Synthesis and structure-activity relationships of novel 8a-aza-8a-homoerythromycin A ketolides

Article abstract of DOI:10.1021/jm100711p

A series of novel 6-O-substituted 8a-aza-8a-homoerythromycin A ketolides was synthesized and evaluated for in vitro antibacterial activity. Key strategic elements of the synthesis include the base-induced E-Z isomerization of 3-O-descladinosyl-6-O-allyler

Full text of DOI:10.1021/jm100711p

5868 J. Med. Chem. 2010, 53, 5868–5880
DOI: 10.1021/jm100711p
Synthesis and Structure-Activity Relationships of Novel 8a-Aza-8a-homoerythromycin A Ketolides
ꢀ
ꢁ
Drazen Pavlovic* and Stjepan Mutak
ꢁ
Pliva Research Institute, Prilaz baruna Filipovica 29, 10000 Zagreb, Croatia
Received June 15, 2010
A seriesofnovel 6-O-substituted 8a-aza-8a-homoerythromycin A ketolideswas synthesized andevaluated
for in vitro antibacterial activity. Key strategic elements of the synthesis include the base-induced E-Z
isomerization of 3-O-descladinosyl-6-O-allylerythromycin A 9(E)-oxime followed by ring-expanding
reaction of the resulting 9(Z)-oxime via Beckmann rearrangement. The ketolides showed potent activity
against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLSB)
resistant Gram-positive and fastidious Gram-negative pathogens. The best compounds in this series
overcome all types of resistance in relevant clinical Gram-positive pathogens and display in vitro activity
comparable to telithromycin and cethromycin.
Introduction
A series of C(11)-C(12) cyclic carbamate ketolides with an
allyl heteroaryl side chain attached to the C-6 hydroxyl group
of erythromycin A was synthesized inAbbott Laboratories, of
which cethromycin (5) was selected for clinical development
(Figure 1).6 Both 4 and 5 demonstrated enhanced antibac-
terial activity against respiratory pathogens and most impor-
tantly against strains resistant to commonly used macrolides.
These results subsequently generated great interest in the
macrolide field, which was further fueled by the rapid deve-
lopment of antibiotic resistance. Thus far, several novel
macrolide series have been developed based on the ketolide
platform.7 Furthermore, it has been proven that the C-11,C-12
cyclic carbamate present in 4 and 5 can be replaced by
properly functionalized C-11,C-12 R-amino lactone ring. This
type of modification led to a novel GlaxoSmithKline lead
series8 exemplified by GW773546X (6) (Figure 1). Recent
studies in this area have unveiled a novel series of orally active
C-6 substituted carbamate ketolides based on 14-membered
erythromycin A (Ery Aa) scaffold.9 The most promising
analogues within this series, 7 and 8, were found to provide
good oral activity in mice that was essentially equivalent to
that of 4 (Figure 1).
Structuralmodificationof Ery A isstillconsidered to be one
of the most effective approaches for producing macrolide
antibiotics having novel characteristics. The chemistry per-
formed on Ery A in the past can be divided into two main
categories: (1) modification of peripheral substituents on the
macrolide nucleus and (2) transformation affecting the agly-
con scaffold, which is expected to lead to significant biological
improvements. From the synthetic point of view, the latter
approach is considered to be more challenging but often
results in a decrease or loss of antibacterial activity. Only a
limited number of such approaches were successful, exempli-
fied by the azalides (e.g., azithromycin).10 In the course of our
exploratory investigation on macrolides, we were attracted to
this later approach andset out tofind a routeto a new nucleus.
The development of bacterial resistance to currently avail-
able antibacterial agents is a growing global health problem.
Of particular concern are infections caused by multidrug-
resistant Gram-positivepathogensespeciallybyStreptococcus
pneumoniae, which is one of the most common and also
most problematic respiratory pathogen.1 Until the 1990s,
S. pneumoniae was readily treatable with a variety of older
and inexpensive antibiotics. Following at least two individual
outbreaks of penicillin-resistant S. pneumoniae, the resistant
forms of the pathogen have persisted worldwide and have
acquired resistance to other antibiotic classes. Today multi-
drug-resistant S. pneumoniae is a major problem in the Pacific
Rim countries and is becoming a significant problem for
physicians in the United States and parts of Europe.2 A recent
surveillance study indicated that among 1601 clinical isolates
of S. pneumoniae collected in 34 U.S. medical centers, 29.5%
were penicillin-resistant, 19.3% were erythromycin-resistant,
and 13.2% were tetracycline-resistant.3 Other macrolides
such as clarithromycin (2) and azithromycin (3) showed
a similar level of resistance compared with erythromycin A (1)
(Figure 1).4 These studies clearly indicated a continuing
medical need for new antibacterial drugs that could overcome
macrolide resistance to currently available antibiotics while
maintaining all the activity and safety attributes characteristic
of this class. One such new drug is telithromycin (4), formerly
known as HMR 3647, a member of a new family of macrolide
antibacterial agents, the ketolides (Figure 1).5 Ketolides are
derived from 14-membered macrolide erythromycin A but
differ from this and other macrolides by having a carbonyl
group at position C-3 of the macrolactone ring instead of the
sugar L-cladinose. In addition, 4 possesses a C(11)-C(12)
carbamate side chain, which is linked via a butyl group to
imidazolyl and pyridinyl rings.
*To whom correspondence should be addressed. Current address:
ꢂ
Laboratorie de Chimie des Polymeres Organiques (LCPO), UMR 5629,
ꢁ
ꢁ
Universite Bordeaux 1/CNRS, Ecole Nationale Superieure de Chimie,
de Biologie et de Physique (ENSCBP), 16 Avenue Pey-Berland, 33607
Pessac Cedex, France. Phone: þ33 (0)5 40 00 31 99. Fax: þ33 (0)5 40 00
84 87. E-mail: dpavlovic@enscbp.fr.
aAbbreviations: Ery A, erythromycin A; PyHCl, pyridinium hydro-
chloride; TMSCl, trimethylsilyl chloride; TMSIm, trimethylsilylimida-
zole; MLSB, macrolide-lincosamide-streptogramin B.
r
pubs.acs.org/jmc
Published on Web 07/20/2010
2010 American Chemical Society

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5869
Figure 1. Structures and numbering scheme of the macrolide anti-
biotics erythromycin A (1), clarithromycin (2), and azithromycin
(3). Novel ketolides based on erythromycin A and clarithromycin
scaffold include telithromycin (4), cethromycin (5), GW773546X
(6), JNJ-17069546 (7), and JNJ-17070885 (8).
Figure 2. Synthesis of 6-O-substituted 8a-aza-8a-homoEry A ke-
tolides via E-Z isomerization-Beckmann rearrangement metho-
dology.
Chart 1. Structural Features Included in the Design of Novel
15-Membered Macrolides
against MLSB resistance and (2) a ketolide backbone for
improving potency and activity against efflux resistance
(Chart 1).
Chemistry
We have developed highly efficient and versatile synthetic
process to access a wide range of 15-membered 8a-aza-8a-
homoerythromycin A analogues. Our strategy for synthesiz-
ing the 6-O-substituted 8a-aza-8a-homoerythromycin A ke-
tolide analogues was planned to involve a ring expanding
reaction via Beckmann rearrangement of the 14-membered
erythromycin A Z-oxime 10. The general method used to
prepare 6-O-substituted 8a-aza-8a-homoerythromycin A deri-
vatives,illustratedinFigure2,involvedtheE-Zisomerization-
Beckmann rearrangement methodology as a key strategic
element of the synthesis.
Base-induced isomerization of 3-O-descladinosyl-6-O-allyl-
erythromycin 9(E)-oxime (9) to 9(Z)-oxime (10) followed by
Beckmann rearrangement and Dess-Martin oxidation of the
C-3 hydroxyl group afforded the 15-membered 8a-aza-8a-
homoerythromycin ketolide (11). The crucialkey intermediate
11 thus obtained allowed a smooth modification of the allyl
substituent at the C-6 position. The target epoxides 13a,b
were prepared by m-CPBA oxidation of 6-O-allyl-8a-aza-8a-
homoerythromycin derivative 11 followed by zinc reduction
of the N-oxide group in 12a,b. The terminal epoxides 13a,b
were subjected to nucleophilic ring opening with selected
This led us to try modifications of the framework of Ery A
derivatives. Our efforts led to the establishment of a synthetic
route to a novel series of 15-membered 8a-aza-8a-homoery-
thromycin ketolides. The synthesis of ketolides based on a
15-membered ring azahomoerythromycin A skeleton repre-
sents a logical extension of the success of 14-membered ring
ketolides.11 However, in contrast to 14-membered ketolides
the structure-activity relationships of their corresponding
15-membered analogues have been relatively unexplored.12
In this paper, we describe the work leading to the discovery
of 15-membered ring ketolides as a new class of macrolide
antibiotics and, in particular, the synthesis of a series of novel
6-O-substituted 8a-azahomoerythromycin A ketolides and
their antibacterial activity against some key erythromycin-
resistant pathogens. Structural features thatguided our design
of novel macrolides included (1) a properly attached and
oriented aryl or heteroaryl group for improving activity

5870 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Pavlovicꢀ and Mutak
Chart 2. Amines Employed as the R1 Substituent in Ketolide Series
amines (Chart 2) to give a mixture of diastereoisomeric
β-amino alcohols 14a,b. The amines, which were not commer-
cially available, were prepared by literature methods13 as
designated.
derivative 18 in 70% isolated yield. When the reaction was
conducted for an extended period of time, usually 5 h, up to
10% of 6,12-di-O-allyl derivative 19 was also observed ac-
cording to LC/MS analysis of the crude reaction mixture.
Finally, removal of the trimethylsilyl and ketal protecting
groups from 18 was accomplished by exposure to formic acid,
furnishing after flash column chromatography the pure 9(E)-
oxime 20 (90% yield).17 In the later stage our standard work-
ing procedure actually omitted the purification step because in
most of the cases the crude reaction mixture was used in the
next step. Selective cleavage of the L-cladinose sugar was
accomplished by treating an ethanolic solution of 20 with
2 M HCl for 12 h at room temperature. The cladinose-related
byproduct was removed in the aqueous workup, whereas
epimeric 3-O-descladinosyl-6-O-allylerythromycin 9(E)-
oxime (9) was advanced into the next step without further
purification.
Base-induced isomerization of 9 proceeded smoothly to
afford the corresponding epimeric oxime 10 of predominantly
Z stereochemistry (9:1 epimeric mixture of Z/E oximes) in
70% yield over two steps. Before base-induced isomerization
was established the main drawback associated with the syn-
thesis of 3-O-descladinosyl-6-O-allyl-8a-aza-8a-homoerythro-
mycin (15) was essentially in a very tedious and time-
consuming procedure for the preparation of Z oxime 10.
Nevertheless, this drawback could be easily circumvented by
treatment of 9 with 4 mol equiv of lithium hydroxide mono-
hydrate in ethanol, a process that generated a 9:1 mixture of
Z/E oximes isomeric at the C-9 position in 90% yield.
The Z-isomer 10 was isolated in an essentially pure form by
recrystallization from methanol in 85% yield. Oxime 10 was
Starting from readily available oxime precursors, the method
provides an easy access to a variety of novel 8a-azahomo Ery A
analogues having various groups tethered to the C-6 posi-
tion of the ketolide skeleton. Moreover, the method is of
additional interest, as it has been demonstrated that the
aromatic and heteroaromatic moieties attached at the C-6
position of the ketolide core through an ether linkage
strongly increase antibacterial activity against the suscep-
tible erythromycin and most importantly against the strains
containing erm(B)-encoded ribosomal methylase constitu-
tively resistant to Ery A.14
The synthesis of these analogues can be divided into a four-
step sequence: (a) introduction of the 6-O-allyl group onto the
erythromycin A scaffold (Scheme 1); (b) base-induced iso-
merization of 3-O-descladinosyl-6-O-allylerythromycin A
9(E)-oxime (9) to the corresponding 9(Z)-oxime (10) followed
by Beckmann rearangement to 3-O-descladinosyl 8a-lactam
(15) (Scheme 2); (c) conversion to the 3-keto group (Scheme 3);
(d) further synthetic modification of the 6-O-allyl group
(Scheme 4). Following a modification of the communicated
protocols, 6-O-allylerythromycin A 9(E)-oxime (20) was pre-
pared as shown in Scheme 1.6,15 Oxime 20 was prepared
starting from commercially available erythromycin A 9(E)-
oxime (16)16 which was first protected as 9-ketaloxime-20,400-
bis(trimethylsilyl)erythromycin A (17). Selective alkylation of
suitably protected oxime 17 with allyl bromide in the presence
of potassium hydroxide in dry DMF afforded 6-O-allyl

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5871
Scheme 1. Synthesis of 6-O-AllylEry A 9(E)-Oxime (20)a
a Reagents and conditions: (a) diisopropoxycyclohexane, PyHCl, CH2Cl2, 90%; (b) TMSCl, TMSIm, CH2Cl2, 85%; (c) allyl bromide, KOH, DMF,
70%; (d) HCO2H, EtOH/H2O (1:1), 90%.
Scheme 2. Base-Induced Isomerization and Beckmann Rearrangement of 3-O-Descladinosyl-6-O-allylEry A 9(Z)-Oxime (10)a
a Reagents and conditions: (a) HCl, EtOH/H2O (2:1), 90%; (b) LiOH H2O, EtOH, 80%; (c) p-TsCl, NaHCO3, acetone/H2O (1:2), 90%.
3
stable to isomerization as a crystalline solid, but in solution it
slowly equilibrated to the E-isomer 9. When 10 was subjected
to acidic conditions, an approximate 9:1 mixture of isomeric
oximes was reestablished, favoring the thermodynamically
more stable 9(E)-isomer. The configuration of oximes 9
and 10 was determined unambiguously on the basis of their
8-Me and 10-Me groups. As shown in Table 1, NMR spectra
of the E-oximes in the cladinosyl series (20 and 22) showed
that the signal attributed to H-8 revealed a characteristic
downfield shift (3.83 and 3.75 ppm) resulting from the de-
shielding effect of the cis-substituted oxime’s hydroxyl group.
On the other hand the upfield shifts seen for the 8-Me (1.01
and 1.00 ppm) and C-8 (26.6 and 24.9 ppm) resonances can be
attributed to the shielding effect due to steric interactions with
1
characteristic H and 13C chemical shifts of the R-carbon
atoms (C-8 and C-10) and chemical shifts of their respective

