Concise synthesis of the anti-HIV nucleoside EFdA

Article abstract of DOI:10.1271/bbb.120134

EFdA (4'-ethynyl-2-fluoro-2'-deoxyadenosine), a nucleoside reverse transcriptase inhibitor with extremely potent anti-HIV activity, was concisely synthesized from (R)-glyceraldehyde acetonide in an 18% overall yield by a 12-step sequence involving highly diastereoselective ethynylation of an α-alkoxy ketone intermediate. The present synthesis is superior, both in overall yield and in the number of steps, to the previous one which required 18 steps from an expensive starting material and resulted in a modest overall yield of 2.5%.

Full text of DOI:10.1271/bbb.120134

Biosci. Biotechnol. Biochem., 76 (6), 1219–1225, 2012
Concise Synthesis of the Anti-HIV Nucleoside EFdA
Masayuki KAGEYAMA,1 Takuho MIYAGI,1 Mayumi YOSHIDA,1 Tomohiro NAGASAWA,1
y
1;
Hiroshi OHRUI,2 and Shigefumi KUWAHARA
1Laboratory of Applied Bioorganic Chemistry, Graduate School of Agricultural Science, Tohoku University,
Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan
2Yokohama College of Pharmacy, 601 Matano-cho, Totsuka-ku, Yokohama 245-0066, Japan
Received February 24, 2012; Accepted March 7, 2012; Online Publication, June 7, 2012
[doi:10.1271/bbb.120134]
EFdA (40-ethynyl-2-fluoro-20-deoxyadenosine), a nu-
cleoside reverse transcriptase inhibitor with extremely
potent anti-HIV activity, was concisely synthesized from
(R)-glyceraldehyde acetonide in an 18% overall yield by
a 12-step sequence involving highly diastereoselective
ethynylation of an ꢀ-alkoxy ketone intermediate. The
present synthesis is superior, both in overall yield and in
the number of steps, to the previous one which required
18 steps from an expensive starting material and
resulted in a modest overall yield of 2.5%.
with the following remarkable pharmacological profiles:
(i) exceptionally potent inhibitory activity against HIV-1
replication [e.g., EC50 for HIV-1NL4-3 ¼ 50 pM in phyto-
hemagglutinin-activated peripheral blood mononuclear
cells (PBMCs), which is several orders of magnitude
more effective than that of any currently prescribed
NRTIs such as AZT (22 nM) and TNF (3300 nM)];5) (ii)
excellent in vitro selectivity indices (SI ¼ CC50/EC50;
e.g., >200,000 for HIV-1NL4-3 in PBMCs, and 134,000
for HIV-1IIIB in MT-4 cells), which are superior to that of
AZT (SI ¼ 10;800 for HIV-1IIIB in MT-4 cells);5,12,13)
(iii) no acute toxicity toward ICR mice at a dose of
100 mg/kg;6,14) (iv) retention of efficacy even against a
wide spectrum of drug-resistant HIV-1 variants including
multidrug-resistant clinical isolates;12–14) and (v) longer
intracellular half-life value (t1=2, 17.2 h) in its active form
(EFdA-50-triphosphate) than that of AZT-50-triphosphate
(2.8 h) which may enable a once-daily or twice-daily
regimen.13) From these favorable properties, EFDA (1),
which is currently under preclinical evaluation, is
attracting rising attention as a potential therapeutic
agent for HIV-infected patients.3,4)
In contrast to the various biological and medicinal
studies on 1 that have been progressively reported, there
has been only one way to supply EFdA (1), the synthesis
by Kohgo and co-workers which required a considerably
lengthy 18-step sequence from the expensive starting
material, 2-amino-20-deoxyadenosine, resulting in a
modest overall yield of 2.5%.6,7) The limited availability
of 1 as well as its promising pharmacological profiles
just described prompted our synthetic efforts to supply a
sufficient amount of 1 to further promote its biological
and clinical research. These efforts have recently
culminated in an enantioselective 12-step total synthesis
of 1 in an 18% overall yield from the simple starting
material, (R)-glyceraldehyde acetonide.15) We describe
in this article a full account of our total synthesis of 1,
including some unsuccessful attempts.
Key words: EFdA; anti-HIV; AIDS; nucleoside; N-
glycosidation
Since the first approval of zidovudine (also called
azidothymidine, AZT) for clinical use in 1987, seven
additional nucleoside reverse transcriptase inhibitors
(NRTIs), including abacavir (ABC) and tenofovir
(TNF), have been approved and prescribed for people
infected by human immunodeficiency virus (HIV) or
patients suffering from acquired immunodeficiency
syndrome (AIDS) caused by HIV infection (Fig. 1).1,2)
All of the furanose or pseudofuranose portions in the
eight NRTIs are structurally devoid of the 30-hydroxyl
(30-OH) group which is present in natural nucleosides
and is indispensable for DNA chain elongation by viral
reverse transcriptases (RTs). Therefore, once incorpo-
rated as their 60-monophosphate into the 30-terminus of
a viral DNA primer, the nucleoside analogs without the
30-OH functionality block further nucleotide addition by
RTs, and thereby serve as obligate DNA chain elonga-
tion terminators.3,4) The absence of the 30-OH group has
long been considered to be a prerequisite for NRTIs to
exert anti-HIV activity, probably due to the reasonable
and readily understandable mode of action.5)
In recent years, however, it has been revealed that
nucleoside derivatives bearing the 30-OH group also
exhibited significant anti-HIV activity by inhibiting viral
reverse transcriptases through several mechanisms of
action.3) Among the NRTIs with the 30-OH group, EFdA
[40-ethynyl-2-fluoro-20-deoxyadenosine (1), also abbre-
viated as 40Ed2FA], designed by Ohrui and co-workers
stands out as a promising anti-HIV agent.6–11) Their
modification made at two positions (2 and 40) of the
parent natural nucleoside 20-deoxyadensine endowed 1
Results and Discussion
Our synthetic plan for EFdA (1) is shown in
Scheme 1. We considered that the target molecule (1)
would be obtained via N-glycosidation of activated
20-deoxyfuranose derivative 2 with 2-fluoroadenine 3,
y
To whom correspondence should be addressed. Fax: +81-22-717-8783; E-mail: skuwahar@biochem.tohoku.ac.jp
Abbreviations: BSA, N,O-bis(trimethylsilyl)acetamide; DMAP, 4-(dimethylamino)pyridine; DMP, Dess-Martin’s periodinane; EDCI, 1-ethyl-3-(3-
dimethylaminopropyl)carbodiimide; MOM, methoxymethyl; MTPA, ꢀ-methoxy-ꢀ-(trifluoromethyl)phenylacetyl; PPTS, pyridinium p-toluenesulfo-
nate; TBDPS, tert-butyldiphenylsilyl; Tf, trifluoromethanesulfonyl; TIPS, triisopropylsilyl; TMS, trimethylsilyl

1220
M. KAGEYAMA et al.
which in turn is commercially available or readily
obtainable from 2,6-diaminopurine in a single step.16,17)
Glycosyl donor 2 could be prepared by oxidative
cleavage of the terminal double bond of 4, followed
by spontaneous hemiacetal ring formation and subse-
quent activation of the resulting anomeric hydroxy
group. To appropriately install the stereochemistry at the
C40 position of 4, we planned to use diastereoselective
addition of an acetylene derivative to suitably protected
hydroxy ketone 5 which could be obtained from the
well-known chiral building block, (R)-glyceraldehyde
acetonide (6), by diastereoselective allylation coupled
with some functional group manipulations.
