Syntheses and biological activities of 3′-azido disaccharide analogues of daunorubicin against drug-resistant leukemia

Article abstract of DOI:10.1021/jm050916m

Anthracyclines, such as daunorubicin (DNR) and doxorubicin (Dox), are widely used for cancer therapy but are limited by drug resistance and cardiotoxicity. To overcome drug resistance, we synthesized a novel class of disaccharide analogues of DNR against

Full text of DOI:10.1021/jm050916m

1792
J. Med. Chem. 2006, 49, 1792-1799
Syntheses and Biological Activities of 3′-Azido Disaccharide Analogues of Daunorubicin against
Drug-Resistant Leukemia
Guisheng Zhang,†,# Lanyan Fang,‡ Lizhi Zhu,† Yanqiang Zhong,§ Peng George Wang,*,† and Duxin Sun*,‡
Department of Chemistry and Biochemistry and DiVision of Pharmaceutics, College of Pharmacy, The Ohio State UniVersity,
Columbus, Ohio 43210, and School of Chemical and EnVironmental Sciences, Henan Normal UniVersity, Xinxiang,
Henan 453007, P. R. China
ReceiVed September 15, 2005
Anthracyclines, such as daunorubicin (DNR) and doxorubicin (Dox), are widely used for cancer therapy
but are limited by drug resistance and cardiotoxicity. To overcome drug resistance, we synthesized a novel
class of disaccharide analogues of DNR against drug-resistant leukemia. In these disaccharide analogues
(1-6) the first (inner) sugar in the carbohydrate chain is a 3-azido-2,3,6-trideoxy-L-lyxo-R-hexopyranose;
the second (outer) sugars that are linked via R(1f4) to the first sugar are a series of uncommon sugars.
Their cytotoxicities were examined in drug-sensitive leukemia cells K562 and doxorubicin-resistant K562/
Dox cells by MTS assay. In drug-sensitive cells, compounds 1-6 were found to be active against leukemia
K562 cells with IC50 in the nanomolar range (200-1100 nM), while compounds 2-5 with 2,6-dideoxy
sugars showed better activity than compounds 1 and 6 with 2,3,6-trideoxy sugars. In doxorubicin-resistant
K562/Dox cells, compounds 1, 3, and 5 exhibited much better activities (with IC50 between 0.29 and 2.0
µM) than DNR (with IC50 > 5 µM). Compound 3 emerged as the most active compound, showing at least
17-fold higher activity against drug-resistant cells than parent compound DNR. The IC50 values of compound
3 in both drug-sensitive and drug-resistant cells are identical, which indicates that compound 3 completely
overcomes drug resistance. Structure-activity relationship (SAR) studies showed that the substitution and
orientation of the 3-OH group in the second sugar significantly influence its activity against drug-resistant
leukemia. These results suggest that sugar modifications of anthracyclines change their activity and overcome
drug resistance.
Introduction
and configurational modifications on the sugar moiety of anthra-
cyclines markedly changed their anticancer activity, toxicity,
the sequence specificity of DNA break sites, and other cellular
process/pathway besides topo II.18 Indeed, modifications on the
sugar structures have led to the second generation of doxorubicin
analogues with promising clinical anticancer efficacy, such as
the monosaccharides epirubicin and idarubicin.19-21 How-
ever, these new analogues still showed MDR-mediated drug
resistance.
The anthracyclines, such as DNR and doxorubicin (Dox)
(Figure 1), are among the most potent and clinically used anti-
cancer agents in cancer chemotherapy.1 Although anthracyclines
are widely used in cancer therapy, two major problems limit
their clinical application: cardiotoxicity and drug resistance.2,3
One of the mechanisms for drug resistance of anthracyclines
in cancer cells is mediated by an ABC transporter protein (P-
glycoprotein, P-gp, MDR1, ABCB1).2-5 P-gp is overexpressed
in many drug-resistant cancer cells.2,3,6-11 P-gp actively exports
a wide range of drugs from cancer cells, which include anti-
cancer drugs anthracyclines, vinca alkaloids, epipodophyllo-
toxins, and taxanes; HIV-1 protease inhibitors; immuno-
suppressants; antibacterial reagents; antifungals; and cardiac
glycosides.12-15 Therefore, P-gp decreases intracellular drug
concentration in cancer cells and thus induces drug resistance.
In the search for better therapeutic agents, a wealth of data
have been published on the SAR of the aglycone portion and
carbohydrate moiety of anthracyclines over the past 30 years.
It has been known that the carbohydrate moiety is a critical
component for anticancer activities. The orientation of the sugar
is critical for DNA binding. R-Glycoside is a required common
motif for anthracyclines’ anticancer activities, while the â-
anomer is even less active than the aglycone itself.16,17 Chemical
Recently, considerable interest in disaccharide anthracyclines
has emerged. In the third-generation anthracycline analogues,
a novel disaccharide analogue MEN1075522-24 (MEN, Figure
1) has been found to show a different activity spectrum against
doxorubicin-resistant tumors compared to doxorubicin. MEN
has the first sugar without the 3′-amino group, substituted for
a hydroxyl group, and the second sugar, daunosamine, linked
via R(1-4) to the first sugar. In comparison, MAR70 (MAR,
Figure 1), a DNR disaccharide analogue, did not show signifi-
cant antitumor activity compared to the parent drugs.1 MAR,
similar to DNR in the aglycone, does not bear the 14-hydroxyl
group. The first sugar in the carbohydrate chain is daunosamine,
like in the parent compounds DNR and doxorubicin; the second
sugar linked via R(1-4) to the first sugar is 4′-epi-2′-
deoxyfucose. MEN and MAR have been shown to exhibit
different antitumor activities compared with the parent com-
pounds doxorubicin and DNR, respectively. Very interestingly,
the crystal structures of MEN and MAR with the same DNA
hexamer suggest that the differences in biological activity
between MEN and MAR depend on the different DNA binding
properties of the sugar moiety.25 In the MAR complex both
sugar rings lie in the minor groove spanning four base pairs. In
the complex of MEN and DNA hexamer (CGATCG),26 two
* To whom correspondence should be addressed. For P.G.W.: phone,
(614) 292-9884; fax, (614) 688-3106; e-mail, wang.892@osu.edu. For
D.S.: phone, (614) 292-4381; fax, (614) 292-7766; e-mail, sun.176@osu.edu.