5872 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Pavlovicꢀ and Mutak
Scheme 3. Dess-Martin Oxidation of 3-O-Descladinosyl-6-O-allyl-8a-aza-8a-homoEry A (15)a
a Reagents and conditions: (a) Ac2O, Et3N, CH2Cl2, 90%; (b) Dess-Martin periodinane, pyridine, NaHCO3, CH2Cl2, 90%; (c) MeOH, reflux, 90%.
Scheme 4. Synthesis and Nucleophilic Ring-Opening of Terminal Epoxides 13a,b with Selected Aminesa
a Reagents and conditions: (a) m-CPBA, NaOAc, CH2Cl2, 60% or dimethyldioxirane, acetone, 65%; (b) Zn powder, NH4Cl, EtOH/H2O (2:1), pH 5,
68%; (c) R1NH2, LiClO4, 2-PrOH, 50-80%.
Table 1. 1H and 13C Chemical Shifts for Descladinosyl-6-O-allyl Ery A Oximes (9 and 10), 6-O-Allyl Ery A Oximes (20 and 21a), and 6-O-Methyl Ery A
Oximes (22 and 23b)c
1H NMR (CDCl3)
13C NMR (CDCl3)d
oxime
H-8
H-10
8-Me
10-Me
C-8
C-10
8-Me
10-Me
9
3.79
4.29
3.83
2.79
3.75
2.74
2.61
2.08
2.70
2.33
2.65
2.57
0.99
1.01
1.01
1.07
1.00
1.06
1.14
1.12
1.16
1.31
1.13
1.32
25.4 (29.7)
32.1 (36.3)
26.6
33.2 (32.5)
29.0 (34.5)
34.2
18.6 (18.6)
18.1 (19.4)
19.6
15.1 (14.6)
15.3 (10.4)
15.6
10
20
6-O-allyl Ery A 9(Z)-oxime (21)
6-O-Me Ery A 9(E)-oxime (22)
6-O-Me Ery A 9(Z)-oxime (23)
37.6
24.9
35.5
32.3
21.0
18.2
11.8
14.6
35.6
34.1
19.6
10.7
a Oxime 21 was prepared according to the experimental procedure described in the Supporting Information. b Clarithromycin oximes 22 and 23 were
prepared according to literature procedure; see ref 20c. c The chemical shifts are in ppm downfield from TMS. The NMR assignements shown were
corroborated by 1H-1H and 1H-13C 2D experiments (COSY, HSQC, and HMBC). d The 13C NMR spectra of oximes 9 and 10 were also recorded in CD3OD, and
their corresponding chemical shifts are shown in parentheses.
the cis hydroxyl group. These results are entirely consistent
with those reported by McGill et al.18a and Gasc et al.20a
When the 13C NMR spectra of oximes in the cladinosyl and
descladinosyl series (9, 10, 20, 21, 22, and 23) were compared,
some regular trends could be observed (see Table 1), among
which we highlight the expected fact that the δC values of
methyne groups (C-8 and C-10) anti to the oxime group are
always higher than those of the corresponding syn groups, as
to the known effect of steric compression.18b The same
regularity was also noticed with the δC values of methyl
groups (8-Me and 10-Me), however, only in the Z-oximes of
both series (10, 21, and 23).
The chemical shift of the 10-Me group for (E)-20 and (E)-22
appears at 15.6 and 14.6 ppm, respectively, whereas the
congested 10-Me group of the Z-oximes 21 and 23 appears
at 11.8 and 10.7 ppm. The chemical shifts of descladinosyl

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5873
E-oxime 9 were almost identical in comparison with their
respective δC and δH values of methyl and methyne groups in
the cladinosyl E-oxime 20. On the other hand, the deshielding
of the H-8 (δ 4.29) in the Z-oxime derivative 10 is accom-
panied by shielding of the H-10 (δ 2.08) in comparison with
the respective hydrogens in the Z-oxime 21 (δ 2.79 and 2.33,
respectively). These differences in the chemical shifts followed
the same trend and were also observed in the 13C NMR
spectra of 10 and 21, particularly in the δC values of methyne
groups (C-8 and C-10).18c Generally the chemical shift
changes upon E-Z isomerization are quite local, and so we
conclude that E-Z isomerization of the 9(E)-oxime 9 intro-
duces a rather substantial alteration in the conformation.
It is interesting to note that in contrast to ready isomeriza-
tion of 9, neither 6-O-allylerythromycin A 9(E)-oxime (20)
nor 3-O-descladinosyl-6,12-di-O-allylerythromycin A 9(E)-
oxime (24)19 participates in an efficient isomerization reac-
tion. While literature precedents exist for the base-catalyzed
isomerization of the E-oxime to the Z-oxime in the erythro-
mycin A series, the same transformation failed when we tried
to apply it to the clarithromycin series.20 To the best of our
knowledge, the base-catalyzed isomerization of 9 represents
the only synthetically viable approach to 6-O-allyl-8a-aza-8a-
homoEry A scaffold (15).21 Therefore, lithium hydroxide
induced isomerization of 9 enabled us to prepare a sizable
amount of 10 for subsequent Beckmann rearrangement stud-
ies. Althoughthesynthesis of10describedinthe Experimental
Section is on a relatively small scale (∼250 mg), the procedure
was also found to be suitable for a larger batch synthesis
(10-50 g). Beckmann rearrangement of 3-O-descladinosyl-6-
O-allylerythromycin A 9(Z)-oxime (10) with p-tosyl chloride
and sodium bicarbonate in aqueous acetone afforded 15-
membered 8a-lactam 15 in 90% isolated yield (Scheme 2).22
As indicated in Scheme 3, selective protection of the C-20-
hydroxyl group in descladinosyl lactam 15 was accomplished
by acylation with acetic anhydride and triethylamine at room
temperature.
Oxidation of the C-3 hydroxyl group with excess
Dess-Martin periodinane23 in the presence of pyridine and
NaHCO3 followed by deprotection of the C-20-acetate 26 in
refluxing methanol afforded ketolide 11 in 70% overall yield
from 15. This compound served as a key intermediate for the
preparation of other analogues. Therefore, from 6-O-allyl-8a-
aza-8a-homoerythromycin A ketolide (11), a series of ketolide
analogues 14aa-ax and 14ba-bx were prepared through
the epoxide intermediate 12a,b (Scheme 4). Treatment of 11
with m-chloroperoxybenzoic acid (5 mol equiv) buffered
with sodium acetate (2.1 mol equiv) using dichloromethane
as solvent afforded syn-epoxy N-oxide 12a and anti-epoxy
N-oxide 12b as a chromatographically inseparable mixture of
isomers in 1:1 ratio according to HPLC/MS analysis.
The epoxidation of 11 was then effected using dimethyl-
dioxirane, as it was felt that this more sterically sensi-
tive oxidant would favor the formation of the sterically less
hindered syn-epoxide 12a. Thus, treatment of 11 with a
solution of dimethyldioxirane24 in acetone afforded epoxides
12a and 12b as a 4.4:1 mixture of isomers. As dimethyldiox-
irane is sensitive to steric factors, the oxygen is delivered
primarily to the upper less hindered R-face of the olefin 11,
and this is reflected in the syn/anti epoxide product ratio of
4.4:1 compared to 1:1 using m-chloroperoxybenzoic acid.
Reduction of the N-oxide functionality in 12a and 12b gave
the target epoxides 13a and 13b as a 4.5:1 mixture of syn- and
anti-isomers in 68% yield. This mixture was carried on to the
following step without separation of the isomers. As it was
demonstrated earlier25 that the introduction of a supplemen-
tary amino group in the macrolide skeleton, e.g., azalides and
some 9-aminooximes, was beneficial for the activity against
H. influenzae, a strategy was put in place to quickly introduce
several amines into the 6-O-propyl side chain of ketolides.
Thus, after successful preparation of epoxides 13a and 13b,
their subsequent amine opening to afford β-amino alcohols
was investigated.
Nucleophilic ring opening of epoxy 8a-lactam 13a,b with
amines a-x (Chart 2) produced a mixture of diastereoiso-
meric β-amino alcohols 14aa-ax and 14ba-bx that were not
easily separable by flash chromatography. Typically a 5-fold
excess of amine and lithium perchlorate was used in this
procedure and the reactions were carried out in refluxing
2-propanol.26 In order to ascertain the importance of C-200
hydroxyl stereochemistry on antibacterial activity of 14av
and 14bv, it was necessary to prepare each diastereoisomeric
β-amino alcohol in pure form. Therefore, the predominant
syn-isomer 14av was isolated by semipreparative HPLC and
crystallization, whereas the isomeric anti-alcohol 14bv was
separated by semipreparative HPLC in small quantities.
Results and Discussion
The antibacterial activity of the 6-O-substituted ketoaza-
lides was tested against a panel of representative pathogens
selected from Pliva Research Institute culture collection.
The in vitro antibacterial activities are reported as minimum
inhibitory concentrations (MICs) that were determined by the
agar microdilution method according to NCCLS standards.27
Table2 showsthe invitroactivityof theketoazalide analogues
and the reference compounds azithromycin (3), telithromycin
(4), and cethromycin (5).
In general, the ketolides were inactive against constitutively
MLSB-resistant strain of Staphylococcus aureus (MIC >
64 μg/mL). The most interesting feature of these new com-
pounds was their effectiveness against inducibly MLSB-
resistant staphylococci and pneumococci as well as constitu-
tively MLSB-resistant pneumoccoci. Moreover, a few of them
(14ar-br, 14av, and 14bv) were more potent than azithromycin
against H. influenzae (Table 2).
Structure-Activity Relationships (SAR) of Aryl- and Hetero-
aryl Substituted 8a-Azaketolides. The 8a-azaketolide ana-
logue 11, which was a synthetic intermediate to the epoxides
12a,b and 13a,b, had only moderate activity against most
of the organisms tested, with MIC values generally in the
1-16 μg/mL range. The diastereoisomeric epoxides, 6-O-(2-
methyloxiranyl)-3-oxo-8a-aza-8a-homoEry A (13a,b), also
had a moderate antibacterial activity against the Gram-
positive organisms and were generally 4- to 64-fold less
active than azithromycin (3). The epoxy N-oxides 12a,b
were essentially inactive with MIC values exceeding 64 μg/
mL, indicating that the C-30 dimethylamino group is a
necessary requirement for potent antibacterial activity.
Comparison of the antibacterial activity within the ketolide
class of 8a-aza-8a-homoEry A with the macrolide standard
azithromycin revealed some interesting features character-
istic of the ketolides. In general, ketolides showed no dec-
rease in activity against inducibly MLSB-resistant S. aureus
relative to the macrolide-susceptible strains whereas azi-
thromycin showed a 64-fold decrease. This insensitivity of
14aa-ax and 14ba-bx to induction of resistance is a well-
known characteristic of ketolides.28 The introduction of an
aryl or heteroaryl moiety to 14aa-ax and 14ba-bx resulted

