Fluorinated phenylcyclopropylamines. Part 5: Effects of electron-withdrawing or -donating aryl substituents on the inhibition of monoamine oxidases A and B by 2-aryl-2-fluoro-cyclopropylamines

Bioorganic & Medicinal Chemistry 16 (2008) 7148–7166

Contents lists available at ScienceDirect

Bioorganic & Medicinal Chemistry

journal homepage: w ww.elsevier.com/locate/bmc

Fluorinated phenylcyclopropylamines. Part 5: Effects of electron-withdrawing

or -donating aryl substituents on the inhibition of monoamine oxidases

A and B by 2-aryl-2-ﬂuoro-cyclopropylamines

Svenja Hruschka ^a, Thomas C. Rosen ^a, Shinichi Yoshida ^b, Kenneth L. Kirk ^c, Roland Fröhlich ^a,

,

Birgit Wibbeling ^a,, Günter Haufe ^a,

*

^aOrganisch-Chemisches Institut and International NRW Graduate School of Chemistry, Universität Münster, Corrensstr. 40, D-48149 Münster, Germany

^bTottori Institute of Industrial Technology, Tottori 689-1112, Japan

^cLaboratory of Bioorganic Chemistry, National Institute of Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human

Services, Bethesda, MD 20892, USA

a r t i c l e i n f o

a b s t r a c t

Article history:

A series of racemic, diastereoisomeric aryl cyclopropylamines substituted with ﬂuorine in the 2-position

and electron-donating and electron-withdrawing groups on the aromatic ring have been prepared. These

represent analogues of the classic MAO inhibitor tranylcypromine (trans-2-phenylcyclopropylamine, 1).

Their activities as inhibitors of recombinant human liver monoamine oxidases A (MAO A) and B (MAO B)

were determined. The trans-compounds were low micromolar inhibitors of both MAO A and MAO B with

moderate MAO A selectivity while the less active cis-analogues were MAO B selective. In the trans-series,

electron-withdrawing para-substituents increased the potency of MAO A inhibition while electron-

donating groups such as methyl or methoxy had no inﬂuence on this activity. In contrast, aromatic ring

substitution in the trans-series had essentially no effect on the inhibition of MAO B. The corresponding

cis-compounds were shown to be 10–100 times less active against MAO A, while trans- and cis-com-

pounds were quite similar in terms of inhibition of MAO B. The best MAO A/MAO B selectivity (7:1) in

the trans-series was found for trans-2-ﬂuoro-2-(para-triﬂuoromethylphenyl)cyclopropylamine (7d),

while a 1:27 selectivity was found for cis-2-ﬂuoro-2-(para-ﬂuorophenyl)cyclopropylamine (10c). These

results are discussed in connection with the pK_aand logD values, the mechanism of action of tranylcy-

promines, and the geometry of the active site of the enzymes.

Received 25 March 2008

Revised 18 June 2008

Accepted 26 June 2008

Available online 28 June 2008

Keywords:

Monoamine oxidase

Tranylcypromine

Fluorinated phenylcyclopropylamine

Irreversible inhibition

Stereochemistry

1. Introduction

tions in the body.³Therefore an abnormal activity of any partic-

ular enzyme can translate uniquely to a speciﬁc pathological

Monoamine oxidases are present in mammals, plants, and both

eukaryotic and prokaryotic microorganisms. They metabolize

amines of dietary origin as well as endogenous amines, including

amine neurotransmitters, to form the corresponding aldehyde,

hydrogen peroxide, and ammonia. Monoamine oxidases are highly

diverse and include the important copper-(EC 1.4.3.6) [CAO or

SSAO (semicarbazide sensitive amine oxidases)] and ﬂavin-depen-

dent (MAO A and MAO B) (EC 1.4.3.4) enzymes.¹Monoamine oxi-

dase B (MAO B) shares 70% of the amino acid sequence with MAO A

and, in particular, the active centers of both enzymes are very

similar.²

condition. For example, depression is associated with an abnor-

mally low level of amine neurotransmitters that can be allevi-

ated by intervention with inhibitors of MAO

A such as

clorgyline and moclobemid⁴whereas MAO B is associated with

neurodegenerative disorders such as Parkinson’s disease⁵and

Alzheimer’s disease.⁶Inhibitors of MAO B (e.g.,

no antidepressant effect.

L-deprenyl) show

In general, increased MAO activity can lead to excessive forma-

tion of the toxic metabolites, hydrogen peroxide and ammonia,

which in turn may contribute to tissue damage and neurodegener-

ation associated with oxidative stress. Adipocytes of diabetes pa-

tients have been shown to contain an increased level of copper-

containing amine oxidases (CAOs).⁷The toxic metabolites formed

may also be involved in typical damages that accompany diabetes

mellitus types I and II.⁸Hydrogen peroxide, in fact, can act as a mi-

mic of insulin and activate the transport of glucose into adipocytes.

In addition, oxidative stress induced by hydrogen peroxide may

Although different types of monoamine oxidase catalyze the

same oxidative deamination process they serve different func-

* Corresponding author. Tel.: +49 251 83 33281; fax: +49 251 83 39772.

E-mail address: haufe@uni-muenster.de (G. Haufe).

X-ray structure analysis.

doi:10.1016/j.bmc.2008.06.048

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7149

lead to damages of different tissues, capillary vessels in the eyes,

kidneys, and others.

trans-2-ﬂuoro-1-phenyl-cyclopropylamine (4) was a potent and

selective inhibitor of MAO A (selectivity index [IC₅₀(MAO B)/

IC₅₀(MAO A)] of 100). Neither 3 nor 4 was an inhibitor of tyra-

mine oxidase.^12,13

Recognition that monoamine oxidases represent promising tar-

gets for intervention in many amine oxidase-related disorders has

led to enormous efforts to produce potent and selective inhibitors

of these enzymes. Recently the therapeutic potential of mono-

amine oxidase inhibitors has been reviewed.^9,10One such inhibitor,

tranylcypromine (trans-2-phenylcyclopropylamine, 1) is a very po-

tent antidepressant that has been in clinical use since the 1960s.

However, side effects associated with this compound preclude its

use as a ﬁrst-line drug and it is prescribed in cases where other

therapies do not work, for example, for the treatment of resistant

depressions.¹¹

There have been previous investigations on the effects of mono-

ﬂuorination on other inhibitors of amine oxidases (Fig. 1). For

example, Palfreyman et al. found 3-ﬂuoroallylamine 5 to be a mod-

erate, but very selective inhibitor of MAO A giving a ratio of

[K_i(MAO B)/K_i(MAO A)] = 100.¹⁷At 20 °C, 5 has a K_i= 231

lM for

MAO A, whereas the inhibition of MAO B was too low to be de-

tected.¹⁸On the other hand, this compound is highly active to-

wards a CAO (IC₅₀= 0.006 l

M).¹⁹

Since the three-membered ring can be seen as a mimic of a dou-

ble bond, the observations reported by Palfreyman prompted us to

synthesize and to test ﬁrst the phenyl-substituted cyclopropane

analogue 6. This compound turned out to be a weaker inhibitor

than tranylcypromine (1). The MAO A/B selectivity was found to

NH₂

be approximately 1:15 (320:24

tion of tyramine oxidase (IC₅₀= 12

l

M), but it showed stronger inhibi-

l

M).^12,15

A further promising class of tranylcypromine derivatives is ana-

logues with a ﬂuorine substituent in the 2-position. Comparison of

trans-2-ﬂuoro-2-phenylcyclopropylamine (7a) with compounds 8

and 9 bearing a spacer between the amino group and the cyclopro-

pane ring showed 7a to be the best inhibitor of all three enzymes,

and was more potent than 1 (Fig. 2). The cis-isomers were also

tested which showed much lower inhibition than the trans-com-

pounds.^12,13,15We also demonstrated that only the (1S,2S)-2-ﬂu-

oro-2-phenylcyclopropylamine [(1S,2S)-7a] enantiomer possessed

inhibitory activity.¹³

1 (trans-isomer)

2 (cis-isomer)

The strategy of our investigations¹²has been to explore the

development of highly active and selective inhibitors of MAO A

and B as well as tyramine oxidase using tranylcypromine as a lead

compound. A particular goal was to ﬁnd more selective inhibitors

that would have fewer side effects.

In our previous work, we found that inhibitor activity and

selectivity could be varied by substitution of the phenyl ring of

cis- and trans-2-ﬂuoro-2-phenylcyclopropylamines [10 (cis) and

7 (trans), compare Scheme 1]. Opposite trends were found for

MAO and CAO. Thus, electron-withdrawing groups such as –Cl

and –F improved the efﬁciency of inhibition of MAO, whereas

electron-donating groups (–CH₃) enhanced the inhibition of tyra-

mine oxidase.¹²Based on these results, we have explored these

substituent effects more thoroughly with the goal both to ﬁnd

more potent inhibitors and to learn more about the interactions

of these compounds with the various enzyme-active sites. In this

paper these earlier results will be brought into context with our

new results on other substituted ﬂuoro-tranylcypromine

derivatives.

2. Results

We have previously reported the syntheses of various racemic

and enantiopure ﬂuorinated tranylcypromine analogues and have

described the results of their evaluation as inhibitors of the FAD-

dependent amine oxidases, MAO A and B, and of tyramine oxi-

dase, a copper-containing amine oxidase.^13–16In the previous

work, we discovered striking effects resulting from ﬂuorine sub-

stitution. For example, in our assays 1-phenylcyclopropylamine

(3) was found to be a modest inhibitor of MAO B, with no activ-

ity apparent for MAO A in the micromolar range. In contrast,

NH₂

2.1. Synthesis of ﬂuorinated arylcylopropylamines

NH₂

The racemic, monoﬂuorinated tranylcypromine derivatives

were synthesized by a six step sequence from substituted styrenes

11a–g. Bromoﬂuorination with NBS and a nucleophilic ﬂuorinating

agent (Et₃Nꢀ3HF or Pyꢀ9HF)²⁰and subsequent HBr elimination from

F

X

F

MeO

the bromoﬂuoride 12a–g produced

a-ﬂuorostyrene derivatives

3 ( X = H)

4 ( X = F)

13a–g.²¹Cyclopropanation of 13a–g with ethyl diazoacetate

(EDA) furnished the diastereomeric monoﬂuorinated cyclopropane-

carboxylic ethyl esters 14a–g (trans) and 15a–g (cis) in a ratio of

5

6

Figure 1. Monoamine oxidase inhibitors.

