UV (MeOH) λmax 273 nm (pH 7); [α]25
D
18.06◦ (c 1.0, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 8.20 (s, 1H), 8.01∼7.98
(m, 2H), 7.89∼7.86 (m, 2H), 7.68∼7.38 (m, 6H), 6.30∼6.24 (m, 1H), 6.13
(d, 1H, J = 1.3 Hz), 5.16∼5.11 (m, 1H), 4.88∼4.83 (m, 1H), 4.69∼4.64
(m, 1H), 4.40∼4.35 (dd, 1H, J = 3.7 and 16.5 Hz), 3.76 (s, 3H); IR (neat)
1726 cm−1; MS (FAB) m/z 571 (M+H); Anal. Calcd for C, 54.65; H, 3.53;
N, 9.81. Found: C, 54.72; H, 3.48; N, 9.96.
2-Chloro-N6-(3-iodobenzyl)-9-(3-C-methylcarbamoyl-3-deoxy-β-D-ribofu-
ranosyl)adenine (3a). To a solution of 15 (76 mg, 0.133 mmol) in EtOH
(3 mL) was added 3-iodobenzylamine (62 mg, 0.266 mmol), and then
the mixture was stirred at 50◦C for 5 hours, evaporated, and extracted
with EtOAc three times. The combined extracts were dried over MgSO4,
filtered, and evaporated. The residue was purified by silica gel column
chromatography (hexane : ethyl acetate = 2:1) to give an iodobenzyl
derivative (82 mg, 81%): UV (MeOH) λmax 272 nm (pH 7); [α]25D -7.48◦ (c
1
1.0, CHCl3); H NMR (CDCl3, 300 MHz) δ 8.02∼7.93 (m, 4H), 7.80∼7.61
(m, 4H), 7.55∼7.26 (m, 6H), 7.11∼7.06 (m, 1H), 6.25 (d, 2H, J = 6.2 Hz),
6.05 (s, 1H), 5.11∼5.07 (m, 1H), 4.85∼4.51 (m, 5H), 3.73 (s, 3H); IR (neat)
3362, 1727 cm−1; MS (FAB) m/z 790 (M+Na). A mixture of protected
nucleoside (18 mg, 0.023 mmol) and MeNH2 (2M in THF, 5 mL) was
stirred at room temperature for 24 hours. The mixture was evaporated and
the residue was purified by silica gel column chromatography (methylene
chloride : methanol = 30:1) to give 3a (6 mg, 45%): mp 222.3∼222.9◦C;
1
UV (MeOH) λmax 273 nm (pH 7); [α]25 −15.56◦ (c 1.0, THF); H NMR
D
(DMSO-d6, 400 MHz) δ 8.50 (s, 1H), 7.74 (s, 1H), 7.61 (d, 1H, J = 8.0
Hz), 7.36 (d, 1H, J = 7.6 Hz), 7.15∼7.11 (dd, 1H, J = 7.6 and 8.0 Hz),
5.93 (d, 1H, J = 5.2 Hz), 5.90 (d, 1H, J = 2.8 Hz), 5.16∼5.11 (m, 1H),
4.73∼4.56 (m, 3H), 4.49∼4.46 (m, 2H), 3.82∼3.76 (m, 1H), 3.59∼3.50 (m,
2H), 3.15∼3.11 (dd, 1H, J = 6.0 and 2.0 Hz), 2.59 (d, 3H, J = 4.8 Hz);
IR (neat) 3331, 1613 cm−1; MS (FAB) m/z 559 (M+H); Anal. Calcd for
C19H20ClIN6O4: C, 40.84; H, 3.61; N, 15.04. Found: C, 40.60; H, 3.56; N,
14.86.

