Synthesis of neamine-carboline conjugates for RNA binding and their antibacterial activities

Article abstract of DOI:10.1016/j.tet.2010.03.034

Three types of neamine-β-carboline conjugates were synthesized in good yields by the coupling of neamine and β-carboline-3-carboxylic acids using aliphatic diamine as a linker. The binding properties of these conjugates to 16S rRNA and 18S rRNA were evaluated by surface plasmon resonance (SPR), showing that some conjugates had stronger binding affinities than neamine. In vitro antimicrobial activities were also evaluated and the results showed that some synthetic compounds exhibited better antibacterial activities than neamine. The preliminary structure-activity relationship was discussed. The present experimental data demonstrated that synthetic neamine-carboline conjugates might hold the potential as new antibiotics.

Full text of DOI:10.1016/j.tet.2010.03.034

Tetrahedron 66 (2010) 3433–3440
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of neamine–carboline conjugates for RNA binding and their
antibacterial activities
*
*
Shan Wu, Yunsha Fu, Ribai Yan, Yanfen Wu , Xiaoping Lei, Xin-Shan Ye
State Key Laboratory of Natural and Biomimetic Drugs, Peking University, and School of Pharmaceutical Sciences, Peking University, Xue Yuan Rd No. 38, Beijing 100191, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three types of neamine-b-carboline conjugates were synthesized in good yields by the coupling of ne-
Received 12 January 2010
Received in revised form 2 March 2010
Accepted 9 March 2010
amine and b-carboline-3-carboxylic acids using aliphatic diamine as a linker. The binding properties of
these conjugates to 16S rRNA and 18S rRNA were evaluated by surface plasmon resonance (SPR), showing
that some conjugates had stronger binding affinities than neamine. In vitro antimicrobial activities were
also evaluated and the results showed that some synthetic compounds exhibited better antibacterial
activities than neamine. The preliminary structure–activity relationship was discussed. The present ex-
perimental data demonstrated that synthetic neamine–carboline conjugates might hold the potential as
new antibiotics.
Available online 12 March 2010
Keywords:
Aminoglycoside
b
-Carboline
Ó 2010 Elsevier Ltd. All rights reserved.
RNA binding
Antibacterial activity
Synthesis
1. Introduction
interactions. It turned out to have limited improvements. On the
other hand, some aromatic compounds14 can act as stackers or
Aminoglycosides have been long used as potent broad-spectrum
antibiotics for the treatment of infections caused by aerobic Gram-
negative and Gram-positive bacteria. Previous studies showed
that aminoglycosides could bind to various RNA targets1–6 such as
rRNA, tRNA and mRNA. However, aminoglycosides are not ideal
antibiotics due to their toxicities and adverse effects caused by the
lack of selectivity towards different RNA targets. That caused sharply
increasing interests in understanding the interactions between RNA
and ligands, resulting in the escalating number of research works
such as studying the three dimensional structures of RNA–ligand
complexes.7 Therefore, many efforts8–12 have been made to design
and synthesize specific RNA binders, which may have potential
activities against bacteria or virus infections. However, there is not
a solid way to design molecules targeting RNA because RNA can
form intricate structures. Previous work disclosed that neamine is
the minimal consensus unit7,13 of aminoglycoside antibiotics bound
to A-site, TAR RNA, or RRE IIB RNA. Since aminoglycosides possess
amino and hydroxyl functionalities and are positively charged
around neutral pH condition, which contribute to the binding with
RNA by hydrogen bonding and electrostatic interactions, most of the
previous efforts tended to strengthen the RNA binding affinities by
increasing the number of hydrogen bonding or electrostatic
intercalators to interact with either double-stranded RNA or DNA.
But polyaromatic hydrocarbons may have potential carcinogenic
activity. The
rally occurring alkaloids, among which
b
-carboline15,16 ring system is present in many natu-
b-carboline-3-carboxylic
acid occurs in Symplocos serchuensis, a food plant indigenous to the
south of China. We assumed that the combination of aminoglyco-
side and b-carboline might enhance both the affinity and specificity
to RNA. Furthermore, it can also decrease the polarity of amino-
glycoside derivatives and improve absorption characteristics of the
designed compounds. We hereby report the synthesis of some
neamine-b-carboline conjugates, their RNA binding affinities, and
their antibacterial activities.
2. Results and discussion
2.1. Chemistry
The neamine structure and carboline moiety were connected by
a flexible tether. Neamine (1),
b-carboline-3-carboxylic acid de-
rivatives 4a, 4b and 5 were obtained according to the known pro-
cedure.17–19 As shown in Scheme 1, neamine was treated with triflyl
azide20 in the presence of CuSO4 and triethylamine to produce
tetraazidoneamine, which was followed by benzoylation, providing
compound 2 in 54% isolated yield. Compound 2 was reacted with
trifluoromethanesulfonic anhydride, providing the triflate in-
termediate, which was subsequently converted to compounds
* Corresponding authors. Tel.: þ86 10 62014949; fax: þ86 10 82802724; e-mail
addresses: wuyanfen@pku.edu.cn (Y. Wu), xinshan@bjmu.edu.cn (X.-S. Ye).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.034

3434
S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
N3
O
N3
O
NH2
O
BzO
BzO
N3
BzO
HO
HO
N3
c,d
O
a,b
BzO
N3
N3
H2N
NH2
N3
O
O
OBz
NH2
N3
NH
n
3a
: n=2
HO
HO
3b: n=4
OH
OBz
3c
: n=6
1
2
NH2
3d
: n=8
O
O
OH
OH
N
N
N
H
N
H
Boc
4a
: R=H
4b:R=CH3
R
5
Scheme 1. Synthesis of compounds 3a–d and the structures of compounds 4a, 4b, 5. Reagents and conditions: (a) TfN3, CuSO4, Et3N, CH3CN; (b) benzoyl chloride, pyridine, 54%;
(c) Tf2O, pyridine, CH2Cl2; (d) NH2(CH2)nNH2, n¼2,4,6,8, CH3CN, 40% for 3a, 48% for 3b, 47% for 3c, 47% for 3d.
3a–d via amination using the corresponding aliphatic diamines. It
is noteworthy that the high regioselectivity was achieved when the
hydroxyl groups of neamine were protected with benzoate instead
of acetate that was previously used in the literatures, leading to the
5-hydroxyl group of compound 2 exposed. Moreover, with more
robust protective group (benzoyl vs acetyl), the side reaction be-
tween esters and diamines was alleviated, resulting in the in-
creased overall yield of compounds 3a–d.
With the amino-containing neamine derivatives 3a–d and car-
boline carboxylic acid derivatives 4a, 4b, 5 in hand, the coupling re-
action was carried out (Scheme 2). Compounds 6a–d and 7a–d were
obtained bythecouplingofamines 3a–d andacids 4a, 4b. Inthesame
way, compound 5 was condensed with 3a–d to yield the corre-
sponding amide products, which were followed by Boc-deprotection
underacidic conditionsat room temperature to produce 8a–d. Due to
thepoorsolubilityofcarbolinecarboxylic acids, thecouplingreaction
was performed in DMF solution. The amide-bond formation was
efficient when 1-hydroxybenzotriazole (HOBT) and O-(benzotriazol-
1-yl)-N,N,N0,N0-tetramethyluronium hexafluorophosphate (TBTU) in
the presence of N,N-diisopropylethylamine (DIPEA) were used, and
the reactionwas completed very soon after the addition of DIPEAwas
finished, showing a single product spot on TLC, which greatly facili-
tated the product purification. Finally, compounds 6a–d, 7a–d and
8a–d were saponificated with sodium methoxide in methanol, and
followed by reductionwith H2Sto provide the target compounds 9a–
d, 10a–d and 11a–d, respectively. The structures of all of the final
products and intermediates were identified by their 1H NMR, 13C
NMR and high resolution mass spectra.
2.2. Bioassay
2.2.1. RNA binding affinities of the neamine–carboline con-
jugates. The interactions between the synthetic compounds and
RNA were evaluated by surface plasmon resonance (SPR) assay21
NH2
O
N3
O
HO
BzO
HO
H2N
BzO
N3
H2N
O
N3
O
O
NH2
N3 c, d
O
OH
NH
OBz
NH
N
H
N
H
n
4a,4b
n
6a
: R=H, n=2
: R=H, n=4
9a
: R=H, n=2
: R=H, n=4
6b
N
N
a
9b
6c: R=H, n=6
N
H
N
H
9c: R=H, n=6
9d
6d
: R=H, n=8
R
: R=H, n=8
7a: R=CH3, n=2
7b: R=CH3, n=4
R
10a: R=CH3, n=2
10b: R=CH3, n=4
10c
7c
: R=CH3, n=6
3a-d
N3
: R=CH3, n=6
7d: R=CH3, n=8
10d:R=CH3, n=8
O
BzO
BzO
NH2
O
N3
N3
5
O
HO
HO
N3
O
H2N
H2N
OBz
c, d
a, b
NH
O
NH2
O
N
H
n
OH
NH
8a
: n=2
NH
N
H
8b: n=4
8c: n=6
11a
: n=2
N
H
n
11b: n=4
11c: n=6
NH
8d
: n=8
N
H
11d
: n=8
Scheme 2. Synthesis of neamine–carboline conjugates 9a–d, 10a–d, 11a–d. Reagents and conditions: (a) TBTU, HOBT, DIPEA, DMF; 65% for 6a, 70% for 6b, 50% for 6c, 74% for 6d, 67%
for 7a, 60% for 7b, 66% for 7c, 79% for 7d; (b) HCl/ethyl acetate, 37% for 8a, 44% for 8b, 75% for 8c, 83% for 8d; (c) CH3OH/CH3ONa; (d) H2S, Py/Et3N/H2O, 70%.