NH₂

F

NH₂

F

NH₂

>

7a (trans

)

1 (trans

)

8 (trans

)

9 (trans)

Figure 2. Rank order of activity as inhibitors of MAO A and B and tyramine oxidase.

7150

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

F

CO₂Et

+

F

N₂CHCO₂Et

cat. Cu(acac)₂

CO₂Et

R¹

R²

R¹

R²

CH₂Cl₂

NBS,

Et₃N·3HF

or: Py·9HF

F

R¹

R²

R¹

R²

Br

14a-g (trans)

15a-g (cis)

KO^tBu

pentane

R²

CH₂Cl₂

11a-g

12a-g

13a-g

CO₂Me

F

N₂C(CO₂Me)Ph

cat. Rh₂(OAc)₄

CO₂Me

+

CH₂Cl₂

16h (cis)

17h (trans)

Series:

a: R¹= H, R²= H, R³= H

b: R¹= H, R²= Cl, R³= H

c: R¹= H, R²= F, R³= H

d: R¹= H, R²= CF₃, R³= H

e: R¹= H, R²= Me, R³= H

f : R¹= H, R²= OMe, R³= H

g: R¹= R²= OMe, R³= H

h: R¹= H, R²= H, R³= Ph

NHBoc

R³

NH₂·HCl

CO₂H

R³

F

NEt₃, DPPA

^tBuOH, DiBoc

R³

KOH, MeOH

HCl

R¹

cyclohexane

or: KOH,

THF/H₂O

R²

18a-g (trans), 18h (cis)

19a-g (cis), 19h (trans)

20a-g (trans), 20h (cis)

21a-g (cis), 21h (trans)

7a-g (trans), 7h (cis)

10a-g (cis), 10h (trans)

Scheme 1. Synthesis of substituted tranylcypromine analogues.^à

F1

C2

F1

O1

C10

C1

C6

C7

C3

C9

F12

O2

F13

C2

F12

C4

C8

C5

C6

C11

C1

C3

C4

C11

C8

C9

C10

O2

F11

C7

O1

F13

F11

19d (cis)

18d (trans)

Figure 3. Crystal structures of the racemic para-triﬂuoromethylcyclopropane carboxylic acids 18d and 19d.

1:1.^àThe reaction of

a

-ﬂuorostyrene (13a) with methyl phenyl diazo

ties include the pK_avalue, which inﬂuences the solubility, adsorp-

tion, and reactivity of a given molecule at physiological pH.

Lipophilicity is also of high importance since it deﬁnes the perme-

ability through membranes (Fig. 4 and Table 1).

acetate leads to the formation of the methyl esters 16h (cis) and 17h

(trans).^àThe diastereomeric ratio in this case was cis:trans = 64:36.²²

Saponiﬁcation of the esters gave the corresponding acids 18a–h and

19a–h which were converted into the Boc-protected amines 20a–h

and 21a–h by Curtius rearrangement with DPPA, tert-butanol and

DiBoc. The last step in the sequence was deprotection with HCl to

obtain the desired monoﬂuorinated tranylcypromine analogues as

their hydrochlorides 7a–h and 10a–h. The relative stereochemistry

within the series of compounds was proved by single crystal X-ray

analysis of 18d and 19d (Fig. 3) and several more analogues (see Sec-

tion 5).

As expected, introduction of the highly electronegative ﬂuorine

atom into the 2-position of the cyclopropane ring decreases the pK_a

value. Similar observations have been reported for other ﬂuori-

nated amines.^23,24For trans-2-ﬂuorotranylcypromine (7a) the pK_a

value of 7.35 is more than one pH unit lower than for its non-ﬂuo-

rinated parent compound 1 (trans). There is an even greater 1.5 pH

unit difference between the corresponding cis-isomers 2 and 10a.

While the two isomeric non-ﬂuorinated tranylcypromines exhibit

similar acidities (ca. 8.50), the ﬂuorinated cis-isomer 10a

(pK_a= 6.98) is about 0.4 units more acidic than the ﬂuorinated

trans-isomer 7a (pK_a= 7.35). This difference can also be observed

for the aryl-ring substituted ﬂuoro-tranylcypromine analogues.

The different relative arrangement of ﬂuorine and the amino group

and hence, different orbital interactions seem to be responsible for

these differences. From quantum chemical calculations of the mod-

el compounds, cyclopropylamine, and cis- and trans-2-ﬂuorocyclo-

propylamine, it becomes obvious that there are hyperconjugative

2.2. Physical–chemical properties

The pharmacokinetics of biologically active compounds can be

predicted by means of physical–chemical properties. These proper-

à

In compounds 14a–g and 15a–g (and resulting derivatives) cis and trans refer to

the arrangement of the aryl ring towards the vicinal substituent, while in compounds

16h and 17h (and resulting derivatives) cis and trans refer to the arrangement of the

phenyl groups.

interactions between

r(C–N) and r

^*(C–F) in the ﬂuorinated

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7151

Table 1

NH₂

Physical–chemical properties of known and new inhibitors of MAO A and MAO B

a

R¹

H

R²

H

R³

H

Compound

pK_a

logD (lipo class)^b

NH₂

1^c

8.50

8.47

7.35

6.98

7.19

6.81

7.31

6.88

7.00

6.60

7.41

7.04

7.50

—

d

2^c

1.41 (medium)

1.53 (medium)

1.78 (medium)

2.23 (medium)

2.66 (high)

1.60 (medium)

2.14 (medium)

2.66 (high)

H

Ph

7a^c

10a^c

7b^c

10b^c

7c^c

10c^c

7d

1 (trans

)

2 (cis

)

H

Cl

F

R₃

F

NH₂

R₃

H

F

H

CF₃

Me

OMe

H

NH₂

10d

7e^c

10e^c

7f

10f

7g

10g

7h^f

10h^f

3.13 (high)

R₁

H

1.83 (medium)

e

—

d

H

R₂

e

d

—

OMe

H

7.40

0.58 (low)

7a-g (trans

)

10a-g (cis

)

e

d

—

7h (cis

)

10h (trans

)

7.20

5.80

2.39 (medium)

d

—

Figure 4. Compounds investigated in this study.

a

pK_avalues were determined titrametrically in 0.1 M KNO₃at 21 °C.

logD values were determined from the partition coefﬁcient for 1-octanol/0.05 N

b

trans-isomer which do not exist in the cis-isomer of these model

compounds. Moreover, the gas-phase proton afﬁnity calculated

for cis-2-ﬂuorocyclopropylamine is about 6 kcal mol^ꢁ1larger than

that of the trans-compound and ﬁnally the p-character of the nitro-

gen lone-pair, which is a measure for the basicity, is larger for the

cis-(sp^4.34) as compared to the trans-isomer (sp^4.07).²⁵

NaOH + 5 Vol% DMSO at pH 7.4.

c

The corresponding data were taken from the literature.¹²

d

Not determined.

Could not be determined.

7h (cis) and 10h (trans): in contrast to the other compounds 7 and 10 here cis

e

f

and trans refer to the arrangement of the two phenyl rings.

As anticipated, 7b–d (trans) and 10b–d (cis) have lower pK_aval-

ues due to their ꢁI-effect substituents whereas +I- and +M-substi-

tuted 7e,f and 7g as well as 10e and 10g have a higher pK_a

compared to 7a or 10a, respectively. A second phenyl group at

the cyclopropane ring decreases the pK_ato give a value for 10h

(pK_a= 7.20) comparable to para-chloro 7b (pK_a= 7.19). The latter

compound has a lower lipophilicity (2.23 for 7b vs 2.39 for 10h).

Thus, although the pK_as are similar the lipophilicities are different

and this could contribute to the different biological activities ob-

served (see Table 3).

The lipophilicity is inﬂuenced by the pK_asince, at a given pH va-

lue, a greater portion of the more basic amine will be protonated.

Moreover, the trans-isomers having both electronegative substitu-

ents, F and NH₂, in cis-orientation are expected to have a larger di-

pole moment. Both effects might contribute to the fact that all

ﬂuorinated cis-isomers have a higher logD than the trans-isomers

at pH 7.4. The logD values of the aryl ring-substituted analogues

reﬂect the expected effects of the inﬂuence of the various substit-

uents. Thus, as already known, non-polar groups improve the lipo-

philicity, while relatively polar groups decrease it. Fluorine is

known to increase the lipophilicity of a given molecule if it is

bonded to an sp²-center.^26,27

Among the para-substituted compounds, the trans-isomers

(relationship of NH₂to aryl) were better inhibitors for both MAO

A and B than the cis-isomers. The para-CF₃compound 7d (trans)

showed the best inhibition for MAO A, being 15 times more potent

than the non-substituted 7a. In contrast, as an inhibitor for MAO B,

7d was essentially equipotent to 7a. The para-OMe compound 7f

was a good inhibitor for both isozymes but did not exhibit the

MAO A selectivity seen with the other trans-isomers. In that regard

it may be signiﬁcant that the inhibition type of 7f for MAO A was

different from that for MAO B. Whereas 7f showed irreversible

inhibition of MAO B similar to the related analogues, it was not a

time- and concentration-dependent inhibitor for MAO A, but in-

stead showed simple competitive inhibition (Fig. 6A). Introduction

of other para-substituents, such as Cl, F, and CF₃into the trans iso-

mer, resulted in MAO A selectivity. All cis-conﬁgured, 2-ﬂuorinated

analogues showed MAO B selectivity. The precise K_iand k_inactval-

ues could not be obtained from the results of time- and concentra-

tion-dependent inactivation experiments. When the inhibitors

were added to the reaction mixture containing MAO, time- and

concentration-dependent inactivation was observed. However,

the decrease of the relative activity at each concentration of inhib-

itor deviated somewhat from the exponential curves as observed

and described in our previous report.¹³One reason for this might

be instability of these inhibitors under assay conditions.