† Department of Chemistry and Biochemistry, The Ohio State University.
# Henan Normal University.
‡ Division of Pharmaceutics, The Ohio State University.
§ Present address: Department of Pharmaceutics, College of Pharmacy,
The Second Military Medical University, Shanghai 200433, China.
10.1021/jm050916m CCC: $33.50 © 2006 American Chemical Society
Published on Web 02/02/2006

3′-Azido Disaccharide Analogues
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5 1793
Figure 1. Structures of daunorubicin, doxorubicin, MAR 70, and MEN 10755.
different DNA binding sites were observed. In one binding site,
the disaccharide resides in the DNA minor groove; in the other
binding site, the second sugar protrudes from the DNA helix
and is linked to guanine of another DNA molecular through
hydrogen bonds. This peculiar behavior suggests that the second
sugar in MEN may interact with other cellular targets such as
topoisomerase.26 In addition, the capability of the second sugar
to protrude out of the minor groove is related to the properties
of the first sugar. If daunosamine is the first sugar linked to the
aglycone, as in the MAR complex, the basic 3′-amino group
contributes an electrostatic interaction to the binding free energy.
This additional interaction further stabilizes the position of the
first sugar, which lies deeply in the minor groove and makes it
difficult for the second sugar to protrude out of the minor
groove. Disaccharide analogues lacking a basic amino group at
the 3′ position in the first sugar, as in the MEN, are more
flexible, and the second sugar will not participate in the DNA
binding but protrude out of the minor groove to influence
external interactions. These interactions could play an important
role in the formation of the drug-DNA-topoisomerase complex
and may affect the ability of the drug in poisoning both
topoisomerases I and II. The interactions with other cellular
targets involved in multidrug resistance genes may also be
affected.25
On the basis of this discovery, a rational design for developing
new disaccharide anthracycline drugs has emerged: replacing
the 3-amino group of the first sugar with a neutral group and
diversifying the second sugar motif with uncommon sugars. The
rationale for modifying the sugar moiety in new anthracycline
analogues is based on the potential functions of the uncommon
sugar structure in anthracyclines and their significant biological
effects. Our results and others have demonstrated that sugar
structures in many anticancer natural products provide an
important function in DNA binding and topoisomerase I/II (topo
I/II) inhibition.27-33 In our previous work, it has been found
that the anticancer activities of the disaccharide analogues of
anthracyclines correlated with their ability to target topo II
mediated genomic DNA damage in vivo. Analogues with
various terminal 2,6-dideoxy showed 30- to 60-fold higher
anticancer activity than those with 2-deoxy- or 6-deoxy sugar.32
These results suggested that the second sugar of disaccharide
analogues should possess 2,6-dideoxy with R-linkage to the first
sugar to exhibit better anticancer activity.
In the present study, we propose to synthesize a series of
anthracyclines with modified disaccharides to improve the
pharmacological efficacy, to overcome MDR-mediated drug
resistance, and to obtain more information on the SAR of
uncommon sugars as the second sugar moiety of disaccharide
anthracyclines. Therefore, we designed six novel disaccharide
analogues of DNR (Figure 2) by connecting 2,6-dideoxy sugars
to the first sugar to reveal its function in anticancer activity
Figure 2. Synthesized compounds.
and to overcome drug resistance. In these compounds, the first
sugar is an 3-azido-2,3,6-trideoxy-L-lyxo-R-hexopyranose; the
second sugar linked via R(1f4) to the first sugar is a series of
uncommon sugars including four 2,6-dideoxy sugars and two
2,3,6-trideoxysugars. The rationale for introducing the azido
group into the first sugar is that the azido group is a neutral
group with high electron density, which might avert P-gp
recognition to overcome drug resistance. Indeed, our previous
research has shown that replacing the amino group on DNR
with an azido group can avert the binding of P-gp and overcome
multidrug resistance (Fang, L.; Zhang, G.; et al. J. Med. Chem.,
in press). The cytotoxicities of the synthesized compounds
were examined in drug-sensitive leukemia cells K562 and
doxorubicin-resistant K562/Dox cells by MTS assay. Indeed,
different uncommon sugars in disaccharide analogues of dauno-
rubicin showed distinct cytotoxicity against drug-resistant cancer
cells.

1794 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5
Zhang et al.
Scheme 1a
a Reagents and conditions: (a) K2CO3, CuSO4,TfN3 solution; (b) (CF3CO)2O/pyridine, -20 °C, 15 min; (c) PhSH, BF3‚Et2O/CH2Cl2, 0 °C, 2 h.
Scheme 2a
effective for the synthesis of these types of disaccharide
anthracyclines.
The synthetic routes of glycosyl acceptors (7 and 8) and
glycosyl donors are outlined in Scheme 1. The glycosyl acceptor
8 was readily prepared by treatment of DNR with TfN3
solution34 in 70% yield. Treatment of DNR with trifluoroacetic
anhydride in pyridine at -20 °C for 15 min gave the glycosyl
acceptor 7 in 95% yield.32 The corresponding glycosyl donors
were prepared from their corresponding precursors (compounds
9-14). The acetyl group was used for protecting the hydroxyl
groups present in the sugar molecule because they were
cleavable under 0.1 M NaOH in THF, which allowed the acid
and strong base sensitive aglycone moiety in the anthracycline
molecule not to be affected in the final deprotection manipula-
tions. As shown in Scheme 3, after treatment with phenylthiol
in the presence of BF3‚Et2O at 0 °C for 2 h, the desired sugar
donors (compounds 15-20) were obtained in excellent yields.
The thiolglycosides were obtained as a mixture of R- and
â-isomers. Since both isomers are able to be used for the
glycosylation to produce the desired R-linked daunorubicin
derivatives, separation of them was unnecessary. Previous
research32 has found that the tertiary hydroxyl group would not
affect further glycosylation; thus, compound 13 can be directly
converted to the sugar donor 19. With the glycosyl acceptors
and donors in hand, the glycosylation was subsequently
performed. The mixture of glycosyl acceptors (7 and 8) and
donors 15-20 in the presence of TTBP and 4 Å molecular
sieves was treated with AgPF6 at 0 °C for 2-4 h to give the
products 21-26 in good yields (Schemes 2 and 3). Glycosyl-
ation of 8 with glycosyl donors 15 and 16 gave exclusively the
R-products 21 and 22 in yields of 62% and 52%, respectively.
a Reagents and conditions: (a) TTBP, AgPF6/ CH2Cl2, 0 °C; (b) 0.1 M
NaOH/THF, 0 °C.
