Conformational constraint in oxazolidinone antibacterials. Synthesis and structure-activity studies of (azabicyclo[3.1.0]hexylphenyl)oxazolidinones

J. Med. Chem. 2005, 48, 5009-5024

5009

Conformational Constraint in Oxazolidinone Antibacterials. Synthesis and

Structure-Activity Studies of (Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Adam R. Renslo,* Priyadarshini Jaishankar, Revathy Venkatachalam, Corinne Hackbarth, Sara Lopez,

Dinesh V. Patel, and Mikhail F. Gordeev*

Discovery Research, Vicuron Pharmaceuticals, 34790 Ardentech Ct, Fremont, California 94555

Received March 4, 2005

The oxazolidinones are a new class of synthetic antibacterials effective against a broad range

of pathogenic Gram-positive bacteria, including multi-drug-resistant strains. Linezolid is the

first drug from this class to reach the market and has become an important new option for the

treatment of serious infections, particularly those caused by methicillin-resistant Staphylococcus

aureus (MRSA) and vancomycin-resistant Enteroccocus faecium (VRE). In the search for novel

oxazolidinones with improved potency and spectrum, we have prepared and evaluated the

antibacterial properties of conformationally constrained analogues in which the morpholine

ring of linezolid is replaced with various substituted azabicyclo[3.1.0]hexyl ring systems. Several

classes of azabicyclic analogues were identified with activity comparable or superior to that of

linezolid. These include analogues bearing hydroxyl, amino, amido, or carboxyl groups on the

azabicyclic ring. The azabicyclic acid analogue 50 was 4 times more potent than linezolid against

key Gram-positive and fastidious Gram-negative pathogens (S. aureus, Streptococcus pneu-

moniae, and E. faecalis MICs e 1 µg/mL; Haemophilus influenzae MIC ) 4 µg/mL).

Introduction

displays more modest activity against the fastidious

Gram-negative respiratory tract pathogens Haemphilus

influenzae and Moraxella catarrhalis (MIC₉₀) 16 and

4 µg/mL, respectively⁵) and is not indicated for use in

infections caused by these bacteria. Not surprisingly,

significant efforts have been mounted by several groups

to broaden the antibacterial spectrum of the oxazolidi-

nones in the hope of expanding the utility of this novel

class of antibacterials.¹²For example, a recent report

described (azolylphenyl)oxazolidinones that possess im-

proved activity against H. influenzae and M. catarrha-

lis.¹³

The emergence of bacterial pathogens resistant to

existing antimicrobials is a problem of increasing

significance^1-4that has attracted the attention of the

medical community and pharmaceutical scientists. The

oxazolidinones,^5-7exemplified by linezolid (1) and ep-

As a part of our own efforts to develop oxazolidinone

agents with improved potency and antibacterial spec-

trum, we chose to examine the effects of conformational

constraint as applied to the saturated 4′-heterocyclic

ring (C-ring) of phenyloxazolidinones. The azabicyclo-

[3.1.0]hexyl ring system, in particular, attracted our

attention as a constrained bicyclic isostere of the pip-

erazine C-ring of eperezolid (2). We expected that this

structural modification would impart a rigidity in the

aliphatic C-ring more characteristic of flat aryl or

heteroayl C-ring oxazolidinones (e.g., azolylphenyl),

many of which exhibit improved potency and an ex-

panded antimicrobial spectrum. Herein, we disclose our

studies on the synthesis and antibacterial activity of a

new class of oxazolidinones featuring substituted

azabicyclo[3.1.0]hexyl C-rings.¹⁴

erezolid (2), comprise a new class of synthetic antibac-

terials with activity against a broad range of Gram-

positive pathogens, including methicillin-resistant

Staphylococcus aureus (MRSA) and Staphylococcus epi-

dermidis (MRSE) and vancomycin-resistant Enterocco-

cus faecium (VRE). The oxazolidinones inhibit bacterial

protein synthesis at the initiation phase via binding to

23S RNA of the 50S ribosomal subunit of prokaryotes.^8-11

This novel mechanism of action is not shared with any

known antibiotics of natural or synthetic origin, so

oxazolidinones do not exhibit cross-resistance with any

of the existing classes of antibacterials.

Linezolid (1) is the first oxazolidinone to receive

regulatory approval and was launched by Pharmacia

in April 2000. Linezolid exhibits an antimicrobial

spectrum that encompasses a broad range of susceptible

and multi-drug-resistant Gram-positive cocci. The drug

Chemistry

Substituted Azabicyclic C-Rings. The preparation

of (azabicyclohexylphenyl)oxazolidinone antibacterials

(3) is illustrated retrosynthetically in Scheme 1. The

oxazolidinone ring (A-ring) is installed at a late stage

of the synthesis using known synthetic protocols.¹⁵

Thus, reaction of an N-aryl carbamate 4 with (S)-acetic

acid 2-acetylamino-1-chloromethylethyl ester¹⁶gener-

* To whom correspondence should be addressed. A.R.: tel, 510-739-

3023; e-mail, arenslo@vicuron.com. M.G.: tel, 510-739-3013; e-mail,

mgordeev@vicuron.com.

Published on Web 06/22/2005

5010 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

Scheme 1

Scheme 3^a

^aReagents: (a) CHBr₃, aq NaOH, CH₂Cl₂, BnEt₃NCl, 50%; (b)

ⁿBuLi, THF, catecholborane, -90 to 50 °C, then H₂O₂, NaOH, 15%

overall.

mediates 9 (exo) and 10 (endo) in two steps (ester

hydrolysis followed by Curtius rearrangement). The

cyclopropanol 12 was prepared from the dibromocyclo-

propane 11 by stereocontrolled conversion to the exo-

cyclopropylborane followed by oxidation with alkaline

hydrogen peroxide (Scheme 3).¹⁹The parent 3-azabicyclo-

[3.1.0]hexane (i.e., 5, Z ) H) was prepared using the

established procedure.²⁰

Scheme 2^a

With the desired bicyclic building blocks 7-12 in

hand, the stage was set for their coupling to fluoroni-

trobenzenes 6a or 6b and subsequent elaboration to

oxazolidinone analogues. The synthesis of azabicyclic

acid analogues 15a and 15b (Scheme 4) is illustrative

of the general protocol used for the synthesis of

(azabicyclo[3.1.0]hexylphenyl)oxazolidinone antibacteri-

als. Removal of the benzyloxycarbonyl group in 7b was

accomplished by hydrogenolysis over Pearlman’s cata-

lyst in methanol. The resulting secondary amine was

then reacted with 3,4-difluoronitrobenzene (6a) or 3,4,5-

trifluoronitrobenzene (6b) in DMF or acetonitrile con-

taining N,N-diisopropylethylamine to provide nitroare-

ne intermediates 13. Reduction of the nitro function was

accomplished under mild conditions by heating with

ammonium chloride and iron metal in ethanol-water.

The resulting anilines were converted directly to benz-

yloxy carbamate (Cbz) derivatives 14 (CbzCl in pyridine/

dichloromethane). Introduction of the oxazolidinone ring

was accomplished in a single step by reaction with

lithium tert-butoxide, (S)-acetic acid 2-acetylamino-1-

chloromethyl-ethyl ester,¹⁶and methanol in DMF. A

final deprotection step (trifluoroacetic acid in dichlo-

romethane) then provided the desired azabicyclic acid

analogues 15a and 15b.

Analogous synthetic procedures were used to convert

the other azabicyclic building blocks (9-12) to oxazoli-

dinone analogues (Schemes 5-7). Thus, azabicyclic

amine analogues 18a and 18b were prepared as shown

in Scheme 5. The bicyclic intermediate 9 was elaborated

to nitro aromatic intermediates 16 and then to the Cbz-

protected anilines 17. The oxazolidinone ring was

installed as before and the 6-amino group unmasked

with HCl in dioxane to provide the azabicyclic amine

analogues 18a and 18b as hydrochloride salts. The

corresponding endo diastereomer 19 was prepared in

an analogous fashion but starting with the endo bicyclic

amine 10.

^aReagents: (a) N₂CHCO₂R, Rh₂(OAc)₄, CH₂Cl₂, 25-35%; (b)

NaOH, MeOH; (c) DPPA, Et₃N, tBuOH, reflux, 50% for two steps.

ates the oxazolidinone ring in a single step and with the

privileged acetamidomethyl side chain disposed in the

biologically active (S)-configuration. Analogues bearing

other amide side chains at C-5 are prepared using a

multistep procedure, the first step involving reaction of

the N-aryl carbamate 4 with (R)-(-)-glycidyl butyrate.

The resulting hydroxymethyl-substituted oxazolidinone

intermediate is then elaborated to generate other C-5

side chain variants.¹⁷The N-aryl carbamate intermedi-

ates 4 are derived from the corresponding nitroarenes,

which are in turn produced by nucleophilic aromatic

substitution reactions between the bicyclic heterocycles

5 and fluoronitroarenes 6. The choice of fluoronitroarene

starting material (6a or 6b) governs the extent of B-ring

fluorination in the final compounds.

The oxazolidinone analogues contemplated here re-

quired the preparation of bicyclo[3.1.0]hexylamines

substituted at the 6-position with suitably protected

amine, alcohol, or carboxylic acid functionality. Prepa-

ration of the amine and carboxylic acid intermediates

(7-10) was accomplished according to the literature

procedure¹⁸as illustrated in Scheme 2. Thus, rhodium-

catalyzed cyclopropanation of benzyl 3-pyrroline-1-car-

boxylate with ethyldiazoacetate or tert-butyldiazoacetate

provided the exo cycloadducts 7a (R ) Et) or 7b (R )

t-Bu) in modest yield after chromatographic separation

from smaller amounts of the endo diastereomers (8a or

8b) and unreacted starting material. The tert-butyl ester

7b was used to prepare carboxylic acid and amide

analogues, while the ethyl esters 7a (exo) and 8a (endo)

were further converted to the protected amine inter-

For the preparation of cyclopropanol analogue 22

(Scheme 6), protection of the hydroxy function as a tert-

butyldimethylsilyl ether was required prior to introduc-

tion of the oxazolidinone ring (i.e., via intermediates 20

and 21). Cleavage of the silyl ether in the final step (HF

in AcOH/THF) provided the desired hydroxy analogue

22. The unsubstituted bicyclic analogues 25a and 25b

were prepared from azabicyclo[3.1.0]hexane²⁰following

the standard protocol via intermediates 23 and 24

(Scheme 7).

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5011

Scheme 4^a

^aReagents: (a) H₂, Pd(OH)₂/C, MeOH, quant.; (b) 6a or 6b, DIEA, DMF, 50 °C, 80-90%; (c) Fe, NH₄Cl, EtOH-H₂O, reflux; (d) CbzCl,

pyridine, CH₂Cl₂, 69% for two steps; (e) LiOtBu, MeOH, DMF, (S)-acetic acid 2-acetylamino-1-chloromethylethyl ester; (f) TFA, CH₂Cl₂,

72% for two steps.

Scheme 5^a

^aReagents: (a) H₂, Pd(OH)₂/C, MeOH, quant.; (b) 6a or 6b, DIEA, DMF, 50 °C, 84-93%; (c) Fe, NH₄Cl, EtOH-H₂O, reflux; (d) CbzCl,

pyridine, CH₂Cl₂, 77-86% for two steps; (e) LiOtBu, MeOH, DMF, (S)-acetic acid 2-acetylamino-1-chloromethylethyl ester; (f) HCl, dioxane

65% for two steps.

Scheme 6^a

Scheme 7^a

^aReagents: (a) H₂, Pd(OH)₂/C, MeOH, quant.; (b) 3,4,5-trifluo-

ronitrobenzene, DIEA, DMF, 50 °C, 91%; (c) tBuMe₂SiCl, imida-

zole, CH₂Cl₂, 88%; (d) Fe, NH₄Cl, EtOH-H₂O, reflux; (e) CbzCl,

pyridine, CH₂Cl₂, 70% for two steps; (f) LiOtBu, MeOH, DMF, (S)-

acetic acid 2-acetylamino-1-chloromethylethyl ester, 73%; (g) HF,

AcOH, THF-H₂O, 85%.

^aReagents: (a) 6a or 6b, DIEA, DMF, 50 °C, 82%; (b) Fe,

NH₄Cl, EtOH-H₂O, reflux; (c) CbzCl, pyridine, CH₂Cl₂, 79-87%

for two steps; (d) LiOtBu, MeOH, DMF, (S)-acetic acid 2-acetyl-

amino-1-chloromethyl-ethyl ester, 62-70%.

ester of 15b (Scheme 8). Likewise, substituted amino

bicyclic analogue 18b could be further elaborated to

amide, sulfonamide, or urea analogues (36-40) using

standard methodology (Scheme 9).

C-5 Amidomethyl Modifications. The synthesis of

analogues bearing C-5 side chains other than acetami-

domethyl is illustrated in Schemes 10 and 11. Thus,

Further elaboration of acid and amine analogues

15a-b and 18a-b provided amide, sulfonamide, and

urea analogues. Hence, substituted carboxamide ana-

logues 26-35 were prepared from the carboxylic acid

analogue 15b directly using HATU-mediated coupling

reactions or via amidation of the pentafluorophenyl

5012 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

Scheme 8^a

Scheme 11^a

^aReagents: (a) CF₃C(dO)OC₆F₅, pyridine, DMF; (b) R¹R²NH,

DIEA, DMF; (c) R¹R²NH, HATU, DIEA, DMF; (d) H₂, Pd/C, EtOH.

^aReagents: (a) LiHMDS, DMF, (R)-glycidyl butyrate, 87%; (b)

MeSO₂Cl, Et₃N, CH₂Cl₂; (c) NaN₃, DMF, 70 °C; (d) Ph₃P, THF,

then H₂O, 40 °C; 86% for three steps; (e) (RC(dO))₂O or

CHF₂C(dO)OEt, Et₃N or pyridine; (f) TFA, CH₂Cl₂.

Scheme 9^a

Results and Discussion

The azabicyclic phenyloxazolidinone analogues de-

scribed herein were evaluated for antimicrobial activity

against a panel of Gram-positive and -negative bacteria

(Tables 1-4). All of the oxazolidinone analogues sub-

mitted for biological assay were g95% pure as judged

1

by H NMR and HPLC analysis (see Supporting Infor-

mation). This level of purity is considered more than

sufficient for meaningful SAR analysis, given the inher-

ent variability of standard broth microdilution assay

methods.²¹

^aReagents: HCOOH, Ac₂O (for 36); Ac₂O, Et₃N (for 37),

AcOCH₂CO₂H, HATU, DIEA, then LiOH (for 38); MeSO₂Cl, Et₃N,

DMF (for 39); PhNCO, Et₃N, NMP (for 40).

Scheme 10^a

The first compounds evaluated for antibacterial activ-

ity were the simple carboxyl (15), amino (18), hydroxyl

(22), and unsubstituted (25) azabicyclic analogues shown

in Table 1. Quite surprisingly, the free carboxyl- and

amino-substituted analogues 15 and 18 exhibited excel-

lent antimicrobial activity, better in some cases than

linezolid itself. Fluorination of the B-ring exerted a

potentiating effect, particularly within the azabicyclic

acid series, where bis-fluoro B-ring analogue 15b was

4-fold more potent than its monofluoro congener 15a.

This remarkable tolerance of either acidic or basic

functionality was quite unexpected in view of previous

oxazolidinone SAR. Particularly relevant to this case are

earlier findings that oxazolidinone analogues bearing

an acidic tetrazole substituent were devoid of antibacte-

rial activity while nonacidic N-methyltetrazole deriva-

tives were active.²²To the best of our knowledge,

analogues such as 15 represent the first active antimi-

crobial oxazolidinones featuring an acidic carboxylic acid

function.²³The presence of carboxylic acid functionality

in a lead molecule is advantageous, as it permits the

rapid generation of new analogues (vide infra) and can

be used to alter solubility and membrane permeability

(via ester prodrugs, alternate salt forms, etc.).

