Novel ketolide antibiotics with a fused five-membered lactone ring - Synthesis, physicochemical and antimicrobial properties

Article abstract of DOI:10.1016/j.bmc.2004.04.039

In an effort to find novel semisynthetic macrolides with extended antibacterial spectrum and improved activity we prepared a series of compounds based on commercially available clarithromycin, a potent and safe antimicrobial agent of outstanding clinical and commercial interest. According to the literature, improvement of antibacterial activity of erythromycin type antibiotics can be achieved by introduction of fused heterocycles such as cyclic carbonates or carbamates at positions 11 and 12 (such as in telithromycin). In the course of the work presented here, a similar, hitherto unprecedented set of compounds bearing a five-membered lactone ring fused to positions 11 and 12 was prepared based on carbon-carbon bond formation via intramolecular Michael addition of a [(hetero)arylalkylthio]acetic acid ester enolate to an α,β-unsaturated ketone as the key step. Some of the ketolide compounds described in this paper were highly active against a representative set of erythromycin sensitive and erythromycin resistant test strains. The best compound showed a similar antimicrobial spectrum and comparable activity in vitro as well as in vivo as telithromycin. Furthermore, some physicochemical properties of these compounds were determined and are presented here. On the basis of these results, the novel ketolide lactones presented in this paper emerged as valuable lead compounds with comparable properties as the commercial ketolide antibacterial telithromycin (Ketek^TM).

Full text of DOI:10.1016/j.bmc.2004.04.039

Bioorganic & Medicinal Chemistry 12 (2004) 3503–3519
Novel ketolide antibiotics with a fused five-membered lactone
ring––synthesis, physicochemical and antimicrobial properties
Daniel Hunziker,a,* Pierre-C. Wyss,a Peter Angehrn,a Aranka Mueller,a
Hans-Peter Marty,a Remy Halm,a Laurenz Kellenberger,b Veronique Bitsch,b
b
a
a
b
€
Gerard Biringer, Wolf Arnold, Andreas Stampfli, Anne Schmitt-Hoffmann
and Denis Cousotb
aF. Hoffmann-La Roche Ltd, Discovery Research, CH-4070 Basel, Switzerland
bBasilea Pharmaceutica Ltd, PO Box, CH-4005 Basel, Switzerland
Received 14 October 2003; accepted 27 April 2004
Abstract—In an effort to find novel semisynthetic macrolides with extended antibacterial spectrum and improved activity we pre-
pared a series of compounds based on commercially available clarithromycin, a potent and safe antimicrobial agent of outstanding
clinical and commercial interest. According to the literature, improvement of antibacterial activity of erythromycin type antibiotics
can be achieved by introduction of fused heterocycles such as cyclic carbonates or carbamates at positions 11 and 12 (such as in
telithromycin). In the course of the work presented here, a similar, hitherto unprecedented set of compounds bearing a five-
membered lactone ring fused to positions 11 and 12 was prepared based on carbon–carbon bond formation via intramolecular
Michael addition of a [(hetero)arylalkylthio]acetic acid ester enolate to an a,b-unsaturated ketone as the key step. Some of the
ketolide compounds described in this paper were highly active against a representative set of erythromycin sensitive and erythro-
mycin resistant test strains. The best compound showed a similar antimicrobial spectrum and comparable activity in vitro as well as
in vivo as telithromycin. Furthermore, some physicochemical properties of these compounds were determined and are presented
here. On the basis of these results, the novel ketolide lactones presented in this paper emerged as valuable lead compounds with
comparable properties as the commercial ketolide antibacterial telithromycin (KetekTM).
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
cin (2) and azithromycin (4)––while featuring improved
pharmacokinetics as compared to 1––did not show any
significant activity against bacterial isolates showing
macrolide-lincosamide-streptogramine B (MLSB) cross-
resistance.
The macrolide antibiotic erythromycin A (1) has been in
successful clinical use as an agent against Gram-positive
pathogens for several decades.1 Due to its limited
chemical stability and its gastro-intestinal side effects it
has been gradually replaced by very effective and safe
semisynthetic second generation derivatives such as
clarithromycin (2),2 roxithromycin (3)3 and azithromy-
cin (4)4 in the last decades (Fig. 1). Very recently how-
ever, extensive spread of erythromycin A resistance
among Gram-positive cocci isolates has raised the ur-
gent need for novel derivatives with improved activity,
stability and antimicrobial spectrum. Yet, clarithromy-
During the last years, industrial researchers from
Aventis and Abbott Laboratories reported two novel
semisynthetic macrolides belonging to the ketolide class5
named telithromycin or HMR3647 (5)6 and ABT773
(6)7 (Fig. 1). These compounds showed significantly
improved activities against macrolide-resistant isolates
of important pathogens such as Staphylococcus aureus
and Streptococcus pneumoniae. Both compounds com-
prise two key structural features: an 11,12-cyclic carba-
mate moiety and
a 3-oxo group (refer to the
erythromycin numbering in Fig. 1). In both cases, anti-
microbial activity is further modulated by attachment of
an additional (hetero)arylalkyl side chain to either the
carbamate nitrogen (such as in 5) or O(6) (such as in 6).
Keywords: Ketolide; Macrolide; Ketolide antibiotic; Macrolide anti-
biotic; Antiinfective; Antibiotic.
* Corresponding author. Tel.: +41-61-688-95-39; fax: +41-61-688-83-
67; e-mail: daniel.hunziker@roche.com
0968-0896/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.04.039

3504
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
O
O
O
O
N
O
N
O
N
N
O
HO
HO
HO
9
9
HO
OCH3
O
HO
OH
O
HO
OH
O
2'
OH
OH
OH
6
12
12
O
1'
O
1'
O
O
5
5
15
O
O
O
O
O
1
O
1''
1
O
O
O
1''
2"
OH
OCH3
OH
OCH3
OH
OCH3
1
2
3
N
N
N
N
N
HO
N
HO
OH
O
O
O
OH
N
O
N
O
9
HO
HO
O
O
O
O
OCH3
O
NH
O
N
O
O
6
O
O
O
1'
O
O
O
13
OH
OCH3
O
O
O
O
1
6
4
5
Figure 1. Structure and numbering scheme of the macrolide antibiotic erythromycin (1). Erythromycin derived semisynthetic macrolides comprise:
clarithromycin (2), roxithromycin (3), azithromycin (4), telithromycin (5) and ABT773 (6).
Telithromycin has been introduced to the market while
ABT773 is reported to be in late stage clinical trials.
Additional possibilities to further enhance antimicrobial
activities of the ketolide class of antibiotics such as
replacement of the hydrogen at C(2) by a fluorine atom
are reported in the literature.8 Many excellent reviews
about the most recent semisynthetic macrolide anti-
biotics have been published by various authors.9
example, chloroacetyl derivative 8. Similarly, treatment
of 7 with S-alkyl- or aryl substituted a-thio acetic acids,
DCC and DMAP in CH2Cl2 gave clean reactions and
high yields of the corresponding esters 9 (Scheme 1).
These substituted a-thio ester derivatives 9 were con-
sidered to be of particular interest since we felt that––
due to the anion stabilizing effect of the sulfur that
should facilitate deprotonation in a-position of the
critical ester carbonyl group––an intramolecular Mi-
chael reaction should now be possible under milder
conditions. In addition, we expected an enhanced
selectivity against proton abstraction at the a-positions
of other carbonyl groups present in the macrocyclic
backbone of 9 which––on the other hand––was found
not to take place that easily. Synthesis of the desired
cyclization precursors 9 by this method (Scheme 1,
2. Results and discussion
2.1. Chemistry and structural analysis
Although much work had been invested towards the
development of novel semisynthetic derivatives of 1 or
its chemically more stable homologue 2 in the last dec-
ades, we felt that innovation in this field might still be
possible especially in the eastern part of the macrocyclic
ring comprising positions C(10) to C(12). It has been
shown earlier that introduction of fused heterocycles
such as carbonates10 and carbamates11 at these positions
lead to improvement of the antimicrobial potency. As a
consequence, we considered 10,11-anhydroclarithromy-
cin (7) initially reported by Baker and co-workers11 as
an ideal starting material for our own chemical pro-
gramme. In analogy to the findings made earlier by
others5;11 we envisioned the introduction of a novel ring
fused to the 11,12-positions of the macrocycle as well,
however, with a clear focus towards the formation of
new carbon–carbon bonds. Similar independent work
along these lines has been published recently.12 We
quickly realized that acylation of the tertiary hydroxy
group at C(12) of 7 can be easily achieved in high yield
by treatment with DCC, DMAP and a-halo-substituted
carboxylic acids such as chloroacetic acid to give, for
method
A)
required
suitable
[[(hetero)aryl-
alkyl]thio]acetic acids 10a–k (Table 1) as starting mate-
rials. Compounds of this type were either commercially
available or were prepared according to literature pro-
cedures.13 Yet, the scope of this formal ester formation
was significantly limited since it could not be performed
with most of the more interesting a-thio acetic acids
carrying more polar, nitrogen containing heterocyclic
substituents due to limited solubility in CH2Cl2. No
reaction took place if CH2Cl2 was substituted with other
solvents such as DMF.14 Nevertheless, this drawback
could be easily circumvented by treatment of chloro-
acetyl derivative 8 with a suitable [(hetero)arylalkyl]thiol
11 in the presence of a base such as DBU (Scheme 1,
method B), a process that again resulted in the desired
cyclization precursor 9. The use of this alternative
method required the adequate side chain precursors in
form of their thiols 11l–s (Table 1). Synthesis of side
chain precursors 10 and 11 will be discussed in more
detail below.

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
3505
O
O
N
O
N
O
R
AcO
AcO
i)
O
S
COOH
HO
OCH3
O
O
OCH3
O
10a-k
S
O
O
R
Method A
O
O
O
O
O
O
O
O
7
O
O
OCH3
OBn
O
OCH3
OBn
9a-s
ii)
iii)
N
O
AcO
O
O
OCH3
O
R
SH
Cl
iv)
11l-s
O
O
O
O
O
O
R
S
O
R
S
N
8
O
OCH3
OBn
AcO
H
N
O
OCH3
HO
H
O
OCH3
16
O
O
6
Method B
O
O
O
1'
O
13
O
O
O
O
O
O
O
O
1
v)
12a-s
O
OCH3
OBn
vii)
15a-s
O
O
R
S
R
N
O
N
O
vi)
S
AcO
AcO
H
H
O
O
OCH3
OCH3
O
O
O
O
O
O
O
O
O
OH
13a-s
14a-s
Scheme 1. Synthesis of ketolides 15 via intramolecular Michael reaction. See Table 1 for definition of side chains R. Reagents and conditions: (i)
DCC, DMAP, CH2Cl2, RT, 48 h; (ii) DCC, DMAP, chloroacetic acid, CH2Cl2, RT, 48 h; (iii) DBU, cat. NaI, acetone, RT; (iv) NaH, DMF, 0 °C, 2 h
(or KOtBu, DMF, 0 °C, 2 h); (v) 3% HCl in MeOH; (vi) EDC*HCl, DMSO, pyridinium trifluoroacetate, CH2Cl2, 5 °C, 2 h; (vii) MeOH, 48 h, RT.
Table 1. Ketolide lactones 15a–s: structures, synthetic methods and starting materials
Ketolide
Method
Side chain building block
Source
O
H
N
O
R
HO
O
OCH3
O
O
O
O
O
R ¼
CH3S
S
COOH
15a
15b
A
A
10a
10b
Commercial
Commercial
PhS
S
C OOH
15c
15d
15e
15f
15g
A
A
A
A
A
10c
10d
10e
10f
10g
Commercial
Lit.a
S
S
C OOH
S
C OOH
S
Lit.a
S
S
S
C OOH
C OOH
Commercial
S
O
O
MeO
MeO
MeO
MeO
Commercial
S
COOH
S
(continued on next page)