Table 1 shows that this is also true for the pseudo-p system of

the cyclopropane ring. In addition, a triﬂuoromethyl group always

increases the lipophilicity when introduced into an aromatic ring

(compare both isomers 7d and 10d). A methyl group (+I) and

two methoxy groups in para (ꢁI/+M) and in meta-positions (ꢁI)

lead to similar pK_avalues [compare 7e (trans) and 7g (trans)]. Since

the methyl group is much less polar than the methoxy groups, 7e

exhibits a medium lipophilicity and 7g has a low logD of 0.58.

Dimethoxy analogues (7g and 10g) were weak inhibitors of

both isozymes, although 7g showed modest inhibition of MAO A.

Diphenyl analogues (7h, 10h) were modest inhibitors for both iso-

zymes, but showed different kinetic behavior with the two en-

zymes, being competitive inhibitors of MAO B and irreversible

inhibitors of MAO A (Table 2, Fig. 6B). These analogues showed

modest MAO A selectivity.

2.3. Inhibition of ﬂavin-dependent amine oxidases MAO A and

B by ﬂuorinated arylcyclopropylamines

3. Discussion

Our new analogues in the series of 2-ﬂuoro-2-phenylcyclopro-

pylamines 7d and 10d (para-CF₃), 7f and 10f (para-OMe), 7g and

10g (para- and meta-OMe), and 7h and 10h (1,2-diphenyl) were

studied as inhibitors of MAO A and B. Table 2 and Figure 5 provide

a summary of our results as well as the data obtained from the ana-

logues we reported previously.^12,13

3.1. Inhibition mechanism of MAO A and B

A brief review of current knowledge of the details of the mech-

anism of MAO A and MAO B will be useful in subsequent discus-

sions of our inhibition studies. In particular, differences in the

7152

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

Table 2

IC₅₀values and types of inhibition of known and new inhibitors of MAO A and MAO B

R¹

R²

R³

Compound

IC₅₀

(

l

M) (type of inhibition)^a

MAO B

Selectivity

MAO A:B

MAO A

H

Ph

1^b

2^b

20 0 (irr.)

11 1 (irr.)

19 0 (irr.)

19 1 (irr.)

1:1

1.7:1

H

7a^b

12 1 (irr.)

65 42 (irr.)

6.4 0.1 (irr.)

19 1 (irr.)

1:2

1:3.4

10a^b

H

Cl

7b^b

1.6 0 (irr.)

89 9 (irr.)

3.7 0.1 (irr.)

4.8 0.1 (irr.)

2.3:1

1:18.5

10b^b

H

F

7c^b

3.6 0.2 (irr.)

270 70 (irr.)

4.9 0.1 (irr.)

10 0 (irr.)

1.4:1

1:27

10c^b

H

CF₃

Me

OMe

H

7d

10d

0.8 0.1 (irr.)

76 17 (irr.)

5.4 0.5 (irr.)

7.1 0.2 (irr.)

6.8:1

1:10.7

H

7e^b

13 0 (irr.)

230 120 (irr.)

13 0 (irr.)

30 1 (irr.)

1:1

1:7.7

10e^b

H

7f

10f

14 5 (comp.)

5.1 0.8 (irr.)

18 6 (irr.)

1:2.8

—

c

—

(—)^d

OMe

H

7g

10g

47 5 (irr.)

230 26 (irr.)

470 310 (—)^d

4.9:1

—

c

—

(—)^d

7h^e

18 3 (irr.)

10 3 (irr.)

37 2 (comp.)

20 1 (comp.)

2:1

10h^e

a

irr., irreversible, comp., competitive. For the determination of the inhibition type see Section 5.3.

The corresponding data were taken from the literature.¹²

No inhibition was observed in micromolar range.

b

c

d

e

Could not be determined.

7h (cis) and 10h (trans): in contrast to the other compounds 7 and 10 here cis and trans refer to the arrangement of the two phenyl rings.

120

100

80

100

80

60

40

20

0

A

without

7f

60

40

20

-4

-2

0

2

4

6

8

1/[S] (mM^-1)

0

120

20

15

10

5

B

without

7h

10h

100

80

60

40

20

0

-4

-2

0

2

4

6

8

1/[S] (mM^-1)

0

5

10

15

20

25

30

35

Figure 6. Lineweaver-Burk plot for inactivation of MAO A by trans-2-ﬂuoro-2-(4-

methoxy)phenylcyclopropylamineꢀHCl (7f, 9.7 M) (A) and MAO B by cis-( )-2-

ﬂuoro-1,2-diphenylcyclopropylamineꢀHCl (7h, 28.2 M) and trans-2-ﬂuoro-1,2-

M) (B). Data were collected after the

inhibition by 7f, 7h, and 10h was checked to be independent of time and

concentration.

Inhibitor (μM)

l

Figure 5. Effect of concentration of ﬂuorinated phenylcyclopropylamines (closed

circle, 7d; open circle, 10d; closed square, 7f; open square, 10f; closed diamond, 7g;

open diamond, 10g; closed triangle, 7f; open triangle, 10f) on MAO A (A) and B (B)

activity. The procedure is described in Section 5.2.

diphenylcyclopropylamineꢀHCl (10h, 8.4

l

structure–activity relationships of the two isozymes will be impor-

tant in the interpretation of our results.

Silverman based his explanation of the inhibition of MAO A and

B by tranylcypromine and other cyclopropylamines on a single

electron transfer (SET) from the inhibitor to the active site oxidized

ﬂavin. This leads to an amine radical cation, which is followed by

cyclopropyl ring opening and subsequent radical coupling of the

inhibitor to the enzyme (Fig. 7).^28,29

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7153

R

N

R

N

O

N

O

NH

N

NH₂

Ph

SET

Ph

Enzyme

S

Enzyme SH

Ph

NH₂

Ph

NH₂

Figure 7. SET mechanism adapted from Ref. 28.

According to this formulation, the opening of the ring would be

an important step in the actual mechanism of inhibition, which

was further conﬁrmed for several 1-phenylcyclopropylamines

and N-benzylcyclopropylamines.^30–39Moreover, the results of bio-

transformation of tranylcypromine in rat liver microsomes also

support such a pathway.⁴⁰This also would be consistent with the

increased activity of our ﬂuorinated analogues of tranylcypromine

since a ﬂuorine substituent increases the strain of a cyclopropane

ring.^41–44According to such a mechanism, from our inhibitors

The most striking evidence against the SET mechanism is the

big difference in one-electron oxidation-reduction potentials of

primary or secondary amines (1.0–1.5 V)⁴⁵and the covalent MAO

B ﬂavin potential of approximately 0.04 V.⁴⁶Also theoretical calcu-

lations do support the polar nucleophilic mechanism.⁴⁷However,

there are also recent results supporting the SET mechanism.⁴⁰

Since tranylcypromine forms a ring-opened adduct V with MAO

B, ring opening presumably occurs after nucleophilic attack.^2,48,49

However, it is not obvious at which step the ring opens, or to what

degree increased strain would affect this process. One can imagine

that nucleophilic attack of the amino group at C(4a) of ﬂavin I gives

an intermediate zwitter ion IVA, having an increased electron den-

sity at nitrogen N(5). Succeeding nucleophilic attack at C(3) of the

tranylcypromine derivative and ring opening leads to the zwitter-

ionic N-alkylated intermediate IVB, which undergoes thermal car-

bon shift from N(5) to C(4a), analogous to the ﬁndings of

Hemmerich et al. in a similar chemical transformation.⁵⁰Final

a-ﬂuorobenzyl radicals would be formed, which in turn could

recombine with the ﬂavin radical to give covalent adducts. Frag-

mentation of these adducts would give back the oxidized ﬂavin

and a-ﬂuorocinnamic aldehydes after hydrolysis.

The relative merits of the original SET mechanism and an alter-

native polar nucleophilic mechanism were discussed recently by

Edmondson et al.²These authors favored the latter, the steps of

which are shown as they illustrated using benzyl amine as the sub-

strate (Fig. 8). Nucleophilic attack of the substrate amino group at

the C(4a) position of ﬂavin I leads to formation of adduct II. This

intermediate has an increased basicity of the N(5) nitrogen which

hydrolysis will give the

r-C–C–bonded product V (Fig. 9), which

(X = H) was found in the crystal structure of the tranylcypro-

mine-MAO B adduct.⁴⁸

then abstracts the pro-R proton at the C -atom of the amine. Extru-

Crystal structures of recombinant human liver MAO A and B ob-

tained in the years 2002–2005 have revealed structural details of

a

sion of the cofactor with the formation of an imine intermediate III

and subsequent hydrolysis to benzaldehyde, ammonia and the

fully reduced ﬂavin, completes the process.

enzyme

S

enzyme

S

R

N

R

N

H₂C

N

O

H₂C

N

O

enzyme

S

enzyme

S

NH

H₃C

N

H₃C

N

H

R

N

R

N

O

H₂C

N

O

H₂C

N

O

Ph

I

NH₂

CHO

X

NH

V

H₃C

N

H₃C

N

X

X = H, F

Ph

1. rearrangement

2. H₂O

NH₂

I

II

H

NH₂

enzyme

S

enzyme

S

Ph

H

R

Ph

H

H₂C

N

O

H₂C

N

O

enzyme

S

R

N

NH

H₃C

N

H₃C

N

H₂C

N

O

NH₂

O

+

Ph

NH₂

NH

Ph

H

IVA

NH₂

H₃C

N

H

X

IVB

III

Ph

Figure 8. Polar nucleophilic mechanism.²

Figure 9. Suggested inhibition mechanism of tranylcypromine derivatives.

7154

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

the active site that support the polar nucleophilic mechanism

rather than the original SET mechanism.^2,51,52For example, this

mechanism is consistent with the presence of an ‘aromatic cage’ lo-

cated around the ﬂavin cofactor in the active site of both enzymes

that is formed by two tyrosine rings that are almost perpendicular

to each other and to the ﬂavin.⁵³Polarization of the approaching

amine by dipole–dipole interactions with these tyrosine residues

serves to increase the nucleophilicity of the amine (see Fig. 12).