To achieve high diastereoselectivity in the ethynyla-
tion step of our synthetic plan (5 ! 4 in Scheme 1), we
chose known MOM-protected acetal 718–20) as the
starting point (Scheme 2), since our literature search
revealed that the addition of acetylide anions to ꢀ-
hydroxy ketones would proceed with high diastereose-
lectivity when the hydroxy group was protected as its
MOM ether.21,22) Compound 7 was readily obtained
from 6 in two steps, comprising highly diastereoselec-
tive allylation of 6 with allylzinc bromide and MOM-
protection of the resulting alcohol according to the
literature.18–20) Selective deprotection of the acetonide
group of 7 was conducted by its treatment with PPTS in
aqueous methanol to form 8, the primary hydroxy group
of which was then protected as its TBDPS ether 9.
Swern oxidation of 9 gave MOM-protected ketone 10,
which was then subjected to an addition reaction with
(triisopropylsilyl)ethynylmagnesium bromide to afford
acetylenic alcohol 11 as a single diastereomer. The
stereochemistry of 11 was determined later at the stage
of 2a by observing a diagnostic NOE correlation
between the C30 proton and the C50 protons (see
structure 2a in Scheme 2). This complete stereoselec-
tivity in the formation of 11 would be explained by
assuming chelation-controlled transition state 100 de-
picted in Scheme 2; the acetylenic nucleophile would
approach the C40 carbonyl from its less-hindered si-
face.21) Ozonolysis of 11 and subsequent spontaneous
cyclization proceeded uneventfully to give furanose
derivative 12, the anomeric hydroxy group of which was
then activated by acetylation to furnish glycosyl donor
2a. N-Glycosidation of 2a with 2-fluoroadenine 3 was
implemented under the silyl-Hilbert–Johnson reaction
conditions.23–25) Fluorinated nucleobase 3 (1.6 eq.) was
thus treated for 4 h with a silylating agent [BSA (13), 1.9
eq.] and Lewis acid (TMSOTf, 1.8 eq.) in refluxing
MeCN to generate the corresponding silylated nucleo-
base, which was then allowed to react with 2a at
refluxing temperature for 2 h to give a mixture of 14ꢀ
NH2
N
O
N
N
NH
O
HO
HO
N
N
F
O
O
NH2
R1O
O
3'
X
N
4'
HO
N3
+
N
1
EFdA (1)
AZT
2'
OR3
N
F
N
H
R2
NH2
N
2
3
HN
N
N
N
N
N
R1O
HO
O
P
N
R1O
HO
O
N
NH2
O
4'
OR3
HO
3'
OR3
OH
O
O
CHO
TNF
ABC
R2
4
5
6
Fig. 1. Structures of EFdA (1) and Related Nucleoside Reverse
Transcriptase Inhibitors.
Scheme 1. Synthetic Plan for EFdA (1).
DMSO
(COCl)2
TBDPSCl
imidazole
HO
HO
TBDPSO
HO
O
O
O
O
2 steps
PPTS
DMF
96%
83%
(Ref. 18)
aq. MeOH
83%
Et3N
CH2Cl2
CHO
OMOM
OMOM
OMOM
6
7
8
9
O3, CH2Cl2
MeOH
TBDPSO
HO
TBDPSO
O
TBDPSO
TIPS
F
Ac2O, Et3N
O
TIPS
OH
4'
OMOM
EtMgBr
THF
85% from 9
Me2S
NaHCO3
84%
DMAP, CH 2Cl2
95%
OMOM
OMOM
TIPS
10
11
12
NH2
5'
N
3, BSA (13)
TBDPSO
TIPS
TBDPSO
TIPS
H
O
8
N
O
H
TMSOTf, MeCN
N
OAc
+
3'
TBDPSO
TIPS
N
N
N
F
N
O
H
0°C to rt, 35%
(14 /14 = 1:1.2)
H
OMOM
OMOM
N
H
NH2
2a
14
OMOM
3, BSA (13)
14
TMSOTf, CH2Cl2
14 + 14
TBDPSO
O
0°C to rt, 27%
(14 /14 = 1:1.3)
H
4'
NTMS
OTMS
13
OMOM
Mg
Br 10'
TIPS
Scheme 2. Preparation of Glycosyl Donor 2a and Its Glycosidation with 2-Fluoroadenine (3).

Synthesis of EFdA
1221
and 14ꢁ in a 35% yield with a poor diastereoselectivity
of 1:1.2, favoring the desired ꢁ-anomer 14ꢁ. The
stereochemistry of the products was assigned on the
basis of NOE correlations observed between the C30
proton and the protons at the C8 and C50 positions in
14ꢁ. Changing the solvent from MeCN to CH2Cl2 did
not improve either the stereoselectivity or the chemical
yield, resulting in the formation of a 1:1.3 anomeric
mixture of 14ꢀ and 14ꢁ in only a 27% yield.
To improve the diastereoselectivity of the N-glyco-
sidation process, we next attempted a highly stereo-
selective method for preparing 20-deoxy-ꢁ-ribonucleo-
sides that has recently been reported by Zhang and
co-workers.26) As shown in Fig. 2, this method takes
advantage of the N-acetylglycinate residue at the C30
position of 20-deoxyfuranose derivative A as a stereo-
directing group, giving ꢁ-N-glycoside C with high
diastereoselectivity (up to 98%) via the formation of
oxocarbenium ion intermediate B stabilized intramolec-
ularly by the N-acetylglycinate residue. Scheme 3 out-
lines the preparation of glycosyl donor 2b bearing the
stereo-directing group. The MOM protecting group of
11 was selectively removed by treating with ZnBr2 and
27,28)
1-dodecanethiol in CH2Cl2
to give diol 15. The
esterification of 15 with N-acetylglycine in the presence
of EDCI and DMAP proceeded considerably sluggishly,
affording 16 in a 67% yield [94% based on the recovered
starting material (brsm)] after reacting at room temper-
ature for 13 h. Ozonolysis of 16 and subsequent
acetylation of lactol intermediate 17 afforded 2b which
was then subjected to N-glycosidation with 3. As shown
in Table 1, the N-glycosidation of 2b with a silylated
nucleobase generated from 3 in dichloroethane, which
had been used as the solvent in the reported protocol,26)
exhibited no stereoselectivity, giving a mixture of 18ꢀ
and 18ꢁ in a ratio of ca. 1:1 with an unsatisfactory yield
of 21% (entry 1). The use of CH3CN, a solvent often
used for this type of N-glycosidation,25,29,30) or toluene, a
typical solvent for Lewis acid-mediated reactions, did
not improve the diastereoselectivity at all, affording a
ca. 1:1 mixture of 18ꢀ and 18ꢁ in both cases (entries 2
and 3). The poor diastereoselectivity in the N-glycosi-
dation of 2b might be ascribable, in part, to the difficulty
in the formation of transition state B0 (Fig. 3), in which
the ꢀ-oriented acetylenic substituent at the C40 position
is located on the sterically congested concave side of the
pseudo-bicyclic ring system.