3506
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
Table 1 (continued)
Ketolide
Method
Side chain building block
Source
O
H
N
O
R
HO
O
OCH3
O
O
O
O
O
R ¼
15h
15i
A
A
10h
Lit.b
Lit.b
N
S
N
S
COOH
10i
N
S
N
N
S
COOH
15j
A
A
B
B
10j
This paper
This paper
This paper
This paper
S
S
S
C OOH
N
N
N
15k
15l
10k
11l
S
C OOH
SH
N
N
S
N
N
N
N
N
S
SH
N
N
15m
11m
N
N
N
S
SH
N
N
N
N
15n
15o
15p
B
B
B
11n
11o
11p
This paper
This paper
This paper
N
N
N
N
S
SH
N
N
N
N
N
N
N
N
S
SH
N
N
N
N
N
N
N
N
S
SH
N
N
H2N
H2N
15q
15r
B
B
11q
11r
This paper
This paper
N
N
N
N
N
N
N
N
S
SH
N
N
N
N
N
N
H2N
H2N
N
S
SH
N
N
N
15s
16
B
11s
This paper
This paper
N
N
N
N
H
nac
na
a Prepared according to Von Braun and Weissbach.13a
b Prepared according to Il’ichev et al.13b
c na: not applicable.
With these substituted a-thio ester derivatives 9 in hand
we turned our attention to the key step of our reaction
sequence being the intramolecular 1,4-addition. To our
delight, treatment of the starting materials 9 with NaH
or KOtBu in DMF resulted in the formation of the
desired cyclization product––the corresponding five-
membered lactone 12––in modest to excellent yields.
THF proved to be a poorer solvent for this reaction
since a substantial amount of deacylated material 7––the
initial starting material––was observed under these
reaction conditions. The cyclization step generally re-
mained somewhat capricious despite some further opti-
mization work. Yields for 12 ranged from 20% to 80%
depending on the starting material used and only pure
starting materials led to good yields. The use of starting
materials with lower purity required addition of excess
base in the cyclization process, leading to side reactions.
In this cyclization process 9 ! 12, three adjacent

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
3507
stereocentres (C(10), C(11) and C(16)) are generated in a
single reaction step (see Scheme 1 for numbering). Since
the pre-existing configuration at carbon C(12) leads to
an attack of the enolate anion to the trans double bond
from the Si-face and the resulting absolute configuration
at C(11) is thus tightly controlled, four diastereomeric
products are expected to be formed in this transforma-
tion. In reality, the course of the reaction turned out to
be less complex since the desired products 12 were ob-
tained as a mixture of two diastereomers at most, as
Lactone 12 obtained from the cyclization step was
usually used without rigorous purification and charac-
terization. Treatment of 12 with 3% HCl in methanol
resulted in selective removal of the cladinose moiety.16 3-
Hydroxy derivative 13 thus obtained was oxidized under
modified Pfitzner–Moffatt conditions as described by
others5 to furnish the corresponding ketolide 14 in high
yield. This compound was deacetylated simply by
treatment with pure methanol to give the target ketolide
15 in excellent yield. To our surprise, if starting material
14 was an epimeric mixture, one diastereomer cleanly
isomerized under these conditions and the final product
was obtained as a single isomer. Spectroscopic evidence
for this isomerization process in the final deprotection
step is presented in Figure 2 with (phenylpropyl-
1
judged by H NMR. In the case of example 15k that is
presented in detail in the experimental section, inter-
mediate 12k consisted of a single epimer. Nevertheless,
the diastereomeric ratio of the reaction products 12
obtained for the various examples proved to be very
variable. We assumed that it was dependent on the
reaction time, the amount and type of base added (e.g.,
NaH vs KOtBu) and––last but not least––on the work
up and purification conditions.15 It turned out that
separation of this epimeric mixture was not necessary
since––most intriguingly, as outlined in more detail be-
low––epimerization in the process of the final depro-
tection step turned out to be feasible and the target
ketolide could be obtained as a single diastereoisomer.
In addition, the Z-protecting group in the cladinose
moiety proved to be somewhat labile under these reaction
conditions and in some cases a side product with a de-
protected cladinose sugar could be isolated. For the time
being, this could be tolerated since the side product was
also a suitable starting material for the next reaction step.
1
thio)ketolide 15e. The H NMR spectrum of starting
material 14e (Fig. 2, spectrum A) revealed two sets of
signals in an approximate ratio of 1.5:1 (with both iso-
mers having identical masses as indicated by MS, data
not shown). We assumed that these compounds were
epimers at position C(10). Stirring of mixture 14e in
methanol for 48 h without any additional reagent fol-
lowed by subsequent removal of the solvent resulted in
the formation of product 15e whose spectrum is de-
picted in Figure 2 (spectrum B). This material consisted
obviously of a single stereoisomer and––as expected––
deacetylation had occurred. More detailed proton NMR
analysis (chemical shifts and coupling constants) sug-
gested natural configuration at C(10) as judged by
comparison of the spectra with those reported for the
Figure 2. Spectroscopic evidence for the facile epimerization process that was observed during ketolide synthesis. Epimerization of the undesired
epimer at C(10) resulted in the formation of a single stereoisomer with the natural configuration at all carbons (shown here with example 15e).

3508
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
references clarithromycin (2), erythromycin (1) and
telithromycin (5) (see below for a more detailed discus-
sion).
structures obtained from the Cambridge Structural
Database of erythromycin (1), clarithromycin (2) and a
11,12-cyclic carbamate revealed the striking fact that the
conformation of the macrocyclic backbone is almost
identical in all three cases (data not shown). We there-
fore assumed that this should also be the case for our
lactones since the absolute configuration of the stereo-
centres C(10), C(11) and C(12) in the macrocyclic
backbone was not expected to be different from those in
a cyclic carbamate. This assumption was supported by
the fact that proton–proton coupling constants within
characteristic spin systems of the eastern part of the
macrocycle of selected examples were essentially the
same as those reported for the cyclic carbamates.5 A
representative sketch of this common backbone con-
formation is presented in Figure 4 with a view along the
axis of the C(10)–C(11) bond of 15b (erythromycin
numbering). Indicative NOE crosspeaks in the eastern
part of the molecule are also given. NOE crosspeak
between C(10)-Me and H(16) was considered as the
most indicative signal since it clearly suggested an (S)-
configuration for C(16) and an (R)-configuration for
C(10) (which is the ‘natural’ configuration). This con-
clusion was supported by the following spectroscopic
observations: vicinal coupling constants between the
proton pairs H(16)–H(11) and H(10)–H(11) are very
small and the multiplicities observed are singlet for
H(16), singlet for H(11) and quartet for H(10). These 1H
NMR data suggested dihedral angles for H(16)–H(11)
and H(11)–H(10) in the range of 90°, which is in
accordance with the structural model depicted in Figure
4. Further support for this analysis might be found in
the absence of a NOE crosspeak between H(16) and
H(13). Since the essential features in the 1H NMR
spectra of the final products 15 were always extremely
similar, we assumed that the conclusions drawn here for
15b are also valid for all other examples.
Synthesis of derivatives bearing a (heteroarylalkylthio)
side chain with a free NH2-group such as adenine
derivative 15q followed essentially the same synthetic
pathway. Yet, synthesis was somewhat less straightfor-
ward, since we omitted the use of protecting groups in
the first attempt. Treatment of the precursor 9q under
standard cyclization conditions resulted in the forma-
tion of a more complex mixture of products according
to TLC analysis. Mass spectrometry suggested the two
main products to be the desired cyclization product 12q-
A and a DMF condensation product 12q-B (Fig. 3). Due
to the complexity of the mixture and insignificant Rf
differences of these products on TLC, further purifica-
tion was not anticipated. Luckily, acidic methanolysis
performed in the subsequent cladinose cleaving step also
led to cleavage of the DMF adduct and the desired
3-hydroxy derivative 13q was obtained as the main
product in 61% yield over two steps. Oxidation of the
hydroxyl group of 13q under the conditions described
earlier again led to partial formation of an unexpected
product that was identified as the corresponding sulfili-
mine derivative 14q-A of the desired O(20)-protected
ketolide by MS and proton NMR. Again, sulfilimine
derivative 14q-A was cleaved in the subsequent reaction
step to give the desired deprotected ketolide 15q as the
main product and as a single diastereomer. Despite this
somewhat more complex reaction procedure, com-
pounds of this type could be prepared on a 500 mg scale
in essentially pure form.
Absolute configuration of the final ketolide products
was investigated by proton NMR with compound 15b
(R ¼ phenylthio, see Table 1) based on coupling con-
stants and NOE patterns. Investigation of crystal
Syntheses of side chain precursors 10 and 11 that were
not commercially available and unknown in the litera-
ture were performed according to Scheme 2. Synthesis of
10j and 10k started with the corresponding commer-
cially available 3-pyridylpropanols 16 that were con-
verted to thioesters 17 by treatment with DIAD, PPh3
R2R1N
S
N
N
N
N
N
N
N
N
O
O
N
N
O
S
AcO
O
O
O
OCH3
N
S
AcO
Me
Me
O
OCH3
O
O
H
6
O
O
O
O
O
O
O
9
O
Indicative NOE's:
H13 - H11
H10 - H11
Me12 - Me10
Me12 - H10
H10 - H7
Me10 - H16
H11 - H16
S
Me
H
H
O
O
OCOOBn
H
16
H
OCH3
12q-A: R1, R2 = H
12q-B: R1, R2 =
14q-A
O
Me
H
H
N
O
H O
O
Me
Me
13
Me
1
Figure 3. Synthesis of derivatives 15q and 15r containing an adenine
moiety. Due to the presence of the unprotected aromatic NH2 func-
tion, two additional intermediates 12q-B and 14q-A are formed in the
course of the synthetic process according to Scheme 1.
Figure 4. Stereochemical analysis of ketolides 15. NOE pattern anal-
ysis was done with phenylthio derivative 15b.

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
Pyr
3509
Pyr
Pyr
O
i)
ii)
S
COOR
OH
S
16
17
18: R = Et
10: R = H
iii)
Pyr = 2- or 4-pyridyl
O
O
O
O
iv)
vi)
K
N
N
S
N
H
n
n
SR
X
19l-q, s
20l-q, s: n = 1, X = OH
21l-q, s: n = 1, X = Cl
22l-q, s: n = 1, R = Ac
11l-q, s: n = 1, R = H
v)
vii)
mono- or
bicyclic
heterocyle
N
H
=
21r: n = 2, X = Cl
22r: n = 2, R = Ac
11r: n = 2, R = H
vii)
Scheme 2. Syntheses of side chain precursors 10 and 11. Reagents and conditions: (i) DIAD, PPh3, thioacetic acid, 0 °C to RT; (ii) NaBH4, EtOH
then NaOEt, ethyl bromoacetate; (iii) NaOH, dioxane, then HCl; (iv) NaOH (cat.), DMF, 160 °C; (v) SOCl2, reflux; (vi) acetone, reflux, 12 h; (vii)
NH3 gas, MeOH.
and thioacetic acid according to Mitsunobu. Com-
pounds 17 were reduced with NaBH4 in ethanol and the
resulting thiolate anions were alkylated in situ with ethyl
bromoacetate to give esters 18. Saponification of 18 re-
sulted in the formation of the desired carboxylic acids
10.
2.2. Biological and physicochemical properties
Solubilities of ketolide lactones were generally in the
range of 3.0–7.0 mg/mL at pH 6.7 and generally ex-
ceeded the solubility of clinically used clarithromycin (2)
(experimental value: 1.5 mg/mL). Thus, this parameter
was not considered as a critical issue for the current lead
series. Lipophilicities (determined as logD values at
pH 7.4) were in the range of 1.2–2.7 for all compounds,
depending on the nature of the alkylthio or (het-
ero)arylalkylthio side chain. Within the lactone series,
logD values were found to be in good agreement with
calculated lipophilicities ClogP (data not shown).
Overall, lipophilicity was considered to be a very
important parameter since membrane impairing prop-
erties appeared with compounds bearing a very lipo-
philic arylalkyl side chain. An example for this effect can
be found in Table 1, example 15e, where the MIC value
of 16 lg/mL against the constitutively resistant strain S.
aureus 745 is most probably due to cytotoxic effects.
With this example in mind, an estimation of the cyto-
toxic potential of selected examples of 15 was attempted
with determination of the IC50 values against HeLa cells
(Table 2). Chart 1 confirms an apparent correlation
Thiol side chain synthesis was based on the mono- or
bicyclic aromatic heterocycles being available in all cases
either commercially or according to literature proce-
dures (see experimental part). Treatment of the suitable
heterocycles 19l–q,s with ethylene carbonate and a cat-
alytic amount of NaOH in DMF at 160 °C directly led
to hydroxyethylated compounds 20l–q,s in good yields.
Regioselectivity was excellent in all cases and products
20l–q,s were obtained as single regioisomers after puri-
fication. NOE experiments confirmed the structures of
all these intermediates. Subsequently, SOCl2 treatment
of 20l–q,s at 70 °C resulted in formation of chlorides
21l–q,s. Chloropropyl intermediate 21r was made di-
rectly in modest yield from adenine by treatment with
base and 1-bromo-3-chloropropane. Chloroalkyl com-
pounds 21 were treated with potassium thioacetate to
give thioesters 22 and thiols 11 were then liberated from
their precursors 22 by treatment with gaseous NH3 in
oxygen-free methanol. Free thiols 11 proved to be very
susceptible to oxidation and in most cases the corre-
sponding disulfide was an impurity. However, disulfide
formation could be essentially suppressed if proper
precautions such as exclusion of oxygen were taken and
further purification steps such as silica gel chromato-
graphy were omitted.
Table 2. Cytotoxic potential of ketolides 15 and references 1, 2 and 5
(see Chart 1 for a graphical representation)
Macrolide
ClogP/logD
IC50 HeLa (lg/mL) pIC50
1
2.48/1.26
3.18/1.57
4.08/1.75
1.70/nda
3.90/nd
45.7
24.9
23.3
18.5
4.34
4.60
4.63
4.73
5.89
5.96
5.62
5.08
5.11
4.87
4.99
4.60
4.46
2
5
15a
15d
15e
15h
15i
15j
15l
15n
15p
15q
1.30
For the sake of completeness, the basic, unsubstituted
lactone 16 was also prepared. This material was ob-
tained in 90% yield from phenyl–propyl derivative 15e
by treatment with Raney nickel in ethyl acetate. Based
on these approaches, about 20 compounds with different
side chains (see Table 1 for an overview) were prepared
initially. Biological data and some physicochemical
properties of these compounds will be discussed in the
following section.
4.40/nd
4.06/nd
1.10
2.40
8.40
7.80
2.70/nd
3.21/nd
2.55/2.16
2.55/2.62
1.73/2.25
1.19/1.68
13.5
10.3
25.4
34.4
a nd: not determined.

