Discovery of azetidinyl ketolides for the treatment of susceptible and multidrug resistant community-acquired respiratory tract infections

Article abstract of DOI:10.1021/jm900729s

Respiratory tract bacterial strains are becoming increasingly resistant to currently marketed macrolide antibiotics. The current alternative telithromycin (1) from the newer ketolide class of macrolides addresses resistance but is hampered by serious safe

Full text of DOI:10.1021/jm900729s

7446 J. Med. Chem. 2009, 52, 7446–7457
DOI: 10.1021/jm900729s
Discovery of Azetidinyl Ketolides for the Treatment of Susceptible and Multidrug Resistant
Community-Acquired Respiratory Tract Infections
Thomas V. Magee,* Sharon L. Ripp, Bryan Li, Richard A. Buzon, Lou Chupak,† Thomas J. Dougherty,‡ Steven M. Finegan,
Dennis Girard,§ Anne E. Hagen, Michael J. Falcone, Kathleen A. Farley, Karl Granskog, Joel R. Hardink, Michael D. Huband,
Barbara J. Kamicker, Takushi Kaneko, Michael J. Knickerbocker, Jennifer L. Liras, Andrea Marra,§ Ivy Medina,
Thuy-Trinh Nguyen, Mark C. Noe, R. Scott Obach, John P. O’Donnell, Joseph B. Penzien, Usa Datta Reilly, John R. Schafer,
Yue Shen, Gregory G. Stone,‡ Timothy J. Strelevitz, Jianmin Sun, Amelia Tait-Kamradt, Alfin D. N. Vaz, David A. Whipple,
Daniel W. Widlicka, Donn G. Wishka, Joanna P. Wolkowski, and Mark E. Flanagan*
Pfizer Global Research & Development, Pfizer, Inc., Groton, Connecticut 06340. †Current address: Bristol-Meyers Squibb Research and
Development, Wallingford, CT 06492. ‡Current address: Astra-Zeneca Research Center, Waltham, MA 02451. §Current address: Rib-X
Pharmaceuticals, New Haven, CT 06511. Current address: TB Alliance, New York, NY 10005.
Received May 28, 2009
Respiratory tract bacterial strains are becoming increasingly resistant to currently marketed macrolide
antibiotics. The current alternative telithromycin (1) from the newer ketolide class of macrolides
addresses resistance but is hampered by serious safety concerns, hepatotoxicity in particular. We have
discovered a novel series of azetidinyl ketolides that focus on mitigation of hepatotoxicity by minimizing
hepatic turnover and time-dependent inactivation of CYP3A isoforms in the liver without compromis-
ing the potency and efficacy of 1.
Introduction
resistant strains and is currently the only marketed ketolide.
Unfortunately, although a promising compound, 1 has been
plagued by safety concerns.8 Cethromycin (2) is the next most
advanced ketolide and is currently in late stage development.9
Both structures derive the moniker ketolide from the ketone
function at position C3. Both also have bicyclic aryl rings
tethered to the macrocylic ring, but in the case of 1 the tether
springs from the N11 of the 11,12-carbamate fused to the
macrocycle, while for 2 the attachment point is the O6 position.
This disclosure focuses on the discovery of a novel series of N11
ketolides addressing some of the safety issues facing 1.
The macrolide class of antibiotics has been very successful
in the treatment of serious bacterial infections.1 These natural
product agents, first discovered over 50 years ago,2 target the
bacterial ribosome to inhibit protein synthesis. Two of the
most successful members of this class are azithromycin and
clarithromycin, first put on the market in the early 1990s and
used extensively to treat community-acquired respiratory
tract infections. The antibacterial spectrum is targeted pri-
marily against Gram-positive bacterial strains including
Streptococcus pneumoniae and S. pyogenes, fastidious Gram-
negative strains including Haemophilus influenzae and Moraxella
catarrhalis, atypicals Mycoplasma pneumoniae, Chlamydia
pneumoniae, and Legionella pneumophilia, and Helicobacter
pylori.3 However, these older agents are becoming less effective
as resistance has emerged over time, creating a medical need for
novel macrolides addressing these resistant strains.4 The two
primary macrolide resistance mechanisms expressed in strepto-
cocci are erythromycin ribosome methylation (erma)5 and active
efflux (mef).6 Newer or “third” generation macrolides (ketolides)
have the advantage that they are poor inducers of the erm
resistance mechanism and are also poor substrates for mef
efflux-mediated resistance. Telithromycin (1, Figure 1)7 is a
third generation macrolide that covers macrolide sensitive and
Synthetic Chemistry
The synthesis of the azetidinyl ketolide template (5) began
with the conversion of the clarithromycin starting material (3)
to the known acylimidazole intermediate (4),10 as shown in
Scheme 1. This was carried out by bis-acetylation of the
desosamine and cladinosesugars of3 followed by dehydration
of the 10-hydroxyl and concomitant transformation of the
11-hydroxyl to the acyl imidazole utilizing 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU) and carbonyl diimidazole (CDI).
These reactions proceeded very smoothly in near-quantitative
yield, requiring no further purification for the subsequent
steps. Incorporation and cyclization of 1-benzhydrylazeti-
dine-3-ylamine into intermediate 4 were unsuccessful under
the standard conditions (triethylamine or diisopropylethyl-
amine in acetonitrile with heating) for reacting amine tethers
with this system likely because of steric crowding intrinsic to
the azetidinylamineand its largebenzhydryl protecting group.
A stronger organic base (DBU) proved to be very effective for
both the displacement of the imidazole and cyclization steps.
Subsequent removal of the 400-acetylcladinose using aqueous
*To whom correspondence should be addressed. For T.V.M.: phone,
(860) 715-0653; fax, (860) 715-4693; e-mail, thomas.v.magee@pfizer.
com. For M.E.F.: phone, (860) 441-0205; fax, (860) 715-4693; e-mail,
mark.e.flanagan@pfizer.com.
a Abbreviations: erm, erythromycin ribosome methylation genotype;
mef, macrolide efflux genotype; RTI, respiratory tract infection; OM,
otitis media; ER, in vitro human hepatic microsomal extraction ratio;
TDI, time-dependent inhibition of cytochrome P450; CYP3A, cyto-
chrome P450 isoform 3A (includes 3A4 and 3A5); DDI, drug-drug
interactions; AO, aldehyde oxidase.
r
pubs.acs.org/jmc
Published on Web 09/23/2009
2009 American Chemical Society

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23 7447
the methyl ketone 10, used in the synthesis of diastereomeric
isomers 6p and 6q. The isomers were separated by reverse-
phase HPLC and the more active 6q recrystallized from ethyl
acetate to unambiguously assign the structure (see Supporting
Information). For the synthesis of the 3-hydroxy intermediate
14 a modified Friedlander reaction12 was found to be much
more efficient than the Skraup approach. Thus, converting 7to
pivalamide 11 followed by treatment with chlorine gas yielded
the 3-chloro intermediate 12, which was dilithiated with tert-
butyllithium in ethyl ether and subsequently condensed with
3-dimethylaminopropenal. Upon treatment with strong acid
the intermediate obtained from the anion addition collapsed in
relatively good overall yield to the [1,8]naphthyridine 13.
Selenium dioxide oxidation followed by methoxide displace-
ment of the chloride proceeded smoothly. Methyl ether clea-
vage was then carried out in 6 N HCl to yield 14.
Figure 1. Structures of leading ketolides.
Scheme 1. Synthesis of the Azetidinyl Ketolide Templatea
The route used to access the [1,5]naphthyridine coupling
partner 22, used in the synthesis of 6s, is given in Scheme 3.
Thus, treatment of dibromide 15 with sodium methoxide in
DMF gave 16 in good yield, which in turn was converted to 17
using palladium-catalyzed coupling of tert-butyl carbamate.
Installation of a methyl group at the 4-position via dilithiation
and methyl iodide treatment yielded 18 after acidic removal of
the protecting group. The Skraup reaction to form the
[1,5]naphthyridine system was generally better than the [1,8]
disposition, and this was particularly true with an electron
donating group in the 5-position (methoxy in this case). Thus,
the conversionof18to19wasaffectedinmodestbutworkable
(45%) yield. Oxidation of 19 with selenium dioxide was not
successful, so we then resorted to a longer sequence of
bromination followed by displacement with potassium acet-
ate and ester hydrolysis to give the benzylic alcohol 20.
Oxidation of 20 with IBX yielded aldehyde 21, which was
subsequently treated with strong acid to cleave the methyl
ether, giving 22.
Results and Discussion
a Reagents and conditions: (i) Ac2O, TEA, DMAP, DCM; (ii) DBU,
CDI, THF, isopropyl ether; (iii) DBU, 1-benzhydrylazetidine-3-yla-
mine, MeCN, 50 °C; (iv) 2 N HCl, EtOH, 40 °C; (v) DMSO, pyridinium
trifluoroacetate, EDC; (vi) MeOH, 50 °C; (vii) Pearlman’s catalyst, H2
(40 psi), MeOH, conc aq HCl (2-3 equiv) in Parr shaker at 35 °C, 2 h,
then TEA (3 equiv), 35% yield over five steps; (viii) aldehyde or ketone,
Gram-positive potency criteria for advancement of a com-
pound was MIC e 1 μg/mL against sensitive and resistant
streptococcal strains, including the constitutive erm strain of
S. pyogenes 1079 (superior to 1, MIC = 32 μg/mL). The
fastidious Gram-negative H. influenzae, with its restriction
on entry into and efflux out of the bacterium, has always been
a challenge for large molecules such as macrolides.13 The
H. influenzae 1325 strain (Table 1) was one of the least
susceptible in our laboratories, and its modal MIC values
were more or less representative of the MIC90 results obtained
from larger populations of this pathogen (N g 30 strains).
Thus, MIC e 4 μg/mL vs H. influenzae 1325 was the standard
for further advancement of a compound, matching the Gram-
negative profile of 1 for its least susceptible strain. Because 1
has generated serious safety concerns,8 particularly with
respect to its hepatotoxicity profile,14 we focused on lowering
the liabilities of our analogues by reducing its elevated hepatic
turnover and the high degree of time-dependent inactivation
(TDI) of cytochrome P450 liver enzymes (specifically 3A
isoforms). In addition to mitigating the hepatic liabilities
associated with 1, this strategy would have the added bene-
fit of improving the pharmacokinetics through reduction
of metabolic clearance and drug-drug interactions (DDI).
Human liver microsomes were used to screen compounds for
metabolic clearance.15 The measured human liver microsomal
extraction ratio (ER) of 1 was 0.7, consistent with the
˚
HOAc, TEA, 4 A powdered molecular sieves, Na(OAc)3BH, 30-70%
yields.
HCl and ethanol yielded the C3 hydroxyl intermediate, which
was oxidized to the C3 ketone using DMSO, pyridinium
triflouroacetate, and 1-(3-dimethylaminopropyl)-3-ethylcar-
bodiimide hydrochloride. After removal of the 20-acetyl group
by heating in methanol, the benzhydryl protecting group was
removed by hydrogenolysis using Pearlman’s catalyst to give
the azetidinyl template 5. From this template target analogues
6a-s were synthesized by reductive amination using standard
conditions.