S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
3435
with Escherichia coli 16S rRNA, which is implicative of the antibiotic
activity, and human 18S rRNA, which may reflect the toxicity to
mammals. Their RNA binding properties were analyzed and char-
strongest antibacterial activity. From the result that compounds 9d
and 10d had stronger activities than compounds 9a and 10a, we
might reason the longer flexible linker could also play an important
role for the antibacterial activity. Compounds 10a–c did not show
significant antibacterial activities as supposed to have from their
RNA binding data, indicating that the antibacterial activity is not
always correlative with the binding affinity.
acterized by the dissociation constants (Kd values in mM), which
were calculated from the slope of the Scatchard plot,22 and the
resulting values are outlined in Table 1.
Table 1
3. Conclusions
The interaction between compounds 9a–d, 10a–d, 11a–d and 16S/18S rRNA
Compound
Kd (16S rRNA) (
m
M)
Kd (18S rRNA) (mM)
In summary, some neamine-b-carboline conjugates 9a–d, 10a–
9a
1.9
3.2
d and 11a–d were synthesized using aliphatic diamine as the linker.
Their binding affinities to E. coli 16S rRNA and human 18S rRNA were
tested using SPR method, suggesting that the synthetic conjugates
9a, 9d, 10a–d had stronger RNA binding affinities than neamine.
Their antibacterial activities were further evaluated in vitro against
P. aeruginosa standard strain. The results showed that compounds
9a, 9d, 10d displayed better antibacterial activities than neamine,
and especially compound 9d displayed the strongest antibacterial
effect. The disclosed approach may lead to the discovery of new
antibiotic entities with improved biological activities.
9b
9c
9d
N/A
N/A
1.9
3.6
3.5
N/A
N/A
3.4
6.9
7.3
10a
10b
10c
10d
11a
11b
11c
11d
Neamine
3.8
3.5
9.6
6.8
N/A
N/A
N/A
N/A
22
N/A
N/A
N/A
N/A
34
N/A: not available.
4. Experimental section
4.1. Chemistry
As shown in Table 1, the neamine–carboline conjugates 9a, 9d
and 10a–d showed significantly stronger binding affinities to 16S
rRNA and 18S rRNA than that of neamine. The results indicated that
the total aromatic carboline ring made an important contribution
to the RNA binding affinities. Compounds 11a–d, in which the
aromatic carboline ring was replaced by the tetrahydrocarboline
ring, displayed a sharp decrease of the binding abilities and they all
showed no binding activities. When the methyl group was in-
troduced to the aromatic ring (compounds 10a–d), the binding
affinities to 16S rRNA and 18S rRNA were decreased slightly. It
seemed that the length of the aliphatic amine linkers also influ-
enced the binding activities. It is interesting that compounds 9a and
9d, with the length of 2- or 8-carbon chain, have shown the
strongest binding affinities, presumably due to the insertion of the
aromatic ring into different base pairs of RNA.
4.1.1. General information. All chemicals were purchased as reagent
grade and used without further purification, unless otherwise
noted. Dichloromethane (CH2Cl2), pyridine and acetonitrile
(CH3CN) were distilled over calcium hydride (CaH2). Methanol was
distilled from magnesium. DMF was stirred with CaH2 and distilled
under reduced pressure. Reactions were monitored with analytical
TLC on silica gel 60-F254 precoated aluminium plates and visualized
under UV (254 nm) and/or by staining with acidic ceric ammonium
molybdate. Column chromatography was performed on silica gel
(35–75
Varian INOVA-500 spectrometer at 25 ꢀC. Chemical shifts (in ppm)
were referenced to tetramethylsilane (
¼0 ppm) in deuterated
chloroform. 13C NMR spectra were obtained by using the same NMR
spectrometers and were calibrated with CDCl3
m
m). 1H NMR spectra were recorded on a JEOL AL-300 or
d
(
d
¼77.00 ppm).
2.2.2. Functional inhibition of bacterial growth. The antibacterial
activities of the synthetic neamine–carboline conjugates were
further evaluated in vitro against Pseudomonas aeruginosa standard
strain with neamine as a positive control.23 The results are outlined
in Table 2. The rate of inhibition for each compound was tested at
Mass spectra were recorded using a PE SCLEX QSTAR spectrometer.
4.1.2. Preparation of compound 2. To a stirred suspension of NaN3
(2.0 g, 30.8 mmol) in acetonitrile (20 mL) was added Tf2O (4.3 mL,
7.3 g, 25.8 mmol) by syringe slowly at 0 ꢀC. The mixture was stirred
for another 2 h at this temperature. The insoluble solids were re-
moved through filtration. At 0 ꢀC, the filtrate was added dropwise
into the mixture of neamine (2.0 g, 6.2 mmol), CuSO4 (29 mg), H2O
(6 mL) and Et3N (3.6 mL). The reaction mixture was stirred for 6 h at
room temperature. The mixture was diluted with EtOAc and washed
with brine. The organic layer was dried over Na2SO4 and evaporated
to yield brown solids. To the solution of these solids in pyridine
(5 mL), benzoyl chloride (3.0 mL, 3.63 g, 25.9 mmol) was added at
0 ꢀC. The reaction mixture was stirred for 5 h at room temperature.
The solvent was removed under reduced pressure. The residue was
subjected to column chromatography on silica gel (petroleum ether/
ethyl acetate 4:1) to afford compound 2 as a white foam (2.5 g, 54%
the concentration of 500 mg/mL. For those compounds showing
good inhibitory activities such as 9a, 9d and 10d, the corresponding
IC50 values were measured. The data obtained in the test indicated
that among all of the synthetic compounds, 9d displayed the
Table 2
The inhibition effects on P. aeruginosa strain in vitro
Compound
IC50
(
m
g/mL)
Rate of inhibitiona (%)
9a
9b
9c
9d
10a
10b
10c
10d
11a
11b
11c
11d
Neamine
312.5
29
29
85.4
yield). 1H NMR (500 MHz, CDCl3):
d 8.09–8.11 (m, 2H), 7.91–7.93 (m,
30
31
31
4H), 7.58–7.61 (m, 1H), 7.46–7.54 (m, 4H), 7.35–7.39 (m, 4H), 5.97
(dd, J¼9.5, 10.5 Hz, 1H), 5.58 (d, J¼4.0 Hz, 1H, H10), 5.48 (t, J¼9.8 Hz,
1H), 5.22 (t, J¼9.8 Hz, 1H), 4.55 (m, 1H), 3.92 (td, J¼3.5, 9.3 Hz, 1H),
3.80 (dd, J¼3.5, 10.5 Hz, 1H), 3.71–3.76 (m, 1H), 3.61–3.65 (m, 2H),
3.53–3.58 (m, 1H), 3.49 (dd, J¼3.0, 13.5 Hz, 1H), 3.42 (dd, J¼5.5,
9.0 Hz, 1H), 2.51 (dt, J1¼13.0 Hz, J2¼J3¼5.0 Hz, 1H, H2eq), 1.75 (q,
145.8
343.8
30
31
30
18
J¼13.0 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3):
d 166.15, 165.67,
a
Rate of inhibition was measured at the concentration of 500
m
g/mL.
165.28,133.61,133.54,129.99,129.87, 129.80,128.98,128.63,128.52,

3436
S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
128.46, 128.44, 98.94, 83.23, 75.63, 74.83, 71.01, 69.99, 69.67, 62.12,
58.49, 58.26, 50.96, 32.08. HRMS (ESI) for C33H30N12O9 calcd
761.2151 [(MþNa)þ]; found: 761.2166.
7.33–7.38 (m, 4H), 6.9–7.20 (br, 2H), 6.00 (t, J¼9.5 Hz, 1H), 5.52 (t,
J¼9.5 Hz, 1H), 5.20 (d, J¼3.5 Hz, 1H, H10), 4.93 (dd, J¼2.5, 10.5 Hz,
1H, H6), 4.45–4.49 (m, 1H), 4.38 (dt, J¼5.0, 12.0 Hz, 1H), 4.09 (dt,
J¼5.0, 11.5 Hz, 1H), 3.82–3.86 (m, 2H), 3.68–3.70 (m, 1H, H5), 3.53
(dd, J¼2.5, 13.5 Hz, 1H), 3.41 (dd, J¼5.0, 8.5 Hz,1H), 2.91 (t, J¼7.8 Hz,
2H), 2.79–2.81 (m, 1H), 2.52 (br, 1H), 2.43 (dt, J¼5.0, 13.5 Hz, 1H),
1.56–1.60 (m, 2H), 1.40–1.47 (m, 3H), 0.92–1.30 (m, 9H). 13C NMR
4.1.3. General procedure for the preparation of compounds 3a–d.
Compound 2 (1.0 g, 1.35 mmol) was dissolved in dichloromethane
(5 mL), followed by the addition of pyridine (1 mL). Tf2O (0.5 mL,
0.84 g, 3.00 mmol) was slowly added for 1.5 h with stirring at 0 ꢀC.
The mixture was stirred for another 2.5 h. The reaction mixture was
diluted with ethyl acetate and washed with brine. The organic layer
was collected and dried over Na2SO4. The solvent was removed
under reduced pressure and the residue was purified by column
chromatography on silica gel (petroleum ether/ethyl acetate 8:1) to
afford a yellow foam. This yellow foam was dissolved in acetonitrile
(6 mL). Diamine (4.05 mmol) was added and the mixture was
stirred overnight at room temperature. The reaction mixture was
diluted with dichloromethane and washed with brine. The organic
layer was concentrated and the residue was subjected to column
chromatography on silica gel to give products.