Moreover, the aromatic cage appears to provide a path to bring

the substrate into the right position for reaction with the ﬂavin.⁵⁴

As noted above, MAO A and B have 70% homology in their ami-

no acid sequences and their binding cavities are very similar.²

There are, however, major differences in the structures of their en-

trance cavities. For MAO A this cavity has a volume of 500 Å³and is

overall shorter but wider than that of MAO B. The latter cavity has

a volume of 700 Å³and is divided into two parts. How those differ-

ences contribute to the substrate and inhibitor selectivities of each

enzyme is yet to be clearly delineated. In addition to the differ-

ences in the sizes of the cavities, Ile-335 in MAO A and Tyr-326

in MAO B are suggested to play important roles in determining

substrate and inhibitor speciﬁcities in human MAO A and B.⁵⁵

which the bond orbitals of the para-substitutent, the aromatic ring,

and the

-carbon are coplanar.⁵⁶Therefore an electron-withdraw-

a

ing substituent can decrease the basicity of the amino group. A

large substituent does not inhibit binding since the cavity is very

broad and wide. In the ﬂat geometry of the MAO B cavity the sub-

strate’s orbitals are not coplanar and this blocks electron transmis-

sion between the substituent and the amino group. Here the

limiting factors are the hydrophobicity and the van der Waals vol-

ume since the substrate comes very close to the non-polar walls of

the pocket. Substrates with a dipole into the same direction as the

tyrosine rings lead to a decrease in conversion.

In the case of phenethylamine analogues, which have alkyl side

chain and are more similar to native substrates than benzylamine,

Edmondson and co-workers reported several interesting observa-

tions.⁵⁸The binding afﬁnity of the deprotonated amine to MAO A

increases with increasing van der Waals volume of the para-sub-

stitutent. The limiting of rate of enzyme reduction decreases with

increasing van der Waals volume of the substituent in a linear

manner with no observable electronic contribution, in contrast to

the electronic effects observed with benzylamine reduction of

MAO A. In addition, the alkyl side chain of arylalkylamine shows

a strong interaction with the enzyme, and this interaction is

linearly correlated with the Taft steric factor (E_s) of the side chain.

These data suggested that the binding site for the aryl ring is

identical for phenethylamine and benzylamine analogues and that

steric interactions of the alkyl side chain with the enzyme strongly

inﬂuence the binding afﬁnities with MAO A. They also reported

that the binding afﬁnity of arylalkylamines to MAO B is less

sensitive to the E_svalues of the side chain, although they have

not completed their analysis. The rate MAO B reduction by phen-

ethylamine is considerably lower than that of benzylamine, which

suggests that some alterations in the transition-state structure

may occur simply by increasing the side chain by one methylene

group.⁵⁹

These observations are in accordance with the results we ob-

tained with our series of inhibitors, which showed that 7b, 7c,

and 7d (trans) with Cl-, F-, and CF₃-substituents have lower IC₅₀

values compared to non-substituted 2-ﬂuorotranylcypromine 7a

(trans) as inhibitors of both MAO A and B. In contrast, the IC₅₀value

for MAO A inhibition by the trans-conﬁgured para-methyl deriva-

tive (7e) was not different from that of 7a. As described above,

the corresponding cis-compounds were signiﬁcantly less effective

as inhibitors of MAO B, this difference in activity being even greater

for MAO A (up to 100 times less active).

3.2. Biological testing of ﬂuorotranylcypromine derivatives on

MAO A and B

As described above, ﬂuorine-containing tranylcypromines have

a 1–1.5 units lower pK_athan their non-ﬂuorinated parent com-

pounds. Fluorine thus decreases the electron density of the neigh-

boring NH₂-group and thereby lowers the nucleophilicity, a factor

that would contribute to a lower rate of conversion involving a

nucleophilic mechanism. In addition, the proposal has been made

that the negative charge associated with the outer mitochondrial

membrane facilitates the attraction of the protonated amine sub-

strate to MAO B, and a lower pK_awould lower the concentration

of protonated amine. However, a lower pK_aalso leads to a higher

concentration of free amine at physiological pH and this should

provide a higher level of substrate available for inclusion in the

aromatic cage of the active site. This would result in an accelerated

conversion of a substrate and to a lower IC₅₀value of an inhibitor.

This might explain the higher activity of ﬂuorotranylcypromines in

comparison to tranylcypromine. The differences between the more

active trans-compounds to the less active cis-isomers may be due

to different interactions with the aromatic cage, possibly reﬂecting

the lower degree of protonation of the trans-isomers. This might

also hold for the more basic (+I substituted) amines, which though

more nucleophilic, are present in lower concentration of non-pro-

tonated form.

The following order of activity was observed for the trans-

compounds:

Edmondson et al. examined a series of para-substituted benzyl-

amines as substrates for human recombinant liver MAO A and B, as

well as for bovine liver mitochondrial MAO B.^53,56,57They showed

that electron-withdrawing substituents accelerate the MAO A-cat-

alyzed oxidation with the para-CF₃analogue being the best sub-

strate.^53,56The MAO A binding data correlated with the van der

Waals volume (V_w) of the substituents but not with electronic

MAO A: CF₃> Cl > F > H ꢂ Me (IC₅₀= 0.8 > 1.6 > 3.6 > 12 ꢂ 13

MAO B: Cl > F ꢂ OMe ꢂ CF₃> H > Me (IC₅₀= 3.7 > 4.9 ꢂ 5.1 ꢂ

5.4 > 6.4 > 13 M)

lM)

l

This order matches the one postulated by Böhm et al.

(Cl > F > H) for a non-speciﬁc increase of binding afﬁnity in pro-

tein-ligand interactions due to higher lipophilicity of ﬂuorinated

compounds compared to the non-ﬂuorinated parent compounds.⁶⁰

The para-triﬂuoromethyl substituted 7d (trans) is the best

inhibitor of MAO A found so far in this series. It is highly lipophilic

(logD = 2.66) and therefore ﬁts very well into the hydrophobic cen-

ter of the enzyme. Its low pK_a-value of 7.0 provides a high concen-

tration of non-protonated amine at physiological pH. In spite of a

similar logD-value, the inhibition by para-chloro 7b is only half

as strong. An explanation for that might be the slightly increased

pK_a-value of 7.19, which leads to a lower concentration of free

amine and thus a weaker inhibition. A ﬂuorine substituent in the

para-position results in pK_aand logD-values of 7c (trans), which

are of similar magnitude to the ones of non-substituted 2-ﬂuor-

properties (r). In contrast, the turnover was strongly dependent

on . In addition, the binding correlation with V_wcould be im-

r

proved by correction for the dissociation constants. This led to

the conclusion that the deprotonated amine is the species that

binds to the active site.

In contrast to the MAO A data, MAO B had a negative correlation

with (V_w) of substituents and showed no dependence on r ⁵⁷

.

The

principal determinant of binding in this case was found to be the

hydrophobicity ( ) and the Taft steric constants (E_s). This differ-

p

ence in substrate speciﬁcities of the two isozymes was ascribed

to the different shapes of the enzyme binding pockets. The broad

cavity of MAO A allows the substrate to take an orientation in

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7155

otranylcypromine 7a (trans). Although the IC₅₀-value of 7c is twice

1

0.8

0.6

0.4

0.2

0

A

as high as that of the para-chloro-substituted 7b (trans) it is still

three times lower than that of 7a (trans), possibly due to attractive

interactions of ﬂuorine with the aromatic cage.

CH₃

H

The above discussion is supported by structure–activity relation

(SAR) analysis. The pK_avalues of these compounds correlate with

IC₅₀values with both MAO A and B, suggesting that basicity of

the inhibitors is important for the inhibition activity against both

isozymes (Fig. 10). Furthermore, the IC₅₀values calculated for the

level of deprotonated amine at pH 7.2 by Eq. 1 showed good linear

correlation with hydrophobicity ‘logD’ for the inhibition of MAO A.

(Table 3 and Fig. 11B). Interestingly, as shown in Figure 10, the cor-

rected IC₅₀values still show good correlation with the electronic

Cl

CF

F

3

-0.2

-0.4

-0.2 -0.1

0

0.1 0.2 0.3 0.4 0.5 0.6

σ_p

factor for para-substituents (r_p), suggesting that electron-with-

1

B

drawing or -donating properties are having some additional effect

and are not related to the pK_avalue of the amino group. Further

work would be needed to explain this effect. However, one possi-

bility might be an inﬂuence on the rate of opening of the cyclopro-

pane ring of ﬂuorinated phenylcyclopropylamines. Electron-

withdrawing groups, such as CF₃, Cl, and F would be expected to

accelerate the rate of ring opening, whereas electron-donating

group would decrease the rate of this reaction in the active site.

00.

CCH₃

00.

H

00.

0.

C

CF₃

F

0

-0

..22

-0..44

observed IC₅₀

Corrected IC₅₀

¼

ð1Þ

_aꢁpH

1 þ 10^pK

1

4

1

.

6

1.

8

2

.

2

2.

4

2

.

6

22.8

Log

D

Such a clear and demonstrative trend of the substituent effects

could not be observed for the inhibition of MAO B. All activities

were found to be in a very narrow range with IC₅₀values between

1

C

CH₃

0.8

0.6

0.4

0.2

0

3.7 and 5.4

lM, marginally better than the IC₅₀of trans-7a

(6.4 M). Weak correlation was observed by SAR analysis in the

l

H

case of MAO B (Figs. 10 and 11).

In contrast to MAO A, the active center of MAO B consists of two

parts. From the crystallographic studies, MAO A was shown to have

a single substrate cavity of ꢃ500 Å³, which combines substrate rec-

CF₃

Cl

F

-0.2

-0.4

1.4

CH₃

0

5

10

15

20

25

1.2

1

Figure 11. Correlation of corrected IC₅₀values with r_p(A), logD (B), and van der

Waals volume (C) of 2-ﬂuoro-2-phenylcyclopropylamines for MAO A (closed circle)

and B (open diamond). Equations of the ﬁtting lines are as follows: MAO A,

H

0.8

0.6

logIC₅₀= ꢁ1.56 ꢄ

r

_p+ 0.44 (R²= 0.85); logIC₅₀= ꢁ0.80 ꢄ logD + 1.81 (R²= 0.69);

Cl

logIC₅₀= ꢁ0.04 ꢄ V_w+ 0.67 (R²= 0.49); MAO B, logIC₅₀= ꢁ0.18 ꢄ

r_p+ 0.47

F

0.4

0.2

0

CF₃

(R²= 0.08); logIC₅₀= 0.03 ꢄ logD + 0.40 (R²= 0.01); logIC₅₀= 0.01 ꢄ V_w+ 0.35

(R²= 0.17).

