Synthesis of biotinylated OSW-1

Article abstract of DOI:10.1016/j.bmcl.2009.07.062

OSW-1 is a highly potent anticancer natural saponin with an unknown mode of action. To determine its cellular target(s) biotinylated OSW-1 was successfully synthesized in nine steps.

Full text of DOI:10.1016/j.bmcl.2009.07.062

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5166–5168
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of biotinylated OSW-1
a
a
b
b
a,*
Ying Kang , Changgang Lou , Kausar Begam Riaz Ahmed , Peng Huang , Zhendong Jin
a
Division of Medicinal and Natural Products Chemistry, College of Pharmacy, The University of Iowa, Iowa City, IA 52242, USA
Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA
b
a r t i c l e i n f o
a b s t r a c t
Article history:
OSW-1 is a highly potent anticancer natural saponin with an unknown mode of action. To determine its
cellular target(s) biotinylated OSW-1 was successfully synthesized in nine steps.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 9 May 2009
Revised 24 June 2009
Accepted 2 July 2009
Available online 14 July 2009
Keywords:
Synthesis
Biotinylated
Natural product
Saponin
OSW-1
OSW-1, a natural product isolated from the bulbs of Ornithog-
alum saundersiae, a perennial grown in southern Africa, exhibited
extremely potent cytotoxicity against the NCI 60-cell in vitro
be a suitable place to link biotin. This is because two OSW-1’s nat-
ural analogs contain a sugar moiety attached to the C-3 position
and both analogs have the same potency against cancer cell lines
1
1
screen, with a mean IC50 of 0.78 nM (Fig. 1). Its in vitro anticancer
as OSW-1. Therefore, it is hypothesized that the attachment of
activities are from 10 to 1000 times more potent than many well-
known anticancer agents in clinical use, including mitomycin C,
adriamycin, cisplatin, camptothecin, 5-Fu, and even pacilitaxel.
the biotin to the C-3 position of the aglycone would not affect
the binding of OSW-1 with the receptor.
Our original total synthesis strategy was modified for the syn-
thesis of the biotinylated OSW-1 (2). In our previous total synthesis
of OSW-1, the hydroxyl groups in the disaccharide were protected
2
In addition, OSW-1 showed equal potency against cancer cells
resistant to other anticancer agents and displayed a characteristic
anticancer profile whereas non-malignant cells are significantly
3
less sensitive to OSW-1. These factors made OSW-1 an attractive
O
4
,5
synthetic target.
The biological study showed that OSW-1 causes cell death by
apoptosis and its cell-killing is cycle independent.3 It was found
that mitochondria play an important role in mediating the antican-
cer activity in cancer cells, and OSW-1 causes structural damage to
the mitochondrial membrane and cristae, leading to the loss of
transmembrane potential, a significant increase of cytosolic cal-
cium, and activation of calcium-dependent apoptosis. The biologi-
OH
H
O
O
AcO
H
H
O OH
O
HO
HO
HO
1
p-MeOC H CO
6
4
2
Figure 1. OSW-1.
cal investigation suggests that OSW-1 may have
a novel
mechanism of action and represent a new type of drug for cancer
chemotherapy.
3
O
Me
Me
Me
Me
To determine its molecular target(s) in cells a biotinylated
OSW-1 (2) was designed (Fig. 2). The biotinylated OSW-1 offers
the feature of a reversible solid-support reagent when combined
O
S
OH
linker
HN
H
NH
H
Me
O
O
AcO
6
O
O
O
OH
with monomeric-avidin sepharose or avidin-coated solid surface.
H
N
HO
HO
p-MeOC H CO
2
We believe that the C-3 position of the aglycone of OSW-1 should
(CH )
O
2 7
6
4
O
Biotinylated OSW-1 (2)
*
Corresponding author.
E-mail address: zhendong-jin@uiowa.edu (Z. Jin).
Figure 2.
0
960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.062

