Synthesis of isoindole and benzoisoindole derivatives of teicoplanin pseudoaglycon with remarkable antibacterial and antiviral activities

Article abstract of DOI:10.1016/j.bmcl.2012.09.079

The primary amino function of teicoplanin pseudoaglycon has been transformed into arylthioisoindole or benzoisoindole and glycosylthioisoindole derivatives, in a reaction with o-phthalaldehyde or naphtalene-2,3- dicarbaldehyde and various thiols. All of t

Full text of DOI:10.1016/j.bmcl.2012.09.079

Bioorganic & Medicinal Chemistry Letters 22 (2012) 7092–7096
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of isoindole and benzoisoindole derivatives of teicoplanin
pseudoaglycon with remarkable antibacterial and antiviral activities
Attila Sipos a, , Zsolt Török , Erzsébet Roth , Attila Kiss-Szikszai , Gyula Batta , Ilona Bereczki ,
⇑
a
a
b
b
a
}
Zsolt Fejes a, Anikó Borbás a, Eszter Ostorházi c, Ferenc Rozgonyi c, Lieve Naesens d, Pál Herczegh a,
⇑
a Department of Pharmaceutical Chemistry, Medical and Health Science Center, University of Debrecen, Egyetem tér 1, H-4010 Debrecen, Hungary
b Department of Organic Chemistry, University of Debrecen, Egyetem tér 1, H-4010 Debrecen, Hungary
c Microbiology Laboratory, Department of Dermatology, Venerology and Dermatooncology, Semmelweis University, Mária u. 41, H-1085 Budapest, Hungary
d Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
The primary amino function of teicoplanin pseudoaglycon has been transformed into arylthioisoindole or
benzoisoindole and glycosylthioisoindole derivatives, in a reaction with o-phthalaldehyde or naphtalene-
2,3-dicarbaldehyde and various thiols. All of the obtained semisynthetic antibiotics exhibited potent anti-
bacterial activities against Gram-positive bacteria in the ng per ml concentration range. A few of them
showed antiviral activity, in particular against influenza virus.
Received 7 August 2012
Revised 18 September 2012
Accepted 22 September 2012
Available online 29 September 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Teicoplanin
Pseudoaglycon
Isoindole
Antibacterial
Antiviral
Influenza
Glycopeptide antibiotics vancomycin and teicoplanin are used
in the treatment of serious Gram-positive bacterial infections that
are resistant to other antibiotics.1 Due to the emergence and
spread of glycopeptide-resistant enterococci (GRE) and glycopep-
tide intermediate-resistant Staphylococcus aureus (GISA), as well
as teicoplanin-resistant Staphylococcus haemolyticus,2 there is an
urgent need for new antibiotics active against resistant bacteria.
Nagarajan et al. reported on lipophilic N-alkyl derivatives of gly-
copeptide antibiotics possessing high activity against vancomycin-
resistant bacteria.3 Later this observation led to the elaboration of
the highly active subclass of lipoglycopeptides oritavancin, tela-
vancin and dalbavancin.4 In the past few years we have synthe-
sized a series of new derivatives of ristocetin aglycon and of
teicoplanin pseudoaglycon exhibiting high antibacterial and, in
some cases, robust ant-influenza virus activity.5 For the elucidation
of the mechanism of biological action fluorescent isoindole- and
benzoisoindole-fused aglycoristocetin derivatives have also pre-
pared in this laboratory.6 The biological evaluation of these deriv-
atives revealed that the introduction of the isoindole and
benzoisoindole moieties into the N-terminal position of the aglyc-
oristocetin molecule resulted in remarkable increase in the anti-
bacterial and anti-influenza virus activity.
In order to get more information about the effect of (benzo)iso-
indole substituents on the biological activity of glycopeptide anti-
biotic derivatives, we decided to prepare
derivatives from teicoplanin pseudoaglycon.
a series of such
The starting pseudoaglycon 2 can be prepared from teicoplanin
(1) by treatment with anhydrous hydrogen fluoride (Scheme 1).7
The widely used three-component isoindole-formation reac-
tion, involving the heteroring closure of o-phthalaldehyde (or its
benzologs) with primary amine and a thiol,8 was chosen for the
derivatization of the N-terminal of the glycopeptide. Reaction of
the primary amino function of 2 with o-phthalaldehyde and vari-
ous thiols such as (hetero)arylthiols, as well as 1-thio-d-glucopyr-
anose or 1-thio-N-acetyl-d-glucosamine derivatives afforded the
corresponding arylthio- (3), heteroarylthio- (4 and 5) and glycosyl-
thioisoindole (9–12) derivatives in reasonably good yields. In a
similar reaction, using naphtalene-2,3-dialdehyde instead of
o-phthalaldehyde the appropriate benzoisoindole derivatives 6–8
were obtained, incorporating the N-terminal nitrogen of the antibi-
otic into the new heteroring system (Table 1).
The new compounds 3–12 were characterized by HPLC, MALDI-
TOF mass spectroscopy (key data and methods are included in the
Supplementary material). The presence of the newly formed
(benzo)isoindole moieties were confirmed by NMR spectroscopy.
⇑
Corresponding authors. Tel.: +36 52 512 900 22895; fax: +36 52 512 914.
E-mail addresses: sipos.attila@pharm.unideb.hu (A. Sipos), herczeghp@gmail.
com (P. Herczegh).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.09.079