Results and Discussion
Chemistry. Our results and others have demonstrated that
the optimal configuration of disaccharide analogues of anthra-
cyclines should be an uncommon sugar linked to the 4 position
of the first sugar through an R(1f4) linkage.22-25,32 Indeed,
natural anthracycline analogues often contain two or more sugars
connected by axial (1f4) linkage. Therefore, for the synthesis
of 3′-azido disaccharide analogues of daunorubicin, the second
uncommon sugars have to be introduced stereoselectively. In
our previous work, we developed a concise promoter system
AgPF6/TTBP (2,4,6-tert-butylpyrimidine) of 2-deoxythioglyco-
sides for syntheses of the disaccharide anthracyclines.32 This
protocol produced the desired R-glycosidic bond with good
yields.
In this work, two strategies were investigated to produce the
3′-azido disaccharide analogues of DNR. Both of them are based
on glycosylation using our catalyst system (AgPF6/TTBP). One
strategy was to transform the amino group of DNR to an azido
group through Wong’s method34 to produce 3′-azidodeamino-
daunorubicin (8) as a glycosyl acceptor for the glycosylation
with the second 2,6-dideoxy sugars (Scheme 2). The second
one was to apply 3′-N-trifluoroacetyldaunorubicin (7) as the
glycosyl acceptor for the glycosylation reaction. The amino
group was converted to an azido group after glycosylation and
deprotection (Scheme 3). Both strategies were proven to be
1
The H NMR data indicated that the desired R-linkage was
formed predominantly R/â > 5:1. Mild deprotection of the ester
groups with 0.1 M NaOH in THF afforded the final products 1
and 2 in yields of 70%, and 60%, respectively. Condensation
of 7 with glycosyl donors 18 and 20 exclusively formed the
R-products 24 and 26 with yields of 81% and 82%, respectively.
However, condensation of 7 with the glycosyl donors 17 and
19 gave the anomeric mixtures (R/â ) 2:1) with yields of 83%
and 60%, respectively. After glycosylation, deprotection of the
desired disaccharide intermediates 21-26 with 0.1 M NaOH
in THF followed by treatment with TfN3 solution in CH2Cl2

3′-Azido Disaccharide Analogues
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5 1795
Scheme 3a
a Reagents and conditions: (a) TTBP, AgPF6/ CH2Cl2, 0 °C; (b) 0.1 M NaOH/THF, 0 °C; (c) K2CO3, CuSO4,TfN3 solution.
Figure 3. Cytotoxicity of synthesized compounds on K562 and K562/Dox cells.
afforded the final compounds 3, 4, 5, and 6 with overall yields
In drug-resistant K562/Dox cells, MDR1 mRNA was induced
of 53%, 50%, 43%, and 37%, respectively.
by 600-fold higher than drug-sensitive K562 cells as measured
by real-time PCR (data not shown). The 2000-10000 cells were
incubated with 0.001-5 µM DNR and its derivatives for 72 h.
Then 20 µL of MTS/PMS assay solution was added to each
well and the absorbance was recorded. The cell survival was
calculated as a percentage of cell control group without
treatment. The anticancer activities are summarized in Figure
3 and Table 1. The IC50 values were calculated by WinNonlin
4.1 (Pharsight) from the dose-response curves of percentage
Biology. Cytotoxicity. The anticancer activities of these
compounds were examined in leukemia cells K562 and doxo-
rubicin-resistant K562/Dox cells by MTS assay as described.35-37
The drug-resistant K562/Dox cell line was induced by doxo-
rubicin treatment. The cell line was cultured in 0.1 µM
doxorubicin 1 week per month, followed by 10 days of
culture without doxrubicin before experiment. This is to main-
tain similar high levels of P-gp expression in each experiment.

1796 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5
Zhang et al.
Table 1. Cytotoxicity (IC50) and Drug Resistance Index (DRI) of Disaccharide Daunorubicins and DNR
compounds
1
2
3
4
5
6
8
DNR
IC50 in K562 (µM)
IC50 in K562/Dox (µM)
DRI
0.787
1.926
2.45
0.287
5.437
18.94
0.278
0.289
1.04
0.225
12.070
53.64
0.448
1.628
3.63
1.132
6.388
5.64
0.075
1
13.3
0.015
>5
>333
of cell growth with the model
higher activity against drug-resistant cells than the parent
compound (DNR). SAR studies showed that the substitution
and orientation of the 3-OH group in the second sugar
significantly influence its activity against drug-resistant cancer
cells. These data indicate that chemical modification of the sugar
structures of anthracyclines not only changes the anticancer
activity but also overcomes drug resistance.
C
E ) Emax - (Emax - E0)
C + EC50
In drug-sensitive cells, compounds 1-6 were found to be
active against leukemia K562 cells with IC50 values in the
nanomolar range (200-1100 nM); yet their IC50 values are
higher than that of parent compound DNR (15 nM). Compounds
2-5 with 2,6-dideoxy sugars showed 3- to 4-fold better activity
than compounds 1 and 6 with 2,3,6-trideoxy sugars. These
results combined with our previous results32 indicate that 2,6-
dideoxy sugars are the best choice to modify the sugar chain of
disaccharide anthracyclines compared with 2-deoxy-, 6-deoxy-,
and 2,3,6-trideoxy sugars.
In doxorubicin-resistant K562/Dox cells, compounds 1, 3, and
5 exhibit much better activities (with IC50 ) 0.29-2.0 µM) than
DNR (with IC50 > 5 µM). The drug resistance index (DRI, ratio
of IC50 in drug-resistant cells to IC50 in drug-sensitive cells) is
a good indicator of the drug’s ability to overcome resistance.
The smaller DRI indicates better capacity to overcome drug
resistance. As summarized in Table 1, DRI values of compounds
1-6 were 6.2- to 320-fold lower than that of DNR with a value
of 333. In comparison, monosaccharide daunorubicin with a
3-azido sugar (compound 8) also showed strong cytotoxicity
against drug-resistant K562 with a DRI of 13.3 (Table 1).