5874 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Pavlovicꢀ and Mutak
Table 2. In Vitro Antibacterial Activity of Selected 6-O-Substituted 8a-aza-8a-homoEry A Ketolidesa
S. aureus
S. pneumoniae
S. pyogenes
B0329
compd Ery-S
B0538
iMLS
B0330
cMLS
B0331 B0541
M
B0627
cMLS
B0326 B0542
Ery-S
B0543
iMLS
>64
B0544
cMLS
B0545 BM. catar.b
H.
inf.cB0529
Ery-S
M
M
0324
11
12a,b
13a,b
8
>64
>64
>64
>64
16
8
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
16
>64 >64
1
>64
>64
4
>64
4
>64
>64
>64
>64
16
16
8
8
>64
8
16
>64
32
16
16
8
>64
>64
1
>64
16
0.5
4
4
4
2
1
16
8
2
0.25
>64
8
16
4
0.5
8
14aa-ba
14ab-bb
14ac-bc
14ad-bd
8
8
1
2
1
8
0.25
e0.125
e0.125
8
4
0.25
0.25
1
0.5
1
1
e0.125
2
2
0.5
1
2
4
16
0.5
1
8
0.5
e0.125
0.25
16
1
14ae-be e0.125
1
1
e0.125 e0.125
2
0.5
e0.125
e0.125
0.25
0.25
0.5
4
1
0.25
0.5
2
14af-bf
14ag-bg
14ah-bh
14ai-bi
14aj-bj
14ak-bk
14al-bl
14am-bm
14an-bn
14ao-bo
14ap-bp
14aq-bq
14ar-br
14as-bs
14at-bt
14au-bu
14av
0.5
4
2
2
e0.125
0.5
1
8
4
1
8
4
2
32
16
4
1
0.5
8
2
0.5
4
4
0.25
e0.125
1
1
4
e0.125 0.5
e0.125 e0.125
1
16
2
1
1
0.5
8
1
0.5
4
e0.125
4
e0.125
8
8
8
16
4
0.25
0.25
4
32
32
>64
16
8
32
4
1
4
2
e0.125
0.5
0.5
2
32
0.5
4
1
4
16
4
16
4
16
4
e0.125
e0.125
0.25
4
4
32
16
8
4
16
4
4
2
1
0.5
1
2
2
e0.125
1
0.5
2
2
1
2
4
2
32
16
8
2
0.5
8
32
16
16
8
4
4
16
32
8
2
2
4
8
e0.125
e0.125
e0.125
e0.125
e0.125
8
4
2
0.5
2
2
1
e0.125
2
4
8
1
2
0.25 e0.125
0.5 e0.125
0.25 e0.125
0.25 e0.125
2
1
2
4
1
0.5
4
1
0.5
2
8
4
4
8
8
2
0.5
1
4
1
2
8
2
1
1
1
1
0.25 e0.125
1
4
0.5
0.5
0.5
4
e0.125
e0.125
0.5
1
e0.125
e0.125
1
0.25
0.25
2
0.25 e0.125 e0.125 e0.125 e0.125 e0.125
1
0.25
0.5
8
14bv
0.5 e0.125
0.5 e0.125
0.5
4
0.25 e0.125
0.5
8
4
14aw-bw
14ax-bx
3
1
e0.125
e0.125
e0.125
e0.06
32
4
4
0.25
1
0.25
>64
0.5
0.25
2
>64
e0.125
1
0.5
4
0.25
8
2
1
2
e0.125 >64
e0.125
>64
4
1
0.25
0.25
e0.125
1
4
e0.125
e0.06
0.25 e0.06
0.25 e0.06
0.5
e0.06
e0.06
1
5
e0.125 e0.06 e0.06
1
e0.125 e0.125
1
a Minimum inhibitory concentration (MIC) values are given in μg/mL. All compounds except 14av and 14bv were tested as diastereoisomeric
mixtures. For instance 14aa-ba stands for diastereoisomeric mixture consisting of syn- and anti-β-amino alcohols 14aa and 14ba. Other analogues of the
β-aminoalcohol series were denoted in the same way. Ery-S: erythromycin-susceptible strains. iMLS: inducibly resistant strains. cMLS: constitutively
resistant strains. M: efflux-resistant strains. b M. catarrhalis. c H. influenzae.
in a dramatic increase of activity against resistant strains
and H. influenzae simultaneously. With the exception of the
constitutively MLSB-resistant S. aureus all the MICs of
14aa-af and 14ba-bf against resistant strains irrespective
of the phenotype were included between 0.125 and 16 μg/mL
(MIC > 64 for azithromycin) and 1-16 μg/mL against
H. influenzae (MIC = 1 for azithromycin). The nitrophenyl-
ethyl analogue 14ae-be was the most potent compound
evaluated within the aryl series, having MIC values of 1 μg/
mL or lower for the majority of the Gram-positive organ-
isms screened. Compounds 14ae-be was particularly potent
against the erm(B)-containing strain of S.pneumoniae B0627
with an MIC value of 0.125 μg/mL. The activity of the
pyridinyl analogues 14ag-ak and 14bg-bk was found to
depend markedly on the point of attachment of the amino-
alkyl side chain on the pyridine ring. The activity of the
3-aminoethyl and 3-aminobutyl analogues 14ag-bg and
14ai-bi was in general 2- to 4-fold better than the corre-
sponding 2-aminoalkyl substituted analogues 14aj-ak and
14bj-bk against most of the strains tested. The length of
the side chain was also critical as shown by compounds
14ah-bh and 14ai-bi compared to 14ag-bg. The ketolides
with the butyl side chain 14ai-bi exhibited the most potent
activity within the pyridinyl substituted series. In compari-
son to phenyl analogues (14aa-ac and 14ba-bc) the corre-
sponding pyridinyl substituted analogues (14ag-ak and
14bg-bk) were slightly more active against constitutively
MLSB-resistant S. pneumoniae. Furthermore, modification
of the side chain attached to the aryl moiety had a significant
effect on the antibacterial activity of the compounds tested.
Analogues with the piperazinyl side chain (14al-ap and
14bl-bp) were less active than the alkylamino analogues
(14aa-af and 14ba-bf), suggesting that steric bulk at this
position might have a negative impact on the antibacterial
activity. The same trend was observed when comparing the
piperazinyl substituted quinolines 14aw-bw, and 14ax-bx
to the ethylenediamino substituted analogues 14au-bu, and
14av-bv, respectively.
To further probe the SAR we prepared a series of ketolides
in which a quinoline ring was appended to the macro-
lide core. To this end, quinolinyl analogues 14aq-ax and
14bq-bx were prepared and evaluated for in vitro antibac-
terial activity. It was found that the activity depends mark-
edly on the point of attachment of the quinoline ring. The
activity of the C-6 substituted quinolines 14ar-br, 14at-bt,
and 14av-bv was in general 2- to 4-fold better than that of
the C-3 substituted analogues 14aq-bq, 14as-bs, and
14au-bu against most strains. In addition, the design of a
tether connecting the ketolide and quinoline substructures
appeared to be critical for antibacterial activity. The piperazine-
linked quinoline analogues 14aw-bw, and 14ax-bx were not
as active as ketolides 14au-bu, 14av, and 14bv, incorporating
quinoline substructures linked via an ethylenediamino group.
Notably, the activity against a variety of susceptible and

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5875
resistant Gram-positive and fastidious Gram-negative
pathogens was markedly superior to that of azithromycin
(3). In fact, the in vitro profile of 14av (syn-14v) compares
favorably with telithromycin (4) and cethromycin (5). For
example, compound 14av is ∼4-fold more active than 4
against both constitutively MLSB-resistant S. pyogenes
and H. influenzae strain.
mixture was made basic with 2 M aqueous NaOH solution and
extracted with ethyl acetate. The organic layer was washed with,
in turn, water and a saturated aqueous sodium chloride solution
and dried over anhydrous K2CO3. The solvent was evaporated
under reduced pressure and the residue was purified by silica gel
column chromatography (eluent, ethyl acetate/n-hexane/
diethylamine, 60:30:2) to give 2.3 g (90%) of 9(E)-oxime 20 as
an off-white solid. Rf = 0.47, ethyl acetate/n-hexane/diethyl-
amine 100:100:20; FAB-MS m/z 789 (MHþ, 85%); IR (KBr)
νmax 2974, 2936, 1746, 1646, 1320, 1053 cm-1 1H NMR
;
Conclusion
(CDCl3) δ 5.96 (1H, 6-OCH2CHCH2), 5.23 (1H, H-13),
5.14 (1H, 6-OCH2CHCH2b), 5.03 (1H, 6-OCH2CHCH2a),
4.90 (1H, H-100), 4.57 (1H, H-10), 4.18 (1H, H-500), 4.06 (1H,
6-OCH2bCHCH2), 3.94 (1H, 6-OCH2aCHCH2), 3.84 (1H, H-5),
3.83 (1H, H-8), 3.77 (1H, H-50), 3.75 (1H, H-3), 3.73 (1H, H-11),
3.37 (3H, 300-OMe), 3.28 (1H, H-20), 3.07 (1H, H-400), 3.01 (1H,
H-2), 2.75-2.65 (2H, H-10, H-30), 2.46 (1H, H-200b), 2.36 (3H,
30-NMe2), 2.11 (1H, H-4), 1.96 (1H, H-14b), 1.75 (1H, H-40b),
1.65 (1H, H-7b), 1.62 (1H, H-200a), 1.52 (3H, 6-Me), 1.50-1.44
(2H, H-14a, H-7a), 1.29 (3H, 500-Me), 1.28 (3H, 300-Me), 1.23
(3H, 2-Me), 1.21 (3H, 50-Me), 1.20 (3H, 12-Me), 1.19 (1H,
H-40a), 1.16 (3H, 10-Me), 1.15 (3H, 4-Me), 1.01 (3H, 8-Me),
0.88 (3H, 15-Me); 13C NMR (CD3OD) δ 177.1 (s, C-1), 169.5 (s,
C-9), 138.2 (d, 6-OCH2CHCH2), 116.3 (t, 6-OCH2CHCH2),
103.7 (d, C-10), 98.1 (d, C-100), 81.0 (s, C-6), 80.6 (d, C-5), 80.1
(d, C-3), 79.3 (d, C-400), 78.1 (d, C-13), 75.6 (s, C-12), 74.3
(s, C-300), 73.1 (d, C-20), 71.6 (d, C-11), 68.9 (d, C-50), 67.1
(t, 6-OCH2CHCH2), 67.0 (d, C-500), 65.4 (d, C-30), 50.1 (q,
300-OMe), 46.2 (d, C-2), 40.9 (q, 30-NMe2), 40.2 (d, C-4), 38.4
(t, C-7), 36.5 (t, C-200), 34.2 (d, C-10), 32.0 (t, C-40), 26.6 (d, C-8),
22.8 (t, C-14), 22.3 (q, 6-Me), 22.0 (q, 50-Me), 21.7 (q, 300-Me), 19.6
(q, 500-Me, 8-Me, 2C), 17.2 (q, 12-Me), 16.6 (q, 2-Me), 15.6 (q,
10-Me), 11.4 (q, 15-Me), 10.3 (q, 4-Me). Anal. Calcd for C40H72-
N2O13: C, 60.89; H, 9.20; N, 3.55. Found: C, 60.52; H, 9.54; N, 3.31.
3-O-Descladinosyl-6-O-allylerythromycin A 9(E)-Oxime (9).
To a stirred suspension of 6-O-allylerythromycin A 9(E)-oxime
(20) (6.2 g, 7.8 mmol) in ethanol (20 mL) and water (40 mL), was
added 2 M aqueous HCl (40 mL, 40.0 mmol) dropwise over
30 min until pH 1.0 was reached. The solution was stirred at
room temperature for 18 h. The reaction mixture was neutra-
lized with 2 M aqueous NaOH and the precipitate was collected
by filtration and washed with cold water to give a white solid,
which was dried under vacuum at 50 °C to afford 3.9 g of 9. The
filtrate was extracted with ethyl acetate (2 ꢀ 40 mL), and the
organic phase was washed with 10% sodium bicarbonate and
brine, dried over K2CO3, and concentrated to give an additional
1.0 g of 9 as a white solid. The combined crude material was puri-
fied by column chromatography (silica gel, 50:50:0.5 hexane/
acetone/aq NH3) to give 4.4 g (90%) of 9 as an off-white
solid. FAB-MS m/z 631 (MHþ, 76%); 1H NMR (CDCl3) δ
7.53 (1H, NOH), 5.92 (1H, 6-OCH2CHCH2), 5.27 (1H, H-13),
5.13 (1H, 6-OCH2CHCH2b), 5.10 (1H, 6-OCH2CHCH2a), 4.47
(1H, H-10), 3.96 (1H, 11-OH), 3.79 (2H, H-11, H-8), 3.76 (2H,
6-OCH2CHCH2), 3.71 (1H, H-5), 3.55 (1H, H-50), 3.51 (1H,
H-3), 3.28 (1H, H-20), 3.22 (1H, 12-OH), 2.67 (1H, H-2), 2.63
(1H, H-30), 2.61 (1H, H-10), 2.33 (6H, 30-NMe2), 2.20 (1H, H-4),
1.95 (1H, H-14b), 1.73 (1H, H-40b), 1.65 (1H, H-7b), 1.50 (1H,
H-14a), 1.45 (3H, 6-Me), 1.31 (1H, H-7a), 1.29-1.24 (7H, 50-
Me, 2-Me, H-40a), 1.21 (3H, 12-Me), 1.14 (3H, 10-Me), 1.12 (3H,
4-Me), 0.98 (3H, 8-Me), 0.83 (3H, 15-Me); 13C NMR (CDCl3) δ
174.9 (s, C-1), 169.9 (s, C-9), 136.0 (d, 6-OCH2CHCH2), 116.7 (t,
6-OCH2CHCH2), 106.3 (d, C-10), 87.8 (d, C-5), 79.2 (s, C-6),
78.9 (d, C-3), 76.7 (d, C-13), 73.8 (s, C-12), 70.6 (d, C-20), 70.4
(d, C-11), 69.9 (d, C-50), 65.8 (d, C-30), 64.9 (t, 6-OCH2CHCH2),
44.5 (d, C-2), 40.3 (q, 30-NMe2), 37.0 (t, C-7), 36.1 (d, C-4), 33.2
(d, C-10), 28.5 (t, C-40), 25.4 (d, C-8), 21.8 (t, C-14), 21.2 (q, 50-
Me), 19.8 (q, 6-Me), 18.6 (q, 8-Me), 16.5 (q, 12-Me), 15.1 (q,
2-Me, 10-Me), 10.5 (q, 15-Me), 8.30 (q, 4-Me). Anal. Calcd for
C32H58N2O10: C, 60.93; H, 9.27; N, 4.44. Found: C, 60.68; H,
9.62; N, 4.24.
Novel 6-O-substituted 15-membered 8a-aza-8a-homoery-
thromycin A ketolides were synthesized and evaluated for
in vitro antibacterial activity against a panel of representa-
tive erythromycin-susceptible and erythromycin-resistant test
strains. Their in vitro antibacterial activity encompasses a
large variety of clinically relevant susceptible bacteria and
MLSB-resistant Gram-positive and fastidious Gram-negative
bacteria. Various 6-O-substituted side chains are tolerated
and through their 3-D orientation influence the resulting
antibacterial spectrum. The most active compound 14av was
as active as telithromycin and cethromycin and overcomes all
types of resistance in relevant clinical Gram-positive patho-
gens. Thebrevityand conciseness of the synthesisas well asthe
excellent antibacterial activity of these molecules will hope-
fully expedite the biological evaluation of numerous ana-
logues of the ketolide-quinoline series.
Experimental Section
Experimental Procedures. 6-O-Allyl-20,400-bis-O-trimethylsi-
lylerythromycin A 9-[O-(1-Isopropoxycyclohexyl)oxime] (18).
To a 0 °C solution of 20,400-bis-O-trimethylsilylerythromycin A
9-[O-(1-isopropoxycyclohexyl)oxime] (17) (15 g, 14.5 mmol),
prepared according to the method of U.S. Patent No. 4,990,602
in 180 mL of DMF was added freshly distilled allyl bromide (7.5
mL, 87.1 mmol, 6 mol equiv). After approximately 5 min,
potassium hydroxide (85% powder, 3.8 g, 58.1 mmol, 4 mol
equiv) was added in small portions over 20 min. After the
mixture was stirred for 2 h at room temperature, the reaction
was quenched with 20% aqueous NaOH (200 mL), hexane
(200 mL) was added, and the layers were separated. The aqueous
layer was extracted with hexane (2 ꢀ 100 mL). The combined
organic extracts were washed with brine (2 ꢀ 150 mL), dried
over K2CO3, filtered, and concentrated in vacuo. The crude
material was purified by column chromatography, eluting with
1% MeOH in methylene chloride containing 1% aqueous NH3
to give 10.9 g (70%) of 18 as a white solid. FAB-MS m/z 1073
(MHþ, 99%); 13C NMR (CDCl3) δ 174.7 (s, C-1), 171.4 (s, C-9),
136.8 (d, 6-OCH2CHCH2), 115.4 (t, 6-OCH2CHCH2), 104.0 (s,
isopropoxycyclohexyl (IPCH), C-1000), 102.8 (d, C-10), 96.1 (d,
C-100), 83.1 (d, C-5), 79.8 (d, C-3), 78.1 (d, C-400), 76.6 (d, C-13),
75.1 (s, C-6), 74.0 (s, C-12), 72.4 (s, C-300), 70.8 (d, C-11), 70.4 (d,
C-20), 68.6 (d, C-50), 65.7 (t, 6-OCH2CHCH2), 65.3 (d, C-500,
C-30, 2C), 63.2 (d, IPCH, C-8000), 49.4 (q, 300-OMe), 44.5 (d, 2C),
40.1 (q, 30-NMe2), 38.8 (d, C-4), 37.4 (t, C-7), 34.9 (t, C-200), 34.3
(t, IPCH, C-6000), 33.3 (t, IPHC, C-2000), 32.9 (d, C-10), 28.6 (t,
C-40), 26.8 (d, C-8), 26.5 (q, 6-Me), 25.2 (t, IPHC, C-5000), 24.1 (t,
IPHC, C-3000), 22.8 (t, IPHC, C-4000), 22.5 (t, C-14), 21.3 (q, 50-
Me, 300-Me, 2C), 20.9 (q, IPHC, 7000-Me2, 2C)18.5 (q, 8-Me), 18.4
(q, 500-Me), 16.1 (q, 12-Me), 16.0 (q, 2-Me), 14.3 (q, 10-Me), 10.4
(q, 15-Me), 9.0 (q, 4-Me). Anal. Calcd for C55H104N2O14Si2: C,
61.53; H, 9.76; N, 2.61. Found: C, 61.24; H, 10.01; N, 2.45.
6-O-Allylerythromycin A 9(E)-Oxime (20). To a solution of
6-O-allyl-20,400-bis-O-trimethylsilylerythromycin A 9-[O-(1-iso-
propoxycyclohexyl)oxime] (18) (3.5 g, 3.3 mmol) in 60 mL
ethanol/water (1:1) was added formic acid at room temperature
until pH 4.0 was reached, and the mixure was stirred at room
temperature for 3 h. Then most of the ethanol was evaporated
under reduced pressure, and water was added to the residue. The