A. Sipos et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7092–7096
7093
O
OH
HN
OH
Cl
OH
OH
O
O
H
O
O
HO
HO
O
O
Cl
H
O
O
AcHN
O
O
H
H
H
H
N
O
N
NH2
H
N
H
N
H
N
H
HN
O
O
HOOC
HO
HO
O
OH
OH
OH
OH
O
1
OH OH
OH
OH
Cl
HO
HF / anizol
-18 °C
2 h
O
O
O
O
80 %
HO
O
Cl
H
O
AcHN
O
H
H
H
H
N
N
NH2
H
O
N
H
N
H
N
H
H
HN
O
O
HOOC
HO
O
OH
OH
HO
OH
2
Scheme 1. Preparation of teicoplanin pseudoaglycon 2.
Table 1
Synthesis and structure of novel teicoplanin pseudoaglycon derivatives 3–12
OH
O
Cl
OH
HO
HO
O
O
O
O
Cl
O
AcHN
H
N
H
H
H
O
H
NR'
H
O
MeOH
CHO
CHO
N
N
N
N
H
H
2
+
+
R-SH
H
H
HN
HOOC
O
O
0 °C, 2 h
HO
O
OH
OH
OH
HO
3 12
-
Product
3
Starting dialdehyde
Thiol reagent (R-SH)
Formed isoindole moiety (R’N-)a
Yield (%)
76
logPb
CHO
SH
N
S
7.21
5.24
CHO
CHO
CHO
SH
N
N
N
N
S
4
65
N
(continued on next page)