Many of the coupling partners for the azetidinyl template 5
were either commercially available or synthesized using well
precedented chemistries. The naphthyridine aromatic head-
pieces, however, had to be constructed from more basic
building blocks as illustrated in Schemes 2 and 3. The
[1,8]naphthyridines were initially accessed via the Skraup
reaction11 on 7, although in poor yields as is typical for such
systems. The Skraup product 8 was subsequently converted to
9 (used to make 6m, Figure 2) by way of selenium dioxide
benzylic oxidation. Aldehyde 9 was further homologated to

7448 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23
Scheme 2. Synthesis of [1,8]Naphthyridinesa
Magee et al.
a Reagents and conditions: (i) m-nitrobenzene sodium sulfonate, conc H2SO4, glycerol, 120 °C, 8 h, then basify, 11% yield; (ii) SeO2, dioxane, water,
80 °C, 77% yield; (iii) MeMgBr, toluene, THF, 24% yield; (iv) IBX, EtOAc, 80 °C, 86% yield; (v) pivoyl chloride, TEA, DCM, 82% yield; (vi) Cl2(g),
Na2HPO4, water, DCM; 86% yield; (vii) t-BuLi (2.1 equiv), Et2O, -65 to -15 °C, then add 3-dimethylaminopropenal, -15 °C to room temp, treat with
concentrated HCl, 52% yield; (viii) NaOMe, MeOH, 67% yield; (ix) 6 N HCl, reflux, 98% yield.
Scheme 3. Synthesis of [1,5]Naphthyridinesa
a Reagents and conditions: (i) NaOMe, DMF, 50 °C, 90% yield; (ii) BocNH2, Pd2(dba)3-CHCl3, xantphos, Cs2CO3, dioxane, 100 °C for 30 h, 84%
yield; (iii) n-BuLi, THF, MeI, MTBE, 100% yield; (iv) 4 N HCl, MeOH, 84% yield; (v) sodium 3-nitrobenzenesulfonate, MeSO3H, FeSO4 7H2O,
3
glycerol, 125-130 °C, 45% yield; (vi) NBS, dibenzoyl peroxide, CCl4, 95% yield; (vii) KOAc, DMF, MeOH, K2CO3, 63% yield; (viii) IBX, EtOAc;
(ix) 6 N HCl, reflux, 90% yield combining steps viii and ix.
relatively high clearance observed in human.16 CYP3A TDI
was assessed using human liver microsomes with midazolam
as a probe substrate for CYP3A. Compounds were evaluated
for time- and concentration-dependent inhibition of midazo-
lam metabolism, and KI and kinact values were determined.
These parameters were then used to predict clinical DDI.17
otitis media (OM) model to ensure that they demonstrated
equivalent or superior oral efficacy to that of 1.
With a clear strategy inmindwethenset out by cyclizing the
tether connecting the critical aryl-alkyl group to the macro-
cylic ring system.19 Additionally, a nitrogen was placed into
the conformationally constrained tether to introduce polarity
and to provide a convenient point of attachment for rapid
SAR exploration and, significantly, modulation of the physi-
cochemical properties of the final analogues. After consider-
able empirical evaluation of tether systems, the azetidine ring
proved to be a rich vein for the program and is the focus of
the present disclosure.20 The unsubstituted azetidinyl tem-
plate 5 had excellent activity against the susceptible strain of
S. pneumoniae (1016), moderate activity against the mef strain
(1175), but very poor erm potency (S. pneumoniae 1095 and
S. pyogenes 1079; Table 1), which is not unexpected given
the well-established need for an aryl ring to capture erm
strains from a macrolide template. Appendage of a simple
benzyl substituent (6a) gave a dramatic improvement in the
erm S. pneumoniae profile, which was not improved upon
with the corresponding pyridylmethyl analogues (6b,c). In-
troduction of a bromine ortho to the methylene bridge of 6c,
however, resulted in 6d, which began to show good strepto-
coccal potency, including against erm S. pyogenes 1079.
TDI measurements of 1 yielded KI = 2.4 μM and kinact
=
0.04 min-1, resulting in a predicted 6-fold increase in area
under the curve (AUC) for a concomitantly administered
CYP3A substrate, consistent with clinical observations.18 In
order to improve on the druglike properties of our analogues
relative to 1, the advancement criteria included in vitro
microsomal ER e 0.3 and TDI values resulting in predicted
AUC increase of e3-fold for concomitantly administered
CYP3A substrates. The cardiotoxicity liabilities (QTc) of 1
are not intrinsic to the compound but appear to be a function
of its TDI and the effect this has on CYP3A object drugs.18
Thus, the QTc potential of new analogues was monitored in a
hERG patch-clamp assay with the goal of not exceeding that
of 1 (IC50 g 40 μM). Finally, the most promising compounds
were evaluated in preclinical infection models using clini-
cally relevant respiratory strains: S. pneumoniae 1095 (erm)
in a murine respiratory tract infection (RTI) model and
H. influenzae 1325 (least susceptible of all strains) in a gerbil

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23 7449
Figure 2. Aryl-alkyl attachments to intermediate 5 (Scheme 1) representing key test compounds 6a-s.
Encouragingly, this level of erm potency was clearly differ-
entiated from that of 1.
bridge connecting the aryl ring to the azetidinyl nitrogen, methyl
substitution was used at this position to block metabolism,
yielding the diastereomers 6p and 6q. Not unexpectedly, the
diastereomers displayed differential activities in the MIC panel,
with 6q having a clear potency advantage. This strategy also
resulted in lowering the ER of 6q relative to the parent 6m
considerably (0.3 vs 0.6); additionally 6q maintained a reason-
able TDI value (3-fold) as well as a hERG IC50 (43 μM)
comparable to that of 1. Consequently 6q was profiled in the
preclinical in vivo RTI and OM models. The oral efficacy results
of 6q compared to 1 and negative control 3 are given in Table 3
and were sufficiently encouraging (in combination with
its predicted human clearance and safety properties) to nomi-
nate 6q for clinical development. Single dose studies in humans,
however, were disappointing, with plasma exposures upon oral
dosing (300-1000 mg) achieving only approximately 20% of
the predicted AUC. Subsequent investigation revealed extensive
nonmicrosomally mediated metabolism of 6q catalyzed by
aldehyde oxidase (AO),21 which halted development of the
compound. Because AO is a cytosolic rather than microsomal
enzyme, an in vitro assay with human liver cytosol was retro-
actively used to analyze the structure-metabolism relation-
ships, in both the presence and absence of an AO inhibitor
(raloxifene22), revealing a clear pattern of vulnerability of the
[1,8]naphthyridine system to AO metabolism (Table 2). Thus,
although the 3-hydroxy[1,8]naphthyridinyl 6r had very promis-
ing in vitro potency, it too was revealed to be a substrate for AO
and was not progressed further as a consequence. Encoura-
gingly, the 3-hydroxy substituent imparted very favorable ER
The metabolism of 6d, however, was high (ER > 0.8), and
this compound was not pursued any further. Extension into
bicyclic aromatics quickly pointed to the advantages of fused
systems, which cover the rest of the analogues (6e-s) in Table 1.
Similar to the o-bromine effect on the monocyclic ring of 6d,
halogens (not shown) and in particular a methoxy substituent
(identified by synthesis of a library array) on the bicyclic-fused
rings ortho to the methylene bridge demonstrated a distinct
potency advantage (6e vs 6f). Quinolines 6g and 6h showed a
relative insensitivity to the placement of the nitrogen, although
the attachment point to the macrolide made a significant
difference, with the R ring junction being consistently preferred
over β (6h vs 6i). To reduce the lipophilicity of the target
compounds, more polar heterocycles were subsequently incor-
porated. The benzimidazole 6k was one such example; however,
it lacked the requisite in vitro potency. The [1,5]naphthyridine
analogue 6l appeared more promising except that both the ER
(0.7) and TDI (5-fold) measurements indicated no differentia-
tion from 1 (Table 2). The [1,8]naphthyridine analogue 6m also
met the potency criteria and showed a distinct advantage over 6l
in the TDI assay (2-fold) but still had a high ER (0.6).
Combining the o-methoxy substituent of 6f with quinoline 6g
and [1,8]naphthyridine 6m gave analogues 6n and 6o, respec-
tively. While both 6n and 6o had extremely good Gram-positive
potencies, their H. influenzae MICs were slightly elevated;
furthermore, both had high ERs (6n=0.6; 6o=0.8). Consider-
ing the potential for metabolism at the benzylic methylene

7450 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23
Magee et al.
Table 1. Minimum Inhibitory Concentrations (MICs, μg/mL) of Telithromycin (1), Clarithromycin (3), the Azetidinyl Ketolide Template (5), and the
Azetidinyl Ketolide Analogues with Varying Aryl-Alkyl Substituents (6a-s) against Susceptible and Resistant Respiratory Pathogens
S. pneumoniae 1016
(susceptible)
S. pneumoniae
1095 (ermB)
S. pneumoniae
1175 (mefA)
S. pyogenes
1079 (ermB)
H. influenzae
1325
compd
1
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
>64
64
e0.06
16
32
4
3
>64
>64
>64
>64
>64
1
16
16
16
8
5
2
0.12
6a
6b
6c
6d
6e
6f
6g
6h
6i
e0.06
e0.06
0.12
2
0.5
4
e0.06
0.12
0.12
e0.06
e0.06
e0.06
0.25
8
8
16
16
4
1
e0.06
e0.06
e0.06
e0.06
0.125
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
e0.06
4
e0.06
0.25
4
16
8
16
8
6j
e0.06
0.5
2
6k
6l
8
8
e0.06
0.12
1
8
6m
6n
6o
6p
6q
6r
6s
1
4
e0.06
e0.06
0.25
e0.06
e0.06
16
8
8
16
4
0.25
e0.06
e0.06
1
0.25
0.5
4
4
Table 2. Summary of Screening Data Used for Compound Selectiona
predicted fold vAUC
for CYP3A
substrate
CYP3A kinact
(min-1)
hERG
IC50 (μM)
compd
hepatic ER
AO metabolism
CYP3A KI (μM)
1
0.7
0.7
no
no
yes
yes
yes
no
2.4
1.2
5.6
5.3
25
0.04
0.02
0.02
0.03
0.03
0.02
6
5
40
196
80
6l
6m
6q
6r
6s
0.6
0.3
2
3
43
<0.3
<0.3
e2
e2
140
67
24
a Methods provided in Supporting Information.