-0.2

ognition and conversion. MAO B consists of two cavities which has

a total size of ꢃ700 Å³(‘entrance cavity’ with a volume of 290 Å³,

and a larger hydrophobic substrate cavity with a volume of about

400 Å³).^52,54The cavity of MAO A is shorter in length and wider

than the longer and narrower cavity in MAO B. An approaching

substrate must pass the entrance cavity to reach the substrate

binding region where it is metabolized. Presumably the transition

from one cavity into another may be rate limiting rather than the

attack on the ﬂavin itself. A consequence of this may be that all

molecules which enter the substrate binding cavity will react with

the enzyme following the same mechanism as proposed for MAO A

and that isozyme selectivity is determined by entrance cavity

selectivity in MAO B. Thus the difference in shape between MAO

A and B seems to be one of the reasons for substrate and inhibitor

selectivity of both enzymes. Since the actual active site is the same

for both enzymes all molecules that pass this ‘gate’ between recog-

nition and binding site in MAO B are expected to be converted by

the enzyme.

6.9

7

7.1

7.2

pKa

7.3

7.4

7.5

Figure 10. Correlation of MAO A and B activities with pK_avalues of 2-ﬂuoro-2-

phenylcyclopropylamines. Fitting lines for MAO

A

and

B

are logIC₅₀= 3.09

ꢄ

pK_aꢁ 21.87 (R²= 0.89), and logIC₅₀= 0.71 ꢄ pK_aꢁ 4.40 (R²= 0.32), respectively.

Table 3

IC₅₀values corrected by pK_aof inhibitors and pH of the assay solution (trans-2-aryl-2-

ﬂuorocyclopropylamines

a

R¹

R²

R³

Compound

Observed IC₅₀

(

lM)

Corrected IC₅₀

(l

M)

MAO A

MAO B

MAO A

MAO B

H

OMe

H

Cl

F

H

Ph

7a

7b

7c

7d

7e

7f

12

1.6

3.6

0.8

13

14

47

18

6.4

3.7

4.9

5.4

13

5.1

230

37

5.0

0.8

1.6

0.5

5.0

4.7

18

2.7

1.9

2.1

3.3

5.0

1.7

89

CF₃

Me

OMe

H

7g

7h

The analogues having smaller substituents showed slightly

higher inhibition activity for MAO B, while strong inhibition of

MAO A was observed by the analogues having larger substituents

9.0

19

a

Corrected IC₅₀values were derived with the use of Eq. 1.

7156

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

(Fig. 11C). The difference in cavity shape and size might explain our

observations. Any effects of the cyclopropyl side chain of the ﬂuo-

rinated phenylcyclopropylamine analogues on binding afﬁnity

might need to be taken into account to discuss the inhibition

mechanism, because binding afﬁnity of tranylcypromine (1) is re-

ported to be better than that of benzylamine and phenethylamine

from the analysis of the steric effect of alkyl side chain of arylalkyl-

amines on the binding afﬁnity of MAO.⁵⁸In addition to this steric

effect, hydrophobicity is shown not to be an important factor for

the inhibition of MAO B by ﬂuorinated phenylcyclopropylamine

in contrast to MAO A (Fig. 11B). This is not consistent with the pre-

vious results that hydrophobicity of the benzylamine is the major

factor inﬂuencing the binding afﬁnity for MAO B.²It appears that

other properties of phenylcyclopropylamines have major impor-

tance. So far QSAR only deals with the interactions of the enzymes

and the speciﬁc compounds used for these studies. For compounds

with different electronic structures/electron densities, hydropho-

bicity may have an inﬂuence or not, depending on the nature of

the compound. So it is quite probable that we have not found a

relation between hydrophobicity and binding afﬁnity of our inhib-

itors, whereas Edmondson observed such a relation for benzylam-

ines, which are substrates. Once more does this stress the

difference between substrates and inhibitors and ﬁts to the general

idea of this paper.

MAO A. However, the IC₅₀for MAO B (13 lM), comparable to the

activity of tranylcypromine (1), is somewhat higher than that pre-

dicted by this analysis.

To study further the effects of electron-donating substituents on

inhibitory activity, the para-methoxy analogues 7f (trans) and 10f

(cis) were synthesized and examined as inhibitors of MAO. In con-

trast to all other inhibitors in this series which showed irreversible

behavior, 7f (trans) proved to be a competitive inhibitor of MAO A,

although it is an irreversible inhibitor of MAO B. Furthermore, 10f

(cis) does not inhibit MAO A at micromolar concentrations and is

only a weak irreversible inhibitor of MAO B, comparable to tranyl-

cypromine (1) itself. The IC₅₀values of 7f (trans) and the para-methyl

analogue 7e (trans) do not signiﬁcantly differ from each other,

whereas the para-methoxy compound is a three-time better inhibi-

tor of MAO B than the para-methyl derivative. The stronger electron-

donating effect of methoxy group that should lead to greater nucle-

ophilicity and contribute to enhanced inhibitory activity apparently

is counterbalanced by the higher polarity of this analogue.

A second methoxy group in the meta-position of the phenyl ring

dramatically decreases the activity of 7g (trans) and 10g (cis) to-

wards both MAO A and MAO B compared to the isomeric para-

methoxy compounds 7f and 10f. The best inhibitory activity was

observed for 7g on MAO A with an IC₅₀-value of 47 lM, which is

two times higher than that of tranylcypromine (1). Although the

pK_avalue (7.40) of the dimethoxy compound 7g is comparable to

the other compounds 7 discussed above, its signiﬁcantly lower

lipophilicity (logD = 0.58) might explain its lower activity. The

introduction of two methoxy groups has a particularly detrimental

inﬂuence on the inhibition of MAO B, leading to a ten-time higher

The cavities in both isozymes are reported to be quite hydro-

phobic,⁵²and this difference in MAO A and B against hydrophobic

parameters might also reﬂect difference of hydrophobicity of the

active site cavity of MAO A and B. Hydrophobic interaction might

also be an important factor in addition to the basicity of ﬂuorinated

phenylcyclopropylamine.

IC₅₀-value (230 lM) for 7g than was observed for 2. A reason for

The +I-effect of a methyl group in para-position on the inhibi-

tion can be discussed in a manner similar to the rationalization

of the increased activities due to the presence of electron-with-

drawing groups. Thus, both pK_aand logD value of 7e (trans) are

slightly higher compared to the values of 7a (trans). Because of this

one would expect a lower inhibitory activity. This is observed with

that might be the dipole moment of the compound. Thus, both iso-

mers of 7g and 10g are weak inhibitors, although they represent

close structural analogies to the 3-ﬂuoro-allylamine 5.

An increased steric demand is to be expected for diphenylcyclo-

propylamines 7h (cis) and 10h (trans) (for the assignment of cis and

trans see remarks at Scheme 1). The physicochemical data of 7h

MAO A

Y407

OH

H

F

6.5 Å

N

substrate cavity

H

OH

~ 550 Å³

R

1. Big effect

Y444

Stronger electron withdrawing

·

(Electronic transmission allowed)

·

Higher hydrophobicity

·

(Hydrophobic environment)

~ 13.5 Å

2. Small effect

Bigger van der Waals volume

(No steric constrains)

·

MAO B

Y398

OH

H

F

7.8 Å

entrance cavity

~ 290 Å³

substrate cavity

OH

N

H

R

1. Small effect

· Stronger electron withdrawing

(Electronic transmission allowed)

~ 400 Å³

Y435

·

Smaller van der Waals volume

(Steric constrains)

·

∼ 20 Å

2. No effect

Hydrophobicity

·

Figure 12. Differences in inhibition of MAO A and B by ﬂuorinated phenylcyclopropylamines.^2,53

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7157

(cis) are similar to those of the para-chloro derivative 7b (trans)

and therefore one could expect similar IC₅₀values, at least towards

MAO A, if these parameters are the only consideration. But the IC₅₀

ian INOVA 500 (499.84 MHz for ¹H, 125.70 MHz for ¹³C and

470.28 MHz for ¹⁹F) and a Bruker ARX300 (300.13 MHz for ¹H,

75.48 MHz for ¹³C and 282.37 MHz for ¹⁹F) in CDCl₃solution.

Chemical shifts are reported in ppm relative to TMS or CFCl₃as

internal standards. The multiplicities of the ¹³C signals, other than

¹³C-¹⁹F couplings, were assigned using the DEPT procedure and are

designated s (singlet), d (doublet), t (triplet), q (quartet), m (multi-

plet), dd (doublet of a doublet), dt (doublet of a triplet), mt (mul-

tiplett of a triplet) etc. Mass spectra (GC/MS, EI and GCToF, EI)

were measured on a Waters-Micromass ‘GCT’ instrument or ‘Quat-

tro Micro GC’ instrument or on a Thermo-Finnigan-MAT ‘MAT

8200’ instrument, all operating at 70 eV. Mass spectra and high res-

olution mass spectra (ESI⁺, ESI^ꢁand HRMS ESI⁺, HRMS ESI^ꢁ) were

measured on a Waters-Micromass ‘Quattro LC-Z’ instrument or a

Bruker Daltonics ‘MicrOToF’ instrument. All analytical measure-

ments were performed by the staff of Organisch-Chemisches Insti-

tut, Universität Münster. Thin layer chromatography was

performed with TLC plates 60 F₂₅₄by Merck. Column chromatogra-

phy was performed using silica gel (Merck, particle size 0.063–

0.200 mm, 70–230 mesh) and preparative MPLC was carried out

on silica gel (Merck, particle size 0.040–0.063 mm, 230–400 mesh).

Solvents and reagents were purchased from Acros, Fluka or Sigma–

Aldrich. Compounds 7a–c and 10a–c as well as 18–19h were pre-

pared as previously described^15,16and illustrated in Scheme 1.

Compounds 7f-h and 10f-h were synthesized analogously.

value of 7h (18

7b and similar to the value of tranylcypromine (1). Towards MAO B

compound trans-7h (37 M), the only competitive inhibitor, of this

enzyme was comparable to 1 (19 M) and as well as to the para-

methoxy compound 7f (trans) (5 M). The IC₅₀values of 10h

(trans) are 10 M (MAO A) and 20 M (MAO B) and only half as

lM) was found to be ten times higher compared to

l

high as that of the corresponding cis-isomer, similar to the value

of tranylcypromine (2) towards MAO B and trans-2-ﬂuorotranylcy-

promine (7a) towards MAO A. Compounds 7h and 10h can also be

viewed as analogues of 2-ﬂuoro-1-phenylcyclopropylamine (4).