7094
A. Sipos et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7092–7096
Table 1 (continued)
Product
Starting dialdehyde
Thiol reagent (R-SH)
Formed isoindole moiety (R’N-)a
Yield (%)
49
logPb
CHO
S
N
SH
N
S
5
7.95
CHO
S
N
CHO
CHO
SH
SH
N
6
7
31
62
8.44
6.47
S
CHO
CHO
N
N
N
N
S
N
CHO
CHO
S
N
N
SH
SH
8
9
58
51
9.18
2.20
S
S
N
CHO
CHO
HO
HO
N
O
OH
S
OH
OH
O
HO
OH
OH
CHO
CHO
AcO
AcO
N
O
OAc
SH
OAc
S
OAc
OAc
10
11
72
6.25
O
AcO
OAc
CHO
CHO
HO
HO
O
N
SH
NHAc
NHAc
S
OH
HO
49
52
3.53
5.03
O
OH
OH
CHO
CHO
AcO
AcO
N
O
NHAc
OAc
SH
NHAc
S
12
O
AcO
OAc
OAc
a
General procedure: 0.11 mmol dialdehyde, 0.11 mmol thiol in 3 mL MeOH (protected from light, under argon) stirred for 20 min at 0 °C. 0.05 mmol 2 in 3 mL MeOH added
and stirred for 2 h at RT.
b
LogP values were calculated with ChemSketch logP add-on.9
Determination of the antibacterial activity of this series of com-
pounds against a panel of Gram positive bacteria10 gave excellent
results, as summarized in Table 2. Almost all of the new derivatives
exhibited better MIC and MBC values than the parent antibiotic
teicoplanin.
teicoplanin resistant Enterococcus faecalis strains containing the
vanA or vanB resistance genes. In comparison, the MIC values
of teicoplanin against these three genotypes were
2 lg/mL
(wild-type), 256 (vanA genotype) and 4 g/mL (vanB genotype),
l
respectively. EUCAST reported 566 observed cases of Staphylococ-
The database of the European Committee on Antibacterial
Susceptibility Testing (EUCAST)11 contains the MIC values for a
wide range of bacteria and antimicrobial agents. These EUCAST
data were aggregated from extended time periods and many coun-
tries. According to the data of EUCAST for 6105 Enterococcus faecal-
cus aureus MRSA infections with successful teicoplanin treatment
having the MIC values mostly between 0.25 and 2
our Staphylococcus aureus MRSA strain, we found teicoplanin effec-
tive with an MIC value of 0.5 g/mL. Notably the new isoindole
derivatives showed efficacy at much lower MIC values, that is
0.0075–1 g/mL. Against Staphylococcus aureus MSSA strains,
teicoplanin was effective in the MIC range of 0.5–2 g/mL (analysis
lg/mL. Against
l
is strains, teicoplanin is effective in the MIC range of 0.06–2
For our newly synthesized derivatives, the MIC values against
Enterococcus faecalis were in the range of 0.0075–4 g/mL, either
tested against the teicoplanin susceptible wild-type strain, or two
lg/mL.
l
l
l
from 571 reported cases). In our studies, the reference teicoplanin
(1) was found to be active against an MSSA strain with an MIC of

A. Sipos et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7092–7096
7095
0.5
in the range of 0.0075–0.5
epidermidis, MIC values for teicoplanin were typically between
0.25 and 16 g/mL, in the EUCAST database for 8578 cases. We
determined the MIC values of teicoplanin and the isoindole deriv-
atives against two S. epidermidis strains to be 2–8 g/mL and
0.0075–4 g/mL, respectively. Compounds 3–12 proved to be very
lg/mL, whereas the isoindole derivatives had lower MIC values
lg/mL. With regard to Staphylococcus
l
l
l
active against vancomycin and teicoplanin resistant enterococci,
with some compounds displaying MIC values in the ng/ml range.
Overall, the most active compounds of the series were 6 and 7
benzoisoindole derivatives. Compound 9, containing d-glucosyl
substituent with free hydroxyl groups displayed better activity
than its acetylated counterpart. Although for obtaining an exact
structure–activity relationship a detailed study involving a higher
number of compounds is required, here it can be concluded that
isoindole derivatisation of 2 led to much more potent antibacteri-
als than the parent teicoplanin.
The anti-influenza virus activities and cytotoxic concentra-
tions12 of our products 3–12, in comparison to four antiviral refer-
ence agents, are summarized in Table 3.
With the exception of compounds 7 and 8, the new teicoplanin
pseudoaglycon derivatives showed no anti-influenza virus activity
at subtoxic concentrations. Compared to unsubstituted teicoplanin
pseudoaglycon 2, which was found to possess weak anti-influenza
A virus activity and no activity against B virus, the new heteroaro-
matic moiety was found to have crucial impact on the activity. For
compound 7, a favorable selectivity index was noted, since its ratio
of MCC to EC50 was 24. The 2-S-heteroarylbenzoisoindole function
at the N-terminus of compounds 7 and 8 appeared to be responsi-
ble for this effect. From a comparison with compound 6, which has
a 2-S-homoarylbenzoisoindole at the N-terminus, it can be con-
cluded that the presence of heteroatoms in the 2-S-substituent
may be advantageous. Most of our new derivatives displayed rela-
tively high cytotoxicity in this assay in Madin Darby canine kidney
cells, since the compound concentrations causing minimal altera-
tions in cell morphology were 20 lM or lower.
Besides this anti-influenza virus testing, compounds 2–13 were
evaluated against a selected panel of DNA viruses as well as one
RNA virus (vesicular stomatitis virus). The antiviral activity and
cytotoxicity of 2–12 in human embryonic lung (HEL) fibroblasts13
are summarized in Table 4.
Table 3
Anti-influenza virus activity and cytotoxicity of compounds 2–12 in MDCK cell
cultures
Compounds Antiviral EC50
(
lM)
MCC(lM)
Influenza A/H1N1 Influenza A/H3N2 Influenza B
(A/PR/8/34)
(A/HK/7/87)
(B/HK/5/72)
2
3
4
5
6
7
8
9
23
17
>100
>100
>100
>100
>100
>50
>100
>100
>100
>100
>100
23
P100
4
20
4
<0.8
13
20
<0.8
20
<0.8
20
>100
100
P500
500
>100
>100
>100
>100
0.54
<4.9
>100
>100
>100
>100
1.6
>100
>100
>100
>100
0.54
1.6
>100
>100
>100
>100
4.8
10
11
12
Zanamivir
Ribavirin
Amantadine 212
Rimantadine 14
6.1
6.0
0.45
0.051
4.6
>500
>500
EC50: 50% effective concentration, or concentration producing 50% inhibition of
virus-inducedcytopathic effect, as determined by visual scoring. MCC: Minimum
compound concentration that causes a microscopically detectable alteration of
normal cell morphology. MDCK cells: Madin Darby canine kidney cells.

