Carbocyclic 4′-epi-formycin

Article abstract of DOI:10.1016/j.tet.2007.10.054

Formycin is a naturally occurring biologically responsive C-nucleoside. In pursuing the design and syntheses of novel C-nucleosides, convenient access to carbocyclic C-nucleosides based on the formycin framework was a goal. One such target was carbocyclic 4′-epi-formycin (4). This compound is reported via a procedure based on an asymmetric aldol/ring closure metathesis strategy. To provide a preliminary glimpse into the biological characterization of 4 an antiviral assay was conducted. Target 4 was found to be inactive and to lack cytotoxicity to the host cells.

Full text of DOI:10.1016/j.tet.2007.10.054

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 433–438
Carbocyclic 40-epi-formycin
*
Jian Zhou, Minmin Yang, Akin Akdag, Haisheng Wang and Stewart W. Schneller
Department of Chemistry and Biochemistry, College of Sciences and Mathematics,
Auburn University, Auburn, AL 36849-5312, United States
Received 30 August 2007; revised 5 October 2007; accepted 12 October 2007
Available online 16 October 2007
Abstract—Formycin is a naturally occurring biologically responsive C-nucleoside. In pursuing the design and syntheses of novel C-nucleo-
sides, convenient access to carbocyclic C-nucleosides based on the formycin framework was a goal. One such target was carbocyclic
40-epi-formycin (4). This compound is reported via a procedure based on an asymmetric aldol/ring closure metathesis strategy. To provide
a preliminary glimpse into the biological characterization of 4 an antiviral assay was conducted. Target 4 was found to be inactive and to
lack cytotoxicity to the host cells.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
requisite pyrazolo[4,3-d]pyrimidine base unit.3d,e,5a–c,e
Because of the numerous examples of stereoselective epox-
Formycin A (1) is the C-nucleoside isomer of adenosine,
which has achieved a place of potential that has not been
fully developed for its value in medicinal agent discovery.1
Similarly, but more thoroughly studied, is the carbocyclic
adenine derivative aristeromycin (2).2 Little attention3 has
been devoted to combining these two structural features
into carbocyclic C-nucleosides (e.g., carbocyclic formycin
A, 3) as a source for a new chemotherapeutic library. Our
goal is to gain access to representatives of this latter group
of compounds. The 40-epimer of 3 (i.e., 4), which is an ana-
log of a-L-lyxoadenosine,4 is a member of that series and it is
described herein (Fig. 1).
ide ring openings as synthetic sequence components,6
5
(Fig. 2) was seen as being accessible from the chiral 6 and
an alkynyl organoaluminum reagent.7 To gain access to 6,
we adapted literature conditions8–10 beginning with (R)-4-
benzyl-2-oxazolidinone (8) (Scheme 1) and called on asym-
metric aldol/ring closure metathesis steps.
With 6 in hand, its reaction with diethyl[(trimethylsilyl)-
ethynyl]aluminum resulted in 13 (Scheme 2) and minor
side-products assigned as 14.11 Desilylation of 13 yielded
5, whose X-ray crystallographic analysis (Fig. 3) confirmed
that the hydroxy, benzyloxy, and benzyloxymethyl were on
same face of cyclopentyl ring and opposite to the alkynyl
unit.
NH2
NH2
H
N
N
N
N
N
N
Formylation of 5 and subsequent reaction of the resultant
substituted propargylic aldehyde with hydrazine, and then
acetylation provided 15.3d,e Debenzylation (boron tribro-
mide was superior to catalytic hydrogenolysis) of 15 and
then acetylation (to 16) was followed by nitration and
cine-cyano substitution3d,e,5c–e to yield 17. Hydrogenation
of 17 gave 18. Deacetylation of 18 (to 19) and subsequent
treatment with formamidine3d,e,5c,e produced the fused
pyrimidine target 4.
R
HOH2C
X
N
N
R'
HO
OH
HO
OH
2
1, R=CH2OH;R'=H;X=O
3, R=CH2OH;R'=H;X=CH2
4, R=H;R'=CH2OH;X=CH2
Figure 1.
2. Chemistry
The plan to 4 required the availability of the cyclopentyl
alkyne 5 as the starting material for construction of the
X
O
BnOH2C
BnO
X,Y=OH,Cl
BnOH2C
BnO
BnOH2C
BnO
Y
OH
Keywords: Cyclopentyl; C-nucleoside; Pyrazolo[4,3-d]pyrimidine; Dia-
stereomeric aldol.
5
6
14
* Corresponding author. Tel.: +1 334 844 5737; fax: +1 334 844 5748;
e-mail: schnest@auburn.edu
Figure 2.