(75 MHz, CDCl3)
d 165.53, 165.28, 133.66, 133.53, 129.90, 129.83,
129.78, 129.10, 128.62, 128.49, 128.44, 93.94, 77.47, 70.91, 70.01,
69.47, 61.58, 57.86, 56.67, 55.78, 50.80, 50.64, 40.38, 32.61, 30.37,
29.02, 28.70, 27.20, 27.00, 26.00. HRMS (ESI) for C41H48N14O8 calcd
865.3852 [(MþH)þ]; found: 865.3902.
4.1.4. General procedure for the preparation of compounds 6a–d, 7a–
d and 8a–d. To a mixture of carboline carboxylic acid (4a, 4b, or 5,
0.15 mmol), amine (3a, 3b, 3c, or 3d, 0.14 mmol), HBTU (0.18 mmol)
and HOBT (0.18 mmol) in DMF (5 mL) was added DIPEA (0.3 mL), and
the mixture was stirred. The reaction process was monitored by TLC.
The solvent was removed and the residue was dissolved in
dichloromethane. The solution was concentrated under reduced
pressure and the residue was purified by column chromatography on
silica gel (dichloromethane/chloroform as eluent) to yield products
6a–d and 7a–d. For the preparation of 8a–d, a Boc-deprotection
operation was followed, using 1 N HCl/ethyl acetate solution.
4.1.3.1. Compound 3a. White foam, 40% yield, chloroform/
methanol 30:1 as eluent: 1H NMR (300 MHz, CDCl3)
d 8.16–8.19 (m,
2H), 7.87–7.92 (m, 4H), 7.43–7.52 (m, 5H), 7.26–7.36 (m, 4H), 5.99 (t,
J¼9.9 Hz, 1H), 5.52 (t, J¼9.8 Hz, 1H), 5.21 (d, J¼3.6 Hz, 1H, H10), 5.02
(dd, J¼2.1, 10.5 Hz, 1H), 4.70–4.76 (m, 1H), 4.48–4.54 (m, 1H), 4.27–
4.36 (m, 1H), 3.86 (dd, J¼3.3, 10.8 Hz, 2H), 3.72 (t, 1H, H5), 3.54 (dd,
J¼2.7, 13.5 Hz, 1H), 3.40 (dd, J¼5.1, 13.5 Hz, 1H), 2.99–3.11 (m, 3H),
2.82–2.96 (m, 1H), 2.51 (dt, J¼4.8, 12.9 Hz, 1H, H2eq), 1.47 (q,
4.1.4.1. Compound 6a. Yield 65%: 1H NMR (300 MHz, CDCl3)
d
8.94–8.96 (m, 2H), 8.81 (m, 1H), 8.65–8.68 (m, 1H), 8.18 (d,
J¼7.8 Hz,1H), 8.02 (d, J¼7.2 Hz, 2H), 7.86–7.97 (m, 4H), 7.44–7.60 (m,
5H), 7.21–7.42 (m, 8H), 6.01 (t, J¼9.9 Hz, 1H), 5.50 (t, J¼9.8 Hz, 1H),
5.24 (d, J¼3.6 Hz, 1H, H10), 4.97 (dd, J¼2.4, 10.2 Hz, 1H), 4.47–4.56
(m, 2H), 4.04–4.09 (m, 1H), 3.74–3.89 (m, 4H), 3.37–3.55 (m, 3H),
3.06–3.09 (m, 1H), 2.89–2.94 (m, 1H), 2.44 (dt, J¼5.0, 12.9 Hz, 1H,
H2eq), 1.43 (q, J¼12.9 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3)
J¼12.3 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3)
d 165.53, 165.38,
165.24, 133.60, 133.41, 130.05, 129.86, 129.75, 128.79, 128.54, 128.44,
128.35, 94.46, 78.10, 70.93, 70.08, 69.33, 61.75, 57.55, 56.36, 56.07,
50.73, 41.12, 32.62. HRMS (ESI) for C35H36N14O8 calcd 781.2913
[(MþH)þ]; found: 781.2899.
d
165.51,165.42,165.29,140.67,140.44,137.07,133.65,133.48,131.91,
4.1.3.2. Compound 3b. White foam, 48% yield, dichloromethane/
129.89,129.75,129.50,128.89,128.63,128.54,128.49,128.40,122.17,
121.81,120.84,114.38,111, 71, 94.19, 70.86, 70.05, 69.52, 61.56, 57.68,
56.91, 55.39, 50.81, 49.86, 39.92, 32.58. HRMS (ESI) for C47H42N16O9
calcd 975.3393 [(MþH)þ]; found: 975.3411.
methanol 25:1 as eluent: 1H NMR (500 MHz, CDCl3)
d 8.08–8.09
(m, 2H), 7.91–7.94 (m, 4H), 7.60–7.62 (m, 1H), 7.48–7.53 (m, 4H),
7.35–7.39 (m, 4H), 5.97 (dd, J¼9.5, 10.5 Hz, 1H), 5.54 (t, J¼9.8 Hz, 1H),
5.20 (d, J¼4.0 Hz, 1H, H10), 4.94 (dd, J¼2.5, 10.5 Hz, 1H), 4.49–4.52
(m, 1H), 4.37–4.42 (m, 1H), 4.08–4.14 (m, 1H), 3.81–3.87 (m, 2H),
3.67 (t, J¼2.8 Hz, 1H, H5), 3.54 (dd, J¼2.5, 10.5 Hz, 1H), 3.41 (dd,
J¼5.5, 14.0 Hz, 1H), 2.84–2.89 (m, 1H), 2.69–2.71 (m, 2H), 2.44–2.55
4.1.4.2. Compound 6b. Yield 70%: 1H NMR (500 MHz, CDCl3)
d
8.90 (s, 1H), 8.81 (s, 1H), 8.73 (d, J¼1.0 Hz, 1H), 8.24 (t, J¼6.0 Hz,
1H), 8.17 (d, J¼8.0 Hz, 1H), 8.07–8.09 (m, 2H), 7.90–7.93 (m, 4H),
7.56–7.59 (m, 2H), 7.45–7.53 (m, 5H), 7.31–7.38 (m, 5H), 6.03 (dd,
J¼9.0, 10.5 Hz, 1H), 5.52 (t, J¼10.0 Hz, 1H), 5.21 (d, J¼4.0 Hz, 1H,
H10), 4.94 (dd, J¼2.5, 10.5 Hz, 1H), 4.46–4.49 (m, 1H), 4.36–4.42 (m,
1H), 4.07–4.13 (m, 1H), 3.81–3.86 (m, 2H), 3.69 (t, J¼2.8 Hz, 1H, H5),
3.48–3.55 (m, 3H), 3.41 (dd, J¼5.0, 14.0 Hz, 1H), 2.85–2.90 (m, 1H),
2.61–2.66 (m, 1H), 2.43 (dt, J¼13.0, 5.0 Hz, 1H, H2eq), 1.56–1.72 (m,
5H), 1.43 (q, J¼13.0 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3)
(m, 4H), 1.40–1.56 (m, 5H). 13C NMR (75 MHz, CDCl3)
d 165.65,
165.49, 165.23, 133.63, 133.55, 129.87, 129.78, 129.00, 128.65, 128.46,
128.42, 94.20, 77.72, 77.25, 70.91, 70.07, 69.27, 61.76, 57.68, 56.58,
56.10, 50.74, 50.52, 41.58, 32.55, 30.53, 27.90. HRMS (ESI) for
C37H40N14O8 calcd 809.3226 [(MþH)þ]; found: 809.3233.
4.1.3.3. Compound 3c. White foam, 47% yield, dichloromethane/
methanol 15:1 as eluent: 1H NMR (500 MHz, CDCl3)
d
8.05–8.07 (m,
d 165.54, 165.46, 165.28, 140.68, 140.51, 137.06, 133.67, 133.64,
2H), 7.90–7.92 (m, 4H), 7.56–7.60 (m, 1H), 7.44–7.52 (m, 4H), 7.32–
7.38 (m, 4H), 5.98 (dd, J¼9.0, 10.0 Hz, 1H), 5.52 (t, J¼9.8 Hz, 1H), 5.19
(d, J¼4.0 Hz,1H, H10), 4.91 (dd, J¼2.5,10.5 Hz,1H), 4.45–4.49 (m,1H),
4.33–4.38 (m, 1H), 4.05–4.10 (m, 1H), 3.80–3.85 (m, 2H), 3.68 (t,
J¼3.0 Hz, 1H, H5), 3.53 (dd, J¼2.5, 10.5 Hz, 1H), 3.41 (dd, J¼5.0,
10.5 Hz, 1H), 2.85 (t, J¼7.8 Hz, 2H), 2.74–2.79 (m, 1H), 2.48–2.53 (m,
1H), 2.43 (dt, J¼5.0,13.5 Hz,1H),1.53–1.57 (m, 2H),1.36–1.45 (m, 3H),
133.46,131.67,129.90,129.80,129.54,129.04,128.86,128.70,128.49,
128.42, 122.17, 121.83, 120.81, 114.35, 111.67, 93.92, 77.48, 77.25,
70.94, 70.00, 69.49, 61.57, 57.89, 56.66, 55.93, 50.81, 50.33, 39.16,
32.67, 27.95, 27.58. HRMS (ESI) for C49H46N16O9 calcd 1003.3706
[(MþH)þ]; found: 1003.3708.