Among the synthesized compounds, compound 3 emerged as
the most active compound against drug-resistant cells with at
least 17-fold higher activity than DNR. It completely overcomes
the drug resistance in this leukemia cell line (DRI ) 1.04, 320-
fold lower than that of parent compound DNR). It is worthy to
be further evaluated as a new drug candidate.
Compound 2 with a 3′′-equatorial hydroxyl group and
compound 3 with a 3′′-equatorial methoxyl group possess similar
sugar moieties and showed similar activity in drug-sensitive
cells. However, compound 3 exhibited 18-fold higher activity
against doxorubicin-resistant cells than compound 2. The
substitution of hydrogen atom in the equatorial 3-OH group of
the second sugar with methyl group resulted in a significant
increase of activity against doxorubicin-resistant cells. In
contrast, compound 5 with a 3′′-axial hydroxyl group exhibited
14-fold higher activity against drug-resistant K562 than com-
pound 4 with a 3′′-axial methoxyl group. These data suggest
that the substituation and orientation of the 3-OH group in the
second sugar may significantly influence its binding to P-gp
and activity against drug-resistant cells. Further SAR studies
are required to clarify this finding.
Experimental Section
Chemistry. All solvents were dried with a solvent-purification
system from Innovative Technology, Inc. All reagents were used
as received from commercial sources. Analytical TLC was carried
out on E. Merck silica gel 60 F254 aluminum-backed plates.
Preparative TLC was carried out on EMD Chemicals, Inc. silica
gel 60 F254 plates (20 cm × 20 cm, 1 mm). The 230-400 mesh
size of the same absorbent was utilized for all chromatographic
1
purifications. H and 13C NMR spectra are at the indicated field
strengths. The high-resolution mass spectra were recorded at The
Ohio State University Campus Chemical Instrumentation Center.
3′-Azidodaunorubicin (8). Daunorubicin hydrochloride (5.24
g, 9.3 mmol) was dissolved in water (30 mL) and treated with
potassium carbonate (1.92 g, 13.9 mmol) and CuSO4‚5H2O (14
mg, 88 µmol). MeOH (60 mL) was added to the sugar solution,
and the TfN3 solution was made using 2 equiv of Tf2O.34 Then,
adequate MeOH was added to homogeneity. The mixture was stirred
overnight. The mixture was diluted with H2O (100 mL) and
extracted with CH2Cl2. The combined extractions were dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
purified through a silica gel column using MeOH/CH2Cl2 (1:50).
Product 8 was obtained as a red solid (4 g, 70%): HRMS (M +
Na)+ (ESI+) calcd for C27H27N3O10Na+ 576.1589, found 576.1612.
1H NMR (500 MHz, CDCl3) δ 13.95 (1H, s), 13.19 (1H, s), 7.98
(1H, d), 7.74 (1H, t), 7.36 (1H, d), 5.54 (1H, d, J ) 3.6 Hz, H-1′),
5.23 (1H, d, J ) 1.9 Hz, H-7), 4.37 (1H, s), 4.10 (1H, m), 4.05
(3H, s), 3.69 (1H, br), 3.60 (1H, m), 3.15 (1H, d), 2.87 (1H, d),
2.38 (3H, s), 2.28 (1H, m), 2.09 (2H, m), 1.91 (1H, m), 1.30 (3H,
d). 13C NMR (125 MHz, CDCl3) δ 211.5, 186.9, 186.7, 161.1,
156.3, 155.7, 135.7, 135.5, 134.2, 133.9, 120.8, 119.8, 118.5, 111.5,
111.3, 100.6, 76.7, 70.1, 69.5, 67.1, 56.8, 56.7, 34.9, 33.3, 28.5,
24.7, 16.8.
General Procedure for Preparation of the Glycosyl Donors
(15-20). To a stirred solution of acetated sugar 12 (0.2 g, 0.77
mmol) in CH2Cl2 (5.0 mL) at 0 °C were added benzenethiol (0.1
mL, 0.98 mmol) and BF3‚Et2O (0.11 mL, 0.87 mmol). The reaction
mixture was allowed to warm slowly to room temperature. After
the mixture was stirred for 4 h, aqueous NaOH (0.1 M, 10 mL)
was added to quench the reaction. Then the reaction mixture was
washed with water. The aqueous layer was extracted with CH2Cl2,
and the combined organic layers were dried over MgSO4 and
concentrated under vacuum. The crude product was purified by
flash column chromatography, giving compound 18 as a syrup (0.23
g, 97% yield).
Conclusion
General Procedure for the Preparation of the Protected
Disaccharide Analogues of Daunorubicin (21-26). A mixture
of sugar donor (4.8 mmol), aglycone (7.2 mmol), TTBP (17.3
mmol), and molecular sieves (4 Å, <5 µm, freshly activated) in
CH2Cl2 (50 mL) was stirred at room temperature for 2 h under N2,
then cooled to 0 °C (ice bath). Powdered AgPF6 (17.3 mmol) was
added and stirred for 3 h. Subsequently pyridine (23 mL) was added,
and the mixture was stirred for a further 0.5 h. Filtration (through
a Celite pad), concentration, and chromatographic purification
provided the products.
In summary, we have developed two effective approaches to
synthesize these novel disaccharide analogues from the parent
DNR using AgPF6/TTBP as a mild activating system for
glycosylation with 2,6-dideoxythioglycosides. A series of the
novel disaccharide analogues have been synthesized and evalu-
ated for their cytotoxicity against drug-resistant leukemia.
Compound 3 emerged as the most active compound, which
completely overcomes drug resistance with at least 17-fold

3′-Azido Disaccharide Analogues
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5 1797
7-[4-O-(4-O-Acetyl-2,3,6-trideoxy-R-L-erythro-hexopyranosyl)-
3-azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]daunorubi-
cinone (21). Pure 21 was obtained as a red solid with a yield of
62% (separated on a column of silica gel, MeOH/CH2Cl2 1:150).