Silylated
nucleobase
+
BnO
BnO
O
O
OAc
TMSOTf
(Ref. 26)
3'
O
O
X
O
O
X
B
A
(X = NHAc)
Nucleobase
BnO
O
O
O
X
C
Fig. 2. ꢁ-Selective N-Glycosidation of 20-Deoxyfuranose Derivative
(A) by Zhang et al.
HO2C
NHAc
ZnBr2
n-C12H25SH
O3, CH2Cl2
MeOH
TBDPSO
HO
TBDPSO
HO
TBDPSO
HO
EDCI, DMAP
NHAc
CH2Cl2
96%
Me2S
NaHCO3
88%
CH2Cl2
67%
(94% brsm)
OMOM
O
OH
O
TIPS
TIPS
TIPS
11
15
16
O
TBDPSO
TIPS
TBDPSO
Ac2O, Et3N
O
OH
OAc
DMAP, CH 2Cl2
96%
O
NHAc
O
NHAc
TIPS
17
O
2b
O
Scheme 3. Preparation of Glycosyl Donor 2b.
Table 1. N-Glycosidation of 2b
NH2
N
N
N
F
TBDPSO
O
N
3
BSA, TMSOTf
TBDPSO
N
F
N
O
N
+
2b
r.t.
O
O
N
TIPS
NH2
O
TIPS
NHAc
O
NHAc
18
18
Entrya
Solvent
3 (eq.)
BSA (eq.)
TMSOTf (eq.)
Time (h)
Product (ratio, yield)
1
2
3
(CH2Cl)2
CH3CN
toluene
1.7
1.8
1.7
2.0
2.0
2.0
1.9
1.9
1.9
12
6
18ꢀ=18ꢁ (ca. 1:1, 21%)
18ꢀ=18ꢁ (ca. 1:1, 33%)
18ꢀ=18ꢁ (ca. 1:1, 36%)
13.5
aA mixture of 3, BSA, and TMSOTf in the solvent indicated was refluxed for 4 h. To the resulting mixture was added a solution of 2b in the same solvent at 0 ꢀC, and
the mixture was stirred at room temperature for the time indicated.

1222
M. KAGEYAMA et al.
Aiming to reduce the steric bulkiness of the C40
resulting lactol 24 provided 2c which was subjected to
an N-glycosidation reaction with 3 (Table 2). All of the
reactions in Table 2 were conducted by using CH3CN as
a solvent, since preliminary experiments indicated that
lesser amounts of undesired impurities were produced in
CH3CN than in other solvents. Table 2 shows that the
N-glycosidation of 2c with 3, under analogous con-
ditions to those employed in entry 2 of Table 1, gave a
mixture of 25ꢀ and 25ꢁ with somewhat improved
diastereoselectivity (25ꢀ=25ꢁ ¼ ca. 1:2), albeit in less
than a 10% yield (not optimized, entry 1). Interestingly,
when a mixture of 3, 2c and BSA (5.6 eq.) in MeCN was
heated at reflux for about 2 h before adding TMSOTf
and subsequent refluxing of the resulting mixture,31,32) a
mixture of N6-trimethylsilylated glycosidation products
(26ꢀ and 26ꢁ) was obtained in a better yield of 46%
with no change in diastereoselectivity (26ꢀ=26ꢁ ¼ ca.
1:2, entry 2). In addition, the reaction led to a complex
mixture when too great an excess of TMSOTf (5.0 eq.)
was used (entry 3).
acetylenic substituent, we next planned to subject
sterically less demanding glycosyl donor 2c (Scheme 4),
which is devoid of the bulky triisopropyllsilyl moiety, to
the N-glycosidation reaction. An outline of the prepa-
ration of 2c is shown in Scheme 4. Dess–Martin
oxidation of compound 9 and subsequent addition of
(trimethylsilyl)ethynylmagnesium bromide to resulting
ketone 10 gave 19 as a single diastereomer. Methano-
lytic removal of the TMS group of 19 afforded 20. Its
MOM group was then deprotected to give diol 21,
whose enantiomeric excess was evaluated to be >95%
by a 1H-NMR analysis of corresponding (R)- and (S)-30-
mono-MTPA esters 22. Acylation of the secondary
hydroxy group of 21 with N-acetylglycine went to
completion by stirring the reaction mixture for 12 h at
room temperature, and provided 23 in an 89% yield
which contrasts with the sluggishness in the acylation of
corresponding TIPS-protected diol 15 (see Scheme 3).
Finally, ozonolysis of 23 and subsequent acetylation of
The experiments conducted so far revealed the poor
diastereoselectivity in the N-glycosidation of the glyco-
syl donors (2a, 2b and 2c), exhibiting an ꢀ/ꢁ selectivity
of 1:2 at best as shown in Table 2. We therefore finally
decided to prioritize the conciseness of the synthetic
route over the diastereoselectivity of the N-glycosidation
step. The modified synthetic route is shown in Scheme 5.
Compound 21 was exposed to ozonolysis conditions to
give cyclic hemiacetal 27 as an anomeric mixture. The
ratio of the ꢀ-anomer to ꢁ-anomer was 2.8:1 as judged by
+
TBDPSO
O
4'
O H
O
X
(i-Pr)3Si
B'
Fig. 3. Unfavorable Steric Interaction in the Transition State Leading
to 18ꢁ.
HO2C
NHAc
DMP
NaHCO3
ZnBr2
n-C12H25SH
TBDPSO
HO
TBDPSO
HO
EDCI, DMAP
TMS
EtMgBr
THF
9
10
3'
CH2Cl2
CH2Cl2
96%
CH2Cl2
89%
OMOM
OR
R
21: R = H
22: R = MTPA
19: R = TMS
20: R = H
K2CO3
MeOH
91% from 9
TBDPSO
TBDPSO
TBDPSO
HO
O3, CH2Cl2
MeOH
O
O
OH
OAc
NHAc
Ac2O, Et3N
NHAc
Me2S
NaHCO3
73%
DMAP, CH 2Cl2
94%
O
NHAc
O
O
O
23
24
O
2c
O
Scheme 4. Preparation of Glycosyl Donor 2c.
