Synthesis and antibacterial evaluation of novel 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives

Article abstract of DOI:10.1016/j.bmcl.2018.06.006

A series of novel 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives were designed, synthesized and evaluated for their in vitro antibacterial activity. The results showed that the majority of the target compounds displayed potent activity against erythromycin-susceptible S. pyogenes, erythromycin-resistant S. pneumoniae A22072 expressing the mef gene and S. pneumoniae AB11 expressing the mef and erm genes. Besides, most of the target compounds exhibited moderate activity against erythromycin-susceptible S. aureus ATCC25923 and B. subtilis ATCC9372. In particular, compounds 11a, 11b, 11c, 11e, 11f and 11h were found to exert favorable antibacterial activity against erythromycin-susceptible S. pyogenes with the MIC values of 0.015–0.125 μg/mL. Furthermore, compounds 10e, 11a, 11b and 11c showed superior activity against erythromycin-resistant S. pneumoniae A22072 with the MIC values of 0.25–0.5 μg/mL. Additionally, compound 11c was the most effective against all the erythromycin-resistant S. pneumoniae strains (A22072, B1 and AB11), exhibiting 8-, 8- and 32-fold more potent activity than clarithromycin, respectively.

Full text of DOI:10.1016/j.bmcl.2018.06.006

Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial evaluation of novel 11-O-aralkylcarbamoyl-3-O-
descladinosylclarithromycin derivatives
Li Jiaa, Yinhu Wanga, Yanxia Wangb, Yinhui Qina, Chaoyu Hua, Juzheng Shengb,⁎, Shutao Maa,⁎
a
Department of Medicinal Chemistry, Key Laboratory of Chemical Biology of Natural Products (Ministry of Education) School of Pharmaceutical Sciences, Shandong
University, 44 West Culture Road, Jinan 250012, China
b
Institute of Biochemical and Biotechnological Drug, Key Laboratory of Chemical Biology of Natural Products (Ministry of Education), School of Pharmaceutical Sciences,
Shandong University, 44 West Culture Road, Jinan 250012, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of novel 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives were designed, synthe-
sized and evaluated for their in vitro antibacterial activity. The results showed that the majority of the target
compounds displayed potent activity against erythromycin-susceptible S. pyogenes, erythromycin-resistant S.
pneumoniae A22072 expressing the mef gene and S. pneumoniae AB11 expressing the mef and erm genes. Besides,
most of the target compounds exhibited moderate activity against erythromycin-susceptible S. aureus
ATCC25923 and B. subtilis ATCC9372. In particular, compounds 11a, 11b, 11c, 11e, 11f and 11h were found to
exert favorable antibacterial activity against erythromycin-susceptible S. pyogenes with the MIC values of
0.015–0.125 μg/mL. Furthermore, compounds 10e, 11a, 11b and 11c showed superior activity against ery-
thromycin-resistant S. pneumoniae A22072 with the MIC values of 0.25–0.5 μg/mL. Additionally, compound 11c
was the most effective against all the erythromycin-resistant S. pneumoniae strains (A22072, B1 and AB11),
exhibiting 8-, 8- and 32-fold more potent activity than clarithromycin, respectively.
11-O-Aralkylcarbamoyl-3-O-
descladinosylclarithromycin derivatives
Design and synthesis
Antibacterial activity
Macrolide antibiotics, which are weakly alkaline and lipophilic
compounds produced by Streptomycetes,1 have been commonly used for
the treatment of upper and lower respiratory tract infections since
1950s because of favorable antibacterial activity, broad antibacterial
spectrum and good tolerance.2 Mechanistic studies demonstrate that
macrolides can serve as potent protein synthesis inhibitors by binding
to the peptide exit tunnel of the large subunit (50S) of bacterial ribo-
some, hence interfering with the elongation of nascent polypeptide
chains.3 Erythromycin A (EMA), which belongs to the first-generation
macrolides, readily degrades under acidic conditions, leading to the loss
of antibacterial activity and the generation of gastrointestinal side ef-
fects.4 Clarithromycin (CAM) and azithromycin (AZM) (Fig. 1), the
representatives of the second-generation macrolides, have better acid-
stability in the stomach and superior bioavailability, as well as fewer
gastrointestinal side effects.
mef gene-mediated membrane protein efflux pump that can limit the
steady-state accumulation of drugs by transporting antibiotics out of
cytoplasm.6 Therefore, it’s urgent to develop novel macrolide anti-
biotics against resistant pathogens. An X-ray cocrystal structure re-
search reveals that 3-O-cladinose is not a necessary moiety for anti-
bacterial activity,7 and modification at the C-3 position results in
enhanced activity against efflux resistance.8 Consequently, in the late
1990s, the third generation macrolides known as ketolides1 and acy-
lides9 (Fig. 1) were designed to tackle bacterial resistance.