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.10.054

434
J. Zhou et al. / Tetrahedron 64 (2008) 433–438
O
O
O
O
O
O
O
HO
O
O
N
O
N
O
a
b
c
HO
NH
N
Ph
Ph
10
Ph
Ph
8
9
11
4
RO
OCOC(Me)3
HO
e
d
O
O
RO
HO
a
12, R=H
6, R=Bn
7
f
Scheme 1. Reaction conditions: (a) (i) n-BuLi/hexanes, THF; (ii) a, TBME, 100% for two steps; (b) (i) n-Bu2BOTf, i-Pr2NEt, CH2Cl2, ꢀ78 ꢁC; (ii) acrolein,
ꢀ78 ꢁC, CH2Cl2, 92% for two steps; (c) Grubbs catalyst, CH2Cl2, 59%; (d) LiBH4, MeOH, THF, 0 ꢁC, 66%; (e) m-CPBA, CH2Cl2; (f) NaH, BnBr, TBAI, THF,
72% (for steps (e) and (f)).
Ac
N
Ac
N
TMS
N
N
b
c
d
e
5
BnO
AcO
H
H
H
BnOH2C
BnO
OH
BnO
OAc
AcO
OAc
13
a
15
16
6
H
N
H
N
H
N
CN
NH2
CN
NH2
CN
NO2
N
N
N
g
HO
f
AcO
AcO
H
H
H
HO
OH
AcO
OAc
AcO
OAc
h
4
19
18
17
Scheme 2. Reaction conditions: (a) Me3SiCCH, BuLi, ꢀ78 ꢁC, N2 followed by Et2AlCl, 0 ꢁC, 62%; (b) TBAF, THF, 92%; (c) (i) n-BuLi/hexanes, TBME fol-
lowed by DMF; (ii) hydrazine monohydrate, AcOH; (iii) Ac2O, pyridine, DMAP, 85% for three steps; (d) (i) BBr3, CH2Cl2, (ii) Ac2O, Et3N, DMAP, CH2Cl2,
76%; (e) (i) ammonium nitrate, TFA, TFAA; (ii) KCN, EtOH/EtOAc, 88% for two steps; (f) H2, Pd/C, MeOH, 92%; (g) NH3, MeOH, 88%; (h) formamidine
acetate, EtOH, 60%.
4. Conclusion
A straightforward chiral synthesis of carbocyclic 40-epi-
formycin has been achieved using practical means and avails
a rare example of a 40-epi-carbocyclic nucleoside.13 The ab-
sence of antiviral activity with 4 may be the consequence of
its failure to undergo conversion to the 50-nucleotide deriva-
tive, anefficientintracellularprocessfortheparentformycin,14
and/or its lack of inhibitory effect on S-adenosylhomocysteine
hydrolase, a site of action of aristeromycin (3).2
Figure 3. X-ray structure for compound 5.
5. Experimental
3. Antiviral analysis
5.1. Materials and methods
To gain preliminary insight into the biological potential of 4,
it was subjected to antiviral screening versus herpes sim-
plex-1, herpes simplex-2, herpes simplex-1 (TKꢀ), vaccinia,
vesicular stomatitis, coxsackie B4, respiratory syncytial,
parainfluenza 3, reovirus-1, Sindbis, and Punta Toro.12 No
activity was found. Also, no cytotoxicity arose in the cell
lines used in the antiviral assays: human erythroleukemia
(HEL), HeLa, and Vero.
Melting points were recorded on a Meltemp II melting point
1
apparatus and are uncorrected. H and 13C NMR spectra
were recorded on a Bruker AV-400 spectrometer or Bruker
AC-250 spectrometer. All H chemical shifts are reported
1
in d relative to internal standard tetramethylsilane (TMS,
d 0.00). 13C chemical shifts are reported in d relative to
CDCl3 (center of triplet, d 77.23). The spin multiplicities are
indicated by the symbols s (singlet), d (doublet), t (triplet),

J. Zhou et al. / Tetrahedron 64 (2008) 433–438
435
q (quartet), m (multiplet) and br (broad), dd (doublet of
doublet). Elemental analyses were performed by Atlantic
Microlabs, Atlanta, Georgia. Reactions were monitored by
thin layer chromatography (TLC) using 0.25 mm E. Merck
silica gel 60-F254 precoated silica gel plates with visualiza-
tion by irradiation with a Mineral light UVGL-25 lamp
or exposure to iodine vapor. Column chromatography was
performed on Whatman silica gel (average particle size 5–
1H), 3.31 (m, 1H), 4.18 (m, 2H), 4.29 (m, 1H), 4.47, (br s,
1H), 4.73 (m, 1H), 5.24 (m, 4H), 5.91 (m, 2H), 7.32 (m,
5H). 13C NMR (100 MHz, CDCl3) d 32.1, 38.1, 47.4, 55.7,
66.1, 73.4, 116.9, 117.4, 127.5, 129.1, 129.6, 135.3, 135.4,
137.4, 153.7, 174.5. Anal. Calcd for C18H21NO4: C, 68.55;
H, 6.71; N, 4.44. Found: C, 68.20; H, 7.07; N, 4.11.
