Novel semi-synthetic glycopeptide antibiotics active against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE): Doubly-modified water-soluble derivatives of chloroorienticin B

Article abstract of DOI:10.1016/S0960-894X(02)00664-9

A series of N-alkylated and aminomethylated derivatives of chloroorienticin B, a vancomycin-related glycopeptide antibiotic, were synthesized. Doubly-modified derivatives having both hydrophobic and hydrophilic substituents exhibited potent antibacterial activity against MRSA and VRE along with considerable water-solubility.

Full text of DOI:10.1016/S0960-894X(02)00664-9

Bioorganic & Medicinal Chemistry Letters 12 (2002) 3027–3031
Novel Semi-Synthetic Glycopeptide Antibiotics Active Against
Methicillin-Resistant Staphylococcus aureus (MRSA) and
Vancomycin-Resistant Enterococci (VRE): Doubly-Modified
Water-Soluble Derivatives of Chloroorienticin B
Osamu Yoshida,a Tatsuro Yasukata,a,* Yukihito Sumino,a Tadashi Munekage,b
Yukitoshi Narukawaa and Yasuhiro Nishitania
aDiscovery Research Laboratories, Shionogi & Co., Ltd., Sagisu 5-12-4, Fukushima-ku, Osaka 553-0002, Japan
bDiscovery Research Laboratories, Shionogi & Co., Ltd., Futaba-cho 3-1-1, Toyonaka, Osaka 561-0825, Japan
Received 28 June 2002;accepted 9 August 2002
Abstract—A series of N-alkylated and aminomethylated derivatives of chloroorienticin B, a vancomycin-related glycopeptide anti-
biotic, were synthesized. Doubly-modified derivatives having both hydrophobic and hydrophilic substituents exhibited potent
antibacterial activity against MRSA and VRE along with considerable water-solubility.
# 2002 Elsevier Science Ltd. All rights reserved.
Introduction
two or more substituents.2e,2i,4 Among them, doubly-mod-
ified glycopeptide derivatives (derivatives of teicoplanin
aglycon) that have both hydrophobic and hydrophilic
substituents have exhibited considerable activity against
gram-positive bacteria including VRE.4 This report
prompted us to prepare the novel semi-synthetic glyco-
peptide antibiotics.
Vancomycin, one of the typical glycopeptide antibiotics,
has been widely used for treatment of gram-positive
bacteria infections especially those caused by methicillin-
resistant Staphylococcus aureus (MRSA). However, the
emergence and spread of vancomycin-resistant enter-
ococci (VRE) is a growing clinical problem worldwide.1
In the last few years, chemical modifications of vanco-
mycin-related glycopeptide antibiotics have been exten-
sively explored and the introduction of a hydrophobic
side chain on the nitrogen of the amino sugar moiety
was found to be effective for potent activity against
VRE.2 Among the derivatives with hydrophobic sub-
stituents on the amino sugar moiety, LY333328 has
shown promise and is currently under clinical study.3
Hydrophobic substituents on the amino sugar moiety
are considered to have unfavorable effects on water-
solubility, therefore another substituent is required to
increase the water-solubility of the derivatives. However
most of the derivatives reported thus far have only one
hydrophobic substituent on the amino sugar moiety and
there are few reports with respect to the derivatives with
We report herein the chemical modification of chloro-
orienticin B,5 a vancomycin-related glycopeptide antibiotic,
and show that its derivatives are active against MRSA and
VRE and possess considerable water solubility (see Fig. 1).
Results and Discussion
We first prepared the derivatives having hydrophobic
substituents on the amino sugar nitrogen to enhance the
antibacterial activity especially against VRE. The
synthesis of N-alkylated derivatives of chloroorienticin B
is shown in Scheme 1. The secondary amino group of the
N-terminus was first protected by a PMZ (p-methoxy-
benzyloxy carbonyl) group6 and the resulting N-protected
intermediate (1) was subjected to reductive N-alkylation.2g
Deprotection of the PMZ group by treatment with
CF3CO2H afforded N-modified derivatives of chloro-
orienticin B.
*Corresponding author. Tel.: +81-6-6458-5861;fax: +81-6-6458-
0987;e-mail: tatsuro.yasukata@shionogi.co.jp
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00664-9

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O. Yoshida et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3027–3031
Figure 1. Chemical structure of vancomycin and chloroorienticin B.
All of the final products were obtained as hydro-
chlorides after purification by reverse-phase (ODS)
column chromatography eluted with dil.HCl aq-CH3CN
followed by lyophilization. The chemical structures of
the compounds obtained were confirmed by H NMR
and mass spectra and their purity was demonstrated by
HPLC and elemental analysis.
derivative having a long aliphatic chain (3a) also
showed potent antibacterial activity. Among them,
compound 3d having
a 4-[(E)-2-(4-chlorophenyl)-
vinyl]benzyl moiety was found to have the most well-
balanced antibacterial activity against MRSA and
VRE.
1
All the compounds having hydrophobic substituents on
the amino sugar nitrogen shown in Table 1 exhibited
potent antibacterial activity, but they were sparingly
soluble in water (less than 1%), which precluded further
pharmacological evaluation. We next focused our
efforts on preparing more water-soluble derivatives by
further modification of the compounds that have potent
activity against MRSA and VRE. We chose compound 3d
The in vitro antibacterial activities of the compounds
prepared as described above are shown in Table 1 with
values of MIC7 (mg/mL) against MRSA and VRE (Van
A enterococci). Compounds with the p-substituted
benzyl group (3b–3f) were found to have potent activ-
ity against MRSA (4–16 times more potent than vanco-
mycin) and VRE (MIC: 3.13–12.5 mg/mL). The
Scheme 1. Reagents and conditions: (a) S-p-methoxybenzyloxycarbonyl-4,6-dimethyl-2-mercaptopyrimidine (MZ-SDP), Et3N, DMSO-DMF;(b)
R1-CHO, NaBH3CN, MeOH–DMF;(c) CF 3CO2H–H2O.