Table 3. Oral Efficacies in Preclinical Infection Models for 1, 3, 6q,
and 6s
infections. The key analogues from this series generally
matched the in vitro potency of 1 against the common
susceptible- and macrolide-resistant strains and exceeded 1
versus the very resistant erm S. pyogenes. We devised a
strategy of focusing on lowering hepatic metabolism and
time-dependent inactivation of hepatic enzymes, specifically
CYP3A isoforms, to address the hepatic safety issues asso-
ciated with the first marketed drug from the ketolide class,
telithromycin (1). Our first clinical candidate from this effort
(6q) contained the [1,8]naphthyridine aryl group which was
subsequently found to be extensively metabolized by AO. We
have subsequently selected the 3-hydroxy[1,5]naphthyridine
analogue (6s), which is differentiated from 6q in that it is not
an AO substrate and which further is differentiated from 1 in
both predicted hepatic ER and CYP3A TDI while not
compromising on its antibacterial potency or preclinical in
vivo efficacy.
PD50 ((mg/kg)/dose)a
in murine RTI model:
S. pneumoniae 1095
ED50 ((mg/kg)/dose)a
in gerbil OM model:
H. infuenzae 1325
compd
1
31.2 ( 5.6b
>100
37.5 ( 11.6c
>100
3
6q
6s
54.5 ( 24.1c
35.6d
26.8e
53.6e
a Mean ( standard deviation (N > 2 studies) or average (N e 2
studies). b N = 5 studies. c N = 3 studies. d N = 1 study. e N = 2 studies.
(<0.3) and TDI (e2-fold) properties to the molecule. Putting
all of these elements together in one molecule, the 3-hydroxy-
[1,5]naphthyridine analogue 6s was found to meet all of the in
vitro criteria for advancement, including antimicrobial potency,
ER (<0.3), TDI (e2-fold), hERG, and AO (no turnover,
Table 2). Furthermore, in vivo profiling of 6s demonstrated
the required efficacy with oral dosing in both mouse RTI and
gerbil OM models (Table 3), comparable to 1. Consequently 6s
was advanced into development and is currently in phase 1
clinical trials.
Experimental Section
General Chemistry Methods. All NMR spectra were recorded
on a Varian Inova 400 MHz spectrometer unless otherwise
specified. Reported data for 6s were recorded on a Bruker
DRX 600 MHz spectrometer. All final test compounds were
purified to g98% analytical purity using preparative HPLC
(Waters autopurification, Luna C-18 column, 250 mm ꢀ 21 mm,
flow rate of 28 mL/min, gradient from 10% to 90% MeOH
in 0.1% formic acid aqueous eluant). MS experiments were
Conclusion
In conclusion, we have discovered a novel azetidinyl tethered
ketolide series addressing the problem of resistant respira-
tory pathogens for the treatment of community-acquired

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23 7451
performed using a Waters Micromass ZMD (electrospray ioni-
zation, chromatography on a Varian Polaris 5 C-18 column with
MeCN, and 0.1% formic acid aqueous gradient eluant).
Reagents were obtained from commercial sources unless other-
wise noted. All reactions were performed under nitrogen unless
otherwise noted.
stirred at ambient temperature for 3 h and then treated with
saturated aqueous NaHCO3 solution (30 mL) and water (30
mL). The resulting mixture was separated, the aqueous layer
was re-extracted with DCM (3 ꢀ 75 mL), and the combined
organic layers were washed with water (50 mL). After the
organics were dried over sodium sulfate, the solvent was re-
moved under vacuum to yield a yellow foam. MS (ESIþ) for m/z
439 (M/2 þ H)þ.
11-Deoxy-20,400-diacetyl-10,11-didehydro-12-O-((1H-imida-
zol-1-yl)carbonyl)-6-O-methylerythromycin A (4). To a solution
of clarithromycin (6-O-methylerythromycin A, 3, 150 g, 201
mmol) in anhydrous dichloromethane (934 mL) cooled in an
ice-water bath were added triethylamine (68.1 mL, 487 mmol),
acetic anhydride (60 mL, 636 mmol), and DMAP (0.49 g, 4
mmol). The mixture was allowed to warm to ambient tempera-
ture for 48 h, then diluted with 0.5 M NaH2PO4 (1500 mL) and
extracted with CHCl3 (3 ꢀ 1 L). The organic layers were
combined and dried over sodium sulfate, filtered, and concen-
trated to under vacuum to give clean 20,400-diacetyl-6-O-methyl-
erythromycin A as an amorphous solid (167 g, 200 mmol). 20,400-
Diacetyl-6-O-methylerythromycin A (100 g, 120 mmol) was
dissolved in anhydrous THF (300 mL) and diisopropyl ether
(700 mL), then treated with 1,10-carbonyldiimidazole (97.4 g,
601 mmol) and DBU (53.9 mL, 366 mmol), and the resulting
mixture was heated to 40 °C for 2 h. The reaction mixture was
then stirred at ambient temperature for 48 h before diluting with
ethyl acetate (1 L) and water (1 L). The organic layer was
separated, and the aqueous layer was re-extracted with ethyl
acetate (2 ꢀ 1 L). The combined organic layers were dried over
sodium sulfate, filtered, and concentrated under vacuum to yield
the title compound and some imidazole-related impurities (121 g
total). This material was of sufficient purity to use in subsequent
reactions and was used as such. MS (ESIþ) for m/z 908.50 (M þ
H)þ. 1H NMR (CDCl3) δ ppm: 0.88-0.95 (m, 6 H), 1.11 (s, 1 H),
1.12-1.13 (m, 6 H), 1.17 (d, 6 H, J=6.00), 1.23 (d, 3 H, J=6.80),
1.34-1.59 (br, 4 H), 1.61-1.67 (m, 6 H), 1.76 (s, 3 H), 1.83-1.99
(br, 6 H), 2.01 (s, 3 H), 2.10 (s, 3 H), 2.24 (s, 6 H), 2.39 (d, 2H, J=
15.2), 3.11 (s, 3 H), 3.32 (s, 3 H), 3.55-3.65 (br, 3 H), 4.33 (m,
1 H), 4.58-4.72 (m, 3 H), 4.96 (br, 1 H), 5.79 (dd, 1 H, J=2.80,
J=10.40), 6.63 (s, 1 H), 7.05 (s, 1 H), 7.35 (s, 1 H), 8.06 (s, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
Step 4. The yellow foam from step 3 was redissolved in MeOH
(200 mL) and heated (50 °C) for 24 h, then concentrated under
vacuum to dryness. This solid material was rinsed with hexanes/
diethyl ether (2/1) and treated with MeOH (50 mL) and the
resulting slurry heated on a steam bath up to the boiling point,
then cooled to ambient temperature. The resulting white solid of
3-descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxycar-
bonyl-(1-benzhydrylazetidin-3-yl)imino)erythromycin A was
filtered and dried under vacuum (10.5 g, 12.6 mmol, 35% yield
over four steps). MS (ESIþ) for m/z 418 (M/2 þ H)þ. 1H NMR
(CDCl3) δ ppm: 4.60 (s, 1 H), 4.88 (br d, 1 H), 7.16 (m, 2 H), 7.21
(m, 4 H), 7.41 (m, 4 H).
Step 5a. The white solid from step 4 was dissolved in MeOH and
treated with concentrated 37 wt % HCl (2.4 mL, 28 mmol). To this
was added palladium hydroxide (20% weight Pd, about 6 g), and
the slurry was subjected to hydrogen gas (40-50 psi) in a Parr
shakerwhile heating(35°C) forupto2 h. TheParrflaskwascooled
to room temperature and purged with nitrogen, and the solids were
filtered off. The filtrate was treated with TEA (6.0 mL, 43 mmol)
and concentrated under vacuum to yield the title compound (5)
along with diphenylmethane (1 equiv) and the hydrochloride salt of
TEA (2.2 equiv) as a free-flowing crude solid (14 g total, approxi-
mately 59% by weight the title compound 5). This material was
used in subsequent coupling reactions. MS (ESIþ) for m/z 335
1
(M/2 þ H)þ. H NMR (CD3OD) δ ppm: 4.16 (br t, 1 H), 4.27
(d, 1 H), 4.33 (d, 1 H), 4.48 (br t, 1 H), 4.71-4.59 (m, 2 H).
Alternatively, the benzhydryl was removed using the proce-
dure in step 5b.
Step 5b. Palladium hydroxide (5.18 kg; 20% on carbon, 50%
water wet) was charged to a 200 L reactor (water wet, nitrogen
purged). To a 100 L glass-lined reactor was charged MeOH
(82.9 L) and concentrated 37 wt % HCl (2.24 L). 3-Descladi-
nosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxycarbonyl-(1-
benzhydrylazetidin-3-yl)imino)erythromycin A (10.29 kg, 12.3
mol) was then added. The resulting solution was transferred to
the 200 L reactor and the dark slurry heated to 40-50 °C for 2 h,
then cooled to 20-25 °C. The mixture was filtered over Celite
and rinsed with MeOH (2 ꢀ 50 L). To a Hastelloy pressure
reactor (prewet with water), palladium hydroxide (1.03 kg; 20%
on carbon, 50% water wet) and the filtrate obtained above were
added. After nitrogen and hydrogen purge, the reaction mixture
was warmed to 40-50 °C. The mixture was held at 50 psi of
hydrogen for 2 h, then cooled to 20-25 °C. After nitrogen purge,
the slurry was filtered through Celite and washed with MeOH
(2 ꢀ 20 L). The filtrate was concentrated and solvent-exchanged
with THF (100 L) to a final volume of ∼40 L (water from the wet
catalyst was removed during the azeotropic distillation at
250 mmHg, 45-50 °C). The resulting mixture was cooled to
20-25 °C and stirred for 3 h. The batch was filtered and the filter
cake rinsed with THF (10 L). The solids were dried under
vacuum to afford 8.27 kg of desired 5 as a pure dihydrochloride
salt (8.27 kg, 11.1 mol, 94%). MS (ESIþ) for m/z 668.4 (M þ
H)þ. 1H NMR (CD3OD) δ ppm: 0.78 (t, 3H, J=7.46 Hz), 0.91
(d, 3H, J=6.64 Hz), 1.06 (d, 3H, J=6.64 Hz), 1.08-1.30 (m,
11H), 1.32-1.79 (m, 2H), 1.95 (m, 1H), 2.38-2.54 (m, 1H), 2.59
(s, 3H), 2.68 (s, 3H). 2.77 (s, 3H), 3.02-3.39 (m, 6H), 3.52-3.65
(m, 3H), 3.94 (q, 1H, J = 7.46 Hz), 4.03-4.30 (m, 5H), 4.42
(t, 2H, J=6.64 Hz), 4.51-4.63 (m, 2H), 4.78-4.93 (m, 2H).
Typical Reductive Amination Coupling Procedure: 3-Descla-
dinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxycarbonyl-(1-
((phenyl)methyl)azetidin-3-yl)imino)erythromycin A (6a). Inter-
mediate 5 (1310 mg, 1.83 mmol) was dissolved in anhydrous
carbonyl(azetidin-3-yl)imino)erythromycin
A Dihydrochloride
(5). Step 1. DBU (10 mL, 67 mmol) was added to 1-benzhy-
drylazetidin-3-ylamine (9.0 g, 37.8 mmol) dissolved in anhy-
drous MeCN (100 mL) at ambient temperature. To this solution
was added 11-deoxy-20,400-diacetyl-10,11-didehydro-12-O-((1H-
imidazol-1-yl)carbonyl)-6-O-methylerythromycin A (4) (32.5 g,
35.8 mmol), and the resulting mixture was heated (50 °C) for
7.5 h, then allowed to stir overnight at ambient temperature.