4.1.4.3. Compound 6c. Yield 50%: 1H NMR (500 MHz, CDCl3)
1.19–1.26 (m, 7H). 13C NMR (75 MHz, CDCl3)
d
165.68,165.55, 165.26,
d
9.02 (d, J¼3.0 Hz, 1H), 8.92 (s, 1H), 8.76 (d, J¼1.0 Hz, 1H), 8.13–8.18
133.72, 133.68, 133.57, 129.89, 129.79, 129.09, 128.66, 128.60, 128.51,
128.46, 93.93, 77.42, 77.32, 70.91, 69.98, 69.44, 61.53, 57.85, 56.67,
55.66, 50.81, 50.37, 40.41, 32.59, 30.16, 27.25, 26.50, 25.90. HRMS
(ESI) for C39H44N14O8 calcd 837.3539 [(MþH)þ]; found: 837.3545.
(m, 2H), 8.07–8.09 (m, 2H), 7.91–7.92 (m, 4H), 7.46–7.60 (m, 7H),
7.31–7.38 (m, 5H), 6.01 (dd, J¼9.5, 10.5 Hz, 1H), 5.51 (t, J¼10.0 Hz,
1H), 5.18 (d, J¼4.0 Hz, 1H, H10), 4.93 (dd, J¼2.0, 10.0 Hz, 1H), 4.45–
4.48 (m, 1H), 4.35–4.41 (m, 1H), 4.05–4.10 (m, 1H), 3.79–3.84 (m,
2H), 3.67 (t, J¼3.0 Hz, 1H, H5), 3.52 (dd, J¼2.5, 13.5 Hz, 1H), 3.46 (q,
J¼7.0 Hz, 2H), 3.40 (dd, J¼5.5, 14.0 Hz, 1H), 2.79–2.84 (m, 1H), 2.50–
2.55 (m, 1H), 2.43 (dt, J¼13.5, 5.0 Hz, 1H, H2eq), 1.73 (br, 1H), 1.56–
1.61 (m, 2H), 1.38–1.50 (m, 3H), 1.26–1.32 (m, 4H). 13C NMR
4.1.3.4. Compound 3d. White foam, 47% yield, chloroform/
methanol 15:1 as eluent: 1H NMR (500 MHz, CDCl3)
d
8.06–8.08 (m,
2H), 7.90–7.92 (m, 4H), 7.53–7.60 (m, 1H), 7.44–7.52 (m, 4H),

S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
3437
(75 MHz, CDCl3)
d
165.53, 165.42, 165.30, 140.74, 140.50, 137.09,
50.80, 50.63, 39.38, 32.63, 30.46, 29.76, 27.00, 26.87, 20.24. HRMS
133.68, 133.64, 133.47, 131.67, 129.89, 129.78, 129.56, 129.09, 128.87,
128.65, 128.48, 128.41, 122.15, 121.83, 120.80, 114.36, 111.73, 93.91,
77.48, 77.26, 70.91, 69.97, 69.50, 61.54, 57.86, 56.66, 55.80, 50.81,
50.61, 39.39, 32.66, 30.41, 29.62, 26.93, 26.80. HRMS (ESI) for
C51H50N16O9 calcd 1031.4019 [(MþH)þ]; found: 1031.4028.
(ESI) for C52H52N16O9 calcd 1045.4176 [(MþH)þ]; found: 1045.4160.
4.1.4.8. Compound 7d. Yield 79%: 1H NMR (500 MHz, CDCl3)
d
9.01 (s, 1H), 8.79 (s, 1H), 8.24 (t, J¼6.0 Hz, 1H), 8.07–8.11 (m, 3H),
7.91–7.93 (m, 4H), 7.45–7.59 (m, 7H), 7.28–7.38 (m, 5H), 6.01 (dd,
J¼11.0, 10.0 Hz, 1H), 5.51 (t, J¼10.0 Hz, 1H), 5.18 (d, J¼4.0 Hz, 1H,
H10), 4.93 (dd, J¼2.0, 10.0 Hz, 1H), 4.45–4.49 (m, 1H), 4.36–4.41 (m,
1H), 4.05–4.10 (m, 1H), 3.80–3.84 (m, 2H), 3.67 (t, J¼3.0 Hz, 1H,
H5), 3.47–3.54 (m, 3H), 3.40 (dd, J¼5.5, 13.5 Hz, 1H), 2.79–2.84 (m,
4H), 2.47–2.52 (m, 1H), 2.43 (dt, J¼13.5, 5.0 Hz, 1H, H2eq), 1.58–1.64
(m, 2H), 1.30–1.50 (m, 6H), 1.17–1.28 (m, 6H). 13C NMR (75 MHz,
4.1.4.4. Compound 6d. Yield 74%: 1H NMR (500 MHz, CDCl3)
d
9.06 (s, 1H), 8.93 (s, 1H), 8.77 (d, J¼1.0 Hz, 1H), 8.14–8.18 (m, 2H),
8.07–8.09 (m, 2H), 7.91–7.93 (m, 4H), 7.45–7.60 (m, 7H), 7.31–7.38
(m, 5H), 6.01 (dd, J¼9.5, 10.5 Hz, 1H), 5.51 (t, J¼10.0 Hz, 1H), 5.17 (d,
J¼3.5 Hz, 1H, H10), 4.93 (dd, J¼2.5, 10.5 Hz, 1H), 4.45–4.48 (m, 1H),
4.36–4.41 (m, 1H), 4.05–4.10 (m, 1H), 3.79–3.84 (m, 2H), 3.67 (t,
J¼3.0 Hz, 1H, H5), 3.47–3.54 (m, 3H), 3.40 (dd, J¼5.0, 13.5 Hz, 1H),
2.79–2.84 (m, 1H), 2.41–2.51 (m, 2H), 1.66 (br, 1H), 1.57–1.62 (m,
CDCl3)
d 165.61, 165.54, 165.49, 165.29, 140.42, 140.13, 139.84,
135.92, 133.62, 133.47, 129.88, 129.79, 129.76, 129.09, 128.74,
128.61, 128.46, 128.40, 122.38, 122.08, 120.67, 112.61, 111.74, 93.91,
77.51, 77.26, 70.91, 69.98, 69.49, 61.57, 57.85, 56.66, 55.83, 50.80,
50.67, 39.48, 32.64, 30.51, 29.76, 29.28, 29.24, 27.19, 26.96, 20.29.
HRMS (ESI) for C54H56N16O9 calcd 1073.4489 [(MþH)þ]; found:
1073.4484.
2H), 1.16–1.47 (m, 11H). 13C NMR (75 MHz, CDCl3)
d 165.57, 165.53,
165.44, 165.31, 140.75, 140.51, 137.09, 133.64, 133.49, 131.66, 129.89,
129.81, 129.77, 129.57, 129.09, 128.86, 128.62, 128.48, 128.42, 122.15,
121.83,120.78,114.37,111.73, 93.89, 77.49, 77.31, 70.92, 69.98, 69.50,
61.56, 57.86, 56.67, 55.82, 50.80, 50.70, 39.48, 32.65, 30.47, 29.63,
29.21, 29.17, 27.12, 26.89. HRMS (ESI) for C53H54N16O9 calcd
1059.4332 [(MþH)þ]; found: 1059.4344.
4.1.4.9. Compound 8a. Yield 37%: 1H NMR (500 MHz, CDCl3)
d
8.05 (dd, J¼1.0, 8.5 Hz, 2H), 7.90–7.91 (m, 2H), 7.83 (dd, J¼1.0,
8.5 Hz, 2H), 7.40–7.55 (m, 6H), 7.35–7.38 (m, 2H), 7.26–7.30 (m, 4H),
7.14–7.17 (m, 1H), 7.09–7.12 (m, 1H), 5.99 (dd, J¼9.5, 10.5 Hz, 1H),
5.51 (t, J¼10.0 Hz, 1H), 5.21 (d, J¼3.5 Hz, 1H, H10), 4.96 (dd, J¼2.0,
10.5 Hz, 1H), 4.48–4.52 (m, 1H), 4.33–4.38 (m, 1H), 4.00–4.11 (m,
3H), 3.81–3.85 (m, 2H), 3.69 (t, J¼3.0 Hz, 1H, H5), 3.63 (q, J¼4.7 Hz,
1H), 3.51–3.58 (m, 2H), 3.41 (dd, J¼5.5, 13.5 Hz, 1H), 3.26–3.32 (m,
1H), 3.21 (dd, J¼4.8,15.5 Hz,1H), 2.84–2.95 (m, 3H), 2.41 (dt, J¼13.5,
5.0 Hz, 1H, H2eq), 1.82 (br, 2H), 1.45 (q, J¼12.5 Hz, 1H, H2ax). 13C
4.1.4.5. Compound 7a. Yield 67%: 1H NMR (300 MHz, CDCl3)
d
9.23 (br, 1H), 8.82 (s, 1H), 8.70–8.74 (m, 1H), 8.11 (d, J¼7.8 Hz, 1H),
8.01 (d, J¼7.2 Hz, 2H), 7.85–8.00 (m, 4H), 7.22–7.53 (m, 12H), 6.02 (t,
J¼9.9 Hz, 1H), 5.52 (t, J¼9.9 Hz, 1H), 5.25 (d, J¼3.6 Hz, 1H, H10), 5.00
(dd, J¼2.7, 10.2 Hz, 1H), 4.47–4.55 (m, 2H), 4.08–4.15 (m, 1H), 3.76–
3.91 (m, 4H), 3.38–3.56 (m, 3H), 2.99–3.08 (m, 2H), 2.82 (s, 3H,
CH3), 2.44 (dt, J¼5.1, 13.2 Hz, 1H, H2eq), 1.85 (br, 1H), 1.46 (q,
J¼12.6 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3)
d
165.86, 165.37,
NMR (75 MHz, CDCl3) d 172.63, 165.65, 165.47, 165.26, 135.96,
165.22, 140.50, 139.27, 136.05, 133.55, 133.37, 129.76, 129.66, 128.56,
128.44, 128.27, 122.15, 121.96, 121.88, 120.47, 112.58, 111, 82, 94.02,
77.42, 76.57, 70.72, 69.93, 69.40, 61.40, 57.60, 56.46, 55.30, 50.69,
49.80, 39.77, 32.37, 20.31. HRMS (ESI) for C48H44N16O9 calcd
989.3550 [(MþH)þ]; found: 989.3582.