A broader range of activities was observed for ana-

logues 15-25 against the Gram-negative pathogens H.

influenzae and Esherichia coli (Table 1). A clear SAR

trend is evident in the case of H. influenzae, with

hydrophilic carboxyl (15), amino (18), and hydroxyl (22)

analogues displaying better activity than more lipophilic

analogues such as 25a-b. B-ring fluorination was

generally beneficial, with bis-fluoro analogues 15b and

18b exhibiting H. influenzae activity consistently su-

perior to that of the monofluoro comparators and

^aReagents: (a) LiHMDS, DMF, (R)-glycidyl butyrate, 81%; (b)

MeSO₂Cl, Et₃N, CH₂Cl₂; (c) NaN₃, DMF, 70 °C; (d) Ph₃P, THF,

then H₂O, 40 °C; 56% for three steps; (e) (RC(dO))₂O or

CHF₂C(dO)OEt, Et₃N or pyridine; (f) HCl, dioxane.

reaction of 17b with lithium hexamethyldisilylamide

and (R)-glycidyl butyrate produced intermediate 41

bearing a hydroxymethyl side chain at C-5. This mate-

rial was elaborated via the azide to a C-5 aminomethyl

intermediate (42) that was then acylated under stan-

dard conditions to provide dihaloacetamides, propiona-

mides, and cyclopropyl amide intermediates. A final

deprotection step employing hydrogen chloride in diox-

ane then provided the desired C-5 amide variants 43-

46. An analogous synthetic route was employed to

access C-5 amide analogues in the azabicyclic acid

series, starting with 14b and proceeding through the

hydroxymethyl and aminomethyl intermediates 47 and

48 (Scheme 11). Cleavage of the tert-butyl ester with

trifluoroacetic acid in dichloromethane provided the C-5

amide variants 49-51.

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5013

Table 1. In Vitro Antibacterial Activity of Selected (Azabicyclo[3.1.0]hexylphenyl)oxazolidinone Analogues

minim um inhibitory concentration (µg/mL)

compd

R

X

S.a.^a

S.a.^b

S.e.^c

S.p.^d

E.f.^e

H.i.^f

E.c.^g

1

-

H

F

H

F

H

F

2-4

8

2-4

4

1

0.5-1

2-4

4

8-16

16

>64

32

16-32

>64

15a

15b

18a

18b

19^h

22

COOH

NH₂

OH

2

4

2

1

0.5-1

1

0.5

1

0.5

1

4-8

8-16

8

2-4

8

2-4

2

4

2-4

4

1-2

2

0.5-1

4

1-2

4

1-2

2

0.5-1

1

32

16

25a

25b

H

32

64

^aMethicillin-susceptible S. aureus UC9213. ^bMethicillin-, ciprofloxacin-, rifampin-, imipenem-resistant S. aureus UC12673. ^cMethicillin-

resistant S. epidermidis UC12084. ^dPenicillin-susceptible S. pneumoniae UC9912. ^eE. faecalis UC9217. ^fAmpicillin-reisitant H. influenzae

UC30063. ^gE. coli UC6674. ^hEndo diastereomer of 18b.

Table 2. In Vitro Antibacterial Activity of Selected (Azabicyclo[3.1.0]hexylphenyl)oxazolidinone Analogues

minimum inhibitory concentration (µg/mL)

compd

R

S.a.^a

S.a.^b

S.e.^c

S.p.^d

E.f.^e

H.i.^f

E.c.^g

1

-

2-4

4

2-4

4

1

0.5-1

2-4

2

8-16

32

>64

26

27

28

29

30

36

37

38

39

40

NH₂C(O)-

2

1

MeNHC(O)-

Me₂NHC(O)-

BnONHC(O)-

HONHC(O)-

HC(O)NH-

2

1

0.5

1

16

4

2

4

64

4

2

1

2

>64

32

4

2

1

2

2-4

4

2-4

4

1

0.5-1

2

32

MeC(O)NH-

HOCH₂CONH-

MeSO₂NH-

1-2

4

1

2

1

2-4

8

64

16

4

8

16

4

64

1

2

32

PhNHC(O)NH-

>64

^aMethicillin-susceptible S. aureus UC9213. ^bMethicillin-, ciprofloxacin-, rifampin-, imipenem-resistant S. aureus UC12673. ^cMethicillin-

resistant S. epidermidis UC12084. ^dPenicillin-susceptible S. pneumoniae UC9912. ^eE. faecalis UC9217. ^fAmpicillin-reisitant H. influenzae

UC30063. ^gE. coli UC6674.

linezolid itself. Hydroxy analogue 22 is structurally the

most similar to linezolid and so it was no surprise that

the compound exhibited antibacterial properties almost

identical to its progenitor. Amino-substituted analogues

18a-b were the only oxazolidinones in this study to

display appreciable activity against the Gram-negative

bacterium Escherichia coli.

The oxazolidinone analogue 19 features a 6-endo-

substituted azabicyclic ring and as a result its 6-amino

group is positioned quite differently than in the dia-

stereomeric 6-exo-azabicyclic analogue 18b. Comparison

of these two analogues in repeated antibacterial screens

revealed the inferiority of the endo configuration, with

19 consistently demonstrating 2-fold poorer Gram-

positive activity than 18b and an even greater deficiency

in the case of H. influenzae. From a practical perspec-

tive, this result was fortuitous, since the exo cycloadduct

7 (Scheme 2) is formed preferentially in the initial

cyclopropanation reaction leading ultimately to oxazo-

lidinone analogues such as 15 and 18. Thus, both

biological and chemical considerations led us to focus

our subsequent efforts exclusively on analogues pos-

sessing the exo configuration in the azabicyclic C-ring.

After being pleasantly surprised by the potency of the

parent azabicyclic acid and amine analogues, we turned

our attention back to the synthetic targets that initially

interested us, namely various amide, urea, and sulfona-

mide analogues derived from azabicyclic acid 15b and

azabicyclic amine 18b. Table 2 presents antibacterial

activity for a number of these derivatives. When com-

pared to the parent amine analogue 18b, the corre-

sponding acetamide (37), sulfonamide (39), and phenyl

urea (40) analogues were less potent, particularly

against the Gram-negative strains. Among the azabi-

cyclic amine-derived analogues, only the formamide 36

and sulfonamide 39 displayed Gram-positive activity

approaching that of the parent amine 18b. Against the

Gram-negative strains, all of the analogues were much

less potent than 18b. Especially surprising was the poor

activity of 38 (S. aureus MIC ) 16 µg/mL), considering

5014 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

Table 3. In Vitro Antibacterial Activity of 6-Carboxamide-Substituted (Azabicyclo[3.1.0]hexylphenyl)oxazolidinone Analogues

minimum inhibitory concentration (µg/mL)

compd

R

S.a.^a

S.a.^b

S.e.^c

S.p.^d

E.f.^e

H.i.^f

1

-

2-4

2

2-4

1

0.25

1

0.5

0.5-1

0.13

0.5

2-4

0.5

1

8-16

>64

31

32

33

34

35

1,3-thiazol-2-yl

6-methoxypyridin-3-yl

2-furylmethyl

pyridin-2-ylmethyl

1,3-benzodioxol-5-yl

2

0.5

1

4

0.5

1

^aMethicillin-susceptible S. aureus UC9213. ^bMethicillin-, ciprofloxacin-, rifampin-, imipenem-resistant S. aureus UC12673. ^cMethicillin-

resistant S. epidermidis UC12084. ^dPenicillin-susceptible S. pneumoniae UC9912. ^eE. faecalis UC9217. ^fAmpicillin-reisitant H. influenzae

UC30063.

Table 4. In Vitro Antibacterial Activity of (Azabicyclo[3.1.0]hexylphenyl)oxazolidinone Analogues with Various C-5 Amide

Substituents

minimum inhibitory concentration (µg/mL)

compd

R

X

Y

S.a.^a

S.a.^b

S.e.^c

S.p.^d

E.f.^e

H.i.^f

1

-

2-4

32

4

2-4

32

4

1

0.5-1

0.5

8

0.5-1

1

0.5

1

1-2

1

0.5

2-4

1-2

32

2-4

2

8-16

18b

43

44

45

46

15b

49

50

51

NH₂

H

0.5-1

16

8

NH₂

cyclopropyl

Me

F

Cl

H

Me

F

Cl

>64

NH₂

H

F

1-2

2

8-16

NH₂

4

2

8

4

NH₂

Cl

H

F

4

2

COOH

2

1

0.5-1

1-2

0.5

1

0.5

4-8

8

4

2

1

0.5

Cl

1

0.5

^aMethicillin-susceptible S. aureus UC9213. ^bMethicillin-, ciprofloxacin-, rifampin-, imipenem-resistant S. aureus UC12673. ^cMethicillin-

resistant S. epidermidis UC12084. ^dPenicillin-susceptible S. pneumoniae UC9912. ^eE. faecalis UC9217. ^fAmpicillin-reisitant H. influenzae

UC30063.

that the glycolyl side chain is often reported to impart

improved antibacterial potency.²⁴This finding high-

lights the distinct SAR profile of 6-aminoazabicyclic

C-ring analogues as compared to their piperazine C-ring

progenitors.

analogues incorporating larger aromatic and heterocy-

clic substituents. The antibacterial activities of these

extended amide analogues are shown in Table 3. These

analogues (31-35) displayed quite similar Gram-posi-

tive activities, comparable and in many cases superior

to that of linezolid. None of the analogues however

exhibited even a hint of activity against H. influenzae,

so this approach was not explored further.

Instead, we focused our attention on the crucial C-5

side chain of the oxazolidinone pharmacophore. Previous

studies have identified various cyclic and acyclic sur-

rogates for the privileged acetamidomethyl side

chain.^25-31In the case at hand, we chose to replace the

acetamide group of linezolid with amides derived from

propionic, cyclopropylcarboxylic, dichloroacetic, or dif-

luoroacetic acids. The resulting analogues were tested

for antimicrobial activity, and the results are presented

in Table 4. In general, these C-5 amide modifications

were well-tolerated; only the cyclopropyl amide 43 was

significantly less potent than its acetamide congener.

The amide and hydroxamate compounds 26-30 (Table

2) are derivatives of the azabicyclic acid analogue 15b.

As in the amine series, the antibacterial activity of these

analogues was inferior to that of the parent acid,

although some clear SAR trends were apparent. Among

the N-alkyl amides, the N-methyl analogue 27 was the

best, exhibiting 2-fold better activity than unsubstituted

amide 26 and a 4-fold improvement over N,N-dimethyl

amide analogue 28. With a pK_abetween that of an acid

and a carboxamide, the hydroxamic acid analogue 30

displayed antibacterial activity much more similar to

that of the carboxamide 26 than the acid 15b. Surpris-

ingly, the corresponding benzyl hydroxamate 29 was

equipotent to 30 against the Gram-positive panel. This

observation prompted us to consider additional amide

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5015

of standard broth microdilution assay methods (generally

considered accurate to within one dilution).

Propionamide analogues 44 and 49 had potencies and

spectrum comparable to their acetamide congeners. The

dihaloacetamide modification proved the most beneficial

with respect to potency, and a notable potentiating effect

was observed when these side chain types were com-

bined with the azabicyclic acid C-ring subtype. Thus,

difluoroacetamide 50 and dichloroacetamide 51 dis-

played exceptional activity against key Gram-positive

pathogens (MICs e 0.5-1 µg/mL) and also exhibited

respectable activity against the fastidious Gram-nega-

tive bacterium H. influenzae (MIC ) 4 µg/mL).

6,6-Dibromo-3-azabicyclo[3.1.0]hexane-3-carboxylic

Acid Benzyl Ester (11). A solution of bromoform (0.94 mL,

10.8 mmol) in 5 mL of dichloromethane was added over 1.5 h

to a stirred solution of benzyl 3-pyrroline-1-carboxylate (1.77

mL, 9.8 mmol) and benzyltriethylammonium chloride (0.055

g, 0.025 mmol) in 1:1 dichloromethane-50% aq NaOH (60 mL).

The black solution was stirred for 18 h at room temperature

and then diluted with dichloromethane and H₂O. The layers

were separated, and the organic phase was washed with satd

NH₄Cl and brine, dried (MgSO₄), filtered, and concentrated.

The crude product was purified by column chromatography

(0-20% ethyl acetate-hexane) to afford 6,6-dibromo-3-aza-

bicyclo[3.1.0]hexane-3-carboxylic acid benzyl ester. Yield: 1.83

Conclusions

1

g (50%). H NMR (300 MHz, CDCl₃): 2.43 (m, 2H), 3.66 (m,

In conclusion, we have identified a novel class of

conformationally constrained (azabicyclo[3.1.0]hexyl-

phenyl)oxazolidinones. The SAR profile of this new class

is quite unusual in that free amino- and carboxyl-

substituted analogues are more potent than their cor-

responding amido derivatives. A remarkable diversity

of functionality is tolerated at C-6 of the azabicyclic

C-ring, including the first potent antibacterial oxazoli-

dinones possessing an acidic, carboxylic acid function

(e.g., compounds 15a,b and 49-51). Nearly all of the

analogues examined exhibited therapeutically useful

activity against Gram-positive pathogens, whereas ac-

tivity against the Gram-negative pathogen H. influenzae

was observed only for analogues bearing compact hy-

drophilic groups at C-6 of the azabicyclic C-ring. The

incorporation of an additional fluorine atom in the

phenyl B-ring was found to be generally beneficial.

Representatives of this new class possess improved

potency and an expanded antibacterial spectrum as

compared to linezolid. Specifically, the new compounds

15b, 46, 50, and 51 are more potent than linezolid

against the key fastidious Gram-negative pathogen H.

influenzae and retain good activity against clinically

relevant Gram-positive bacteria. These analogues merit

further evaluation. On whole, these findings augur well

for the development of second-generation oxazolidinones

with an expanded antimicrobial spectrum encompassing

important Gram-negative pathogens.

4H), 5.11 (s, 2H), 7.33 (m, 5H).

(1r,5r,6r)-6-Hydroxy-3-azabicyclo[3.1.0]hexane-3-car-

boxylic Acid Benzyl Ester (12). n-BuLi (1.64 mL of a 1.6 M

solution, 2.62 mmol) was added dropwise over 1 h to a cooled

(-95 °C) solution of 6,6-dibromo-3-azabicyclo[3.1.0]hexane-3-

carboxylic acid benzyl ester (0.85 g, 2.28 mmol) in THF (20

mL). After 10 min, a solution of catechol borane (4.56 mL of a

1.0 M solution, 4.56 mmol) was added dropwise over 30 min.

The reaction mixture was allowed to warm slowly to room

temperature and then heated at 50 °C for 16 h. After cooling

to 0 °C, the reaction mixture was treated with 50% H₂O₂(0.53

mL, 9.12 mmol) and 2.5 M NaOH (2.7 mL, 6.84 mmol) and

stirred for 18 h. The reaction was quenched by addition of satd

Na₂S₂O₃and 2.5% NaHCO₃. The aqueous solution was con-

centrated to remove THF and then extracted with three

portions of ethyl acetate. Combined organic phases were

washed with satd Na₂S₂O₃and brine, dried (MgSO₄), filtered,

and concentrated. The crude product was purified by column

chromatography (20-50% ethyl acetate-hexane) to afford

(1R,5R,6R)-6-hydroxy-3-azabicyclo[3.1.0]hexane-3-carboxylic acid

benzyl ester. Yield: 0.076 g (15%). ¹H NMR (300 MHz,

CDCl₃): 1.73 (m, 2H), 1.92 (s, 1H), 3.22 (s, 1H), 3.46 (m, 2H),

3.63 (m, 2H), 5.09 (s, 2H), 7.32 (m, 5H).

(1r,5r,6r)-3-(2-Fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hexane-6-carboxylic Acid tert-Butyl Ester (13a). Diiso-

propylethylamine (2.3 mL, 13.2 mmol) and 3,4-difluoroni-

trobenzene (1.2 g, 10.8 mmol) were added to a solution of

(1R,5R,6R)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-bu-

tyl ester¹⁸(2.2 g, 12.0 mmol) in acetonitrile (20 mL). The

mixture was heated at reflux for 4 h and then cooled to room

temperature. The solution was concentrated; diluted with ethyl

acetate (75 mL); washed with 0.1 M HCl, satd NaHCO₃, and

brine; and dried (MgSO₄). The mixture was filtered and

concentrated to give (1R,5R,6R)-3-(2-fluoro-4-nitrophenyl)-3-

azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl ester as a

Experimental Section

General. ¹H NMR spectra were recorded on a Varian

Gemini 2000 300 MHz spectrometer. Chemical shifts are

reported in δ units (ppm) relative to TMS as an internal

standard. Coupling constants (J) are reported in hertz (Hz).

All reagents and solvents were purchased from Aldrich

Chemical or Acros Organics and used as received unless

otherwise indicated. Air and/or moisture sensitive reactions

were carried out under a nitrogen atmosphere in oven-dried

glassware using anhydrous solvents from commercial suppli-

ers. Air and/or moisture sensitive reagents were transferred

via syringe or cannula and were introduced into reaction

vessels through rubber septa. Solvent removal was accom-

plished with a rotary evaporator at ca. 10-50 Torr. Column

chromatography was carried out using EM Science Silica Gel

60 (230-400 mesh). Preparative TLC purification was ac-

complished using Analtech Uniplate Silica Gel GF (20 × 20

cm) plates with a layer thickness of 2000 µm. Analytical TLC

plates from EM Science (Silica Gel 60 F₂₅₄) were employed for

TLC analyses.