5876 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Pavlovicꢀ and Mutak
LiOH-Induced Isomerization of 3-O-Descladinosyl-6-O-allylery-
thromycin A 9(E)-Oxime (9) to 3-O-Descladinosyl-6-O-allylery-
thromycin A 9(Z)-Oxime (10). To a solution of 3-O-descl-
adinosyl-6-O-allylerythromycin A 9(E)-oxime (9) (260 mg,
0.4 mmol) in methanol (10 mL) was added LiOH-H2O
(67.1 mg, 1.6 mmol, 4 mol equiv) at room temperature. The
mixture was kept stirring for 2 days, after which LC/MS analysis
showed a 9:1 ratio of (Z)- versus (E)-oximes. The solvent was
evaporated to dryness and the residue dissolved in ethyl acetate
(100 mL). The organic layer was washed with water (30 mL),
saturated aqueous NaCl solution (30 mL) and dried over K2CO3.
The solvent was removed in vacuo to give 250 mg of the crude
product. The crude product was purified by column chromato-
graphy, eluting with E1 system to give 208 mg (80%) of Z-oxime
10 as a colorless solid. Analytically pure sample was obtained by
recrystallization from methanol. FAB-MS m/z 631 (MHþ, 83%);
1H NMR (CDCl3) δ 5.89 (1H, 6-OCH2CHCH2), 5.17 (1H,
H-13), 5.16 (1H, 6-OCH2CHCH2b), 5.08 (1H, 6-OCH2CHCH2a),
4.52 (1H, H-10), 4.29 (1H, H-8), 3.98 (1H, 6-OCH2b), 3.95 (1H,
11-OH), 3.89 (1H, 6-OCH2a), 3.77 (1H, H-11), 3.74 (1H, H-5),
3.58 (1H, H-50), 3.49 (1H, H-3), 3.47 (1H, 12-OH), 3.31 (1H,
H-20), 2.77 (1H, H-30), 2.68 (1H, H-2), 2.42 (6H, 30-NMe2), 2.22
(1H, H-4), 2.08 (1H, H-10), 1.89 (1H, H-14b), 1.70 (1H, H-40b),
1.64 (1H, H-7b), 1.49 (3H, 6-Me), 1.46 (1H, H-14a), 1.38 (1H,
H-7a), 1.34 (1H, H-40a), 1.28-1.25 (6H, 50-Me, 2-Me), 1.21 (3H,
12-Me), 1.12 (3H, 10-Me), 1.11 (3H, 4-Me), 1.01 (3H, 8-Me), 0.83
(3H, 15-Me); 13C NMR (CD3OD) δ 175.3 (s, C-1), 166.8 (s, C-9),
136.3 (d, 6-OCH2CHCH2), 115.0 (t, 6-O-CH2CHCH2), 101.6 (d,
C-10), 80.5 (d, C-5), 79.1 (s, C-6), 76.8 (d, C-3), 76.6 (d, C-13), 74.8
(s, C-12), 71.1 (d, C-11), 70.6 (d, C-20), 68.4 (d, C-50), 64.7
(d, C-30), 64.1 (t, 6-OCH2), 43.9 (d, C-2), 39.3 (q, 30-NMe2),
37.7 (t, C-7), 37.1 (d, C-4), 36.3 (d, C-8), 34.5 (d, C-10), 30.7
(t, C-40), 21.6 (t, C-14), 20.0 (q, 50-Me), 19.4 (q, 8-Me, 6-Me), 16.3
(q, 12-Me), 14.4 (q, 2-Me), 10.4 (q, 10-Me), 9.6 (q, 15-Me), 7.8
(q, 4-Me). Anal. Calcd for C32H58N2O10: C, 60.93; H, 9.27; N,
4.44. Found: C, 60.73; H, 9.49; N, 4.28.
Beckmann Rearrangement of 3-O-Descladinosyl-6-O-allylery-
thromycin A 9(Z)-Oxime (10). Preparation of 3-O-Descladino-
syl-6-O-allyl-8a-aza-8a-homoerythromycin A (15). The 9(Z)-
oxime 10 (1.20 g, 1.9 mmol) was dissolved in acetone (50 mL),
and the solution was cooled to 0-5 °C in an ice bath. Sub-
sequently, solutions of p-toluenesulfonyl chloride (1.84 g,
14.0 mmol) in acetone (56 mL) and sodium hydrogen carbonate
(1.16 g, 14.0 mmol) in water (180 mL) were simultaneously
added within 1 h under stirring. The reaction mixture was stirred
at room temperature for an additional 2 h, acetone was evapo-
rated at reduced pressure, and the aqueous layer was washed
with chloroform (70 mL). The pH of the aqueous layer was
adjusted to 9.0 with 2 M aqueous NaOH and extracted twice
with chloroform (2 ꢀ 70 mL). The combined organic extracts at
pH 9.0 were dried over K2CO3 and evaporated in vacuo,
yielding the crude rearranged product, which was purified by
chromatography on a silica gel column using methylene chloride-
methanol-conc ammonium hydroxide (90:9:1.5) as eluent to give
1.1 g of 15 (90%) as a colorless solid. FAB-MS m/z 631 (MHþ,
100%); 1H NMR (CDCl3) δ 6.03 (1H, 8a-CONH), 5.96
(1H, 6-OCH2CHCH2), 5.28 (1H, 6-OCH2CHCH2b), 5.15 (1H,
6-OCH2CHCH2a), 5.01 (1H, H-13), 4.52 (1H, H-10), 3.93 (2H,
6-OCH2CHCH2), 3.82 (1H, H-8), 3.78 (1H, H-3), 3.73 (1H, H-5),
3.56 (1H, H-50), 3.39 (1H, H-11), 3.28 (1H, H-20), 2.69 (1H, H-30),
2.64 (1H, H-2), 2.45 (1H, H-10), 2.37 (6H, 30-NMe2), 2.24 (1H,
H-7b), 2.14 (1H, H-4), 1.91 (1H, H-14b), 1.75 (1H, H-40b),
1.57-1.46 (2H, H-14a, H-7a), 1.39 (3H, 6-Me), 1.32 (3H,
8-Me), 1.31 (3H, 2-Me), 1.29 (1H, H-40a), 1.25 (3H, 50-Me),
1.19 (3H, 10-Me), 1.13 (3H, 12-Me), 1.11 (3H, 4-Me), 0.88 (3H,
15-Me); 13C NMR (CDCl3) δ 176.4 (s, C-1), 174.8 (s, 8a-CONH),
136.0 (d, 6-OCH2CHCH2), 116.1 (t, 6-OCH2CHCH2), 105.9 (d,
C-10), 89.5 (d, C-5), 78.5 (s, C-6), 78.1 (d, C-3), 76.4 (d, C-13), 74.9
(s,C-12), 70.6(d, C-11), 70.1(d, C-20), 69.5 (d, C-50), 65.4(d, C-30),
63.4 (t, 6-OCH2CHCH2), 43.8 (d, C-2), 43.1 (d, C-8), 42.9
(d, C-10), 41.6 (t, C-7), 39.9 (q, 30-NMe2), 35.6 (d, C-4), 28.0 (t,
C-40), 22.4 (q, 8-Me), 21.8 (q, 6-Me), 21.1 (t, C-14), 20.8 (q,
50-Me), 16.2 (q, 12-Me), 15.7 (q, 2-Me), 10.5 (q, 15-Me), 10.3 (q,
10-Me), 8.0 (q, 4-Me). Anal. Calcd for C32H58N2O10: C, 60.93; H,
9.27; N, 4.44. Found: C, 60.75; H, 9.53; N, 4.32.
Preparation of 3-O-Decladinosyl-3-oxy-6-O-allyl-8a-aza-8a-
homoerythromycin A 20-O-Acetate (25). To a solution of homo-
erythromycin A derivative 15 (757.0 mg, 1.2 mmol) in methylene
chloride (25 mL), Et3N (141.7 mg, 1.4 mmol) and acetic acid
anhydride (0.128 mL, 1.3 mmol) were added. The reaction
mixture was stirred for 3 h at room temperature. To the reaction
mixture saturated aqueous NaHCO3 (30 mL) was added. The
layers were separated, and the aqueous portion was additionally
extracted with methylene chloride (2 ꢀ 20 mL). The combined
organic extracts were washed successively with saturated aqu-
eous NaHCO3 solution (30 mL) and water (30 mL), dried over
K2CO3, and concentrated under reduced pressure. The residue
was purified by flash chromatography (silica gel, hexane/
acetone/aq NH3, 50:50:0.5) to furnish 726.8 mg of 25 (90%) as
a colorless solid. Rf = 0.40, ethyl acetate/n-hexane/diethylamine,
100:100:20; FAB-MS m/z 673 (MHþ, 87%). Anal. Calcd for
C34H60N2O11: C, 60.77; H, 8.99; N, 4.17. Found: C, 60.31; H,
9.32; N, 4.36.
Dess-Martin Oxidation. Preparation of 3-O-Descladinosyl-3-
oxo-6-O-allyl-8a-aza-8a-homoerythromycin A (11). To a solu-
tion of 20-O-acetyl derivative 25 (1.48 g, 2.2 mmol) in CH2Cl2
(5 mL) was added NaHCO3 (1.86 mg, 22 mmol, 10.0 equiv),
pyridine (887.9 μL, 11 mmol, 5.0 equiv), and Dess-Martin
reagent (1.87 g, 4.4 mmol, 2.0 equiv), and the mixture was
stirred for 3 h at ambient temperature. The reaction was
quenched by consecutive addition of saturated aqueous NaH-
CO3 (20 mL) and Na2S2O3 5H2O (1.17 g, 4.7 mmol, 13.9 equiv).
3
The resulting solution was stirred for an additional 30 min,
extracted with methylene chloride (2 ꢀ 25 mL), dried over
K2CO3, and concentated in vacuo. This crude residue was then
dissolved in MeOH (20.0 mL) and refluxed for 3 h. After
evaporation of the solvent, the residue was taken up in water,
the pH adjusted to 11 with 2 M aqueous sodium hydroxide, and
the mixture extracted with ethyl acetate. The extracts were
washed with water, dried over K2CO3, and evaporated to
dryness. The residue was purified by column chromatography,
eluting with acetone/hexane/aq NH3 (50:50:0.5) solvent system
to afford 1.1 g (81%) of 11 as a white solid. FAB-MS m/z
1
629 (MHþ, 89%); H NMR (CDCl3) δ 6.17 (1H, 8a-CONH),
5.89 (1H, 6-OCH2CHCH2), 5.18 (1H, 6-OCH2CHCH2b), 5.15
(1H, 6-OCH2CHCH2a), 5.09 (1H, H-13), 4.31 (1H, H-5),
4.25 (1H, H-10), 3.94 (1H, H-8), 3.80 (1H, H-2), 3.73 (2H,
6-OCH2CHCH2), 3.60 (1H, H-50), 3.55 (1H, H-11), 3.22 (1H,
H-20), 3.11 (1H, H-4), 2.62 (1H, H-30), 2.44 (1H, H-10), 2.36 (6H,
30-NMe2), 1.98-1.93 (2H, H-14b, H-7b), 1.77 (1H, H-40a), 1.61
(1H, H-7a), 1.52 (1H, H-14a), 1.37 (3H, 2-Me), 1.34 (3H, 4-Me),
1.26 (3H, 6-Me), 1.24 (3H, 50-Me), 1.19 (3H, 8-Me), 1.18 (3H,
12-Me), 0.88 (3H, 15-Me); 13C NMR (CDCl3) δ 206.2 (s, C-3),
174.4 (s, C-9), 170.5 (s, C-1), 136.8 (d, 6-OCH2CHCH2), 115.6 (t,
6-OCH2CHCH2), 102.6 (d, C-10), 78.8 (s, C-6), 77.8 (d, C-5),
77.6 (d, C-13), 74.3 (s, C-12), 70.7 (d, C-11), 69.9 (d, C-20), 69.0
(d, C-50), 65.6 (d, C-30), 64.0 (t, 6-OCH2CHCH2), 49.9 (d, C-2),
46.9 (d, C-4), 42.5 (d, C-8), 42.2 (d, C-10), 41.9 (t, C-7), 40.0 (q,
30-NMe2), 28.6 (t, C-40), 22.7 (q, 8-Me), 22.1 (q, 6-Me), 21.2 (t,
C-14), 20.9 (q, 50-Me), 16.0 (q, 12-Me), 14.6 (q, 4-Me), 13.9 (q,
2-Me), 10.5 (q, 15-Me), 9.7 (q, 10-Me). Anal. Calcd for
C32H56N2O10: C, 61.12; H, 8.98; N, 4.45. Found: C, 61.47; H,
9.28; N, 4.38.
syn-3-O-Descladinosyl-3-oxo-6-O-(200-methyloxiranyl)-8a-aza-
8a-homoerythromycin A N-Oxide (12a) and anti-3-O-Descladino-
syl-3-oxo-6-O-(200-methyloxiranyl)-8a-aza-8a-homoerythromycin
A N-Oxide (12b). (a) Using m-Chloroperoxybenzoic Acid. To a
solution of 11 (629 mg, 1.0 mmol) in dry dichloromethane (7 mL)
cooled to 0 °C in an ice/water bath was added sodium acetate
(175 mg, 2.1 mmol) followed by m-CPBA (1.88 g, 50% w/w,