133.80, 133.67, 133.54, 129.88, 129.78, 129.75, 128.84, 128.75,
128.50, 128.42, 127.37, 121.84, 119.63, 118.13, 110.73, 94.41, 77.77,
70.92, 70.12, 69.42, 61.81, 57.62, 57.13, 56.73, 55.83, 50.83, 49.54,
42.72, 39.84, 32.46, 24.32. HRMS (ESI) for C47H46N16O9 calcd
979.3706 [(MþH)þ]; found: 979.3856.
4.1.4.6. Compound 7b. Yield 60%: 1H NMR (500 MHz, CDCl3)
4.1.4.10. Compound 8b. Yield 44%: 1H NMR (500 MHz, CDCl3)
d
8.77 (s, 1H), 8.41 (s, 1H), 8.23 (t, J¼6.3 Hz, 1H), 8.15 (d, J¼8.0 Hz,
d 8.07–8.09 (m, 2H), 7.89–7.92 (m, 3H), 7.77 (br, 1H), 7.60 (t,
1H), 8.08–8.10 (m, 2H), 7.89–7.92 (m, 4H), 7.46–7.60 (m, 7H), 7.31–
7.38 (m, 5H), 6.00 (dd, J¼9.5, 10.5 Hz, 1H), 5.50 (t, J¼10.0 Hz, 1H),
5.21 (d, J¼4.0 Hz, 1H, H10), 4.94 (dd, J¼2.5, 10.5 Hz, 1H), 4.45–4.49
(m, 1H), 4.37–4.43 (m, 1H), 4.06–4.12 (m, 1H), 3.80–3.86 (m, 2H),
3.69 (t, J¼3.0 Hz, 1H, H5), 3.47–3.54 (m, 3H), 3.40 (dd, J¼5.0,
14.0 Hz, 1H), 2.87–2.92 (m, 1H), 2.76 (s, 3H, CH3), 2.61–2.65 (m, 1H),
2.44 (dt, J¼13.0, 5.0 Hz, 1H, H2eq), 1.56–1.73 (m, 5H), 1.43 (q,
J¼7.5 Hz, 1H), 7.47–7.53 (m, 5H), 7.26–7.38 (m, 5H), 7.08–7.17 (m,
3H), 5.99 (t, J¼10.0 Hz, 1H), 5.51 (t, J¼10.0 Hz, 1H), 5.18 (d, J¼3.5 Hz,
1H, H10), 4.93 (dd, J¼2.5, 10.5 Hz, 1H), 4.46–4.49 (m, 1H), 4.34–4.39
(m, 1H), 4.04–4.10 (m, 1H), 3.94–4.02 (m, 2H), 3.82 (dt, J¼4.0,
10.5 Hz, 2H), 3.67 (t, J¼3.0 Hz, 1H, H5), 3.51–3.55 (m, 2H), 3.41 (dd,
J¼5.0, 13.5 Hz, 1H), 3.20–3.31 (m, 3H), 2.79–2.88 (m, 2H), 2.57–2.60
(m, 1H), 2.42 (dt, J¼13.5, 5.0 Hz, 1H, H2eq), 1.67 (br, 2H), 1.39–1.60
J¼12.5 Hz, 1H, H2ax). 13C NMR (75 MHz, CDCl3)
d
165.56, 165.53,
(m, 5H). 13C NMR (75 MHz, CDCl3)
d 172.40, 165.56, 165.26, 135.95,
165.44, 165.29, 140.25, 140.03, 139.97, 135.78, 133.67, 133.63, 133.43,
129.92, 129.83, 129.80, 129.07, 128.83, 128.70, 128.56, 128.49,
128.39, 122.48, 122.20, 120.85, 112.68, 111.64, 94.01, 77.58, 77.26,
70.88, 70.02, 69.52, 61.58, 57.89, 56.64, 55.95, 50.84, 50.37, 39.28,
32.69, 28.10, 27.75, 20.19. HRMS (ESI) for C50H48N16O9 calcd
1017.3863 [(MþH)þ]; found: 1017.3850.
133.71, 133.66, 133.53, 132.11, 129.89, 129.81, 129.79, 129.04, 128.72,
128.62, 128.49, 128.46, 127.36, 121.81, 119.60, 118.12, 110.68, 108.66,
94.12, 77.69, 70.94, 70.01, 69.43, 61.62, 57.83, 57.25, 56.65, 55.92,
50.81, 50.15, 42.82, 38.93, 32.62, 27.87, 27.41, 24.49. HRMS (ESI) for
C49H50N16O9 calcd 1007.4019 [(MþH)þ]; found: 1007.4050.
4.1.4.11. Compound 8c. Yield 75%: 1H NMR (500 MHz, CDCl3)
4.1.4.7. Compound 7c. Yield 66%: 1H NMR (500 MHz, CDCl3)
d
8.07–8.09 (m, 2H), 7.90–7.92 (m, 5H), 7.61 (t, J¼7.5 Hz, 1H), 7.46–
d
9.00–9.01 (m, 1H), 8.78 (s, 1H), 8.23 (t, J¼5.5 Hz, 1H), 8.07–8.11 (m,
7.53 (m, 5H), 7.29–7.38 (m, 5H), 7.08–7.17 (m, 2H), 7.02 (br, 1H), 6.00
(t, J¼10.0 Hz, 1H), 5.51 (t, J¼10.0 Hz, 1H), 5.18 (d, J¼3.5 Hz, 1H, H10),
4.93 (dd, J¼2.5, 10.5 Hz, 1H), 4.45–4.49 (m, 1H), 4.35–4.40 (m, 1H),
4.01–4.10 (m, 3H), 3.79–3.85 (m, 2H), 3.68 (t, J¼2.5 Hz, 1H, H5), 3.53
(dd, J¼2.5, 13.5 Hz, 2H), 3.41 (dd, J¼5.0, 13.5 Hz, 1H), 3.20–3.24 (m,
3H), 2.76–2.84 (m, 2H), 2.49–2.53 (m, 1H), 2.43 (dt, J¼13.5, 5.0 Hz,
1H, H2eq), 1.99 (br, 2H), 1.39–1.46 (m, 5H), 1.22–1.30 (m, 5H). 13C
3H), 7.91–7.92 (m, 4H), 7.45–7.59 (m, 7H), 7.25–7.37 (m, 5H), 6.00 (dd,
J¼9.5, 10.0 Hz, 1H), 5.51 (t, J¼10.0 Hz, 1H), 5.17 (d, J¼3.5 Hz, 1H, H10),
4.93 (dd, J¼2.5, 10.0 Hz, 1H), 4.45–4.49 (m, 1H), 4.36–4.41 (m, 1H),
4.05–4.10 (m,1H), 3.79–3.84 (m, 2H), 3.68 (t, J¼2.8 Hz,1H, H5), 3.38–
3.54 (m, 4H), 2.79–2.84 (m, 4H), 2.50–2.55 (m, 1H), 2.43 (dt, J¼13.5,
5.0 Hz, 1H, H2eq), 1.58–1.61 (m, 3H), 1.39–1.47 (m, 3H), 1.26–1.31 (m,
4H).13C NMR (75 MHz, CDCl3)
d
165.58,165.54,165.47,165.29,140.38,
NMR (75 MHz, CDCl3) d 172.27, 165.53, 165.27, 135.98, 133.70,
140.10, 139.84, 135.88, 133.66, 133.61, 133.44, 129.88, 129.77, 129.07,
128.74, 128.63, 128.47, 128.38, 122.38, 122.09, 120.70, 112.61, 111.72,
93.93, 77.51, 77.25, 70.87, 69.97, 69.49, 61.54, 57.85, 56.64, 55.79,
133.65, 133.51, 131.94, 129.89, 129.81, 129.78, 129.10, 128.65, 128.49,
128.43, 127.27, 121.81, 119.58, 118.07, 110.76, 108.51, 93.96, 77.53,
70.91, 69.98, 69.46, 61.54, 57.85, 57.27, 56.67, 55.86, 50.81, 50.61,

3438
S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
42.85, 39.08, 32.62, 30.44, 29.40, 26.90, 26.74, 24.61. HRMS (ESI) for
(d, J¼10.5 Hz, 1H), 4.12 (dd, J¼3.0, 10.5 Hz, 1H), 3.95–4.03 (m, 3H),
3.67–3.76 (m, 2H), 3.44–3.53 (m, 3H), 3.38 (t, J¼7.0 Hz, 2H), 3.25–
3.31 (m, 2H), 3.00–3.06 (m, 1H), 2.54 (dt, J¼13.0, 4.5 Hz, 1H, H2eq),
1.85 (q, J¼12.5 Hz, 1H, H2ax), 1.68 (br, 4H), 1.45 (br, 4H). 13C NMR
C51H54N16O9 calcd 1035.4332 [(MþH)þ]; found: 1035.4334.