HRMS (M + Na)+ (ESI+) calcd for C35H39N3O13Na+ 732.2375,
found 732.2378. 1H NMR (500 MHz, CDCl3) δ 13.84 (1H, s), 13.07
(1H, s), 7.90 (1H, d, J ) 7.7 Hz), 7.70 (1H, t, J ) 8.1 Hz), 7.31
(1H, d, J ) 8.5 Hz), 5.49 (1H, d, J ) 3.0 Hz, H-1′), 5.17 (1H, s,
H-7), 4.82 (1H, s, H-1′′), 4.39 (2H, m), 4.16 (1H, m), 4.04 (1H,
m), 4.02 (3H, s), 3.71 (2H, m), 3.01 (1H, d, J ) 18.6 Hz), 2.78
(1H, d, J ) 18.6 Hz), 2.36 (3H, s), 2.23 (1H, m), 2.09-1.78 (11H,
m), 1.22 (3H, d, J ) 6.5 Hz), 0.1.11 (3H, d, J ) 6.2 Hz). 13C
NMR (125 MHz, CDCl3) δ 211.5, 186.8, 186.4, 170.4, 160.9, 156.3,
155.6, 135.7, 135.3, 134.2, 133.9, 120.7, 119.7, 118.4, 111.3, 111.2,
100.6, 98.2, 76.7, 75.1, 73.5, 69.9, 67.9, 67.6, 56.7, 56.6, 34.9, 33.2,
29.6, 29.1, 24.7, 24.1, 21.2, 17.9, 17.5.
7-[4-O-(3,4-O-Diacetyl-2,6-dideoxy-R-L-arabino-hexopyrano-
syl)-3-azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]daunorubi-
cinone (22). The pure 22 was obtained as a red solid with a yield
of 52% (separated on a column of silica gel, MeOH/CH2Cl2 1:150).
HRMS (M + Na)+ (ESI+) calcd for C37H41N3O15Na+ 790.2430,
found 790.2423. 1H NMR (500 MHz, CDCl3) δ 13.94 (1H, s), 13.23
(1H, s), 8.00 (1H, d, J ) 7.7 Hz), 7.75 (1H, t, J ) 8.1 Hz), 7.37
(1H, d, J ) 8.5 Hz), 5.52 (1H, s, H-1′), 5.25 (1H, m), 5.24 (1H, s,
H-7), 4.95 (1H, d, J ) 3.3 Hz, H-1′′), 4.69 (1H, t, J ) 9.6 Hz),
4.40 (1H, br), 4.21 (1H, m), 4.04 (5H, m), 3.79 (1H, d, J ) 12.6
Hz), 3.68 (1H, s), 3.20, (1H, d, J ) 18.7 Hz), 2.92 (1H, d, J )
18.4 Hz), 2.38 (3H, s), 2.37 (1H, m), 2.26 (1H, m), 2.12-1.95
(8H, m), 1.85 (2H, m), 1.24 (3H, d, J ) 6.0 Hz), 1.15 (3H, d, J )
6.2 Hz). 13C NMR (125 MHz, CDCl3) δ 211.5, 187.0, 186.8, 170.3,
170.2, 161.1, 156.4, 155.8, 135.7, 135.5, 134.2, 133.9, 120.9, 119.8,
118.5, 111.5, 111.4, 100.6.
7-[4-O-(4-O-Acetyl-2,6-dideoxy-3-O-methyl-R-L-arabino-hexo-
pyranosyl)-2,3,6-trideoxy-3-N-trifluoroacetyl-R-L-lyxo-hexopyranosyl]-
daunorubicinone (23). The pure 23 was obtained as a red solid
with a yield of 55% (separated on a column of silica gel, MeOH/
CH2Cl2 1:100). HRMS (M + Na)+ (ESI+) calcd for C38H42F3-
NO15Na+ 832.2398, found 832.2387. 1H NMR (500 MHz, CDCl3)
δ 13.89 (1H, s), 13.15 (1H, s), 8.11 (1H, d), 7.94 (1H, d), 7.71
(1H, t), 7.34 (1H, d), 5.51 (1H, d, J ) 3.3 Hz, H-1′), 5.23 (1H, d,
J ) 1.8 Hz), 4.89 (1H, br), 4.71 (1H, m), 4.35 (1H, br), 4.21 (2H,
m), 4.20 (3H, s), 3.95 (1H, m), 3.65 (1H, m), 3.53 (1H, br), 3.36
(3H, s), 3.11 (1H, d), 2.85 (1H, d), 2.37 (3H, s), 2.25 (2H, m),
2.09 (4H, m), 1.83 (3H, m,), 1.27 (3H, d), 1.20 (3H, d). 13C NMR
(125 MHz, CDCl3) δ 211.9, 186.9, 186.6, 170.1, 160.9, 156.7,
156.3, 155.7, 135.6, 135.4, 134.3, 133.9, 120.8, 119.8, 118.4, 116.9,
111.5, 111.3, 100.4, 99.3, 80.1, 76.7, 75.4, 73.3, 69.9, 69.4, 67.4,
57.1, 56.6, 45.5, 35.1, 34.1, 33.4, 30.6, 24.1, 21.0, 17.2, 17.0.
7-[4-O-(4-O-Acetyl-2,6-dideoxy-3-C-methyl-3-O-methyl-R-L-
ribo-hexopyranosyl)-2,3,6-trideoxy-3-N-trifluoroacetyl-R-L-lyxo-
hexopyranosyl]daunorubicinone (24). The pure 24 was obtained
as a red solid with a yield of 81% (separated on a column of silica
gel, MeOH/CH2Cl2 1:100). HRMS (M + Na)+ (ESI+) calcd for
C39H44F3NO15Na+ 846.2555, found 846.2545. 1H NMR (500 MHz,
CDCl3) δ 13.90 (1H, s), 13.20 (1H, s), 7.98 (1H, d), 7.73 (2H, m),
7.34 (1H, d), 5.48 (1H, d, J ) 3.5 Hz, H-1′), 5.24 (1H, d, J ) 1.6
Hz, H-7), 4.92 (1H, d, J ) 4.3 Hz, H-1′′), 4.68 (1H, d), 4.38 (1H,
s), 4.26 (2H, m), 4.18 (1H, m), 4.04 (3H, s), 3.61 (1H, br), 3.30
(3H, s), 3.17 (1H, d), 2.85 (1H, d), 2.46 (1H, m), 2.37 (3H, s),
2.25 (1H, m), 2.12 (4H, m), 1.83 (2H, m), 1.65 (1H, m), 1.29 (3H,
d), 1.14 (3H, s), 1.08 (3H, d). 13C NMR (125 MHz, CDCl3) δ 211.9,
187.0, 186.6, 170.6, 161.0, 156.7, 156.4, 155.8, 135.6, 135.5, 134.3,
133.9, 120.9, 119.8, 118.4, 116.9, 111.5, 111.3, 100.5, 98.2, 77.7,
76.9, 76.7, 72.9, 69.9, 67.8, 63.9, 56.7, 49.8, 45.6, 35.6, 35.1, 33.4,
30.7, 24.8, 21.1, 20.8, 17.8, 17.1.