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5877
5.0 mmol) in five portions over 5 min. The reaction mixture was
allowed to warm to room temperature and stirred for 24 h under
a drying tube. After filtration through a short pad of Celite, the
mixture was washed with aqueous Na2SO3 (10% w/v), saturated
aqueous NaHCO3 and water, anddried over K2CO3. Removal of
the solvent under reduced pressure gave a pale-tan solid that was
purified by flash chromatography using CH2Cl2/MeOH/aq NH3
(90:9:0.5) as eluent to afford a mixture of syn- and anti-epoxy
N-oxides 12a and 12b as a colorless needles (397.7 mg, 60%; syn/
anti ratio of 1:1 according to LC/MS analysis).
Reduction of syn- and anti-6-O-(200-Methyloxiranyl)-3-oxo-
8a-aza-8a-homoerythromycin N-Oxides (12a and 12b) with Zinc.
Preparation of syn- and anti-6-O-(200-Methyloxiranyl)-3-oxo-8a-
aza-8a-homoerythromycin A (13a and 13b). To a solution of
epoxy N-oxides 12a,b (994.2 mg, 1.5 mmol) in ethanol/water
(2:1, 25 mL) was added Zn powder (980.7 mg, 15 mmol, 10 mol
equiv) and NH4Cl (803 mg, 15 mmol, 10 mol equiv). The
reaction mixture was stirred at room temperature for 3 h. The
mixture was filtered over short pad of Celite, and the filtrate was
evaporated to dryness. The residue was redissolved in CH2Cl2
(25 mL) and washed with saturated aqueous NaHCO3 solu-
tion (2 ꢀ 20 mL). The organic layer was dried over K2CO3 and
evaporated to dryness. The resulting residue was purified by
column chromatography, eluting with a gradient of CHCl3 to
7% MeOH/CHCl3 to give a 4.5:1 mixture of syn- and anti-
epoxides (657.7 mg, 68%) as a white solid.
syn-Isomer 12a. FAB-MS m/z 661 (MHþ, 78%); IR (KBr)
νmax 2945, 2870 (CH), 1271 [CO (epoxide)], 892 [CO (epoxide)]
cm-1; 1H NMR (CDCl3) δ 5.85 (d, 1H, 8aNH), 5.01-4.93 (m,
1H, H-13), 4.49 (d, 1H, H-10), 4.21 (s, 1H, 11-OH), 4.20-4.10
(m, 1H, H-8), 3.82 (d, 1H, H-100b), 3.80 (m, 1H, H-2), 3.77-3.67
(m, 2H, H-20, H-5), 3.65-3.58 (m, 1H, H-50), 3.49 (s, 1H, H-11),
3.42-3.37 (m, 1H, H-30), 3.28-3.22 (m, 2H, H-100a, H-200),
3.20 (s, 6H, 30-N(O)Me2), 3.10 (1H, H-4), 2.84 (t, 1H, H-300b),
2.60-2.54 (m, 1H, H-300a), 2.35-2.29 (m, 1H, H-10), 2.06-1.87
(m, 2H, H-40b, H-14b), 1.84 (dd, 1H, H-7b), 1.60 (d, 1H, H-7a),
1.51-1.45 (m, 1H, H-14a), 1.41 (s, 3H, 6-Me), 1.39-1.36 (m,
1H, H-40a), 1.34 (d, 3H, 2-Me), 1.32 (d, 3H, 4-Me), 1.27 (d, 3H,
50-Me), 1.18 (d, 3H, 10-Me), 1.17 (s, 3H, 12-Me), 1.14 (d, 3H,
8-Me), 0.86 (t, 3H, 15-Me); 13C NMR (CDCl3) δ 205.4 (s, C-3),
174.0 (s, C-9), 170.5 (s, C-1), 102.8 (d, C-10), 80.5 (d, C-5), 79.6
(s, C-6), 77.2 (d, C-13), 76.3 (d, C-30), 74.5 (s, C-12), 72.5
(d, C-20), 71.3 (d, C-11), 67.3 (d, C-50), 65.8 (t, C-100), 59.0
(q, 30-N(O)Me), 52.1 (q, 30-N(O)Me), 51.5 (d, C-200), 49.7 (d,
C-2), 46.7 (d, C-4), 45.6 (t, C-300), 43.1 (t, C-7), 42.5 (d, C-10),
41.3 (d, C-8), 35.0 (t, C-40), 23.9 (q, 8-Me), 23.7 (q, 6-Me), 21.6
(t, C-14), 21.5 (q, 50-Me), 16.4 (q, 12-Me), 14.6 (q, 4-Me), 13.8
(q, 2-Me), 11.0 (q, 15-Me), 9.4 (q, 10-Me). Anal. Calcd for
C34H56N2O12: C, 58.16; H, 8.54; N, 4.24. Found: C, 58.28; H,
8.72; N, 4.10.
1
syn-Isomer 13a. FAB-MS m/z 645 (MHþ, 78%); H NMR
(CDCl3) δ 6.12 (d, 1H, 8aNH), 5.00 (dd, 2H, H-13), 4.40 (d, 1H,
H-10), 4.29 (s, 1H, 11-OH), 4.17-4.06 (m, 1H, H-8), 3.94 (d, 1H,
H-3), 3.81 (m, 1H, H-2), 3.78 (dd, 1H, H-100b), 3.74-3.67 (m,
1H, H-5), 3.52 (s, 1H, H-11), 3.50-3.46 (m, 1H, H-50),
3.37-3.33 (m, 1H, H-200), 3.28-3.22 (m, 1H, H-100a), 3.21-
3.14 (m, 1H, H-20), 3.12 (s, 1H, 12-OH), 3.11 (m, 1H, H-4), 2.85
(t, 1H, H-300b), 2.60-2.54 (m, 1H, H-300a), 2.52-2.43 (m, 1H,
H-30), 2.34-2.30 (m, 1H, H-10), 2.29 (s, 6H, 30-NMe2),
2.15-1.88 (m, 2H, H-7b, H-14b), 1.74-1.66 (m, 1H, H-40b),
1.63 (d, 1H, H-7a), 1.52-1.45 (m, 1H, H-14a), 1.41 (s, 3H,
6-Me), 1.35 (d, 3H, 2-Me), 1.31 (d, 3H, 4-Me), 1.26-1.19 (m,
1H, H-40a), 1.22 (d, 3H, 50-Me), 1.19 (d, 3H, 10-Me), 1.16 (s, 3H,
12-Me), 1.14 (d, 3H, 8-Me), 0.86 (t, 3H, 15-Me); 13C NMR
(CDCl3) δ 205.2 (s, C-3), 174.2 (s, C-9), 170.4 (s, C-1), 103.4 (d,
C-10), 80.8 (d, C-5), 79.8 (s, C-6), 77.2 (d, C-13), 74.4 (s, C-12),
71.3 (d, C-11), 70.7 (d, C-20), 69.2 (d, C-50), 66.1 (t, C-100), 51.3 (d,
C-200), 49.7 (d, C-2), 46.7 (d, C-4), 45.8 (t, C-300), 42.8 (t, C-7),
42.4 (d, C-10), 41.5 (d, C-8), 40.4 (q, 30-NMe2), 28.7 (t, C-40),
24.5 (q, 6-Me), 23.6 (q, 8-Me), 21.4 (t, C-14), 21.3 (q, 50-Me),
16.3 (q, 12-Me), 14.7 (q, 4-Me), 13.6 (q, 2-Me), 10.9 (q, 15-Me),
9.5 (q, 10-Me). Anal. Calcd for C34H56N2O11: C, 59.61; H, 8.75;
N, 4.34. Found: C, 59.28; H, 8.99; N, 4.22.
anti-Isomer 12b. FAB-MS m/z 661 (MHþ, 85%); IR (KBr)
νmax 2950, 2875 (CH), 1270 [CO (epoxide)], 890 [CO (epoxide)]
1
cm-1; H NMR (CDCl3) δ 6.14 (d, 1H, 8aNH), 5.01-4.93 (m,
1H, H-13), 4.53 (d, 1H, H-10), 4.44 (s, 1H, 11-OH), 4.20-4.10 (m,
1H, H-8), 3.79 (m, 1H, H-2), 3.71 (d, 1H, H-100b), 3.77-3.67
(m, 2H, H-20, H-5), 3.65-3.58 (m, 1H, H-50), 3.55 (s, 1H, H-11),
3.42-3.37 (m, 1H, H-30), 3.33-3.29 (m, 2H, H-100a, H-200), 3.18 (s,
6H, 30-N(O)Me2), 3.12 (1H, H-4), 2.82 (t, 1H, H-300b), 2.60-2.54
(m, 1H, H-300a), 2.35-2.29 (m, 1H, H-10), 2.06-1.87 (m, 3H,
H-40b, H-7b, H-14b), 1.63 (d, 1H, H-7a), 1.51-1.45 (m, 1H,
H-14a), 1.43 (s, 3H, 6-Me), 1.39-1.32 (m, 1H, H-40a), 1.36 (d, 3H,
2-Me), 1.34 (d, 3H, 4-Me), 1.27 (d, 3H, 50-Me), 1.18 (d, 3H, 10-
Me), 1.14 (d, 3H, 8-Me), 0.86 (t, 3H, 15-Me); 13C NMR(CDCl3) δ
205.0 (s, C-3), 174.5 (s, C-9), 170.8 (s, C-1), 103.0 (d, C-10), 81.5 (d,
C-5), 79.9 (s, C-6), 77.2 (d, C-13), 76.1 (d, C-30), 74.6(s, C-12), 72.5
(d, C-20), 71.1 (d, C-11), 67.4 (d, C-50), 66.1 (t, C-100), 59.1 (q, 30-
N(O)Me), 52.1 (q, 30-N(O)Me), 51.7 (d, C-200), 46.0 (t, C-300), 49.5
(d, C-2), 46.8 (d, C-4), 42.6 (t, C-7), 42.4 (d, C-10), 41.2 (d, C-8),
35.0 (t, C-40), 24.7 (q, 6-Me), 23.8 (q, 8-Me), 21.6 (t, C-14), 21.5 (q,
50-Me), 16.4 (q, 12-Me), 14.5 (q, 4-Me), 13.7 (q, 2-Me), 11.0 (q, 15-
Me), 9.4 (q, 10-Me). Anal. Calcd for C34H56N2O12: C, 58.16; H,
8.54; N, 4.24. Found: C, 58.25; H, 8.81; N, 4.20.
1
anti-Isomer 13b. FAB-MS m/z 645 (MHþ, 53%); H NMR
(CDCl3) δ 6.57 (d, 1H, 8aNH), 5.00 (dd, 2H, H-13), 4.52 (s, 1H,
11-OH), 4.39 (d, 1H, H-10), 4.17-4.06 (m, 1H, H-8), 3.80 (m,
1H, H-2), 3.74-3.67 (m, 1H, H-5), 3.65 (dd, 1H, H-100b), 3.58 (s,
1H, H-11), 3.50-3.46 (m, 1H, H-50), 3.37-3.33 (m, 1H, H-100a),
3.28-3.22 (m, 1H, H-200), 3.21-3.14 (m, 1H, H-20), 3.12 (s, 1H,
12-OH), 3.10 (m, 1H, H-4), 2.83 (t, 1H, H-300b), 2.60-2.54 (m,
1H, H-300a), 2.52-2.43 (m, 1H, H-30), 2.34-2.30 (m, 1H, H-10),
2.29 (s, 6H, 30-NMe2), 2.15-1.88 (m, 2H, H-7b, H-14b),
1.74-1.66 (m, 1H, H-40b), 1.63 (d, 1H, H-7a), 1.52-1.45 (m,
1H, H-14a), 1.43 (s, 3H, 6-Me), 1.34 (d, 3H, 2-Me), 1.31 (d, 3H,
4-Me), 1.26-1.19 (m, 1H, H-40a), 1.22 (d, 3H, 50-Me), 1.19 (d,
3H, 10-Me), 1.16 (s, 3H, 12-Me), 1.14 (d, 3H, 8-Me), 0.86 (t, 3H,
15-Me); 13C NMR (CDCl3) δ 205.2 (s, C-3), 174.8 (s, C-9), 170.5
(s, C-1), 103.7 (d, C-10), 82.0 (d, C-5), 80.0 (s, C-6), 77.2 (d, C-13),
74.3 (s, C-12), 71.1 (d, C-11), 70.8 (d, C-20), 69.4 (d, C-50), 65.9 (t,
C-100), 51.5 (d, C-200), 49.6 (d, C-2), 46.6 (d, C-4), 46.2 (t, C-300),
42.8 (t, C-7), 42.4 (d, C-10), 41.4 (d, C-8), 40.4 (q, 30-NMe2), 28.6
(t, C-40), 25.7 (q, 6-Me), 23.4 (q, 8-Me), 21.4 (t, C-14), 21.2 (q, 50-
Me), 16.2 (q, 12-Me), 14.7 (q, 4-Me), 13.5 (q, 2-Me), 10.8 (q, 15-
Me), 9.6 (q, 10-Me). Anal. Calcd for C34H56N2O11: C, 59.61; H,
8.75; N, 4.34. Found: C, 59.32; H, 8.87; N, 4.18.
Lithium Perchlorate Induced Regioselective Ring Opening of
Epoxides (13a,b). A mixture of syn- and anti-epoxides 13a,b
(644 mg, 1.0 mmol), LiClO4 3H2O (802.2 mg, 5.0 mmol, 5.0 mol
equiv), and amines a-x (5.0 mmol, 5.0 mol equiv) in 2-propanol
(2.5 mL) was heated at reflux for 24 h. Upon completion of the
reaction, the solution was cooled to room temperature, and
CH2Cl2 (25 mL) was added. The organic layer was washed
with water (2 ꢀ 25 mL), dried, and concentrated in vacuo. The
residual solid was purified by chromatography on silica gel using
syn-3-O-Descladinosyl-3-oxo-6-O-(200-methyloxiranyl)-8a-aza-
8a-homoerythromycin A N-Oxide (12a) and anti-3-O-Descladino-
syl-3-oxo-6-O-(200-methyloxiranyl)-8a-aza-8a-homoerythromycin A
N-Oxide (12b). (b) Using Dimethyldioxirane. To a solution of 6(629
mg, 1.0 mmol) in acetone (10 mL) was added dimethyldioxirane
(11.0 mL, 1.1 mmol as a 0.1 mmol/mL solution in acetone), and the
reaction mixture allowed to stir for 16 h at room temperature.
Removal of the solvent under reduced pressure afforded a colorless
solid, which was dissolved in dichloromethane and dried over
K2CO3. Removal of the solvent under reduced pressure and
purification by flash chromatography using methylene chloride/
methanol/aq NH3 (90:9:0.5) as eluent gave a mixture of syn- and
anti-epoxy N-oxides 12a,b (430.8 mg, 65%) in a ratio of 4.4:1
according to LC/MS analysis.