4.1.4.12. Compound 8d. Yield 83%: 1H NMR (500 MHz, CDCl3)
d
8.06–8.09 (m, 2H), 7.90–7.93 (m, 5H), 7.59–7.63 (m, 1H), 7.47–7.53
(75 MHz, D2O) d 166.01, 141.91, 136.37, 135.94, 130.94, 130.47,
(m, 5H), 7.33–7.38 (m, 4H), 7.29 (d, J¼8.0 Hz, 1H), 7.08–7.17 (m, 2H),
7.01 (t, J¼5.5 Hz,1H), 6.00 (dd, J¼9.5,10.5 Hz,1H), 5.50 (t, J¼10.0 Hz,
1H), 5.16 (d, J¼4.0 Hz, 1H, H10), 4.93 (dd, J¼2.5, 10.0 Hz, 1H), 4.45–
4.48 (m, 1H), 4.35–4.41 (m, 1H), 3.98–4.10 (m, 3H), 3.78–3.84 (m,
2H), 3.67 (t, J¼2.5 Hz, 1H, H5), 3.50–3.54 (m, 2H), 3.41 (dd, J¼5.0,
13.5 Hz, 1H), 3.23–3.27 (m, 3H), 2.74–2.85 (m, 2H), 2.47–2.52 (m,
1H), 2.43 (dt, J¼13.5, 5.0 Hz, 1H, H2eq), 1.64 (br, 2H), 1.38–1.51 (m,
129.52, 122.25, 121.52, 120.54, 114.45, 112.78, 93.05, 73.69, 71.15,
70.48, 70.09, 69.41, 58.06, 53.89, 51.75, 49.08, 47.82, 40.70, 40.46,
29.24, 28.55, 26.74, 26.70. HRMS (ESI) for C30H46N8O6 calcd
615.3613 [(MþH)þ]; found: 615.3624.
4.1.5.4. Compound 9d. 1H NMR (500 MHz, D2O)
d 8.52 (s, 1H),
8.27 (s, 1H), 7.86 (d, J¼8.0 Hz, 1H), 7.57 (t, J¼7.5 Hz, 1H), 7.38 (d,
J¼8.5 Hz, 1H), 7.26 (t, J¼7.5 Hz, 1H), 5.67 (d, J¼3.5 Hz, 1H, H10), 4.51
(d, J¼10.0 Hz, 1H), 4.33–4.37 (m, 2H), 4.10 (t, J¼9.3 Hz, 1H), 4.01–
4.05 (m, 1H), 3.80–3.85 (m, 2H), 3.60–3.64 (m, 2H), 3.34–3.52 (m,
6H), 2.64 (dt, J¼13.0, 4.5 Hz, 1H, H2eq), 1.97–2.07 (m, 1H), 1.83 (br,
2H), 1.38–1.73 (m, 2H), 1.42 (br, 8H). 13C NMR (75 MHz, D2O)
5H), 1.20–1.23 (m, 8H). 13C NMR (75 MHz, CDCl3)
d 172.46, 165.53,
165.48, 165.27, 135.96, 133.64, 133.49, 132.34, 129.88, 129.81, 129.76,
129.10, 128.62, 128.47, 128.42, 127.34, 121.76, 119.56, 118.06, 110.72,
108.70, 93.91, 77.50, 77.30, 70.89, 69.97, 69.47, 61.54, 57.85, 57.42,
56.67, 55.85, 50.80, 50.68, 43.08, 39.11, 32.62, 30.50, 29.47, 29.25,
29.10, 27.14, 26.82, 24.75. HRMS (ESI) for C53H58N16O9 calcd
1063.4645 [(MþH)þ]; found: 1063.4676.
d
162.38, 143.37, 135.22, 132.41, 132.03, 131.87, 127.73, 122.79,
122.71, 119.91, 114.72, 113.19, 92.70, 72.05, 71.59, 70.45, 68.72, 67.84,
59.10, 53.47, 49.07, 47.71, 41.07, 40.40, 29.23, 29.08, 29.05, 28.61,
26.98, 26.79, 26.58, 22.01. HRMS (ESI) for C32H50N8O6 calcd
643.3926 [(MþH)þ]; found: 643.3914.
4.1.5. General procedure for the preparation of compounds 9a–d,
10a–d and 11a–d. Compounds (6a–d, 7a–d, or 8a–d, 0.05 mmol)
were suspended in methanol (15 mL), followed by the addition of
30% sodium methoxide (1 mL in methanol). The mixture was stir-
red overnight at room temperature. The solvent was removed
under reduced pressure to give white solids. These solids were
dissolved in a mixed solvent (4 mL of pyridine, 2 mL of triethyl-
amine and 1 mL of water). The mixture was stirred for 1 h when
H2S gas was introduced into the reaction flask. The gas was dis-
continued after the reaction solution turned dark green. The re-
action mixture was stirred overnight. The solvent was removed
under reduced pressure. The residue was subjected to column
chromatography on silica gel (ammonia aqueous solution/metha-
nol 1:5 as eluent) to give products. The resulting products were
dissolved in water, and the pH values of solutions were adjusted to
around 6.0 using diluted hydrochloride acid. Lyophilization yielded
the products as white foams in 70% overall yield.
4.1.5.5. Compound 10a. 1H NMR (500 MHz, D2O)
d 8.16 (s, 1H),
7.90 (d, J¼7.5 Hz, 1H), 7.56 (t, J¼7.5 Hz, 1H), 7.40 (d, J¼8.5 Hz, 1H),
7.26 (t, J¼7.5 Hz, 1H), 5.61 (d, J¼4.0 Hz, 1H, H10), 4.17 (dd, J¼3.5,
11.0 Hz, 1H), 4.09 (dd, J¼9.0, 10.5 Hz, 1H), 3.94–3.99 (m, 2H), 3.75–
3.87 (m, 3H), 3.65 (t, J¼6.5 Hz, 2H), 3.50–3.56 (m, 3H), 3.31–3.37 (m,
2H), 3.13–3.18 (m, 1H), 2.62 (s, 3H, CH3), 2.54 (dt, J¼12.5, 4.8 Hz, 1H,
H2eq), 1.83 (q, J¼12.5 Hz, 1H, H2ax). 13C NMR (75 MHz, D2O)
d
165.78, 141.06, 141.18, 135.34, 134.45, 130.83, 129.05, 122.39,
121.95,120.86,113.37,112.82, 92.00, 73.96, 71.96, 71.20, 70.11, 69.23,
57.05, 53.98, 49.53, 48.92, 47.91, 41.00, 40.71, 29.28, 18.22. HRMS
(ESI) for C27H40N8O6 calcd 573.3144 [(MþH)þ]; found: 573.3121.
4.1.5.6. Compound 10b. 1H NMR (500 MHz, D2O)
d 7.94 (s, 1H),
7.76 (d, J¼8.0 Hz, 1H), 7.49 (t, J¼7.5 Hz, 1H), 7.29 (d, J¼8.5 Hz, 1H),
7.18 (t, J¼7.5 Hz, 1H), 5.57 (d, J¼3.0 Hz, 1H, H10), 4.24 (d, J¼10.0 Hz,
1H), 4.12 (dd, J¼11.0, 3.5 Hz, 1H), 4.05 (dd, J¼10.0, 9.0 Hz, 1H), 3.95–
3.99 (m, 2H), 3.74–3.79 (m, 2H), 3.40–3.53 (m, 5H), 3.27–3.31 (m,
2H), 3.03–3.15 (m, 1H), 2.56 (dt, J¼12.5, 4.5 Hz, 1H, H2eq), 2.49 (s,
3H, CH3), 1.88 (q, J¼12.5 Hz, 1H, H2ax), 1.76 (br, 4H). 13C NMR
4.1.5.1. Compound 9a. 1H NMR (500 MHz, D2O)
d 8.68 (d,
J¼0.5 Hz, 1H), 8.50 (s, 1H), 8.03 (d, J¼8.0 Hz, 1H), 7.66 (td, J¼1.0,
8.5 Hz, 1H), 7.52 (d, J¼8.0 Hz, 1H), 7.35 (td, J¼1.0, 8.5 Hz, 1H), 5.65
(d, J¼4.0 Hz, 1H, H10), 4.25 (dd, J¼3.5, 11.0 Hz, 1H), 4.11 (dd, J¼9.0,
10.5 Hz, 1H), 4.06 (dd, J¼3.0, 10.5 Hz, 1H), 3.95–4.00 (m, 2H), 3.78–
3.90 (m, 2H), 3.72 (t, J¼6.5 Hz, 2H), 3.51–3.60 (m, 3H), 3.43–3.48 (m,
1H), 3.35 (dd, J¼6.5,13.5 Hz,1H), 3.25–3.30 (m,1H), 2.57 (dt, J¼12.5,
4.5 Hz, 1H, H2eq), 1.88 (q, J¼12.5 Hz, 1H, H2ax). 13C NMR (75 MHz,
(75 MHz, D2O)
d 165.46, 141.75, 140.89, 135.07, 134.69, 130.59,
128.66, 122.16, 121.75, 120.72, 112.92, 112.64, 92.70, 73.60, 71.19,
70.41, 69.31, 57.78, 53.90, 51.14, 49.06, 47.86, 40.72, 40.25, 39.85,
29.20, 27.09, 26.56, 18.22. HRMS (ESI) for C29H44N8O6 calcd
601.3457 [(MþH)þ]; found: 601.3454.
D2O)
d 164.51, 143.26, 135.96, 132.94, 132.04, 131.56, 129.11, 122.92,
122.53, 120.36, 115.34, 113.32, 92.14, 73.54, 71.23, 71.05, 70.36,
69.15, 57.49, 53.90, 49.95, 48.93, 47.87, 40.73, 40.65, 29.15. HRMS
(ESI) for C26H38N8O6 calcd 559.2987 [(MþH)þ]; found: 559.3047.