Table 2. N-Glycosylation of 2c
NHR
6
N
F
N
TBDPSO
O
N
3
BSA, TMSOTf
TBDPSO
N
N
F
N
O
N
+
2c
MeCN
6
O
O
N
NHR
O
O
NHAc
NHAc
25 : R = H
26 : R = TMS
25 : R = H
26 : R = TMS
Entry
3 (eq.)
BSA (eq.)
TMSOTf (eq.)
Temperature
Time (h)
Product (ratio, yield)
1a
2b
3b
1.5
1.7
1.5
1.9
5.6
5.5
1.9
2.1
5.0
r.t.
reflux
reflux
16
22
23
25ꢀ=25ꢁ (ca. 1:2, <10%)
26ꢀ=26ꢁ (ca. 1:2, 46%)
decomposition
aA mixture of 3, BSA, and TMSOTf in CH3CN was refluxed for 4 h. To the mixture was added a solution of 2c in CH3CN at 0 ꢀC, and the mixture was stirred at room
temperature for 16 h.
bA mixture of 3, BSA, and 2c in CH3CN was refluxed for ca. 2 h. To the mixture was added TMSOTf at 0 ꢀC, and the mixture was refluxed for the time indicated.

Synthesis of EFdA
1223
O3, CH2Cl2
MeOH
TBDPSO
TBDPSO
O
O
Ac2O, Et3N
OH
OAc
21
Me2S
NaHCO3
84%
DMAP, CH2Cl2
94%
3, BSA
TMSOTf, MeCN
46%
HO
OAc
27
2d
NH2
N
N
Diagnostic NOE correlations
R3SiO R3SiO
TBDPSO
N
N
F
O
R3SiO
H
H
H
O
O
O
OH
OAc
OAc
H
OAc
28
+
-anomer
(25%)
HO
HO
HO
H
H
H
H
H
27
2d
2d
NH2
N
N
NH4F, MeOH
CH2Cl2
HO
N
N
F
O
then NaOH
MeOH
87%
HO
1
Scheme 5. Completion of the Synthesis of EFdA (1).
the 1H-NMR analysis; the stereochemistry of each
anomer was determined from the NOEs indicated in
Scheme 5 for ꢀ-anomer 27ꢀ. The two hydroxy groups of
27 were acetylated to afford glycosyl donor 2d as a 1:1.4
anomeric mixture, favoring the ꢁ-anomer in this case; the
stereochemistry of the anomers (2dꢀ and 2dꢁ) was
determined by observing the NOEs indicated in
Scheme 5. N-Glycosidation of 2d with 3 under analo-
gous conditions to those employed in entry 2 of Table 2
proceeded considerably cleanly, furnishing a 1.6:1
mixture of ꢁ-anomer 28 and the corresponding ꢀ-
anomer; in this case, no corresponding N6-silylated
products were obtained (cf. 26ꢁ in Table 2). Chromato-
graphic purification of the mixture gave 28 in a 46%
isolated yield together with the ꢀ-anomer (25%). Finally,
the two protecting groups of 27 were easily removed by
successively treating with NH4F33,34) and a methanolic
solution of NaOH in one pot, providing EFdA (1) as a
white crystalline solid [mp 220.0–221.4 ꢀC (dec.)] in a
stated. All solvents for the reactions were distilled prior to use: THF
from Na and benzophenone; MeOH from Mg and I2; and CH2Cl2,
MeCN and DMF from CaH2.
(R)-4-[(S)-1-Methoxymethoxy-3-butenyl]-2,2-dimethyl-1,3-dioxolane
(7). Compound 7 was obtained by diastereoselective allylation of 6,
with subsequent MOM-protection and chromatographic purification
21
according to the procedure reported in Refs. 18–20. ½ꢀꢂ
þ23.5
D
(c 1.10, CHCl3); IR ꢂmax: 3080 (w), 1643 (w), 1213 (s), 1153 (s);
1H-NMR (400 MHz) ꢃ: 1.35 (3H, s), 1.41 (3H, s), 2.28–2.42 (2H, m),
3.38 (3H, s), 3.74 (1H, ddd, J ¼ 5:5, 5.5, 5.5 Hz), 3.89 (1H, dd,
J ¼ 8:0, 6.4 Hz), 4.04 (1H, dd, J ¼ 8:0, 6.4 Hz), 4.10 (1H, ddd, J ¼
6:4, 6.4, 5.5 Hz), 4.70 (1H, d, J ¼ 7:2 Hz), 4.72 (1H, d, J ¼ 7:2 Hz),
5.10 (1H, dm, J ¼ 10:0 Hz), 5.13 (1H, dm, J ¼ 17:1 Hz), 5.87 (1H,
dddd, J ¼ 17:1, 10.0, 7.1, 7.1 Hz); 13C-NMR (100 MHz) ꢃ: 25.3, 26.4,
36.0, 55.7, 66.0, 76.8, 77.1, 96.3, 109.0, 117.6, 134.1; HRMS (FAB)
m=z: calcd. for C11H21O4, 217.1440; found, 217.1444 (½M þ Hꢂþ).
(2R,3S)-3-Methoxymethoxy-5-hexene-1,2-diol (8). To
a stirred
solution of 7 (3.87 g, 17.9 mmol) in MeOH/H2O (100:1, 182 mL)
was added PPTS (227 mg, 0.903 mmol) at room temperature. After
1.5 h, the mixture was stirred at 55 ꢀC for 1.5 h and then at 60 ꢀC for an
additional 2 h. The mixture was quenched with solid NaHCO3 and
concentrated in vacuo. The residue was diluted with ether, and the
resulting ethereal solution was dried (MgSO4) and concentrated in
1
good yield of 87%. The H-NMR spectrum of 1 was
identical with that of an authentic sample of EFdA.
In conclusion, the enantioselective total synthesis of
EFdA (1) was accomplished in an 18% overall yield from
commercially available protected aldehyde 6 via 12
steps, this being much better both in overall yield and in
the number of steps than the previous synthesis by Kohgo
and co-workers (2.5% overall yield in 18 steps from
2-amino-20-deoxyadenosine). Attempts to improve the
diastereoselectivity of the N-glycosidation step as well as
to convert the undesired ꢀ-anomer of 28 into desired
anomer 28 in the presence of various Lewis acids are
currently underway and will be reported in due course.
vacuo. The residue was purified by silica gel column chromatography
23
(CHCl3=MeOH ¼ 20:1) to give 2.62 g (83%) of 8. ½ꢀꢂ
þ60.9
D
(c 1.13, CHCl3); IR ꢂmax: 3400 (br s), 3077 (w), 1641 (w), 1098 (s);
1H-NMR (400 MHz) ꢃ: 2.30–2.45 (3H, m), 3.04 (1H, d, J ¼ 7:4 Hz),
3.42 (3H, s), 3.62–3.82 (4H, m), 4.66 (1H, d, J ¼ 6:6 Hz), 4.70 (1H, d,
J ¼ 6:6 Hz), 5.10 (1H, dm, J ¼ 10:2 Hz), 5.14 (1H, dm, J ¼ 17:2 Hz),
5.83 (1H, dddd, J ¼ 17:2, 10.2, 7.0, 7.0 Hz); 13C-NMR (100 MHz) ꢃ:
36.1, 55.9, 62.9, 72.7, 81.0, 97.3, 117.8, 134.1; HRMS (FAB) m=z:
calcd. for C8H17O4, 177.1127; found, 177.1133 (½M þ Hꢂþ).