5.1.3. [3(1R,2S),4S]-4-Benzyl-3-(2-hydroxycyclopent-3-
enecarbonyl)oxazolidin-2-one (11). A solution of com-
pound 10 (22.2 g, 70.4 mmol) in CH2Cl2 (300 mL) was
degassed by passing through a stream of N2 for 25 min and
0.5 mol % of Grubbs catalyst (first generation) was then
added under an atmosphere of N2. After stirring overnight,
the reaction mixture was exposed to air for 1 h, and purified
by flash silica gel column chromatography (hexanes/EtOAc,
˚
25 mm, 60 A) and elution with the indicated solvent system.
Yields refer to chromatographically and spectroscopically
(1H and 13C NMR) homogeneous materials. The reactions
were generally carried out in an N2 atmosphere under anhy-
drous conditions.
5.1.1. (4R)-Benzyl-3-(pent-4-enoyl)oxazolidin-2-one (9).
Triethylamine (15.3 mL, 0.11 mol) was added to a solution
of 4-pentenoic acid (11.6 mL, 11.3 g, 0.11 mol) in t-butyl
methyl ether (800 mL) cooled to ꢀ78 ꢁC. The solution
was stirred for 5 min, and pivaloyl chloride (13.5 mL,
0.11 mol) was added. After 15 min, the bath was removed
and replaced by an ice H2O bath. The heterogeneous mixture
(containing a) was mechanically stirred at 0 ꢁC for 1 h. In
a separate flask, a solution of (R)-4-benzyl-2-oxazolidinone
(8, 19.2 g, 0.11 mol) in THF (200 mL) was cooled to
ꢀ78 ꢁC, whereupon n-BuLi (44.0 mL, 2.5 M in hexanes,
0.11 mol) was added slowly. This solution was stirred for
10 min at ꢀ78 ꢁC. The flask containing the mixed anhydride
was cooled to ꢀ78 ꢁC, and the lithiated oxazolidinone trans-
ferred via cannula into the mixed anhydride a. After being
stirred at ꢀ78 ꢁC for 15 min, the reaction mixture was
warmed to 0 ꢁC and stirred for 30 min, then the reaction
was quenched by addition of aqueous, saturated NH4Cl. Af-
ter extraction twice with CH2Cl2, the combined organic
phases were dried (anhyd Na2SO4), filtered, and the filtrate
concentrated. Purification by flash silica gel column chroma-
tography (hexanes/EtOAc, 3:1) gave 9 (28.5 g, 100%) as
1
1:1) to yield 11 (12 g, 59%) as a colorless oil. H NMR
(400 MHz, CDCl3) d 2.43 (m, 1H), 2.76 (m, 1H), 2.86 (d,
1H, J¼7.5 Hz), 3.14 (m, 1H), 3.27 (m, 1H), 4.09 (m, 1H),
4.22 (m, 1H), 4.40 (m, 1H), 4.69, (m, 1H), 5.10 (br s, 1H),
5.72 (m, 1H), 5.99 (m, 1H), 7.26 (m, 5H). 13C NMR
(100 MHz, CDCl3) d 33.0, 37.9, 47.2, 55.4, 66.2, 76.9,
127.2, 128.8, 129.4, 130.9, 134.4, 135.5, 153.7, 172.0.
Anal. Calcd for C16H17NO4: C, 66.89; H, 5.96; N, 4.88.
Found: C, 66.69; H, 6.04; N, 4.71.
5.1.4. (1S,5S)-5-Hydroxymethyl-2-cyclopenten-1-ol (7).
A solution of LiBH4 (1.0 g, 43.0 mmol) in THF (55 mL)
cooled at 0 ꢁC was added into a solution of 11 (11.0 g,
38.3 mmol) in THF (150 mL) and MeOH (1.7 mL). The
reaction mixture was stirred at 0 ꢁC for 45 min and then
allowed to warm to room temperature. After 1 h, 10%
NaOH (61 mL) was added, and stirring continued until
both phases were clear. The mixture was extracted with
Et2O. The organic phase was washed with brine, dried (an-
hyd Na2SO4), filtered, and the filtrate concentrated in vacuo.