4.1.5.7. Compound 10c. 1H NMR (500 MHz, D2O)
d 8.51 (s, 1H),
8.07 (d, J¼8.0 Hz, 1H), 7.69 (td, J¼1.0, 8.0 Hz, 1H), 7.54 (d, J¼8.0 Hz,
1H), 7.38 (t, J¼7.5 Hz, 1H), 5.69 (d, J¼3.5 Hz, 1H, H10), 4.54 (d,
J¼9.5 Hz, 1H), 4.37–4.39 (m, 2H), 4.11 (t, J¼8.8 Hz, 1H), 4.02–4.06
(m, 1H), 3.81–3.86 (m, 2H), 3.62–3.65 (m, 2H), 3.49–3.53 (m, 4H),
3.39–3.45 (m, 2H), 2.89 (s, 3H, CH3), 2.65 (dt, J¼13.0, 4.5 Hz, 1H,
H2eq), 2.01 (q, J¼12.5 Hz, 1H, H2ax), 1.86–1.91 (m, 2H), 1.74–1.79 (m,
4.1.5.2. Compound 9b. 1H NMR (500 MHz, D2O)
d 8.39 (s, 1H),
8.11 (s, 1H), 7.86 (d, J¼8.0 Hz, 1H), 7.53 (t, J¼7.5 Hz, 1H), 7.37 (d,
J¼8.5 Hz, 1H), 7.23 (t, J¼7.5 Hz, 1H), 5.56 (d, J¼8.5 Hz, 1H, H10), 4.24
(dd, J¼2.5, 10.5 Hz, 1H), 4.11 (dd, J¼3.0, 11.0 Hz, 1H), 4.04 (dd, J¼9.0,
10.5 Hz, 1H), 3.95–3.99 (m, 2H), 3.71–3.78 (m, 2H), 3.45–3.54 (m,
5H), 3.28–3.32 (m, 2H), 3.07–3.09 (m, 1H), 2.55 (dt, J¼12.5, 4.5 Hz,
1H, H2eq), 1.86 (q, J¼12.5 Hz, 1H, H2ax), 1.74 (br, 4H). 13C NMR
2H), 1.51 (br, 4H). 13C NMR (75 MHz, D2O)
d 162.15, 143.61, 140.34,
134.89, 132.60, 131.46, 131.16, 123.03, 120.50, 113.93, 113.28, 92.75,
71.80, 71.63, 70.38, 68.69, 67.78, 59.21, 53.44, 49.06, 47.70, 40.98,
40.36, 29.06, 28.52, 26.69, 26.59, 26.29, 16.33. HRMS (ESI) for
C31H48N8O6 calcd 629.3770 [(MþH)þ]; found: 629.3773.
(75 MHz, D2O) d 165.87,142.16,136.37,135.55,130.76,129.87,122.39,
121.72,120.53,114.65,112.91, 92.69, 73.56, 71.09, 70.49, 69.27, 57.88,
53.86, 51.21, 49.04, 47.86, 40.68, 40.16, 29.18, 27.04, 26.43. HRMS
(ESI) for C28H42N8O6 calcd 587.3300 [(MþH)þ]; found: 587.3314.
4.1.5.8. Compound 10d. 1H NMR (500 MHz, D2O)
d 7.83 (s, 1H),
7.66 (d, J¼7.5 Hz,1H), 7.44 (t, J¼7.5 Hz,1H), 7.21 (d, J¼8.0 Hz,1H), 7.14
(t, J¼7.5 Hz, 1H), 5.55 (d, J¼3.5 Hz, 1H, H10), 4.28 (dd, J¼3.0, 10.5 Hz,
1H), 4.17(dd,J¼3.5,10.5 Hz,1H), 3.97–4.05(m, 3H), 3.67–3.77(m, 2H),
3.54 (t, J¼9.5 Hz,1H), 3.47–3.51 (m, 2H), 3.38–3.41 (m, 2H), 3.27–3.35
4.1.5.3. Compound 9c. 1H NMR (500 MHz, D2O)
d 8.29 (s, 1H),
8.00 (s, 1H), 7.80 (d, J¼7.5 Hz, 1H), 7.48 (t, J¼7.5 Hz, 1H), 7.31 (d,
J¼8.0 Hz, 1H), 7.19 (t, J¼7.5 Hz, 1H), 5.52 (d, J¼3.5 Hz, 1H, H10), 4.22

S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
3439
(m, 2H), 3.05–3.10 (m, 1H), 2.56 (dt, J¼12.5, 4.7 Hz, 1H, H2eq), 2.44 (s,
3H, CH3),1.87 (q, J¼12.5 Hz, 1H, H2ax),1.68–1.70 (m, 4H),1.35–1.48 (m,
on a Biocore 3000 system from Biocore AB and performed as de-
scribed in the literature.9b Streptavidin coated sensor-chip (SA-
chip) were obtained from Biocore and loaded with RNA fragments
to 591–648 RU. An empty cell was used as reference surface. Cal-
culation of dissociation constants by fitting the steady state re-
sponses was performed by using the formulae as R¼Rmax[c/(Kdþc)],
where R¼response, Rmax¼maximum response of one binding site
occupied, c¼concentration.
8H). 13C NMR (75 MHz, D2O)
d 164.68, 141.75, 140.45, 134.73, 134.25,
130.72, 128.69, 122.02, 121.80, 120.49, 112.64, 112.53, 93.13, 73.47,
71.04, 70.64, 69.67, 69.32, 58.23, 53.83, 52.04, 49.08, 47.79, 40.76,
40.66, 29.35, 29.27, 29.21, 28.29, 27.06, 26.95, 17.89. HRMS (ESI) for
C33H52N8O6 calcd 657.4083 [(MþH)þ]; found: 657.4079.
4.1.5.9. Compound 11a. 1H NMR (500 MHz, D2O)
d 7.61 (d,
J¼8.0 Hz, 1H), 7.51 (d, J¼8.0 Hz, 1H), 7.28 (t, J¼7.5 Hz, 1H), 7.20 (t,
J¼7.5 Hz, 1H), 5.49 (d, J¼4.0 Hz, 1H, H10), 4.55 (d, J¼16.0 Hz, 1H),
4.48 (d, J¼16.0 Hz, 1H), 4.29 (dd, J¼11.0, 5.0 Hz, 1H), 3.98–4.06 (m,
2H), 3.88–3.96 (m, 2H), 3.65–3.72 (m, 3H), 3.38–3.53 (m, 6H), 3.30
(dd, J¼13.5, 7.5 Hz, 1H), 3.07–3.16 (m, 2H), 2.97–3.02 (m, 1H), 2.47
(dt, J¼12.5, 4.5 Hz, 1H, H2eq), 1.74 (q, J¼12.5 Hz, 1H, H2ax). 13C NMR
4.2.2. Antibacterial activity assay. The antibacterial activities were
measured according to the published method.24 The P. aeruginosa
standard strain was grown in 1 mL tubes and Mueller-Hinton broth
to an optical density OD600 of 0.5 units. The desired concentrations
of antibiotic were added from stock solutions. The samples were
incubated at 37 ꢀC for 12 h, when the control culture (with no an-
tibiotic) had an OD600 of 1.2–1.6. The OD at 600 nm of each sample
was recorded.
(75 MHz, D2O)
d 170.79, 137.24, 126.86, 126.25, 123.38, 120.58,
118.81, 112.54, 105.54, 92.70, 74.64, 72.07, 71.45, 70.05, 69.89, 57.38,
56.61, 54.29, 49.69, 49.11, 47.79, 41.33, 40.86, 29.90, 23.80. HRMS
(ESI) for C26H42N8O6 calcd 563.3300 [(MþH)þ]; found: 563.3296.
Acknowledgements
4.1.5.10. Compound 11b. 1H NMR (500 MHz, D2O)
d 7.61 (d,
This work was financially supported by the National Natural
Science Foundation of China, and ‘973’ grant from the Ministry of
Science and Technology of China.
J¼8.0 Hz, 1H), 7.51 (dd, J¼1.0, 7.5 Hz, 1H), 7.29 (td, J¼8.0, 1.0 Hz, 1H),
7.20 (td, J¼8.0, 1.0 Hz, 1H), 5.55 (d, J¼4.0 Hz, 1H, H10), 4.60 (dd,
J¼1.0, 15.5 Hz, 1H), 4.54 (d, J¼15.5 Hz, 1H), 4.34 (dd, J¼11.0, 5.5 Hz,
1H), 4.19 (dd, J¼10.8, 3.3 Hz, 1H), 4.02–4.08 (m, 2H), 3.95–3.99 (m,
1H), 3.88 (t, J¼8.5 Hz, 1H), 3.70–3.79 (m, 2H), 3.42–3.56 (m, 4H),
3.29–3.40 (m, 3H), 3.13–3.20 (m, 2H), 2.91–2.95 (m, 1H), 2.55 (dt,
J¼12.5, 4.5 Hz, 1H, H2eq), 1.85 (q, J¼12.5 Hz, 1H, H2ax), 1.61–1.67 (m,
Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2010.03.034.
4H). 13C NMR (75 MHz, D2O)
d 170.01, 137.31, 126.25, 126.16, 123.46,
120.63, 118.85, 112.56, 105.50, 92.69, 73.88, 71.22, 70.90, 70.31,
69.38, 57.70, 56.64, 53.95, 50.90, 49.05, 47.88, 41.32, 40.75, 39.94,
29.31, 26.83, 26.66, 23.79. HRMS (ESI) for C28H46N8O6 calcd
591.3613 [(MþH)þ]; found: 591.3637.
References and notes
1. Moazed, D.; Noller, H. F. Nature 1987, 327, 389–394.
2. Fourmy, D.; Recht, M. I.; Blanchard, S. C.; Puglisi, J. D. Science 1996, 274,
1367–1371.