(2R,3S)-1-(tert-Butyldiphenylsilyloxy)-3-methoxymethoxy-5-hexen-2-
ol (9). To a stirred solution of 8 (4.03 g, 22.9 mmol) in DMF (110 mL)
were successively added imidazole (3.89 g, 57.2 mmol) and TBDPSCl
(6.2 mL, 23.8 mmol) at room temperature in a nitrogen atmosphere.
After 2 h, the mixture was diluted with brine and extracted with ether.
The extract was successively washed with water and brine, dried
(Na2SO4), and concentrated in vacuo. The residue was purified by
Experimental
IR spectra were recorded by a Jasco FT/IR-4100 spectrometer,
using an ATR (ZnSe) attachment, and are reported in cmꢁ1. NMR
spectra were recorded with TMS as an internal standard in CDCl3 by a
Varian MR-400 spectrometer (400 MHz for 1H and 100 MHz for 13C)
or a Varian 600TT spectrometer (600 MHz for 1H and 125 MHz for
13C) unless otherwise stated. Optical rotation values were measured
with a Jasco DIP-371 polarimeter or a Horiba Septa-300 polarimeter,
and the mass spectra were obtained with a Jeol JMS-700 spectrometer
operated in the FAB mode. Melting point (mp) data were determined
with Yanaco MP-J3 apparatus and are uncorrected. Merck silica gel 60
(7–230 mesh) was used for column chromatography unless otherwise
silica gel column chromatography (hexane/EtOAc ¼ 8:1) to give
22
9.12 g (96%) of 9. ½ꢀꢂ
þ8.9 (c 1.18, CHCl3); IR ꢂmax: 3459 (w),
D
1641 (w), 1105 (vs), 1033 (vs), 770 (vs); 1H-NMR (400 MHz) ꢃ: 1.07
(9H, s), 2.26–2.42 (2H, m), 2.70 (1H, d, J ¼ 4:3 Hz), 3.26 (3H, s),
3.62–3.82 (4H, m), 4.59 (1H, d, J ¼ 6:9 Hz), 4.62 (1H, d, J ¼ 6:9 Hz),
5.05 (1H, dm, J ¼ 10:1 Hz), 5.08 (1H, dm, J ¼ 17:2 Hz), 5.83 (1H,
dddd, J ¼ 17:2, 10.1, 7.1, 7.1 Hz), 7.34–7.48 (6H, m), 7.60–7.70 (4H,
m); 13C-NMR (100 MHz) ꢃ: 19.2, 26.8 (3C), 35.3, 55.7, 64.6, 72.7,
78.6, 96.5, 117.3, 127.8 (4C), 129.8 (2C), 133.05, 133.08, 134.6, 135.5

1224
M. KAGEYAMA et al.
(2C), 135.6 (2C); HRMS (FAB) m=z: calcd. for C24H35O4Si, 415.2305;
found, 415.2310 (½M þ Hꢂþ).
at ꢃ 3.73 (1H, d, J ¼ 10:3 Hz) and d 3.75 (1H, d, J ¼ 10:3 Hz). A
comparison of the two spectra indicated the enantiomeric excess of 21
to be more than 95%.
(3R,4S)-3-[(tert-Butyldiphenylsilyloxy)methyl]-4-methoxymethoxy-6-
hepten-1-yn-3-ol (20). To a stirred solution of 9 (4.42 g, 10.4 mmol) in
CH2Cl2 (100 mL) were successively added solid NaHCO3 (4.38 g,
52.2 mmol) and DMP (5.74 g, 13.5 mmol) at room temperature in a
nitrogen atmosphere. After 25 min, additional NaHCO3 (5.35 g,
63.6 mmol) and DMP (1.37 g, 3.23 mmol) were added, and the
resulting mixture was stirred for 20 min. The mixture was quenched
with a mixture of satd. aq. NaHCO3, satd. aq. Na2S2O3 and water
(1:1:1), and then extracted with CH2Cl2. The extract was washed with
brine, dried (Na2SO4), and concentrated in vacuo. The residue was
purified by silica gel column chromatography (hexane/EtOAc ¼ 9:1)
to give 10 which was then taken up in THF (88 mL). A solution of
bromo(trimethylsilylethynyl)magnesium was prepared by adding
(2R/S,4S,5R)-5-[(tert-Butyldiphenylsilyloxy)methyl]-5-ethynyltetra-
hydrofuran-2,4-diol (27). Ozone was bubbled into a solution of 21
(3.21 g, 8.13 mmol) in CH2Cl2/MeOH (4:1, 100 mL) at ꢁ78 ꢀC for
25 min. After removing excess ozone by a stream of O2 (for about
10 min), NaHCO3 (3.33 g, 39.6 mmol) and Me2S (6.0 mL, 81.7 mmol)
were successively added, and the resulting mixture was gradually
warmed to room temperature. The mixture was filtered, and the filtrate
was concentrated in vacuo. The residue was purified by silica gel
column chromatography (hexane/EtOAc ¼ 2:1{3:2) to give 2.71 g
(84%) of 27 as an anomeric mixture (ꢀ-anomer=ꢁ-anomer ¼ 2:8:1).
24
½ꢀꢂ
þ5.7 (c 0.99, CHCl3); IR ꢂmax: 3411 (br s), 3291 (s), 1084 (vs),
D
701 (vs); 1H-NMR (400 MHz) ꢃ: 1.05 (0:74 ꢃ 9H, s), 1.09 (0:26 ꢃ 9H,
s), 2.10 (0.26H, d, J ¼ 6:9 Hz), 2.16 (0.74H, ddd, J ¼ 13:6, 1.4,
0.8 Hz), 2.16–2.24 (0.26H, m), 2.31 (0.26H, ddd, J ¼ 13:5, 6.5,
2.2 Hz), 2.36 (0.74H, ddd, J ¼ 13:6, 5.3, 5.3 Hz), 2.65 (0.26H, s), 2.70
(0.74H, s), 2.80 (0.74H, d, J ¼ 5:5 Hz), 3.00 (0.26H, d, J ¼ 6:1 Hz),
3.57 (0.74H, d, J ¼ 7:2 Hz), 3.63 (0.74H, d, J ¼ 10:6 Hz), 3.76 (0.74H,
d, J ¼ 10:6 Hz), 3.81 (0.26H, d, J ¼ 10:5 Hz), 3.85 (0.26H, d,
J ¼ 10:5 Hz), 4.42 (0.74H, ddd, J ¼ 5:5, 5.3, 1.4 Hz), 4.62 (0.26H,
br q, J ¼ 6:9 Hz), 5.51 (0.74H, br dd, J ¼ 7:2, 5.0 Hz), 5.58 (0.26H,
ddd, J ¼ 6:1, 5.5, 5.2 Hz), 7.34–7.50 (6H, m), 7.60–7.74 (4H, m);
13C-NMR (100 MHz) ꢃ: 19.2, 26.7/26.8 (3C), 41.2/41.8, 67.1/67.5,
72.3/74.0, 77.7, 80.7, 84.3/85.9, 97.9/100.2, 127.8/127.9 (4C),
129.88/129.92/129.96/130.03 (2C), 132.61/132.64 (2C), 135.6/
135.7 (4C); HRMS (FAB) m=z: calcd. for C23H28O4SiNa, 419.1655;
found, 419.1656 (½M þ Naꢂþ).
