A semisynthesis of isepamicin by fragmentation method

Article abstract of DOI:10.1016/j.tetlet.2004.11.130

Garamine derivative, key intermediate, was obtained from acid cleavage of sisomicin derivative. Its subsequent product was glycosylated with 6-azido-2,3,4-tri-O-benzyl-6-deoxy-α-d-glucopyranosyl chloride using silver triflate as a promoter to give isepamicin.

Full text of DOI:10.1016/j.tetlet.2004.11.130

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 607–609
A semisynthesis of isepamicin by fragmentation method
Man Sik Moon,b Sook Jin Jun,b So Ha Lee,a Chan Seong Cheong,a,*
Kwan Soo Kimb and Byung Suk Leec
aMedicinal Chemistry Research Center, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650, Korea
bDepartment of Chemistry, Yonsei University, Shinchon 134, Seoul 120-749, Korea
cKyungdong Pharmaceutical Co., Ltd 535-3, Daeyangri, Yangammyun, Hwasungsi, Kyunggido 445-931, Korea
Received 20 October2004; revised 25 November2004; accepted 26 November2004
Available online 10 December2004
Abstract—Garamine derivative, key intermediate, was obtained from acid cleavage of sisomicin derivative. Its subsequent product
was glycosylated with 6-azido-2,3,4-tri-O-benzyl-6-deoxy-a-D-glucopyranosyl chloride using silver triflate as a promoter to give
isepamicin.
Ó 2004 Elsevier Ltd. All rights reserved.
The aminoglycoside antibiotics are a large and diverse
class of carbohydrate-based substance, which has shown
the extensive clinical application forailments such as
tuberculosis and septicemia.1 Various aminoglycoside
antibiotics such as kanamycin2 in 1957, gentamicin3 in
1964, sisomicin4 in 1970, netilmicin5 in 1975, isepamicin6
in 1978 and arbekacin7 in 1987 have been vigorously
investigated and marketed since the development of
streptomycin8 by Waksman in 1944. Also, many amino-
glycosides exhibit inhibitory activity against HIV virus.9
The ready availability of suitably protected garamine
derivative14,15 made it possible to contemplate the syn-
thesis not only of isepamicin, but also otheraminoglyco-
side derivatives. With these objectives in mind, we wish
to describe the synthesis of isepamicin using 6-azido-
2,3,4-tri-O-benzyl-6-deoxy-a-D-glucopyranosyl chloride
(6-ABGC) as a glycosyl donor, 1-[(2-benzyloxy-3-N-
benzyloxycarbonyl)-L-isoserinyl]-3,300-di-N-benzyloxy-
carbonylgaramine as a glycosyl acceptor and silver tri-
flate as a promoter.
Although resistance10 and the risk of serious side-
effects11 in ototoxicity and nephrotoxicity have reduced
the use of aminoglycoside drug in recent years, these
drawbacks have been met with improved dosing regi-
mens and have stimulated the development of semi-syn-
thetic derivatives such as isepamicin and arbekacin.
Scheme 1 presents a retrosynthetic analysis leading to
the key intermediate used for the synthesis of garamine
derivative and isepamicin. Isepamicin can be divided
into two moieties of glucose and garamine derivatives.
Glucose derivative was synthesized by methyl-a-D-
glucopyranoside, while garamine derivative was synthe-
sized by sisomicin in a few steps.
Isepamicin developed by Schering–Plough6 is a novel
broad-spectrum aminoglycoside, which possesses a high
level of stability to aminoglycoside inactivating enzymes
and low level12 of toxicity to the kidney and innerear.
Schering–Plough synthesized isepamicin from gentami-
cin B,13 which was co-produced in the gentamicin fer-
mentation. Afterthen, the othersynthetic method of
isepamicin was not tried.
Cbz-protected 1 was synthesized by selective acylation
of sisomicin with N-(benzyloxycarbonyloxy)succinimide
(N-BCSI) using the complexing method16 between zinc
acetate and available neighboring amino and hydroxy
group pairs of sisomicin as shown in Scheme 2.
Compound 1 was reacted with (2S)-benzyloxycarbonyl-
3-benzyloxycarbonylamino-propionic acid (BBPA, 9)15
in the presence of hydroxybenzotriazole (HOBT) and
dicyclohexylcarbodiimide (DCC) to afford the coupling
product 2 in 80% yield. The 300-amino group of com-
pound 2 was protected by N-(benzyloxycarbonyloxy)-
succinimide and then hydrolyzed with sulfuric acid to
Keywords: Garamine; Isepamicin; Aminoglycoside; Antibiotics.
*
Corresponding author. Tel.: +82 029585153; fax: +82 029585189;
e-mail: c2496@kist.re.kr
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.11.130