5878 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Pavlovicꢀ and Mutak
CH2Cl2/methanol/aq NH3 (90:9:1.5) as eluent to give a mixture
of diastereisomeric β-amino alcohols (14aa-ax and 14ba-bx,
50-80% isolated yield) in ratio 4.5:1 according to LC/MS
analysis.
(d, 3H, 10-Me), 1.16 (s, 3H, 12-Me), 1.14 (d, 3H, 8-Me), 0.84 (t,
3H, 15-Me); 13C NMR (CDCl3) δ 205.1 (s, C-3), 175.1 (s, C-9),
170.6 (s, C-1), 151.5 (s, C-Ar), 141.0 (s, C-Ar), 122.9 (d, C-Ar),
121.0 (d, C-Ar), 118.4 (d, C-Ar), 112.5 (d, C-Ar), 103.4 (d,
C-10), 80.2 (d, C-5), 79.9 (s, C-6), 77.8 (d, C-13), 74.5 (s, C-12),
71.2 (d, C-11), 70.8 (d, C-20), 69.2 (d, C-50), 67.7 (t, C-100), 66.9
(d, C-200), 65.7 (d, C-30), 63.6 (t, OCH2CH3), 59.9 (t, C-300), 53.3
(t, C-500, 2C), 49.6 (d, C-2), 46.8 (d, C-4), 42.8 (t, C-7), 42.3 (d,
C-10), 41.8 (t, C-400, 2C), 41.2 (d, C-8), 40.4 (q, 30-NMe2, 2C),
28.8 (t, C-40), 24.8 (q, 6-Me), 23.8 (q, 8-Me), 21.5 (q, 50-Me),
21.3 (t, C-14), 16.4 (q, 12-Me), 15.0 (q, OCH2CH3), 14.7 (q,
4-Me), 13.5 (q, 2-Me), 11.0 (q, 15-Me), 9.4 (q, 10-Me). Anal.
Calcd for C44H74N4O12: C, 62.10; H, 8.76; N, 6.58. Found: C,
62.39; H, 8.91; N, 6.43.
6-[200-(syn,anti)-Hydroxy-300-phenethylaminopropoxy]-3-oxo-
8a-aza-8a-homoerythromycin A (14aa-ba). FAB-MS m/z 766
1
(MHþ, 65%); H NMR (CDCl3) δ 7.33-7.24 (4H, H-1Ar þ
H-5Ar, H-2Ar þ H-4Ar), 7.20 (1H, H-3Ar), 5.92 (1H, 8a-
CONH), 4.98-4.92 (1H, H-13), 4.40 (1H, H-10), 4.26 (1H,
H-8), 3.82 (1H, H-2), 3.80 (1H, H-5), 3.78 (1H, H-200), 3.71
(1H, H-100b), 3.52 (1H, H-50), 3.41-3.35 (2H, H-11, H-100a),
3.16 (1H, H-20), 3.12 (1H, H-400b), 3.07 (1H, H-4), 2.97-2.91
(3H, H-500b, H-500a, H-400a), 2.80 (1H, H-300b), 2.67 (1H, H-300a),
2.45 (1H, H-30), 2.40 (1H, 12-OH), 2.30 (7H, H-10, 30-NMe2),
2.03 (1H, 11-OH), 1.92-1.83 (2H, H-14b, H-7b), 1.71-1.63
(2H, H-7a, H-40b), 1.42 (3H, 6-Me), 1.32 (3H, 2-Me), 1.30 (3H,
4-Me), 1.24 (3H, 50-Me), 1.21 (3H, 8-Me), 0.78 (3H, 15-Me); 13C
NMR (CDCl3) δ 205.4 (s, C-3), 175.2 (s, C-9), 170.3 (s, C-1),
139.7 (s, C-Ar), 128.8 (d, C-1Ar þ C-5Ar), 128.4 (d, C-2Ar þ
C-4Ar), 125.9 (d, C-3Ar), 103.3 (d, C-10), 79.6 (s, C-6), 79.2 (d,
C-5), 77.4 (d, C-13), 74.5 (s, C-12), 70.9 (d, C-11), 70.7 (d, C-20),
69.2 (d, C-50), 67.7 (d, C-200), 67.2 (t, C-100), 65.8 (d, C-30), 50.6 (t,
C-300), 50.0 (t, C-400), 49.9 (d, C-2), 46.7 (d, C-4), 43.1 (t, C-7),
42.4 (d, C-10), 40.8 (d, C-8), 40.3 (q, 30-NMe2), 35.9 (t, C-500),
28.5 (t, C-40), 24.5 (q, 6-Me), 24.1 (q, 8-Me), 21.5 (q, 50-Me), 21.1
(t, C-14), 16.5 (q, 12-Me), 14.9 (q, 4-Me), 13.6 (q, 2-Me), 10.7 (q,
15-Me), 9.4 (q, 10-Me). Anal. Calcd for C40H67N3O11: C, 62.72;
H, 8.82; N, 5.49. Found: C, 62.49; H, 9.04; N, 5.26.
The mixture of 14av and 14bv was separated by reversed-
phase HPLC to afford 14av and its epimeric β-hydroxy alcohol
14bv as separate solutions in MeOH-H2O. Solvents were re-
moved in vacuo to give pure 14av (17.5 mg) and 14bv (6.0 mg) as
colorless films.
6-{200-syn-Hydroxy-300-[2-(quinolin-6-ylamino)ethylamino]-
propoxy}-3-oxo-8a-aza-8a-homoerythromycin A (14av). FAB-
1
MS m/z 832 (MHþ, 91%); H NMR (CDCl3) δ 9.03 (d, 1H,
H-4Ar), 8.09 (m, 2H, H-6Ar, H-2Ar), 7.82 (d, 1H, H-5Ar), 7.65
(dd, 1H, H-1Ar), 7.51 (dd, 1H, H-3Ar), 6.07 (bs, 1H, 8aNH),
5.10 (dd, 1H, H-13), 4.97 (m, 1H), 4.38 (d, 1H, H-10), 4.25-4.13
(m, 1H, H-8), 3.85 (bs, 1H, H-200), 3.82-3.72 (m, 2H, H-5, H-2),
3.65 (d, 1H, H-100b), 3.57-3.48 (m, 1H, H-50), 3.35 (s, 1H,
H-11), 3.32 (t, 1H, H-100a), 3.25-3.15 (m, 2H, H-4, H-20),
2.92-2.82 (m, 4H, H-400, H-500), 2.53 (t, 1H, H-300b),
2.46-2.38 (m, 1H, H-30), 2.29 (s, 6H, 30-NMe2), 2.25 (dd, 1H,
H-10), 2.20 (dd, 1H, H-300a), 1.96 (ddq, 1H, H-14b), 1.70 (dd,
1H, H-7b), 1.55 (d, 1H, H-7a), 1.41 (ddq, 1H, H-14a), 1.37 (s,
3H, 6-Me), 1.34 (d, 3H, 2-Me), 1.30 (d, 3H, 4-Me), 1.23 (d, 3H,
50-Me), 1.14 (d, 3H, 10-Me), 1.12 (s, 3H, 12-Me), 1.08 (d, 3H,
8-Me), 0.90 (t, 3H, 15-Me). Anal. (C43H69N5O11) C, H, N.
6-{200-anti-Hydroxy-300-[2-(quinolin-6-ylamino)ethylamino]-
propoxy}-3-oxo-8a-aza-8a-homoerythromycin A (14bv). FAB-
6-[200-(syn,anti)-Hydroxy-300-(4-phenylbutylamino)propoxy]-
3-oxo-8a-aza-8a-homoerythromycin A (14ac-bc). FAB-MSm/z
794 (MHþ, 91%); 1H NMR (CDCl3) δ 7.29-7.23 (2H, H-1Ar þ
H-5Ar), 7.19-7.12 (3H, H-2Ar þ H-4Ar, H-3Ar), 6.14 (1H, 8a-
CONH), 4.99 (1H, H-13), 4.37 (1H, H-10), 4.16 (1H, H-8), 3.87
(1H, H-200), 3.80 (1H, H-2), 3.77 (1H, H-5), 3.69 (1H, H-100b),
3.49 (1H, H-50), 3.38 (1H, H-11), 3.34 (1H, H-100a), 3.15 (1H,
H-20), 3.09 (1H, H-4), 2.93 (1H, H-400b), 2.82 (1H, H-400a), 2.80
(1H, H-300b), 2.72 (1H, H-300a), 2.62 (2H, H-700), 2.44 (1H, H-30),
2.37 (1H, 12-OH), 2.35-2.29 (1H, H-10), 2.28 (3H, 30-NMe2),
2.02 (1H, 11-OH), 1.96-1.84 (2H, H-14b, H-7b), 1.75-1.65 (5H,
H-600, H-500, H-40b), 1.63 (1H, H-7a), 1.46 (1H, H-14a), 1.41 (3H,
6-Me), 1.33 (3H, 2-Me), 1.29 (3H, 4-Me), 1.23 (3H, 50-Me), 1.22
(1H, H-40a), 1.17 (3H, 10-Me), 1.14 (3H, 12-Me), 1.13 (3H,
8-Me), 0.80 (3H, 15-Me); 13C NMR (CDCl3) δ 205.0 (s, C-3),
175.4 (s, C-9), 170.8 (s, C-1), 142.2 (s, C-Ar), 128.4 (d, C-1Ar þ
C-5Ar), 128.3 (d, C-2Ar þ C-4Ar), 125.7 (d, C-3Ar), 103.4 (d,
C-10), 79.8 (d, C-5), 79.7 (s, C-6), 77.7 (d, C-13), 74.5 (s, C-12),
71.3 (d, C-11), 70.7 (d, C-20), 69.2 (d, C-50), 67.0 (d, C-200), 66.8 (t,
C-100), 65.7 (d, C-30), 50.2 (t, C-300), 49.8 (d, C-2), 48.1 (t, C-400),
46.9 (d, C-4), 42.9 (t, C-7), 42.2 (d, C-10), 41.1 (d, C-8), 40.3 (q, 30-
NMe2), 35.6 (t, C-700), 28.9 (t, C-500), 28.5 (t, C-40), 28.1 (t, C-600),
24.9 (q, 6-Me), 23.8 (q, 8-Me), 21.5 (q, 50-Me), 21.2 (t, C-14), 16.5
(q, 12-Me), 14.8 (q, 4-Me), 13.7 (q, 2-Me), 10.8 (q, 15-Me), 9.4 (q,
10-Me). Anal. Calcd for C42H71N3O11: C, 63.53; H, 9.01; N, 5.29.
Found: C, 63.86; H, 9.31; N, 5.16.
1
MS m/z 832 (MHþ, 78%); H NMR (CDCl3) δ 9.03 (d, 1H,
H-4Ar), 8.09 (m, 2H, H-6Ar, H-2Ar), 7.81 (d, 1H, H-5Ar),
7.69 (dd, 1H, H-1Ar), 7.54 (dd, 1H, H-3Ar), 6.74 (d, 1H,
8aNH), 4.63 (dd, 1H, H-13), 4.40 (d, 1H, H-10), 4.27-4.16 (m,
1H, H-8), 3.95-3.90 (m, 2H, H-5, H-2), 3.64 (bs, 1H, H-200),
3.43 (d, 1H, H-100b), 3.39-3.30 (m, 1H, H-50), 3.28 (s, 1H,
H-11), 3.24 (t, 1H, H-100a), 3.22-3.15 (m, 1H, H-20), 3.10 (m,
1H, H-4), 2.95-2.86 (m, 4H, H-400, H-500), 2.50 (t, 1H, H-300b),
2.48-2.40 (m, 1H, H-30), 2.37 (s, 1H, 12-OH), 2.30 (s, 6H, 30-
NMe2), 2.28 (dd, 1H, H-10), 2.25 (dd, 1H, H-300a), 2.00 (s, 1H,
11-OH), 1.93 (ddq, 1H, H-14b), 1.72 (dd, 1H, H-7b), 1.59 (d,
1H, H-7a), 1.44 (ddq, 1H, H-14a), 1.35 (s, 3H, 6-Me), 1.32 (d,
3H, 2-Me), 1.31 (d, 3H, 4-Me), 1.21 (d, 3H, 50-Me), 1.14 (d,
3H, 10-Me), 1.13 (s, 3H, 12-Me), 1.11 (d, 3H, 8-Me), 0.85 (t,
3H, 15-Me). Anal. (C43H69N5O11) C, H, N.
ꢁ
Acknowledgment. The authors thank S. Milkovic for ex-
6-{300-[4-(2-Ethoxyphenyl)piperazin-1-yl]-200-(syn,anti)-hydroxy-
cellent technical assistance and colleagues from the Department
of Chemistry and Microbiology, Pliva Research Institute,
Croatia, for their help.
propoxy}-3-oxo-8a-aza-8a-homoerythromycin
A (14ap-bp).
1
FAB-MS m/z 851 (MHþ, 94%); H NMR (CDCl3) δ 7.02-
6.93 (m, 2H, H-Ar), 6.92-6.88 (m, 1H, H-Ar), 6.86-6.82 (m,
1H, H-Ar), 6.17 (bs, 1H, 8aNH), 4.99 (dd, 1H, H-13), 4.39 (d,
1H, H-10), 4.20-4.11 (m, 1H, H-8), 4.07 (q, 2H, OCH2CH3),
3.83 (m, 1H, H-2), 3.78 (d, 1H, H-5), 3.72 (d, 1H, H-100b),
3.68-3.62 (m, 1H, H-200), 3.56-3.46 (m, 1H, H-50), 3.44 (s, 1H,
H-11), 3.40 (dd, 1H, H-100a), 3.18 (dd, 1H, H-20), 3.08 (dd, 2H,
H-400b), 3.07 (m, 1H, H-4), 3.05-2.99 (m, 1H, H-300b),
2.54-2.44 (m, 1H, H-30), 2.32 (s, 6H, 30-NMe2), 2.30-2.25
(m, 1H, H-10), 2.20 (d, 1H, H-300a), 1.98-1.87 (m, 2H, H-14b,
H-7b), 1.77-1.70 (m, 1H, H-40b), 1.68-1.63 (m, 1H, H-7a),
1.57-1.53 (m, 2H, H-400a), 1.51-1.47 (m, 1H, H-14a), 1.45 (t,
3H, OCH2CH3), 1.42 (s, 3H, 6-Me), 1.35 (d, 3H, 2-Me), 1.31 (d,
3H, 4-Me), 1.24 (d, 3H, 50-Me), 1.23-1.22 (m, 1H, H-40a), 1.18
Supporting Information Available: General experimental
methods, synthesis and characterization procedures, and spec-
tral data for selected new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) (a) Doern, G. V.; Heilmann, K. P.; Huynh, H. K.; Rhomberg,
P. R.; Coffman, S. L.; Brueggemann, A. B. Antimicrobial Resis-
tance among Clinical Isolates of Streptococcus pneumoniae in the
United States during 1999-2000, Including a Comparison of
Resistance Rates Since 1994-1995. Antimicrob. Agents Chemother.
2001, 45, 1721–1729. (b) Baquero, F. Gram-Positive Resistance:

Article
Challenge for the Development of New Antibiotics. J. Antimicrob.
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15 5879
Discovery. Exp. Opin. Invest. Drugs 2005, 14, 117–134. (b) Henninger,
T. C. Recent Progress in the Field of Macrolide Antibiotics. Expert
Opin. Ther. Pat. 2003, 13, 787–805. (c) Asaka, T.; Manaka, A.;
Sugiyama, H. Recent Developments in Macrolide Antimicrobial
Research. Curr. Med. Chem. 2003, 3, 961–989. (d) Wu, Y.-J.; Su,
W.-G. Recent Developments on Ketolides and Macrolides. Curr. Med.
Chem. 2001, 8, 1727–1758. (e) Kaneko, T.; McArthur, H.; Sutcliffe, J.
Recent Developments in the Area of Macrolide Antibiotics. Exp.
Opin. Ther. Pat. 2000, 10, 403–425.
Chemother. 1997, 39 (Suppl. A), 1–6.
(2) Thornsberry, C.; Ogilvie, P. T.; Holley, H. P.; Sahm, D. F. Survey
of Susceptibilities of Streptococcus pneumoniae, Haemophilus
influenzae, and Moraxella catarrhalis Isolates to 26 Antimicrobial
Agents: A Prospective U.S. Study. Antimicrob. Agents Chemoter.
1999, 43, 2612–2623.
(3) Hoban, D. J.; Doern, G. V.; Fluit, A. C.; Roussel-Delvallez, M.;
Jones, R. N. Worldwide Prevalence of Antimicrobial Resistance in
Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella
catarrhalis in the SENTRY Antimicrobial Surveillance Program,
1997-1999. Clin. Infect. Dis. 2001, 32, S81–S93.
(4) Doern, G. V.; Jones, R. N.; Pfaller, M. A.; Kugler, K.; The
SENTRY Participants Group. Haemophilus influenzae and
Moraxella catarrhalis from Patients with Community-Asquired
Respiratory Tract Infections: Antimicrobial Susceptibility Patterns
from the SENTRY Antimicrobial Surveillance Program (United
States and Canada, 1997). Antimicrob. Agents Chemoter. 1999, 43,
385–389.
(5) Agouridas, C.; Denis, A.; Auger, J.-M.; Benedetti, Y.; Bonnefoy,
A.; Bretin, F.; Chantot, J.-F.; Dussarat, A.; Fromentin, C.;
D’Ambrieres, S. G.; Lachaud, S.; Laurin, P.; Le Martret, O.;
Loyau, V.; Tessot, N. Synthesis and Antibacterial Activity of Keto-
lides (6-O-Methyl-3-oxoerythromycin Derivatives): A New Class of
Antibacterials Highly Potent against Macrolide-Resistant and Sus-
ceptible Respiratory Pathogens. J. Med. Chem. 1998, 41, 4080–4100.
(6) Ma, Z.; Clark, R. F.; Brazzale, A.; Wang, S.; Rupp, M. J.; Li, L.;
Greisgraber, G.; Zang, S.; Yong, H.; Phan, L. T.; Nemoto, P. A.;
Chu, D. T. W.; Plattner, J. J.; Zhang, X.; Zhong, P.; Cao, Z.; Nilius,
A. M.; Shortridge, V. D.; Flamm, R.; Mitten, M.; Meulbroek, J.;
Ewing, P.; Alder, J.; Or, Y. S. Novel Erythromycin Derivatives
with Aryl Groups Tethered to the C-6 Position Are Potent Protein
Synthesis Inhibitors and Active against Multidrug-Resistant
Respiratory Pathogens. J. Med. Chem. 2001, 44, 4137–4156.
(7) (a) Magee, T. V.; Ripp, S. L.; Li, B.; Buzon, R. A.; Chupak, L.;
Dougherty, T. J.; Finegan, S. M.; Girard, D.; Hagen, A. E.;
Falcone, M. J.; Farley, K. A.; Granskog, K.; Hardink, J. R.;
Huband, M. D.; Kamicker, B. J.; Kaneko, T.; Knickerbocker,
M. J.; Liras, J. L.; Marra, A.; Medina, I.; Nguyen, T.-T.; Noe,
M. C.; Obach, R. S.; O’Donnell, J. P.; Penzien, J. B.; Reilly, U. D.;
Schafer, J. R.; Shen, Y.; Stone, G. G.; Strelevitz, T. J.; Sun, J.; Tait-
Kamradt, A.; Vaz, A. D. N.; Whipple, D. A.; Widlicka, D. W.;
Wishka, D. G.; Wolkowski, J. P.; Flanagan, M. E. Discovery of
Azetidinyl Ketolides for the Treatment of Susceptible and Multi-
drug Resistant Community-Acquired Respiratory Tract Infec-
tions. J. Med. Chem. 2009, 52, 7446–7457. (b) Keyes, R. F.; Carter,
J. J.; Englund, E. E.; Daly, M. M.; Stone, G. G.; Nilius, A. M.; Ma, Z.
Synthesis and Antibacterial Activity of 6-O-Arylbutynyl Ketolides with
Improved Activity against Some Key Erythromycin-Resistant Patho-
(12) (a) For the synthesis and in vitro activity of 6-O-substituted
azithromycin ketolides, see the following: Denis, A.; Agouridas,
C. Synthesis of 6-O-Methyl-azithromycin and Its Ketolide Analo-
gue via Beckmann Rearrangement of 9(E)-6-O-Methyl-erythro-
mycin Oxime. Bioorg. Med. Chem. Lett. 1998, 8, 2427–2432.(b) For
the synthesis and in vitro activity of 6-O-methyl-8a- and 9a-azahomo-
erythromycins derived from clarithromycin, see the following: Lazar-
ꢀ
ꢁ
evski, G.; Kobrehel, G.; Kelneric, Z. Ketolides from the Class of 15-
Membered Lactams. U.S. Patent 6,110,965 A1, 2000.(c) For the
synthesis of 8a-azahomoerythromycins via Beckmann rearrangement
of erythromycin A oxime, see the following: Wilkening, R. R.;
Ratcliffe, R. W.; Doss, G. A.; Bartizal, K. F.; Graham, A. C.; Herbert,
C. M. The Synthesis of Novel 8a-Aza-erythromycin Derivatives via the
Beckmann Rearrangement of (9Z)-Erythromycin A Oxime. Bioorg.
Med. Chem. Lett. 1993, 3, 1287–1292. (d) For the synthesis of 6-O-
alkyl substituted 8a-aza and 9a-azahomoerytromycins and their in vitro
ꢁ
ꢁ
activity, see the following: Alihodꢀzic, S.; Fajdetic, A.; Kobrehel, G.;
ꢀ
ꢀ
ꢁ
ꢀ ꢁ
Lazarevski, G.; Mutak, S.; Pavlovic, D.; Stimac, V.; Cipcic, H.;
ꢁ
ꢁ
ꢀ ꢁ
Kramaric, M. D.; Erakovic, V.; Hasenohrl, A.; Marsic, N.; Schoenfeld,
W. Synthesis and Antibacterial Activity of Isomeric 15-Membered
Azalides. J. Antibiot. 2006, 59, 753–769.
(13) Muci, A. R.; Buchwald, S. L. Practical Palladium Catalysts for
C-N and C-O Bond Formation. In Topics in Current Chemistry;
Miyaura, N., Ed.; Springer-Verlag: Berlin and Heidelberg, Germany,
2002; Vol. 219, p 137.
(14) Ma, Z.; Nemoto, P. Discovery and Development of Ketolides as a
New Generation of Macrolide Antimicrobial Agents. Curr. Med.
Chem.: Anti-Infect. Agents 2002, 1, 15–34.
(15) Morimoto, S.; Adachi, T.; Matsunaga, T.; Kashimura, M.; Asaka,
T.; Watanabe, Y.; Sota, K.; Sekiuchi, K. Erythromycin A Deriva-
tives. U.S. Patent 4,990,602 A1, 1991.
ꢁ
(16) For the synthesis of Ery A 9(E)-oxime, see the following: (a) ^okic,
ꢀ
S.; Tamburasev, Z. Erythromycin Oxime and 9-Amino-3-O-cladi-
nosyl-6,11,12-trihydroxy-2,4,6,8,10,12-hexamethylpentadecane-
ꢁ
ꢀ
13-olide. GB Patent 1,100,504, 1966.(b) ^okic, S.; Tamburasev, Z.
Erythromycin Study: 9-Amino-3-O-cladinosyl-5-O-desosaminyl-
6,11,12-trihydroxy-2,4,6,8,10,12-hexamethylpentadecane-13-olide.
Tetrahedron Lett. 1967, 1645–1647. (c) Pandey, D.; Katti, S. B.;
Haq, W.; Tripathi, C. K. M. Synthesis and Antimicrobial Activity of
Erythromycin A Oxime Analogs. Bioorg. Med. Chem. 2004, 12,
3807–3813. We have shown in the course of this work, however, that
the NMR assignment of Ery A oxime (16) previously reported by
Pandey et al. was incorrect. To address this question, an unambiguous
NMR assignment was made by using a combination of two-dimensional
NMR techniques. The complete assignment of 16 was corroborated by
COSY (proton-proton correlation), HSQC (one bond proton-carbon
correlation), and HMBC (two to three bond proton-carbon correlation)
spectra in the Supporting Information.
ꢀ ꢁ
gens. J. Med. Chem. 2003, 46, 1795–1798. (c) Mutak, S.; Marsic, N.;
ꢁ
ꢁ
Dominis Kramaric, M.; Pavlovic, D. Semisynthetic Macrolide Anti-
bacterials Derived from Tylosin. Synthesis and Structure-Activity
Relationships of Novel Desmycosin Analogues. J. Med. Chem.
2004, 47, 411–431.
(8) (a) Andreotti, D.; Biondi, S.; Lociuro, S. Macrolide Antibiotics.
PCT Int. Appl. WO 0250092 A1, 2002. (b) Andreotti, D.; Arista, L.;
Biondi, S.; Cardullo, F.; Damiani, F.; Lociuro, S.; Marchioro, C.; Merlo,
G.; Mingardi, A.; Niccolai, D.; Paio, A.; Piga, E.; Pozzan, A.; Seri, C.;
Tarsi, L.; Terreni, S.; Tibasco, J. Macrolide Antibiotics. PCT Int. Appl.
WO 0250091 A1, 2002.(c) Andreotti, D.; Bientinesi, I.; Biondi, S.;
Donati, D.; Erbetti, I.; Lociuro, S.; Marchioro, C.; Pozzan, A.; Ratti, E.;
Terreni, S. A Novel Ketolide Class: Synthesis and Antibacterial
Activity of a Lead Compound. Bioorg. Med. Chem. Lett. 2007, 17,
5265–5269.
(9) Henninger, C. T.; Xu, X.; Abbanat, D.; Baum, E. Z.; Foleno, B. D.;
Hilliard, J. J.; Bush, K.; Hlasta, D. J.; Macielag, M. J. Synthesis and
Antibacterial Activity of C-6 Carbamate Ketolides, a Novel Series
of Orally Active Ketolide Antibiotics. Bioorg. Med. Chem. Lett.
2004, 14, 4495–4499.
(17) The synthesis of the initial quantities of epimeric 6-O-allyl Ery A
9(Z)-oxime (21) was achieved via oximation (NH2OH HCl/
Na2CO3/MeOH, reflux) of the 6-O-allyl Ery A6 followed by silica
gel chromatography of the 9:1 E/Z epimeric mixture of oximes.
Resubmission of the purified E-isomer to deoximation
((NaHSO3-HCOOH-EtOH)/water 1:1, reflux) followed by oxi-
mation actually served to reestablish the equilibrium mixture that
consisted of about 10% of the Z-isomer. Laborious repetition of
this procedure could serve to completely isomerize the sample of
6-O-allyl Ery A 9(E)-oxime (20). Almost the same methodology
was used by Merck scientists to synthesize the initial quantities of
pure 6-O-methyl Ery A 9(Z)-oxime (23).20c Although authors claim
that a small number of such iterations on multigram scale provided
useful amounts of material, in practice to synthesize larger quan-
tities of 9(Z)-oxime, this procedure obviously does not represent
either a synthetically useful or economically viable solution. For
the synthesis and spectroscopic characterization of 6-O-allyl Ery A
9(Z)-oxime (21), see Supporting Information.
ꢁ
ꢀ
(10) (a) ^okic, S.; Kobrehel, G.; Lazarevski, G.; Lopotar, N.; Tamburasev,
Z. Erythromycin Series. Part 11. Ring Expansion of Erythromycin
A Oxime by the Beckmann Rearrangement. J. Chem. Soc., Perkin
Trans. 1 1986, 1881–1890. (b) Bright, G. M.; Nagel, A. A.; Bordner,
J.; Desai, K. A.; Dibrino, J. N.; Nowakowska, J.; Vincent, L.; Watrous,
R. M.; Sciavolino, F. C.; English, A. R.; Retsema, J. A.; Anderson,
M. R.; Brennan, L. A.; Borovoy, R. J.; Cimochowsky, C. R.; Fiaella,
J. A.; Girard, A. E.; Girard, D.; Herbert, C.; Manousos, M.; Mason, R.
Synthesis, in Vitro and in Vivo Activity of Novel 9-Deoxo-9a-aza-9a-
homoerythromycin A Derivatives: A New Class of Macrolide Anti-
biotics, the Azalides. J. Antibiot. 1988, 41, 1029–1047.
(18) For a conformational analysis and chemical shifts of E- and
Z-oximes in erythromycin A and clarithromycin series, see the
following: (a) McGill, J. M.; Johnson, R. Structural and Con-
formational Analysis of (E)-Erythromycin A Oxime. Magn. Reson.
Chem. 1993, 31, 273–277. (b) Esteban, J.; Costa, A. M.; Urpí, F.;
Vilarrasa, J. From (E)- and (Z)-Ketoximes to N-Sulfenylimines, Keti-
mines or Ketones at Will. Application to Erythromycin Derivatives.
(11) For reviews on 14-membered ketolides, see the following: (a)
Alekshun, M. N. New Advances in Antibiotic Development and