EtMgBr (1.0 M in THF, 14.0 mL, 14.0 mmol) to
a solution of
ethynyltrimethylsilane (2.00 mL, 1.36 mmol) in THF (14 mL) at 0 ꢀC
and subsequently stirring the resulting mixture at room temperature for
1 h. To the Grignard reagent was added the solution of 10 in THF just
obtained at ꢁ78 ꢀC in a nitrogen atmosphere, and the mixture was
gradually warmed to 0 ꢀC over 3 h and stirred for an additional 13 h. To
the mixture containing 19 were successively added MeOH (100 mL)
and K2CO3 (2.88 g, 20.8 mmol), and the mixture was stirred at reflux
for 2 h. Since the desilylation was sluggish with the THF/MeOH
solvent, these solvents (THF and MeOH) were evaporated, and the
residue was diluted with MeOH (100 mL) and mixed with additional
K2CO3 (2.71 g, 19.6 mmol). The mixture was stirred at room temper-
ature for 20 min, quenched with satd. aq. NH4Cl, and extracted with
EtOAc. The extract was washed with brine, dried (MgSO4), and
concentrated in vacuo. The residue was purified by silica gel column
chromatography (hexane/EtOAc ¼ 10:1) to give 4.17 g (91%) of 20.
(2R,3S,5R/S)-5-Acetoxy-2-[(tert-butyldiphenylsilyloxy)methyl]-2-
ethynyltetra-hydrofuran-3-yl acetate (2d). To a stirred solution of 27
(135 mg, 0.340 mmol) and DMAP (25.8 mg, 0.211 mmol) in CH2Cl2
(3.5 mL) were successively added Et3N (210 mL, 1.51 mmol) and
Ac2O (130 mL, 1.38 mmol) at room temperature. After 1.5 h, the
mixture was quenched with satd. aq. NH4Cl and extracted with
CH2Cl2. The extract was washed with brine, dried (Na2SO4), and
concentrated in vacuo. The residue was purified by silica gel column
23
½ꢀꢂ
ꢁ5.0 (c 1.04, CHCl3); IR ꢂmax: 3462 (w), 3302 (m), 1641 (w),
D
1040 (vs), 701 (vs); 1H-NMR (400 MHz) ꢃ: 1.09 (9H, s), 2.43 (1H,
dddm, J ¼ 14:7, 8.8, 7.7 Hz), 2.49 (1H, s), 2.69 (1H, ddddd, J ¼ 14:7,
6.5, 3.3, 1.6, 1.6), 3.22 (3H, s), 3.32 (1H, s), 3.73 (1H, dd, J ¼ 8:8,
3.3 Hz), 3.80 (1H, d, J ¼ 9:8 Hz), 3.85 (1H, d, J ¼ 9:8 Hz), 4.62 (1H,
d, J ¼ 6:8 Hz), 4.69 (1H, d, J ¼ 6:8 Hz), 5.05 (1H, dm, J ¼ 10:2 Hz),
5.13 (1H, dddd, J ¼ 17:0, 1.7, 1.7, 1.6 Hz), 5.91 (1H, dddd, J ¼ 17:0,
10.2, 7.7, 6.5 Hz), 7.34–7.48 (6H, m), 7.64–7.76 (4H, m); 13C-NMR
(100 MHz) ꢃ: 19.3, 26.8 (3C), 35.7, 56.0, 67.8, 73.4, 73.7, 80.9, 83.7,
97.6, 117.1, 127.76 (2C), 127.78 (2C), 129.9 (2C), 132.6, 132.7, 135.5,
135.6 (2C), 135.7 (2C); HRMS (FAB) m=z: calcd. for C26H35O4Si,
439.2304; found, 439.2302 (½M þ Hꢂþ).
chromatography (hexane/EtOAc ¼ 4:1) to give 153 mg (94%) of 2d
24
as an anomeric mixture (ꢀ-anomer=ꢁ-anomer ¼ 1:1:4). ½ꢀꢂ
ꢁ11.4
D
(c 0.97, CHCl3); IR ꢂmax: 3281 (w), 1744 (vs), 1227 (s), 702 (s);
1H-NMR (400 MHz) ꢃ: 1.05 (0:42 ꢃ 9H, s), 1.09 (0:58 ꢃ 9H, s), 1.86
(0:58 ꢃ 3H, s), 2.11 (0:42 ꢃ 3H, s), 2.12 (0:58 ꢃ 3H, s), 2.15
(0:42 ꢃ 3H, s), 2.24 (0.42H, dm, J ¼ 14:5 Hz), 2.44 (0.58H, ddd,
J ¼ 13:7, 7.0, 5.6 Hz), 2.508 (0.58H, ddd, J ¼ 13:7, 7.0, 2.5 Hz), 2.509
(0.42H, s), 2.53 (0.58H, s), 2.70 (0.42H, ddd, J ¼ 14:5, 7.8, 5.4 Hz),
3.82 (0.58H, d, J ¼ 10:8 Hz), 3.83 (0.42H, d, J ¼ 10:8 Hz), 3.86
(0.58H, d, J ¼ 10:8 Hz), 3.90 (0.42H, d, J ¼ 10:8 Hz), 5.65 (0.42H, dd,
J ¼ 7:8, 1.6 Hz), 5.73 (0.58H, t, J ¼ 7:0 Hz), 6.41 (0.42H, d,
J ¼ 5:4 Hz), 6.43 (0.58H, dd, J ¼ 5:6, 2.5 Hz), 7.34–7.48 (6H, m),
7.64–7.74 (4H, m); 13C-NMR (100 MHz) ꢃ: 19.2/19.3, 21.0, 21.2/
21.3, 26.68/26.71 (3C), 37.3/38.9, 66.5/67.9, 72.0/73.5, 76.40/76.43,
79.0/79.2, 84.1/85.9, 96.5/98.6, 127.72/127.76 (2C), 127.82/127.83
(2C), 129.7/129.8/129.9 (2C), 132.4/132.6, 132.7/132.9, 135.5 (2C),
135.6/135.7 (2C), 169.96/169.97, 170.35/170.38; HRMS (FAB) m=z:
calcd. for C27H32O6SiNa, 503.1866; found, 503.1864 (½M þ Naꢂþ).