Extensive investigation has been carried out on the chemical mod-
ifications of 14-membered macrolides to effectively cope with bacterial
resistance over the past years. Compound EP-1553 (Fig. 1), bearing an
arylalkyl group at the C-11 position, exhibited good activity against
macrolide-resistant bacteria.10 We reported a 15-membered macrolide
azithromycin derivative (A) (Fig. 1), which was modified at the C-11
and C-4″ positions, as well as showed remarkably improved anti-re-
sistant activity compared to CAM and AZM.11 In addition, we designed
and synthesized a series of 11-O-carbamoyl clarithromycin ketolides (B)
(Fig. 1), showing comparable activity against susceptible bacteria and
improved activity against resistant bacteria in comparison with CAM
and AZM.12 Furthermore, the compound FSM-100573 synthesized by
However, more and more inappropriate use of macrolides leads to
the increasing drug resistance, which severely threatens the therapeutic
effectiveness of macrolides and limits the clinical use of macrolides.5
Two distinguished mechanisms have accounted for the majority of
macrolide resistance: the erm gene-mediated base-specific mono- or di-
methylation of 23S rRNA, which leads to the MLSB resistance, and the
⁎
Corresponding authors.
E-mail addresses: shengjuzheng@163.com (J. Sheng), mashutao@sdu.edu.cn (S. Ma).
https://doi.org/10.1016/j.bmcl.2018.06.006
Received 16 March 2018; Received in revised form 31 May 2018; Accepted 1 June 2018
0960-894X/©2018PublishedbyElsevierLtd.
Pleasecitethisarticleas:Jia,L.,Bioorganic&MedicinalChemistryLetters(2018),https://doi.org/10.1016/j.bmcl.2018.06.006

L. Jia et al.
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Fig. 1. Structures of clarithromycin, azithromycin, ketolides, acylides, EP-1553, A, B and FSM-100573.
Scheme 1. Synthesis of propiolic acids. Reagents and conditions: a) methanol, sulfuric acid, 75 °C, 12 h, 86–100%; b) bromine, CH2Cl2, 25 °C, 24 h, 40–100%; c)
KOH, ethanol, 85 °C, 36 h, 34–81%.
2

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Scheme 2. Synthesis of 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives (10a–10i). Reagents and conditions: a) HCl, H2O, 25 °C, 3 h, 84%; b)
Ac2O, Et3N, DCM, 0–25 °C, 36 h, 97%; c) pyridine, BTC, DCM, 0–25 °C, 20 h, 99%; d) PCC, DCM, 25 °C, 24 h, 91%; e) ethylenediamine, pyridine hydrochloride, 15 °C,
6 h, 43%; f) HOBt, DCC, THF, 0–25 °C, 10 h, 100%; g) CH3OH, 55 °C, 24 h, 36–55%; h) ethylenediamine, 25 °C, 6 h, 21%.
the convergent assembly of simple chemical building blocks was found
to displayed superior potencies against Gram-positive and Gram-nega-
tive bacteria.13
ethanol.
The synthetic method for 11-O-aralkylcarbamoyl-3-O-de-
scladinosylclarithromycin derivatives is shown in Schemes 2 and 3
14,15 Clarithromycin was used as the starting material for the synthesis
On the basis of the consideration detailed above, we designed and
.
synthesized
a
series of novel 11-O-aralkylcarbamoyl-3-O-de-
of the target compounds, which was treated with 36% hydrochloric
acid to generate the 3-descladinosylclarithromycin (1). Then, it was
coupled with acetic anhydride in the presence of triethylamine to give
the acetyl product (2) that was subsequently reacted with bis(tri-
chloromethyl)carbonate (BTC) to afford the 11,12-cyclic carbonate (3)
in the presence of pyridine. After that, the 3-hydroxy group of 3 was
converted into 3-ketone to obtain the ketone (4) under pyridinium
chlorochromate (PCC) oxidation, which was treated with ethylenedia-
mine and pyridine hydrochloride at 15 °C to give 2′-O-acetyl-11-O-
scladinosylclarithromycin derivatives to prevent the erm- or mef-medi-
ated bacterial resistance and broaden their antibacterial spectra. On the
one hand, the removal of 3-O-cladinose can avoid the induction of
bacterial resistance. On the other hand, the 11-O-arylalkylcarbamoyl
side chain is beneficial to bind with A752 in domain II through addi-
tional forces such as hydrogen bonding, π-π stacking or van der Waals
interactions to improve the antibacterial activity. Besides, we hope that
the introductions of propynylamide group and 3-pyridyl acetate group
are able to enhance the antibacterial activity.
