Synthesis of aminoglycoside derivatives on a Cbz-type heavy fluorous tag

Article abstract of DOI:10.1016/j.tetlet.2006.10.064

Four aminoglycoside derivatives containing a 2,6-diamino-2,6-dideoxy-d-glucopyranose disaccharide structure were successfully prepared by using a Cbz-type heavy fluorous tag in a fluorous synthesis. A Cbz-type heavy fluorous tag was prepared using the hex

Full text of DOI:10.1016/j.tetlet.2006.10.064

Tetrahedron Letters 47 (2006) 8831–8835
Synthesis of aminoglycoside derivatives on a Cbz-type heavy
fluorous tag
Mamoru Mizuno,a,* Hiroharu Matsumoto,a,b Kohtaro Gotoa and Keita Hamasakib
aGlyco-organic Chemistry Laboratory, The Noguchi Institute, 1-8-1, Kaga, Itabashi-ku, Tokyo 173-0003, Japan
bDepartment of Applied Chemistry, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
Received 19 September 2006; revised 11 October 2006; accepted 12 October 2006
Available online 31 October 2006
Abstract—Four aminoglycoside derivatives containing a 2,6-diamino-2,6-dideoxy-D-glucopyranose disaccharide structure were suc-
cessfully prepared by using a Cbz-type heavy fluorous tag in a fluorous synthesis. A Cbz-type heavy fluorous tag was prepared using
the hexakis(fluorous chain)-type alcohol 11, and the fluorous alcohol 11 was recovered in good yield after the synthesis of amino-
glycoside derivatives.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Targeting RNA with small organic molecules is a pro-
mising approach for controlling gene expression and
viral replication and for identifying new antibiotics.
Aminoglycosides are well-known RNA-binding mole-
cules, and some are important natural products with
antibacterial activity against both gram-positive and
gram-negative bacteria.1,2 Furthermore, some types of
aminoglycoside, such as the neamines, neomycin B
and kanamycin B (Fig. 1), bind to the trans-activator
responsive region (TAR) and retroviral protein respon-
sive element (RRE) of HIV RNA, and inhibit the bind-
ing of regulatory proteins of HIV (Tat for TAR RNA,
and Rev for REE RNA).3–5
NH
O
NH
O
2
2
HO
HO
HO
HO
NH
2
H N
H N
2
NH
2
2
O
HO
NH
O
2
O
NH
2
HO
O
OH
OH
O
OH
O
HO
Kanamycin B
NH
2
O
OH
O
NH
2
H N
OH
2
OH
NH
2
Neomycin B
O
HO
HO
NH
2
Neomycin and kanamycin have a pseudodisaccharide
H N
2
O
neamine structure. Neamine is
a glycoconjugate
NH
2
HO
structure in which the anomeric position of 2,6-diami-
no-2,6-dideoxy-D-glucopyranose is connected by an
a-linkage to the hydroxyl group at the 4-position of
2-deoxystreptamine.
OH
Neamine
Figure 1. Structures of neomycin B, kanamycin B, and neamine.
We synthesized aminoglycoside derivatives containing a
2,6-diamino-2,6-dideoxy-D-glucopyranose disaccharide
structure to study if the geometry of the glycosidic bond
of neamine influences the binding to RNA. A fluorous
synthesis method6–9 was used to prepare the aminogly-
coside disaccharide derivatives. Fluorous synthesis (the
fluorous tag method) is a strategic alternative to solid-
phase synthesis. This strategy is very efficient because,
unlike the solid-phase method, it does not rely on chro-
matography to perform separations. Syntheses of oligo-
saccharides and peptides by using various fluorous tags
have been achieved.10–16 Recently, the concept of a
novel recyclable fluorous tag system to realize a practical
fluorous synthesis was described.17 In this study, we pre-
pared a benzyloxycarbonyl (Cbz)-type heavy fluorous
tag and used it in the synthesis of aminoglycoside deriv-
atives with the recyclable system.