3510
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
keto group resulted in high activity against erythromy-
6.50
6.00
5.50
5.00
4.50
4.00
cin-resistant but josamycin-sensitive S. aureus 1086 as
exemplified in Table 3 with basic, unsubstituted ketolide
lactone 16. All compounds including 5 remained, how-
ever, inactive against the constitutively resistant strain S.
aureus 745. Generally, the lactones 15 seemed to be
slightly more active against S. aureus than 5. Activity
against S. pneumoniae with various degrees of macrolide
resistance was strongly dependent on the nature of the
side chain attached to the five-membered lactone ring
via the sulfide bridge. Examples of 15 comprising a
bicyclic (hetero)aryl moiety in the side chain were gen-
erally more active against highly macrolide-resistant S.
pneumoniae such as strains SL199T and 12288 than
compounds containing monocyclic aryl moieties. The
influence of chain length of the thioether linker was
investigated within the phenyl series comprising com-
pounds 15b–15e. Here, the most active compound
against S. aureus was phenethyl derivative 15d, while
homologous compounds with either a shorter or longer
side chain showed decreased activity (see Table 3). This
fact led us to focus on compounds carrying an aryl–ethyl
side chain in the initial phase of the programme; how-
ever, with compounds bearing more complex side chains
such as 15q and 15r this effect was less dramatic or even
absent. Within the series presented in Table 3, the most
active and the most balanced compounds in terms of
antimicrobial spectrum proved to be [3-(6-amino-9H-
purine-9-yl)propyl]thio derivative 15r and [3-(6-amino-
9H-purine-9-yl)ethyl]thio derivative 15q. Both com-
pounds showed high activity against macrolide-sensitive
and resistant Gram-positive bacteria––in about the same
range as telithromycin (5). They also showed some
5
3
2
1
0
1
2
4
5
ClogP/logD
Chart 1. Apparent correlation between macrolide/ketolide lipophilic-
ity (ClogP/logD) and cytotoxic potential (pIC50).
between ClogP/logD of different compounds 15 and their
pIC50 against HeLa cells. An IC50 value of 10 lg/mL
was considered as an acceptable limit for the cytotoxic
potential and therefore only compounds with a calcu-
lated ClogP value of less than about 2.5 were considered
to be acceptable for synthesis in the later stage of the
project.
Generally, ketolide lactones 15 proved to be very effec-
tive antimicrobial agents and all compounds were highly
active against macrolide sensitive strains of S. aureus
and S. pneumoniae (Table 3). Similar to other known
ketolide series such as the carbamates that include teli-
thromycin (5), replacement of the cladinose sugar by a
Table 3. Antimicrobial properties of ketolides 15 and16 against various bacterial isolates [references: erythromycin (1), clarithromycin (2), teli-
thromycin (5) and josamycin]
Macrolide
Minimum inhibitory concentration (MIC, lg/mL)
S. aureus
ATCC29213
S. aureus
1086
S. aureus
745
E. coli
ATCC25922
S. pneumoniae S. pneumoniae S. pneumoniae S. pneumoniae
12288
1/1
1/4
SL199T
15a
15b
15c
15d
15e
15f
15g
15h
15i
0.5
0.5
0.5
0.5
>16
>16
>16
>16
16
>16
>16
>16
>16
>16
>16
>16
>16
16
6 0.5
32
2
16
16
>32
16
16
32
16
8
6 0.5
1
1
6 0.5
8
16
4
6 0.25
1
6 0.25
1
6 0.5
1
6 0.5
1
8
6 0.25
0.5
0.25
6 0.25
0.5
0.25
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>16
>64
>16
>64
>16
6 0.5
4
4
8
6 0.5
1
0.25
16
2
6 0.12
6 0.5
0.5
2
6 0.25
6 0.12
6 0.12
0.25
6 0.25
6 0.12
6 0.12
0.25
1
0.25
8
15j
>16
>16
>16
>16
>16
>16
>16
8
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
6 0.25
6 0.25
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
2
8
15k
15l
6 0.12
6 0.12
6 0.12
6 0.12
1
2
8
2
2
15m
15n
15o
15p
15q
15r
15s
16
6 0.12
6 0.12
0.25
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
6 0.12
1
1
4
0.5
4
0.5
>16
1
6 0.12
6 0.12
6 0.12
0.25
6 0.12
0.25
1
0.25
6 0.25
1
0.25
16
6 0.25
6 0.25
16
0.25
2
>16
>16
>16
>16
16
0.5
0.5
0.5
>16
>32
16
>16
1
>32
16
32
16
>32
>16
2
0.25
6 0.12
2
5
Josamycin
6 0.12
2
6 0.12
6 4
6 0.12
>16
0.25
>16
>16

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
Table 5. In vivo efficacies of selected ketolides 15 in mice
3511
activity against selected Gram-negatives such as Esche-
richia coli (MIC ¼ 8 lg/mL for 15q) but were inactive
against Pseudomonas aeroguinosa. Interestingly, ketolide
15l with a ‘telithromycin-like’ side chain was only
moderately active against both macrolide sensitive and
resistant strains.
Macrolide
ED50 (mg/kg)
scb
poa
Erythromycin (1)
Telithromycin (5)
20.0
5.0
ꢀ1.5
1.2
15n
15q
15r
7.1
2.5
1.2
12.0
7.1
As compound 15q was one of the most active and most
balanced compounds of the series presented in Table 3,
it was further tested against various isolates of the
important respiratory tract pathogen Haemophilus in-
fluenzae (Table 4). Among the reference compounds,
azithromycin (4) was clearly the most active compound
if all MIC values were considered. Telithromycin (5) was
less active than 4 but more powerful than 1 and 2. To
our delight, ketolide 15q seemed to be slightly more
active than 5 on the basis of all MIC values. On
the other hand, 15q remained somewhat less effective
than 4.
<1.5
a Oral administration (gavage).
b Subcutaneous administration.
life of 0.4 h in vivo. Clarithromycin (2) exhibited better
properties (F % ¼ 13%) and higher plasma levels, but
still in vivo half life remained quite short (0.6 h). In
contrast, both ketolide lactones investigated in this
model showed markedly higher oral bioavailabilities
around 60% and low total clearances and therefore,
plasma levels were found to be significantly higher. In
vivo half lives in plasma were found to be in the range of
1.1–1.2 h in mice; values that would allow to predict a
half life in humans suitable for once a day dosing. Based
on these preliminary pharmacokinetic results an in vivo
experiment with compounds 15n and 15q as well as with
other examples seemed to be justified.
As a summary, the best compounds 15n, 15q and 15r out
of the lactone series presented in this paper showed a
similar antimicrobial spectrum as the reference ketolide
telithromycin (5). They were slightly less active against
macrolide resistant strains of S. pneumoniae but seemed
to be more active against the important respiratory tract
pathogen H. influenzae. In addition, 15q seemed to be
slightly more potent against selected Gram-negative
bacteria such as E. coli (MIC ¼ 8 lg/mL).
Subsequently, compounds 15n, 15q and 15r were tested
in vivo in a mouse infection model with erythromycin
sensitive Streptococcus pyogenes as the pathogen.
Compounds were administered both per os and subcu-
taneously and compared to placebo, 1 and 5, respec-
tively. ED50 values determined in this experiment are
presented in Table 5. Telithromycin (5) was the most
potent compound after oral administration, while 15n
and 15r were slightly less active but nevertheless in the
same range as 5. Adenyl-ethyl derivative 15q was about
twofold less active than 5 but significantly more potent
than erythromycin (1). These data are in reasonable
agreement with the pharmacokinetic properties pre-
sented above. All compounds exhibited similar in vivo
efficacies in terms of ED50 after subcutaneous adminis-
tration.
Pharmacokinetic properties of 15n and 15q were deter-
mined in mice and compared to reference compounds 1
and 2. As expected, erythromycin (1) showed the poor-
est properties with oral bioavailabilities (F %) below 10%
resulting in very low plasma levels and short plasma half
Table 4. Inhibitory activity of ketolide 15q and of selected reference
compounds against H. influenzae (erythromycin (1); clarithromycin (2);
azithromycin (4); telithromycin (5))
H. influenzae
Minimum inhibitory concentration (MIC, lg/mL)
1
2
4
5
15q
H. influenzae 1
3201
3457
4
4
0.5
2
4
4
4
2
2
1
4
4
2
4
4
4
4
4
4
4
4
8
2
4
1
16
1
2
4
4
0.5
1
0.25
2
0.25
2
3. Conclusion
3640
12214
4
8
2
4
2
23145
23369
8
2
4
4
The novel semisynthetic ketolide lactones 15 presented
in this paper contain a fused five-membered lactone ring
unprecedented so far. The aforementioned ring has been
formed via intramolecular 1,4-addition of an [(het-
ero)arylalkylthio]acetic acid ester enolate to an a,b-
unsaturated ketone. While the formation of four dia-
stereomers had to be expected principally in this reac-
tion, only two of them were observed by proton NMR
and the minor isomer was converted into the other one
later in the reaction sequence. Final ketolide products––
obtained as single diastereoisomers––exhibited excellent
antimicrobial properties against both erythromycin
sensitive and resistant strains of Gram-positive patho-
gens such as S. aureus and S. pneumoniae with the
exception of constitutively resistant S. aureus. In
16
4
4
4
4
H20 HDL
H28 HEL
4139
1
2
1
4
1
2
2
4
0.5
2
2
2
H36 ODL
11
16
16
2
4
2
2
4
4
QK 12/87
2947
0.5
2
1
0.5
2
16
8
4
ATCC 9334
QK 50
B 1501
2
2
4
8
2
2
2
8
1
2
1
H13 LAH
ATCC 49247
Rd KW20
Christy
8
2
2
2
8
2
4
1
8
2
4
4
8
2
4
2