1

yellow solid. Yield: 2.4 g (63%). H NMR (300 MHz, CDCl₃):

1.48 (s, 9H), 1.96-2.01 (m, 2H), 2.20 (s, 1H), 3.62 (d, J ) 9

Hz, 2H), 3.89 (d, J ) 9 Hz, 2H), 7.84-8.01 (m, 3H).

(1r,5r,6r)-3-(4-Benzyloxycarbonylamino-2-fluoro-phen-

yl)-3-azabicyclo[3.1.0]hexane-6-carboxylic Acid tert-Bu-

tyl Ester(14a). Iron metal (1.25 g, 22.3 mmol) was added in

five portions over 1 h to a refluxing solution of (1R,5R,6R)-3-

(2-fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hexane-6-carboxy-

lic acid tert-butyl ester (2.4 g, 7.44 mmol) and ammonium

chloride (4.0 g, 74.4 mmol) in 60 mL of 2:1 ethanol-H₂O. The

rust-colored mixture was refluxed for another 30 min and then

cooled and filtered to remove iron oxide. H₂O (50 mL) was

added to the filtrate and the mixture concentrated to remove

ethanol. The resulting aqueous solution was extracted with

three 35 mL portions of ethyl acetate, and the combined

organic phases were washed with H₂O and brine and dried

(MgSO₄). Filtration and concentration gave the crude amine

(2.2 g, 7.44 mmol), which was dissolved in 10 mL of dichlo-

romethane. Pyridine (1.2 mL, 14.9 mmol) was added to the

amine solution and after cooling to 0 °C, benzyl chloroformate

(1.2 mL, 8.2 mmol) was added. The mixture was stirred for 1

h at 0 °C and for 30 min at room temperature. The reaction

mixture was then diluted with dichloromethane (50 mL),

Purity of Oxazolidinone Analogues. All oxazolidinone

analogues submitted for biological assay were g 95% pure as

judged by ¹H NMR and HPLC analysis (see Supporting

Information). This level of purity is more than sufficient for

meaningful SAR analysis, considering the intrinsic variability

5016 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

washed with H₂O and brine, and then dried (MgSO₄). Con-

centration gave an oil that was purified by column chroma-

tography (0-20% EtOAc-hexane) to afford (1R,5R,6R)-3-(4-

benzyloxycarbonylamino-2-fluorophenyl)-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid tert-butyl ester. Yield: 2.2 g (69%).

¹H NMR (300 MHz, CDCl₃): 1.43 (s, 9H), 1.74 (t, J ) 3 Hz,

1H), 2.07 (s, 2H), 3.23 (d J ) 9 Hz, 2H), 3.70 (d, J ) 9 Hz,

2H), 5.15 (s, 2H), 6.45 (s, 1H), 6.54 (t, J ) 9 Hz, 1H), 7.92 (d,

J ) 9 Hz, 1H), 7.38-7.44 (m, 6H). ¹³C NMR (75 MHz, DMSO-

d₆): 23.8, 25.3, 27.8, 50.9 (J_C-F) 5 Hz), 65.7, 79.9, 106.6 (J_C-F

) 22 Hz), 114.4, 116.8 (J_C-F) 6 Hz), 127.9, 127.95, 128.2,

128.3, 131.15 (m), 136.5, 151.3 (J_C-F) 239 Hz), 153.1, 171.2.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2-fluorophenyl}-3-azabicyclo[3.1.0]hexane-6-

carboxylic Acid (15a). Lithium butoxide solution (2.1 mmol

of a 1.0 M THF solution, 2.1 mmol) was added to a cooled (0

°C) solution of (1R,5R,6R)-3-(4-benzyloxycarbonylamino-2-fluo-

rophenyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl

ester (0.30 g, 0.7 mmol) in DMF (0.5 mL) and MeOH (0.057

mL, 1.4 mmol). Solid (S)-acetic acid 2-acetylamino-1-chlorom-

ethylethyl ester¹⁶(0.27 g, 1.4 mmol) was then added and the

solution allowed to warm to room temperature and stirred for

20 h. Satd aq ammonium chloride was added, the solution was

extracted with three portions of ethyl acetate, and the com-

bined organic phases were washed with H₂O and brine, dried

(MgSO₄), filtered, and concentrated. The crude product was

purified by preparative TLC (5% MeOH-dichloromethane) to

provide pure (S)-(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-

oxooxazolidin-3-yl]-2-fluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester. Yield: 0.11 g (36%). ¹H NMR

(300 MHz, CDCl₃): 1.46 (s, 9H), 1.74 (tr, J ) 3 Hz, 1H), 2.11

(m, 2H), 2.02 (s, 3H), 3.29 (d, J ) 9 Hz, 2H), 3.54-3.78 (m,

5H), 3.99 (tr, J ) 9 Hz, 1H), 4.74 (m, 1H), 5.93 (br s, 1H), 6.61

(tr, J ) 9 Hz, 1H), 7.02 (d, J ) 9 Hz, 1H), 7.30 (dd, J ) 18, 2

Hz, 1H). ESI-MS (m/z): [M + H]⁺) 434.

Trifluoroacetic acid (0.75 mL) was added to a solution of

(S)-(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2-fluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

tert-butyl ester (0.11 g, 0.25 mmol) in 3 mL of dichloromethane.

The solution was stirred for 3 h, concentrated, and lyophilized

from H₂O-CH₃CN to provide (S)-(1R,5R,6R)-3-{4-[5-(acetyl-

aminomethyl)-2-oxooxazolidin-3-yl]-2-fluorophenyl}-3-azabi-

cyclo[3.1.0]hexane-6-carboxylic acid. Yield: 0.090 g (95%). ¹H

NMR (300 MHz, DMSO): 1.58 (tr, J ) 3 Hz, 1H), 1.81 (s, 3H),

2.09 (m, 2H), 3.23 (d, J ) 9 Hz, 2H), 3.38 (tr, J ) 5 Hz, 2H),

3.60-3.68 (m, 3H), 4.03 (tr, J ) 9 Hz, 1H), 4.67 (m, 1H), 6.76

(tr, J ) 10 Hz, 1H), 7.08 (dd, J ) 9, 2 Hz, 1H), 7.38 (dd, J )

16, 2 Hz, 1H), 8.23 (tr, J ) 6 Hz, 1H). ESI-MS (m/z): [M +

H]⁺) 378.

(1r,5r,6r)-3-(2,6-Difluoro-4-nitrophenyl)-3-azabicyclo-

[3.1.0]hexane-6-carboxylic Acid tert-Butyl Ester (13b).

Palladium hydroxide (10% on carbon, 0.25 g) was added to a

solution of (1R,5R,6R)-3-benzyloxycarbonyl-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid tert-butyl ester (0.800 g, 2.52 mmol)

in 15 mL of methanol. The mixture was stirred under a

hydrogen atmosphere for 1.5 h. The palladium was then

removed by filtration through a pad of Celite and the filtrate

concentrated to give 0.423 g of (1R,5R,6R)-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid tert-butyl ester.

added in five portions over 1 h to a refluxing solution of

(1R,5R,6R)-3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid tert-butyl ester (0.79 g, 2.32 mmol)

and ammonium chloride (1.25 g, 23.2 mmol) in 50 mL of 2:1

ethanol-H₂O. The rust colored mixture was refluxed for

another 30 min and then cooled and filtered to remove iron

oxide. H₂O (50 mL) was added to the filtrate and the mixture

concentrated to remove ethanol. The resulting aqueous solu-

tion was extracted with three 25 mL portions of ethyl acetate,

and the combined organic phases were washed with H₂O and

brine and dried (MgSO₄). Filtration and concentration gave

the crude amine (0.59 g, 1.9 mmol) which was dissolved in 30

mL of dichloromethane. Pyridine (0.31 mL, 3.8 mmol) was

added to the amine solution, and after cooling to 0 °C, benzyl

chloroformate (0.32 mL, 2.2 mmol) was added. The mixture

was stirred for 1 h at 0 °C and for 30 min at room temperature.

The reaction mixture was then diluted with dichloromethane,

washed with H₂O and brine, and then dried (MgSO₄). Con-

centration gave a yellow oil that was triturated with hexane

to afford (1R,5R,6R)-3-(4-benzyloxycarbonylamino-2,6-difluoro-

phenyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl

ester as a yellow solid. Yield: 0.71 g (69%). ¹H NMR (300 MHz,

CDCl₃): 1.46 (s, 9H), 1.84 (m, 1H), 2.01 (m, 2H), 3.48 (s, 4H),

5.18 (s, 2H), 6.55 (s, 1 H), 6.91 (d, J ) 11 Hz, 2H), 7.35-7.40

(m, 5 H). ESI-MS (m/z): [M + H]⁺) 445.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic Acid (15b). Lithium butoxide solution (3.6 mmol

of a 1.0 M THF solution, 3.6 mmol) was added to a cooled (0

°C) solution of (1R,5R,6R)-3-(4-benzyloxycarbonylamino-2,6-

difluorophenyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-

butyl ester (0.53 g, 1.19 mmol) in DMF (0.8 mL) and MeOH

(0.097 mL, 2.4 mmol). Solid (S)-acetic acid 2-acetylamino-1-

chloromethylethyl ester (0.457 g, 2.4 mmol) was then added

and the solution allowed to warm to room temperature and

stirred for 20 h. Satd aq NH₄Cl (3 mL) was added, along with

15 mL of H₂O and 15 mL of brine. The solution was extracted

with three portions of dichloromethane, and the combined

organic phases were dried (MgSO₄), filtered, and concentrated.

The crude product was purified by column chromatography

(0-2% MeOH-dichloromethane) to provide pure (S)-(1R,5R,6R)-

3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-2,6-difluo-

rophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-

1

butyl ester. Yield: 0.4 g (72%). H NMR (300 MHz, CDCl₃):

1.47 (s, 9 H), 1.81 (m, 1H), 2.01 (m, 2 H), 2.02 (s, 3H), 3.49-

3.72 (m, 7 H), 3.97 (tr, J ) 9 Hz, 1H), 4.75 (m, 1H), 6.10 (tr, J

) 6 Hz, 1H), 7.03 (d, J ) 11 Hz, 2H). ESI-MS (m/z): [M + H]⁺

) 452.

Trifluoroacetic acid (0.75 mL) was added to a solution of

(S)-(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxyl-

ic acid tert-butyl ester (0.129 g, 0.29 mmol) in 3 mL of

dichloromethane. The solution was stirred for 3 h and then

concentrated to give the trifluoroacetic acid salt of (S)-

(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

as a tan solid. Yield: 0.148 g (99%). ¹H NMR (300 MHz,

DMSO): 1.65 (tr, J ) 3 Hz, 1H), 1.82 (s, 3H), 2.03 (m, 2H),

3.37-3.69 (m, 7H), 4.05 (tr, J ) 9 Hz, 1H), 4.71 (m, 1H), 7.23

(d, J ) 12 Hz, 2H), 8.23 (tr, J ) 6 Hz, 1H). ESI-MS (m/z): [M

+ H]⁺) 396.

Diisopropylethylamine (0.55 mL, 3.15 mmol) and 3,4,5-

trifluoronitrobenzene (0.372 g, 2.1 mmol) were added to a

solution of (1R,5R,6R)-3-azabicyclo[3.1.0]hexane-6-carboxylic

acid tert-butyl ester (0.423 g, 2.31 mmol) in 5 mL of DMF. The

mixture was heated for 20 h at 50 °C and then cooled to room

temperature. The solution was diluted with ethyl acetate;

washed with 0.5 M HCl, satd. NaHCO₃, and brine; and dried

(MgSO₄). The mixture was filtered and concentrated to give

[(1r,5r,6r)-3-(2-Fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hex-6-yl]carbamic Acid tert-Butyl Ester (16a). Diisoprop-

ylethylamine (0.19 mL, 1.095 mmol) and 3,4-difluoronitroben-

zene (0.105 g, 0.66 mmol) were added to a solution (1R,5R,6R)-

6-tert-butoxycarbonylamine-3-azabicyclo[3.1.0]hexane (0.144 g,

073 mmol) in DMF (2 mL). The mixture was heated for 18 h

at 50 °C and then cooled to room temperature. The solution

was diluted with ethyl acetate; washed with 0.5 M HCl, satd

NaHCO₃, and brine; and dried (MgSO₄). The mixture was

filtered and concentrated to give [(1R,5R,6R)-3-(2-fluoro-4-

nitrophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic acid tert-

1

the product as a yellow solid. Yield: 0.791 g (92%). H NMR

(300 MHz, CDCl₃): 1.46 (s, 9H), 1.60 (m, 1 H), 2.13 (m, 2H),

3.77 (d, J ) 11 Hz, 2H), 3.99 (d, J ) 11 Hz, 2H), 7.72 (d, J )

9 Hz, 2H).

(1r,5r,6r)-3-(4-Benzyloxycarbonylamino-2,6-difluo-

rophenyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic Acid

tert-Butyl Ester (14b). Iron metal (0.39 g, 7.0 mmol) was

1

butyl ester as a yellow solid. Yield: 0.208 g (84%). H NMR

(300 MHz, CDCl₃): 1.46 (s, 9H), 1.90 (s, 2H), 2.41 (s, 1H), 3.62

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5017

(d, J ) 9 Hz, 2H), 3.91 (br d, J ) 8 Hz, 2H), 4.75 (br s, 1H),

6.51 (tr, J ) 9 Hz, 1H), 7.83-7.93 (m, 2H).

was heated for 3 h at reflux and then cooled to room

temperature. The solution was concentrated, diluted with ethyl

acetate, and washed with 0.5 M HCl, satd NaHCO₃, brine, and

dried (Na₂SO₄). The mixture was filtered and concentrated to

give [(1R,5R,6R)-3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo-

[3.1.0]hex-6-yl]carbamic acid tert-butyl ester as a yellow solid.

Yield: 0.210 g (93%). ¹H NMR (300 MHz, CDCl₃): 1.45 (s, 9H),

1.80 (s, 2H), 2.47 (s, 1H), 3.75 (d, J ) 10.8 Hz, 2H), 4.02 (d, J

[(1r,5r,6r)-3-(4-Benzyloxycarbonylamino-2-fluoro-

phenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic Acid tert-

Butyl Ester (17a). Iron metal (0.102 g, 1.82 mmol) was added

in five portions over 1 h to a refluxing solution of [(1R,5R,6R)-

3-(2-fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbam-

ic acid tert-butyl ester (0.205 g, 0.608 mmol) and ammonium

chloride (0.367 g, 6.8 mmol) in 4.5 mL of 2:1 ethanol-H₂O.

The rust-colored mixture was refluxed for another 30 min and

then cooled and filtered to remove iron oxide. H₂O was added

to the filtrate and the mixture concentrated to remove ethanol.

The resulting aqueous solution was extracted with three 20

mL portions of ethyl acetate, and the combined organic phases

were washed with H₂O and brine, and dried (MgSO₄). Filtra-

tion and concentration gave the crude amine (0.171 g, 0.55

mmol) which was dissolved in 3.0 mL of dichloromethane.

Pyridine (0.089 mL, 1.1 mmol) was added to the amine

solution, and after cooling to 0 °C, benzyl chloroformate (0.090

mL, 0.63 mmol) was added. The mixture was stirred for 30

min at 0 °C and for 30 min at room temperature. The reaction

mixture was then diluted with dichloromethane, washed with

H₂O and brine, and then dried (MgSO₄). Concentration gave

a yellow oil that was triturated with hexane to afford

[(1R,5R,6R)-3-(4-benzyloxycarbonylamino-2-fluorophenyl)-3-

azabicyclo[3.1.0]hex-6-yl]carbamic acid tert-butyl ester as a

yellow solid. Yield: 0.230 g (86%). ¹H NMR (300 MHz,

CDCl₃): 1.45 (s, 9H), 1.74 (s, 2H), 2.61 (s, 1H), 3.22 (d, J )

8.7 Hz, 2H), 3.75 (d, J ) 8.4 Hz, 2H), 4.71 (br s, 1H), 5.17 (s,

2H), 6.52-6.58 (m, 2H), 6.88 (d, J ) 7 Hz, 1H), 7.15-7.41 (m,

6H). ¹³C NMR (75 MHz, DMSO-d₆): 23.8, 25.3, 27.8, 50.8 (J_C-F

) 10.2 Hz, 2H), 4.70 (br s, 1H), 7.70 (dd, J ) 9, 2 Hz, 2H). ¹³

C

NMR (75 MHz, DMSO-d₆): 23.0, 28.2, 32.1, 52.4 (t, J_C-F) 8

Hz), 77.8, 109.2 (J_C-F) 30 Hz), 132.2 (t, J_C-F) 11 Hz), 135.4,

151.0 (dd, J_C-F) 244, 11 Hz), 155.6.