*
Corresponding author. E-mail: mmizuno@noguchi.or.jp
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.10.064

8832
M. Mizuno et al. / Tetrahedron Letters 47 (2006) 8831–8835
The 2,6-diazido-glucose derivatives 9 and 10 were first
prepared as building blocks. The peracetylated 2-azi-
do-2-deoxyglucose 2 was obtained by conventional ami-
no–azido conversion from glucosamine 1, followed by
acetylation.18 Treatment of 2 with benzenethiol and bor-
on trifluoride–ethyl ether complex gave the thioglyco-
side 3. Deacetylation followed by treatment with
benzaldehyde dimethyl acetal afforded the 4,6-di-O-benz-
ylidene derivative 4. Benzylation of 4 followed by re-
moval of the benzylidene group of 5 provided the
monobenzyl derivative 6. Selective tosylation of 6 in
the 6-position gave the monotosylate 7. Treatment of
7 with sodium azide in the presence of tetrabutylammo-
nium hydrogen sulfate (TBAHS) at room temperature
gave the 2,6-diazido-2,6-dideoxy derivative 8. The hy-
droxyl group of 8 was protected by a 9-fluorenylmeth-
oxycarbonyl (Fmoc) group or an acetyl group to
afford the derivatives 9 and 10, respectively (Scheme 1).
tained in a straightforward manner simply by partition-
ing between the fluorocarbon solvent FC7221 and
MeOH. Compound 13, including the fluorous tag, was
extracted into the FC72 layer, whereas the other re-
agents remained in the MeOH layer. No further purifi-
cation, such as silica gel column chromatography, was
necessary. The crude 13 was treated with 2-aminoetha-
nol in THF, and fluorous compound 1422 was obtained
in an 80% yield from 12 (two steps) after purification by
silica gel column chromatography. Glycosylationof 14
with a 2-fold excess of the glycosyl donor 9 in the mixed
homogeneous solvents CH2Cl2 and EtOC4F9 gave gly-
coside 15. This was deprotected by removal of the Fmoc
group by using the FC72–10% piperidine/DMF (1:1)
immiscible system to give 16. This was treated with a
2-fold excess of glycosyl donor 10 under similar glyco-
sylation conditions to those described above to give
the fluorous disaccharide 17. Each of the fluorous inter-
mediates 15, 16, and 17 was isolated by simple partition-
ing between FC72 and an organic solvent such as
MeOH or MeCN, without purification by column chro-
matography. The fluorous disaccharide 17 was treated
with NaOMe in the mixed homogeneous solvents
MeOH and EtOC4F9 to give the crude disaccharide
18, which was extracted into a MeOH layer by partition-
ing the mixture between FC72 and MeOH. After purifi-
cation by silica gel column chromatography, the
aminoglycoside disaccharide derivative 18 was obtained
in a 32% yield as an anomeric mixture. The fluorous
alcohol 11 was recovered from the FC72 layer in a
93% yield (Scheme 2).
Next, a Cbz-type heavy fluorous tag was prepared. The
synthesis and application of a tris(fluorous chain)-type
fluorous Cbz tag was reported.19 In this study, we
decided to use a hexakis(fluorous chain)-type Cbz tag
[Cbz(HexF)] to keep the high partition coefficient of flu-
orous aminoglycoside intermediates in a fluorous sol-
vent. The hexakis(fluorous chain)-type benzyl alcohol
12 was prepared from the fluorous alcohol 11.17 The flu-
orous benzyl alcohol 12 was coupled with 4-nitrophenyl
chloroformate in a homogeneous mixture of CH2Cl2
20
and EtOC4F9 to afford the fluorous-type benzyl-4-
nitrophenyl carbonate 13. Compound 13 could be ob-
OH
O
OAc
O
OAc
O
HO
HO
AcO
c
AcO
AcO
a, b
AcO
OH
HCl
SPh
OAc
H N
N
3
N
2
3
1
2
3
OH
O
O
O
Ph
Ph
O
N
O
N
O
HO
f
g
O
d, e
BnO
BnO
SPh
SPh
HO
SPh
N
3
3
3
4
5
6
N
OTs
N
3
3
O
O
O
h
i
j
FmocO
BnO
HO
BnO
HO
BnO
SPh
SPh
SPh
N
3
N
N
3
3
7
8
9
N
3
k
O
AcO
BnO
SPh
N
3
10
Scheme 1. Synthesis of building blocks 9 and 10. Reagents and conditions: (a) TfN3, CuSO4, K2CO3, MeOH, H2O, CH2Cl2; (b) Ac2O, DMAP,
pyridine, 83% (two steps); (c) PhSH, BF3 ÆOEt2, CH2Cl2, 95%; (d) NaOMe, MeOH; (e) PhCH(OMe)2, CSA, MeCN, 75% (two steps); (f) NaH, BnBr,
DMF; (g) 80% aq AcOH, CH2Cl2, 60 ꢁC, 96% (two steps); (h) TsCl, pyridine, 95%; (i) NaN3, TBAHS, DMF, 98%; (j) FmocCl, DMAP, pyridine,
50% and (k) Ac2O, pyridine, quant DMAP = 4-dimethylaminopyridine, CSA = (+)-10-camphorsulfonic acid, Bn = benzyl, DMF = N,N-
dimethylformamide, Ts = p-toluenesulfonyl, TBAHS = Bu4N+ HSO4À, Fmoc = 9-fluorenylmethoxycarbonyl.