Purification by silica gel flash chromatography (gradient elu-
tion from 50% to 70% EtOAc/hexanes) yielded 7 (2.9 g,
66.3%) as a colorless liquid, [a]2D2.8 124.0 (c 0.26, methanol)
(lit.10 reported [a]2D4 ꢀ125.1 (c 0.47, CH2Cl2) for the enan-
1
a colorless oil. H NMR (400 MHz, CDCl3) d 2.42 (m,
2H), 2.76 (dd, 1H, J¼9.4, 13.4 Hz), 3.03 (m, 2H), 3.24
(dd, 1H, J¼10.1, 13.4 Hz,), 4.12 (m, 2H), 4.64 (m, 1H),
5.04 (m, 2H), 5.86 (m, 1H), 7.28 (m, 5H). 13C NMR
(100 MHz, CDCl3) d 28.6, 35.2, 38.2, 55.5, 66.6, 116.0,
127.7, 129.3, 129.8, 135.8, 137.2, 153.8, 172.8. Anal. Calcd
for C15H17NO3: C, 69.48; H, 6.61; N, 5.40. Found: C, 69.44;
H, 6.65; N, 5.31.
1
tiomer of 7). H NMR (400 MHz, CDCl3) d 2.19 (m, 1H),
2.37 (m, 2H), 3.75 (br s, 2H), 4.24 (d, 2H, J¼16.8 Hz),
4.85 (br s, 1H), 5.81 (m, 1H), 5.97 (m, 1H). 13C NMR
(100 MHz, CDCl3) d 33.6, 42.7, 62.2, 76.9, 132.4, 134.7.
Anal. Calcd for C6H10O2: C, 63.14; H, 8.83. Found: C,
63.04; H, 8.98.
5.1.2. [3(2R,3S),4R]-3-(2-Allyl-3-hydroxypent-4-enoyl)-
4-benzyloxazolidin-2-one (10). To a solution of 9 (26 g,
0.10 mol)inCH2Cl2 (50 mL)atꢀ78 ꢁC underN2 atmosphere
was added diisopropylethylamine (39 mL, 0.22 mol) fol-
lowed by dibutylboron triflate (200 mL, 0.20 mol, 1.0 M so-
lution in CH2Cl2). The reaction mixture was allowed to stir
for 1 h at room temperature. After re-cooling to ꢀ78 ꢁC, a so-
lution of acrolein (16 mL, 0.22 mol) in CH2Cl2 (100 mL) was
added dropwise. The mixture was stirred for 2 h at ꢀ78 ꢁC.
Then, the reaction mixture was slowly warmed to room tem-
perature and allowed to stir overnight. It was quenched with
saturated NaHCO3 solution and extracted with CH2Cl2. The
organic phase was washed with brine, dried (anhyd
Na2SO4), filtered, and the filtrate evaporated under reduced
pressure. Purification of the residue via silica gel flash chro-
matography (gradient elution from 10% to 25% EtOAc/hex-
5.1.5. (1S,2R,3S,4S)-1-Benzyloxymethyl-2-benzyloxy-3,4-
epoxyclopentane (6). A solution of 7 (2.1 g, 18.4 mmol),
m-chloroperoxybenzoic acid (7.2 g), and CH2Cl2 (100 mL)
was stirred at room temperature overnight. The solvent
was removed and the residue partitioned between Et2O
and H2O. The solvent was then removed in vacuo to obtain
12 (2.2 g), which was used in the next step without further
1
purification. H NMR (400 MHz, CDCl3) d 2.02 (m, 1H),
2.13 (m, 1H), 2.43 (m, 1H), 3.40 (m, 2H), 3.52 (m, 1H),
3.61 (m, 1H), 3.69 (m, 2H), 4.60 (dd, 1H, J¼1.5, 9.0 Hz).
13C NMR (100 MHz, CDCl3) d 31.4, 37.8, 56.2, 61.5,
64.0, 75.2.
To a solution of 12 (2.2 g) in anhyd THF (50 mL) at
0 ꢁC, NaH (2 g, 50 mmol, 60% dispersion in mineral
oil) was added in several portions. After 30 min, benzyl
bromide (6.1 mL, 51.3 mmol) and a catalytic amount of
1
anes) afforded 10 (29 g, 92%) as a colorless oil. H NMR
(400 MHz, CDCl3) d 2.52 (m, 1H), 2.66 (m, 2H), 2.86 (br s,

436
J. Zhou et al. / Tetrahedron 64 (2008) 433–438
tetrabutylammonium iodide were added. The reaction mix-
ture was then allowed to stir at room temperature overnight.