3512
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
addition, efficacy has been proven in vivo in a mouse
infection model with S. pyogenes as the pathogen and
compounds were active both per os and after subcuta-
neous administration. In vitro activities as well as in
vivo efficacies of the best compounds were in the same
range as the reference ketolide telithromycin. On the
basis of these synthetic efforts, other novel classes of
macrolides seem to be accessible as well. For example,
the sulfur atom presented in 15a–s may be oxidized to
give the corresponding sulfone, a process that alters the
lipophilicity of the side chain and therefore of the entire
molecule while activity is retained. First steps along
these lines showed promising results and further data
are presented elsewhere.17 As a summary, the novel class
of ketolides presented in this paper emerged as a valu-
able lead series that might be useful in the fight against
spreading pathogens showing resistance against the
common macrolide antibiotics that are currently in
clinical use.
To determine pharmacokinetic properties, aqueous
solutions of ketolides 15 were applied orally by gavage
(at 30 mg/kg) or injected iv (at 10 mg/kg) to mice and
plasma levels (ng/mL) were determined by LC–MS at
0.08, 0.25, 0.5, 0.75, 1, 2, 4 and 6 h post-administration.
Some standard parameters calculated from these raw
data sets (data not shown) are presented in the main
section of this paper.
Thermodynamic solubilities were determined at the pH
indicated in the text (mostly at pH 6.7) in 0.05 M phos-
phate buffer with photometric quantification of the
amount of dissolved compound. Lipophilicities (logD
values, distribution coefficients) were determined
photometrically at pH 7.4 in 1-octanol/50 mM TAPSO
buffer in the presence of 5% (v/v) DMSO. Octanol/water
partition coefficients ClogP were calculated using the
kowClogP software KOW 1.57, which is commercially
available.
TLC was performed on Merck TLC plates with the
solvent system indicated in the experimental section.
Compounds were visualized using either UV at 254 nm,
1% aqueous KMnO4 solution or cer-ammonium-
molybdate solution (20 g (NH4)6Mo7O24Æ4H2O, 4 g
Ce(SO4)2Æ4H2O, 360 mL water, 40 mL H2SO4 concd).
Merck silica gel 60 (0.040–0.063 mesh) was used for flash
4. Experimental section
Certain abbreviations are used repeatedly in the fol-
lowing specification. These include: TLC for thin layer
chromatography; HPLC for high performance liquid
chromatography; DMSO for dimethylsulfoxide; DBU
for 1,8-diazabicyclo[5,4,0]undec-7-ene; DIPEA for di-
isopropylethylamine (Huenig’s base); DIAD for diiso-
propyl azodicarboxylate; DMF for dimethylformamide;
THF for tetrahydrofuran; DCC for N,N0-dicyclohexyl-
carbodiimide; DMAP for 4-dimethylaminopyridine;
EDC*HCl for N-(3-dimethylaminopropyl)-N0-ethylcar-
bodiimide hydrochloride; MS for mass spectrometry;
NMR for nuclear magnetic resonance; RT for room
temperature; HRMS for high resolution mass spec-
trometry; EI for electron impact ionization; ESI for
electrospray ionization. Other abbreviations are defined
consecutively in the text.
1
chromatography. H NMR spectra were measured on a
Bruker DPX NMR-spectrometer at 250 and 400 MHz,
respectively, in the solvent indicated. Chemical shifts are
given in ppm relative to TMS; coupling constants are
given in Hz. Assignments of resonances (where possible)
were made based on chemical shifts and by comparison
with completely assigned spectra of 1 and 218 and based
on two-dimensional COSY and HSQC spectra. MS
spectra were taken with the ionization method indicated
in the experimental part on API 365 (ESI) or Finnegan
MAT 95 (EI, ESI) mass spectrometers.
Reagents were generally purchased in the highest purity
available and used without further purification except
where indicated in the text. Doubly protected 10,11-
didehydroclarithromycin derivative 7 was synthesized in
four steps from commercially available clarithromycin
(2) (obtained from Senn Chemicals, Switzerland)
according to literature procedures by Baker and co-
workers.11
Minimum inhibitory concentrations (MIC values) were
determined by broth microdilution in 96-well plates.
Mueller–Hinton broth (Difco) was used for staphylo-
cocci, E. coli and P. aeruginosa, while iso-sensitest broth
(Oxoid) supplemented with 3% laked horse blood (Ox-
oid) was used for S. pneumoniae. The final inoculum was
approx 106 colony forming units (CFU) per mL for S.
pneumoniae and 105 CFU’s for all other organisms.
Plates were incubated for 24 h at 35 °C and then read for
turbidity. The lowest compound concentration that
showed no turbidity was taken as the MIC value.
The numbering convention for ketolide lactones 15 used
in the text is based on the numbering for erythromycin
(1) as indicated in Figure 1 and Scheme 1, respectively.
Note however, that the systematic names in the experi-
mental part are based on CA nomenclature and not
on 1.
In vivo mouse infection experiments were conducted as
follows: mice (five animals per dose) were infected ip
(intraperitoneally) with erythromycin susceptible S. py-
ogenes b15 and solutions of macrolide antibiotics were
administered per os (gavage) or subcutaneously at dif-
ferent dosages 1 and 3 h post-infection. Erythromycin
(1) and telithromycin (5) were used as reference com-
pounds in these experiments. ED50 values (mg/kg) were
calculated from the survival rates of infected and treated
animals at day 3 after infection.
4.1. Synthesis of ketolides 15 via method A
4.1.1. Ethanethioic acid, S-[3-(pyridin-4-yl)propyl]ester
(17k). Diisopropyl azodicarboxylate (DIAD) (9.8 mL,
51 mmol) was added dropwise to a solution of 13.3 g
(51 mmol) triphenylphosphine in 125 mL THF kept at
0 °C. The mixture was stirred for 30 min and then a

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
3513
solution of 3.47 g (25 mmol) 3-pyridin-4-yl-propanol
(16k) and 3.6 mL (51 mmol) thioacetic acid in 50 mL
THF was added. Stirring was continued for 12 h and the
mixture was allowed to warm to room temperature. The
yellow solution was concentrated in vacuo and the res-
idue was purified by flash chromatography (ethyl ace-
tate/hexanes 1:1) to give 3.2 g (65%) of the desired
product 17k as a yellow liquid. This material was used
without in depth characterization. Rf : 0.20 (ethyl ace-
tate/hexanes 1:1). MS (ESI): 196.3 (MHþ).
aqueous NaHCO3 solution and brine, dried over
MgSO4 and evaporated in vacuo. Purification of the
residue by flash chromatography gave 413 mg (85%) of
the desired product 9k as a foam. Rf : 0.26 (CH3CN/
1
CH2Cl2/NH4OH 1:1:0.1). H NMR (CDCl3): 8.51 (m,
2H, pyridine Ha), 7.36 (m, 5H, phenyl), 7.12 (m, 2H,
pyridine Hb), 6.62 (s, 1H, H11), 5.73 (dd, 1H, J1 ¼ 10:8,
J2 ¼ 2:4, H13), 5.26 (d, 1H, J ¼ 12:5, OCH2Ph), 5.13 (d,
1H, J ¼ 12:5, OCH2Ph), 4.98 (m, 1H, H100), 4.68 (dd,
1H, J1 ¼ 10:8, J2 ¼ 6:6, H20), 4.56 (d, 1H, J ¼ 7:2, H10),
4.47 (d, 1H, J ¼ 9:0, H400), 4.36 (m, 1H, H500), 3.91 (m,
1H, H3), 3.52–3.70 (m, 2H, H5, H50), 3.33 (s, 3H, OMe),
3.25 (m, 1H, H8), 3.16 (s, 3H, OMe), 3.13 (s, 2H,
SCH2CO), 2.88 (m, 1H, H2), 2.70 (t, 2H, J ¼ 6:6) and
2.60 (t, 2H, J ¼ 6:6, SCH2CH2CH2pyr), 2.60 (m, 2H,
H30), 2.41 (d, 1H, J ¼ 15:0, H200), 2.23 (s, 6H, NMe2),
2.00 (s, 2H, CH3COO), 1.88 (s, 3H, 10Me), 2.00–
1.80 (m, 4H, SCH2CH2CH2pyr, H4, H7), 1.59 (s, 3H,
quart. CCH3), 1.40–1.00 (m, ꢀ22H, H40, 7*CH3),
0.93 (d, 3H, CHCH3), 0.88 (t, 3H, CH3CH2). HRMS:
Calcd for MHþ (C58H87O16N2S): 1099.5771; found:
1099.5776.
4.1.2. [[3-(Pyridin-4-yl)propyl]thio]acetic acid ethyl ester
(18k). Compound 17k (3.2 g, 16.4 mmol) was dissolved
in 50 mL ethanol and 620 mg (16.4 mmol) NaBH4 was
added in one portion. The mixture was stirred at room
temperature overnight and then 377 mg (17.4 mmol)
NaOEt and 1.81 mL (16.4 mmol) ethyl bromoacetate
were added. Stirring was continued until TLC analysis
showed the presence of a single new product. Water was
added and the mixture was extracted with ethyl acetate.
The organic layer was washed with brine, dried
(Na2SO4) and evaporated to give 3.4 g (87%) of a
crude product 18k that was used without further puri-
fication.
4.1.6. (3S,3aR,4R,6R,8R,9R,10S,11S,12R,15R,15aS)-9-
[[2-O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b-
hexopyranosyl]oxy]-11-[[2,6-dideoxy-3-C-methyl-3-O-meth-
yl-4-O-[(phenylmethoxy)carbonyl]-a- -ribo-hexopyranos-
D
-xylo-
L
4.1.3. [[3-(Pyridin-4-yl)propyl]thio]acetic acid (10k).
Compound 18k (3.4 g, 14.3 mmol) was dissolved in
dioxane (40 mL) and 7.9 mL (15.05 mmol) of 2 N NaOH
was added. The mixture was allowed to stir at room
temperature for 12 h and 7.9 mL (15.1 mmol) 2 N HCl
was added until the pH was about 7.0. Water was added
and the aqueous phase was extracted continuously with
ethyl acetate to give––after removal of the solvent
in vacuo––704 mg (23%) of the desired product 10k as a
yl]oxy]-15-ethyldecahydro-8-methoxy-4,6,8,10,12,15a-
hexamethyl-3-[[3-(pyridin-4-yl)propyl]thio]-2H-furo[2,3-c]
oxacyclotetradecin-2,5,13 (3H,6H)-trione (12k). Com-
pound 9k (413 mg, 0.376 mmol) was dissolved in DMF
(11 mL) and cooled to 0 °C by means of an ice bath. A
1 M solution of potassium tert-butylate in THF
(0.564 mL, 0.564 mmol) was added dropwise over a
period of 50 min and the resulting mixture was allowed to
stir at 0 °C for 3 h. The resulting mixture was partitioned
between aqueous 0.5 M KH2PO4 and diethyl ether. The
organic layer was washed with water and brine, dried
over MgSO4 and evaporated. The residue was purified by
flash chromatography (silica gel, CH3CN/CH2Cl2/
NH4OH 1:1:0.01 and ethyl acetate/MeOH 20:1) to give
the desired product 12k (88 mg, 21%) as a single diaste-
reomer as a foam. Rf : 0.12 (CH3CN/CH2Cl2/NH4OH
1
white powder. H NMR (CDCl3): 9.20 (br s, 1H), 8.35
(m, 2H), 7.27 (m, 2H), 3.26 (s, 2H), 2.83 (t, 2H, J ¼ 7:2),
2.64 (t, 2H, J ¼ 7:2), 2.02 (m, 2H). MS (EI): 212.2
(MHþ).
4.1.4. [[3-(Pyridin-2-yl)propyl]thio]acetic acid (10j). Was
obtained in analogy to the previous reaction sequence
16k ! 10k from 3-(pyridin-2-yl)-propanol (16j): 1H
NMR (CDCl3): 13.60 (s (br), 1H), 8.60 (m, 1H), 7.73 (m,
1H), 7.26 (m, 2H), 3.31 (s, 2H), 2.98 (t, 2H, J ¼ 7:6),
2.77 (t, 2H, J ¼ 7:6), 2.07 (m, 2H). MS (EI): 212.2
(MHþ).
1
1:1:0.1). H NMR (CDCl3, measured at 2 °C): 8.51 (m,
2H, pyridine Ha), 7.37 (m, 5H, phenyl), 7.22 (m, 2H,
pyridine Hb), 5.48 (dd, J1 ¼ 10:0, J2 ¼ 2:4, H13), 5.26 (d,
1H,J1 ¼ 12:0, OCH2Ph), 5.12 (d, 1H, J ¼ 12:0,
OCH2Ph), 4.95 (d, 1H, J ¼ 4:8, H100), 4.73 (dd, 1H,
J1 ¼ 10:0, J2 ¼ 7:6, H20), 4.63 (d, 1H, J ¼ 7:6, H10), 4.47
(d, 1H, J ¼ 9:6, H400), 4.38 (s, 1H, SCHCOO), 2.29 (m,
1H, H500), 3.89 (d, 1H, J ¼ 8:8, H3), 3.65 (m, 1H, H50),
3.57 (d, 1H, J ¼ 6:8, H5), 3.34 (s, 3H, OMe), 3.09 (s, 3H,
OMe), hidden below (m, 1H), 2.99 (br q, 1H, J ¼ 6:4,
H10), 2.86 (m, 2H) and 2.70 (m, 3H, pyrCH2CH2CH2S)
and H2, 2.57 (s, 1H, H11), 2.53 (m, 1H, H30), 2.42 (m,
1H, H200), 2.24 (s, 6H, NMe2), 2.15–2.00 (m, 1H), 2.07 (s,
3H, CH3COO), 1.95–1.80 (m, 3H), 1.80–1.50 (m, ꢀ10H),
1.44, 1.32, 1.12 3*(s, 3H, quart. CCH3), 1.23, 1.16, 1.13,
1.10, 1.07, 0.93 6*(d, 3H, CHCH3), hidden below (m, 1H,
H40), 0.88 (t, 3H, CH3CH2). MS (ESI): 1099.5 (MHþ),
550.6 ([MH2]þþ). HRMS: Calcd for MHþ
(C58H87O16N2S): 1099.5771; found: 1099.5776.
4.1.5. (10E)-10,11-Didehydro-11-deoxy-6-O-methyl-ery-
thromycin 20-acetate 400-(phenylmethyl carbonate) 12-
[[[3-(pyridin-4-yl)propyl]thio]acetate]
(9k).
Starting
material 7 (400 mg, 0.441 mmol) was dissolved in
CH2Cl2 (15 mL) and 210 mg (1.32 mmol) [[3-(pyridin-4-
yl)propyl]thio]acetic acid (10k) and DMAP (10 mg,
0.81 mmol) were added. DCC (275 mg, 1.32 mmol) was
added in one portion and the initially clear solution
turned into a yellow suspension within 5 min. The mix-
ture was allowed to stir for 48 h and was then filtered.
The filtrate was diluted with CH2Cl2, washed with 5%