M. Mizuno et al. / Tetrahedron Letters 47 (2006) 8831–8835
8833
O
C8F17
C8F17
O
N
a
O
O
N
C8F17
HO
H
N
O
O
F
N
N
C8F17
HO
N
H
O
12
O
N
C8F17
C8F17
O
HO
F
11
Cbz(HexF)
O
O
c
b
O
HO
O2N
H
O
N
Cbz(HexF)
N
H
O
F
O
14
13
N3
O
N3
O
d
f
e
FmocO
BnO
HO
BnO
O
O
Cbz(HexF)
Cbz(HexF)
N
N
N3
N3
H
H
15
16
N3
O
N3
O
AcO
BnO
O
BnO
O
N3
Cbz(HexF)
N
N3
H
17
N3
O
O
N3
O
OMe
HO
N
H
g
BnO
O
H
organic
layer
N
O
O
BnO
O
N3
N3
O
18
11
FC72 layer
Scheme 2. Synthesis of aminoglycoside disaccharide derivative 18. Reagents and conditions: (a) see Ref. 18; (b) 4-nitrophenyl chloroformate, Et3N,
CH2Cl2, EtOC4F9; (c) 2-aminoethanol, THF, 80% (two steps); (d) 9, NIS, TfOH, CH2Cl2, (e) 10% piperidine/DMF, FC72; (f) 10, NIS, TfOH,
CH2Cl2, EtOC4F9 and (g) NaOMe, MeOH, EtOC4F9. NIS = N-iodosuccinimide, Tf = trifluoromethylsulfonyl.
HPLC analysis of crude 18 showed four major peaks
(Fig. 2A–D). The product disaccharide was estimated
as the mixture of the four anomeric isomers. These com-
pounds associated with these peaks were isolated and
1
then identified by H NMR as a 18aa (A, 13%), 18ba
(B, 4%), 18ab (C, 11%), 18bb (D, 4%), respectively.23
Finally, compounds 18aa, 18ba , 18ab, and 18bb were
subjected to hydrogenation in the presence of Pd(OH)2/
C to reduce the azido groups and cleave the benzyl and
Cbz groups, giving the corresponding aminoglycoside
compounds 19aa, 19ba, 19ab, and 19bb24 (Scheme 3).
In conclusion, four aminoglycoside derivatives contain-
ing a 2,6-diamino-2,6-dideoxy-D-glucopyranose disac-
charide structure were successfully prepared by using a
Cbz-type heavy fluorous tag. The recyclable fluorous
tag system was applied to Cbz-type fluorous tag, and
fluorous alcohol 11 was recovered in excellent yield.
Figure 2. HPLC profile of the crude disaccharide 18 produced by the
The mixture of anomers was separated by HPLC. The
inhibition potentials of the resulting aminoglycoside
compounds for HIV TAR–Tat interaction are now
fluorous synthesis. Elution conditions: column, GL Sciences Inertsil
SIL 100A (20 · 250 mm); eluent, 8–15% ethanol/n-hexane (v/v),
50 min; Flow rate, 30.0 mL/min.