7096
A. Sipos et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7092–7096
Table 4
the European Social Fund. The work was also supported by
the Hungarian Research Fund OTKA through Grants K 79126,
T-46186, OTKA-NKTH CK 77515, and NK 68578. L.N. acknowledges
the technical assistance from Leentje Persoons and Wim van Dam,
and the financial support from the Flemish Fonds voor
Wetenschappelijk Onderzoek (FWO No. 9.0188.07) and the
Geconcerteerde Onderzoeksacties (GOA/10/014).
Antiviral activity and cytotoxicity of compounds 2–12 in HEL cell cultures
Compounds
Antiviral EC50
(
l
M)
MCC
M)
(
l
HSV-
1
KOS
HSV-
2 G
Vaccinia
virus
Vesicular
stomatitis
virus
HSV-1
TK- KOS
ACVr
2
3
4
5
6
7
8
9
>100
9
47
45
>20
40
>100
45
40
47
40
>100
9
45
45
>20
27
>100
40
11
45
40
>100
>20
P58
47
>20
10
>100
>20
>100
>100
>20
>100
>100
52
>100
P20
50
45
>20
45
>100
P45
40
45
45
>100
P20
>100
P100
100
P100
>100
P100
P100
P100
>100
>250
>250
>250
>100
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.
09.079.
>100
45
10
11
12
45
48
47
52
45
10
21
P250
>100
>250
>250
>250
>100
Brivudin
Cidofovir
Acyclovir
Ganciclovir
0.024 198
1.5
0.14
50
1.5
44
References and notes
0.9
0.14
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0.015 0.013 >100
4
HEL: human embryonic lung fibroblasts; HSV-1 KOS: herpes simplex virus type 1
strain KOS; HSV-2 G: herpes simplex virus type 2 strain G; TKÀ: thymidine kinase-
deficient HSV-1 KOS strain resistant to acyclovir (ACVr); EC50
: 50% effective
concentration, or concentration required for 50% decrease of virus-induced
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Whereas teicoplanin pseudoaglycon (2) was found to be inac-
tive against these viruses, several of the isoindole and benzoisoin-
dole derivatives 3–12 showed weak inhibitory effect, although
their antiviral EC50 values were relatively high and in the same or-
der of magnitude as the compound concentrations causing cyto-
toxicity. The 2-S-phenylisoindole derivatized glycopeptide 3 was
the most active, in particular against herpes simplex virus. It is
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In conclusion, we have extended the series of isoindole- and
benzoisoindole-fused glycopeptides with the synthesis of a set of
teicoplanin pseudoaglycon derivatives. These compounds were
found to possess remarkably high antibacterial activity against a
panel of Gram positive bacteria including some resistant strains.
Almost all of the new derivatives exhibited better MIC and MBC
values than the parent antibiotic teicoplanin. The antiviral tests
of these (benzo)isoindoles showed mixed results. We were able
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and DNA viruses were only weakly inhibited. On the basis of these
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ˇ
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Acknowledgments
The work is supported by the TÁMOP 4.2.1/B-09/1/KONV-2010-
0007 project. The project is co-financed by the European Union and