3ꢁ-Acetamidoadenosine Derivatives
417
2-Chloro-N6-methyl-9-(3-C-methylcarbamoyl-3-deoxy-β-D-ribofuranosyl)
adenine (3b). To a solution of 15 (33 mg, 0.058 mmol) in anhydrous
THF (2 mL) was added anhydrous 0.642M MeNH2·AcOH (2.16 mL, 1.39
mmol), and then the reaction mixture was stirred overnight. Solvents
were removed under reduced pressure and the residue was purified by
silica gel column chromatography (hexane : ethyl acetate = 1:1) to afford
a methyl derivative (31.5 mg, 96%): UV (MeOH) λmax 268 nm (pH 7);
1
[α]25 4.80◦ (c 1.0, CHCl3); H NMR (CDCl3, 300 MHz) δ 8.04∼7.86 (m,
D
4H), 7.79 (s, 1H), 7.66∼7.37 (m, 6H), 6.27 (d, 1H, J = 6.2 Hz), 6.05 (d,
1H, J = 1.3 Hz), 5.13∼5.07 (m, 1H), 4.91∼4.77 (m, 1H), 4.71∼4.63 (m,
1H), 4.58∼4.53 (m, 1H), 3.73 (s, 3H), 3.16 (s, 3H); IR (neat) 2925, 1725
cm−1; MS (FAB) m/z 566 (M+H). A solution of protected nucleoside
(113 mg, 0.200 mmol) in 40% MeNH2 : THF (1:1, 4 mL) was stirred
overnight at room temperature. Solvents were removed under reduced
pressure and the residue was purified by silica gel column chromatography
(methylene chloride : methanol = 20:1) and then purified again by prep.
TLC (methylene chloride : methanol = 20:1, five times) to provide 3b
(16 mg, 23%): mp 227.1∼229.9◦C; UV (MeOH) λmax 273 nm (pH 7);
[α]25 −16.49◦ (c 0.5, THF); H NMR(CD3OD, 400 MHz) δ 8.34 (s, 1H),
1
D
6.00∼5.95 (dd, 1H, J = 3.6 and 14.0 Hz), 4.83∼4.79 (m, 1H), 4.71∼4.63
(m, 1H), 4.00∼3.97 (dd, 1H, J = 2.4 and 12.4 Hz), 3.71∼3.67 (dd, 2H, J
= 2.4 and 12.6 Hz), 3.07 (s, 3H), 2.76 (s, 3H); IR (neat) 3431, 2934, 1631
cm−1; MS (FAB) m/z 357 (M+); Anal. Calcd for C13H17ClN6O4: C, 43.77;
H, 4.80; N, 23.56. Found: C, 43.94; H, 4.94; N, 23.92.
2-Chloro-N6-(2-methylbenzyl)-9-(3-C-methylcarbamoyl-3-deoxy-β-D-
ribofuranosyl)adenine (3c). To a stirred solution of 15 (127 mg, 0.222
mmol) in THF (4 mL), 2-methylbenzylamine (29.6 mg, 0.244 mmol) and
TEA (0.28 mL, 2.00 mmol) were added, and the mixture was stirred at room
temperature for 4 hours. Solvents were removed under reduced pressure
and the residue was purified by silica gel column chromatography (hexane
: ethyl acetate = 3:1 to 2:1) to afford a 2-methylbenzyl derivative (110 mg,
1
75%): UV (MeOH) λmax 272 nm (pH 7); [α]25 -7.63◦ (c 1.0, CHCl3); H
D
NMR (CDCl3, 300 MHz) δ 8.02∼7.93 (m, 4H), 7.73 (s, 1H), 7.66∼7.60 (m,
1H), 7.54∼7.31 (m, 6H), 7.23∼7.18 (m, 3H), 6.26 (d, 1H, J = 6.2 Hz), 6.11
(s, 1H), 6.04 (d, 1H, J = 1.0 Hz), 5.12∼5.06 (m, 1H), 4.85∼4.80 (m, 3H),
4.69∼4.63 (dd, 1H, J = 4.4 and 12.3 Hz), 4.57∼4.52 (m, 1H), 3.73 (s, 3H),
2.38 (s, 3H); IR (neat) 3431, 2924, 1727 cm−1; MS (FAB) m/z 657 (M+H);
Anal. Calcd for C34H30ClN5O7: C, 62.24; H, 4.61; N, 10.67. Found: C, 62.43;
H, 4.58; N, 10.66. A solution of protected nucleoside (58 mg, 0.0884 mmol)
in 40% MeNH2 : THF (1:1, 2 mL) was stirred at room temperature for 1
hour. Solvents were removed under reduced pressure and the residue was
purified by prep. TLC (methylene chloride : methanol = 20:1, twice) to
give 3c (10 mg, 25%): mp 245.3∼246.1◦C; UV (MeOH) λmax 273 nm (pH