3514
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
4.1.7. (3S,3aR,4R,6R,8R,9R,10S,11S,12R,15R,15aS)-9-
[[2-O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b- -xylo-
1.16, 1.11 5*(d, 3H, CHCH3), hidden below (m, 1H,
H40), 0.89 (t, 3H, CH3CH2). MS (ESI): 805.4 (MHþ),
403.8 ([MH2]þþ). HRMS: Calcd for MNaþ
(C42H64N2O11SNa): 827.4128; found: 827.4128.
D
hexopyranosyl]oxy]-15-ethyldecahydro-11-hydroxy-8-meth-
oxy-4,6,8,10,12,15a-hexamethyl-3-[[3-(pyridin-4-yl)-prop-
yl]thio]-2H-furo[2,3-c]oxacyclotetradecin-2,5,13 (3H,6H)-
trione (13k). Compound 12k (200 mg, 0.182 mmol) was
subjected to acidic methanolysis in 3% HCl in methanol
(2 mL) at RT for 48 h. The mixture was then diluted
with CH2Cl2 and washed with 5% aqueous NaHCO3
and brine. The organic layer was dried (MgSO4), filtered
and evaporated to give the crude product. This was
purified by flash chromatography (silica gel, CHCl3/
MeOH/NH4OH 9:1:0.1) to give 109 mg (74%) of the
desired product 13k as a single diastereomer according
4.1.9. (3S,3aR,4R,6R,8R,9R,10R,12R,15R,15aS)-15-Eth-
yloctahydro-8-methoxy-4,6,8,10,12,15a-hexamethyl-3-
[[3-(pyridin-4-yl)propyl]thio]-9-[[3,4,6-trideoxy-3-(dimeth-
ylamino)-b- -xylo-hexopyranosyl]oxy]-2H-furo[2,3-c]oxa-
D
cyclotetradecin-2,5,11,13 (3H,6H,12H)-tetrone (15k).
Protected ketolide 14k (59 mg, 0.073 mmol) was dis-
solved in methanol (2.0 mL) and allowed to stir for 48 h.
The solution was then concentrated in vacuo and the
residue was purified by flash chromatography (silica gel,
CH3CN/CH2Cl2/NH4OH 1:1:0.01) to give the desired
deprotected ketolide 15k as a single diastereomer. Col-
orless foam: 48 mg (86%). Rf : 0.10 (CHCl3/MeOH/
1
to NMR. Rf : 0.43 (CHCl3/MeOH/NH4OH 9:1:0.1). H
NMR (CDCl3, measured at 2 °C): 8.49 (m, 2H, pyridine
Ha), 7.21 (m, 2H, pyridine Hb), 5.58 (dd, 1H, J1 ¼ 10:0,
J2 ¼ 2:4, H13), 4.77 (dd, 1H, J1 ¼ 10:4, J2 ¼ 7:6, H20),
4.65 (d, 1H, J ¼ 7:6, H10), 4.48 (s, 1H, SCHCOO), 3.74
(s, 1H, H3), 3.49 (m, 2H, H5, H50), 3.13–3.00 (m, 2H,
H10), 3.03 (s, 3H, OMe), 2.90–2.70 (m, 5H,
SCH2CH2CH2pyr), 2.67 (s, 1H, H11), 2.51 (m, 1H, H8),
2.26 (s, 6H, NMe2), hidden below (m, 1H), 2.09 (s, 3H,
CH3COO), hidden below (m, 3H, SCH2CH2CH2pyr),
1.91 (m, 1H), 1.80–1.20 (m, ꢀ9H, aliphatic H), 1.51,
1.27 2*(s, 3H, quart. CCH3), 1.28, 1.23, 1.12, 1.10, 0.98
5*(s, 3H, CHCH3), 0.86 (t, 3H, CH3CH2). MS (ESI):
807.4 (MHþ), 404.8 ([MH2]þþ). HRMS: Calcd for MHþ
(C42H67N2O11S): 807.4465; found: 807.4466.
1
NH4OH 9:1:0.1). H NMR (CDCl3): 8.49 (m, 2H, pyri-
dine Ha), 7.18 (m, 2H, pyridine Hb), 5.50 (dd, 1H,
J1 ¼ 10:0, J2 ¼ 2:4, H13), 4.33 (d, 1H, J ¼ 7:2, H10), 4.28
(d, 1H, J ¼ 7:2, H5), 4.26 (s, 1H, SCHCOO), 3.86 (q, 1H,
J ¼ 6:8, H2), 3.56 (m, 1H, H50), 3.50 (br, 1H, OH), 3.18
(dd, 1H, J1 ¼ 10:0, J2 ¼ 7:2, H20), 3.14–3.00 (m, 3H, H4,
H10, SCH2CH2CH2pyr), 2.79 (s, 3H, OMe), 3.88–2.65
(m, 3H, SCH2CH2CH2pyr), 2.63 (s, 1H, H11), 2.57 (m,
1H, H8), 2.47 (m, 1H, H30), 2.27 (s, 6H, NMe2), 2.05 (m,
2H, SCH2CCHCH2pyr), 1.94 (m, 1H, CHCH2CH3
(H14)), 1.80–1.63 (m, 3H, H7, H7, H40), 1.59 (m, 1H,
CHCH2CH3 (H14)), 1.52, 1.32 2*(s, 3H, quart. CCH3),
1.38, 1.33, 1.24, 1.14, 1.12 5*(d, 3H, CHCH3), hidden
below (m, 1H, H40), 0.89 (t, CH3CH2). MS (ESI): 763.3
(MHþ), 382.3 ([MH2]þþ). HRMS: Calcd for MNaþ
(C40H63N2O10SNa): 785.4021; found: 785.4023.
4.1.8. (3S,3aR,4R,6R,8R,9R,10R,12R,15R,15aS)-9-[[2-
O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b- -xylo-hexo-
D
pyranosyl]oxy]-15-ethyloctahydro-8-methoxy-4,6,8,10,12,
15a-hexamethyl-3-[[3-(pyridin-4-yl)propyl]-thio]-2H-furo-
[2,3-c]oxacyclotetradecin-2,5,11,13 (3H,6H,12H)-tetrone
(14k). Intermediate 13k (100 mg, 0.124 mmol) was dis-
solved in CH2Cl2 (4.5 mL) and EDC*HCl (158 mg,
0.826 mmol) and DMSO (173 mg, 2.22 mmol) were
added. The mixture was cooled to 5 °C by means of a
water bath and a solution of pyridinium trifluoroacetate
(158 mg, 0.826 mmol) in CH2Cl2 (4.5 mL) was added
slowly. The resulting mixture was allowed to stir at 5 °C
for 45 min. Water was added and the resulting mixture
was partitioned between ether and 3% aqueous
NaHCO3 solution. The organic layer was washed with
water and brine, dried over MgSO4, filtered and evap-
orated. The residue was purified by flash chromatogra-
phy (silica gel, CH3CN/CH2Cl2/NH4OH 1:1:0.01) to
yield the desired protected ketolide 14k (59 mg, 59%) as
a single diastereomer as a foam. Rf : 0.60 (CHCl3/MeOH/
4.2. Synthesis of ketolides 15 via method B
4.2.1. (10E)-10,11-Didehydro-11-deoxy-6-O-methyl-ery-
thromycin 20-acetate 12-[chloroacetate] 400-(phenyl-meth-
yl carbonate) (8). 10,11-Anhydroclarithromycin (7)
(250 mg, 0.276 mmol) synthesized according to Baker
and co-workers11 was dissolved in CH2Cl2 (5 mL) under
argon and chloroacetic acid (156 mg, 1.66 mmol) and
DMAP (5 mg, 0.16 mmol) were added. N,N-Di-
cyclohexylcarbodiimide (341 mg, 1.65 mmol) was added
in one portion and the clear solution turned into a
suspension within 5 min. The resulting mixture was al-
lowed to stir for 112 days. The reaction mixture was fil-
tered and the filtrate was diluted with CH2Cl2, washed
with 5% aqueous NaHCO3 and saturated NaCl solu-
tion, dried over MgSO4 and evaporated in vacuo. The
residue was purified by flash chromatography on silica
gel using CH3CN/CH2Cl2/NH4OH 1:1:0.01 as an eluent.
Evaporation of the fractions containing the desired
product gave 213 mg (79%) of a brownish foam. Rf : 0.61
1
NH4OH 9:1:0.1). H NMR (CDCl3, measured at 2 °C):
8.50 (m, 2H, pyridine Ha), 7.19 (m, 2H, pyridine Hb),
5.50 (dd, 1H, J1 ¼ 10:4, J2 ¼ 2:4, H13), 4.75 (dd,
J1 ¼ 10:4, J2 ¼ 7:6, H20), 4.40 (d, 1H, J ¼ 7:6, H10), 4.28
(s, 1H, SCHCOO), 4.24 (d, 1H, J ¼ 6:8, H5), 3.85 (q,
1H, J ¼ 6:8, H2), 3.56 (m, 1H, H50), 3.11–3.00 (m, 3H,
H4, H10, SCH2CH2CH2pyr), 2.82–2.62 (m, 4H, H8,
SCH2CH2CH2pyr), 2.78 (s, 3H, OMe), 2.61 (s, 1H,
H11), 2.57 (m, 1H, H30), 2.25 (s, 6H, NMe2), 2.07 (s, 3H,
CH3COO), hidden below (m, 2H, SCH2CH2CH2pyr),
1.94 (m, 1H, CH3CH2CH), 1.80–1.55 (m, ꢀ4H, aliphatic
H), 1.51, 1.31 2*(s, 3H, quart. CCH3), 1.40, 1.26, 1.18,
1
(CH2Cl2/MeOH/NH4OH 100:10:1). H NMR (CDCl3):
7.36 (m, 5H, phenyl), 6.60 (s, 1H, H11), 5.71 (dd, 1H,
J1 ¼ 10:4, J2 ¼ 2:4, H13), 5.25 (d, 1H, J ¼ 12:4,
OCH2Ph), 5.14 (d, 1H, J ¼ 12:4, OCH2Ph), 4.97 (m,
1H, H100), 4.68 (m, 1H, H20), 4.56 (d, 1H, J ¼ 7:2, H10),
4.45 (d, 1H, J ¼ 9:6, H400), 4.35 (m, 1H, H500), 3.99 (s,
2H, ClCH2CO), 3.81 (m, 1H, H3), 3.60 (m, 1H, H50),