However, a combination of structural features of both leads, 4

and 7a, did not result in a better inhibition.

The relationship between structural parameters and efﬁciency

of inhibition of MAO A and B by 1-ﬂuoro-1-phenylcyclopropyl-

amine analogues postulated from the present study are summa-

rized in Figure 12. Electron-withdrawing groups on the para-

position increase the ratio of the deprotonated form of the ana-

logues, an effect that should facilitate entry into the ‘aromatic cage’

of the active site. Since the active sites of both isomers are quite

hydrophobic, hydrophobicity of the analogues might further

promote the interaction with enzyme cavities. Cyclopropane ring

opening is thought to be a signiﬁcant step in the inhibition by

phenylcyclopropylamine analogues. The rate of ring opening might

be increased by electron-withdrawing groups, also increasing

inhibitory activity. The correlation with van der Waals volume of

the substituents is consistent with the larger binding pocket of

MAO A, while steric constraint of the larger substituents adversely

affects the inhibitory activity of the analogues towards MAO B.⁶¹

5.2. Enzyme assay

Recombinant human mitochondrial MAO A and B, kindly pro-

vided by Professor D.E. Edmondson, Emory University, Atlanta,

GA, USA,^62,63were used for the inhibition experiments. The as-

says were carried out by the method previously reported.^12–14

Prior to use, the enzyme stock solution was passed through a

gel-ﬁltration column (PD 10 desalting column, Amersham Biosci-

ences) pre-equilibrated with 50 mM K phosphate (pH 7.2) con-

4. Conclusion

A series of racemic tranylcypromine (trans-2-phenylcyclopro-

pylamine) analogues bearing a ﬂuorine substituent at the cyclopro-

pane ring and electron-withdrawing or -donating substituents in

the para-position of the phenyl ring were synthesized and their

activities as inhibitors of recombinant human liver MAO A and

MAO B were examined. Electron-withdrawing substituents such

as chlorine, ﬂuorine, and the triﬂuoromethyl group in the para-po-

sition increased the potency of inhibition of MAO A up to a factor of

15 compared to the lead trans-2-ﬂuoro-2-phenylcyclopropylamine

(7a), while electron-donating groups such as methyl or methoxy

had no inﬂuence on this activity. In contrast, there is almost no dif-

ference in the action as inhibitors of MAO B of all substituted trans-

compounds. The corresponding cis-compounds were shown to be

10–100 times less active as inhibitors of MAO A compared to the

trans-isomers, while trans- and cis-compounds were quite similar

in their inhibition of MAO B. The trans-compounds are moderate

inhibitors of both MAO A and MAO B exhibiting IC₅₀values in

the low micromolar range. All para-substituted trans-compounds

7 (except the para-methoxy compound 7f) are MAO A selective,

while all cis-compounds 10 (except 10h), though much less active,

are MAO B selective. The best MAO A/MAO B selectivity (7:1) in the

trans-series was found for trans-2-(para-triﬂuoromethylphenyl)-

cyclopropylamine (7d), while a 1:27 selectivity was found for cis-

2-(para-ﬂuorophenyl)cyclopropylamine (10c).

taining 0.8% octyl-glucoside. The activity of MAO

A was

measured spectrophotometrically at 25 °C by the modiﬁed meth-

od of Li et al.⁶³using 0.7 mL of standard reaction mixture con-

taining 1 mM kynuramine hydrobromide, 50 mM potassium

phosphate buffer (pH 7.2), 0.5% Triton X-100 (reduced), 6%

dimethylsulfoxide, and MAO A. The reaction was monitored at

316 nm, which is the maximum absorption wavelength of 4-

hydroxyquinoline. The enzyme activity was calculated by using

12,300 M^ꢁ1cm^ꢁ1as the extinction coefﬁcient of 4-hydroxyquin-

oline at 316 nm. One unit of the enzyme oxidizes 1 lmol of

kynuramine to 4-hydroxyquinoline per 1 min. The activity of

MAO B was also measured spectrophotometrically at 25 °C by

the modiﬁed method of Houslay and Tipton,⁶⁴using 0.7 mL of

standard reaction mixture containing 1 mM benzylamine, 0.1 M

potassium phosphate buffer (pH 7.2), 6% dimethylsulfoxide, and

MAO B. The reaction was monitored at 250 nm which is the

maximum absorption wavelength of benzaldehyde. The enzyme

activity was calculated by using 13,800 M^ꢁ1cm^ꢁ1as the extinc-

tion coefﬁcient of benzaldehyde at 250 nm. One unit of the en-

zyme oxidizes

1 lmol of benzylamine to benzaldehyde per

1 min. Protein concentration was determined by the method of

Bradford⁶⁵using bovine serum albumin as a standard. Each

inhibitor was dissolved in DMSO and diluted with the same sol-

vent to give the appropriate concentration. The solution was

immediately divided into several vials and wrapped with alumi-

num foil. These vials were stocked in ice-bath until used for

inhibition experiments. Inhibition experiments were carried out

as follows: Varying concentrations of inhibitor were added to

the reaction mixture described above (without substrate; MAO

5. Experimental

5.1. General methods

NMR spectra were recorded on a Varian 600 Unity Plus

(600.0 MHz for ¹H, 150.66 MHz for ¹³C and 564.3 MHz for ¹⁹F), Var-

A, 4.4

lg; MAO B, 7.0 lg), and allowed to stand for 10 min at

10 °C. The reaction was started by the addition of substrate

7158

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

stock, and the time course of the absorption increase of the reac-

tion product was monitored as described above.

ethyl acetate, 1:1) 12g was obtained as a colorless liquid (yield:

3.01 g, 75% pure (GC), 43%).

5.3. Determination of the inhibition type

5.5. Synthesis of a-ﬂuorostyrenes

The type of inhibition was determined by examining time- and

concentration-dependent inactivation⁶⁶of MAO A and B in the

presence of the inhibitor. The incubation of MAO B with an inhib-

itor was carried out at 4 °C in the 0.1 mL of 0.1 M potassium

5.5.1. 1-(1-Fluorovinyl)-4-triﬂuoromethylbenzene (13d)

According to the general procedure^15,212-bromo-1-ﬂuoro-1-(4-

triﬂuoromethylphenyl)ethane (12d) (3.42 g, 12.6 mmol) was trea-

ted with potassium tert-butoxide. After distillation 13d was iso-

lated as a colorless liquid (yield: 1.41, 59%). Bp 49 °C/9 mbar. ¹H

NMR (CDCl₃, 300 MHz): d 4.98 (dd, 1 H, J = 17.5 Hz and 3.7 Hz,

H_A), 5.14 (dd, 1H, J = 48.9 Hz and 3.7 Hz, H_B), 7.58–7.70 (m, 4H,

4-CH, 5-CH, 7-CH, and 8-CH). ¹³C NMR (CDCl₃, 75 MHz): d 91.8

(dt, J = 22.5 Hz, C-2), 123.9 (qs, J = 272.2 Hz, C-9), 124.9 (dd,

J = 6.8 Hz, C-4 and C-8), 125.5 (qd, J = 3.5 Hz, C-5 and C-7), 131.3

(qs, J = 33.0 Hz, C-6), 135.4 (ds, J = 29.2 Hz, C-3), 161.7 (ds,

J = 250.3 Hz, C-1). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ63.42 (s, 3F,

CF₃), ꢁ108.72 (dd, 1F, J = 50.8 Hz and 17.7 Hz, 1-CF). MS (GCToF,

EI): m/z 190 (100) [M⁺], 189 (3), 171 (15), 169 (15), 151 (5), 140

(15), 121 (35), 120 (4), 101 (16), 75 (4).

phosphate (pH 7.2) containing 11.2

sulfoxide and different concentration of an inhibitor. Aliquots

(20 L) were taken out periodically from the mixture, and diluted

lg of enzyme, 6% of dimethyl-

l

with 0.68 mL of assay solution. The increase of absorbance at

250 nm was monitored as described above. Incubation of MAO A

was carried out at 4 °C in 0.1 mL of 50 mM potassium phosphate

(pH 7.2) containing 0.5% of Triton X-100 (reduced), 19.1

zyme, 6% of dimethylsulfoxide and different concentration of

inhibitor. Aliquots (20 L) were taken out periodically from the

lg of en-

l

mixture and diluted with 0.68 mL of assay solution. The increase

of absorbance at 316 nm was monitored as described above.

5.4. Bromoﬂuorinations of substituted styrenes

5.5.2. 1-(1-Fluorovinyl)-4-methoxybenzene (13f)

According to the general procedure²¹2-bromo-1-ﬂuoro-1-(4-

methoxyphenyl)ethane (12f) (crude product) was treated with

potassium tert-butoxide (8.55 g). After distillation 13f was isolated

as a colorless liquid (yield: 1.85 g, 37% over two steps). Bp 80 °C/

3 mbar. The spectroscopic data agreed with published ones.⁶⁷

5.4.1. 2-Bromo-1-ﬂuoro-1-(4-triﬂuoromethylphenyl)ethane

(12d)