A white precipitate was collected by filtration (21 g, 19.5 mmol).
The filtrate was concentrated toabout 25mL before adding water
(20 mL) and saturated aqueous NaHCO3 solution (30 mL) and
extracting the resulting mixture with DCM (dichloromethane,
50 mL). The organic layer was washed with saturated aqueous
NaHCO3 solution, dried over sodium sulfate, and concentrated
undervacuum toa tan foam. MS(ESIþ) for m/z 540 (M/2þ H)þ.
Step 2. The product from step 1 was dissolved in EtOH (100
mL) and 2 N HCl (100 mL), heated (40 °C) for 3 h, then cooled to
30 °C and stirred overnight. The resulting mixture was concen-
trated under vacuum, maintaining the bath at 28 °C, to about
half of the original volume. To the resulting concentrate was
added DCM (100 mL), followed by careful addition of solid
potassium carbonate to basify the aqueous layer (to pH 10). The
organic layer was separated, and the aqueous layer was re-
extracted with DCM (3 ꢀ 100 mL). The combined organic layers
were dried over sodium sulfate and concentrated to a white
foam. MS (ESIþ) for m/z 440 (M/2 þ H)þ.
Step 3. The crude product from step 2 was redissolved in
anhydrous DCM (200 mL) and to which were added anhydrous
DMSO (20 mL, 282 mmol), pyridinium trifluoroacetate (15 g,
77.7 mmol), and finally 1-(3-dimethylaminopropyl)-3-ethylcar-
bodiimide hydrochloride (30 g, 156.5 mmol). The mixture was

7452 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23
Magee et al.
THF (40 mL), followed by TEA (0.78 mL, 5.58 mmol), acetic
acid (0.32 mL, 5.58 mmol), benzaldehyde (0.203 mL, 2.01
Hz, 1 H), 7.45-7.69 (m, 4 H), 7.89-8.00 (m, 2 H), 8.21 (d, J=
8.40 Hz, 1 H).
˚
mmol), and powdered molecular sieves (4 A, 1310 mg). The
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((2-methoxynaphth-1-yl)methyl)azetidin-3-yl)imino)-
resulting mixture was heated (49 °C) and stirred for 4 h, where-
upon sodium triacetoxyborohydride (1971 mg, 9.30 mmol) was
added with continued heating for an additional 1 h, then cooled
to ambient temperature overnight. The reaction mixture was
diluted with DCM (40 mL), filtered to remove solids, and
extracted with saturated aqueous NaHCO3 (50 mL) and water
(50 mL). The aqueous layer was separated and re-extracted with
DCM (4 ꢀ 100 mL). The combined organic extracts were dried
over anhydrous sodium sulfate, filtered, and concentrated to
dryness to afford 1.29 g of crude coupled product, which was
purified by reverse phase preparative HPLC to afford desired
titled compound 6a (650 mg, 0.86 mmol, 47% yield). MS (ESIþ)
for m/z 379.7 (M/2 þ H)þ. 1H NMR (CD3OD) δ ppm:
0.84-0.96 (m, 6 H), 1.02 (d, J = 6.63 Hz, 3 H), 1.16 (d, J =
7.02 Hz, 3 H), 1.23-1.39 (m, 17 H), 1.44-1.54 (m, 1 H), 1.57 (s, 2
H), 1.62-1.73 (m, 1 H), 1.77 (d, J=6.83 Hz, 1 H), 1.81-1.93 (m,
1 H), 2.00-2.09 (m, 1 H), 2.56 (s, 1 H), 2.62-2.69 (m, 2 H), 2.82
(s, 6 H), 3.17 (s, 2 H), 3.34-3.52 (m, 2 H), 3.67 (s, 1 H), 3.73 (br s,
1 H), 4.01-4.16 (m, 2 H), 4.24 (t, J=8.10 Hz, 1 H), 4.31 (s, 1 H),
4.38 (s, 2 H), 4.42-4.52 (m, 2 H), 4.56 (s, 1 H), 4.96 (dd, J=
10.44, 2.24 Hz, 1 H), 7.26-7.74 (m, 5 H).
1
erythromycin A (6f). MS (ESIþ) for m/z 839.3 (M þ H)þ. H
NMR (CD3OD) δ ppm: 0.86-0.91 (m, 5 H), 0.99 (d, J=6.64 Hz,
3 H), 1.14 (d, J=7.03 Hz, 3 H), 1.27-1.32 (m, 15 H), 1.50 (q, J=
11.72 Hz, 1 H), 1.56 (s, 3 H), 1.63-1.72 (m, 1 H), 1.76 (d, J=7.03
Hz, 2 H), 1.81-1.90 (m, 1 H), 2.02 (br d, J=12.31 Hz, 1 H), 2.53
(q, J=7.10 Hz, 1 H), 2.61 (s, 3 H), 2.79 (s, 6 H), 3.11-3.19 (m, 2
H), 3.37 (dd, J=12.01, 4.00 Hz, 1 H), 3.41-3.45 (m, 1 H), 3.65 (s,
1 H), 3.69-3.73 (m, 1 H), 4.04 (d, J=6.84 Hz, 1 H), 4.07 (s, 3 H),
4.17-4.27 (m, 2 H), 4.29 (d, J=8.01 Hz, 1 H), 4.36 (d, J=7.03
Hz, 1 H), 4.54-4.60 (m, 1 H), 4.71 (t, J = 10.25 Hz, 1 H),
4.75-4.79 (m, 1 H), 4.90 (dd, J=10.54, 2.44 Hz, 1 H), 4.99 (s, 2
H), 7.43 (t, J=7.52 Hz, 1 H), 7.51 (d, J=9.18 Hz, 1 H), 7.90 (d,
J=7.81 Hz, 1 H), 8.05 (d, J=9.18 Hz, 1 H), 8.19 (d, J=8.59 Hz,
1 H), 8.49 (s, 2 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((quinolin-4-yl)methyl)azetidin-3-yl)imino)erythromy-
cin A (6g). MS (ESIþ) for m/z 810.2 (M þ H)þ. 1H NMR
(CD3OD) δ ppm: 0.86-0.91 (m, 4 H), 1.01 (d, J=6.64 Hz, 3 H),
1.16 (d, J=7.03 Hz, 3 H), 1.28-1.33 (m, 13 H), 1.47-1.51 (m, 1
H), 1.55 (s, 3 H), 1.62-1.70 (m, 1 H), 1.76 (d, J=7.82 Hz, 2 H),
1.82-1.91 (m, 1 H), 1.99 (br d, J=14.65 Hz, 1H), 2.51-2.59 (m,
1 H), 2.64 (s, 3 H), 2.75 (s, 6 H), 3.15-3.22 (m, 2 H), 3.25-3.28
(m, 1 H), 3.42 (dd, J=10.55, 7.23 Hz, 1 H), 3.60-3.64 (m, 1 H),
3.67 (s, 1 H), 3.69-3.72 (m, 1 H), 4.01-4.07 (m, 1 H), 4.18 (m, 1
H), 4.28-4.37 (m, 4 H), 4.96 (br d, J=12.89 Hz, 1 H), 7.53 (d, J=
4.49 Hz, 1 H), 7.61-7.68 (m, 1 H), 7.79 (t, J=8.24 Hz, 1 H), 8.04
(d, J=7.81 Hz, 1 H), 8.22 (d, J=8.98 Hz, 1 H), 8.53 (s, 1 H), 8.80
(d, J=4.69 Hz, 1 H).
Final test compounds 6b-o,r were synthesized with the same
procedure used for 6a. The procedures for 6p-q,s were altered
as described below.