After the starting material was no longer present (TLC), ice
H2O was added to quench the reaction. The resultant mixture
was extracted with CH2Cl2. The combined extracts were
washed with brine, dried (anhyd Na2SO4), filtered, and the
filtrate concentrated in vacuo. The residue was purified by
silica gel flash column chromatography (hexanes/EtOAc,
THF) by injection at 0 ꢁC. The mixture was stirred overnight
at room temperature. The solution was absorbed on silica
gel, and the crude product purified by silica gel flash column
chromatography (hexanes/EtOAc, 4:1) to give 5 (2.4 g,
1
92%) as a white solid, mp 66–67 ꢁC. H NMR (400 MHz,
CDCl3) d 1.84 (m, 1H), 1.96 (m, 1H), 2.11 (d, 1H,
J¼2.5 Hz), 2.54 (m, 1H), 2.78 (m, 1H), 3.19 (d, 1H,
J¼8.7 Hz), 3.53 (m, 2H), 4.12 (m, 2H), 4.51 (m, 2H), 4.64
(dd, 2H, J¼11.5, 13.7 Hz), 7.30 (m, 10H). 13C NMR
(100 MHz, CDCl3) d 31.4, 35.4, 39.7, 69.3, 69.9, 73.5,
73.6, 78.3, 80.9, 86.6, 127.9 (2C), 128.6 (2C), 128.7 (2C),
138.1, 138.5. Anal. Calcd for C22H24O3: C, 78.54; H, 7.19.
Found: C, 78.56; H, 7.22.
1
4:1) affording 6 (4.1 g, 72% over two steps) as an oil. H
NMR (400 MHz, CDCl3) d 1.92 (m, 1H), 2.32 (d, 1H,
J¼14.9 Hz), 2.53 (m, 1H), 3.48 (m, 1H), 3.58 (m, 2H),
3.90 (dd, 1H, J¼4.7, 9.2 Hz), 4.23 (dd, 1H, J¼1.2,
8.5 Hz), 4.56 (s, 2H), 4.70 (q, 2H, J¼12.0 Hz), 7.41 (m,
10H). 13C NMR (100 MHz, CDCl3) d 30.2, 35.7, 54.9,
57.8, 72.5, 72.6, 73.7, 80.9, 127.6, 127.7, 127.9, 128.0,
128.5, 128.6, 138.3, 138.9. Anal. Calcd for C20H22O3: C,
77.39; H, 7.14. Found: C, 77.42; H, 7.10.
5.1.8. (1S,2R,3S,5S)-1-Acetyl-5-(1-acetyl-1H-pyrazol-3-
yl)-2-benzyloxy-3-(benzyloxymethyl)cyclopentane (15).
To a solution of 5 (2.4 g, 7.1 mmol) in anhydrous t-butyl
methyl ether (90 mL) with stirring at ꢀ78 ꢁC under N2
was added n-butyllithium (7.1 mL, 17.8 mmol, 2.5 M solu-
tion in hexanes), and the reaction mixture stirred at the
same temperature for 30 min. An excess of DMF (2.7 mL,
35.0 mmol) was added in one portion and the cold bath re-
moved. The reaction mixture was allowed to warm to
room temperature and aged for 30 min. The TBME solution
was poured into a vigorously stirred, biphasic solution pre-
pared from a 10% aqueous solution of KH2PO4 (45 mL)
and TBME (45 mL) cooled over ice to ca. +5 ꢁC. The result-
ing layers were separated and the organic extract was
washed with H2O. The combined aqueous layers were
back extracted with TBME. The combined organic layers
were dried (anhyd Na2SO4), filtered, and the filtrate concen-
trated to give the crude acetylenic aldehyde as an oil. The
crude product thus isolated was used to the next step without
further purification.
5.1.6. (1S,2R,3S,5S)-2-Benzyloxy-3-benzyloxymethyl-5-
(trimethylsilylethynyl)cyclopentanol (13). To a solution
of trimethylsilylacetylene (15.3 mL, 108.2 mmol) in anhy-
drous toluene (390 mL) with stirring at ꢀ78 ꢁC under N2
was added n-butyllithium (43.3 mL, 108.3 mmol, 2.5 M so-
lution in hexanes), and the reaction mixture was stirred at
the same temperature for 30 min. Then, a solution of diethyl-
aluminum chloride (60.1 mL, 108.2 mmol, 1.8 M solution
in toluene) was added at 0 ꢁC. Upon the addition a slow pre-
cipitation of LiCl was observed. The reaction mixture was
stirred for 5 h at 10 ꢁC. A solution of epoxide 6 (6.6 g,
21.3 mmol) in toluene (20 mL) was then added immediately.