4-Triﬂuoromethylstyrene (11d) (2.16 g, 12.5 mmol) was dis-

solved in dry dichloromethane (30 mL) in a teﬂon ﬂask under ice

cooling. Pyridiniumhydrogenﬂuoride (Pyꢀ9HF, Olah’s reagent,

3.2 mL, 13.8 mmol, 1.1 equiv) and subsequently N-bromosuccini-

mide (NBS, 2.46 g, 13.8 mmol, 1.1 equiv) were added in small por-

tions. After 30 min at 0 °C the solution was allowed to warm to

room temperature and stirred overnight. The reaction mixture

was poured into ice-water (100 mL) and neutralized with concen-

trated ammonia. After separation of the phases the aqueous layer

was extracted with dichloromethane (3ꢄ 70 mL). The combined

organic layers were washed with 6 M hydrochloric acid and 5%

NaOH solution (each 1ꢄ 70 mL). The phases were dried over mag-

nesium sulfate and the solvent was removed in vacuo. After silica

gel chromatography (25ꢄ 3 cm, pentane) 12d was obtained as a

colorless liquid (yield: 2.51 g, 74%). ¹H NMR (CDCl₃, 300 MHz): d

3.59–3.72 (m, 2-CH₂Br), 5.70 (dt, 1 H, J_H,F= 46.5 Hz and 4.6 Hz,

1-CHF), 7.49 (dm, 2H, J = 7.9 Hz, 4-CH and 8-CH), 7.69 (dm, 2H,

J = 7.9 Hz, 5-CH and 7-CH). ¹³C NMR (CDCl₃, 75 MHz): d 33.6 (dt,

J = 27.7 Hz, C-2), 91.7 (ds, J = 180.0 Hz, C-1), 123.8 (qs,

J = 272.1 Hz, C-9), 125.7 (qd, J = 4.6 Hz, C-5 and C-7), 126.1 (dd,

J = 7.3 Hz, C-4 and C-8), 131.4 (qs, J = 33.4 Hz, C-6), 141.0 (ds,

J = 20.8 Hz, C-3). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ63.37 (s, 3F, 9-

CF₃), ꢁ176.52 (dt, 1F, J_F,H= 40.2 Hz, J_F,H= 20.1 Hz, 1-CHF). MS

(GCToF, EI) m/z 272/270 (13/15) [M⁺], 250/252 (6/6), 251/253 (6/

6), 191 (2), 190 (6), 178.0 (6), 177 (100), 172.0 (72), 171 (24),

153 (6), 151 (42), 145 (12), 127 (35), 122 (6), 103 (32), 102 (5),

77 (10), 75 (14), 69 (6), 63 (5), 50 (10).

5.5.3. 1-(1-Fluorovinyl)-3,4-dimethoxybenzene (13g)

According to the general procedure²¹2-bromo-1-ﬂuoro-1-(3,4-

dimethoxyphenyl)-ethane (12g) (8.18 g, 75% purity (GC), ca.

23 mmol) was treated with potassium tert-butoxide to give 13g

(yield: 5.29 g, 77% purity (GC), 96%). Due to polymerization 13g

was used in the next reaction without any puriﬁcation. The spec-

troscopic data were taken from the crude product. ¹H NMR (CDCl₃,

300 MHz): d 3.89 (s, 6H, 9-OCH₃and 10-OCH₃), 4.75 (dd, 1H,

J = 18.9 Hz and 3.6 Hz, H_A), 4.89 (dd, 1 H, J = 49.9 Hz and 3.5 Hz,

H_B), 6.75-7.16 (m, 3H, 4-CH, 7-CH and 8-CH). ¹³C NMR (CDCl₃,

75 MHz): d 55.9 (q, C-9 and C-10), 87.8 (dd, J = 24.5 Hz, C-2),

107.8 (dd, J = 7.2 Hz, C-4), 110.9 (d, C-7), 117.7 (dd, J = 7.6 Hz,

C-8), 124.9 (ds, J = 29.9 Hz, C-3), 148.8 (s, C-6), 150.1 (s, C-5), 162.8

(ds, J = 247.8 Hz, C-1). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ107.10 (dd,

1F, J = 50.1 Hz and 18.7 Hz, 1-CF). MS (GCToF, EI) m/z 183 (3),

182 (56) [M⁺], 180 (2), 168 (1), 167 (13), 162 (100), 148 (2), 147

(29), 146 (2), 139 (15), 137 (2), 121 (3), 119 (19), 109 (11), 104

(3), 101 (11), 96 (12), 91 (29), 89 (9), 88 (3), 83 (3), 77 (10), 76

(12), 75 (10), 74 (5), 65 (11), 62 (9), 51 (8), 50 (9).

5.6. Cyclopropanations

5.6.1. cis- and trans-2-Fluoro-2-(4-triﬂuoromethylphenyl)-

cyclopropanecarboxylic acid ethylesters (14d and 15d)

According to the general procedure^15,68(1-ﬂuorovinyl)-4-tri-

ﬂuoromethyl benzene (13d) (0.5 g, 2.6 mmol) was treated with

ethyl diazoacetate (1.19 mg, 1.12 mL, 11.7 mmol, 4.5 equiv, EDA)

in the presence of Cu(acac)₂(153 mg, 0.59 mmol, 5 mol% relating

to EDA), whereas EDA was added within 12 h. After silica gel col-

umn chromatography (25 ꢄ 3 cm, pentane/diethyl ether, 80:1)

the isomers were separated and each isolated as a colorless oil.

Data for 14d. Yield: 296 mg (42%): ¹H NMR (CDCl₃, 300 MHz): d

1.30 (t, 3H, J = 7.1 Hz, 13-CH₃), 1.66 (ddd, 1H, J = 10.5 Hz, 9.5 Hz

and 7.0 Hz, H_B), 2.23 (ddd, 1H, J = 9.3 Hz, 7.8 Hz and 3.0 Hz, H_X),

2.37 (ddd, 1H, J = 20.2 Hz, 7.8 Hz and 7.1 Hz, H_A), 4.24 (qm, 2H,

J = 7.2 Hz, 12-CH₂), 7.39 (dm, 2H, J = 8.2 Hz, 6-CH and 10-CH),

7.64 (dm, 2H, J = 8.6 Hz, 7-CH and 9-CH). ¹³C NMR (CDCl₃,

5.4.2. 2-Bromo-1-ﬂuoro-1-(4-methoxyphenyl)ethane (12f)

According to the general procedure²⁰4-methoxystyrene (11f)

(4.37 g, 32.6 mmol) was treated with triethylamine–trishydroﬂuo-

ride (Et₃Nꢀ3HF) and NBS to give 12f (yield: 6.12 g crude product).

Due to its instability on silica gel 12f was used in the next step

without any puriﬁcation. Crude product spectra agreed with the

published ones.⁶⁷

5.4.3. 2-Bromo-1-ﬂuoro-1-(3,4-dimethoxyphenyl)ethane (12g)

According to the general procedure^15,213,4-dimethoxystyrene

(11g) (3.28 g, 20 mmol) was treated with triethylamine–trishydro-

ﬂuoride (Et₃Nꢀ3HF) and NBS. Several side products were separated

partially by silica gel chromatography (15 ꢄ 3 cm, cyclohexane/

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7159

75 MHz): d 14.1 (q, C-13), 19.4 (dt, J = 11.7 Hz, C-3), 29.7 (dd,

J = 11.6 Hz, C-1), 61.3 (t, C-12), 80.0 (ds, J = 228.9 Hz, C-2), 123.9

(qs, J = 273.1 Hz, C-11), 124.9 (dd, J = 8.5 Hz, C-6 and C-10), 125.6

(qd, J = 3.7 Hz, C-7 and C-9), 130.4 (qs, J = 32.5 Hz, C-8), 141.7 (ds,

J = 21.8 Hz, C-5), 167.1 (ds, J = 2.8 Hz, C-4). ¹⁹F NMR (CDCl₃,

282 MHz): d ꢁ63.34 (s, CF₃), ꢁ190.02 (not completely resolved

ddd, J = 18.4 Hz and 8.9 Hz, aliphatic F). MS (GCToF, EI) m/z 276

(10 [M⁺], 257 (10), 248 (38), 232 (1), 228 (27), 221 (12), 212

(10), 203 (91), 193 (100), 184 (12), 183 (89), 171 (13), 173 (33),

151 (17), 135 (3), 134 (21), 133 (85), 131 (10), 115 (36), 107 (7),

101 (5), 81 (4), 75 (8), 69 (4), 57 (5), 55 (11), 44 (10). HRMS

(q, C-13), 16.6 (dt, J = 13.1 Hz, C-3), 27.6 (dd, J = 16.6 Hz, C-1), 55.2

(q, C-11), 60.6 (t, C-12), 82.8 (ds, J = 220.8 Hz, C-2), 113.7 (d, C-7

and C-9), 125.4 (ds, J = 22.3 Hz, C-5), 130.1 (d, C-6 and C-10),

160.3 (s, C-8), 169.0 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d

ꢁ150.32 (m, 1F, 2-CF). MS (GCToF, EI): m/z 238 (62) [M⁺], 220

(8), 218 (12), 209 (74), 193 (23), 189 (69), 183 (31), 174 (36),

165 (100), 163 (60), 155 (61), 149 (30), 145 (81), 135 (62), 133

(60), 121 (35), 115 (60), 109 (27), 103 (38), 101 (26), 96 (22), 91

(19), 89 (10), 77 (27), 63 (12), 55 (5), 51 (7). C₁₃H₁₅FO₃(238.25)

calcd C 65.54% H 6.35%, found C 65.70% H 6.65%.

(ESI⁺) C₁₃H₁₂F₄O₂

₁₃H₁₂F₄O₂(276.2): calcd C 56.53% H 4.38%, found C 56.99% H

4.27%.

+

Na⁺: calcd 299.0666, found 299.0655.