[(1r,5r,6r)-3-(4-Benzyloxycarbonylamino-2,6-difluo-

rophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic Acid tert-

Butyl Ester (17b). Iron metal (0.047 g, 0.84 mmol) was added

in five portions over 1 h to a refluxing solution of [(1R,5R,6R)-

3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hex-6-yl]car-

bamic acid tert-butyl ester (0.10 g, 0.28 mmol) and ammonium

chloride (0.148 g, 2.8 mmol) in 2.5 mL of 2:1 ethanol-H₂O.

The rust-colored mixture was refluxed for another 30 min and

then cooled and filtered to remove iron oxide. H₂O was added

to the filtrate and the mixture concentrated to remove ethanol.

The resulting aqueous solution was extracted with three 15

mL portions of ethyl acetate, and the combined organic phases

were washed with H₂O and brine and dried (MgSO₄). Filtration

and concentration gave the crude amine (0.091 g, 0.28 mmol)

which was dissolved in 1.5 mL of dichloromethane. Pyridine

(0.046 mL, 0.57 mmol) was added to the amine solution, and

after cooling to 0 °C, benzyl chloroformate (0.046 mL, 0.32

mmol) was added. The mixture was stirred for 30 min at 0 °C

and for 30 min at room temperature. The reaction mixture

was then diluted with dichloromethane, washed with H₂O and

brine, and then dried (MgSO₄). Concentration gave a yellow

oil that was triturated with hexane to afford [(1R,5R,6R)-3-(4-

benzyloxycarbonylamino-2,6-difluorophenyl)-3-azabicyclo-

[3.1. 0]hex-6-yl]carbamic acid tert-butyl ester as a yellow solid.

Yield: 0.100 g (77%). ¹H NMR (300 MHz, CDCl₃): 1.45 (s, 9H),

1.67 (s, 2H), 2.75 (s, 1H), 3.49 (m, 4H), 4.65 (br s, 1H), 5.18 (s,

2H), 6.56 (br s, 1H), 6.90 (d, J ) 11 Hz, 2H), 7.36 (m, 5H).

(S)-N-{3-[4-((1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]hex-

3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

acetamide (18b). Lithium butoxide solution (0.61 mL of a 1.0

M THF solution, 0.61 mmol) was added to a cooled (0 °C)

solution of [(1R,5R,6R)-3-(4-benzyloxycarbonylamino-2,6-dif-

luorophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic acid tert-

butyl ester (0.093 g, 0.203 mmol) in DMF (0.14 mL) and MeOH

(0.016 mL, 0.406 mmol). Solid (S)-acetic acid 2-acetylamino-

1-chloromethylethyl ester (0.078 g, 0.406 mmol) was then

added and the solution allowed to warm to room temperature

and stirred for 20 h. Satd aq ammonium chloride (0.5 mL) was

added, along with 4 mL of H₂O and 3 mL of brine. The solution

was extracted with three portions of dichloromethane, and the

combined organic phases were dried (MgSO₄), filtered, and

concentrated. The crude product was purified by column

chromatography (0-2% MeOH-dichloromethane) to provide

(S)-((1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid

tert-butyl ester. Yield: 0.066 g (70%). ESI-MS (m/z): [M + H]⁺

) 467.

) 5 Hz), 65.7, 79.8, 106.6 (J_C-F) 25 Hz), 114.4, 116.8 (J_C-F

)

5 Hz), 127.8, 127.9, 128.1, 128.3, 131.1 (m), 136.4, 151.3 (J_C-F

) 238 Hz), 153.1, 171.2

(S)-N-{3-[4-((1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]hex-

3-yl)-3-fluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

acetamide (18a). Lithium butoxide solution (1.15 mL of a 1.0

M THF solution, 1.15 mmol) was added to a cooled (0 °C)

solution of [(1R,5R,6R)-3-(4-benzyloxycarbonylamino-2-fluo-

rophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic acid tert-butyl

ester (0.170 g, 0.385 mmol) in DMF (0.35 mL) and MeOH

(0.031 mL, 0.771 mmol). Solid (S)-acetic acid 2-acetylamino-

1-chloromethylethyl ester¹⁶(0.149 g, 0.771 mmol) was then

added and the solution allowed to warm to room temperature

and stirred for 20 h. Satd aq ammonium chloride (0.8 mL) was

added, along with 7 mL of H₂O and 6 mL of brine. The solution

was extracted with three portions of dichloromethan and the

combined organic phases were dried (MgSO₄), filtered, and

concentrated. The crude product was purified by column

chromatography (0-3% MeOH-CH₂Cl₂) to provide (S)-

((1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2-fluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid tert-

butyl ester. Yield: 0.115 g (66%). ESI-MS (m/z): [M + H]⁺

449.

)

A 4.0 M solution of HCl in dioxane (1.0 mL) was added to

(S)-((1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2-fluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid

tert-butyl ester (0.046 g, 0.103) in 1.0 mL of dioxane. The

reaction mixture was stirred at room temperature for 2 h and

then concentrated to provide (S)-N-{3-[4-((1R,5R,6R)-6-amino-

3-azabicyclo[3.1.0]hex-3-yl)-3-fluorophenyl]-2-oxooxazolidin-5-

ylmethyl}acetamide as the hydrochloride salt. Yield: 0.039 g

A 4.0 M solution of HCl in dioxane (1.5 mL) was added to

(S)-((1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid

tert-butyl ester (0.066 g, 0.142) in 1.5 mL of dioxane. The

reaction mixture was stirred at room temperature for 2 h and

then concentrated. The resulting solid was lyophilized from

acetonitrile-water to provide (S)-N-{3-[4-((1R,5R,6R)-6-amino-

3-azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-

5-ylmethyl}acetamide as the hydrochloride salt. Yield: 0.054

g (95%). ¹H NMR (300 MHz, CDCl₃-CD₃OD): 1.85 (s, 3H),

1.89 (br s, 2H), 2.60 (br s, 1H), 3.21-3.42 (m, 6H), 3.58 (tr, J

) 6 Hz, 1H), 3.87 (tr, J ) 3 Hz, 1H), 4.62 (m, 1H), 6.93 (d, )

11 Hz, 2H). ESI-MS (m/z): [M + H]⁺) 367.

1

(99%). H NMR (300 MHz, DMSO): 1.82 (s, 3H), 2.02 (br s,

2H), 2.58 (br s, 1H), 3.20 (d, J ) 9 Hz, 2H), 3.34-3.69 (m, 5

H), 4.05 (tr, J ) 9 Hz, 1H), 4.68 (m, 1H), 6.79 (tr, J ) 9 Hz,

1H), 7.10 (dd, J ) 9, 2 Hz, 1H), 7.40 (dd, J ) 16, 2 Hz, 1H),

8.20 (br s, 2H), 8.25 (tr, J ) 6 Hz, 1H). ESI-MS (m/z): [M +

H]⁺) 349.

[(1r,5r,6r)-3-(2,6-Difluoro-4-nitrophenyl)-3-azabicyclo-

[3.1.0]hex-6-yl]carbamic Acid tert-Butyl Ester (16b). Di-

isopropylethylamine (0.17 mL, 0.96 mmol) and 3,4,5-trifluo-

ronitrobenzene (0.113 g, 0.64 mmol) were added to a solution

of (1R,5R,6R)-6-tert-butoxycarbonylamine-3-azabicyclo[3.1.0]-

hexane (0.14 g, 0.7 mmol) in acetonitrile (3 mL). The mixture

(S)-N-{3-[4-((1r,5r,6â)-6-Amino-3-azabicyclo[3.1.0]hex-

3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

5018 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

acetamide (19). Lithium butoxide solution (1.53 mL of a 1.0

M THF solution, 1.53 mmol) was added to a cooled (0 °C)

solution of [(1R,5R,6â)-3-(4-benzyloxycarbonylamino-2,6-dif-

luorophenyl)-3-azabicyclo[3.1. 0]hex-6-yl]carbamic acid tert-

butyl ester (0.175 g, 0.38 mmol, prepared in an analogous

fashion as 17b) in DMF (0.25 mL) and MeOH (0.031 mL, 0.76

mmol). Solid (S)-acetic acid 2-acetylamino-1-chloromethylethyl

ester (0.147 g, 0.76 mmol) was then added and the solution

allowed to warm to room temperature and stirred for 20 h.

Satd aq ammonium chloride (0.5 mL) was added, along with

4 mL of H₂O and 3 mL of brine. The solution was extracted

with three portions of dichloromethane, and the combined

organic phases were dried (MgSO₄), filtered, and concentrated.

The crude product was purified by column chromatography

(0-3% MeOH-dichloromethane) to provide (S)-((1R,5R,6â)-3-

{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-2,6-difluorophe-

nyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid tert-butyl ester.

Yield: 0.102 g (58%). ¹H NMR (300 MHz, CDCl₃): 1.46 (m,

9H), 1.72 (d, J ) 8 Hz, 2H), 2.03 (s, 3H), 3.23 (q, J ) 8 Hz,

1H), 3.34 (d, J ) 9 Hz, 2H), 3.63-3.68 (m, 4H), 3.75 (dd, J )

9, 7 Hz, 1H), 4.00 (tr, J ) 9 Hz, 1H), 4.78 (m, 1H), 5.48 (br s,

1H), 6.46 (br s, 1H), 7.09 (d, J ) 11 Hz, 2H). ESI-MS (m/z):

[M + H]⁺) 467.

another 30 min and then cooled and filtered to remove iron

oxide. H₂O was added to the filtrate and the mixture concen-

trated to remove ethanol. The resulting aqueous solution was

extracted with three 15 mL portions of ethyl acetate, and the

combined organic phases were washed with H₂O and brine and

dried (MgSO₄). Filtration and concentration gave the crude

amine (0.078 g, 0.23 mmol) which was dissolved in 1.5 mL of

dichloromethane. Pyridine (0.037 mL, 0.46 mmol) was added

to the amine solution and after cooling to 0 °C, benzyl

chloroformate (0.037 mL, 0.26 mmol) was added. The mixture

was stirred for 30 min at 0 °C and for 30 min at room

temperature. The reaction mixture was then diluted with

dichloromethane, washed with H₂O and brine, and then dried

(MgSO₄). Concentration gave an oil that was triturated with

hexane and purified by column chromatography (0-10% ethyl

acetate-hexane) to afford {4-[(1R,5R,6R)-6-(tert-butyldimeth-

ylsilanyloxy)-3-azabicyclo[3.1.0]hex-3-yl]-3,5-difluorophenyl}-

carbamic acid benzyl ester. Yield: 0.078 g (70%). ¹H NMR (300

MHz, CDCl₃): 0.12 (s, 6H), 0.91 (s, 9H), 1.60 (m, 2H), 3.44

(m, 5H), 5.18 (s, 2H), 6.51 (br s, 1H), 6.89 (d, J ) 12 Hz, 2H),

7.28-7.40 (m, 5H).

(S)-N-{3-[3,5-Difluoro-4-((1r,5r,6r)-6-hydroxy-3-

azabicyclo[3.1.0]hex-3-yl)phenyl]-2-oxooxazolidin-5-

ylmethyl}acetamide (22). Lithium butoxide solution (0.53

mL of a 1.0 M THF solution, 0.53 mmol) was added to a cooled

(0 °C) solution of {4-[(1R,5R,6R)-6-(tert-butyldimethylsilan-

yloxy)-3-azabicyclo[3.1.0]hex-3-yl]-3,5-difluorophenyl}carbamic

acid benzyl ester (0.077 g, 0.16 mmol) in DMF (0.1 mL) and

MeOH (0.013 mL, 0.32 mmol). Solid (S)-acetic acid 2-acety-

lamino-1-chloromethylethyl ester (0.062 g, 0.32 mmol) was

then added and the solution allowed to warm to room tem-

perature and stirred for 20 h. Satd aq ammonium chloride (0.5

mL) was added, along with 4 mL of H₂O and 3 mL of brine.

The solution was extracted with three portions of dichloro-

methane, and the combined organic phases were dried (Mg-

SO₄), filtered, and concentrated. The crude product was

purified by column chromatography (0-2% MeOH-dichlo-

romethane) to provide (S)-N-(3-{4-[(1R,5R,6R)-6-(tert-butyl-

dimethylsilanyloxy)-3-azabicyclo[3.1.0]hex-3-yl]-3,5-difluorophe-

nyl}-2-oxooxazolidin-5-ylmethyl)acetamide. Yield: 0.056 g (73%).

Hydrogen fluoride (2.0 µL of a 48% solution) was added to

a solution of (S)-N-(3-{4-[(1R,5R,6R)-6-(tert-butyldimethylsila-

nyloxy)-3-azabicyclo[3.1.0]hex-3-yl]-3,5-difluorophenyl}-2-oxoox-

azolidin-5-ylmethyl)acetamide (0.027 g, 0.056 mmol) in 4 mL

of acetic acid-THF-H₂O (2:1:1). The reaction mixture was

stirred for 4 h at room temperature and then the THF was

removed in vacuo. The aqueous solution was diluted with 2.5%

NaHCO₃and extracted with three portions of ethyl acetate.

The combined organic phases were washed with brine, dried

(MgSO₄), filtered, and concentrated. The product was tritu-

rated with hexane to provide pure (S)-N-{3-[3,5-difluoro-4-

((1R,5R,6R)-6-hydroxy-3-azabicyclo[3.1.0]hex-3-yl)phenyl]-2-

oxooxazolidin-5-ylmethyl}acetamide as a white solid. Yield:

0.017 g (85%). ¹H NMR (300 MHz, CD₃OD): 1.62 (s, 2H), 1.95

(s, 3H), 3.43-3.54 (m, 7H), 3.72 (m, 1H), 4.06 (tr, J ) 9 Hz,

1H), 4.76 (m, 1H), 7.13 (d, J ) 12 Hz, 2H). ESI-MS (m/z):

[M + H]⁺) 368.

3-(2-Fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hexane

(23a). Diisopropylethylamine (0.56 mL, 3.2 mmol) and 3,4-

difluoronitrobenzene (0.184 g, 1.16 mmol) were added to a

solution 3-azabicyclo[3.1.0]hexane (0.152 g of HCl salt, 1.28

mmol) in DMF (3.2 mL). The mixture was heated for 3 days

at 45 °C and then cooled to room temperature. The solution

was diluted with ethyl acetate; washed with 0.5 M HCl, satd

NaHCO₃, and brine; and dried (MgSO₄). The mixture was

filtered and concentrated to give 3-(2-fluoro-4-nitrophenyl)-3-

azabicyclo[3.1.0]hexane as a yellow solid. Yield: 0.233 g (82%).

¹H NMR (300 MHz, CDCl₃): 0.33 (qt, J ) 4.5 Hz, 1H), 0.75-

0.82 (m, 1H), 1.68 (m, 2H), 3.58 (d, J ) 10 Hz, 2H), 3.80 (dd,

J ) 10, 3 Hz, 2H), 6.53 (tr, J ) 9 Hz, 1H), 7.82-7.93 (m, 2H).

A 4.0 M solution of HCl in dioxane (2.0 mL) was added to

(S)-((1R,5R,6â)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-

yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)carbamic acid

tert-butyl ester (0.100 g, 0.215) in 2.0 mL of dioxane. The

reaction mixture was stirred at room temperature for 2 h and

then concentrated to give (S)-N-{3-[4-((1R,5R,6â)-6-amino-3-

azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-

5-ylmethyl}acetamide as the hydrochloride salt. Yield: 0.086

1

g (99%). H NMR (300 MHz, DMSO): 1.82 (s, 3H), 1.90 (d, J

) 8 Hz, 2H), 2.73 (tr, J ) 8 Hz, 1H), 3.28-3.61 (m, 7H), 4.08

(tr, J ) 9 Hz, 1H), 4.74 (m, 1H), 7.29 (d, J ) 12 Hz, 2H), 7.96

(br s, 2H), 8.26 (tr, J ) 6 Hz, 1H). ESI-MS (m/z): [M + H]⁺

367.