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
3515
3.55 (d, 1H, J ¼ 6:8, H5), 3.32 (s, 3H, OCH3), 3.20 (m,
1H, H8), 3.12 (s, 3H, OCH3), 2.87 (m, 1H, H2), 2.66 (m,
1H, H30), 2.40 (d, 1H, J ¼ 15:2, H200), 2.23 (s, 6H,
NMe2), 2.01 (s, 3H, CH3COO), 1.86 (s, 3H, C10-CH3),
1.93–1.80 (m, 2H, H4, H7), 1.78–1.50 (m, 4H, H20, H20,
H40, H200), 1.65 (s, 3H, quart. C–CH3), 1.42 (m, 1H, H7),
1.40–1.10 (m, ꢀ10H, H40, 3CH3), 1.08, 0.92 2*(d, 3H,
CHCH3), 0.89 (t, 3H, J ¼ 7:2, CH3CH2). MS (ESI):
982.4 (MHþ). HRMS: Calcd for MHþ (C50H77NO16Cl):
982.4934; found: 982.4932.
1H NMR (DMSO-d6): 2.50 (1H, covered by DMSO),
2.96 (br q, 2H), 4.30 (t, 2H), 7.20 (br s, 2H), 8.14 (s, 2H).
MS (EI): 195.1 (Mþ). The product was contaminated
with approx. 5% of the corresponding disulfide.
In a similar fashion, the following side chain building
blocks 11 were obtained:
[4-(Pyridin-3-yl)-1H-imidazole]-1-ethanethiol (11l) from
(19l):19
4-(pyridin-3-yl)-1H-imidazole
1H
NMR
(CDCl3): 1.44 (br t, 1H), 2.94 (br q, 2H), 4.20 (t, 2H),
7.31 (dd, 1H), 7.32 (s, 1H), 7.62 (s, 1H), 8.11 (m, 1H),
8.49 (m, 1H), 8.97 (d, 1H). MS (EI): 206.0 (MHþ).
4.2.2. 9-(2-Hydroxyethyl)-6-amino-9H-purine (20q).
Adenine (19q, 2.7 g, 20 mmol) was suspended in DMF
(100 mL) and 1.76 g (20 mmol) ethylene carbonate was
added. After addition of a catalytic amount of NaOH
(15 mg), the mixture was stirred at 160 °C for 2 h. DMF
was removed in vacuo and the residue was crystallized
from EtOH (350 mL) to give 2.1 g (59%) of 20q as a
brownish solid. 1H NMR (DMSO-d6): 3.74 (q, 2H,
CH2OH), 4.18 (t, 2H, NCH2), 4.99 (t, 1H, OH), 7.16 (br
s, 2H, NH2), 8.07 (s, 1H, adenine H), 8.13 (s, 1H, ade-
nine H). MS (EI): 179.1 (Mþ).
[3-(Pyridin-4-yl)-1H-pyrazole]-1-ethanethiol (11m) from
3-(pyridin-4-yl)-1H-pyrazole (19m):12 1H NMR (CDCl3):
1.38 (t, 1H), 3.05 (td, 2H), 4.36 (t, 2H), 6.65 (d, 1H), 7.52
(d, 1H), 7.67 (m, 2H), 8.62 (m, 2H). MS (EI): 205.1 (Mþ).
[3-(Pyridin-3-yl)-1H-pyrazole]-1-ethanethiol (11n) from
3-(pyridin-3-yl)-1H-pyrazole (19n):20 1H NMR (DMSO-
d6): 2.41 (br t, 1H), 2.96 (br q, 2H), 4.32 (t, 2H), 6.83 (d,
1H), 7.42 (m, 1H), 7.87 (d, 1H), 8.14 (m, 1H), 8.49 (m,
1H), 9.01 (d, 1H). MS (ESI): 206.2 (MHþ).
4.2.3. 9-(2-Chloroethyl)-6-amino-9H-purine (21q). Com-
pound 20q (1.97 g, 11 mmol) was suspended in 20 mL
thionyl chloride and heated at 70 °C for 45 min. Excess
thionyl chloride was removed in vacuo and the residue
was dissolved in water (100 mL). The aqueous solution
was basified with NaHCO3 solution (10%) and the
resulting slurry was stirred for 15 min. The product was
isolated by filtration, washed with water and dried to
give 1.25 g of a brownish solid. The crystallization step
was repeated to give another 220 mg of product 21q.
Total yield: 1.47 g (68%). 1H NMR (DMSO-d6): 4.07 (t,
2H), 4.50 (t, 2H), 7.23 (br s, 2H), 8.15 (s, 1H), 8.17 (s,
1H). MS (EI): 197.1 (Mþ).
[3-(Pyridin-4-yl)-1H-1,2,4-triazole-1-yl]-1-ethanethiol (11o)
1
from 3-(pyridin-4-yl)-1H-1,2,4-triazole (19o): H NMR
(DMSO-d6): 2.51 (br t, 1H), 2.99 (br q, 2H), 4.43 (t, 2H),
7.91 (m, 2H), 8.68 (m, 2H), 8.71 (s, 1H). MS (EI): 206.1
(Mþ).
[3-(Pyridin-3-yl)-1H-1,2,4-triazole-1-yl]-1-ethanethiol (11p)
from 3-(pyridin-3-yl)-1H-1,2,4-triazole (19p):21 1H
NMR (DMSO-d6): 2.50 (br t, 1H), 2.98 (br q, 2H), 4.41
(t, 2H), 7.51 (m, 1H), 8.31 (m, 1H), 8.62 (m, 1H), 8.67 (s,
1H), 9.17 (s, 1H). MS (EI): 206.1 (Mþ).
(6-Amino-9H-purine)-1-propanethiol (11r) from 9-(3-
chloropropyl)-6-amino-9H-purine (21r) (made accord-
ing to the literature22 from adenine and 1-bromo-3-
chloropropane) in analogy to the procedure outlined in
Scheme 2. 1H NMR (DMSO-d6): 8.14 (s, 2H), 7.20 (br s,
2H), 4.24 (t, 2H), 2.56 (br t, 1H), 2.31 (br q, 2H), 2.08
(m, 2H). MS (ESI): 210.2 (MHþ).
4.2.4. Ethanethioic acid, S-[[6-amino-9H-purine-9-yl]-
ethyl]ester (22q). Compound 21q (1.2 g, 6.07 mmol)
was suspended in acetone (30 mL). After addition of
solid potassium thioacetate (870 mg, 7.6 mmol), the
mixture was heated to reflux for 12 h. The suspension
was concentrated in vacuo, suspended in CH2Cl2 and
chromatographed on 120 g of silica gel, eluting with a
gradient of 0–9% methanol in CH2Cl2. The appropriate
fractions were combined and evaporated to give 1.4 g
(97%) of 22q as a brownish solid. 1H NMR (DMSO-d6):
2.30 (s, 3H), 3.40 (t, 2H), 4.32 (t, 2H), 7.20 (br s, 2H),
8.11 (s, 1H), 8.14 (s, 1H). MS (EI): 237.1 (Mþ).
(N,N-Dimethyl-6-amino-9H-purine)-1-ethanethiol (11s)
1
from N,N-dimethyl-6-amino-9H-purine (19s): H NMR
(CDCl3): 8.34 (s, 1H), 7.80 (s, 1H), 4.37 (t, H), 3.54 (br s,
6H), 3.01 (m, 2H), 1.37 (t, 1H). MS (EI): 223.1 (Mþ).
4.2.6. (10E)-10,11-Didehydro-11-deoxy-6-O-methyl-ery-
thromycin 20-acetate 12-[[[2-[6-amino-9H-purine-9-yl]-
ethyl]thio]acetate] 400-(phenylmethyl carbonate) (9q). To
a solution of 214 mg (218 lmol) 8 in 8 mL acetone were
added 36 lL DBU and a catalytic amount of NaI. (6-
Amino-9H-purine)-1-ethanethiol (11q, 45 mg, 230 lmol)
was added in one portion and the resulting suspension
was allowed to stir at room temperature. The suspension
gradually cleared to give a slightly hazy solution. The
reaction mixture was diluted with CH2Cl2, extracted
with 5% aqueous NaHCO3, dried over Na2SO4 and
evaporated. The crude product was purified by flash
4.2.5. (6-Amino-9H-purine)-1-ethanethiol (11q). Com-
pound 22q (1.3 g, 5.5 mmol) was suspended in 50 mL
degassed methanol, kept under argon. Gaseous ammo-
nia was bubbled through the solution for 5 min and the
internal temperature rose to 40 °C. The resulting solu-
tion was stirred for 60 min and a colorless precipitate
was observed. The suspension was filtered and the fil-
trate was concentrated and the fluffy solid thus obtained
was dried at 60 °C in vacuo. Yield of 11q: 850 mg (79%).