O. Yoshida et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3027–3031
Table 1. In vitro antibacterial activity against MRSA and VRE
3029
Compd
R
MIC (mg/mL)
Staphylococcus aureus
SR3637 (MRSA)
Enterococcus faecalis
SR7914 (VRE)
Enterococcus faecium
SR7917 (VRE)
3a
3b
–(CH2)12CH3
0.2
12.5
25
6.25
12.5
0.39
3c
3d
3e
3f
0.1
0.2
12.5
6.25
12.5
12.5
6.25
6.25
6.25
3.13
0.2
0.39
Chloroorientation B
Vancomycin
–H
0.78
1.56
>100
>100
>100
>100
Scheme 2. Reagents and conditions: (a) R2-NH2, 37%-HCHO aq, NaOH aq, CH3CN–H2O;(b) CF 3CO2H–H2O.

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O. Yoshida et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3027–3031
Table 2. In vitro antibacterial activity of the aminomethylated derivatives of 3d
Compd
R0
H
MIC (mg/mL)
Solubility in watera
(%)
Staphylococcus aureus
SR3637 (MRSA)
Enterococcus faecalis
SR7914 (VRE)
Enterococcus faecium
SR7917 (VRE)
3d
5g
0.2
6.25
12.5
6.25
6.25
<1
0.39
10
5h
5i
0.39
0.78
12.5
12.5
6.25
6.25
10
10
5j
0.39
0.78
12.5
6.25
12.5
3.13
8
5k
10
Chloroorienticin B
Vancomycin
0.78
1.56
>100
>100
>100
>100
>10
>10
aSolubility as hydrochlorides.
as a parent compound for further chemical modification
leading to a derivative with better water-solubility.
the resultant compounds. In the previous reports con-
cerning doubly-modified teicoplanin derivatives that have
both hydrophobic and hydrophilic substituents,4 the most
active compounds had the activity comparable to 5k.
However these compounds were derivatives of teicoplanin
aglycon, which are structurally different from chloroor-
ienticin B derivatives, and are devoid of the sugar moiety
which plays an important role in water-solubility. The
doubly-modified compound 5k presented herein with a
hydrophobic substituent on an amino sugar moiety and a
hydrophilic one on a resorcinol moiety is a novel deriva-
tive of vancomycin-related glycopeptide antibiotics that
has potent antibacterial activity against MRSA and VRE
with considerable water-solubility (10%).
Preparation of more water-soluble derivatives of 3d was
achieved by aminomethylation8 (Mannich reaction) of the
resorcinol moiety as shown in Scheme 2. Intermediate 2d
was subjected to the Mannich reaction affording the ami-
nomethylated products 4g–k, followed by removal of the
PMZ group to give aminomethylated derivatives 5g–k.
As shown in Table 2, the water-solubility of the amino-
methylated derivatives prepared was much greater than
that of the parent compound 3d. As for the antibacterial
activity, compounds having tertiary and quaternary
amino groups (5g–i) and the amino acid moiety (5j)
have somewhat decreased antibacterial activity against
MRSA and VRE (especially against Enterococcus faecalis).
However, the compound with the 5,6,7,8-tetrahydro-
imidazo[1,5-c]pyrimidine-6-methyl moiety (5k)9 was
found to be as active as its parent 3d against E. faecalis
and more active against Enterococcus faecium along
with improved water-solubility. The activity of 5k
against MRSA was less potent than 3d, but comparable
to chloroorienticin B and vancomycin.
In conclusion, the results presented in this paper
demonstrate the possibility that more water-soluble
semi-synthetic glycopeptide antibiotics with potent
activity against MRSA and VRE can be prepared by
modification of the parent glycopeptide by introducing
both hydrophobic and hydrophilic substituents. This
methodology is considered to be useful for discovering
novel semi-synthetic glycopeptide antibiotics.
The introduction of hydrophobic side chains is con-
sidered to be essential for potent antibacterial activity
especially against VRE, but such hydrophobic sub-
stituents have the negative effect on water-solubility of
Acknowledgements
We are indebted to Dr. Yuji Ikenishi (Discovery
Research Laboratories, Shionogi & Co., Ltd.) for

O. Yoshida et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3027–3031
3031
measurement of the mass spectra and to Dr. Yoshihiro
Terui and Dr. Yohko Yoshimura (Discovery Research
Laboratories, Shionogi & Co., Ltd.) for taking the NMR
spectra. We also wish to thank Dr. Yasuo Kimura and
Dr. Hideaki Miwa (Discovery Research Laboratories,
Shionogi & Co., Ltd.) for their helpful discussions.
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