(3R,4S)-3-[(tert-Butyldiphenylsilyloxy)methyl]-6-hepten-1-yne-3,4-
diol (21). To a stirred solution of 20 (1.23 g, 2.80 mmol) in CH2Cl2
(28 mL) were successively added ZnBr2 (805 mg, 3.58 mmol) and 1-
dodecanethiol (1.3 mL, 5.43 mmol) at room temperature. After 30 min,
the mixture was quenched with satd. aq. NaHCO3 and extracted with
CH2Cl2. The extract was washed with brine, dried (MgSO4), and
concentrated in vacuo. The residue was purified by silica gel column
chromatography (hexane/EtOAc ¼ 6:1) to give 1.06 g (96%) of 21.
24
½ꢀꢂ
ꢁ2.4 (c 1.05, CHCl3); IR ꢂmax: 3512 (m), 3303 (m), 1643 (w),
D
1111 (vs), 700 (vs); 1H-NMR (400 MHz) ꢃ: 1.09 (9H, s), 2.17 (1H, d,
J ¼ 5:7 Hz), 2.23 (1H, ddddd, J ¼ 14:5, 10.3, 7.8, 1.0, 1.0 Hz), 2.48
(1H, s), 2.65 (1H, ddddd, J ¼ 14:5, 6.2, 2.5, 1.3, 1.3 Hz), 3.30 (1H, s),
3.77 (1H, ddd, J ¼ 10:3, 5.7, 2.5 Hz), 3.85 (1H, d, J ¼ 10:0 Hz), 3.92
(1H, d, J ¼ 10:0 Hz), 5.14 (1H, dm, J ¼ 10:2 Hz), 5.17 (1H, dm,
J ¼ 17:2 Hz), 5.90 (1H, dddd, J ¼ 17:2, 10.2, 7.8, 6.2 Hz), 7.36–7.48
(6H, m), 7.64–7.74 (4H, m); 13C-NMR (100 MHz) ꢃ: 19.3, 26.8 (3C),
36.1, 67.7, 73.2, 73.7, 74.3, 82.9, 117.8, 127.8 (2C), 127.9 (2C),
130.00, 130.01, 132.4, 132.5, 135.0, 135.56 (2C), 135.63 (2C); HRMS
(2R,3S,5R)-5-(6-Amino-2-fluoropurin-9-yl)-2-[(tert-butyldiphenyl-
silyloxy)-methyl]-2-ethynyltetrahydrofuran-3-yl acetate (28). To com-
pound 3 (188 mg, 1.23 mmol) were added a solution of 2d (387 mg,
0.805 mmol) in CH3CN (8.0 mL) and BSA (1.10 mL, 4.50 mmol) at
room temperature. The mixture was stirred at reflux for 2.5 h and then
cooled to 0 ꢀC. To the resulting solution was added TMSOTf
(0.300 mL, 1.66 mmol), before the mixture was stirred at room
temperature for 15 min and then at reflux for an additional 17 h. The
mixture was quenched with satd. aq. NaHCO3 and filtered through a
pad of Celite. The filtrate was diluted with water and extracted with
CH2Cl2. The extract was washed with brine, dried (MgSO4), and
concentrated in vacuo. The residue was purified by silica gel column
chromatography (CHCl3=MeOH ¼ 100:1) to give 213 mg (46%) of 28
(FAB) m=z: calcd. for
(½M þ Hꢂþ).
C24H31O3Si, 395.2043; found, 395.2045
Determination of the enantiomeric excess of 21. (R)- and (S)-Mono-
MTPA esters 22 were prepared by respectively treating 21 with 4.8
equiv of (S)- and (R)-MTPACl in pyridine overnight at room
temperature; the disappearance of starting material 21 was checked
by TLC. The TBDPSO-bearing methylene protons of the (R)-MTPA
ester were observed as a singlet at ꢃ 3.65 (2H, s) in 1H-NMR
(600 MHz, CDCl3), while those of the (S)-MTPA ester were detected
and 115 mg (25%) of the corresponding ꢀ-anomer. Compound 28. Mp
26
182.6–183.3 ꢀC; ½ꢀꢂ
þ24.3 (c 1.13, CHCl3); IR ꢂmax: 1747 (m),
D

Synthesis of EFdA
1635 (s), 1362 (s), 702 (vs); 1H-NMR (600 MHz, DMSO-d6) ꢃ: 0.96
1225
References
(9H, s), 2.13 (3H, s), 2.61 (1H, ddd, J ¼ 14:0, 6.8, 4.7 Hz), 3.20 (1H,
ddd, J ¼ 14:0, 6.8, 6.8 Hz), 3.74 (1H, s), 3.78 (1H, d, J ¼ 10:6 Hz),
3.95 (1H, d, J ¼ 10:6 Hz), 5.82 (1H, dd, J ¼ 6:8, 4.7 Hz), 6.37 (1H, dd,
J ¼ 6:8, 6.8 Hz), 7.32–7.38 (4H, m), 7.42–7.48 (2H, m), 7.54–7.64
(4H, m), 7.78–7.85 (1H, br s), 7.85–8.04 (1H, br s), 8.27 (1H, s);
13C-NMR (150 MHz) ꢃ: 19.1, 21.1, 26.7 (3C), 34.6, 66.7, 72.9, 79.6,
79.8, 83.0, 83.3, 118.0, 128.03 (2C), 128.05 (2C), 130.16, 130.18,
132.5, 132.7, 135.3 (2C), 135.4 (2C), 140.3, 150.5 (d, JCF ¼ 20:2 Hz),
157.9 (d, JCF ¼ 21:3 Hz), 158.7 (d, JCF ¼ 204:4 Hz), 169.6; HRMS
1) Nikolenko GN, Kotelkin AT, Oreshkova SF, and Ilyichev AA,
Mol. Biol., 45, 93–109 (2011).
2) Sharma B, Neurobehav. HIV Med., 2, 27–40 (2011).
3) Deval J, Drugs, 69, 151–166 (2009).
4) Sarafianos SG, Marchand B, Das K, Himmel DM, Parniak MA,
Hughes SH, and Arnold E, J. Mol. Biol., 385, 693–713 (2009).
5) Michailidis E, Marchand B, Kodama EN, Singh K, Matsuoka
M, Kirby KA, Ryan EM, Sawani AM, Nagy E, Ashida N,
Mitsuya H, Parniak MA, and Sarafianos SG, J. Biol. Chem.,
284, 35681–35691 (2009).