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((pyridin-3-yl)methyl)azetidin-3-yl)imino)erythromycin
A (6b). MS (ESIþ) for m/z 380 (M/2 þ H)þ. 1H NMR (CD3OD)
δ ppm: 0.89 (t, J=7.32 Hz, 2 H), 1.00 (d, J=6.64 Hz, 2 H), 1.15
(d, J=7.03 Hz, 2 H), 1.23-1.38 (m, 7 H), 1.40-1.57 (m, 3 H),
1.61-1.72 (m, 1 H), 1.75 (d, J=7.03 Hz, 1 H), 3.65 (s, 1 H),
3.70-3.78 (m, 1 H), 3.93-4.00 (m, 1 H), 4.00-4.08 (m, 2 H),
4.12-4.17 (m, 1 H), 4.31 (d, J=8.01 Hz, 1 H), 4.38 (d, J=6.64
Hz, 1 H), 4.94 (dd, J=10.54, 2.54 Hz, 1 H), 7.39-7.53 (m, 1 H),
7.84-7.91 (m, 1 H), 8.51 (dd, J=5.08, 1.56 Hz, 1 H), 8.56 (d, J=
1.76 Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((quinolin-5-yl)methyl)azetidin-3-yl)imino)erythro-
1
mycin A (6h). MS (ESIþ) for m/z 810.2 (M þ H)þ. H NMR
(CD3OD) δ ppm: 0.89-0.93 (m, 4 H), 1.01 (d, J=6.84 Hz, 3 H),
1.15 (d, J=7.03 Hz, 3 H), 1.28-1.33 (m, 14 H), 1.43-1.53 (m, 1
H), 1.56 (s, 3 H), 1.63-1.71 (m, 1 H), 1.75 (d, J=7.03 Hz, 2 H),
1.83-1.92 (m, 1 H), 2.03 (br d, J=15.63 Hz, 1 H), 2.49-2.56 (m,
1 H), 2.60 (s, 3 H), 2.82 (s, 6 H), 3.12-3.22 (m, 2 H), 3.38-3.46
(m, 2 H), 3.66 (s, 1 H), 3.68-3.76 (m, 2 H), 3.99-4.07 (m, 2 H),
4.15-4.21 (m, 3 H), 4.30 (d, J=8.01 Hz, 1 H), 4.37 (d, J=6.64
Hz, 1 H), 4.48 (d, J=13.28 Hz, 1 H), 4.57 (d, J=13.48 Hz, 1 H),
4.95 (br d, J=10.35 Hz, 1 H), 7.63 (dd, J=8.59, 4.30 Hz, 1 H),
7.68 (d, J=7.81 Hz, 1 H), 7.76-7.79 (m, 1 H), 8.05 (d, J=8.04
Hz, 1 H), 8.41 (br s, 2 H), 8.74 (br d, J=10.94 Hz, 1 H), 8.90 (dd,
J=4.30, 1.55 Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((pyridin-4-yl)methyl)azetidin-3-yl)imino)erythromy-
cin A (6c). MS (ESIþ) for m/z 380 (M/2 þ H)þ. 1H NMR
(CD3OD) δ ppm: 0.86-0.94 (m, 3 H), 1.01 (d, J=6.83 Hz, 3 H),
1.12-1.20 (m, 3 H), 1.23-1.39 (m, 13 H), 1.55 (s, 3 H),
1.62-1.72 (m, 1 H), 1.76 (d, J=6.83 Hz, 2 H), 1.82-1.93 (m,
1 H), 2.00-2.10 (m, 1 H), 2.55 (s, 1 H), 2.66 (s, 3 H), 2.82 (s, 6 H),
3.18 (s, 2 H), 3.35-3.53 (m, 2 H), 3.67 (s, 1 H), 3.70-3.82 (m, 2
H), 3.90 (br s, 1 H), 3.98-4.25 (m, 6 H), 4.35 (dd, J=27.05, 7.32
Hz, 2 H), 4.94 (dd, J=10.45, 2.64 Hz, 1 H), 7.43 (d, J=6.05 Hz, 2
H), 8.45-8.61 (m, 2 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxycar-
bonyl-(1-((quinolin-6-yl)methyl)azetidin-3-yl)imino)erythromy-
cin A (6i). MS (ESIþ) for m/z 810.2 (M þ H)þ. 1H NMR
(CD3OD) δ ppm: 0.89-0.91 (m, 5 H), 1.01 (d, J=6.84 Hz, 3 H),
1.15 (d, J=7.03 Hz, 3 H), 1.27-1.33 (m, 15 H), 1.47-1.53 (m, 1
H), 1.56 (s, 3 H), 1.63-1.71 (m, 1 H), 1.74 (d, J=7.03 Hz, 2 H),
1.82-1.88 (m, 1 H), 2.02 (br d, J=12.69 Hz, 1 H), 2.53 (dd, J=
14.16, 6.93 Hz, 1 H), 2.58 (s, 3 H), 2.81 (s, 6 H), 3.12-3.19 (m, 2
H), 3.35-3.46 (m, 2 H), 3.65 (br s, 1 H), 3.68-3.74 (m, 1 H),
4.01-4.06 (m, 2 H), 4.22-4.26 (m, 1 H), 4.28 (d, J=8.01 Hz, 1
H), 4.36 (d, J=6.64 Hz, 1 H), 4.39-4.44 (m, 2 H), 4.48 (d, J=
3.71 Hz, 1 H), 4.50-4.55 (m, 1 H), 4.95 (br d, J=10.45 Hz,
1 H), 7.59 (dd, J=8.40, 4.30 Hz, 1 H), 7.83 (dd, J=8.69, 1.86
Hz, 1 H), 8.06 (d, J = 1.76 Hz, 1 H), 8.08 (d, J = 8.60 Hz,
1 H), 8.42 (dd, J=8.40, 1.17 Hz, 1 H), 8.89 (dd, J=4.39, 1.66
Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((quinoxalin-5-yl)methyl)azetidin-3-yl)imino)erythro-
mycin A (6j). MS (ESIþ) for m/z 405.7 (M/2 þ H)þ. 1H NMR
(CD3OD) δ ppm: 0.88 (t, J=7.32 Hz, 3 H), 0.99 (d, J=6.83 Hz, 3
H), 1.16 (d, 3 H), 1.20-1.37 (m, 14 H), 1.48-1.92 (m,8 H), 2.38
(s, 6 H), 2.47-2.77 (m, 6 H), 3.07-3.29 (m, 3 H), 3.49-3.70 (m,
4 H), 3.87-4.06 (m, 2 H), 4.15 (s, 1 H), 4.24-4.33 (m, 2 H),
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxycar-
bonyl-(1-((3-bromopyridin-4-yl)methyl)azetidin-3-yl)imino)ery-
1
thromycin A (6d). MS (ESIþ) for m/z 419.9 (M/2 þ H)þ. H
NMR (CD3OD) δ ppm: 0.86-0.97 (m, 4 H), 1.02 (d, J=6.83 Hz,
3 H), 1.19 (d, J=7.03 Hz, 3 H), 1.27-1.38 (m, 15 H), 1.56 (s, 3
H), 1.61-1.71 (m, 1 H), 1.75-1.82 (m, 2 H), 1.82-1.99 (m, 2 H),
2.58 (br s, 7 H), 2.70 (s, 3 H), 3.12-3.26 (m, 2 H), 3.60-3.75 (m, 4
H), 3.86-3.97 (m, 3 H), 4.05 (s, 2 H), 4.13-4.24 (m, 1 H),
4.29-4.40 (m, 2 H), 4.94 (dd, J=10.45, 2.64 Hz, 1 H), 7.49 (d, J=
5.08 Hz, 1 H), 8.48 (d, J=5.08 Hz, 1 H), 8.65 (s, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((naphth-1-yl)methyl)azetidin-3-yl)imino)erythromy-
1
cin A (6e). MS (ESIþ) for m/z 404.7 (M/2 þ H)þ. H NMR
(CD3OD) δ ppm: 0.87-0.96 (m, 6 H), 1.03 (d, J=6.83 Hz, 3 H),
1.16 (d, J=7.03 Hz, 3 H), 1.21-1.40 (m, 18 H), 1.52 (d, J=10.94
Hz, 1 H), 1.57 (s, 2 H), 1.65-1.74 (m, 1 H), 1.76 (d, 1 H),
1.81-1.96 (m, 1 H), 2.02 (d, J=9.96 Hz, 1 H), 2.50-2.59 (m, 1
H), 2.62 (s, 2 H), 2.81 (s, 5 H), 3.11-3.25 (m, 2 H), 3.34-3.51 (m,
2 H), 3.67 (s, 1 H), 3.69-3.81 (m, 1 H), 3.87-3.97 (m, 1 H),
4.01-4.11 (m, 1 H), 4.16-4.28 (m, 1H), 4.28-4.41 (m, 4 H), 4.48
(t, J=8.40 Hz, 1 H), 4.64-4.80 (m, 2 H), 4.97 (dd, J=10.64, 2.64

Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23 7453
4.37-4.55(m, 2 H), 4.85-4.96 (m, 1 H), 7.77-7.89 (m, 2 H), 8.03
(dd, J=7.13, 2.83 Hz, 1 H), 8.91 (dd, J=20.89, 1.76 Hz, 2 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-(([1,5]naphthyridin-4-yl)methyl)azetidin-3-yl)imino)-
erythromycin A (6l). MS (ESIþ) for m/z 406.4 (M/2 þ H)þ. 1H
NMR (CD3OD) δ ppm: 0.89 (t, J=7.41 Hz, 3 H), 1.03 (d, J=
6.83 Hz, 3 H), 1.12-1.20 (m, 4 H), 1.24-1.38 (m, 13 H),
1.47-1.60 (m, 4 H), 1.61 -1.91 (m, 5 H), 2.00-2.09 (m, 1 H),
2.66 (s, 2 H), 2.83 (s, 6 H), 3.11-3.23 (m, 2 H), 3.39-3.50 (m, 2
H), 3.67-3.80 (m, 2 H), 4.01-4.10 (m, 1 H), 4.24-4.34 (m, 2 H),
4.39 (d, J=6.83 Hz, 1 H), 4.59-4.63 (m, 1 H), 4.64-4.75 (m,
2 H), 4.95 (dd, J=10.54, 2.34 Hz, 1 H), 5.07 (s, 2 H), 7.84-7.93
(m, 2 H), 8.53 (dd, J=8.59, 1.76 Hz, 1 H), 9.04 (d, J=4.29 Hz, 1
H), 9.09 (dd, J=4.20, 1.66 Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-(([1,8]naphthyridin-4-yl)methyl)azetidin-3-yl)imino)-
erythromycin A (6m). MS (ESIþ) for m/z 406.7 (M/2 þ H)þ. 1H
NMR (CD3OD) δ ppm: 0.90 (t, J=7.41 Hz, 3 H), 0.98-1.07 (m,
3 H), 1.12-1.21 (m, 3 H), 1.26-1.40 (m, 13 H), 1.49-1.60(m, 4
H), 1.62-1.93 (m, 4 H), 1.99-2.09 (m, 1 H), 2.50-2.60 (m, 1 H),
2.62 (s, 2 H), 2.83 (s, 6 H), 3.13-3.24 (m, 2 H), 3.36-3.50 (m, 2
H), 3.59-3.79 (m, 4 H), 3.94-4.09 (m, 3 H), 4.13-4.22 (m, 1 H),
4.28-4.45 (m, 4 H), 4.96 (dd, J=10.24, 2.63 Hz, 1 H), 7.64 (d, J=
4.49 Hz, 1 H), 7.69 (dd,J=8.39, 4.29 Hz, 1 H), 8.79 (dd, J=8.49,
1.85 Hz, 1 H), 9.03 (d, J=4.49 Hz, 1 H), 9.08 (dd, J=4.29, 1.76
Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-(([1,5]naphthyridin-4-yl)methyl)azetidin-3-yl)imino)-
erythromycin A (6n). MS (ESIþ) for m/z 420.2 (M/2 þ H)þ. 1H
NMR (CD3OD) δ ppm: 0.87 (t, J=7.42 Hz, 3 H), 0.97 (d, J=
6.64 Hz, 3 H), 1.07-1.38 (m, 16 H), 1.52 (s, 3 H), 1.56-1.89 (m,
5 H), 2.33 (s, 5 H), 2.45-2.69 (m, 5 H), 3.08-3.27 (m, 3 H),
3.35 (s, 1 H), 3.41 (t, 1 H), 3.53-3.66 (m, 3 H), 3.85 (d,
J = 7.81 Hz, 2 H), 3.98-4.17 (m, 5H), 4.21-4.34 (m, 4 H),
4.82-4.89 (m, 2 H), 7.58-7.67 (m, 2 H), 7.94-8.02 (m, 1 H),
8.14-8.23 (m, 1 H), 8.84 (s, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-(([1,5]naphthyridin-4-yl)methyl)azetidin-3-yl)imino)-
erythromycin A (6o). MS (ESIþ) for m/z 420.7 (M/2 þ H)þ. 1H
NMR (CD3OD) δ ppm: 0.87 (t, J=7.42 Hz, 3 H), 0.96 (d, 3 H),
1.08-1.37 (m, 17 H), 1.52 (s, 3 H), 1.57-1.87 (m, 5 H), 2.33 (s, 6
H), 2.45-2.54 (m, 1 H), 2.54-2.58 (m, 3 H), 2.57-2.66 (m, 1 H),
3.07-3.26 (m, 3 H), 3.36-3.43 (m, 1 H), 3.52-3.64 (m, 3 H),
3.79-3.87 (m, 2 H), 3.97-4.10 (m, 2 H), 4.13-4.19 (m, 3 H),
4.23-4.32 (m, 3 H), 4.83-4.89 (m, 1 H), 7.62 (dd, J=8.49, 4.20
Hz, 1 H), 8.71 (dd, J=8.59, 1.76 Hz, 1 H), 8.92 (dd, J=4.10, 1.76
Hz, 1 H), 9.05 (s, 1 H).
B over 10 min, where A=acetonitrile containing 0.1% formic
acid and B = water containing 0.1% formic acid). The more
polar peak (6q) eluted at 4.00 min (1.1 g total collected) and the
less polar peak (6p) just after at 4.38 min (1.0 g total collected).