)

(1r,5r,6r)-6-(tert-Butyldimethylsilyloxy)-3-(2,6-difluoro-

4-nitrophenyl)-3-azabicyclo[3.1.0]hexane (20). Palladium

hydroxide (0.030 g, 10% on carbon) was added to a solution of

(1R,5R,6R)-6-hydroxy-3-azabicyclo[3.1.0]hexane-3-carboxylic acid

benzyl ester (0.071 g, 0.3 mmol) in methanol (2 mL). The

mixture was stirred under a hydrogen atmosphere for 3 h and

then filtered through a pad of Celite and concentrated to give

(1R,5R,6R)-3-azabicyclo[3.1.0]hexan-6-ol as a solid film. The

amine was dissolved in DMF (0.75 mL) and treated with

diisopropylethylamine (0.078 mL, 0.45 mmol) and 3,4,5-

trifluoronitrobenzene (0.048 g, 0.27 mmol). The mixture was

heated for 12 h at 50 °C; diluted with ethyl acetate; washed

with 0.5 M HCl, satd NaHCO₃, and brine; and dried (MgSO₄).

The mixture was filtered and concentrated to give (1R,5R,6R)-

3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hexan-6-ol.

Yield: 0.070 g (91%).

Imidazole (0.033 g, 0.49 mmol) and tert-butyldimethylsilyl

chloride (0.065 g, 0.43 mmol) were added to a solution of

(1R,5R,6R)-3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hexan-6-ol (0.070 g, 0.27 mmol) in dichloromethane (3.0 mL).

After 3 h, satd NaHCO₃was added, and the layers were

separated. The aqueous phase was extracted with more

dichloromethane, and the combined organic phases were

washed with 0.3 M HCl, satd. NaHCO₃, and brine and dried

(MgSO₄). The mixture was filtered and concentrated to provide

(1R,5R,6R)-6-(tert-butyldimethylsilyloxy)-3-(2,6-difluoro-4-ni-

trophenyl)-3-azabicyclo[3.1.0]hexane. Yield: 0.088 g (88%). ¹H

NMR (300 MHz, CDCl₃): 0.12 (s, 6H), 0.90 (s, 9H), 1.73 (m,

2H), 3.19 (s, 1H), 3.74 (dd, J ) 9, 2 Hz, 2H), 3.93 (m, 2H), 7.70

(dd, J ) 9, 2 Hz, 2H).

{4-[(1r,5r,6r)-6-(tert-Butyldimethylsilanyloxy)-3-

azabicyclo[3.1.0]hex-3-yl]-3,5-difluorophenyl}carbamic

Acid Benzyl Ester (21). Iron metal (0.039 g, 0.713 mmol)

was added in five portions over 1 h to a refluxing solution of

(1R,5R,6R)-6-(tert-butyldimethylsilanyloxy)-3-(2,6-difluoro-4-ni-

trophenyl)-3-azabicyclo[3.1.0]hexane (0.088 g, 0.24 mmol) and

ammonium chloride (0.129 g, 2.38 mmol) in 2.5 mL of 2:1

ethanol-H₂O. The rust-colored mixture was refluxed for

[4-(3-Azabicyclo[3.1.0]hex-3-yl)-3-fluorophenyl]carbam-

ic Acid Benzyl Ester (24a). Iron metal (0.168 g, 3.15 mmol)

was added in five portions over 1 h to a refluxing solution of

3-(2-fluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]hexane (0.233 g,

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5019

1.05 mmol) and ammonium chloride (0.566 g, 10.5 mmol) in

7.5 mL of 2:1 ethanol-H₂O. The rust-colored mixture was

refluxed for another 30 min and then cooled and filtered to

remove iron oxide. H₂O was added to the filtrate and the

mixture concentrated to remove ethanol. The resulting aque-

ous solution was extracted with three 20 mL portions of ethyl

acetate, and the combined organic phases were washed with

H₂O and brine and dried (MgSO₄). Filtration and concentration

gave the crude amine (0.194 g, 0.99 mmol) which was dissolved

in 8.0 mL of dichloromethane. Pyridine (0.160 mL, 2.0 mmol)

was added to the amine solution, and after cooling to 0 °C,

benzyl chloroformate (0.162 mL, 1.14 mmol) was added. The

mixture was stirred for 30 min at 0 °C and for 30 min at room

temperature. The reaction mixture was then diluted with

dichloromethane, washed with H₂O and brine, and then dried

(MgSO₄). Concentration gave a yellow oil that was triturated

with hexane to afford [4-(3-azabicyclo[3.1.0]hex-3-yl)-3-fluo-

rophenyl]carbamic acid benzyl ester as a yellow solid. Yield:

0.299 g (87%). ¹H NMR (300 MHz, CDCl₃): 0.61 (m, 2H), 1.56

(br s, 2H), 3.21 (d, J ) 8.5 Hz, 2H), 3.65 (dd, J ) 9, 2 Hz, 2H),

5.18 (s, 2H), 6.49 (br s, 1H), 6.63 (br s, 1H), 6.88 (d, J ) 9 Hz,

1H), 7.17-7.41 (m, 6H). ¹³C NMR (75 MHz, CDCl₃): 8.5, 15.5,

51.7 (J_C-F) 6 Hz), 66.9, 108.4 (J_C-F) 30 Hz), 115.1, 116.0,

128.15, 128.17, 128.3, 128.5, 133.6 (J_C-F) 9 Hz), 136.0, 151.8

(J_C-F) 241 Hz), 153.4.

(S)-N-{3-[4-(3-Azabicyclo[3.1.0]hex-3-yl)-3-fluorophenyl]-

2-oxooxazolidin-5-ylmethyl}acetamide (25a). Lithium bu-

toxide solution (2.5 mL of a 1.0 M THF solution, 2.5 mmol)

was added to a cooled (0 °C) solution of [4-(3-azabicyclo[3.1.0]-

hex-3-yl)-3-fluorophenyl]carbamic acid benzyl ester (0.267 g,

0.82 mmol) in DMF (0.6 mL) and MeOH (0.060 mL, 1.64

mmol). Solid (S)-acetic acid 2-acetylamino-1-chloromethylethyl

ester (0.316 g, 1.64 mmol) was then added and the solution

allowed to warm to room temperature and stirred for 20 h.

Satd aq ammonium chloride (1.0 mL) was added, along with

9 mL of H₂O and 8 mL of brine. The solution was extracted

with three portions of dichloromethane, and the combined

organic phases were dried (MgSO₄), filtered, and concentrated.

The crude product was purified by column chromatography

(0-3% MeOH-dichloromethane) to provide (S)-N-{3-[4-(3-

azabicyclo[3.1.0]hex-3-yl)-3-fluorophenyl]-2-oxooxazolidin-5-

ylmethyl}acetamide. Yield: 0.169 g (62%). ¹H NMR (300 MHz,

CDCl₃): 0.49 (m, 1H), 0.61 (m, 1H), 1.56 (m, 2H), 2.01 (s, 3H),

3.22 (d, J ) 9 Hz, 2H), 3.56-3.68 (m, 5 H), 3.97 (tr, J ) 9 Hz,

1H), 4.75 (m, 1H), 6.46 (tr, J ) 6 Hz, 1H), 6.59 (tr, J ) 9 Hz,

1H), 6.96 (dd, J ) 9, 3 Hz, 1H), 7.27 (dd, J ) 15, 2 Hz, 1H).

ESI-MS (m/z): [M + H]⁺) 334.

3-(2,6-Difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hexane (23b). Diisopropylethylamine (0.39 mL, 2.25 mmol)

and 3,4,5-trifluoronitrobenzene (0.143 g, 0.81 mmol) were

added to a solution 3-azabicyclo[3.1.0]hexane (0.106 g of the

HCl salt, 0.9 mmol) in DMF (2 mL). The mixture was heated

for 3 days at 45 °C and then cooled to room temperature. The

solution was diluted with ethyl acetate; washed with 0.5 M

HCl, satd NaHCO₃, and brine; and dried (MgSO₄). The mixture

was filtered and concentrated to give 3-(2,6-difluoro-4-nitro-

phenyl)-3-azabicyclo[3.1.0]hexane as a yellow solid. Yield:

0.177 g (82%). ¹H NMR (300 MHz, CDCl₃): 0.35 (q, J ) 4 Hz,

1H), 0.66 (m, 1H), 1.58 (m, 2H), 3.70 (d, J ) 10.5 Hz, 2H),

3.90 (d tr, J ) 10.5, 2 Hz, 2H), 7.71 (dd, J ) 10, 2 Hz, 2H).

[4-(3-Azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]car-

bamic Acid Benzyl Ester (24b). Iron metal (0.120 g, 2.15

mmol) was added in five portions over 1 h to a refluxing

solution of 3-(2,6-difluoro-4-nitrophenyl)-3-azabicyclo[3.1.0]-

hexane (0.172 g, 0.72 mmol) and ammonium chloride (0.385

g, 7.2 mmol) in 6.0 mL of 2:1 ethanolH₂O. The rust-colored

mixture was refluxed for another 30 min and then cooled and

filtered to remove iron oxide. H₂O was added to the filtrate

and the mixture concentrated to remove ethanol. The resulting

aqueous solution was extracted with three 20 mL portions of

ethyl acetate, and the combined organic phases were washed

with H₂O and brine and dried (MgSO₄). Filtration and

concentration gave the crude amine (0.145 g, 0.69 mmol) which

was dissolved in 5.0 mL of dichloromethane. Pyridine (0.111

mL, 1.38 mmol) was added to the amine solution, and after

cooling to 0 °C, benzyl chloroformate (0.113 mL, 0.79 mmol)

was added. The mixture was stirred for 30 min at 0 °C and

for 30 min at room temperature. The reaction mixture was

then diluted with dichloromethane, washed with H₂O and

brine, and then dried (MgSO₄). Concentration gave a yellow

oil that was triturated with hexane to afford [4-(3-azabicyclo-

[3.1.0]hex-3-yl)-3,5-difluorophenyl]carbamic acid benzyl ester

as a yellow solid. Yield: 0.195 g (79%). ¹H NMR (300 MHz,

CDCl₃): 0.52 (m, 1H), 0.61 (q, J ) 4 Hz, 1H), 1.45 (br s, 2H),

3.43 (m, 4H), 5.18 (s, 2H), 6.54 (br s, 1H), 6.90 (d, J ) 11 Hz,

2H), 7.36 (m, 5H).

(S)-N-{3-[4-(3-Azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophe-

nyl]-2-oxooxazolidin-5-ylmethyl}acetamide (25b). Lithium

butoxide solution (1.6 mL of a 1.0 M THF solution, 1.6 mmol)

was added to a cooled (0 °C) solution of [4-(3-azabicyclo[3.1.0]-

hex-3-yl)-3,5-difluorophenyl]carbamic acid benzyl ester (0.180

g, 0.52 mmol) in DMF (0.35 mL) and MeOH (0.042 mL, 1.05

mmol). Solid (S)-acetic acid 2-acetylamino-1-chloromethylethyl

ester (0.203 g, 1.05 mmol) was then added and the solution

allowed to warm to room temperature and stirred for 20 h.

Satd aq ammonium chloride (0.8 mL) was added, along with

7 mL of H₂O and 6 mL of brine. The solution was extracted

with three portions of dichloromethane, and the combined

organic phases were dried (MgSO₄), filtered, and concentrated.

The crude product was purified by column chromatography

(0-2% MeOH-dichloromethane) to provide (S)-N-{3-[4-(3-

azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-

5-ylmethyl}acetamide. Yield: 0.127 g (70%). ¹H NMR (300

MHz, CDCl₃): 0.53 (m, 2H), 1.47 (m, 2H), 2.02 (s, 3H), 3.48

(m, 4H), 3.50-3.74 (m, 3H), 3.96 (tr, J ) 9 Hz, 1H), 4.74 (m,

1H), 5.98 (tr, J ) 5 Hz, 1H), 7.00 (d, J ) 12 Hz, 2H). ESI-MS

(m/z): [M + H]⁺) 352.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic Acid Amide (26). Diisopropylethylamine (19

µL, 0.11 mmol) and HATU (21 mg, 0.055 mmol) were add to a

solution of (S)-(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxoox-

azolidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-

carboxylic acid (14 mg of the TFA salt, 0.028 mmol) in 0.7 mL

of DMF. Ammonium chloride (3.0 mg, 0.055 mmol) was then

added and the mixture stirred at room temperature for 5 h.

The reaction mixture was then concentrated and the crude

product purified by preparative HPLC to provide (S)-(1R,5R,6R)-

3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-2,6-difluo-

rophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid amide.

Yield: 0.005 g (47%). ¹H NMR (300 MHz, DMSO): 1.76 (tr, J

) 3 Hz, 1H), 1.82 (s, 3H), 1.87 (m, 2H), 3.37-3.70 (m, 7H),

4.06 (tr, J ) 9 Hz, 1H), 4.71 (m, 1H), 6.81 (s, 1H), 7.23 (d, J )

12 Hz, 2H), 7.57 (s, 1H), 8.24 (tr, J ) 6 Hz, 1H). ESI-MS

(m/z): [M + H]⁺) 395.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

1

6-carboxylic Acid Methylamide (27). H NMR (300 MHz,

DMSO): 1.74 (m, 1H), 1.82 (s, 3H), 1.88 (m, 2H), 2.57 (d, J )

5 Hz, 3H), 3.16-3.41 (m, 6H), 3.66 (tr, J ) 8 Hz, 1H), 4.06 (tr,

J ) 9 Hz, 1H), 4.71 (m, 1H), 7.23 (d, J ) 12 Hz, 2H), 8.02 (q,

J ) 5 Hz, 1H), 8.23 (m, 1H). ESI-MS (m/z): [M + H]⁺) 409.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic Acid Dimethylamide (28). Diisopropylethy-

lamine (23 µL, 0.13 mmol) and HATU (24 mg, 0.064 mmol)

were add to a solution of (S)-(1R,5R,6R)-3-{4-[5-(acetylami-

nomethyl)-2-oxooxazolidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo-

[3.1.0]hexane-6-carboxylic acid (17 mg of the TFA salt, 0.033

mmol) in 0.8 mL of DMF. Dimethylamine (6.3 µL of a 40% aq

solution, 0.049 mmol) was then added and the mixture stirred

at room temperature for 4 h. The reaction mixture was then

concentrated and the crude product purified by preparative

HPLC to provide (S)-(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-

2-oxooxazolidin-3-yl]-2,6-difluorophenyl}-3-azaicyclo[3.1.0]-

hexane-6-carboxylic acid dimethylamide. Yield: 0.005 g (37%).

¹H NMR (300 MHz, DMSO): 1.82 (s, 3H), 1.94 (m, 2H), 1.97

(tr, J ) 3 Hz, 1H), 2.83 (s, 3H), 3.09 (s, 3H), 3.37-4.05 (m,

5020 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

8H), 4.71 (m, 1H), 7.23 (d, J ) 13 Hz, 2H), 8.23 (tr, J ) 6 Hz,

1H). ESI-MS (m/z): [M + H]⁺) 423.

The title compound was prepared in 67% yield using the

procedure described for 33, but using 2-(aminomethyl)pyridine

in reaction with the pentafluorophenyl ester intermediate. ¹H

NMR (300 MHz, DMSO-d₆): 1.82 (br s, 2H), 1.90 (br s, 1H),

1.92 (s, 3H), 3.26-3.44 (m, 6H), 3.63-3.69 (m, 1H), 4.05 (tr, J

) 9 Hz, 1H), 4.36 (m, 2H), 4.67-4.73 (m, 1H), 7.19-7.28 (m,

4H), 7.76 (dt, J ) 8, 2 Hz, 1H), 8.22 (tr, J ) 6 Hz, 1H), 8.48 (d,

J ) 3 Hz, 1H), 8.71 (tr, J ) 3 Hz, 1H). ESI-MS (m/z): [M +

H]⁺) 486.5.