The general synthetic method for the propiolic acids is shown in
Scheme 1. The reaction of different acrylic acids gave corresponding
methyl acrylates in the presence of methanol and concentrated sulfuric
acid. Then, they were dibrominated by Br2. Finally, the corresponding
propiolic acids (A1–A8) were prepared in the presence of KOH and
(aminoethyl)carbamoyl-3-O-descladinosyl-3-ketoclarithromycin
(5).
The structure of 5 was confirmed by 1H and 13C NMR spectra which
displayed in the Supplementary material in detail and further HMBC
spectrum (correlation of CH-11 (δ 4.67)/CO (δ 156.12)) indicated that
the ethylenediamine side chain was linked to the C-11 position. Finally,
the target compounds (10a–10h) were prepared by coupling 5 with the
3

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Scheme 3. Synthesis of 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives (11a–11i). Reagents and conditions: a) 3-pyridylacetic acid hydro-
chloride, pyridine, DCC, DMAP, CH2Cl2, 0–25 °C, 7 h, 85%; b) ethylenediamine, pyridine hydrochloride, 15 °C, 6 h, 46%; c) HOBt, DCC, THF, 0–25 °C, 10 h, 96–100%;
d) CH3OH, 55 °C, 24 h, 46–67%; e) ethylenediamine, 25 °C, 6 h, 21%.
corresponding propiolic acids (A1-A8) in the presence of 1-hydro-
xybenzotrizole (HOBt) and dicyclohexylcarbodiimide (DCC), followed
by methanolysis. Besides, treatment of 4 treated with ethylenediamine
at 25 °C gave 2′-O-acetyl-10,11-dehydration-3-O-descladinosyl-3-keto-
clarithromycin (6), and the target compound (10i) was prepared after
deprotection in methanol.16
3-Hydroxy group of 3 was converted into 3-pyridyl acetate product
(7) under 3-pyridylacetic acid hydrochloride, DCC, DMAP and pyridine,
which was treated with ethylenediamine and pyridine hydrochloride to
give 11-O-(aminoethyl)carbamoyl intermediate (8). After that, the
target compounds (11a–11h) were prepared by coupling 8 with the
selected acids in the presence of HOBt and DCC, followed by metha-
nolysis. In addition, 7 was treated with ethylenediamine at 25 °C to give
2′-O-acetyl-10,11-anhydro-3-O-descladinosyl-3-O-(2-(3′-pyridyl)acetyl)
clarithromycin (9), and the target compound (11i) was prepared after
deprotection in methanol.17
the erm gene), Streptococcus pneumoniae AB11 (erythromycin-resistant
strain expressing the erm and mef genes) and Streptococcus pyogenes R1
(erythromycin-resistant strain isolated clinically). The MIC results are
shown in Table 1.
Compared to comparators AZM and CAM, the 11-O-aralkylcarba-
moyl-3-O-descladinosylclarithromycin derivatives (10a–10h) uni-
versally exhibited excellent antibacterial activity against S. pneumoniae
A22072 and S. pneumoniae AB11, and good antibacterial activity
against S. pyogenes and B. subtilis ATCC9372, but failed to show im-
proved antibacterial activity against E. coli ATCC25922 and P. aerugi-
nosa ATCC27853. It was noteworthy that compound 10i showed almost
no antibacterial activity against all tested strains. Surprisingly, the 11-
O-aralkylcarbamoyl-3-O-descladinosylclarithromycin
derivatives
(11a–11i) displayed comparable antibacterial activity against all the
five susceptible strains and superior antibacterial activity against all the
five resistant strains compared with CAM and AZM.