After recrystallization from ethyl acetate, the structure of
the more potent 6q was assigned unambiguously by X-ray
(Supporting Information): MS (ESIþ) for m/z 825.2 (M þ
1
H)þ. H NMR (CD3OD) δ ppm: 0.85 (t, J = 7.33 Hz, 3 H),
1.04 (d, J=6.64 Hz, 3 H), 1.17 (d, J=7.03 Hz, 3 H), 1.24-1.29
(m, 13 H), 1.42 (d, J=6.44 Hz, 3 H), 1.54 (s, 3 H), 1.60-1.68 (m,
1 H), 1.71-1.85 (m, 4 H), 2.33 (s, 6 H), 2.35 (s, 3 H), 2.52-2.64
(m, 2 H), 3.07-3.15 (m, 1 H), 3.18-3.25 (m, 3 H), 3.55-3.58 (m,
1 H), 3.60 (br s, 1 H), 3.85-3.89 (m, 1 H), 3.98-4.03 (m, 1 H),
4.14-4.19 (m, 2 H), 4.25 (d, J=7.42 Hz, 2 H), 4.51 (q, J=6.45
Hz, 1 H), 4.99 (br d, J=10.55 Hz, 1 H), 7.69-7.72 (m, 2 H), 8.97
(d, J=8.59 Hz, 1 H), 9.04 (d, J=4.69 Hz, 1 H), 9.09 (dd, J=4.20,
1.66 Hz, 1 H). The structure of the 6p diastereomer was assigned
1
by inference: MS (ESIþ) for m/z 825.4 (M þ H)þ. H NMR
(CD3OD) δ ppm: 0.91-0.94 (m, 6 H), 1.15 (d, J=7.03 Hz, 3 H),
1.30-1.32 (m, 6 H), 1.34-1.36 (m, 6 H), 1.39 (d, J=6.64 Hz, 3),
1.54 (s, 3 H), 1.64-1.70 (m, 1 H), 1.72-1.81 (m, 2 H), 1.85-1.92
(m, 2 H), 2.56 (s, 6 H), 2.73 (s, 3 H), 2.95-3.03 (m, 1 H),
3.17-3.25 (m, 2 H), 3.34-3.37 (m, 1 H), 3.57 (t, J=7.62 Hz, 1
H), 3.65-3.77 (m, 4 H), 4.05-4.10 (m, 1 H), 4.11-4.19 (m, 1 H),
4.35 (d, J=7.23 Hz, 2 H), 4.51-4.55 (m, 1 H), 4.99 (br d, J=
10.55 Hz, 1 H), 7.70 (dd, J=8.40, 4.20 Hz, 1 H), 7.78 (d, J=4.69
Hz, 1 H), 8.55 (s, 1 H), 8.95 (dd, J=8.60, 1.76 Hz, 1 H), 9.06 (d,
J=4.69 Hz, 1 H), 9.09 (dd, J=4.20, 1.86 Hz, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((3-hydroxy[1,8]naphthyridin-4-yl)methyl)azetidin-
3-yl)imino)erythromycin A (6r). MS (ESIþ) for m/z 414.2 (M/
2 þ H)þ. 1H NMR (CD3OD) δ ppm: 0.87 (t, J=7.42 Hz, 3 H),
0.99 (d, J=6.64 Hz, 3 H), 1.14 (d, J=7.03 Hz, 3 H), 1.24-1.36
(m, 11 H), 1.39-1.51 (m, 1 H), 1.54 (s, 3 H), 1.59-1.69 (m, 1 H),
1.71-1.78 (m, 2 H), 1.79-1.91 (m, 1 H), 1.92-2.02 (m, 1 H),
2.47-2.59 (m, 1 H), 2.61 (s, 2 H), 2.65 (s, 3 H), 2.71 (s, 5 H),
3.11-3.28 (m, 3 H), 3.36- 3.45 (m, 1 H), 3.60-3.76 (m, 3 H), 3.86
(t, J=7.81 Hz, 1 H), 3.97-4.23 (m, 4 H), 4.26-4.39 (m, 2 H),
4.49 (s, 2 H), 4.87-4.96 (m, 1 H), 7.53-7.60 (m, 1 H), 8.48-8.60
(m, 2 H), 8.68 (s, 1 H), 8.76-8.84 (m, 1 H).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-((3-hydroxy[1,5]naphthyridin-4-yl)methyl)azetidin-
3-yl)imino)erythromycin A Tosylate Salt (6s). 3-Hydroxy-
[1,5]naphthyridine-4-carbaldehyde (22) (10 g, 57.6 mmol) and
intermediate 5 prepared by step 5b (41 g, 55.3 mmol) were
combined in THF (410 mL). TEA (21.9 mL, 157 mmol) was then
added. The mixture was stirred for 30 min, followed by the
addition of pivalic acid (21.4 g, 210 mmol). The mixture was
heated to reflux, and approximately 600 mL of solvent was
removed by concentration under atmospheric pressure to ensure
complete removal of water (400 mL of additional amount of
anhydrous THF was added during the concentration). The
mixture was then cooled to 20-25 °C and transferred to a
reaction flask that contained sodium triacetoxyborohy-
dride (55.5 g, 262 mmol), acetonitrile (164 mL), and EtOAc
(1230 mL) at 20-25 °C under agitation. After the mixture was
stirred for 30 min, 5% aqueous sodium bicarbonate (205 mL)
was added and the layers were separated. The aqueous layer was
extracted with EtOAc (205 mL). The combined organic phase
was treated with anhydrous MgSO4, and then active carbon
(10.3 g) was added. The mixture was filtered and concentrated
under vacuum. The resulting residue was purified by reverse-
phase chromatography (column, Kromasil C-18; mobile phase,
A (acetonitrile) and B (0.06% phosphoric acid in water);
gradient, 15% A for 0-2 min to 90% A over 30 min, hold
90% A for 3 min, return to 10% A, and hold for 5 min). Desired
fractions were combined, and the acetonitrile was removed by
concentration in vacuo under 20 °C. The remaining aqueous
mixture was pH adjusted to 8.34 using 4% aqueous sodium
bicarbonate solution, then extracted with EtOAc (3 ꢀ 400 mL).
3-Descladinosyl-11,12-dideoxy-6-O-methyl-3-oxo-12,11-(oxy-
carbonyl-(1-(1S-([1,8]naphthyridin-4-yl)ethyl)azetidin-3-yl)imino)-
erythromycin A (6p) and 3-Descladinosyl-11,12-dideoxy-6-O-
methyl-3-oxo-12,11-(oxycarbonyl-(1-(1R-([1,8]naphthyridin-4-yl)-
ethyl)azetidin-3-yl)imino)erythromycin
A (6q). Intermediate
5 (4.21 g) was treated with anhydrous THF (35 mL),
1-[1,8]naphthyridin-4-ylethanone (10) (0.7 g, 4.07 mmol), acetic
acid (0.33 mL, 5.8 mmol), TEA (1.55 mL, 11.1 mmol), and
˚
powdered 4 A powdered molecular sieves (4.5 g), and the slurry
was heated with stirring for 4 h at 49 °C. At this point, sodium
triacetoxyborohydride (2.35 g, 11 mmol) was added, and heat-
ing was continued for another hour before removing the heat
source and allowing the reaction flask to come to ambient
temperature overnight with continuous stirring. The solids were
then filtered off, and to the filtrate were added saturated
aqueous NaHCO3 (15 mL) and water (15 mL), and the layers
were separated. The aqueous layer was re-extracted with DCM
(5 ꢀ 40 mL). The solid filtrant was rinsed into a separatory
funnel and extracted as the filtrate was. The combined organic
layers were dried (sodium sulfate), filtered, and concentrated
under vacuum to give 4 g of a crude mixture of diastereomers.
The diastereomers were separated by reverse phase preparative
HPLC multiple injections (using gradient from 8% to 30% A in

7454 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23
Magee et al.
The combined organic phase was washed with saturated brine
solution, dried over anhydrous MgSO4, and concentrated to
dryness. The residue was dissolved in acetone (350 mL), and
a solution of tolunesulfonic acid hydrate (5.90 g, 31 mmol)
in acetone (90 mL) was added dropwise. After the addition
was complete, the mixture was stirred for 2 h at 20-25 °C.
The product that crystallized out was filtered, rinsed with
cold acetone (100 mL), and dried under vacuum to give the
desired product (23.2 g, 23.2 mmol, 42% yield). FTMS (ESIþ)
for m/z 826.459 85 (M þ H)þ for C43H64N5O11 (theoretical=
temperature. Saturated aqueous ammonium chloride was added
until the solution reached a bright-yellow color and precipitate
was apparent. The solution was passed through a syringe filter
and into water, then extracted with EtOAc (3 ꢀ 30 mL). The
combined organic fractions were dried over sodium sulfate,
filtered, and concentrated under vacuum. The product was
purified (silica gel with MeCN/hexanes eluant in 1:1 ratio initi-
ally, then to DCM/MeOH/NH4OH eluant (89:10:1), yielding the
title compound (0.079 g, 0.45 mmol, 24% yield). MS (ESIþ) for
m/z 175 (M þ H)þ. 1H NMR (CDCl3) δ ppm: 1.48 (s, 3 H), 5.58
(dd, 1 H), 6.32 (br s, 1 H), 7.25 (dd, 1 H), 7.52 (d, 1 H), 8.38 (m, 1
H), 8.64 (d, 1 H), 8.73 (m, 1 H).
1
826.459 69). H NMR (600 MHz, DMSO-d6) δ ppm: 0.80 (t,
J=7.42 Hz, 3 H), 0.89 (d, J=6.66 Hz, 3 H), 1.10 (d, J=7.17 Hz, 3
H), 1.18-1.24 (m, 12 H), 1.36 (dd, J=12.29, 10.75 Hz, 1 H), 1.48
(s, 3 H), 1.55-1.60 (m, 1 H), 1.60-1.64 (m, 1 H), 1.65-1.71 (m, 1
H), 1.71-1.77 (m, 1 H), 1.90 (dd, J=10.24, 3.07 Hz, 1 H), 2.29 (s,
3 H), 2.44 (dd, J=7.17, 2.56 Hz, 1 H), 2.51 (s, 3 H), 2.61 (s, 6 H),
3.05-3.12 (m, 2 H), 3.16-3.26 (m, 1 H), 3.29 (dd, J=10.75, 7.68
Hz, 1 H), 3.46 (s, 1 H), 3.60-3.66 (m, 1 H), 3.69 (dd, J=6.61 Hz,
1 H), 3.83 (dd, J=6.62 Hz, 1 H), 3.96-4.00 (m, 1 H), 4.00-4.05
(m, 2 H), 4.06 (q, J=6.66 Hz, 1 H), 4.12 (d, J=8.19 Hz, 1 H), 4.27
(d, J=7.17 Hz, 1 H), 4.65 (s, 2 H), 4.79 (dd, J=10.24, 0.66 Hz, 1
H), 5.97 (br s, 1 H), 7.07-7.14 (m, 2 H), 7.44-7.52 (m, 2 H), 7.56
(dd, J=8.19, 4.35 Hz, 1 H), 8.29 (dd, J=8.19, 1.54 Hz, 1 H), 8.64
(s, 1 H), 8.88 (dd, J=4.35, 1.79 Hz, 1 H). 13C NMR (151 MHz,
DMSO-d6) δ ppm: 10.20, 13.45, 13.60, 13.93, 15.35, 17.62, 19.48,
20.74, 21.66, 29.80, 37.78, 38.11, 40.05, 44.63, 45.33, 46.43,
49.11, 50.07, 52.19, 57.36, 58.90, 61.74, 64.38, 67.74, 68.76,
75.76, 77.69, 77.78, 82.61, 102.60, 120.48, 121.26, 125.47,
127.99, 136.84, 136.85, 137.53, 142.83, 144.73, 145.76, 150.57,
153.66, 155.13, 169.61, 204.18, 216.04.