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic Acid Benzyloxyamide (29). Pyridine (0.014

mL, 0.17 mmol) and then pentafluorophenyltrifluoroacetate

(0.015 mL, 0.086 mmol) were added to a solution of (S)-

(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

(0.022 g, 0.055 mmol) in 0.2 mL of DMF. The mixture was

stirred at room temperature for 2 h. The solution was then

diluted with ethyl acetate, washed with dilute HCl and brine,

dried (MgSO₄), filtered, and concentrated to give (S)-(1R,5R,6R)-

3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-2,6-difluo-

rophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid pen-

tafluorophenyl ester (0.031 g, 0.055 mmol) that was dissolved

in 0.3 mL of DMF. Diisopropylethylamine (0.014 mL, 0.083

mmol) and O-benzylhydroxylamine (7 µL, 0.066 mmol) were

added to this solution. After 2 h, the reaction mixture was

diluted with ethyl acetate, washed with dilute HCl and brine,

dried (MgSO₄), filtered, and concentrated. Purification by

preparative TLC (5% MeOH-dichloromethane) gave pure (S)-

(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

benzyloxyamide. Yield: 0.017 g (63%). ¹H NMR (300 MHz,

DMSO): 1.64 (m, 1H), 1.82 (s, 3H), 1.95 (m, 2H), 3.33-3.45

(m, 6H), 3.67 (m, 1H), 4.05 (tr, J ) 10 Hz, 1H), 4.71 (m, 1H),

4.79 (s, 2H), 7.23 (d, J ) 12 Hz, 2H), 7.36-7.38 (m, 5H), 8.24

(S)-(1r,5r,6r)-3-(4-{(5S)-5-[(Acetylamino)methyl]-2-oxo-

1,3-oxazolidin-3-yl}-2,6-difluorophenyl)-N-(1,3-thiazol-2-

yl)-3-azabicyclo[3.1.0]hexane-6-carboxamide (31). The

title compound was prepared in 66% yield using the procedure

described for 33, but using 2-aminothiazole in reaction with

the pentafluorophenyl ester intermediate. ¹H NMR (300 MHz,

DMSO-d₆): 1.83 (s, 3H), 2.14 (br s, 2H), 2.25 (tr, J ) 2 Hz,

1H), 3.40 (tr, J ) 4 Hz, 2H), 3.50 (br s, 4H), 3.68 (dd, J ) 7, 5

Hz, 1H), 4.07 (tr, J ) 7 Hz, 1H), 4.72 (m, 1H), 7.18 (d, J ) 3

Hz, 1H), 7.26 (d, J ) 9 Hz, 2H), 7.44 (d, J ) 3 Hz, 1H), 8.24

(tr, J ) 6 Hz, 1H), 12.3 (s, 1H). ESI-MS (m/z): [M + H]⁺

478.5.

)

(S)-(1r,5r,6r)-3-(4-{(5S)-5-[(Acetylamino)methyl]-2-oxo-

1,3-oxazolidin-3-yl}-2,6-difluorophenyl)-N-(6-methoxy-

pyridin-3-yl)-3-azabicyclo[3.1.0]hexane-6-carboxamide

(32). The title compound was prepared using the procedure

described for 33, but using 5-amino-2-methoxypyridine in

reaction with the pentafluorophenyl ester intermediate. ¹H

NMR (300 MHz, DMSO-d₆): 1.82 (s, 3H), 2.01 (m, 1H), 2.03

(br s, 2H), 3.38 (m, 2H), 3.47 (m, 4H), 3.67 (m, 1H), 3.79 (s,

3H), 4.06 (tr, J ) 9 Hz, 1H), 4.70 (m, 1H), 6.77 (d, J ) 9 Hz,

1H), 7.24 (d, J ) 12 Hz, 2H), 7.87 (dd, J ) 9, 3 Hz, 1H), 8.23

(tr, J ) 6 Hz, 1H), 8.33 (d, J ) 2.5 Hz, 1H), 10.2 (s, 1H). ESI-

MS (m/z): [M + H]⁺) 502.5.

(S)-(1r,5r,6r)-3-(4-{(5S)-5-[(Acetylamino)methyl]-2-oxo-

1,3-oxazolidin-3-yl}-2,6-difluorophenyl)-N-(1,3-benzodiox-

ol-5-yl)-3-azabicyclo[3.1.0]hexane-6-carboxamide (35). The

title compound was prepared using the procedure described

for 33, but using 3,4-(methylenedioxy)aniline in reaction with

the pentafluorophenyl ester intermediate. ¹H NMR (300 MHz,

DMSO-d₆): 1.81 (s, 3H), 1.97 (m, 1H), 2.00 (br s, 2H), 3.29-

3.47 (m, 6H), 3.66 (m, 1H), 4.06 (tr, J ) 9 Hz, 1H), 4.71 (m,

1H), 5.95 (s, 2H), 6.81 (d, J ) 8 Hz, 1H), 6.94 (dd, J ) 8, 2 Hz,

1H), 7.24 (d, J ) 12 Hz, 2H), 7.29 (d, J ) 2 Hz, 1H), 8.23 (tr,

J ) 6 Hz, 1H), 10.1 (s, 1H). ESI-MS (m/z): [M + H]⁺) 515.5.

(tr, J ) 5 Hz, 1H), 11.1 (s, 1H). ESI-MS (m/z): [M + H]⁺

502.

)

(S)-(1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxooxazo-

lidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-

6-carboxylic Acid Hydroxyamide (30). Palladium (5 mg of

10% Pd on carbon) was added to a solution of (S)-(1R,5R,6R)-

3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-2,6-difluo-

rophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid benz-

yloxyamide (0.013 g, 0.026 mmol) in 2 mL of ethanol. The

mixture was stirred 2 h under a hydrogen atmosphere and

then filtered through Celite. The filtrate was concentrated and

the glassy solid obtained was lyophilized to give pure (S)-

(1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2,6-difluorophenyl}-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

1

hydroxyamide as a white solid. Yield: 9 mg (84%). H NMR

(300 MHz, CD₃OD): 1.74 (tr, J ) 3 Hz, 1H), 1.95 (s, 3H), 2.03

(m, 2H), 3.50-3.76 (m, 7H), 4.07 (tr, J ) 9 Hz, 1H), 4.76 (m,

1H), 7.16 (d, J ) 12 Hz, 2H). ESI-MS (m/z): [M + H]⁺) 411.

(S)-N-{3-[3,5-Difluoro-4-((1r,5r,6r)-6-formylamino-3-

azabicyclo[3.1.0]hex-3-yl)phenyl]-2-oxooxazolidin-5-

ylmethyl}acetamide (36). A solution of (S)-N-{3-[4-((1R,5R,6R)-

6-amino-3-azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-

oxooxazolidin-5-ylmethyl}acetamide hydrochloride (0.010 g,

0.025 mmol) in formic acid (0.5 mL) and acetic anhydride (0.25

mL) was stirred at room temperature for 3 days in a sealed

vial. The solution was concentrated and purified by preparative

HPLC to afford (S)-N-{3-[3,5-difluoro-4-((1R,5R,6R)-6-formy-

lamino-3-azabicyclo[3.1.0]hex-3-yl)phenyl]-2-oxooxazolidin-5-

(S)-(1r,5r,6r)-3-(4-{(5S)-5-[(Acetylamino)methyl]-2-oxo-

1,3-oxazolidin-3-yl}-2,6-difluorophenyl)-N-(2-furylmethyl)-

3-azabicyclo[3.1.0]hexane-6-carboxamide (33). A solution

of (S)-(1R,5R,6R)-3-(4-{(5S)-5-[(acetylamino)methyl]-2-oxo-1,3-

oxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid (0.8 g, 1.57 mmol) in DMF (6 mL) and

pyridine (0.51 mL, 6.28 mmol) was treated with pentafluo-

rophenyl trifluoroacetate (0.54 mL, 3.14 mmol) and the

mixture was stirred at room temperature for 2 h. The reaction

mixture was dissolved in EtOAc; washed with 0.1 N HCl,

water, and brine; dried over MgSO₄; and concentrated. The

resulting pentafluorophenyl ester intermediate (0.075 g, 0.13

mmol) was dissolved in DMF (2 mL), and to this solution,

furfurylamine (0.035 mL, 0.4 mmol) was added and the

mixture stirred at room temperature for 16 h. The reaction

mixture was dissolved in EtOAc, washed with water and brine,

dried over MgSO₄, and concentrated. The title compound was

isolated by pTLC (5% MeOH/dichloromethane). Yield: 0.043

1

ylmethyl}acetamide. Yield: 6 mg (61%). H NMR (300 MHz,

DMSO): 1.67 (m, 2H), 1.82 (s, 3H), 2.76 (m, 1H), 3.35-4.02

(m, 7H), 4.06 (tr, J ) 9 Hz, 1H), 4.71 (m, 1H), 7.23 (d, J ) 9

Hz, 2H), 7.98 (s, 1H), 8.17 (d, J ) 3 Hz, 1H), 8.24 (tr, J ) 6

Hz, 1H). ESI-MS (m/z): [M + H]⁺) 395.

(S)-N-{3-[4-((1r,5r,6r)-6-Acetylamino-3-azabicyclo[3.1.0]-

hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

acetamide (37). Triethylamine (0.012 mL, 0.086) and acetic

anhydride (2.8 µL, 0.029 mmol) were added to a solution of

(S)-N-{3-[4-((1R,5R,6R)-6-amino-3-azabicyclo[3.1.0]hex-3-yl)-

3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}acetamide hy-

drochloride (0.010 g, 0.025 mmol) in DMF (0.2 mL), The

reaction mixture was stirred for 3 h at room temperature and

then diluted with ethyl acetate (10 mL). This solution was

washed with 2.5% aq NaHCO₃and brine and dried (Na₂SO₄).

The mixture was filtered and concentrated and the crude

product purified by preparative TLC (5% MeOH-dichlo-

romethane) to afford (S)-N-{3-[4-((1R,5R,6R)-6-acetylamino-3-

azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-

5-ylmethyl}acetamide. Yield: 6 mg (60%). ¹H NMR (300 MHz,

1

g (70%). H NMR (300 MHz, DMSO-d₆): 1.81-1.84 (m, 4H)

1.90 (s, 2H), 3.35-3.41 (m, 6H), 3.62-3.68 (m, 1H), 4.01-4.07

(t, J ) 9 Hz, 1H), 4.23-4.25 (d, J ) 9 Hz, 3H), 4.67-4.72 (m,

1H), 6.21-6.23 (d, J ) 4 Hz, 1H), 6.36-6.38 (d, J ) 4 Hz, 1H),

7.19-7.23 (d, J ) 9 Hz, 2H), 7.56 (s, 1H), 8.20-8.24 (t, J ) 4

Hz, 1H), 8.53-8.57(t, J ) 4 Hz, 1H). ESI-MS (m/z): [M + H]⁺

) 475.4.

(S)-(1r,5r,6r)-3-(4-{(5S)-5-[(Acetylamino)methyl]-2-oxo-

1,3-oxazolidin-3-yl}-2,6-difluorophenyl)-N-(pyridin-2-yl-

methyl)-3-azabicyclo[3.1.0]hexane-6-carboxamide (34).

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5021

CDCl₃-CD₃OD): 1.59 (m, 2 H), 1.87 (s, 3H), 1.93 (s, 3H), 2.76

(m, 1H), 3.19-3.67 (m, 7H), 3.92 (tr, J ) 9 Hz, 1H), 4.68 (m,

added to a cooled (-78 °C) solution of [(1R,5R,6R)-3-(4-

benzyloxycarbonylamino-2,6-difluorophenyl)-3-azabicyclo[3.1.0]-

hex-6-yl]carbamic acid tert-butyl ester (0.57 g, 1.24 mmol) in

THF (2.5 mL). After stirring for 1.5 h, (R)-(-)-glycidyl butyrate

(0.193 mL, 1.36 mmol) was added and the reaction mixture

allowed to warm to room temperature and stirred for 16 h.

The reaction was quenched with satd NH₄Cl (50 mL) and

extracted with ethyl acetate. The organic layers were washed

with H₂O and brine, dried (MgSO₄), filtered, and concentrated.

Purification by column chromatography (0-5% MeOH-di-

chloromethane) provided pure (S)-{(1R,5R,6R)-3-[2,6-difluoro-

4-(5-hydroxymethyl-2-oxooxazolidin-3-yl)phenyl]-3-azabicyclo-

[3.1.0]hex-6-yl}carbamic acid tert-butyl ester. Yield: 0.43 g

1H), 6.94 (dq, J ) 10, 2 Hz, 2H). ESI-MS (m/z): [M + H]⁺

)

409.

(S)-N-((1r,5r,6r)-3-{4-[5-(Acetylaminomethyl)-2-oxoox-

azolidin-3-yl]-2,6-difluorophenyl}-3-azabicyclo[3.1.0]hex-

6-yl)-2-hydroxyacetamide (38). A mixture of acetoxyacetic

acid (0.033 g, 0.28 mmol), diisopropylethylamine (0.131 mL,

0.75 mmol), and HATU (0.105 g, 0.28 mmol) in DMF (0.1 mL)

was stirred for 15 min and then added to a solution of (S)-N-

{3-[4-((1R,5R,6R)-6-amino-3-azabicyclo[3.1.0]hex-3-yl)-3,5-dif-

luorophenyl]-2-oxooxazolidin-5-ylmethyl}acetamide hydrochlo-

ride (0.10 g, 0.25 mmol) in DMF (0.1 mL). After stirring for 1

h, the solution was diluted with 15 mL of ethyl acetate; washed

with 10% citric acid, H₂O, and brine; dried (MgSO₄); filtered;

and concentrated to an oil (0.08 g, 0.17 mmol). The crude

acetate was dissolved in methanol (1 mL) and treated with

0.1 M LiOH in methanol (1 mL). After stirring for 30 min the

solution was concentrated and the residue purified by pre-

parative TLC (6% MeOH-dichloromethane) to provide (S)-N-

((1R,5R,6R)-3-{4-[5-(acetylaminomethyl)-2-oxooxazolidin-3-yl]-

2,6-difluorophenyl}-3-azabicyclo[3.1.0]hex-6-yl)-2-hy-

droxyacetamide. Yield: 0.010 g (9%). ¹H NMR (300 MHz,

DMSO): 1.76 (m, 2H), 1.82 (s, 3H), 2.79 (m, 1H), 3.33-3.42

(m, 6H), 3.68 (m, 1H), 3.78 (d, J ) 6 Hz, 2H), 4.06 (tr, J ) 9

Hz, 1H), 4.71 (m, 1H), 5.40 (tr, J ) 6 Hz, 1H), 7.23 (d, J ) 9

Hz, 2H), 7.83 (d, J ) 5 Hz, 1H), 8.23 (br tr, 1H). ESI-MS

(m/z): [M + H]⁺) 425.

(S)-N-{3-[3,5-Difluoro-4-((1r,5r,6r)-6-methanesulfon-

ylamino-3-azabicyclo[3.1.0]hex-3-yl)phenyl]-2-oxooxazolidin-

5-ylmethyl}acetamide (39). Triethylamine (8 µL, 0.057) and

methanesulfonyl chloride (2.2 µL, 0.029 mmol) were added to

a solution of (S)-N-{3-[4-((1R,5R,6R)-6-amino-3-azabicyclo-

[3.1.0]hex-3-yl)-3,5-difluoro-phenyl]-2-oxooxazolidin-5-ylmethyl}-

acetamide hydrochloride (7.6 mg, 0.019 mmol) in DMF (0.2

mL). After stirring for 2 h at room temperature, the solution

was diluted with ethyl acetate (10 mL) and 2.5% NaHCO₃(5

mL). The layers were separated, and the aqueous solution was

extracted with two portions of ethyl acetate. The combined

organic phases were washed with brine and dried (MgSO₄).

The mixture was filtered and concentrated and the crude

product purified by preparative TLC (5% MeOH-dichloro-

methane) to afford (S)-N-{3-[3,5-difluoro-4-((1R,5R,6R)-6-meth-

anesulfonylamino-3-azabicyclo[3.1.0]hex-3-yl)phenyl]-2-oxoox-

azolidin-5-ylmethyl}acetamide. Yield: 5.8 mg (70%). ¹H NMR

(300 MHz, CDCl₃-CD₃OD): 1.84 (br s, 2H), 1.95 (s, 3H), 2.64

(br s, 1H), 2.98 (s, 3H), 3.42-3.55 (m, 6H), 3.64 (m, 1H), 3.93

(tr, J ) 9 Hz, 1H), 4.70 (m, 1H), 6.98 (d, J ) 11 Hz, 2H). ESI-

MS (m/z): [M + H]⁺) 445.

(S)-N-(3-{3,5-Difluoro-4-[(1r,5r,6r)-6-(3-phenylureido)-

3-azabicyclo[3.1.0]hex-3-yl]phenyl}-2-oxooxazolidin-5-yl-

methyl)acetamide (40). Triethylamine (6.0 µL, 0.042) and

phenyl isocyanate (3.3 µL, 0.029 mmol) were added to a

solution of (S)-N-{3-[4-((1R,5R,6R)-6-amino-3-azabicyclo[3.1.0]-

hex-3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

acetamide hydrochloride (8.6 mg, 0.021 mmol) in dichloro-

methane (0.1 mL) and NMP (0.1 mL). After stirring for 2 h at

room temperature, the solution was diluted with ethyl acetate

(10 mL) and 2.5% NaHCO₃(5 mL). The layers were separated,

and the aqueous solution was extracted with two portions of

ethyl acetate. The combined organic phases were washed with

brine and dried (MgSO₄). The mixture was filtered and

concentrated and the crude product purified by preparative

TLC (5% MeOH-dichloromethane) to afford (S)-N-(3-{3,5-

difluoro-4-[(1R,5R,6R)-6-(3-phenylureido)-3-azabicyclo[3.1.0]-

hex-3-yl]phenyl}-2-oxooxazolidin-5-ylmethyl)acetamide.