3. Recht, M. I.; Fourmy, D.; Blanchard, S. C.; Dahlquist, K. D.; Puglisi, J. D. J. Mol. Biol.
1996, 262, 421–436.
4. Spahn, C. M.; Prescott, C. D. J. Mol. Med. 1996, 74, 423–439.
5. Carter, A. P.; Clemons, W. M.; Brodersen, D. E.; Morgan-Warren, R. J.; Wimberly,
B. T.; Ramakrishnan, V. Nature 2000, 407, 340–348.
6. Ye, X.-S.; Zhang, L.-H. Curr. Med. Chem. 2002, 9, 929–939.
7. Woodcock, J.; Moazed, D.; Cannon, M.; Davies, J.; Noller, H. F. EMBO J. 1991, 10,
3099–3100.
8. (a) Tor, Y. ChemBioChem 2003, 4, 998–1007; (b) Zhou, J.; Wang, G. N.; Zhang,
L.-H.; Ye, X.-S. Med. Res. Rev. 2007, 27, 279–316.
9. (a) Sucheck, S. J.; Wong, A. L.; Koeller, K. M.; Boehr, D. D.; Draker, K.; Sears, P.;
Wright, G. D.; Wong, C.-H. J. Am. Chem. Soc. 2000, 122, 5230–5231; (b) Green-
berg, W. A.; Priestley, E. S.; Sears, S. P.; Alper, P. B.; Rosenbohm, C.; Hendrix, M.;
Hung, S.-C.; Wong, C.-H. J. Am. Chem. Soc. 1999, 121, 6527–6541.
10. Haddad, J.; Kotra, L. P.; Llano-Sotelo, B.; Kim, C.; Azucena, E. F.; Liu, M.; Vaku-
lenko, S. B.; Chow, C. S.; Mobashery, S. J. Am. Chem. Soc. 2002, 124, 3229–3237.
11. (a) Ding, Y. L.; Hofstadler, S. A.; Swayze, E. E.; Risen, L.; Griffey, R. H. Angew.
Chem., Int. Ed. 2003, 42, 3409–3412; (b) Blount, K. F.; Zhao, F.; Hermann, T.; Tor,
Y. J. Am. Chem. Soc. 2005, 127, 9818–9829; (c) Chang, C.-W. T.; Hui, Y.; Elcher, B.;
Wang, J.; Li, J.; Rai, R. Org. Lett. 2002, 4, 6403–6406; (d) Fridman, M.; Belakhov,
V.; Yaron, S.; Baasov, T. Org. Lett. 2003, 5, 3575–3578; (e) Asensio, J. L.; Hidalgo,
A.; Bastida, A.; Torrado, M.; Corzana, F.; Chiara, J. L.; Garcia-Junceda, E.; Canada,
J.; Jimenez-Barbero, J. J. Am. Chem. Soc. 2005, 127, 8278–8279; (f) Bastida, A.;
Hidalgo, A.; Chiara, J. L.; Torrado, M.; Corzana, F.; Perez-Canadillas, J. M.; Groves,
P.; Garcia-Junceda, E.; Gonzalez, C.; Jimenez-Barbero, J.; Asensio, J. L. J. Am.
Chem. Soc. 2006, 128, 100–116.
12. (a) Nunns, L. C.; Spence, A. L.; Slater, J. M.; Berrisford, J. D. Tetrahedron Lett. 1999,
40, 9341–9345; (b) Pang, L.-J.; Wang, D.; Zhou, J.; Zhang, L.-H.; Ye, X.-S. Org.
Biomol. Chem. 2009, 7, 4252–4266.
13. Jiang, L. C.; Majumdar, A.; Hu, W. D.; Jaishree, T. J.; Xu, W. J.; Patel, J. D. Structure
1999, 7, 817–834.
14. (a) Hamasaki, K.; Woo, W.-C.; Ueno, A. Tetrahedron Lett. 2000, 41, 8327–8332;
(b) Gelus, N.; Hamy, F.; Bailly, C. Bioorg. Med. Chem. 1999, 7, 1075–1079.
15. Ishida, J.; Wang, H. K.; Bastow, K. F.; Hu, C. Q.; Lee, K. Bioorg. Med. Chem. Lett.
1999, 9, 3319–3324.
16. (a) Kusurkar, S. R.; Goswami, K. S. Tetrahedron 2004, 60, 5315–5318; (b) Yu, X.;
Yang, M. Bioorg. Med. Chem. Lett. 2004, 14, 3127–3130.
4.1.5.11. Compound 11c. 1H NMR (500 MHz, D2O)
d 7.59 (d,
J¼8.0 Hz, 1H), 7.51 (d, J¼8.0 Hz, 1H), 7.28 (t, J¼7.5 Hz, 1H), 7.19 (t,
J¼7.5 Hz, 1H), 5.36 (d, J¼3.5 Hz, 1H, H10), 4.50 (d, J¼16.0 Hz, 1H),
4.42 (d, J¼15.5 Hz, 1H), 4.15 (dd, J¼11.0, 5.0 Hz, 1H), 3.93–4.01 (m,
3H), 3.86 (t, J¼10.0 Hz, 1H), 3.78 (t, J¼3.5 Hz, 1H, H5), 3.64 (dt,
J¼12.0, 4.5 Hz, 1H), 3.43–3.53 (m, 3H), 3.32–3.38 (m, 2H), 3.18–3.27
(m, 3H), 3.05–3.15 (m, 2H), 2.84–2.91 (m, 1H), 2.42 (dt, J¼12.5,
4.5 Hz, 1H, H2eq), 1.67 (q, J¼12.5 Hz, 1H, H2ax), 1.45–1.57 (m, 4H),
1.34 (br, 4H). 13C NMR (75 MHz, D2O)
d 170.56,137.21,127.21,126.32,
123.30, 120.55, 118.77, 112.51, 105.63, 94.51, 75.36, 71.77, 71.19,
71.04, 69.82, 58.29, 56.64, 54.63, 51.81, 49.37, 47.73, 41.33, 41.06,
40.11, 30.67, 29.00, 28.91, 26.67, 26.50, 23.91. HRMS (ESI) for
C30H50N8O6 calcd 619.3926 [(MþH)þ]; found: 619.3935.
4.1.5.12. Compound 11d. 1H NMR (500 MHz, D2O)
d 7.60 (d,
J¼8.0 Hz, 1H), 7.51(d, J¼7.5 Hz, 1H), 7.28 (t, J¼7.5 Hz, 1H), 7.20 (t,
J¼7.5 Hz,1H), 5.46 (d, J¼3.5 Hz,1H, H10), 4.58 (d, J¼16.0 Hz,1H), 4.50
(d, J¼15.5 Hz, 1H), 4.27 (dd, J¼10.0, 5.0 Hz, 1H), 4.12 (dd, J¼10.5,
3.0 Hz, 1H), 4.05 (dd, J¼10.5, 3.0 Hz, 1H), 3.94–3.98 (m, 2H), 3.87 (s,
1H, H5), 3.68 (td, J¼12.0, 4.5 Hz, 1H), 3.61 (td, J¼12.0, 4.0 Hz, 1H),
3.47–3.52 (m, 2H), 3.12–3.42 (m, 7H), 2.87–2.94 (m, 1H), 2.49 (dt,
J¼12.5, 4.5 Hz, 1H, H2eq), 1.78 (q, J¼12.5 Hz, 1H, H2ax), 1.54–1.58 (m,
4H), 1.28 (br, 8H). 13C NMR (75 MHz, D2O)
d 169.81, 137.26, 126.34,
126.20, 123.40, 120.59, 118.82, 112.53, 105.45, 93.51, 74.37, 71.45,
70.56, 70.09, 69.98, 57.95, 56.46, 54.16, 51.62, 49.16, 47.82, 41.19,
40.88, 40.25, 29.73, 29.17, 28.97, 28.92, 27.00, 26.60, 23.63. HRMS
(ESI) for C32H54N8O6 calcd 669.4058 [(MþNa)þ]; found: 669.4062.
4.2. Biological assay
17. Zhao, M.; Bi, L. R.; Wang, W.; Wang, C.; Baudy-Floc’h, M.; Ju, J. F.; Peng, S. Q.
Bioorg. Med. Chem. 2006, 14, 6998–7010.
18. Wu, Y. F.; Zhao, M.; Wang, C.; Peng, S. Q. Bioorg. Med. Chem. Lett. 2002, 12,
2331–2333.
4.2.1. SPR binding studies. Biotin-labelled RNA fragments were
purchased at Bioneer (Korea). SPR measurements were conducted

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S. Wu et al. / Tetrahedron 66 (2010) 3433–3440
19. Park, K. C. W.; Auer, M.; Jaksche, H.; Wong, C.-H. J. Am. Chem. Soc. 1996, 118,
22. Davis, T. M.; Wilson, W. D. Methods Enzymol. 2001, 340, 22–51.
23. -Carboline-3-carboxylic acid derivatives 4a and 4b were also used for the
10150–10155.
b
20. Yan, R. B.; Yang, F.; Wu, Y. F.; Zhang, L.-H.; Ye, X.-S. Tetrahedron Lett. 2005, 46,
preliminary screening against P. aeruginosa standard strain, but they did not
8993–8995.
show any obvious antibacterial activity.
21. Hendrix, M.; Priestley, E. S.; Joyce, G. F.; Wong, C.-H. J. Am. Chem. Soc. 1997, 119,
24. Waterworth, P. M. In Laboratory Methods in Antimicrobial Chemotherapy; Gar-
3641–3648.
rod, L., Ed.; Churchill Livingstone: Edinburgh, 1978; pp 31–40.