All the 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin de-
rivatives (10a–10i and 11a–11i), as well as CAM and AZM as refer-
ences, were tested for their in vitro antibacterial activity. The minimal
inhibitory concentration (MIC) values of antibacterial activity in vitro
were determined with the application of the standard broth micro-
dilution method recommended by NCCLS. The tested strains included
five susceptible strains of Staphylococcus aureus ATCC25923 (ery-
thromycin-susceptible strain), Streptococcus pyogenes (erythromycin-
susceptible strain isolated clinically), Bacillus subtilis ATCC9372 (peni-
cillin-susceptible strain), Escherichia coli ATCC25922 (penicillin-sus-
ceptible strain) and Pseudomonas aeruginosa ATCC27853 (penicillin-
susceptible strain), and five resistant strains of Staphylococcus aureus
ATCC43300 (methicillin-resistant strain), Streptococcus pneumoniae
A22072 (erythromycin-resistant strain expressing the mef gene),
Streptococcus pneumoniae B1 (erythromycin-resistant strain expressing
Among them, compounds 11a, 11b and 11c exhibited the best an-
tibacterial activity against S. pyogenes with MIC values of
0.015–0.03 µg/mL, as well as against S. aureus ATCC25923 with MIC
value of 1 µg/mL. Additionally, compounds 10d, 10e, 10g, 10h, 11b,
11c and 11i displayed the best antibacterial activity with MIC value of
1 µg/mL against B. subtilis ATCC9372. As for E. coli ATCC25922 and P.
aeruginosa ATCC27853, the activity of all the compounds was weak,
with a MIC value of only 64 µg/mL. In the inhibition of S. aureus
ATCC43300, the most active compounds 11c and 11f exerted MIC va-
lues of 32 µg/mL, 4-fold better than CAM and AZM. Furthermore,
compounds 10e, 11a, 11b and 11c showed the strongest activity
against S. pneumoniae A22072 with the MIC ≤0.5 µg/mL, showing 4-
fold and 8-fold more potent activity than AZM and CAM, respectively.
Besides, compound 11c demonstrated 8-fold better antibacterial ac-
tivity with MIC value of 16 µg/mL against S. pneumoniae B1 than CAM
4

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Table 1
In vitro antibacterial activity of 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives.
Compound S. aureus
ATCC
E. coli ATCC S. pyogenesc P. aeruginosa
B. subtilis
S. aureus
S. pneumoniae
S. pneumoniae
S. pneumoniae
S. pyogenes
25922b
ATCC27853d
ATCC 9372e ATCC
43300f
B1g
A22072h
AB11i
R1j
25923a
10a
10b
10c
10d
10e
10f
10g
10h
10i
11a
11b
11c
11d
11e
11f
11g
11h
11i
32
16
8
8
8
16
16
16
> 128
1
1
1
2
8
16
8
4
1
0.25
0.25
> 128
> 128
> 128
128
> 128
> 128
> 128
> 128
> 128
64
2
1
1
1
0.25
1
1
> 128
> 128
> 128
> 128
128
> 128
> 128
> 128
64
64
64
64
128
4
2
2
1
1
4
1
1
128
2
1
1
4
4
8
2
2
128
128
64
128
128
128
128
128
128
128
128
> 128
32
32
16
64
32
64
64
32
32
4
2
2
2
0.5
2
2
128
64
64
32
64
128
128
128
> 128
8
4
4
32
8
16
32
16
16
> 128
> 128
128
16
64
128
128
128
64
> 128
128
64
64
32
64
32
128
64
128
> 128
> 128
> 128
> 128
128
0.5
1
64
> 16
0.03
0.015
0.03
0.5
0.125
0.125
0.25
0.125
0.25
0.03
0.03
64
0.5
0.5
0.25
1
1
1
1
1
> 128
> 128
128
128
32
> 128
> 128
> 128
32
128
> 128
> 128
64
64
128
128
128
128
> 128
> 128
> 128
128
16
64
> 128
> 128
128
16
64
1
0.25
0.25
1
4
2
AZM
CAM
> 128
> 128
> 128
128
a
S. aureus ATCC25923: erythromycin-susceptible strain.
E. coli ATCC25922: penicillin-susceptible strain.
S. pyogenes: erythromycin-susceptible strain isolated clinically.
P. aeruginosa ATCC27853: penicillin-susceptible strain.
B. subtilis ATCC9372: erythromycin-susceptible strain.
S. aureus ATCC43300: methicillin-resistant strain.
S. pneumoniae B1: erythromycin-resistant strain encoded by the ermB gene.
S. pneumoniae A22072: erythromycin-resistant strain encoded by the mefA gene.
S. pneumoniae AB11: erythromycin-resistant strain encoded by the ermB and mefA genes.
S. pyogenes R1: erythromycin-resistant strain isolated clinically.
b
c
d
e
f
g
h
i
j
and AZM. For S. pneumoniae AB11, the MIC values of 11b and 11c
reached 4 µg/mL, 32-fold better than CAM and AZM. In addition,
compounds 11d and 11h displayed the best antibacterial activity
against S. pyogenes R1 with MIC value of 32 µg/mL, 4-fold better than
CAM and AZM.