418
M. W. Chun et al.
1
7); [α]25 −11.63◦ (c 1.0, THF); H NMR(CD3OD, 300 MHz) δ 8.36 (s,
D
1H), 7.33 (d, 1H, J = 5.9 Hz), 7.18∼7.14 (m, 2H), 6.92 (d, 1H, J = 0.8 Hz),
6.01 (d, 1H, J = 3.5 Hz), 4.82∼4.79 (m, 1H), 4.74 (s, 2H), 4.65∼4.63 (m,
1H), 4.01∼3.96 (dd, 1H, J = 2.2, 2.4 and 12.5 Hz), 3.71∼3.66 (dd, 2H, J
= 2.6 and 12.6 Hz), 2.75 (s, 3H), 2.39 (s, 3H); IR (neat) 3421, 2937, 1739
cm−1; MS (FAB) m/z 447 (M+H); Anal. Calcd for C20H23ClN6O4: C, 53.75;
H, 5.19; N, 18.81. Found: C, 53.85; H, 5.12; N, 18.92.
2-Chloro-N6-cyclopropyl-9-(3-C-methylcarbamoyl-3-deoxy-β-D-ribofur-
anosyl)adenine (3d). To a stirred solution of 15 (36 mg, 0.0630 mmol) in
THF (2 mL), a solution of AcOH (23 mg, 0.383 mmol) in THF (1 mL)
and cyclopropyl amine (22 mg, 0.385 mmol) were added, and the mixture
was stirred at room temperature for 2 hours. Solvents were removed under
reduced pressure and the residue was purified by silica gel chromatography
(hexane : ethyl acetate = 4:1 to 3:1) to give a cyclopropyl derivative (36
mg, 97%): UV (MeOH) λmax 273 nm (pH 7); [α]25 1.72◦ (c 1.0, CHCl3);
D
1H NMR (CDCl3, 300 MHz) δ 8.01∼7.93 (m, 4H), 7.80 (s, 1H), 7.66∼7.39
(m, 6H), 6.26∼6.04 (m, 2H), 6.05∼6.00 (m, 1H), 5.11∼5.07 (m, 1H),
4.85∼4.80 (dd, 1H, J = 3.1 and 12.3 Hz), 4.68∼4.62 (dd, 1H, J = 4.4, 4.6
and 12.4 Hz), 4.58∼4.52 (m, 1H), 3.73 (s, 3H), 3.09 (s, 1H), 0.95∼0.93 (m,
2H), 0.67∼0.62 (m, 2H); IR (neat) 3355, 2952, 1727 cm−1; MS (FAB) m/z
593 (M+H); Anal. Calcd for C29H26ClN5O7: C, 58.84; H, 4.43; N, 11.83.