5880 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 15
Tetrahedron Lett. 2004, 45, 5563–5567. (c) For the application of 13
Pavlovicꢀ and Mutak
C
(22) On the other hand ring enlargement of 3-O-descladinosyl-6-O-
allylerythromycin A 9(E)-oxime (9) yielded 9a-aza-9a-homoery-
thromycin derivative in 85% yield. To our delight, the scope of the
Beckmann rearrangement proved to be quite broad, as it turned out
that it could readily be applied to other 14-membered ring macro-
lides. For example, ring enlargement of descladinosyl-6,12-di-O-
allylerythromycin-9(E)-oxime (24) and the other two oximes in the
cladinosyl series, 6-O-allylerythromycin 9(E)- and 9(Z)-oximes (20
and 21), under the same reaction conditions as those applied in
Beckmann rearrangement of 9 and 10, provided the corresponding
15-membered ring macrolides in high yield.
(23) Dess, D. B.; Martin, J. C. Readily Accessible 12-I-5 Oxidant for the
Conversion of Primary and Secondary Alcohols to Aldehydes and
Ketones. J. Org. Chem. 1983, 48, 4155–4156.
(24) Forreviewondioxiranes,seethefollowing: Adam,W.;Hadjiarapoglou,
L. Dioxiranes: Oxidation Chemistry Made Easy. In Organic Per-
oxygen Chemistry; Herrmann, W. A., Ed.; Topics in Current Chemistry,
Vol. 164; Springer-Verlag, Berlin and Heidelberg, Germany, 1993; pp
45-62.
NMR spectra to determine configuration of oximes, see the following:
Hawkes, G. E.; Herwig, K.; Roberts, J. D. Nuclear Magnetic Resonance
Spectroscopy. Use of 13C Spectra To Establish Configuration of
Oximes. J. Org. Chem. 1974, 39, 1017–1028.
(19) 3-O-Descladinosyl-6,12-di-O-allylerythromycin A 9(E)-oxime (24)
was conveniently prepared in a two-reaction one-pot sequence.
Thus, deprotection and selective cleavage of the cladinose sugar
were accomplished by treating an aqueous ethanolic solution of 19
with 2 M HCl for 18 h at room temperature. Oxime 24 was isolated
by selective extraction with methylene chloride at pH 9. On the
other hand, the same process at pH 1 was used to efficiently remove
the cladinose-related byproduct from the aqueous workup. For
detailed experimental procedure and spectroscopic data, see Sup-
porting Information.
(20) For the preparation of Ery A 9(Z)-oxime via base-catalyzed isomer-
ization of Ery A 9(E)-oxime, see the following: (a) Gasc, J. C.;
D’Ambrieres, S. G.; Lutz, A.; Chantot, J. F. New Ether Oxime
Derivatives of Erythromycin A. A Structure-Activity Relationship
Study. J. Antibiot. 1991, 44, 313–330.(b) See also ref 12c for the
independently developed synthesis of Ery A 9(Z)-oxime by means of
base-catalyzed isomerization. (c) For the attempted preparation of 6-O-
methyl Ery A 9(Z)-oxime via E-Z isomerization, see the folloiwng:
Waddell, S. T.; Santorelli, G. M.; Blizzard, T. A.; Graham, A.; Occi, J.
Bioorg. Med. Chem. Lett. 1998, 8, 1321–1326. To prepare a sizable
amount of 6-O-methyl Ery A 9(Z)-oxime (23) for the Beckmann rearran-
gement studies, these authors have used an equilibration method based on
the successive oximation of the purified E-isomer 22. It would be
interesting to investigate whether the E-Z isomerization in the clarithro-
mycin series may be achievable using 3-O-descladinosyl-3-oxy-6-O-
methyl Ery A 9(E)-oxime as a starting material instead of 6-O-methyl
Ery A 9(E)-oxime. However, such a study is outside the scope of this work.
(21) Another approach to 15 includes a tedious and time-consuming
chromatographic separation of an E-Z epimeric mixture of 6-O-
allyl Ery A oximes 20 and 21 (E/Z ratio of 9:1 according to HPLC)
obtained via oximation procedure described in ref 17. Subsequent
Beckmann rearrangement of the isolated 9(Z)-oxime 21 followed by
acidic hydrolysis of the resulting 6-O-allyl-8a-aza-8a-homoEry A (27)
afforded 3-O-descladinosyl-8a-aza-8a-homoEryA (15). Despite this
somewhat more complex isolation procedure and significantly lower
yields in comparison to E-Z isomerization-Beckmann rearrangement
methodology, compound 15 could be prepared on a 500 mg scale in
essentially pure form. For the preparation and structure confirmation of
27, see Supporting Information.
(25) Retsema, J. A.; Girard, A. E.; Schekly, W.; Manousos, M.;
Anderson, M. R.; Bright, G. M.; Borovoy, R. J.; Brennan, L. A.;
Mason, R. Spectrum and Mode of Action of Azithromycin (CP-
62,993), a New 15 Membered-ring Macrolide with Improved
Potency against Gram negative Organisms. Antimicrob. Agents
Chemother. 1987, 31, 1939–1947.
(26) Rao, A. S.; Paknikar, S. K.; Kirtane, J. G. Recent Advances in the
Preparation and Synthetic Applications of Oxiranes. Tetrahedron
1983, 39, 2323–2367.
(27) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria
That Grow Aerobically, 5th ed.; Approved Standard NCCLS Docu-
ment M7-A5; National Committee for Clinical Laboratory Standards,
2000.
(28) (a) Allen, N. E. Macrolide Resistance in Staphylococcus aureus:
Inducers of Macrolide Resistance. Antimicrob. Agents Chemother.
1977, 11, 669–674. (b) Pestka, S.; Vince, R.; LeMahieu, R.; Weiss, F.;
Fern, L.; Unowsky, J. Induction of Erythromycin Resistance in
Staphylococcus aureus by Erythromycin Derivatives. Antimicrob. Agents
Chemother. 1976, 9, 128–130. (c) Denis, A.; Agouridas, C.; Auger,
J.-M.; Benedetti, Y.; Bonnefoy, A.; Bretin, F.; Chantot, J.-F.; Dussarat, A.;
Fromentin, C.; D'Ambrieres, S. G.; Lachaud, S.; Laurin, P.; Martret,
O. L.; Loyau, V.; Tessot, N.; Pejac, J.-M.; Perron, S. Synthesis and
Antibacterial Activity of HMR 3647. A New Ketolide Highly Potent
against Erythromycin-Resistant and Susceptible Pathogens. Bioorg.
Med. Chem. Lett. 1999, 9, 3075–3080.