δ 13.87 (1H, s), 13.83 (1H, s), 7.99 (1H, d, NHCOCF3), 7.87 (1H,
d), 7.66 (1H, t), 7.30 (1H, d), 5.44 (1H, d, J ) 3.3 Hz, H-1′), 5.14
(1H, s), 4.97 (1H, d, J ) 3.5 Hz, H-1′′), 4.65 (1H, d), 4.19 (4H,
m), 3.99 (3H, s), 3.61(1H, s), 3.09 (1H, d), 2.80 (1H, d), 2.35 (3H,
s), 2.10, 1.91, (9H, m), 1.27 (3H, d), 1.45 (6H, m). 13C NMR (125
MHz, CDCl3) δ 211.7, 186.7, 186.5, 170.4, 160.9, 156.7, 156.3,
155.6, 135.6, 135.3, 134.1, 133.8, 120.7, 119.7, 118.4, 116.9, 111.5,
111.2, 100.4, 99.9, 79.7, 76.6, 70.2, 69.4, 67.2, 64.6, 56.6, 45.5,
41.28, 35.1, 33.3, 30.7, 26.0, 24.8, 20.7, 17.5, 17.1.
7-[4-O-(4-O-Acetyl-3-azido-2,3,6-trideoxy-R-L-lyxo-hexopyran-
osyl)-2,3,6-trideoxy-3-N-trifluoroacetyl-R-L-lyxo-hexopyranosyl]-
daunorubicinone (26). The pure 26 was obtained as a red solid
with a yield of 82% (separated on a column of silica gel, MeOH/
CH2Cl2 1:75). HRMS (M + Na)+ (ESI+) calcd for C37H39F3-
N4O14Na+ 843.2307, found 843.2331. 1H NMR (500 MHz, CDCl3)
δ 13.94 (1H, s), 13.21 (1H, s), 8.60 (1H, d), 7.99 (1H, d), 7.73
(1H, m), 7.33 (1H, m), 5.50 (1H, d, J ) 3.4 Hz, H-1′), 5.24 (1H,
br, H-7), 5.21 (1H, br), 4.99 (1H, br, H-1′′), 4.20 (3H, m), 4.04
(3H, s), 3.92 (1H, m), 3.58 (1H, br), 3.18 (1H, d), 2.90 (1H, d),
2.38 (3H, s), 2.17 (1H, m), 2.17 (3H, s). 2.13 (2H, m), 2.02 (1H,
m), 1.86 (1H, m), 1.77 (1H, m), 1.27 (3H, d), 1.14 (3H, d). 13C
NMR (125 MHz, CDCl3) δ 211.8, 187.1, 186.7, 170.3, 161.0, 156.3,
155.8, 150.4, 135.7, 135.5, 134.3, 133.8, 124.3, 120.9, 119.8, 118.4,
111.5, 111.4, 100.4, 100.2, 80.9, 76.6, 69.9, 69.7, 67.4, 67.3, 56.7,
53.9, 45.6, 35.1, 33.5, 30.8, 30.1, 24.8, 20.7, 17.3, 16.4.
General Procedure for the Preparation of Disaccharide
Analogues of Daunorubicin (1 and 2). A solution of protected
disaccharide daunorubicin (100 mg) in THF (5 mL) was cooled in
an ice bath to 0 °C, and then 0.1 M NaOH aqueous solution (70
mL), which was cooled in advance in an ice bath, was added. After
being stirred for 6-8 h, the reaction mixture was neutralized with
0.1 M citric acid and extracted with CHCl3. The extractions were
washed with saturated aqueous NaHCO3 solution. Concentration
and chromatographic purification provided the products.
7-[4-O-(2,3,6-Trideoxy-R-L-erythro-hexopyranosyl)-3-azido-
2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]daunorubicinone (1). Pure
1 was obtained as a red solid with a yield of 70% (separated on a
column of silica gel, MeOH/CH2Cl2 1:75). HRMS (M + Na)+
1
(ESI+) calcd for C33H37N3O12Na+ 690.2269, found 690.2267. H
NMR (500 MHz, CDCl3) δ 13.92 (1H, s), 13.17 (1H, s), 7.96 (1H,
d, J ) 7.6 Hz), 7.74 (1H, t, J ) 8.0 Hz), 7.35 (1H, d, J ) 8.5 Hz),
5.53 (1H, s, H-1′), 5.21 (1H, s, H-7), 4.83 (1H, s, H-1′′), 4.83 (1H,
br), 4.43 (4H, m), 3.95 (1H, m), 3.72 (2H, m), 3.24 (1H, m), 3.13
(1H, d, J ) 18.8 Hz), 2.87 (1H, d, J ) 18.8 Hz), 2.37 (3H, s), 2.25
(1H, m), 2.08 (3H, m), 1.83 (6H, m), 1.24 (6H, m). 13C NMR (125
MHz, CDCl3) δ 211.6, 186.9, 186.6, 161.0, 156.3, 155.7, 135.7,
135.4, 134.2, 133.9, 120.8, 119.8, 118.4, 111.4, 111.3, 100.6, 98.1,
76.7, 74.9, 72.1, 70.0, 69.8, 68.0, 56.7, 56.6, 34.9, 33.3, 29.7, 29.6,
29.5, 27.6, 24.7, 17.9, 17.5.