608
M. S. Moon et al. / Tetrahedron Letters 46 (2005) 607–609
NH
2
NH
2
O
NHC
O
NH
2
NHCbz
OH
O
OH
OH
HO
O
OH
NHC
N
3
NHCbz
OH
O
BnO
HO
O
HO
OBn
+
BnO
Cl
OBn
HN CH
3
O
H C
O
3
HO
OH
Isepamicin
N CH
3
O
H C
3
Cbz
OH
Garamine derivative
OH
O
cleavage
OH
HO
OCH
3
OH
NH
2
NH
2
O
NH
2
1
1'
OH
O
NH
2
O
OH
1"
NHCH
3
CH
3
O
OH
Sisomicin
Scheme 1. Retrosynthetic analysis of isepamicin.
NH2
NH2
NHCbz
O
NHCbz
OH
O
NH2
1'
1
NH2
OH
a)
O
O
NH2
NHCbz
OH
O
OH
1"
O
NHCH3
CH3
O
NHCH3
O
CH3
OH
OH
Sisomicin
1
b)
NHCbz
O
O
NH
NHCbz
O
O
NHCbz
OH
NHCbz
NHCbz
OBn
NHCbz
OBn
NH
c)
OH
O
O
NHCbz
OH
NHCbz
OH
O
O
Cbz
NCH3
CH3
NHCH3
O
CH3
O
OH
OH
3
2
d)
N3
O
NH
O
NHCbz
NHCbz
OH
NHCbz
OBn
O
NH
NHCbz
OBn
OH
OBn
e)
f)
BnO
HO
O
Isepamicin
OBn
OH
O
OH
O
Cbz
NCH3
NHCH3
O
CH3
O
CH3
OH
OH
4
5
Scheme 2. Synthesis of isepamicin. Reagents and conditions: (a) Zn(OAc)2, TEA, THF, N-BCSI, 65%; (b) BBPA, DCC, HOBT, MeOH, 80%; (c) N-
BCSI, THF, NEt3, 76%; (d) H2SO4, MeOH, 75%; (e) 6-ABGC, AgOTf, molecularsieve, benzene/1,4-dioxane (1:3, v/v), 52%; (f) 10% Pd/C, H
MeOH/THF (5:1, v/v), 57%.
,
2
afford the garamine derivative 4 in yield of 75%. Com-
pound 3 was extremely labile towards sulfuric acid when
pH reached 1 and the vinylic ether group of sisomicin
derivative 3 was at first rendered susceptible to acid