Yield: 8.0 mg (80%). ¹H NMR (300 MHz, CDCl₃-CD₃OD):

1.72 (br s, 2H), 1.96 (s, 3H), 2.73 (br s, 1H), 3.51-3.67 (m, 7H),

3.93 (tr, J ) 9 Hz, 1H), 4.70 (m, 1H), 7.00 (d, J ) 12 Hz, 2H),

7.21-7.32 (m, 5H). ESI-MS (m/z): [M + H]⁺) 486.

1

(81%). H NMR (300 MHz, CDCl₃): 1.43 (s, 9H), 1.64 (s, 2H),

2.69 (s, 1H), 3.43-3.56 (m, 4H), 3.69-3.76 (m, 1H), 3.83-3.99

(m, 3H), 4.67-4.75 (m, 2H), 7.06 (d, J ) 6 Hz, 2H).

(S)-{(1r,5r,6r)-3-[4-(5-Aminomethyl-2-oxooxazolidin-3-

yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hex-6-yl}-

carbamic Acid tert-Butyl Ester (42). Triethylamine (0.28

mL, 2.02 mmol) and methanesulfonyl chloride (0.078 mL, 1.01

mmol) were added to a cooled (0 °C) solution of (S)-{(1R,5R,6R)-

3-[2,6-difluoro-4-(5-hydroxymethyl-2-oxooxazolidin-3-yl)phenyl]-

3-azabicyclo[3.1.0]hex-6-yl}carbamic acid tert-butyl ester (0.43

g, 1.01 mmol) in dichloromethane (5 mL). After 30 min, the

reaction mixture was warmed to room temperature and diluted

with dichloromethane (20 mL). The organic solution was

washed with H₂O and brine, dried (MgSO₄), filtered, and

concentrated to provide crude (S)-methanesulfonic acid 3-[4-

((1R,5R,6R)-6-tert-butoxycarbonylamino-3-azabicyclo[3.1.0]hex-

3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl

Yield: 0.50 g (99%).

ester.

Sodium azide (0.328 g, 5.05 mmol) was added to a solution

of (S)-methanesulfonic acid 3-[4-((1R,5R,6R)-6-tert-butoxycar-

bonylamino-3-azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-

oxooxazolidin-5-ylmethyl ester (0.50 g, 1.01 mmol) in DMF (5

mL). The reaction mixture was heated at 70 °C for 15 h, cooled,

and diluted with ethyl acetate. The organic solution was

washed with H₂O and brine, dried (MgSO₄), filtered, and

concentrated to provide (S)-{(1R,5R,6R)-3-[4-(5-azidomethyl-

2-oxooxazolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]-

hex-6-yl}carbamic acid tert-butyl ester. Triphenylphosphine

(0.618 g, 2.36 mmol) was added to a solution of the crude azide

in THF (5 mL). After 3 h at room temperature, H₂O (0.3 mL)

was added and the reaction mixture was heated at 40 °C for

16 h. The reaction mixture was then concentrated and the

crude product purified by column chromatography (0-5%

MeOH-dichloromethane) to provide (S)-{(1R,5R,6R)-3-[4-(5-

aminomethyl-2-oxooxazolidin-3-yl)-2,6-difluorophenyl]-3-

azabicyclo[3.1.0]hex-6-yl}carbamic acid tert-butyl ester.

Yield: 0.24 g (56% over three steps). ¹H NMR (300 MHz,

CDCl₃): 1.43 (s, 9H), 1.64 (s, 2H), 2.69 (s, 1H), 2.95-3.07 (m,

2H), 3.43-3.55 (m, 4H), 3.72-3.77 (m, 1H), 3.92 (t, J ) 9 Hz,

1H), 4.59-4.65 (m, 1H), 7.06 (d, J ) 9 Hz, 2H).

(S)-N-{3-[4-((1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]hex-

3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

2,2-dichloroacetamide (46). Dichloroacetic anhydride (0.20

mL, 1.36 mmol) and pyridine (0.22 mL, 2.72 mmol) were added

to a solution of (S)-{(1R,5R,6R)-3-[4-(5-aminomethyl-2-oxoox-

azolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hex-6-yl}-

carbamic acid tert-butyl ester (0.29 g, 0.68 mmol) in DMF (5

mL). The mixture was stirred for 15 h at room temperature.

The reaction mixture was then poured into ethyl acetate and

washed with 5% citric acid, H₂O, and brine. The organic layer

is dried (MgSO₄), filtered, and concentrated. Purification by

column chromatography (0-3% MeOH-dichloromethane) pro-

vided (S)-[(1R,5R,6R)-3-(4-{5-[(2,2-dichloroacetylamino)methyl]-

2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]-

hex-6-yl]carbamic acid tert-butyl ester. Yield: 0.27 g (74%).

A 4 M solution of HCl in dioxane (4 mL) was added to a

solution of (S)-[(1R,5R,6R)-3-(4-{5-[(2,2-dichloroacetylamino)-

methyl]-2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo-

[3.1.0]hex-6-yl]carbamic acid tert-butyl ester (0.27 g, 0.50

mmol) in dioxane (4 mL). The reaction mixture was stirred

for 3 h and the solvent was removed in vacuo. The residue

(S)-{(1r,5r,6r)-3-[2,6-Difluoro-4-(5-hydroxymethyl-2-

oxooxazolidin-3-yl)phenyl]-3-azabicyclo[3.1.0]hex-6-yl}-

carbamic Acid tert-Butyl Ester (41). Lithium hexameth-

yldisilylamide (2.5 mL of a 1.0 M THF solution, 2.5 mmol) was

5022 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

was dissolved in H₂O (5 mL) and washed with two portions of

dichloromethane. The layers were separated, and the aqueous

layer was frozen and lyophilized to afford the pure (S)-N-{3-

[4-((1R,5R,6R)-6-amino-3-azabicyclo[3.1.0]hex-3-yl)-3,5-difluo-

rophen yl]-2-oxooxazolidin-5-ylmethyl}-2,2-dichloroacetamide.

Yield: 0.22 g (99%). ¹H NMR (300 MHz, DMSO): 1.95 (m, 2H),

2.58 (m, 1H), 3.36 (m, 4H), 3.51 (tr, J ) 6 Hz, 2H), 3.65-3.70

(m, 1H), 4.09 (tr, J ) 9 Hz, 1H), 4.79 (m, 1H), 6.49 (s, 1H),

7.22 (d, J ) 12 Hz, 2H), 8.18 (m, 2H), 9.01 (br tr, 1H). ESI-MS

(m/z): [M + H]⁺) 435.

N-[((5S)-3-{4-[(1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]-

hex-3-yl]-3,5-difluorophenyl}-2-oxo-1,3-oxazolidin-5-yl)-

methyl]cyclopropanecarboxamide (43). The title com-

pound was prepared according to the procedure described

above for 46 but using cyclopropane carboxylic acid in the

coupling reaction. ¹H NMR (300 MHz, DMSO): 0.59-0.65 (m,

4H), 1.53-1.65 (m, 3H), 2.43 (s, 1H), 3.26-3.39 (m, 6H), 3.63-

3.68 (m, 1H), 4.04 (t, J ) 9 Hz, 1H), 4.68-4.72 (m, 1H), 7.20

(d, J ) 9 Hz, 2H), 8.45 (t, J ) 6 Hz, 1H). ESI-MS (m/z): [M +

H]⁺) 393.5.

N-[((5S)-3-{4-[(1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]-

hex-3-yl]-3,5-difluorophenyl}-2-oxo-1,3-oxazolidin-5-yl)-

methyl]propanamide (44). The title compound was prepared

according to the procedure described above for 46 but using

propionic acid in the coupling reaction. ¹H NMR (300 MHz,

DMSO): 0.94 (tr, J ) 8 Hz, 3H), 1.95 (s, 2H), 2.07 (q, J ) 8

Hz, 2H), 2.57 (br s, 1H), 3.35 (br s, 4H), 3.67 (m, 2H), 4.04 (tr,

J ) 9 Hz, 1H), 4.22 (m, 1H), 4.70 (m, 1H), 7.22 (d, J ) 12 Hz,

2H), 8.17 (tr, J ) 6 Hz, 1H), 8.19 (br s, 2H). ESI-MS (m/z): [M

+ H]⁺) 381.5.

(S)-N-{3-[4-((1r,5r,6r)-6-Amino-3-azabicyclo[3.1.0]hex-

3-yl)-3,5-difluorophenyl]-2-oxooxazolidin-5-ylmethyl}-

2,2-difluoroacetamide (45). Ethyl difluoroacetate (0.50 mL,

5.0 mmol) and triethylamine (0.278 mL, 2.1 mmol) were added

to a solution of (S)-{(1R,5R,6R)-3-[4-(5-aminomethyl-2-oxoox-

azolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hex-6-yl}-

carbamic acid tert-butyl ester (0.30 g, 0.70 mmol) in MeOH (3

mL). The solution was stirred for 15 h at room temperature

and then concentrated. Purification by column chromatogra-

phy (0-2% MeOH-dichloromethane) provided (S)-[(1R,5R,6R)-

3-(4-{5-[(2,2-difluoroacetylamino)methyl]-2-oxooxazolidin-3-

yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]hex-6-yl]carbamic acid

tert-butyl ester. Yield: 0.35 g (99%).

A 4 M solution of HCl in dioxane (4 mL) was added to a

solution of (S)-[(1R,5R,6R)-3-(4-{5-[(2,2-difluoroacetylamino)-

methyl]-2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo-

[3.1.0]hex-6-yl]carbamic acid tert-butyl ester (0.34 g, 0.68

mmol) in dioxane (4 mL). The reaction mixture was stirred

for 3 h and the solvent was removed in vacuo and lyophilized

from H₂O and CH₃CN to afford (S)-N-{3-[4-((1R,5R,6R)-6-

amino-3-azabicyclo[3.1.0]hex-3-yl)-3,5-difluorophenyl]-2-oxoox-

azolidin-5-ylmethyl}-2,2-difluoroacetamide. Yield: 0.27 g (99%).

¹H NMR (300 MHz, DMSO): 1.91 (m, 2H), 2.48 (m, 1H), 3.28

(m, 4H), 3.43 (m, 2H), 3.65 (m, 1H), 4.02 (tr, J ) 9 Hz, 1H),

4.71 (m, 1H), 6.18 (tr, J ) 54 Hz, 1H), 7.15 (d, J ) 12 Hz, 2H),

8.31 (d, J ) 4 Hz, 2H), 9.14 (tr, J ) 5 Hz, 1H). ESI-MS (m/z):

[M + H]⁺) 403.

(S)-(1r,5r,6r)-3-[2,6-Difluoro-4-(5-hydroxymethyl-2-

oxooxazolidin-3-yl)phenyl]-3-azabicyclo[3.1.0]hexane-6-

carboxylic Acid tert-Butyl Ester (47). Lithium hexameth-

yldisilylamide (9.0 mL of a 1.0 M THF solution, 9.0 mmol) was

added to a cooled (-78 °C) solution of (1R,5R,6R)-3-(4-benz-

yloxycarbonylamino-2,6-difluorophenyl)-3-azabicyclo[3.1. 0]-

hexane-6-carboxylic acid tert-butyl ester (2.0 g, 4.5 mmol) in

THF (10 mL). After stirring for 1.5 h, (R)-(-)-glycidyl butyrate

(0.70 mL, 4.95 mmol) was added and the reaction mixture

allowed to warm to room temperature and stirred for 16 h.

The reaction was quenched with satd NH₄Cl (50 mL) and

extracted with ethyl acetate. The organic layers were washed

with H₂O and brine, dried (MgSO₄), filtered, and concentrated.

Purification by column chromatography (0-5% MeOH-dichlo-

romethane) provided pure (S)-(1R,5R,6R)-3-[2,6-difluoro-4-(5-

hydroxymethyl-2-oxooxazolidin-3-yl)phenyl]-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid tert-butyl ester. Yield: 1.6 g (87%).

¹H NMR (300 MHz, CDCl₃): 1.45 (s, 9H), 1.82 (tr, J ) 3 Hz,

1H), 2.02 (m, 2H), 3.48-3.56 (m, 4H), 3.72-4.02 (m, 4H), 4.73

(m, 1H), 7.07 (d, J ) 12 Hz, 2H). ESI-MS (m/z): [M + H]⁺

)

411.

(S)-(1r,5r,6r)-3-[4-(5-Aminomethyl-2-oxooxazolidin-3-

yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hexane-6-car-

boxylic Acid tert-Butyl Ester (48). Triethylamine (0.5 mL,

5.5 mmol) and methanesulfonyl chloride (0.28 mL, 3.65 mmol)

were added to a cooled (0 °C) solution of (S)-(1R,5R,6R)-3-[2,6-

difluoro-4-(5-hydroxymethyl-2-oxooxazolidin-3-yl)phenyl]-3-

azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl ester (1.5

g, 3.65 mmol) in dichloromethane (15 mL). After 30 min, the

reaction mixture was warmed to room temperature and diluted

with dichloromethane (30 mL). The organic solution was

washed with H₂O and brine, dried (MgSO₄), filtered, and

concentrated to provide (S)-(1R,5R,6R)-3-[2,6-difluoro-4-(5-

methanesulfonyloxymethyl-2-oxooxazolidin-3-yl)phenyl]-3-

azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl ester.

1

Yield: 1.7 g (99%). H NMR (300 MHz, CDCl₃): 1.46 (s, 9H),

1.81 (tr, J ) 3 Hz, 1H), 2.03 (m, 2H), 3.11 (s, 3H), 3.50-3.58

(m, 4H), 3.86 (dd, J ) 9, 6 Hz, 1H), 4.07 (tr, J ) 9 Hz, 1H),

4.45 (dq, J ) 12, 4 Hz, 2H), 4.91 (m, 1H), 7.05 (d, J ) 11 Hz,

2H).

Sodium azide (1.20 g, 18.3 mmol) was added to a solution

of (S)-(1R,5R,6R)-3-[2,6-difluoro-4-(5-methanesulfonyloxymethyl-

2-oxooxazolidin-3-yl)phenyl]-3-azabicyclo[3.1.0]hexane-6-car-

boxylic acid tert-butyl ester (1.7 g, 3.5 mmol) in DMF (5 mL).

The reaction mixture was heated at 70 °C for 15 h, cooled,

and diluted with ethyl acetate. The organic solution was

washed with H₂O and brine, dried (MgSO₄), filtered, and

concentrated to provide (S)-(1R,5R,6R)-3-[4-(5-azidomethyl-2-

oxooxazolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester (1.5 g, 3.44 mmol). Triphen-

ylphosphine (1.5 g, 3.8 mmol) was added to a solution of the

crude azide in THF (11 mL). After 3 h at room temperature,

H₂O (0.36 mL) was added and the reaction mixture was heated

at 40 °C for 16 h. The reaction mixture was then concentrated

and the crude product purified by column chromatography (0-

7% MeOH-dichloromethane) to provide pure (S)-(1R,5R,6R)-

3-[4-(5-aminomethyl-2-oxooxazolidin-3-yl)-2,6-difluorophenyl]-

3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl ester.

Yield: 1.20 g (86%). ¹H NMR (300 MHz, CDCl₃): 1.46 (s, 9H),

1.83 (tr, J ) 3 Hz, 1H), 2.03 (m, 2H), 2.95 (dd, J ) 14, 6 Hz,

1H), 3.12 (dd, J ) 14, 4 Hz, 1H), 3.42-3.52 (m, 4H), 3.78 (dd,

J ) 9, 7 Hz, 1H), 3.95 (tr, J ) 9 Hz, 1H), 4.66 (m, 1H), 7.08 (d,

J ) 10 Hz, 2H). ESI-MS (m/z): [M + H]⁺) 410.

(S)-(1r,5r,6r)-3-(4-{5-[(2,2-Difluoroacetylamino)methyl]-

2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo-

[3.1.0]hexane-6-carboxylic Acid (50). Pyridine (0.12 mL,

1.46 mmol) and difluoroacetic acid (0.05 mL, 0.8 mmol) were

added to a solution of (S)-(1R,5R,6R)-3-[4-(5-aminomethyl-2-

oxooxazolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester (0.30 g, 0.73 mmol) in DMF

(3.0 mL). 1,3-Diisopropylcarbodiimide (0.125 mL, 0.8 mmol)

was then added and the mixture stirred for 16 h at room

temperature. The mixture was diluted with ethyl acetate,

washed with H₂O and brine, dried (MgSO₄), filtered, and

concentrated. The crude product was purified by column

chromatography (0-2% MeOH-dichloromethane) to provide

(S)-(1R,5R,6R)-3-(4-{5-[(2,2-difluoroacetylamino)methyl]-2-oxoox-

azolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]hexane-6-

1

carboxylic acid tert-butyl ester. Yield: 0.22 g (60%). H NMR

(300 MHz, CDCl₃): 1.46 (s, 9H), 1.80 (tr, J ) 3 Hz, 1H), 2.03

(m, 2H), 3.44-3.57 (m, 4H), 3.61-3.70 (m, 2H), 3.82-3.89 (m,

1H), 4.03 (tr, J ) 9 Hz, 1H), 4.80 (m, 1H), 5.93 (tr, J ) 54 Hz,

1H), 6.9 (br s, 1H), 7.02 (d, J ) 12 Hz, 2H). ESI-MS (m/z): [M

+ H]⁺) 488.