their activity against resistant strains. We hypothesized that the sub-
stituents at the C-11 position could interact directly with the nucleotide
A752 and the removal of cladinose enhanced activity against efflux
resistance at the same time, resulting in excellent antibacterial activity.
From the data mentioned above, we could summarize their SARs as
follows. Introduction of the novel aralkylcarbamoyl side chains into the
C-11 position could greatly improve activity against erythromycin-re-
sistant S. pneumoniae compared with CAM and AZM due to the addi-
tional binding interaction with A752. The propynylamide-linked com-
pounds were more potent than the compounds linked via arylamide
groups, suggesting that appropriate linking groups were beneficial to
enhance antibacterial activity. In addition, proper length of side chain
could reach the chloramphenicol binding site in bacterial ribosomes,
thereby inhibiting peptide formation, so that proper length was favor-
able to increase the antibacterial activity while the too long or short
side chains tended to decrease the antibacterial activity. Besides, the
electron-withdrawing groups on the benzene ring of the side chains
were good for the improvement of the antibacterial activity, and
compounds with bulkier groups at the end of side chains exhibited
higher antibacterial activity, indicating that the terminal group might
affect the hydrogen bonding, π-π stacking or the electrostatic interac-
tion between the compounds and the bacterial ribosomes. Moreover, in
the case of same C-11 side chains, compounds with the C-3-hydroxyl
into C-3-pyridyl acetate displayed more potent activity against sus-
ceptible and resistant bacteria than compounds with the C-3 ketone.
Furthermore, compound 10i with the C-3 ketone and dehydration at
the C-10,11 lost antibacterial activity, possibly due to that these com-
pounds cannot bind with bacterial ribosome well, thus affecting the
antibacterial activity.
Generally, in comparison with acrylamide-linked compounds12
synthesized before, the propynylamide-linked compounds 10a–10i ex-
hibited more potent antibacterial activity. Besides, compounds 11a
bearing a phenyl side chain of six atoms distance from the O-11 posi-
tion, exerted better antibacterial activity against susceptible strains
than compounds 11e which correspondingly had the same phenyl side
chain of eight atoms distance from the O-11 position. In particular,
among all the synthesized target compounds, compounds 10d, 11a,
11b, 11c and 11e, bearing the side chains of 4-bromophenyl groups or
nitrophenyl groups, were the most active against all the types of tested
bacteria. Compounds 11d and 11h, bearing bigger groups at the end of
side chains, showed excellent antibacterial activity against resistant
strains including S. aureus ATCC43300 and S. pyogenes R1. In addition,
in the case of same C-11 side chains, compounds 11g, 11h and 11i
demonstrated more potent activity against both susceptible and re-
sistant bacteria than compounds 10e, 10h and 10i. Furthermore,
compound 10i almost lost antibacterial activity, while compound 11i
displayed superior antibacterial activity.