(FAB) m=z: calcd. for C30H33FN5O4Si, 574.2286; found, 574.2290
25
(½M þ Hꢂþ). ꢀ-Anomer of 28. Mp 221.0–221.7 ꢀC; ½ꢀꢂ
þ16.7
D
(c 1.03, CHCl3); IR ꢂmax: 3330 (w), 3276 (w), 1759 (m), 1372 (s), 700
(vs); 1H-NMR (600 MHz, DMSO-d6) ꢃ: 1.05 (9H, s), 2.08 (3H, s), 2.81
(1H, ddd, J ¼ 14:4, 3.8, 3.5 Hz), 3.05 (1H, ddd, J ¼ 14:4, 7.3, 7.3 Hz),
3.75 (1H, d, J ¼ 10:6 Hz), 3.77 (1H, s), 3.79 (1H, d, J ¼ 10:6 Hz), 5.71
(1H, dd, J ¼ 7:3, 3.5 Hz), 6.37 (1H, dd, J ¼ 7:3, 3.8 Hz), 7.44–7.54
(6H, m), 7.66–7.74 (4H, m), 7.80–7.98 (2H, br m), 8.29 (1H, s); 13C-
NMR (150 MHz) ꢃ: 19.1, 21.1, 26.8 (3C), 36.6, 67.5, 73.3, 79.2, 80.5,
83.4, 84.8, 117.4, 128.26 (2C), 128.27 (2C), 130.3, 130.4, 132.3, 132.4,
135.4 (2C), 135.5 (2C), 139.1, 150.9 (d, JCF ¼ 20:2 Hz), 157.9 (d,
JCF ¼ 21:3 Hz), 159.0 (d, JCF ¼ 203:6 Hz), 169.5; HRMS (FAB) m=z:
calcd. for C30H33FN5O4Si, 574.2286; found, 574.2285 (½M þ Hꢂþ).
6) Kohgo S, Ohrui H, Kodama E, Matsuoka M, and Mitsuya H,
Can. Patent Appl., CA 2502109 (Mar. 22, 2005).
7) Kohgo S, Yamada K, Kitano K, Iwai Y, Sakata S, Ashida N,
Hayakawa H, Nameki D, Kodama E, Matsuoka M, Mitsuya H,
and Ohrui H, Nucleosides Nucleotides Nucleic Acids, 23, 671–
690 (2004).
8) Ohrui H, Chem. Rec., 6, 133–143 (2006).
9) Ohrui H, Hayakawa H, Kohgo S, Matsuoka M, Kodama E, and
Mitsuya H, J. Synth. Org. Chem. Jpn., 64, 716–723 (2006).
10) Ohrui H, Kohgo S, Hayakawa H, Kodama E, Matsuoka M,
Nakata T, and Mitsuya H, Nucleosides Nucleotides Nucleic
Acids, 26, 1543–1546 (2007).
11) Ohrui H, Proc. Jpn. Acad. B, 87, 53–65 (2011).
12) Kawamoto A, Kodama E, Sarafianos SG, Sakagami Y, Kohgo
S, Kitano K, Ashida N, Iwai Y, Hayakawa H, Nakata H,
Mitsuya H, Arnold E, and Matsuoka M, Int. J. Biochem. Cell
Biol., 40, 2410–2420 (2008).
(2R,3S,5R)-5-(6-Amino-2-fluoropurin-9-yl)-2-ethynyl-2-(hydroxy-
methyl)-tetrahydrofuran-3-ol (1). To a stirred solution of 28 (66.2 mg,
0.115 mmol) in MeOH/CH2Cl2 (2:1, 1.5 mL) was added NH4F
(85.1 mg, 2.30 mmol) at room temperature. After 16 h, MeOH
(0.5 mL) was added, and the resulting mixture was stirred for an
additional 27 h. To the mixture was added 10% (w/v) methanolic
NaOH (1.5 mL) to adjust the pH value of the mixture to ca. 10. After
10 min, Dowex 50Wꢃ8 (200–400 mesh (H)) was added until the pH
value of the mixture reached ca. 4. To the resulting mixture was added
CaCO3 (259 mg, 2.59 mmol), and the mixture was stirred for 30 min.
The mixture was filtered through a pad of Celite, and the filtrate was
concentrated in vacuo. The residue was purified by silica gel column
13) Nakata H, Amano M, Koh Y, Kodama E, Yang G, Bailey CM,
Kohgo S, Hayakawa H, Matsuoka M, Anderson KS, Cheng
Y-C, and Mitsuya H, Antimicrob. Agents Chemother., 51, 2701–
2708 (2007).
14) Hattori S, Ide K, Nakata H, Harada H, Suzu S, Ashida N, Kohgo
S, Hayakawa H, Mitsuya H, and Okada S, Antimicrob. Agents
Chemother., 53, 3887–3893 (2009).
15) Kageyama M, Nagasawa T, Yoshida M, Ohrui H, and
Kuwahara S, Org. Lett., 13, 5264–5266 (2011).
chromatography (CHCl3=MeOH ¼ 10:1) to give 29.3 mg (87%) of 1.
25
Mp 220.0–221.4 ꢀC (dec.); ½ꢀꢂ
þ12.4 (c 0.97, MeOH); IR ꢂmax
:
D
3315 (br m), 3179 (br m), 1690 (vs), 1356 (vs); 1H-NMR (600 MHz,
DMSO-d6) ꢃ: 2.43 (1H, ddd, J ¼ 13:2, 7.3, 7.3 Hz), 2.70 (1H, ddd,
J ¼ 13:2, 6.8, 5.1 Hz), 3.52 (1H, s), 3.54 (1H, dd, J ¼ 11:7, 6.4 Hz),
3.65 (1H, dd, J ¼ 11:7, 5.0 Hz), 4.57 (1H, m), 5.32 (1H, m), 5.60 (1H,
m), 6.24 (1H, dd, J ¼ 7:2, 5.1 Hz), 7.82 (1H, br s), 7.92 (1H, br s), 8.31
(1H, s); 13C-NMR (150 MHz) ꢃ: 38.3, 64.4, 70.3, 79.2, 81.7, 82.2, 85.4,
117.6, 140.0, 150.4 (d, JCF ¼ 20:7 Hz), 157.8 (d, JCF ¼ 21:2 Hz), 158.8
(d, JCF ¼ 203:4 Hz); HRMS (FAB) m=z: calcd. for C12H13FN5O3,
294.1002; found, 294.1000 (½M þ Hꢂþ).
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2dꢁ. 2a (400 MHz, CDCl3): between the C30 proton (ꢃ: 4.69, 1H, dd,
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the C20-ꢁ proton (ꢃ: 2.508, 0.58H, ddd, J ¼ 13:7, 7.0, 2.5 Hz) and the
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Acknowledgments
This work was supported, in part, by a grant aid for
scientific research (B) from the Ministry of Education,
Culture, Sports, Science and Technology of Japan
(no. 19380065). We thank Ms. Yamada (Tohoku
University) for measuring the NMR and MS spectra.
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