(S)-(1R,5R,6R)-3-(4-{5-[(2,2-Difluoroacetylamino)methyl]-2-

oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester (0.21 g, 0.4 mmol) was

dissolved in trifluoroacetic acid-dichloromethane (5 mL, 1:4)

and stirred for 3 h at room temperature. The solution was then

concentrated and the oil lyophilized from CH₃CN-H₂O to

provide (S)-(1R,5R,6R)-3-(4-{5-[(2,2-difluoroacetylamino)methyl]-

(Azabicyclo[3.1.0]hexylphenyl)oxazolidinones

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15 5023

(4) Sievert, D. M.; Boulton, M. L.; Stoltman, G.; Johnson, D.;

Stobierski, M. G.; Dowens, F. P.; Somsel, P. A.; Rudrik, J. T.;

Brown, W.; Hafeez, W.; Lundstrom, T.; Flanagan, E.; Johnson,

R.; Mitchell, J.; Chang, S. Staphylococcus aureus Resistant to

Vancomycin-United States, 2002. Morbidity Mortality Weekly

Rep. 2002, 51, 565-567.

2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]-

1

hexane-6-carboxylic acid. Yield: 0.18 g (99%). H NMR (300

MHz, DMSO): 1.64 (tr, J ) 3 Hz, 1H), 2.03 (m, 2H), 3.39-

3.52 (m, 2H), 3.43 (m, 4H), 3.71 (dd, J ) 9, 6 Hz, 1H), 4.08 (tr,

J ) 9 Hz, 1H), 4.78 (m, 1H), 6.24 (tr, J ) 54 Hz, 1H), 7.21 (d,

J ) 12 Hz, 2H), 9.15 (tr, J ) 6 Hz, 1H). ESI-MS (m/z): [M +

H]⁺) 432.

(5) Brickner, S. J. Oxazolidinone Antibacterial Agents. Curr. Pharm.

Des. 1996, 2, 175-194.

(6) Barbachyn, M. R.; Ford, C. W. Oxazolidinone Structure-Activity

Relationships Leading to Linezolid Angew. Chem., Int. Ed. 2003,

42, 2010-2023.

(7) Nilus, A. M. Have the oxazolidinones lived up to their billing?

Future perspectives for this antibacterial class. Curr. Opin.

Invest. Drugs. 2003, 4, 149-155.

(8) Shinabarger, D. Mechanism of Action of the Oxazolidinone

Antibacterial Agents Exp. Opin. Invest. Drugs 1999, 8, 1195-

1202.

(9) Kloss, P.; Xiong, L.; Shinabarger, D. L.; Mankin, A. S. Resistance

Mutations in 23 S rRNA Identify the Site of Action of the Protein

Synthesis Inhibitor Linezolid in the Ribosomal Peptidyl Trans-

ferase Center. J. Mol. Biol. 1999, 294, 93-101.

(10) Shinabarger, D. L.; Marotti, K. R.; Murray, R. W.; Lin, A. H.;

Melchior, E. P.; Swaney, S. M.; Dunyak, D. S.; Demyan, W. F.;

Buysse, J. M. Mechanism of Action of Oxazolidinones: Effects

of Linezolid and Eperezolid on Translation Reactions. Anti-

microb. Agents Chemother. 1997, 41, 2132-2136.

(11) Lin, A. H.; Murray, R. W.; Vidmar, T. J.; Marotti, K. R. The

Oxazolidinone Eperezolid Binds to the 50S Ribosomal Subunit

and Competes with Binding of Chloramphenicol and Lincomycin.

Antimicrob. Agents Chemother. 1997, 41, 2127-2131.

(12) For a review of recent efforts, see: Hutchinson, D. K. Oxazoli-

dinone Antibacterial Agents: A Critical Review. Curr. Topics

Med. Chem. 2003, 3, 1021-1042.

(13) Genin, M. J.; Allwine, D. A.; Anderson, D. J.; Barbachyn, M. R.;

Emmert, D. E.; Garmon, S. A.; Graber, D. R.; Grega, K. C.;

Hester, J. B.; Hutchinson, D. K.; Morris, J.; Reischer, R. J.; Ford,

C. W.; Zurenko, G. E.; Hamel, J. C.; Schaadt, R. D.; Stapert, D.;

Yagi, B. H. Substituent Effects on the Antibacterial Activity of

Nitrogen-Carbon-Linked (Azolylphenyl)oxazolidinones with Ex-

panded Activity Against the Fastidious Gram-Negative Organ-

isms Haemophilus influenzae and Moraxella catarrhalis. J. Med.

Chem. 2000, 43, 953-970.

(14) After our filing a patent application on this class, similar bicyclic

oxazolidinone antibacterials were disclosed by another group;

see Fukuda, Y. and Hammond, M. L. Bicyclo[3.1.0]hexane

Containing Oxazolidinone Antibiotic and Derivatives Thereof.

International Publication PCT WO 03/027083.

(15) Perrault, W. R.; Pearlman, B. A.; Godrej, D. B.; Jeganathan, A.;

Yamagata, K.; Chen, J. J.; Lu, C. V.; Herrinton, P. M.; Gadwood,

R. C.; Chan, L.; Lyster, M. A.; Maloney, M. T.; Moeslein, J. A.;

Greene, M. L.; Barbachyn, M. R. The Synthesis of N-Aryl-5(S)-

aminomethyl-2-oxazolidinone Antibacterials and Derivatives in

One Step from Aryl Carbamates. Org. Process. Res. Dev. 2003,

7, 533-546.

(16) Perrault, W. R.; Pearlman, B. A.; Godrej, D. B. Process to Prepare

Oxazolidinones. U.S. Patent Application Publication US 2002/

0169312.

(17) Barbachyn, M. R.; Brickner, S. J.; Hutchinson, D. K. Substituted

Oxazine and Thiazine Oxazolidinone Antibacterials. U.S. Patent

5,880,118, 1999.

(18) Brighty, K. E.; Castaldi, M. J. Synthesis of (1R,5R,6R)-6-Amino-

3-azabicyclo[3.1.0]hexane, a Novel Achiral Diamine. Synlett

1996, 1097-1099.

(S)-(1r,5r,6r)-3-(4-{5-[(2,2-Dichloroacetylamino)methyl]-

2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo-

[3.1.0]hexane-6-carboxylic Acid (51). Pyridine (0.20 mL, 2.4

mmol) and dichloroacetic anhydride (0.20 mL, 1.3 mmol) were

added to a solution of (S)-(1R,5R,6R)-3-[4-(5-aminomethyl-2-

oxooxazolidin-3-yl)-2,6-difluorophenyl]-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester (0.25 g, 0.61 mmol) in DMF

(0.75 mL) at room temperature. The mixture was stirred for

16 h, diluted with ethyl acetate, washed with H₂O and brine,

dried (MgSO₄), filtered, and concentrated. The crude product

was purified by preparative TLC (7% MeOH-10% CH₃CN-

dichloromethane) to provide (S)-(1R,5R,6R)-3-(4-{5-[(2,2-dichlo-

roacetylamino)methyl]-2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-

3-azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl ester.

Yield: 0.22 g (62%). ¹H NMR (300 MHz, CDCl₃): 1.46 (s, 9H),

1.80 (tr, J ) 3 Hz, 1H), 2.03 (m, 2H), 3.57 (m, 4H), 3.71-3.77

(m, 3H), 4.03 (tr, J ) 9 Hz, 1H), 4.83 (m, 1H), 5.94 (s, 1H),

7.02 (d, J ) 12 Hz, 2H), 7.06 (br s, 1H). ESI-MS (m/z): [M +

H]⁺) 521.

(S)-(1R,5R,6R)-3-(4-{5-[(2,2-Dichloroacetylamino)methyl]-2-

oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]hexane-

6-carboxylic acid tert-butyl ester (0.22 g, 0.40 mmol) was

dissolved in trifluoroacetic acid-dichloromethane (5 mL, 1:4)

and stirred for 3 h at room temperature. The solution was then

concentrated and the oil lyophilized from CH₃CN-H₂O to

provide (S)-(1R,5R,6R)-3-(4-{5-[(2,2-dichloroacetylamino)methyl]-

2-oxooxazolidin-3-yl}-2,6-difluorophenyl)-3-azabicyclo[3.1.0]-

hexane-6-carboxylic acid. Yield: 0.185 g (89%). ¹H NMR (300

MHz, DMSO): 1.64 (tr, J ) 3 Hz, 1H), 2.02 (m, 2H), 3.43 (m,

4H), 3.50 (m, 2H), 3.67 (dd, J ) 9, 6 Hz, 1H), 4.09 (tr, J ) 9

Hz, 1H), 4.78 (m, 1H), 6.47 (s, 1H), 7.21 (d, J ) 12 Hz, 2H),

8.96 (tr, J ) 5 Hz, 1H). ESI-MS (m/z): [M + H]⁺) 521.

(1r,5r,6r)-3-(2,6-Difluoro-4-{(5S)-2-oxo-5-[(propiony-

lamino)methyl]-1,3-oxazolidin-3-yl}phenyl)-3-azabicyclo-

[3.1.0]hexane-6-carboxylic Acid (49). The title compound

was prepared as described above for 51 but using propionic

1

anhydride in the acylation reaction. Yield: 0.120 g (79%). H

NMR (300 MHz, CDCl₃): 1.13 (tr, J ) 8 Hz, 3H), 1.93 (m, 1H),

2.16 (br s, 2H), 2.25 (q, J ) 8 Hz, 2H), 3.58 (m, 4H), 3.65-

3.75 (m, 3H), 3.97 (tr, J ) 9.5 Hz, 1H), 4.77 (m, 1H), 6.14 (tr,

J ) 6 Hz, 1H), 7.04 (d, J ) 11 Hz, 2H). ESI-MS (m/z): [M +

H]⁺) 410.

In Vitro Susceptibility Tests. Minimum inhibitory con-

centrations (MICs) of oxazolidinone analogues were deter-

mined by standard broth microdilution methods.³²

(19) Danheiser, R. L.; Savoca, A. C. Applications of Cyclopropyl-

boranes in Organic Synthesis 1. A Stereocontrolled Route to

Substituted Cyclopropanol Derivatives. J. Org. Chem. 1985, 50,

2401-2403.

Acknowledgment. We thank members of the ox-

azolidinone teams at Vicuron and Pfizer for helpful

discussions and encouragement.

(20) Kollmeyer, W. D. 3-Benzyl-3-azabicyclo(3.1.0)hexane-2,4-dione

U.S. Patent 4,183,857, 1980.

Supporting Information Available: ¹H NMR spectra

and/or HPLC data for all new oxazolidinone analogues. This

material is available free of charge via the Internet at http://

pubs.acs.org.

(21) Single point MIC determinations are generally considered

accurate within one dilution (2-fold numerically).

(22) Jo, Y. W.; Im, W. B.; Rhee, J. K.; Shim, M. J.; Kim, W. B.; Choi,

E. C. Synthesis and antibacterial activity of oxazolidinones

containing pyridine substituted with heteroaromatic ring. Bioorg.

Med. Chem. Lett. 2004, 12, 5909-5915.

(23) Hybrid quinolone-oxazolidinone antibacterials with a carboxylic

acid function on the quinolone ring have been reported, see

Gordeev, M. F.; Hackbarth, C.; Barbachyn, M. R.; Banitt, L. S.;

Gage, J. R.; Luehr, G. W.; Gomez, M.; Trias, J.; Morin, S. E.;

Zurenko, G. E.; Parker, C. N.; Evans, J. M.; White, R. J.; Patel,

D. V. Novel Oxazolidinone-Quinolone Hybrid Antimicrobials.

Bioorg. Med. Chem. Lett. 2003, 13, 4213-4216. and Hubschw-

erlen, C.; Specklin, J.-L.; Sigwalt, C.; Schroeder, S.; Locher, H.

H. Design, Synthesis and Biological Evaluation of Oxazolidinone-

Quinolone Hybrids. Bioorg. Med. Chem. 2003, 11, 2313-2319.

References

(1) Jones, R. N.; Sader, H. S. The Clinical Impact of Enterococcal

Resistance. Challenges Infect. Dis. 1993, 1, 1-5.

(2) Appelbaum, P. C. Emerging Resistance to Antimicrobial Agents

in Gram-positive Bacteria: Pneumococci. Drugs 1996, 51 (Suppl.

1), 1-5.

(3) Hiramatsu, K.; Hanaki, H.; Ino, T.; Yabuta, K.; Oguri, T.;

Tenover, F. C. Methicillin-resistant Staphylococcus aureus Clini-

cal Strain with Reduced Vancomycin Susceptibility. J. Anti-

microbial Chemother. 1997, 40, 135-146.

5024 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 15

Renslo et al.

(24) Johnson, P. D.; Aristoff, P. A.; Zurenko, G. E.; Schaadt, R. D.;

Yagi, B. H.; Ford, C. W.; Hamel, J. C.; Stapert, D.; Moerman, J.

K. Synthesis and Biological Evaluation of Benzazepine Oxa-

zolidinone Antibacterials Bioorg. Med. Chem. Lett. 2003, 13,

4197-4200.

Agents. 3. Synthesis and Evaluation of 5-Thiocarbamate

Oxazolidinones. Chem. Pharm. Bull. 2001, 49, 361-367.

(29) Gravestock, M. B. Heterocyclyl Aminomethyl Oxazolidinones as

Antibacterials. International Publication WO 00/21960, 2000.

(30) Gravestock, M. B.; Hales, N. J.; Carcanague, D. R. Hydroxy-

methyl substituted dihydroisoxazole derivatives useful as anti-

biotic agents. WO04078753, 16 September, 2004.

(31) Reck, F.; Zhou, F.; Girardot, M.; Kern, G.; Eyermann, C. J.;

Hales, N. J.; Ramsay, R. R.; Gravestock, M. B. Identification of

4-Substituted 1,2,3-Triazoles as Novel Oxazolidinone Antibacte-

rial Agents with Reduced Activity against Monoamine Oxidase

A J. Med. Chem. 2005, 48, 499-506.

(25) Riedl, B.; Haebich, D.; Stolle, A.; Ruppelt, M.; Bartel, S.;

Guarnieri, W.; Endermann, R.; Kroll, H.-P. Neue Substitueirte

Oxazolidinone. Ger. Offen. Patent 19604223, 1997.

(26) Hester, J. B.; Nidy, E. G.; Perricone, S. C.; Poel, T.-J. Oxazoli-

dinone Antibacterial Agents having a Thiocarbonyl Functional-

ity. WO 9854161, 1998.

(27) Tokuyama, R. Takahashi, Y.; Tomita, Y.; Suzuki, T.; Yoshida,

T.; Iwasaki, N.; Kado, N.; Okezaki, E.; Nagata, O. Structure-

Activity Relationship (SAR) Studies on Oxazolidinone Antibacte-

rial Agents. 1. Conversion of 5-substituent on Oxazolidinone.

Chem. Pharm. Bull. 2001, 49, 347-352.

(28) Tokuyama, R. Takahashi, Y.; Tomita, Y.; Tsubouchi, M.; Iwasaki,

N.; Kado, N.; Okezaki, E.; Nagata, O. Structure-Activity

Relationship (SAR) Studies on Oxazolidinone Antibacterial

(32) National Committee for Clinical Laboratory Standards. Methods

for Dilution Antimicrobial Susceptibility Tests for Bacteria That

Grow Aerobically, 4^thed. (Approved Standard); NCCLS Docu-

ment M7-A4; NCCLS: Wayne, Pa. 1997.

JM058204J

Article Doi

Conformational constraint in oxazolidinone antibacterials. Synthesis and structure-activity studies of (azabicyclo[3.1.0]hexylphenyl)oxazolidinones

DOI: 10.1021/jm058204j

Source and publish data:

Authors:

Article abstract of DOI:10.1021/jm058204j

Full text of DOI:10.1021/jm058204j

Products guided by the article

R&D Labs maybe for 681425-42-3

Relevant to this article

Hot Product