3516
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
chromatography on silica gel (ethyl acetate/methanol/
NEt3 9:1:0.1) to give 193 mg (76%) of the desired
product 9q as a glass. Rf : 0.37 (CHCl3/MeOH/NH4OH
with brine, dried over Na2SO4 and evaporated. The res-
idue was purified by flash chromatography on silica gel
(5 g cartridge) using ethyl acetate/MeOH/NEt3 9:1:0.1 as
an eluent. The product 13q was obtained as a slightly
yellow solid. Yield: 407 mg (85%). Rf : 0.40 (CHCl3/
MeOH/NH4OH 9:1:0.1). 1H NMR (CDCl3): 8.32 (s, 1H,
adenine H), 8.21 (s, 1H, adenine H), 5.54 (br s, 2H, NH2),
5.45 (dd, 1H, J1 ¼ 10:0, J2 ¼ 1:5, H13), 4.47 (dd, 1H,
J1 ¼ 10:0, J2 ¼ 8:0, H20), 4.71 (m, 1H, NCH2CH2S), 4.68
(d, J ¼ 4:0, H10), 4.59 (s, 1H, SCHCOO), 4.55 (m, 1H,
NCH2CH2S), 3.77 (s, 1H), 3.62 (m, 1H, NCH2CH2S),
3.50 (m, 1H), 3.43 (m, 1H, NCH2CH2S), 3.20–3.05 (m,
3H, H4, H10 and ?), 2.97 (s, 3H, OMe), 2.77–2.65 (m, 2H,
H2, H8), 2.65 (s, 1H, H11), 2.60–2.50 (m, 2H, H30, OH?),
2.26 (s, 6H, NMe2), 2.06 (s, 3H, CH3COO), 1.90 (m, 1H,
CH2CH3), 1.80–1.50 (m, several aliphatic H), 1.47, 1.33
2*(s, 3H, quart. CCH3), 1.25, 1.20, 1.16, 1.14, 0.98 5*(d,
3H, CHCH3), 8.82 (t, 3H, CH2CH3). MS (ESI): 849.3
(MHþ), 425.7 ([MH2]þþ). HRMS: Calcd for MHþ
(C41H65N6O11S): 849.4436; found: 849.4432.
1
9:1:0.1). H NMR (CDCl3): 8.35 (s, 1H, adenine H),
7.86 (s, 1H, adenine H), 7.36 (m, 5H, phenyl), 6.60 (s,
1H, H11), 5.71 (dd, 1H, J1 ¼ 10:0, J2 ¼ 2:4, H13), 5.51
(br s, 2H, NH2), 5.24 (d, 1H, J ¼ 12:4, OCH2Ph), 5.13
(d, 1H, J ¼ 12:4, OCH2Ph), 4.97 (m, 1H, H100), 4.68 (dd,
1H, J1 ¼ 10:4, J2 ¼ 1:8, H20), 4.56 (d, 1H, J ¼ 7:2, H10),
4.45 (d, 1H, J ¼ 9:6, H400), 4.40 (t, 2H, J ¼ 6:4,
NCH2CH2S), 4.37 (m, 1H, H500), 3.79 (m, 1H, H3), 3.60
(m, 1H, H50), 3.56 (d, 1H, J ¼ 6:8, H5), 3.32 (s, 3H,
OMe), 3.24 (m, 1H, H8), 3.16 (s, 2H, SCH2COO), 3.15
(s, 3H, OCH3), 3.09 (t, 2H, J ¼ 6:8, NCH2CH2S), 2.88
(m, 1H, H2), 2.67 (m, 1H, H30), 2.40 (d, 1H, J ¼ 15:2,
H200), 2.23 (s, 6H, NMe2), 2.00 (s, 3H, CH3COO), 1.87
(s, 3H, C10-CH3), hidden below (m, 3H, H4, H7, H7),
1.61 (s, 3H, quart. CCH3), 1.75–1.45 (m, 4H, aliphatic
H), 1.40–1.05 (m, ꢀ22H, H40 and 7*CH3), 0.92 (d, 3H,
CHCH2), 0.87 (t, 3H, CH3CH2). MS (ESI): 1141.5
(MHþ), 571.3 ([MH2]þþ). HRMS: Calcd for MHþ
(C57H85N6O16S): 1141.5743; found: 1141.5739.
4.2.9. (3S,3aR,4R,6R,8R,9R,10R,12R,15R,15aS)-9-[[2-
O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b- -xylo-hexo-
D
4.2.7. (3S,3aR,4R,6R,8R,9R,10S,11S,12R,15R,15aS)-9-
pyranosyl]oxy]-3-[[2-[6-amino-9H-purine-9-yl]ethyl]thio]-
15-ethyloctahydro-8-methoxy-4,6,8,10,12,15a-hexamethyl-
2H-furo[2,3-c]oxacyclotetradecin-2,5,11,13 (3H,6H,12H)-
tetrone-sulfilimine derivative (14q-A). To a suspension of
13q (390 mg, 0.459 mmol), EDC*HCl (587 mg,
3.06 mmol) and DMSO (0.587 mL, 8.27 mmol) in 4.5 mL
CH2Cl2 was added a solution of pyridinium trifluoroac-
etate (592 mg, 3.06 mmol) in 12 mL in CH2Cl2 slowly at
5 °C. The mixture gradually cleared and stirring was
continued at 5 °C for 30 min and then for two hours at
RT. The mixture was poured into 5% NaHCO3 solution
and extracted with CH2Cl2. The organic layer was wa-
shed with brine, dried over Na2SO4 and evaporated to
give a crude product. The product was purified on silica
gel (10 g cartridge) using ethyl acetate/MeOH/NEt3 as an
eluent. The fractions containing the product were com-
bined and evaporated to give the desired compound
as the sulfilimine derivative 14q-A. Yield: 348 mg (89%).
Rf : 0.44 (CHCl3/MeOH/NH4OH 9:1:0.1). 1H NMR
(CDCl3): 8.24 (s, 1H, adenine H), 8.04 (s, 1H, adenine H),
5.38 (dd, 1H, J1 ¼ 10:0, J2 ¼ 2:0, H13), 4.77 (m, 1H, H20),
4.63 (m, 1H, NCH2CH2S), 4.48 (m, 1H, NCH2CH2S),
4.43 (d, 1H, J ¼ 7:6, H10), 4.41 (s, 1H, SCHCOO), 4.26
(d, 1H, J ¼ 5:6, H5), 3.80 (q, 1H, J ¼ 6:8, H2), 3.65–3.50
(m, 2H, H50, NCH2CH2S), 3.18–3.04 (m, ꢀ7H), 2.84 (s,
6H, NSMe2), 2.72 (s, 3H, OMe), hidden below (m, 1H,
H8), 2.65 (s, 1H, H11), 2.60 (m, 1H, H30), 2.29 (br s, 6H,
NMe2), 2.05 (s, 3H, CH3COO), 1.93 (m, 1H, CH3CH2),
1.71–1.52 (m, ꢀ7 aliphatic H), 1.52 (s, 3H, quart. CCH3),
1.40–1.10 (m, ꢀ19H, 6*CH3, 1 aliphatic H), 0.86 (t, 3H,
CH3CH3). MS (ESI): 907.6 (MHþ).
[[2-O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b- -xylo-
hexopyranosyl]oxy]-3-[[2-[6-amino-9H-purine-9-yl]ethyl]-
thio]-11-[[2,6-dideoxy-3-C-methyl-3-O-methyl-4-O-[(phen-
D
ylmethoxy)carbonyl]-a- -ribo-hexopyranosyl]oxy]-15-
L
ethyldecahydro-8-methoxy-4,6,8,10,12,15a-hexamethyl-
2H-furo[2,3-c]oxacyclotetradecin-2,5,13 (3H,6H)-trione
(12q-A) and corresponding DMF condensation product
(12q-B). Sodium hydride dispersion (approx. 55% in oil,
77 mg, 1.6 mmol) was suspended in DMF (4 mL) and
cooled to 0 °C by means of an ice bath. A solution of 9q in
10 mL DMF was added slowly by syringe and the
resulting mixture was allowed to stir for 90 min. TLC
analysis revealed the complete consumption of the
starting material and three major new product spots were
observed. The reaction mixture was partitioned between
0.5 M KH2PO4 and diethyl ether. The organic layer was
separated, washed with water and brine, dried over
MgSO4 and evaporated to give 641 mg (88%) of crude
product that was used without further purification.
Mixture of two compounds 12q-A and 12q-B with dif-
ferent molecular weight: 12q-A; MS (ESI): 1141.4
(MHþ), 571.8 ([MH2]þþ), 12q-B; 1196.2 ([MH+
DMF)H2O]þ), 599.1 ([MH2+DMF)H2O]þþ). Rf values:
three major spots at Rf 0.50–0.65 (CHCl3/MeOH/
NH4OH 9:1:0.1).
4.2.8. (3S,3aR,4R,6R,8R,9R,10S,11S,12R,15R,15aS)-9-
[[2-O-Acetyl-3,4,6-trideoxy-3-(dimethylamino)-b- -xylo-
D
hexopyranosyl]oxy]-3-[[2-[6-amino-9H-purine-9-yl]ethyl]-
thio]-15-ethyldecahydro-11-hydroxy-8-methoxy-4,6,8,10,
12,15a-hexamethyl-2H-furo[2,3-c]oxacyclo-tetradecin-2,
5,13 (3H,6H)-trione (13q). Compound mixture 12q-A/
12q-B obtained in the previous step (640 mg, 0.561 mmol)
was subjected to acidic methanolysis in 20 mL methanol
containing 3% HCl at RT for 20 h. The reaction mixture
was concentrated in vacuo, taken up in 5% NaHCO3 and
extracted with CH2Cl2. The organic layer was washed
4.2.10. (3S,3aR,4R,6R,8R,9R,10R,12R,15R,15aS)-3-[[2-
[6-Amino-9H-purine-9-yl]ethyl]thio]-15-ethyloctahydro-8-
methoxy-4,6,8,10,12,15a-hexamethyl-9-[[3,4,6-trideoxy-
3-(dimethylamino)-b- -xylo-hexopyranosyl]oxy]-2H-furo-
D
[2,3-c]oxacyclotetradecin-2,5,11,13 (3H,6H,12H)-tetrone
(15q). Protected compound 14q-A (340 mg, 0.4 mmol)