8834
M. Mizuno et al. / Tetrahedron Letters 47 (2006) 8831–8835
(A)
N3
O
HO
BnO
N3
NH2
O
O
N3
O
HO
a
NH2
O
O
BnO
HO
N3
H2N
O
O
N
H
O
O
H
N
HO
H2N
O
OMe
19αα
18αα
NH2
O
N3
(B)
N3
NH2
O
O
NH2
O
HO
BnO
O
a
a
a
O
BnO
O
HO
HO
O
N3
N3
HO
O
O
N
O
NH2
19βα
H
H2N
H
O
N
NH2
OMe
18βα
O
N3
(C)
NH2
O
O
HO
BnO
N3
HO
HO
O
NH2
O
O
N3
O
O
H2N
N
H
O
O
O
O
BnO
NH2
H
N
HO
N3
OMe
OMe
NH2
19αβ
18αβ
18ββ
O
(D)
NH2
O
N3
NH2
O
N3
O
O
O
HO
HO
O
HO
O
O
HO
O
NH2
N
O
O
BnO
BnO
H
H
N
NH2
NH2
19ββ
N3
N3
O
Scheme 3. Reagents and conditions: (a) H2 (8 atm), Pd(OH)2/C (20 wt%), AcOH, EtOH, 2–5 days. 19aa (53%), 19ba (75%), 19ab (77%), 19 bb (71%).
14. Mizuno, M.; Goto, K.; Miura, T.; Matsuura, T.; Inazu, T.
Tetrahedron Lett. 2004, 45, 3425.
being examined, and the results will be reported in due
course.
15. Goto, K.; Miura, T.; Mizuno, M.; Takaki, H.; Imai, N.;
Murakami, Y.; Inazu, T. Synlett 2004, 2221.
16. Mizuno, M.; Goto, K.; Miura, T. Chem. Lett. 2005, 34,
426.
References and notes
17. Goto, K.; Miura, T.; Mizuno, M. Tetrahedron Lett. 2005,
46, 8293.
1. Kim, M. K.; Nicolaou, D. P. Infect Dis. Ther. 2002, 28,
125.
18. Alper, P. B.; Hung, S.-C.; Wong, C.-H. Tetrahedron Lett.
1996, 37, 6029.
19. Schwinn, D.; Bannwarth, W. Helv. Chim. Acta 2002, 85,
255.
2. Aminoglycoside Antibiotics; Umezawa, H., Hooper, I. R.,
Eds.; Springer: New York, Heidelberg, 1982.
3. Hamasaki, K.; Woo, M.-C.; Ueno, A. Tetrahedron 2004,
41, 8372.
20. EtOC4F9 is a commercially available fluorocarbon solvent
called NovecTM HFE-7200 (3M, Tokyo), that is, miscible
in common organic solvents and fluorous solvents.
21. FC72 is a commercially available fluorocarbon solvent
that consists mainly of perfluorohexane (C6F14) iso-
mers and is called FluorinertTM FC-72.
4. Hamasaki, K.; Ueno, A. Bioorg. Med. Chem. Lett. 2001,
11, 591.
5. Yajima, S.; Shionoya, H.; Akagi, T.; Hamasaki, K.
Bioorg. Med. Chem. 2006, 14, 2799.
´
´
6. Horvath, I. T.; Rabai, J. Science 1994, 266, 72.
7. Vallin, K. S. A.; Zhang, Q.; Larhed, M.; Curran, D. P.;
Hallberg, A. J. Org. Chem. 2003, 68, 6639.
22. Compound 14: 1H NMR (600 MHz, CDCl3): d = 1.77–
1.95 (m, 9H), 2.00–2.16 (m, 8H), 2.40–2.75 (m, 13H), 3.28–
3.49 (m, 15H), 3.51–3.63 (m, 8H), 3.69–3.74 (m, 2H),
4.12–4.35 (m, 5H), 5.13 (s, 2H), 7.42 (s, 2H), 7.81 (s, 2H).