In summary, the synthesized target compounds showed comparable
activity against susceptible bacteria and improved activity against re-
sistant bacteria in comparison with CAM and AZM. In addition, most of
the compounds exhibited favorable activity against Gram-positive
bacteria but weak activity against Gram-negative bacteria. The results
indicated that the introduction of the arylalkyl group into the C-11
position of CAM was favorable for the potency of compounds against
some susceptible and resistant strains. Furthermore, modification of the
C-11 and C-3 positions of CAM at the same time could greatly improve
In
a word, a series of novel 11-O-aralkylcarbamoyl-3-O-de-
scladinosylclarithromycin derivatives were designed, synthesized and
evaluated for their in vitro antibacterial activity against various Gram-
5

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Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxx–xxx
positive and Gram-negative bacteria. Among them, a majority of the
target compounds exerted potent activity against erythromycin-sus-
ceptible S. pyogenes and penicillin-susceptible B. subtilis ATCC9372, and
significantly improved activity against the three phenotypes of resistant
S. pneumoniae compared to CAM and AZM. In particular, compounds
11b and 11c possessed the best antibacterial activity against both
sensitive and resistant strains including S. pyogenes (MIC ≤0.03 µg/
mL), S. aureus ATCC25923 (MIC = 1 µg/mL), B. subtilis ATCC9372
(MIC = 1 µg/mL), S. pneumoniae A22072 (MIC ≤0.5 µg/mL), S. pneu-
moniae B1 (MIC ≤32 µg/mL) and S. pneumoniae AB11 (MIC = 4 µg/
mL). Compounds 10d (MIC = 16 µg/mL) displayed potent activity
against S. aureus ATCC43300, showing 8-fold higher activity than CAM
and AZM. Besides, compounds 11d and 11h (MIC = 32 µg/mL) ex-
hibited the strongest antibacterial activity against susceptible S. pyo-
genes R1, 4-fold better than CAM and AZM. More importantly, the re-
sults demonstrated that the modification of both C-11 and C-3 positions
of clarithromycin could dramatically enhance the antibacterial activity.
Further optimization of clarithromycin derivatives with potent anti-
bacterial activity should continue to be investigated.
14. Agouridas C, Denis A, Auger JM, et al. J Med Chem. 1998;41:4080.
15. Wei X, You Q. Org Process Res. 2006;10:446.
16. The representative experimental procedure and analytical data of 11-O-(2-(3-(4-me-
thylphenyl)propionamido)ethyl)carbamoyl-3-O-descladinosyl-3-ketoclarithromycin
(10e). To a solution of 4-methylphenypropiolic acid (80 mg, 0.50 mmol) and HOBt
(85 mg, 0.63 mmol) in THF (6.0 mL) was stirred at 0 °C for 30 min. Afterwards, DCC
(130 mg, 0.63 mmol) was added to the solution. The resulting solution was allowed to
stir at 0 °C for 6 h and then added 5 (300 mg, 0.42 mmol). The reaction mixture was
stirred for 4 h at room temperature and evaporated in vacuum to dryness. The residue
was dissolved in CH2Cl2 (15 mL) and then filtered. The resulting solution was washed
by saturated NaHCO3 solution and brine. The organic layers was combined and dried
over anhydrous Na2SO4, filtered, and concentrated in vacuum to afford crude pro-
duct. The above crude product was dissolved in methanol, and stirred for 24 h at
55 °C. The reaction solution was subsequently concentrated to provide the crude
product. The above crude product was purified by flash column chromatography
(dichloromethane/methanol, 30:1) to afford the desired product 10e (151 mg, 37%)
as white solids. mp 128–131 °C, Rf = 0.51 (dichloromethane/methanol, 10:1); 1H
NMR (400 MHz, CDCl3, δ ppm): 7.42 (d, J = 8.1 Hz, 2H), 7.16 (d, J = 7.8 Hz, 2H),
5.01 (d, J = 11.1 Hz, 1H), 4.79 (s, 1H), 4.40 (d, J = 7.1 Hz, 1H), 4.11 (d, J = 10.2 Hz,
1H), 3.75 (d, J = 6.9 Hz, 2H), 3.55 (s, 1H), 3.45 (s, 1H), 3.26 (s, 1H), 2.81 (s, 3H),
2.38 (s, 3H), 2.34 (s, 1H), 2.18 (d, J = 6.3 Hz, 1H), 1.98 (s, 1H), 1.93 (s, 1H), 1.85 (s,
1H), 1.66 (q, J = 6.7 Hz, 3H), 1.48 (s, 3H), 1.32 (d, J = 7.2 Hz, 3H), 1.27 (t,
J = 6.2 Hz, 15H), 1.23-1.19 (m, 6H), 0.89 (d, J = 7.2 Hz, 3H), 0.88-0.85 (m, 3H),
0.83 (s, 3H); 13C NMR (150MHz, DMSO-d6, δ ppm): 213.76, 212.75, 169.94, 156.48,
153.21, 140.79, 132.45, 130.75, 130.03, 129.59, 128.30, 117.22, 107.36, 104.33,
86.76, 84.05, 82.53, 79.81, 78.18, 70.65, 68.80, 64.97, 63.47, 52.28, 49.30, 47.63,
46.04, 30.25, 29.10, 26.78, 23.48, 23.08, 21.60, 21.54, 21.31, 19.55, 18.91, 16.14,
16.04, 15.08, 14.47, 11.67, 11.49; MS (ESI) m/z calcd. for C43H65N3O12 815.5; found
[M+H]+ 817.5.