The reaction mixture was stirred at 0 ꢁC for 45 min and 3 h at
room temperature, monitored by TLC analysis, and
quenched with MeOH (caution: gas evolution). After adding
H2O (4.2 mL), 15% NaOH solution (4.2 mL), and H2O
(12.6 mL), the reaction mixture was filtered, washed with
CH2Cl2, and the organic layer then washed with brine, and
dried (anhyd Na2SO4). The solvent was evaporated, and the
crude residue was purified by silica gel column chromato-
graphy (hexanes/EtOAc, 6:1) to give 13 (5.4 g, 62%) as
To a solution of crude aldehyde (from the previous process)
in glacial AcOH (78 mL) was added a solution of hydrazine
monohydrate (3.7 g, 34.9 mmol) in glacial AcOH (38 mL).
The resulting solution was heated at reflux for 8 h and then
concentrated in vacuo to afford a dark brown oil. This crude
product was dissolved in pyridine (20 mL), and Ac2O
(9.3 mL, 98.4 mmol) and DMAP were added. The resulting
solution was stirred for 16 h at room temperature. The sol-
vent was removed in vacuo, and the crude residue dissolved
in EtOAc (800 mL), washed with 10% HCl and brine, dried
(anhyd Na2SO4), concentrated, and purified by silica gel col-
umn chromatography to afford 15 (2.8 g, 85% over three
1
a white solid, mp 47–48 ꢁC. H NMR (250 MHz, CDCl3)
d 0.24 (s, 9H), 1.98 (m, 2H), 2.64 (m, 1H), 2.91 (m, 1H),
3.33 (m, 1H), 3.62 (m, 2H), 4.21 (m, 2H), 4.61 (s, 2H),
4.74 (d, 2H, J¼2.8 Hz), 7.41 (m, 10H). 13C NMR
(62.5 MHz, CDCl3) d 0.46, 31.8, 36.7, 39.8, 69.4, 73.6,
78.4, 80.9, 85.9, 109.2, 128.0 (2C), 128.1(2C), 128.5 (2C),
128.7 (2C), 138.6. Anal. Calcd for C25H32O3Si: C, 73.49;
H, 7.89. Found: C, 73.36; H, 7.93.
1
steps) as a light yellow oil. H NMR (400 MHz, CDCl3)
Further elution of the column gave 14 (1.8 g, 24.4%) as a col-
orless oil. 1H NMR (400 MHz, CDCl3) d 2.01 (m, 1H), 2.31
(m, 1H), 2.65 (m, 1H), 3.48 (dd, 1H, J¼5.7, 9.1 Hz), 3.56
(dd, 1H, J¼4.3, 9.1 Hz), 3.75 (m, 1H), 4.15 (m, 2H), 4.30
(dd, 1H, J¼4.1, 7.7 Hz), 4.51 (s, 2H), 4.60 (dd, 2H,
J¼11.4, 36.9 Hz), 7.31 (m, 10H). 13C NMR (100 MHz,
CDCl3) d 34.7, 38.7, 62.2, 68.6, 73.2, 73.5, 78.3, 79.3,
127.8 (2C), 128.0 (2C), 128.6 (2C), 137.7, 138.2. Anal.
Calcd for C20H23ClO3: C, 69.26; H, 6.68. Found: C, 69.17;
H, 6.73.
d 1.99 (s, 3H), 2.00 (m, 2H), 2.63 (s, 3H), 2.95 (m, 1H),
3.48 (dd, 1H, J¼6.4, 9.0 Hz), 3.60 (m, 1H), 3.72 (t, 1H,
J¼8.7 Hz), 4.29 (t, 1H, J¼4.0 Hz), 4.50 (dd, 2H, J¼11.9,
13.6 Hz), 4.60 (q, 2H, J¼11.6 Hz), 5.20 (dd, 1H, J¼3.7
9.4 Hz), 6.28 (d, 1H, J¼2.8 Hz), 7.29 (m, 10H),
8.14 (d, 1H, J¼2.8 Hz). 13C NMR (100 MHz, CDCl3)
d 21.1, 21.8, 29.9, 39.3, 40.4, 69.8, 73.3, 74.1, 79.6, 80.5,
108.7, 127.7, 127.7, 127.8, 127.8, 128.5, 128.5, 129.1,
138.5, 138.9, 159.0, 169.6, 170.8. Anal. Calcd for
C27H30N2O5: C, 70.11; H, 6.54; N, 6.06. Found: C, 70.10;
H, 6.48; N, 6.08.