4-Methyl[1,8]naphthyridine (8). m-Nitrobenzene sodium sul-
fonate (202 g, 897 mmol) was weighed into a 3 L three-necked
flask equipped with an overhead stirrer, and the flask was
immersed in an ice-water bath before adding concentrated
sulfuric acid (260 mL), glycerol (145 mL, 1987 mmol),
4-methylpyridin-2-ylamine 7 (50 g, 463 mmol), and finally water
(260 mL). The mixture was heated to 120 °C for 8 h, then cooled
to ambient temperature to yield a chocolate brown slurry.
Aqueous sodium hydroxide (20 N) was added slowly with
cooling (such that the temperature did not exceed 40 °C) until
the pH of the mixture approximated 10. The resulting sludge
was filtered through Celite and the filtrate extracted with DCM
(3 ꢀ 100 mL). The organic layers were dried over sodium sulfate,
filtered, and concentrated under vacuum to a black oil. The
desired product 8 (7.32 g, 50.8 mmol, 11% yield) was isolated by
silica gel chromatography (DCM/MeOH, 95:5). MS (ESIþ) for
m/z 145 (M þ H)þ.
Step 2. 1-[1,8]Naphthyridin-4-ylethanol (1.44 g, 8.26 mmol)
was dissolved in ethyl acetate (250 mL), treated with 2-iodoxy-
benzoic acid (7.8 g, 24.8 mmol) and heated to 80 °C for 6 h. The
solution was cooled to ambient temperature, and the solids were
removed by filtration. The product was purified (silica gel using
MeCN eluant) yielding the title compound (1.22 g 7.09 mmol,
86% yield). MS (ESIþ) for m/z 173 (M þ H)þ. 1H NMR
(CDCl3) δ ppm: 2.64 (s, 3 H), 7.46 (dd, 1 H), 7.70 (d, 1 H),
8.85 (dd, 1 H), 9.03 (dd, 1 H), 9.13 (d, 1 H).
N-(4-Methylpyridin-2-yl)pivalamide (11). To a solution of
4-methylpyridin-2-ylamine (7) (150 g, 1.40 mol) in DCM
(1.5 L) was added triethylamine (205 mL, 1.50 mol). Pivoyl
chloride (190 mL, 1.55 mol) was added dropwise over ∼1 h with
stirring under nitrogen and under cooling with an ice-water
bath. The resulting pale-yellow suspension was warmed to room
temperature and stirred overnight. The reaction mixture was
poured into water (500 mL) and saturated sodium bicarbonate
(400 mL). The clear orange-yellow organic layer was separated,
washed with saturated sodium bicarbonate (500 mL), satu-
rated brine (300 mL), dried over Na2SO4, filtered, and evapo-
rated to dryness. The resulting off-white solid product was
recrystallized from heptanes to afford pure 11 as pale-yellow
needles (220 g, 1.14 mol, 82% yield). 1H NMR (CDCl3) δ ppm:
1.32 (s, 9H), 2.35 (s, 3H), 6.85 (d, 1H), 7.96 (br s, 1H), 8.11
(m, 2H).
N-(5-Chloro-4-methylpyridin-2-yl)pivalamide (12). N-(4-Methyl-
pyridin-2-yl)pivalamide 11 (252 g, 1.31 mol) was suspended in
water (4 L). Na2HPO4 (468 g, 3.3 mol) was added, followed by
DCM (1.5 L). The mechanically stirred mixture was cooled to 0 °C,
and a gentle stream of chlorine gas was slowly passed through the
reaction mixture for ∼75 min, during which the reaction mixture
turned pale-yellow. The aqueous layer was separated and extracted
with DCM (2 ꢀ 500 mL). The combined organic layers were
washed with saturated brine, dried over Na2SO4, filtered, and
concentrated to dryness. The crude orange oil (∼350 g) was purified
by silica gel chromatography (heptanes/EtOAc, 9:1 to 3:1) to afford
[1,8]Naphthyridin-4-carbaldehyde (9). 4-Methyl[1,8]naphthyr-
idine (8) (0.743 g, 5.15 mmol) was dissolved in dioxane (32 mL)
and water (4 mL). Selenium dioxide (1.14 g, 103 mmol) was
added, and the solution washeatedto 80 °C for 1 h. Subsequently
more selenium dioxide (0.020 g, 1.80 mmol) was added and the
solution heated for 30 min and then allowed to cool to room
temperature. The solution was passed through a syringe filter to
remove solids and poured into a solution of water/saturated
aqueous NaHCO3 (1:1) (60 mL). The organic layer was sepa-
rated, and the remaining aqueouslayer extracted with DCM (2 ꢀ
100 mL and 1 ꢀ 50 mL). The organic fractions were combined,
dried over Na2SO4, filtered, and concentrated under vacuum.
The product was purified (silica gel chromatography using
MeCN/hexanes in 1:1 ratio) to yield the title compound
(0.63 g, 3.99 mmol, 77% yield). MS (ESIþ) for m/z 159 (M þ
H)þ. 1H NMR (CDCl3) δ ppm: 7.61 (dd, 1 H), 7.85 (d, 1 H), 9.16
(d, 1H), 9.37-9.39 (m, 2H), 10.39 (s, 1H).
1
12 as an orange solidifying oil (253 g, 1.11 mol, 86% yield). H
NMR (CDCl3): δ ppm: 1.32 (s, 9H), 2.39 (s, 3H), 7.98 (br s, 1H),
8.15 (s, 1H), 8.21 (s, 1H).
3-Chloro-4-methyl[1,8]naphthyridine (13). A solution of 12
(129 g, 0.57 mol) in diethyl ether (1.25 L) was cooled to
-65 °C. To the resulting yellow suspension was slowly added
a 1.5 M solution of tert-butyllithium (800 mL, 1.2 mol, 2.1
equiv). The resulting mixture was warmed to 15 °C when
3-dimethylaminopropenal (77.3 mL, 90% purity, 0.69 mol)
was added neat under the cooling of an ice-water bath. After
the mixture was stirred at room temperature overnight, the
solvents were removed under reduced pressure, and the resulting
yellow powder was treated with water (700 mL), followed by
concentrated HCl (325 mL) while cooling the mixture in ice. The
resulting dark-red reaction mixture was heated to 80 °C for 1 h,
cooled in ice, and basified to pH 8 with NaOH. The mixture was
extracted with DCM (4 ꢀ 1 L), and the combined organic layers
were dried over Na2SO4, filtered, and concentrated to dryness.
The crude product was purified by silica gel chromatography
(EtOAc eluant) to afforded 13 as a yellow solid (52.6 g, 0.295
1-[1,8]Naphthyridin-4-yl-ethanone (10). Step 1. [1,8]Naphthyr-
idin-4-carbaldehyde (9) (0.300 g, 1.90 mmol) was dissolved in a
mixture of anhydrous toluene (10 mL) and anhydrous THF
(10 mL). The solution was cooled to 0 °C. Methylmagnesium
bromide (1.62 mL of 1.4 M in THF/toluene) was added slowly
and the solution stirred for 1 h while warming to ambient
1
mol, 52% yield). H NMR (CDCl3) δ ppm: 2.78 (s, 3H), 7.55
(dd, 1H), 8.41 (dd, 1H), 9.02 (s, 1H), 9.11 (dd, 1H).

Article
3-Hydroxy[1,8]naphthyridine-4-carbaldehyde Hydrochloride
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23 7455
The yellow-green solution was cooled to -78 °C, and a 2.0 M
solution of MeI in MTBE (225 mL, 0.45 mol, 1.5 equiv) was
added dropwise, keeping Tint < -70 °C. The resulting cloudy
yellow solution was stirred for 1 h at -70 °C and next quenched
by addition of water (250 mL). The mixture was poured into
water (750 mL) and DCM (1.5 L). The aqueous layer was
extracted with DCM (3 ꢀ 0.5 L). The combined organic layers
were washed with saturated brine, dried over Na2SO4, filtered,
and concentrated to dryness to afford tert-butyl 5-methoxy-4-
methylpyridin-3-ylcarbamate as an orange-yellow sticky oil
Salt (14). Step 1. To an orange-red solution of 13 (14.4 g,
81 mmol) in 4:1 dioxane/water (200 mL) was added selenium
dioxide (28.3 g, 0.242 mol), and the resulting mixture was heated
at gentle reflux (Tintern = 90 °C) for 3 h. The resulting dark
mixture was cooled to room temperature and carefully poured
into saturated sodium bicarbonate (150 mL) and water
(150 mL). The mixture was treated with DCM (400 mL), filtered
over Celite, which was then rinsed with DCM. The combined
organic layers were dried over Na2SO4, filtered, and concen-
trated to dryness. The crude green product was purified by silica
gel chromatography (1:1 DCM/MeCN) to afford 3-chloro-
[1,8]naphthyridine-4-carbaldehyde as an orange solid (4.0 g,
1
(73 g, 0.30 mol, 100% yield). H NMR (CDCl3) δ ppm: 1.52
(s, 9H), 2.13 (s, 3H), 3.91 (s, 3H), 6.17 (br s, 1H), 8.01 (s, 1H),
8.58 (s, 1H).
1
21 mmol, 26% yield). MS (ESIþ) for m/z 192 (M þ H)þ. H
Step 2. To a cooled (0 °C) solution of tert-butyl 5-methoxy-4-
methylpyridin-3-ylcarbamate (70 g, 0.29 mol) in methanol
(450 mL) was added 4 N HCl in dioxane (450 mL, 1.8 mol) in
one portion. The resulting effervescent solution was stirred
overnight at room temperature. The solvents were removed
under reduced pressure, and the pale-yellow solid residue was
triturated with diethyl ether and dried in vacuo. This afforded
the HCl salt as a pale-yellow solid. The HCl salt was suspended
in water (250 mL), basified to pH 10 with 25% NaOH, and
extracted with DCM (3 ꢀ 250 mL). The combined organic layers
were washed with saturated brine, dried over Na2SO4, filtered,
and evaporated to dryness, giving 18 as an orange oil (33.7 g,
NMR (CDCl3) δ: 7.67 (dd, 1H), 9.18 (dd, 1H), 9.22 (s, 1H), 9.33
(dd, 1H), 10.84 (s, 1H).