Y. Kang et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5166–5168
5167
Biotinylated OSW-1 (2)
CH
3
SO
2
Cl, NEt
3
NaN , DMF
3
HO(CH
2
8
) OH
HO(CH
2 8
) OMs
0
ºC, 5 h, 70%
reflux, 5 h, 94%
1
2
13
HOOC(CH2)7N3
O
O
S
PDC, DMF, 2d
0%
Me
Me
4
Me
Me
HO(CH
2
) N
8 3
2 7 3
HOOC(CH ) N
HN
H
NH
H
6
O
OH
14
4
Me
O
O
AcO
(CH2)4CH2O
N
Scheme 3.
O
O
TESO
OTES
TESO
3
HO
p-MeOC6H4CO2
O
5
departure. Deprotection of the TBS group of compound 8 by TBAF
gave C-3 alcohol 9 in 98% yield, which reacted with allyl chlorofor-
mate to provide carbonate 10 in 84% yield. Ketone 10 underwent a
O
Me
Me
Me
Me
OC(NH)CCl3
O
chemo- and stereo-selective reduction by LiAlH
4
at À78 °C to pro-
OH
OH
vide trans-diol 6 in 87% yield. Glycosylation between the protected
Me
AcO
O
O
5a
TESO
aglycone 6 and disaccharide donor 7 afforded the compound 11
O
OTES
TESO
p-MeOC6H4CO2
in 77% yield. The allyl carbonate moiety was chemoselectively
cleaved under palladium[0] conditions to furnish the requisite
fragment 5 in 95% yield.
The preparation of the linker 4 between biotin and OSW-1 is
illustrated in Scheme 3. Diol 12 was mono-mesylated in 70% yield
O
O
6
7
Scheme 1.
by PMB groups.5b To avoid possible problems in the oxidative
N
to give compound 13, which underwent S 2 substitution by so-
dium azide to afford azide 14 in 94% yield. PDC-mediated oxidation
of alcohol 14 provided linker 4 in 60% yield.
deprotection of PMB groups in the presence of the biotin moiety
at the end of the synthesis, we decided to employ the disaccharide
with TES protecting groups that was first synthesized by Yu and his
DCC coupling between alcohol 5 and carboxylic acid 4 followed
by Staudinger reduction of the azide moiety with tri-n-butyl phos-
phine afforded amine 16 in excellent yield (Scheme 4). Amine 16
was coupled with compound 3 to provide fully protected biotinyl-
ated OSW-1 17. Treatment of compound 17 with a catalytic
amount of PPTS in methanol for two days resulted in the deprotec-
tion of the acetal group and three TES groups and furnished the
biotinylated OSW-1 (2) in 98% yield.
5
a
coworkers. The retrosynthetic analysis of the biotinylated OSW-1
(2) is outlined in Scheme 1.
The synthesis of the key fragment 5 is outlined in Scheme 2.
Compound 8, an advanced intermediate in the synthesis of the pro-
tected aglycone of OSW-1 in our total synthesis,5b was the point of
To test if biotinylated OSW-1 (2) has any biological activity, we
used MTT assay to evaluate its anti-proliferative effect in several
human cancer cell lines. As shown in Figure 3, biotinylated OSW-
O
O
O
O
OH
O TBAF, THF
OH
O
1
exhibited potent inhibitory activity against human leukemia cells
1
2 h, 98%
HO
8
9
TBSO
O
O
O
O
4
, DCC, DMAP, 25 °C
CH2Cl2, 2 d, 87%
O2CCl
5
OH
O
O
OH
O
O
AcO
Pyridine, THF, 20 h, 84%
O
TESO
OTES
O
TESO
_
N3(CH2)7COO
p MeOC6H4CO2
1
0
1
5
O
O
O
O
O
O
n
LAH, THF, -78 °C
P Bu3, H2O, THF
12 h, 90%
OH
OH
OH
3
0 min, 87%
O
O
O
AcO
O
TESO
O
OTES
TESO
_
6
NH2(CH2)7COO
6 4 2
p MeOC H CO
OC(NH)Cl3
O
O
O
1
6
O
AcO
O
O
O
O
TESO
OTES
HN
H
NH
H
TESO
_
O
p MeOC
6
H
4
CO
2
7
O
OH
S
(CH2)4CON
7
, TMSOTf, CH2Cl2
O
O
O
AcO
3
-
20-25 ºC, 1 d, 77%
O
O
OTES
O
TESO
3
, Et3N, DMF, 1 d, 77%
O
O
TESO
_
O
O
p MeOC6H4CO2
1
1
O
S
OH
O
O
O
HN
H
NH
H
O
AcO
p-O2NC6H4OH
O
O
TESO
OTES
OH
TESO
(
CH2)4CONH(CH2)7CO2
_
Bu3SnH, Pd(PPh3)4, THF, 3 h
5%
p MeOC6H4CO2
O
O
O
1
7
AcO
9
O
TESO
_
OTES
PPTS, CH3OH, 2 d, 98%
TESO
HO
p MeOC6H4CO2
5
2
Scheme 2.
Scheme 4.