5.1.7. (1S,2R,3S,5S)-2-Benzyloxy-3-benzyloxymethyl-5-
ethynylcyclopentanol (5). To a solution of 13 (3.2 g,
7.8 mmol) in THF (60 mL) under N2 was added tetrabutyl-
ammonium fluoride (7.8 mL, 7.8 mmol, 1 M solution in
5.1.9. (1S,2R,3S,5S)-1,2-Diacetoxy-5-acetoxymethyl-3-
(1-acetyl-1H-pyrazol-3-yl)cyclopentane (16). To a stirred
solution of 15 (2.0 g, 4.3 mmol) in anhyd CH2Cl2 (180 mL)

J. Zhou et al. / Tetrahedron 64 (2008) 433–438
437
was added boron tribromide (43.2 mL, 43.2 mmol, 1.0 M so-
lution in CH2Cl2) at ꢀ78 ꢁC and the reaction mixture stirred
at the same temperature for 1 h. To this mixture was added
MeOH (400 mL) and the reaction mixture neutralized with
Ag2CO3 and filtered through a pad of Celite. The filtrate
was evaporated and the crude product dissolved in CH2Cl2
(300 mL). To this triethylamine (4.8 mL), Ac2O (1.9 mL)
and a catalytic amount of DMAP were added, and the result-
ing solution stirred overnight. The mixture was then washed
with brine, dried (anhyd Na2SO4), concentrated, and the res-
idue chromatographed (silica gel, hexanes/EtOAc, 3:1) to af-
3.51 (m, 1H), 4.12 (m, 2H), 5.28 (m, 1H), 5.50 (m, 1H). 13C
NMR (100 MHz, CDCl3) d 20.9 (2C), 21.1, 28.7, 36.4, 37.8,
63.1, 73.1, 78.0, 110.1, 112.6, 133.8, 135.7, 170.4, 171.0,
171.4. Anal. Calcd for C16H20N4O6: C, 52.74; H, 5.53; N,
15.38. Found: C, 52.81; H, 5.89; N, 15.62.
5.1.12. (1S,2R,3S,5S)-1,2-Dihydroxy-3-hydroxymethyl-5-
(4-amino-5-cyano-1H-pyrazol-3-yl)cyclopentane (19).
Anhyd NH3 was introduced to a solution of compound 18
(0.59 g, 1.6 mmol) in MeOH (80 mL) at 0 ꢁC. The reaction
mixture was stirred at room temperature. After the starting
material was no longer present (TLC), the solvent was re-
moved in vacuo and the residue purified by silica gel chro-
matography (CH2Cl2/MeOH, 6:1) to afford 19 (0.33 g,
1
ford 16 (1.2 g, 76% over two steps) as a syrup. H NMR
(400 MHz, CDCl3) d 2.07 (m, 11H), 2.66 (m, 3H), 3.56 (m,
1H), 4.11 (m, 3H), 5.35 (m, 1H), 5.55 (m, 1H), 6.30 (m,
1H), 8.18 (d, 1H, J¼2.5 Hz). 13C NMR (100 MHz, CDCl3)
d 20.9, 21.0, 21.1, 21.9, 29.8, 37.9, 39.3, 62.9, 73.3, 78.1,
108.6, 129.5, 157.8, 170.3 (2C), 170.4, 171.2. Anal. Calcd
for C17H22N2O7: C, 55.73; H, 6.05; N, 7.05. Found: C,
55.85; H, 6.19; N, 7.67.
1
88%) as a light yellow solid, mp 174–176 ꢁC. H NMR
(400 MHz, CDCl3) d 1.73 (m, 2H), 2.08 (m, 1H), 3.18 (m,
1H), 3.37 (m, 1H), 3.60 (m, 1H), 3.89 (m, 2H), 4.34 (m,
3H), 4.52 (m, 1H), 4.75 (m, 1H), 13.17 (s, 1H). 13C NMR
(100 MHz, CDCl3) d 29.2, 37.1, 41.9, 61.0, 72.7, 79.1,
114.1, 115.4, 131.7, 132.9. Anal. Calcd for C10H14N4O3:
C, 50.41; H, 5.92; N, 23.52. Found: C, 50.39; H, 6.03; N,
23.35.
5.1.10. (1S,2R,3S,5S)-1,2-Diacetoxy-5-acetoxymethyl-3-
(5-cyano-4-nitro-1H-pyrazol-3-yl)cyclopentane (17). Tri-
fluoroacetic anhydride (2.1 mL) was added dropwise to
a stirred solution of 16 (0.99 g, 2.7 mmol) and ammonium
nitrate (1.9 g) in TFA (30 mL) at 0 ꢁC. The resulting solution
was allowed to warm to room temperature and stirred over-
night. The solvent was evaporated in vacuo at room temper-
ature and then diluted with CH2Cl2, washed with H2O,
saturated aqueous NaHCO3 solution and brine, dried (anhyd
Na2SO4), and the organic phase concentrated in vacuo to
give the 1,4-dinitro pyrazole derivative (1.1 g) as a syrup.
The crude product thus isolated was used to the next step
without further purification.