Found : C, 58.40; H, 4.62; N, 11.52. A solution of protected nucleoside (73
mg, 0.123 mmol) in 40% MeNH2 : THF (1:1, 2 mL) was stirred at room
temperature for 4 hours. Solvents were removed under reduced pressure
and the residue was purified by prep. TLC (methylene chloride : methanol
= 20:1, three times) to give 3d (15 mg, 32%): UV (MeOH) λmax 273 nm
1
(pH 7); [α]25 −15.97◦ (c 1.0, THF); H NMR (CD3OD, 300 MHz) δ 8.37
D
(s, 1H), 6.01 (d, 1H, J = 3.5 Hz), 4.83∼4.78 (m, 1H), 4.66∼4.62 (m, 1H),
4.01∼3.96 (dd, 1H, J = 2.2, 2.4 and 12.5 Hz), 3.72∼3.67 (dd, 1H, J =
2.6, 2.7 and 12.5 Hz), 3.34 (d, 1H, J = 2.0 Hz), 2.76 (s, 3H), 0.91∼0.85
(m, 2H), 0.66∼0.61 (m, 2H); MS (FAB) m/z 383 (M+H); Anal. Calcd for
C15H19ClN6O4: C, 47.06; H, 5.00; N, 21.95. Found: C, 47.35; H, 5.18; N,
22.37.
2-Chloro-N6-cyclopentyl-9-(3-C-methylcarbamoyl-3-deoxy-β-D-
ribofuranosyl)adenine (3e). To a stirred solution of 15 (125 mg, 0.219
mmol) in THF (4 mL), a mixture of AcOH (79 mg, 1.32 mmol) and
cyclopentyl amine (112 mg, 1.32 mmol) was added, and the reaction
mixture was stirred for 4 hours at room temperature. Solvents were
removed under reduced pressure and the residue was purified by silica
gel column chromatography (hexane : ethyl acetate = 3:1 to 2:1) to give a
cyclopentyl derivative (101 mg, 75%): UV (MeOH) λmax 273 nm (pH 7);
[α]25 −0.26◦ (c 1.0, CHCl3); 1H NMR(CDCl3, 300 MHz) δ 8.02∼7.93 (m,
D
4H), 7.77 (s, 1H), 7.65∼7.39 (m, 6H), 6.26 (d, 1H, J = 5.9 Hz), 6.04 (d, 1H,

3ꢁ-Acetamidoadenosine Derivatives
419
J = 1.1 Hz), 5.92 (s, 1H), 5.12∼5.06 (m, 1H), 4.85∼4.80 (dd, 1H, J = 2.9
and 12.3 Hz), 4.68∼4.54 (m, 3H), 3.73 (s, 3H), 2.13 (m, 2H), 1.77∼1.69 (m,
4H), 1.56∼1.52 (m, 2H); IR (neat) 3355, 2955, 1726 cm−1; MS (FAB) m/z
621 (M+H); Anal. Calcd for C31H30ClN5O7: C, 60.05; H, 4.88; N, 11.29.
Found: C, 60.36; H, 5.01; N, 10.85. A solution of protected nucleoside (128
mg, 0.206 mmol) in 40% MeNH2 : THF(1:1, 4 mL) was stirred at room
temperature for 3 hours. Solvents were removed under reduced pressure
and the residue purified by prep. TLC (methylene chloride : methanol =
20:1, twice) to give 3e (19 mg, 22%): mp 245.0∼245.6◦C; UV (MeOH) λmax
273 nm (pH 7); [α]25 −17.66◦ (c 0.8, THF); 1H NMR (CD3OD, 400 MHz)
D
δ 8.34 (s, 1H), 5.99 (d, 1H, J = 2.7 Hz), 4.80∼4.79 (m, 1H), 4.63∼4.62 (m,
1H), 4.50 (s, 1H), 3.99∼3.96 (dd, 1H, J = 1.6 and 10.0 Hz), 3.70∼3.67 (dd,
1H, J = 1.9, 2.0 and 10.0 Hz), 3.32 (s, 1H), 2.75 (s, 3H), 2.10∼2.00 (m, 2H),
1.79 (m, 2H), 1.76∼1.67 (m, 2H), 1.63∼1.58 (m, 2H); IR (neat) 3430, 2955,
1640 cm−1; MS (FAB) m/z 411 (M+H); Anal. Calcd for C17H23ClN6O4: C,
49.70; H, 5.64; N, 20.45. Found: C, 49.56; H, 5.92; N, 20.71.
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