M. S. Moon et al. / Tetrahedron Letters 46 (2005) 607–609
609
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hydrolysis, leading to the formation of garamine deriva-
tive 4.14 Subsequently glycosylation reaction of com-
pound 4 with 6-azido-2,3,4-tri-O-benzyl-6-deoxy-a-D-
glucopyranosyl chloride17 gave the azide 5. To perform
the glycosidation reaction, Koenigs–Knorr18 method
and trichloroacetimidate method19 were employed and
the reactions were proceeded by the change of solvent,
reaction temperature, catalyst and glycosyl donor. Regio-
selectivity can be generally achieved when glycosyl
donor possesses selectively protected hydroxy groups
and an activating group at the anomeric C atom. There-
fore, it was more favorable than other protecting group
to obtain a-glycosidic product that glycosyl donor in
which the H atom on 2-OH was replaced by a benzyl
group. To obtain a-glycosidic product diastereoselec-
tively, the nucleophilic substitution with glycosyl accep-
tor 4 was conducted in such a way that it proceeded as
completely as possible with retention in the sense of an
SN1 reaction. This can be done in a solvent of low pola-
rity in the presence of an active catalyst such as AgOTf,
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688; (c) Tann, C.-H.; Thiruvengadam, T. K.; Chiu, J. S.;
Colon, C.; Green, M. D. USP 5,442,047.
7. Watanabe, T.; Goi, H.; Hara, T.; Sugano, T.; Tanaka, Y.;
Kazuno, Y.; Matsuhashi, Y.; Yamamoto, H.; Yokota, T.
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AgClO4 orAgClO /Ag2CO3. Among various reaction
4
8. Schatz, A.; Bugie, E.; Waksman, S. A. Proc. Soc. Exp.
Biol. Med. 1944, 55, 66.
9. Park, W. K.; Auer, M.; Jaksche, H.; Wong, C.-H. J. Am.
Chem. Soc. 1996, 118, 10150.
conditions, the best result was obtained by the following
method. To the mixture of 6-azido-2,3,4-tri-O-benzyl-6-
deoxy-a-D-glucopyranosyl chloride and 4 A molecular
˚
sieves in dry benzene–dioxane (3:1, v/v), 4 and silvertri-
flate were added at 0 °C. After stirring for 12 h at room
temperature, silver triflate was again added at 0 °C. The
reaction mixture was stirred for 5 h and quenched with
water. The solution was evaporated and extracted with
chloroform. The concentrated residue was purified by
column chromatography (CHCl3/MeOH, 60:1, v/v) to
give stereoselectively only 5 in 52% yield. Deprotection
of 5 was carried out using hydrogen gas in balloon
in the presence of 10% palladium on charcoal to give
10. Heinemann, J. A.; Ankenbauer, R. G.; Ambile-Cuevas,
C. F. DDT 2000, 5, 195.
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Agents Chemother. 1979, 15, 780; (b) Ohtani, I.; Ohtsuki,
K.; Omata, T.; Ouchi, J.; Saito, T. Chemotherapy (Tokyo)
1977, 25, 2348.
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Weinstein, M. J. Antimicrob. Agents Chemother. 1972, 2,
464.
14. Kugelman, M.; Mallams, A. K.; Vernay, H. F.; Crowe, D.
F.; Tanabe, M. J. Chem. Soc., Perkin Trans. 1 1976, 1088.
15. Moon, M. S.; Jun, S. J.; Lee, S. H.; Cheong, C. S.; Kim,
K. S.; Lee, B. S. Bull. Korean Chem. Soc. 2003, 24, 163.
16. (a) Lee, S. H.; Cheong, C. H. Tetrahedron 2001, 57, 4801;
(b) Nagabhushan, T. L.; Cooper, A. B.; Turner, W. N.;
Tsai, H.; Mc Combie, S.; Mallams, A. K.; Rane, D.;
Wright, J. J.; Reichert, P.; Boxler, D. L.; Weinstein, J. J.
Am. Chem. Soc. 1978, 100, 5253.
1
isepamicin in 57% yield, which showed the specific H
NMR peak of 3.86 (J = 3.86 Hz, H-10) and 3.05 ppm
(J = 3.96 Hz, H-100), respectively. The synthesized
isepamicin was identified by comparison with commer-
cial isepamicin using 1H NMR, 13C NMR and thin layer
chromatography.
In conclusion, we successfully carried out the synthesis
of new garamine derivative 420 as intermediate for the
synthesis of isepamicin. A stereocontrolled synthesis of
the isepamicin has been achieved using the 6-azido-
2,3,4-tri-O-benzyl-6-a-D-glucopyranosyl chloride as a
glycosyl donor, silver triflate as a promoter and suitable
protected garamine derivative 4 as a glycosyl acceptor.
Also, the new garamine analogue 4 is capable to use
fordevelopment of new aminoglycosides antibiotics.
17. (a) Ogawa, S.; Funaki, Y.; Iwata, K.; Suami, T. Bull.
Chem. Soc. Jpn. 1976, 49, 1975; (b) Takagi, Y.; Tsuchiya,
T.; Umezawa, S. Bull. Chem. Soc. Jpn. 1971, 44, 2541.
18. Kikuo, I. Adv. Carbohydr. Chem. Biochem. 1977, 34, 243.
19. Schmidt, R. R.; Willy, K. Adv. Carbohydr. Chem.
Biochem. 1994, 50, 21.
20. Compound 4: Rf: 0.37 (CHCl3/MeOH/NH4OH = 5:1:0.1);
20
D
1
mp: 172–172.5 °C; ½aŠ þ 26:3 (c 0.75, MeOH); H NMR
(600 MHz, MeOH–d4) d 7.35–7.23 (m, 20H), 4.62 (d,
J = 12.0 Hz, 1H), 4.56 (d, J = 12.0 Hz, 1H), 4.26–4.19 (m,
2H), 4.15 (dd, J = 3.6, 9.4 Hz, 1H), 4.02 (m, 1H), 3.89 (m,
1H), 3.69 (dd, J = 4.2, 14.4 Hz, 1H), 3.60 (t, J = 9.6 Hz,
1H), 3.51–3.45 (m, 1H), 3.44–3.38 (m, 2H), 3.26 (m, 1H),
3.17 (dd, J = 12.6, 18.6 Hz, 1H), 2.91 (s, 3H), 1.95–1.88
(m, 1H), 1.44 (m, 1H), 1.00 (s, 2H), 0.95 (s, 1H); 13C NMR
(150 MHz, CDCl3) d 173.32, 173.25, 159.93, 159.58,
158.97, 158.55, 138.78, 138.73, 138.35, 138.29, 138.14,
129.52, 129,45, 129.04, 129.00, 128.93, 128.87, 128.59,
100.90, 100.80, 81.70, 81.33, 79.51, 76.84, 76.73, 76.35,
76.28, 74.89, 74.56, 73.23, 70.75, 68.43, 68.31, 68.27, 67.52,
67.48, 65.92, 60.29, 60.17, 52.90, 50.77, 42.28, 42.20, 35.38,
30.99, 30.75, 22.49, 22.25; IR (KBr) 3282, 1684, 1544,
1274, 1036, 696 cmꢀ1; FAB MS m/z 901.38 (MH).
Acknowledgements
This work was supported by a grant of Kyungdong
Pharmaceutical Co., Ltd.
References and notes
1. (a) Umezawa, H.; Hooper, I. R. Aminoglycoside Antibiot-
ics; Springer: Berlin, Heidelberg, New York, 1982; (b)
Umezawa, S.; Kondo, S.; lto, Y. Aminoglycoside Antibio-