7-[4-O-(2,6-Dideoxy-R-L-arabino-hexopyranosyl)-3-azido-2,3,6-
trideoxy-R-L-lyxo-hexopyranosyl]daunorubicinone (2). Pure 2
was obtained as a red solid with a yield of 60% (separated on a
column of silica gel, MeOH/CH2Cl2 1:40). HRMS (M + Na)+
1
(ESI+) calcd for C33H37N3O12Na+ 706.2218, found 706.2231. H
NMR (500 MHz, CDCl3) δ 13.93 (1H, s), 13.16 (1H, s), 7.96 (1H,
d, J ) 7.3 Hz), 7.73 (1H, t, J ) 7.9 Hz), 7.35 (1H, d, J ) 8.4 Hz),
5.51 (1H, s, H-1′), 5.21 (1H, s, H-7), 4.93 (1H, d, J ) 2.4 Hz,
H-1′′), 4.04 (3H, s), 3.95 (4H, m), 3.70 (3H, m), 3.13 (2H, m),
2.87 (1H, d, J ) 18.4 Hz), 2.38 (3H, s), 2.07 (3H, m), 1.83 (1H,
m), 1.71 (2H, m). 13C NMR (125 MHz, CDCl3) δ 211.6, 186.9,
186.6, 161.0, 156.3, 155.7, 135.7, 135.4, 134.2, 133.9, 120.8, 119.8,
118.4, 111.5, 111.3, 100.6, 99.4, 78.0, 75.4, 69.8, 69.0, 68.7, 67.8,
56.7, 56.5, 37.7, 34.9, 33.3, 29.7, 29.6, 24.7, 17.7, 17.5.
General Procedure for the Preparation of Disaccharide
Analogues of Daunorubicin (3-6). A solution of protected
disaccharide analogues (150 mg) in THF (8 mL) was cooled in an
ice bath to 0 °C, and then 0.1 M NaOH aqueous solution (90 mL),
which was cooled in advance in an ice bath, was added. After being
stirred for 6-8 h, the reaction mixture was neutralized with 0.1 M
citric acid and extracted with CHCl3. The extractions were washed
with saturated aqueous NaHCO3 solution. Removal of the solvent
7-[4-O-(4-O-Acetyl-2,6-dideoxy-3-C-methyl-R-L-ribo-hexo-
pyranosyl)-2,3,6-trideoxy-3-N-trifluoroacetyl-R-L-lyxo-hexo-
pyranosyl]daunorubicinone (25). The pure 25 was obtained as a
red solid with a yield of 40% (separated on a column of silica gel,
MeOH/CH2Cl2 1:75). HRMS (M + Na)+ (ESI+) calcd for C38H42F3-
NO15Na+ 832.2398, found 832.2391. 1H NMR (500 MHz, CDCl3)

1798 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5
Zhang et al.
provided the crude deprotected products, which were used in the
next reaction without further purification.
CDCl3) δ 211.5, 186.8, 186.5, 161.0, 156.3, 155.6, 135.7, 135.4,
134.2, 133.9, 120.7, 119.8, 118.5, 111.4, 111.2, 100.5, 98.6, 76.7,
75.2, 69.9, 69.8, 67.7, 66.9, 56.8, 56.6, 34.9, 33.2, 29.6, 28.5, 24.7,
17.5, 16.8.
The crude compound (100 mg) was mixed in water (0.4 mL)
and treated with potassium carbonate (24 mg) and CuSO4‚5H2O
(0.2 mg). MeOH (1.8 mL) and the TfN3 solution was made using
2 equiv of Tf2O.34 Then, adequate MeOH was added to homogene-
ity. The mixture was stirred overnight. The mixture was diluted
with H2O (10 mL) and extracted with CH2Cl2. The combined
extractions were dried over anhydrous Na2SO4. After removal of
solvent, the residue was purified on a column of silica gel to afford
the final product.
7-[4-O-(2,6-Dideoxy-3-O-methyl-R-L-arabino-hexopyran-
osyl)-3-azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]dauno-
rubicinone (3). Pure 3 was obtained as a red solid with a yield of
53% (separated on a column of silica gel, MeOH/CH2Cl2 1:75).
HRMS (M + Na)+ (ESI+) calcd for C34H39N3O13Na+ 720.2375,
found 720.2382. 1H NMR (500 MHz, CDCl3) δ 13.91 (1H, s), 13.13
(1H, s), 7.95 (1H, d, J ) 7.5 Hz), 7.73 (1H, t, J ) 8.2 Hz), 7.34
(1H, d, J ) 8.4 Hz), 5.51 (1H, d, J ) 3.4 Hz, H-1′), 5.21 (1H, d,
J ) 1.9 Hz, H-7), 4.93 (1H, d, J ) 3.5 Hz, H-1′′), 4.40 (1H, br),
4.06 (2H, m), 4.04 (3H, s), 3.70 (2H, m), 3.50 (1H, m), 3.40 (3H,
s), 3.12 (2H, m), 2.83 (1H, d, J ) 18.7 Hz), 2.40 (1H, m), 2.39
(3H, s), 2.24 (1H, m), 2.08 (2H, m), 1.83 (1H, m), 1.52 (1H, m),
1.27 (6H, m). 13C NMR (125 MHz, CDCl3) δ 211.6, 186.9, 186.6,
161.0, 156.3, 155.7, 135.7, 135.4, 134.2, 133.9, 120.8, 119.8, 118.4,
111.4, 111.3, 100.6, 99.3, 78.1, 76.7, 75.2, 69.8, 68.5, 67.9, 56.7,
56.6, 56.5, 34.9, 34.0, 33.3, 29.5, 24.7, 17.8, 17.5.
Biology. Cell Culture. Drug-sensitive cells K562 and drug-
resistant cells K562/Dox were cultured in RPMI 1640 supplemented
with 10% fetal bovine serum (FBS), 1% nonessential amino acid,
and penicillin (100 units/mL)/streptomycin (100 µg/mL) in a
humidified atmosphere of 5% CO2 and 95% air at 37 °C. The
culture mediums were changed every 2-3 days. Before each
experiment, K562/Dox cells were stimulated with 0.1 µM doxo-
rubicin for 1 week per week, and then cultured for 10 days without
doxorubicin stimulation. It was ensured that the P-gp expression
level was similar in every experiment.
Cytotoxicity of Daunorubicin Analogues by MTS Assay.