D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
3517
was dissolved in methanol (50 mL) and allowed to stir at
RT for 48 h. After completion of the reaction, the mix-
ture was concentrated in vacuo. The residue was taken
up in CH2Cl2 and the organic layer was washed with 3%
aqueous NaHCO3 solution and brine. The organic layer
was dried (Na2SO4) and evaporated. The residue was
purified by flash chromatography (10 g silica gel car-
tridge) using ethyl acetate/MeOH/NEt3 9:1:0.1 as an
eluent. Fractions containing pure product were com-
bined and evaporated to give 205 mg (63%) of the de-
sired product 15q as a foam. Rf : 0.4 (CHCl3/MeOH/
(MHþ), 403.7 ([MH2]þþ). HRMS: Calcd for MHþ
(C39H61N6O10S): 805.4170; found: 805.4166.
4.2.11. (3aR,4R,6R,8R,9R,10R,12R,15R,15aS)-15-Eth-
yloctahydro-8-methoxy-4,6,8,10,12,15a-hexamethyl-9-[[3,
4,6-trideoxy-3-(dimethylamino)-b- -xylo-hexopyranosyl]-
D
oxy]-2H-furo[2,3-c]oxacyclotetradecin-2,5,11,13 (3H,6H,
12H)-tetrone (16). To a solution of 20 mg (26.7 lmol) 15e
in 1.0 mL ethyl acetate was added Raney nickel (previ-
ously washed successively with water, methanol and
ethyl acetate). The mixture was stirred vigorously for
12 h and filtered. Removal of the solvent in vacuo gave
15 mg (92%) of a colorless solid. 1H NMR (CDCl3,
diagnostic signals only): 0.86 (t, 3H), 1.06 (d, 3H), 1.13
(d, 3H), 1.24 (d, 3H), 1.31 (s, 3H), 1.32 (d, 3H), 1.37 (d,
3H), 1.49 (s, 3H), 2.27 (s, 6H), 2.62 (s, 3H), 3.02 (br q,
1H), 3.49 (br s, 1H), 3.56 (m, 1H), 3.88 (q, 1H), 4.25 (d,
1H), 4.32 (d, 1H), 4.88 (dd, 1H). MS (ESI): 612.3 (MHþ).
1
NH4OH 9:1:0.1). H NMR (CDCl3): 8.34 (s, 1H, ade-
nine H), 8.22 (s, 1H, adenine H), 5.48 (br s, 2H, NH2),
5.38 (dd, 1H, J1 ¼ 10:0, J2 ¼ 2:4, H13), 4.68 (m, 1H,
NCH2CH2S), 4.51 (m, 1H, NCH2CH2S), 4.39 (s, 1H,
SCHCOO), 4.33 (d, 1H, J ¼ 7:2, H10), 4.29 (d, 1H,
J ¼ 6:8, H5), 3.84 (q, 1H, J ¼ 6:8, H2), 3.60–3.52 (m,
2H, H50, NCH2CH2S), 3.50 (br, 1H, OH), 3.19 (dd, 1H,
J1 ¼ 10:4, J2 ¼ 7:2, H20), 3.17–3.05 (m, 3H, H4, H10,
NCH2CH2S), 2.70 (s, 3H, OMe), 2.62 (s, 1H, H11),
hidden below (m, 1H, H8), 2.45 (m, 1H, H30), 2.27 (6H,
NMe2), 1.92 (m, 1H, CH3CH2), 1.72–1.50 (m, 5 ali-
phatic H), 1.53, 1.38 2*(s, 3H, quart. CCH3), 1.33, 1.32,
1.26, 1.17, 1.16 5*(d, 3H, CHCH3), hidden below (m,
1H, H400), 0.85 (t, 3H, CH2CH3). MS (ESI): 805.5
All ketolides that were synthesized in analogy to the
examples 15k and 15q, respectively, are summarized in
Table 6. The synthetic method is indicated. Structures of
all compounds are confirmed by selected spectroscopic
properties.
Table 6. Spectroscopic properties of ketolides 15a–s
Ketolide Method
MS (ESI)
MHþ found
HRMS (ESI, MHþ)
1H NMR (d, CDCl3), representative signals only
Calcd
Found
15a
15b
15c
A
A
A
658.2
720.5
734.4
658.3625
658.3622
0.88 (t, 3H), 1.11 (d, 3H), 1.13 (d, 3H), 1.25 (d, 3H), 1.31 (s, 3H), 1.32 (d,
3H), 1.37 (d, 3H), 1.51 (s, 3H), 2.27 (s, 6H), 2.41 (s, 3H), 2.58 (s, 1H), 2.77
(s, 3H), 3.03 (q, 1H), 3.11 (m, 1H), 3.19 (dd, 1H), 3.58 (m, 1H), 3.85 (q, 1H),
4.16 (s, 1H), 4.27 (d, 1H), 4.33 (d, 1H), 5.58 (dd, 1H)
720.3781
720.3790
0.93 (t, 3H), 1.09 (t, 3H), 1.13 (t, 3H), 1.26 (t, 3H), 1.34 (d, 3H), 1.35 (s, 3H),
1.40 (d, 3H), 1.52 (s, 3H), 2.27 (s, 6H), 2.82 (s, 1H), 2.86 (s, 3H), 3.08 (q,
1H), 3.10–3.22 (m, 2H), 3.57 (m, 1H), 3.87 (q, 1H), 4.30 (d, 1H), 4.35 (d,
1H), 4.62 (s, 1H), 5.38 (dd, 1H), 7.28–7.37 (m, 3H), 7.70 (dd, 2H)
0.88 (t, 3H), 1.03 (d, 3H), 1.09 (d, 3H), 1.24 (d, 3H), 1.30 (s, 3H), 1.31 (d,
3H), 1.49 (s, 3H), 2.26 (s, 6H), 2.59 (s, 1H), 2.75 (s, 3H), 3.57 (m, 1H), 4.83
(q, 1H), 4.02 (d, 1H), 4.15 (d, 1H), 4.18 (s, 1H), 4.25 (d, 1H), 4.33 (d, 1H),
5.53 (dd, 1H), 7.20–7.43 (m, 5H)
nda
15d
15e
A
A
748.5
762.4
748.4094
762.4251
748.4100
762.4246
0.88 (t, 3H), 1.14 (2d, 6H), 1.25 (d, 3H), 1.32 (s, 3H), 1.33 (d, 3H), 1.37 (d,
3H), 1.51 (s, 3H), 2.26 (s, 6H), 2.62 (s, 1H), 2.73 (s, 3H), 3.86 (q, 1H), 4.27
(d, 1H), 4.34 (d, 1H), 4.35 (s, 1H), 5.53 (dd, 1H), 7.13–7.28 (m, 5H)
0.89 (t, 3H), 1.11 (d, 3H), 1.13 (d, 3H), 1.24 (d, 3H), 1.32 (s, 3H), 1.33 (d,
3H), 1.38 (d, 3H), 1.51 (s, 3H), 2.03 (m, 2H), 2.27 (s, 6H), 2.62 (s, 1H), 2.80
(s, 3H), 3.86 (q, 1H), 4.26 (s, 1H), 4.28 (d, 1H), 4.33 (1H), 5.53 (dd, 1H),
7.12–7.32 (m, 5H)
15f
A
A
764.3
780.5
nd
nd
0.88 (t, 3H), 1.10 (d, 3H), 1.13 (d, 3H), 1.23–1.40 (3d, 1s), 1.51 (s, 3H), 2.26
(s, 6H), 2.67 (s, 1H), 2.75 (s, 3H), 3.58 (m, 1H), 3.87 (q, 1H), 4.23–4.38 (m,
5H), 5.47 (dd, 1H), 6.89–7.00 (m, 3H), 7.21–7.32 (m, 2H)
15g
0.93 (t, 3H), 1.07 (d, 3H), 1.13 (d, 3H), 1.27 (d, 3H), 1.34 (d, 3H), 1.36 (s,
3H), 1.40 (d, 3H), 1.51 (s, 3H), 2.27 (s, 6H), 2.82 (s, 1H), 2.88 (s, 3H), 3.58
(m, 1H), 3.87 (s, 3H), 3.88 (q, 1H), 3.93 (s, 3H), 4.31 (d, 1H), 4.35 (d, 1H),
4.51 (s, 1H), 5.36 (dd, 1H), 6.84 (d, 1H), 7.28 (d, 1H), 7.30 (s, 1H)
0.86 (t, 3H), 1.51 (s, 3H), 2.27 (s, 6H), 2.63 (s, 1H), 2.65 (s, 3H), 3.83 (q,
1H), 4.25 (d, 1H), 4.33 (d, 1H), 4.41 (s, 1H), 5.50 (dd, 1H), 7.46 (t, 1H), 7.49
(d, 1H), 7.68 (td, 1H), 7.77 (d, 1H), 8.03 (d, 1H), 8.05 (d, 1H)
0.87 (t, 3H), 1.13 (2d, 6H), 1.25 (d, 3H), 1.31 (s, 3H), 1.32 (d, 3H), 1.35 (d,
3H), 1.50 (s, 3H), 2.27 (s, 6H), 2.62 (s, 1H), 2.67 (s, 3H), 3.57 (m, 1H), 3.84
(q, 1H), 4.27 (d, 1H), 3.33 (d, 1H), 4.35 (s, 1H), 5.48 (dd, 1H), 7.08 (dd, 1H),
7.35 (d, 1H), 7.57 (td, 1H), 8.52 (d, 1H)
15h
15i
A
A
799.4
749.5
799.4203
749.4047
799.4197
749.4049
(continued on next page)

3518
D. Hunziker et al. / Bioorg. Med. Chem. 12 (2004) 3503–3519
Table 6 (continued)
Ketolide Method
MS (ESI)
MHþ found
HRMS (ESI, MHþ)
1H NMR (d, CDCl3), representative signals only
Calcd
Found
15j
A
763.3
nd
0.89 (t, 3H), 1.10 (d, 3H), 1.13 (d, 1H), 1.24 (d, 3H), 1.32 (s, 3H), 1.33 (d,
3H), 1.37 (d, 3H), 1.50 (s, 3H), 2.26 (s, 6H), 2.63 (s, 1H), 2.80 (s, 3H), 3.56
(m, 1H), 3.86 (q, 1H), 4.27 (s, 1H), 4.28 (d, 1H), 4.35 (d, 1H), 5.53 (dd, 1H),
7.09 (dd, 1H), 7.22 (d, 1H), 7.58 (td, 1H), 8.52 (d, 1H)
15k
15l
A
B
763.1
815.3
763.4203
763.4199
See experimental part for a full description
nd
0.87 (t, 3H), 1.14 (2 overlapping d, 6H), 1.53 (s, 3H), 2.32 (s, 6H), 2.61 (s,
1H), 2.64 (s, 3H), 3.83 (q, 3H), 4.24 (d, 1H), 4.30–4.40 (m, 4H), 5.43 (dd,
1H), 7.27 (m, 1H), 7.54 (s, 1H), 7.69 (s, 1H), 8.07 (m, 1H), 8.44 (m, 1H),
9.00 (d, 1H)
15m
15n
B
B
815.4
815.6
815.4265
815.4265
815.4262
815.4270
0.86 (t, 3H), 1.15 (2d, 6H), 1.26 (d, 3H), 1.31 (d, 3H), 1.33 (s, 3H), 1.35 (d,
3H), 1.52 (s, 3H), 2.27 (s, 6H), 2.61 (s, 1H), 2.68 (s, 3H), 3.84 (q, 1H), 4.28
(s, 1H), 4.33 (s, 1H), 4.33 (d, 1H), 4.56 (m, 2H), 5.41 (dd, 1H), 6.57 (d, 1H),
7.66 (m, 2H), 7.79 (d, 1H), 8.60 (m, 2H)
0.87 (t, 3H), 1.15 (2d, 6H), 1.27 (d, 3H), 1.32 (d, 3H), 1.33 (s, 3H), 1.34 (d,
3H), 1.52 (s, 3H), 2.29 (s, 6H), 2.63 (s, 1H), 2.67 (s, 3H), 2.84 (q, 1H), 4.28
(d, 1H), 4.34 (s, 1H), 4.35 (d, 1H), 4.45–4.51 (m, 2H), 5.42 (dd, 1H), 6.50 (d,
1H), 7.29 (m, 1H), 7.78 (d, 1H), 8.08 (m, 1H), 8.52 (m, 1H), 8.98 (d, 1H)
0.86 (t, 3H), 1.16 (2d, 6H), 1.53 (s, 3H), 2.29 (s, 6H), 2.61 (s, 1H), 2.65 (s,
3H), 3.84 (q, 1H), 4.22–4.38 (m, 3H), 4.62 (m, 2H), 5.33 (dd, 1H), 7.93 (br
m, 2H), 8.54 (s, 1H), 8.68 (br m, 2H)
15o
15p
B
B
816.2
816.4
816.4217
816.4217
816.4218
816.4223
0.86 (t, 3H), 1.16 (2d, 6H), 1.26 (d, 3H), 1.53 (s, 3H), 2.29 (s, 6H), 2.61 (s,
1H), 2.66 (s, 3H), 3.83 (q, 1H), 4.29 (d, 1H), 4.33 (s, 1H), 4.33 (s, 1H), 4.61
(m, 2H), 5.36 (dd, 1H), 7.36 (m, 1H), 8.33 (m, 1H), 8.53 (s, 1H), 8.62 (m,
1H), 9.29 (s, 1H)
15q
15r
B
B
805.5
819.4
805.4170
805.4166
See experimental part for a full description
nd
nd
0.90 (t, 3H), 1.14 (2d, 6H), 1.25 (d, 3H), 1.32 (s, 3H), 1.33 (d, 3H), 1.38 (d,
3H), 1.59 (s, 3H), 2.35 (s, 6H), 2.81 (s, 3H), 3.05–3.18 (m, 3H), 3.23 (dd,
1H), 3.57 (m, 1H), 3.86 (q, 1H), 4.27 (s, 1H), 4.28 (d, 1H), 4.34 (d, 1H),
4.32–4.50 (m, 2H), 5.53 (dd, 1H), 5.51 (br s, 2H), 8.15 (s, 1H), 8.36 (s, 1H)
0.87 (t, 3H), 1.15 (2d, 6H), 1.16 (d, 3H), 1.33 (2d, 6H), 1.36 (s, 3H), 1.52 (s,
3H), 2.27 (s, 6H), 2.46 (m, 1H), 2.62 (s, 1H), 2.69 (s, 3H), 3.07–3.13 (m, 2H),
3.15–3.25 (m, 2H), 3.40–3.62 (m, 10H), 3.83 (q, 1H), 4.28 (d, 1H), 4.33 (d,
1H), 4.37 (s, 1H), 4.48 (m, 1H), 4.63 (m, 1H), 5.38 (dd, 1H), 8.10 (s, 1H),
8.31 (s, 1H)
15s
B
833.5
a nd: not determined.
4. Retsema, J. A.; Girard, A. E.; Schekly, W.; Manousos,
M.; Anderson, M. R.; Bright, G. M.; Borovoy, R. J.;
Brennan, L. A.; Mason, R. Antimicrob. Agents Chemother.
1987, 31, 1939–1947.
5. Agouridas, C.; Denis, A.; Auger, J.-M.; Benedetti, Y.;
Bonnefoy, A.; Bretin, F.; Chantot, J.-F.; Dussarat, A.;
Fromentin, C.; Gouin d’Ambrieres, S.; Lachaud, S.;
Laurin, P.; Le Martret, O. L.; Loyau, V.; Tessot, N. J.
Med. Chem. 1998, 41, 4080–4100.
6. Denis, A.; Agouridas, C.; Auger, J.-M.; Benedetti, Y.;
Bonnefoi, A.; Bretin, F.; Chantot, J.-F.; Dussarat, A.;
Fromentin, C.; Gouin d’Ambrieres, S.; Lachaud, S.;
Laurin, P.; Le Martet, O.; Loyau, V.; Tessot, N.; Pejac,
J.-M.; Perron, S. Bioorg. Med. Chem. Lett. 1999, 9, 3075–
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95-400987, 1995.
Acknowledgements
We thank Mrs. Veronique Schirmer for excellent tech-
nical assistance with the investigation of in vitro activi-
ties and in vivo efficacies of our ketolides. Dr. Cornelia
Zumbrunn-Acklin is greatly acknowledged for the syn-
thesis of basic ketolide lactone 16. Furthermore, we are
indebted to the laboratory of Walter Meister for the
measurement of mass spectra and to Mr. Louis Alle-
mann for the determination of HR-mass spectra. Prof.
Sir Jack Baldwin, Prof. Elias J. Corey and Prof. Andrea
Vasella are greatly acknowledged for many fruitful and
helpful discussions in the course of this project.
References and notes
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