5
168
Y. Kang et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5166–5168
1
00
100
80
60
40
20
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
0
100 101 102 103 104 105 106
Drug concentration (pM)
1
00 101 102 103 104 105 106
Drug concentration (pM)
100 101 102 103 104 105 106
Drug concentration (pM)
1
00
100
80
60
40
20
80
60
40
20
0
0
1
00 101 102 103 104 105 106
Drug concentration (pM)
100 101 102 103 104 105 106
Drug concentration (pM)
Figure 3. Human leukemia cells (HL-60), pancreatic cancer cells (Panc1 and AsPC1), and melanoma cells (A375 and WM35) were incubated with the indicated concentrations
of biotinylated OSW-1 for 72 h. Cell growth inhibition was measured by MTT assay. Each data point represents the average value of triplicate determinations.
(
HL-60), pancreatic cancer cells (Panc1 and AsPC1), and melanoma
cells (A375 and WM35). The IC50 values ranged from 0.1 nM to
.1 nM, indicating that this compound is highly potent in inhibit-
References and notes
1.
Mimaki, Y.; Kuroda, M.; Kameyama, A.; Sashida, Y.; Hirano, T.; Oka, K.;
1
Maekawa, R.; Wada, T.; Sugita, K.; Beutler, J. A. Bioorg. Med. Chem. Lett. 1997,
ing cancer cell growth, like the parent natural product OSW-1.
The biological testing suggests that the attachment of biotin to
the C-3 position of the aglycone does not significantly affect the
interaction of OSW-1 with its putative target in the cells.
7
, 633. and references cited therein.
2. For the GI50, TGI, and LC50 values of OSW-1 against the NCI 60 cell-line
tumor panel, see the Supporting Information of the following reference:
Kuroda, M.; Mimaki, Y.; Yokosuka, A.; Sashida, Y.; Beutler, J. A. J. Nat. Prod.
2001, 64, 88.
In summary, the biologically active biotinylated OSW-1 has
been successfully synthesized from compound 8 in nine steps in
very good yield. This synthetic approach can also be used in the
preparation of other OSW-1 bioconjugates, which will be very use-
ful in the pharmacological and medicinal investigation of OSW-1.
Application of the biotinylated-OSW-1 in the search of OSW-1’s
cellular target(s) is underway, and will be reported in due course.
3. Zhou, Y.; Garcia-Prieto, C.; Carney, D.; Xu, R.; Pelicano, H.; Kang, Y.; Yu, W.; Lou,
C.; Kondo, S.; Liu, J.; Harris, D.; Estrov, Z.; Keating, M. J.; Jin, Z.; Huang, P. J. Natl.
Cancer Inst. 2005, 97, 1781.
4.
For the synthesis of OSW-1 aglycone, see: (a) Guo, C.; Fuchs, P. L. Tetrahedron
Lett. 1998, 39, 1099; (b) Guo, C.; LaCour, T. G.; Fuchs, P. L. Bioorg. Med. Chem. Lett.
1999, 9, 419; (c) Morzycki, J. W.; Gryszkiewicz, A.; Jastrzebska, I. Tetrahedron
Lett. 2000, 41, 3751; (d) Xu, Q.; Peng, X.; Tian, W. Tetrahedron Lett. 2003, 44,
9375.
5
.
For the total synthesis of OSW-1, see: (a) Deng, S.; Yu, B.; Lou, Y.; Hui, Y. J. Org.
Chem. 1999, 64, 202; (b) Yu, W.; Jin, Z. J. Am. Chem. Soc. 2001, 123, 3369; (c) Yu,
W.; Jin, Z. J. Am. Chem. Soc. 2002, 124, 6576; (d) Morzycki, J. W.; Wojtkielewicz,
A. Carbohydr. Res. 2002, 337, 1269; (e) Shi, B.; Tang, P.; Hu, X.; Liu, J. O.; Yu, B. J.
Org. Chem. 2005, 70, 10354; (f) Tsubuki, M.; Matsuo, S.; Honda, T. Tetrahedron
Lett. 2008, 49, 229; (g) Xue, J.; Liu, P.; Pan, Y.; Guo, Z. J. Org. Chem. 2008, 73, 157.
Sche, P. P.; McKenzie, K. M.; White, J. D.; Austin, D. J. Chem. Biol. 1999, 6, 707. and
references cited therein.
Acknowledgment
This work was supported by a Grant (5R21CA105073-02) from
the National Institutes Health.
6
.