Drug-sensitive K562 and drug-resistant K562/Dox cells (2000-
10000) were seeded in 96-well plates in RPMI-1640 and incubated
for 24 h. The exponentially growing cancer cells were incubated
with various concentrations of compounds for 72 h at 37 °C
(5% CO2, 95% humidity). After 72 h of incubation, tetrazolium-
[3-(4,5-dimethythiazol-2-yl)]-5-(3-carboxymethoxyphenyl)-2-(4-
sulfophenyl)-2H-tetrazolium, inner salt (MTS, final concentration,
2 mg/mL) and phenazine methosulfate (PMS, final concentration
of 25 µM) were mixed and added directly to the cells. After
incubation for 3 h at 37 °C, the absorbance of formazan (the
metabolite of MTS by viable cells) was measured at 490 nm. The
IC50 values of the compounds for cytotoxicity were calculated by
WinNonlin software from the dose-response curves.
7-[4-O-(2,6-Dideoxy-3-C-methyl-3-O-methyl-R-L-ribo-hexo-
pyranosyl)-3-azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]dauno-
rubicinone (4). Pure 4 was obtained as a red solid with a yield of
50% (separated on a column of silica gel, MeOH/CH2Cl2 1:100).
HRMS (M + Na)+ (ESI+) calcd for C35H41N3O13Na+ 734.2531,
found 734.2515. 1H NMR (500 MHz, CDCl3) δ 13.87 (1H, s), 13.08
(1H, s), 7.93 (1H, d, J ) 7.2 Hz), 7.71 (1H, t, J ) 7.9 Hz), 7.33
(1H, d, J ) 8.1 Hz), 5.47 (1H, s, H-1′), 5.18 (1H, s, H-7), 4.75
(1H, d, J ) 3.9 Hz, H-1′′), 4.40 (1H, br), 4.21 (1H, m), 4.02 (3H,
s), 3.74 (1H, m), 3.63 (1H, s), 3.30 (3H, s), 3.10 (1H, d, J ) 18.6
Hz), 2.98 (1H, d, J ) 9.6 Hz), 2.42 (1H, d, J ) 18.6 Hz), 2.40
(1H, m), 2.36 (3H, s), 2.25 (1H, m), 2.01 (3H, m), 1.81 (1H, m),
1.55 (1H, m), 1.22 (9H, m). 13C NMR (125 MHz, CDCl3) δ 211.6,
186.8, 186.5, 160.9, 156.3, 155.6, 135.7, 135.3, 134.2, 133.9, 120.7,
119.8, 118.4, 111.3, 111.2, 100.7, 98.2, 78.1, 76.7, 75.5, 72.7, 69.8,
67.9, 56.7, 56.6, 49.3, 35.4, 34.8, 33.2, 29.8, 24.7, 21.5, 17.9, 17.5.
7-[4-O-(2,6-Dideoxy-3-C-methyl-R-L-ribo-hexopyranosyl)-3-
azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]daunorubicinone
(5). Pure 5 was obtained as a red solid with a yield of 43%
(separated on a column of silica gel, MeOH/CH2Cl2 1:75). HRMS
(M + Na)+ (ESI+) calcd for C34H39N3O13Na+ 720.2375, found
Acknowledgment. This work was supported by NSF (Grant
CH-0316806) and a fund from Michigan Life Science Corridor
Fund (Grant 1632) to P. G. Wang. This work was partially
supported by a research grant from Ohio Cancer Research
Associates to D. Sun. D. Sun thanks The Ohio State University
for providing research resources, analysis instruments, and
funding support.
Supporting Information Available: 1H and 13C NMR and
HRMS spectra for 1-6, 21, and 22. This material is available free
of charge via the Internet at http://pubs.acs.org.
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1
720.2390. H NMR (500 MHz, CDCl3) δ 13.90 (1H, d, J ) 6.4
Hz), 13.16 (1H, d, J ) 9.8 Hz), 7.97 (1H, d, J ) 6.8 Hz), 7.72
(1H, t, J ) 8.1 Hz), 7.35 (1H, d, J ) 8.3 Hz), 5.47 (1H, s, H-1′),
5.19 (1H, s, H-7), 4.99 (1H, d, J ) 3.4 Hz, H-1′′), 4.30 (1H, br),
4.07 (2H, m), 4.04 (3H, s), 3.84 (1H, m), 3.75 (1H, s), 3.15 (1H,
m), 2.96 (1H, d, J ) 9.8 Hz), 2.81 (1H, m), 2.37 (3H, s), 2.18 (2H,
m), 2.11 (1H, m), 1.88 (1H, m), 1.82 (2H, m), 1.30 (1H, d, J ) 6.4
Hz), 1.23 (6H, m). 13C NMR (125 MHz, CDCl3) δ 211.4, 186.8,
186.5, 161.0, 156.3, 155.6, 135.7, 135.4, 134.1, 133.8, 120.2, 119.8,
118.5, 111.3, 111.2, 100.4, 99.2, 76.6, 76.5, 75.1, 70.0, 69.7, 67.4,
66.6, 56.7, 56.5, 40.8, 34.9, 33.2, 30.0, 25.6, 24.7, 18.1, 17.6.
7-[4-O-(3-Azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl)-3-
azido-2,3,6-trideoxy-R-L-lyxo-hexopyranosyl]daunorubicinone
(6). Pure 6 was obtained as a red solid with a yield of 37%
(separated on a column of silica gel, MeOH/CH2Cl2 1:100). HRMS
(M + Na)+ (ESI+) calcd for C33H36N6O12Na+ 731.2283, found
731.2266. 1H NMR (500 MHz, CDCl3) δ 13.87 (1H, s), 13.11 (1H,
s), 7.94 (1H, d, J ) 7.7 Hz), 7.72 (1H, t, J ) 8.2 Hz), 7.34 (1H,
d, J ) 8.5 Hz), 5.50 (1H, d, J ) 3.3 Hz, H-1′), 5.18 (1H, s, H-7),
5.01 (1H, d, J ) 2.9 Hz, H-1′′), 4.36 (1H, br), 4.29 (1H, q), 4.06
(1H, m), 4.03(3H, s), 3.76 (4H, m), 3.12 (1H, d, J ) 18.7 Hz),
2.82 (1H, d, J ) 18.7 Hz), 2.36 (3H, s), 2.26 (1H, J ) 14.8 Hz),
2.06 (5H, m), 1.84 (1H, m), 1.23 (6H, m). 13C NMR (125 MHz,

3′-Azido Disaccharide Analogues
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 5 1799
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