Acknowledgments
This research was supported financially by the National Natural
Science Foundation of China (81673284), Major Project of Research
and Development of Shandong Province (2016GSF201202), Key
Research and Development Project of Shandong Province
(2017CXGC1401), and Major Project of Science and Technology of
Shandong Province (2015ZDJS04001).
17. The representative experimental procedure and analytical data of 11-O-(2-(2-amino-
4-nitrobenzamido)ethyl)carbamoyl-3-O-descladinosyl-3-O-(2-(3′-pyridyl)acetyl)clari-
thromycin (11c). To a solution of 2-amino-4-nitrobenzoic acid (80 mg, 0.44 mmol)
and HOBt (73 mg, 0.54 mmol) in THF (6.0 mL) was stirred at 0 °C for 30 min.
Afterwards, DCC (111 mg, 0.54 mmol) was added to the solution. The resulting so-
lution was allowed to stir at 0 °C for 6 h and then added 8 (300 mg, 0.36 mmol). The
reaction mixture was stirred for 4 h at room temperature and evaporated in vacuum
to dryness. The residue was dissolved in CH2Cl2 (15 mL) and then filtered. The re-
sulting solution was washed by saturated NaHCO3 solution and brine. The organic
layer was combined and dried over anhydrous Na2SO4, filtered, and concentrated in
vacuum to afford crude product. The above crude product was dissolved in methanol,
and stirred for 24 h at 55 °C. The reaction solution was subsequently concentrated to
provide the crude product. The above crude product was purified by flash column
chromatography (dichloromethane/methanol, 30:1) to afford the desired product 11c
(211 mg, 50%) as yellow solids. yield 50%, mp 127–130 °C, Rf = 0.23 (di-
chloromethane/methanol, 10:1); 1H NMR (400 MHz, DMSO-d6, δ ppm): 8.67 (t,
J = 5.6 Hz, 1H), 8.51 (t, J = 2.5 Hz, 1H), 8.48 (d, J = 4.7 Hz, 1H), 8.02 (dd, J = 9.2,
2.9 Hz, 1H), 7.78 (d, J = 8.1 Hz, 2H), 7.72 (d, J = 8.4 Hz, 1H), 7.38 (td, J = 7.8,
4.7 Hz, 1H), 7.30-7.21 (m, 1H), 6.79 (d, J = 9.3 Hz, 2H), 5.50 (d, J = 7.9 Hz, 1H),
5.35 (d, J = 8.8 Hz, 1H), 4.95 (t, J = 8.9 Hz, 1H), 4.68 (dd, J = 8.5, 3.9 Hz, 1H), 4.39
(d, J = 7.6 Hz, 1H), 4.04 (s, 1H), 3.83 (s, 1H), 3.68-3.62 (m, 1H), 3.59-3.49 (m, 2H),
3.21 (d, J = 6.5 Hz, 2H), 3.06 (s, 1H), 3.00 (s, 3H), 2.35 (d, J = 3.8 Hz, 5H), 2.32 (s,
2H), 1.35 (s, 1H), 1.31 (s, 2H), 1.25-1.18 (m, 6H), 1.07 (s, 3H), 1.05 (s, 3H), 1.00 (d,
J = 6.4 Hz, 6H), 0.95 (d, J = 7.2 Hz, 6H), 0.90 (d, J = 6.2 Hz, 3H), 0.87 (d,
J = 7.1 Hz, 6H); 13C NMR (150 MHz, DMSO-d6, δ ppm): 202.89, 175.07, 170.54,
167.86, 156.91, 155.82, 150.94, 148.58, 137.60, 135.36, 127.84, 126.31, 123.84,
118.91, 116.31, 113.23, 85.28, 81.53, 77.82, 71.73, 70.34, 68.77, 67.62, 65.19,
63.11, 48.81, 47.66, 46.69, 46.36, 43.50, 37.95, 37.40, 36.71, 30.82, 30.47, 27.34,
23.96, 21.86, 21.41, 20.46, 19.12, 18.03, 16.53, 13.43, 12.30, 11.95, 11.50; MS (ESI)
m/z calcd. for C47H70N6O15 958.5; found [M+H]+ 959.7, [M+2H]2+/2 480.6.
A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.bmcl.2018.06.006.
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