Step 2. To a solution of 3-chloro[1,8]naphthyridine-4-carbal-
dehyde (23.4 g, 121 mmol) in methanol (400 mL) was added a
5.4 M solution of sodium methoxide in methanol (112 mL, 0.607
mol, 5 equiv), and the resulting mixture was heated at 80 °C for 1
h. After cooling, the dark red reaction mixture was evaporated
1
to ∼ /2 volume, acidified with acetic acid, and evaporated to
dryness. The orange residue was partitioned between EtOAc
(1 L) and saturated sodium bicarbonate (1 L). The aqueous layer
was extracted with EtOAc (1 L and 3 ꢀ 500 mL). The combined
organic layers were washed with saturated brine (1 L), dried
over Na2SO4, filtered, and concentrated to dryness to give
3-methoxy[1,8]naphthyridine-4-carbaldehyde as an orange-
brown solid (15.3 g, 81 mmol, 67% yield). MS (ESIþ) for m/z
1
0.24 mol, 84% yield). H NMR (CDCl3) δ ppm: 2.03 (s, 3H),
3.61 (br s, 2H), 3.87 (s, 3H), 7.71 (s, 1H), 7.76 (s, 1H).
3-Methoxy-4-methyl[1,5]naphthyridine (19). m-Nitrobenzene
sodium sulfonate (35 g, 0.16 mol) was added to methanesulfonic
acid (125 mL) at room temperature, followed by powdered
1
188 (M þ H)þ. H NMR (CDCl3): δ ppm: 4.26 (s, 3H), 7.57
FeSO4 7H2O (2.0 g, 7.2 mmol). This addition was slightly
(dd,1H), 9.03 (dd,1H), 9.25 (s, 1H), 9.43 (dd,1H), 10.85 (s, 1H).
Step 3. A mixture of 3-methoxy[1,8]naphthyridine-4-carbal-
dehyde (21.5 g, 114 mmol) and 6 N HCl was stirred at gentle
reflux (Tbath=155 °C) for 2 h. The volatiles were removed under
reduced pressure (<50 °C) and the resulting black solid
was dried in vacuo to give 14 (23.6 g, as crude HCl salt and
hydrate used directly in coupling to the 5). MS (ESIþ) for m/z
175 (M þ H)þ.
3
exothermic, causing Tint to rise to 27 °C. To the resulting mixture
was added 18 (33.7 g, 0.24 mol) in portions over ∼20 min, during
which Tint increased to 55-60 °C. After being stirred for 15 min,
the dark reaction mixture was heated to 125-130 °C, and
glycerol (50 mL; 0.68 mol) was added dropwise over ∼5 h. 1H
NMR of a sample (poured into saturated sodium bicarbonate,
extracted with EtOAc, dried over Na2SO4, filtered, evaporated)
indicated approximately 60% conversion of starting material to
the desired product. The mixture was reheated at 125 °C for 20 h,
after which 1H NMR of a sample indicated full conversion. The
dark reaction mixture was cooled to room temperature, diluted
with water (150 mL), and basified with 10 M NaOH, keeping
Tint < 10 °C. The dark mixture was next filtered over Celite,
rinsed with MTBE, and extracted with MTBE (4 ꢀ 300 mL).
The combined organic layers were washed with saturated brine,
dried over Na2SO4, filtered, and concentrated to dryness. This
afforded 19 as a yellow-brown crystalline solid (19.0 g, 0.109
3-Bromo-5-methoxypyridine (16). To a solution of 3,5-dibro-
mopyridine (100 g, 0.42 mol) in DMF (1.0 L) was added sodium
methoxide (5.4 M in methanol, 125 mL, 0.68 mol), and the
resulting mixture was heated to 50 °C for 5 h and cooled to room
temperature overnight. Water (4 L) was then added, and the
mixture was extracted with MTBE (3 ꢀ 1 L). The combined
organic layers were washed with saturated brine (2ꢀ), dried over
Na2SO4, filtered, and evaporated to dryness. This afforded
crude 16 as a yellow solidifying oil, recrystallized from pentane
1
(71.1 g, 0.38 mol, 90% yield). H NMR (CDCl3) δ ppm: 3.85
(s, 3H), 7.36 (m, 1H), 8.24 (m, 1H), 8.28 (m, 1H).
1
mol, 45% yield). H NMR (CDCl3) δ ppm: 2.71 (s, 3H), 4.11
tert-Butyl 5-Methoxypyridin-3-ylcarbamate (17). A mixture
of tert-butyl carbamate (67.9 g, 0.58 mol), Pd2(dba)3 CHCl3
(s, 3H), 7.50 (dd, 1H), 8.32 (dd, 1H), 8.81 (s, 1H), 8.95 (dd, 1H).
(3-Methoxy[1,5]naphthyridin-4-yl)methanol (20). Step 1.
Nitrogen was bubbled through a solution of purified 19 (note:
must be very pure) (10.6 g, 61 mmol) in CCl4 for 10 min.
N-Bromosuccinimide (freshly recrystallized from water; 16.2 g,
92 mmol) and dibenzoyl peroxide (75%, 5.9 g, 18.3 mmol) were
then added, and the resulting mixture was heated to gentle reflux
(Tint=75 °C) for 4 h. TLC/1H NMR indicated full conversion,
and the orange reaction mixture was cooled to 10-15 °C and
filtered to remove insoluble material. The filtrate was diluted
with DCM (500 mL) and washed with saturated sodium bicar-
bonate (750 mL). The aqueous layer was extracted with DCM (2
ꢀ 400 mL), and the combined organic layers were dried over
Na2SO4, filtered, and concentrated to dryness. This afforded (3-
methoxy[1,5]naphthyridin-4-yl)methyl bromide as a yellow so-
lid (14.7 g, 58 mmol, 95% yield). 1H NMR (CDCl3) δ ppm: 4.21
(s, 3H), 5.19 (s, 2H), 7.55 (dd, 1H), 8.35 (dd, 1H), 8.90 (s, 1H),
9.02 (dd, 1H).
3
(2.48 g, 2.4 mmol), xantphos (4.17 g, 7.2 mmol), and Cs2CO3
(220 g, 0.68 mol) was stirred under vacuum for 20 min. The flask
was filled with N2. This evacuation/backfill sequence was
repeated twice. Next, a solution of 16 (90.9 g, 0.48 mol) in dry,
degassed 1,4-dioxane (500 mL) was added, and the resulting
suspension was heated to 100 °C for 30 h (followed by TLC).
After cooling, the orange-red suspension was diluted with DCM
(1 L), filtered over Celite, and evaporated to dryness. The crude
orange solid product (130 g) was combined with that of a
0.87 mol batch to a total of 386 g and purified by silica gel
chromatography (1:1 heptanes/EtOAc) to afford pure 17 as a
pale-yellow solid (255 g, 1.14 mol, 84% for the combined yield).
1H NMR (CDCl3) δ ppm: 1.53 (s, 9H), 3.86 g (s, 3H), 6.55 (br s,
1H), 7.71 (br s, 1H), 7.95 (m, 1H), 7.99 (m, 1H).
3-Amino-5-methoxy-4-methylpyridine (18). Step 1. A solu-
tion of 17 (67.5 g, 0.30 mol) in THF (1.5 L) was cooled to
-70 °C. Then n-BuLi (2.5 M, 300 mL, 0.75 mol, 2.5 equiv) was
added dropwise, keeping Tint < -65 °C. The resulting mixture
was warmed to -25 °C and stirred at that temperature for 1 h.
Step 2. To an orange solution of (3-methoxy[1,5]-
naphthyridin-4-yl)methyl bromide (14.7 g, 58 mmol) from step
1 in DMF (325 mL) was added KOAc (42 g, 0.43 mol), and the

7456 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 23
Magee et al.
resulting mixture was heated to Tint=70-72 °C for 4 h until 1H
NMR/TLC indicated full conversion. DMF was evaporated
under reduced pressure, and the dark residue was partitioned
between water (400 mL) and EtOAc (400 mL), filtered, sepa-
rated, and the aqueous layer was extracted with EtOAc (3 ꢀ
400 mL). The combined organic layers were washed with
saturated brine, dried over Na2SO4, filtered, and concentrated
to dryness to afford crude acetate as a dark oil (12.8 g, 55 mmol,
95%), which was then dissolved in methanol (500 mL). K2CO3
(40 g, 0.29 mol) was added, and the resulting mixture was stirred
at room temperature overnight. The mixture was filtered to
remove insoluble material and concentrated under reduced
pressure (Tbath=25-30 °C). The residue was diluted with water
(400 mL) and extracted with EtOAc (4 ꢀ 250 mL). The
combined organic layers were washed with saturated brine,
dried over Na2SO4, filtered, and concentrated to dryness. The
product was combined with another batch (from starting from
38.5 mmol (3-methoxy[1,5]naphthyridin-4-yl)methyl bromide)
and the composite crude material purified by silica gel chroma-
tography (EtOAc/heptane, 1:1 to 9:1), affording 20 as a pale-
yellow solid (10.7 g, 56 mmol, 63% yield). 1H NMR (CDCl3) δ
ppm: 4.12 (s, 3H), 5.31 (d, 2H), 5.78 (br t, 1H), 7.54 (dd, 1H),
8.38 (dd, 1H), 8.86 (s, 1H), 8.87 (dd, 1H).
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3-Hydroxy[1,5]naphthyridine-4-carbaldehyde (22). To a solu-
tion of 20 (2.0 g, 10.5 mmol) in EtOAc (175 mL) was added
2-iodoxybenzoic acid (8.8 g, 32 mmol), and the resulting
suspension was heated to gentle reflux for 3.5 h (Tint=76 °C).
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the mixture was cooled to room temperature overnight. The
mixture was cooled to 0 °C, filtered over a P4 glass filter, and
rinsed with cold EtOAc. The filtrate was concentrated in vacuo
to afford a yellow solid. 1H NMR analysis revealed the product
to be a mixture of desired intermediate aldehyde (21) and
reagent-derived benzoic acid residues. Several attempts to
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(s, 1H).
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Acknowledgment. We thank Jian Lin and Chris Foti for
performing compound stability assessments, and Tom
O’Connell for NMR spectroscopy studies. We also thank
Karen Leach and Seva Kostrubsky for performing in vitro
safety assays, and finally we thank Maik Schuler and Bill
McConnell for assisting with the interpretation of safety data.
(17) Mayhew, B. S.; Jones, D. R.; Hall, S. D. An in Vitro Model for
Predicting in Vivo Inhibition of Cytochrome P450 3A4 by Meta-
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2000, 28, 1031–1037.
Supporting Information Available: Methods for measurement
of MIC, ER, AO, TDI; in vivo efficacy data (RTI, OM); and
single crystal X-ray data for 6q. This material is available free of
charge via the Internet at http://pubs.acs.org.
(18) Ketek (telithromycin) product label.
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Macrolide-Resistant and -Susceptible Respiratory Pathogens. J. Med.
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