MALDI-TOF-MS: calcd for C95H72F102N8O12Na m/z
[M+Na]+: 3477.4. Found: 3480.2.
8. Studer, A.; Hadida, S.; Ferritto, R.; Kim, S.-Y.; Jeger, P.;
Wipf, P.; Curran, D. P. Science 1997, 275, 823.
9. Handbook of Fluorous Chemistry; Gladysz, J. A., Curran,
´
D. P., Horvath, I. T., Eds.; VCH-Wiley: Weinheim, 2004.
10. Miura, T.; Hirose, Y.; Ohmae, M.; Inazu, T. Org. Lett.
2001, 3, 3947.
1
23. Compound 18aa: H NMR (600 MHz, CDCl3): d = 2.05
(s, 1H), 3.24 (dd, J = 6.2, 9.7 Hz, 1H), 3.32 (dd, J = 4.9,
13.1 Hz, 1H), 3.39–3.44 (m, 2H), 3.45–3.66 (m, 4H), 3.72
(t, J = 9.6 Hz, 1H), 3.79 (s, 3H), 3.81–3.90 (m, 2H), 4.04–
4.07 (t, J = 8.9 Hz, 1H), 4.16–4.21 (m, 2H), 4.72 (d,
J = 10.9 Hz, 1H), 4.87 (d, J = 11.0 Hz, 1H), 4.90 (d,
J = 10.3 Hz, 1H), 4.97 (d, J = 3.4 Hz, 1H), 5.00 (d,
J = 10.3 Hz, 1H), 5.07 (d, J = 13.0 Hz, 1H), 5.27–5.33
11. Miura, T.; Goto, K.; Hosaka, D.; Inazu, T. Angew. Chem.,
Int. Ed. 2003, 42, 2047.
12. Mizuno, M.; Goto, K.; Miura, T.; Hosaka, D.; Inazu, T.
Chem. Commun. 2003, 972.
13. Miura, T.; Goto, K.; Waragai, H.; Matsumoto, H.;
Ohmae, M.; Ishida, H.; Satoh, A.; Inazu, T. J. Org.
Chem. 2004, 69, 5348.

M. Mizuno et al. / Tetrahedron Letters 47 (2006) 8831–8835
8835
(m, 2H), 5.67 (d, J = 3.5 Hz, 1H), 6.71 (s, 1H), 7.30–7.45
(m, 12H), 7.81–7.83 (m, 2H). MALDI-TOF-MS: calcd for
C40H46N14O12Na m/z [M+Na]+: 937.3. Found: 937.9.
3.84 (t, J = 7.6 Hz, 1H), 3.89–3.93 (m, 1H), 4.23
(d,J = 5.5 Hz, 2H), 4.26–4.31 (m, 1H), 4.34 (d,
J = 8.4 Hz, 1H), 4.66 (d, J = 11.0 Hz, 1H), 4.79 (d,
J = 11.7 Hz, 1H), 4.87 (d, J = 11.0 Hz, 1H), 4.94 (d,
J = 11.7 Hz, 1H), 5.14 (s, 2H), 5.26–5.30 (m, 1H), 6.60 (s,
1H), 7.24–7.42 (m, 12H), 7.78–7.79 (m, 2H). MALDI-
TOF-MS: calcd for C40H46N14O12Na m/z [M+Na]+:
937.3. Found: 937.5.
1
Compound 18ab: H NMR (600 MHz, CDCl3): d = 3.03
(dd, J = 6.2, 13.0 Hz, 1H), 3.21–3.29 (m, 4H), 3.34–3.39
(m, 2H), 3.41–3.46 (m, 1H), 3.48–3.54 (m, 2H), 3.57–3.64
(m, 2H), 3.80–3.81 (m, 3H), 3.82–3.87 (m, 1H), 3.88–3.92
(m, 2H), 4.14–4.19 (m, 1H), 4.22–4.26 (m, 1H), 4.36 (d,
J = 8.2 Hz, 1H), 4.69 (d, J = 11.0 Hz, 1H), 4.81 (d,
J = 11.6 Hz, 1H), 4.90 (d, J = 3.4 Hz, 1H), 4.96 (d,
J = 11.6 Hz, 1H), 5.16 (s, 2H), 5.30–5.33 (m, 1H), 7.26–
7.45 (m, 12H), 7.80–7.81 (m, 2H). MALDI-TOF-MS:
calcd for C40H46N14O12Na m/z [M+Na]+: 937.3. Found:
937.7. Compound 18ba: 1H NMR (600 MHz, CDCl3):
d = 3.26 (dd, J = 3.4, 9.6 Hz, 1H), 3.39 (dd, J = 5.5,
13.1 Hz, 1H), 3.43–3.55 (m, 8H), 3.59–3.63 (m, 1H), 3.67
(t, J = 9.7 Hz, 1H), 3.80–3.83 (m, 5H), 3.92–3.98 (m, 1H),
4.24 (d, J = 4.8 Hz, 1H), 4.39 (d, J = 7.5 Hz, 1H), 4.71 (d,
J = 11.7 Hz, 1H), 4.83 (d, J = 10.4 Hz, 1H), 4.96 (d,
J = 11.0 Hz, 1H), 5.06 (d, J = 10.3 Hz, 1H), 5.16 (s, 2H),
5.28–5.32 (m, 1H), 5.63 (d, J = 3.4 Hz, 1H), 6.65 (s, 1H),
7.29–7.45 (m, 12H), 7.80–7.81 (m, 2H). MALDI-TOF-
MS: calcd for C40H46N14O12Na m/z [M+Na]+: 937.3.
Found: 937.5. Compound 18bb: 1H NMR (600 MHz,
CDCl3): d = 2.08 (s, 1H), 3.12 (dd, J = 6.2, 13.0 Hz, 1H),
3.19–3.31 (m, 4H), 3.34–3.53 (m, 8H), 3.64 (d,
J = 11.0 Hz, 1H), 3.70–3.75 (m, 1H), 3.77–3.80 (m, 3H),
24. Compound 19aa: 1H NMR (600 MHz, D2O): d = 2.76–
2.82 (m, 1H), 2.88–2.92 (m, 1H), 2.96–3.06 (m, 1H), 3.15–
3.23 (m, 4H), 3.26–3.35 (m, 3H), 3.41–3.50 (m, 1H),
3.53–3.62 (m, 2H), 3.69–3.73 (m, 1H), 3.81–3.87 (m, 1H),
3.88–3.93 (m, 1H), 4.96–5.04 (m, 1H), 5.29–5.34 (m, 1H).
Compound 19ba: 1H NMR (600 MHz, D2O): d = 2.59–
2.64 (m, 1H), 2.99–3.12 (m, 3H), 3.14–3.19 (m, 2H), 3.22–
3.31 (m, 2H), 3.31–3.37 (m, 2H), 3.49–3.54 (m, 1H),
3.54–3.58 (m, 1H), 3.63–3.63 (m, 1H), 3.67–3.77 (m, 1H),
3.85–3.95 (m, 2H), 4.67–4.42 (m, 1H), 4.93–4.98 (m, 1H).
Compound 19ab: 1H NMR (600 MHz, D2O): d = 2.62–
2.67 (m, 1H), 2.99–3.17 (m, 5H), 3.24–3.33 (m, 3H),
3.46–3.55 (m, 2H), 3.58–3.62 (m, 1H), 3.64–3.71 (m, 2H),
3.72–3.77 (m, 1H), 4.03–4.08 (m, 1H), 4.38–4.40 (m, 1H),
5.46 (d, J = 3.4 Hz, 1H). Compound 19bb: 1H NMR
(600 MHz, D2O): d = 2.61–2.64 (m, 1H), 2.66–2.70 (m, 1H),
3.03–3.18 (m, 4H), 3.21–3.30 (m, 4H), 3.31–3.40 (m, 4H),
3.43–3.48 (m, 1H), 3.48–3.57 (m, 1H), 3.65–3.71 (m, 1H),
3.72–3.78 (m, 1H), 4.01–4.08 (m, 1H), 4.35–4.46 (m, 2H).