5.1.13. (1S,2R,3S,5S)-1,2-Dihydroxy-3-hydroxymethyl-5-
(7-amino-1H-pyrazolo[4,3-d]pyrimidin-3-yl)cyclopen-
tane (4). A solution of 19 (0.25 g, 1.0 mmol) in EtOH
(30 mL) was stirred with formamidine acetate (0.16 g,
1.5 mmol) under reflux for 50 min. The resulting white pre-
cipitate was isolated by filtration, washed with EtOH, and
dried to afford analytically pure 4 (0.16 g, 60%) as a white
solid, mp 269–270 ꢁC (dec), [a]2D2.5 ꢀ53.5 (c 0.26, DMSO).
1H NMR (400 MHz, CDCl3) d 1.83 (m, 2H), 2.28 (m, 1H),
3.41 (m, 2H), 3.62 (m, 1H), 3.98 (m, 1H), 4.34 (m, 3H),
4.94 (s, 1H), 7.24 (br s, 2H), 8.13 (s, 1H), 12.37 (m, 1H).
13C NMR (100 MHz, CDCl3) d 30.8, 40.1, 42.8, 61.3, 73.3,
79.0, 122.2, 139.8, 148.2, 150.8, 151.2. Anal. Calcd for
C11H15N5O3: C, 49.81; H, 5.70; N, 26.40. Found: C, 50.00;
H, 5.83; N, 26.30.
At room temperature, a solution of the 1,4-dinitro compound
in EtOH (9.3 mL) and EtOAc (9.3 mL) was added dropwise
over 5 min to a stirred solution of KCN (1.3 g, 19.5 mmol) in
EtOH (23.0 mL) and H2O (5.5 mL). Following an additional
5 min at room temperature, the reaction mixture was neutral-
ized with AcOH (2.0 mL). After evaporation of the solvent
in vacuo, the residue was diluted with EtOAc (110 mL),
washed with H2O and brine, dried (anhyd Na2SO4), and
concentrated in vacuo to a residue that was subjected to
chromatographic purification (silica gel, CH2Cl2/MeOH,
20:1) to afford 17 (0.94 g, 88% over two steps) as a light
5.2. X-ray data for compound 5
Crystallographic data (excluding structure factors) for 5
have been deposited with Cambridge Crystallographic
Data Centre as supplementary publication number CCDC
642212. Copies of the data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax: +44(0)1223 336033 or e mail: deposit@
ccdc.cam.ac.uk].
1
yellow syrup. H NMR (400 MHz, CDCl3) d 2.00 (s, 3H),
2.09 (s, 3H), 2.11 (m, 2H), 2.21 (s, 3H), 2.36 (m, 1H),
2.96 (m, 1H), 4.21 (m, 3H), 5.58 (m, 1H), 5.64 (m, 1H).
13C NMR (100 MHz, CDCl3)
d 20.6, 20.7, 20.8,
30.0, 36.9, 37.8, 62.5, 72.9, 76.4, 110.7, 122.6, 133.9,
145.0, 170.6, 171.4, 171.8. Anal. Calcd for C16H18N4O8:
C, 48.73; H, 4.60; N, 14.21. Found: C, 48.29; H, 4.59; N,
13.90.
Acknowledgements
This research has been supported by funds from the Depart-
ment of Health and Human Services (Al 56540), which is ap-
preciated. We are also indebted to the following individuals
for providing the antiviral data12 following their standard
protocols: Dr. Erik De Clercq, the Rega Institute, Leuven,
Belgium; Dr. Earl Kern, University of Alabama at Birming-
ham, Birmingham, AL; Dr. Robert Sidwell, Utah State
University, Logan, UT; Dr. Brent Korba, Georgetown,
University, Rockville, MD; Dr. John Huggins, the US
Army Medical Research Institute of Infectious Diseases,
Ft. Detrick, MD 21702.
5.1.11 (1S,2R,3S,5S)-1,2-Diacetoxy-3-acetoxymethyl-5-
(4-amino-5-cyano-1H-pyrazol-3-yl)cyclopentane (18). A
catalytic amount of Pd/C was added to a solution of 17
(0.83 g, 2.1 mmol) in MeOH (30 mL). The resulting mixture
was shaken under 30 psi of H2 overnight. After the reaction
was complete, the solvent was evaporated in vacuo and the
product purified by silica gel chromatography (CH2Cl2/
EtOAc/MeOH, 8:1:0.5) to afford 18 (0.7 g, 92%) as a syrup.
1H NMR (400 MHz, CDCl3) d 2.07 (m, 14H), 2.72 (m, 1H),

438
J. Zhou et al. / Tetrahedron 64 (2008) 433–438
7. (a) Shanmugam, P.; Miyashita, M. Org. Lett. 2003, 5, 3265–
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