5.6.3. cis- and trans-2-Fluoro-2-(3,4-dimethoxyphenyl)cyclo-

propanecarboxylic acid ethylesters (14g and 15g)

C

According to the general procedure^15,68(1-ﬂuorovinyl)-3,4-

dimethoxy benzene (13g) (2.73 g, 15 mmol) was treated with

(2.30 g, 2.1 mL, 22.5 mmol, 1.5 equiv) in the presence of Cu(acac)₂

(294 mg, 1.125 mmol, 5 mol% relating to one portion of EDA). After

silica gel column chromatography (20 ꢄ 3 cm, pentane/diethyl

ether, 10:1) a 1:1 mixture of both isomers was isolated as a pale

yellow oil (yield: 1.33 g, 33%, 14g/15g, 1:1). HRMS (ESI⁺):

Data for 15d. Yield: 326 mg (46%): ¹H NMR (CDCl₃, 300 MHz): d

1.03 (t, 3 H, J = 7.2 Hz, 13-CH₃), 1.87 (ddd, 1H, J = 19.4 Hz, 10.5 Hz

and 7.2 Hz, H_A), 2.02 (ddd, 1H, J = 15.1 Hz, 7.4 Hz and 7.4 Hz, H_B),

2.60 (ddd, 1H, J = 18.2 Hz, 10.4 Hz and 7.8 Hz, H_X), 3.94 (qm, 2H,

J = 7.2 Hz, 12-CH₂), 7.63 (dm, 2H, J = 8.6 Hz, 6-CH and 10-CH),

7.58 (dm, 2H, J = 8.7 Hz, 7-CH and 9-CH). ¹³C NMR (CDCl₃,

75 MHz): d 13.9 (q, C-13), 16.8 (dt, J = 10.2 Hz, C-3), 28.4 (dd,

J = 18.3 Hz, C-1), 61.0 (t, C-12), 82.2 (ds, J = 221.6 Hz, C-2), 125.2

(qd, J = 3.6 Hz, C-7 and C-9), 125.9 (m, C-11), 128.4 (dd, J = 4.5 Hz,

C-6 and C-10), 130.8 (qs, J = 32.6 Hz, C-8), 137.2 (ds, J = 19.3 Hz,

C-5), 168.4 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ63.34 (s, 3F,

CF₃), ꢁ158.32 (not completely resolved ddd, 1F, J = 18.2 Hz and

13.0 Hz, 2-CF). MS (GCToF, EI): m/z 276 (10 [M⁺], 257 (10), 248

(38), 232 (1), 228 (27), 221 (12), 212 (10), 203 (82), 193 (100),

184 (12), 183 (89), 171 (13), 173 (33), 151 (17), 135 (3), 134

(21), 133 (85), 131 (10), 115 (36), 107 (7), 101 (5), 81 (4), 75 (8),

69 (4), 57 (5), 55 (11), 44 (10). C₁₃H₁₂F₄O₂(276.2) calcd C 56.53%

H 4.38%, found C 56.60% H 4.46%.

C

₁₄H₁₇FO₄+ Na⁺calcd 291.1003, found 291.1001. C₁₄H₁₇FO₄

(268.3): calcd C 62.68%, H 6.39%, found C 61.96% H 6.42%. Subse-

quently the mixture of diasteromers was separated on a silica gel

column (30 ꢄ 3 cm, cyclohexane/ethyl acetate, 15:1) giving a

mixed fraction (1.17 g, 29%, 14g/15g, 1:1) and two diastereomeric

enriched fractions of each isomer that were taken for spectroscopic

analyses.

Data for 14g. Yield: 42 mg (1%, 14g/15g cis/trans = 93:7): ¹H

NMR (CDCl₃, 300 MHz): d 1.31 (t, 3H, J = 7.1 Hz, 14-CH₃), 1.58

(ddd, 1H, J = 10.3 Hz, 9.0 Hz and 6.6 Hz, H_B), 2.15 (ddd, 1H,

J = 10.0 Hz, 7.7 Hz and 2.8 Hz, H_X), 2.24 (ddd, 1H, J = 19.4 Hz,

7.6 Hz and 6.6 Hz, H_A), 3.88 and 3.90 (2s, each 3H, 11-OCH₃and

12-OCH₃), 4.19 (qm, 2H, J = 7.1 Hz, 13-CH₂), 6.86-7.02 (m, 3H, 6-

CH, 9-CH and 10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 14.1 (q, C-14),

18.4 (dt, J = 12.4 Hz, C-3), 28.4 (dd, J = 13.4 Hz, C-1), 56.0 (q, C-11

and C-12), 61.1 (t, C-13), 81.1 (ds, J = 227.8 Hz, C-2), 109.4 (dd,

J = 4.9 Hz, C-6), 111.1 (d, C-9), 117.8 (dd, J = 4.6 Hz, C-10), 129.8

(ds, J = 21.5 Hz, C-5), 149.1 (s, C-8), 149.4 (dd, J = 2.6 Hz, C-7),

167.9 (ds, J = 2.4 Hz, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ182.53

(ddd, 1 F, J = 19.1 Hz, 10.9 Hz and 4.4 Hz, 2-CF). MS (GC/MS, EI):

m/z 269 (12), 268 (69) [M⁺], 250 (2), 249 (1), 240 (4), 239 (26),

237 (6), 224 (2), 223 (22), 219 (12), 213 (18), 197 (3), 196 (14),

195 (100), 185 (21), 175 (9), 166 (2), 165 (17), 164 (30), 163

(14), 151 (5), 149 (16), 145 (4), 137 (6), 133 (12), 131 (4), 121

(10), 115 (5), 109 (10), 107 (5), 96 (3), 83 (6), 77 (2), 70 (1), 63

(2), 55 (2), 51 (2).

5.6.2. cis- and trans-2-Fluoro-2-(4-methoxyphenyl)cyclo-

propanecarboxylic acid ethylesters (14f and 15f)

According to the general procedure^15,68(1-ﬂuorovinyl)-4-

methoxybenzene (13f) (0.76 g, 5 mmol) was treated with two por-

tions of ethyldiazoacetate (each 0.86 g, 1.12 mL, 7.5 mmol,

1.5 equiv) in the presence of Cu(acac)₂(98 mg, 0.375 mmol,

5 mol% relating to one portion of EDA). After silica gel column chro-

matography (20ꢄ 3 cm, pentane/diethyl ether, 10:1) a 1:1-mixture

of both isomers of 14f and 15f was isolated as a colorless oil. Spec-

trometric data were taken from this mixture (yield: 1.06 g, 89%,

14f/15f, 1:1).

Data for 14f. ¹H NMR (CDCl₃, 300 MHz): d 1.27–1.33 (m, 3 H, 13-

CH₃), 1.55 (ddd, J = 10.3 Hz, 9.2 Hz and 6.9 Hz, 1H, H_B), 2.12 (ddd,

J = 9.2 Hz, 7.6 Hz, and 3.2 Hz, 1H, H_X), 2.23 (ddd, J = 19.5 Hz,

7.6 Hz, and 6.9 Hz, 1H, H_A), 3.80 (s, 3H, 11-OCH₃), 4.19–4.28 (m,

2H, 12-CH₂), 6.88–6.92 and 7.27–7.31 (2m, each 2H, 6-CH, 7-CH,

9-CH and 10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 14.2 (q, C-13),

18.3 (dt, J = 12.6 Hz, C-3), 28.3 (dd, J = 12.2 Hz, C-1), 55.3 (q, C-

11), 61.1 (t, C-12), 81.0 (ds, J = 229.7 Hz, C-2), 114.0 (d, C-7 and

C-9), 127.1 (dd, J = 5.1 Hz, C-6 and C-10), 129.4 (ds, J = 22.9 Hz, C-

5), 159.9 (s, C-8), 168.0 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d

ꢁ182.36 (m, 1F, 2-CF). MS (GCToF, EI): m/z 238 (27) [M⁺], 220

(4), 218 (7), 209 (45), 193 (17), 189 (35), 183 (21), 174 (21), 165

(100), 161 (40), 155 (39), 149 (19), 145 (50), 135 (34), 133 (32),

121 (18), 115 (33), 109 (12), 103 (18), 101 (15), 96 (14), 91 (7),

83 (5), 77 (12), 63 (5), 57 (4), 51 (3). C₁₃H₁₅FO₃(238.25) calcd C

65.54% H 6.35%, found C 65.63% H 6.63%.

Data for 15g. Yield: 111 mg (3%, 15g/14g = 89:11). ¹H NMR

(CDCl₃, 300 MHz): d 1.06 (t, 3H, J = 8.3 Hz, 14-CH₃), 1.78 (ddd,

1H, J = 18.9 Hz, 10.3 Hz, and 7.0 Hz, H_A), 1.93 (ddd, 1H,

J = 14.4 Hz, 6.9 Hz, and 6.9 Hz, H_B), 2.53 (ddd, 1H, J = 17.7 Hz,

10.3 Hz, and 7.6 Hz, H_X), 3.88 and 3.89 (2s, each 3H, 11-OCH₃

and 12-OCH₃), 3.95 (q, 2 H, J = 7.1 Hz, 5-CH₂), 6.83–7.05 (m, 3H,

6-CH, 9-CH and 10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 14.1 (q, C-

14), 16.7 (dt, J = 10.7 Hz, C-3), 27.8 (dd, J = 16.1 Hz, C-1), 55.9 (2q,

C-11 and C-12), 60.7 (t, C-13), 83.1 (ds, J = 219.9 Hz, C-2), 110.6

(d, C-9), 111.8 (dd, J = 2.0 Hz, C-6), 121.4 (dd, J = 5.2 Hz, C-10),

130.0 (ds, J = 19.5 Hz, C-5), 148.8 (s, C-8), 149.9 (s, C-7), 169.0 (s,

C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ150.42 (not completely re-

solved ddd, 1F, J = 16.7 Hz and 11.7 Hz, 2-CF). MS (GC/MS, EI): m/

z 269 (6), 268 (41) [M⁺], 248 (1), 240 (3), 239 (19), 237 (7), 224

(2), 223 (13), 219 (10), 213 (16), 197 (2), 196 (13), 195 (100),

193 (19), 185 (24), 175 (10), 169 (2), 165 (23), 164 (40), 163

(19), 160 (4), 151 (9), 149 (25), 145 (6), 137 (10), 133 (18), 131

(6), 121 (15), 115 (8), 109 (17), 96 (6), 91 (8), 83 (17), 77 (6), 70

(2), 63 (6), 55 (9), 51 (6), 43 (2).

Data for 15f. ¹H NMR (CDCl₃, 300 MHz): d 1.03 (t, J = 7.2 Hz, 3H,

13-CH₃), 1.76 (ddd, J = 19.1 Hz, 10.2 Hz, and 6.9 Hz, 1H, H_A), 1.91

(ddd, J = 12.1 Hz, 7.5 Hz, and 6.9 Hz, 1H, H_B), 2.52 (ddd,

J = 17.5 Hz, 10.2 Hz, and 7.5 Hz, 1H, H_X), 3.79 (s, 3H, 11-OCH₃),

3.93 (q, J = 7.2 Hz, 2H, 12-CH₂), 6.84–6.90 and 7.37–7.41 (2m, each

2H, 6-CH, 7-CH, 9-CH and 10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 14.0

7160

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

5.7. Synthesis of cyclopropanecarboxylic acids

7.30 (dm, 2H, J = 8.1 Hz, 7-CH and 9-CH), 11.67 (br s, 1H, 4-

CO₂H).¹³C NMR (CDCl₃, 75 MHz): d 18.9 (dt, J = 13.1 Hz, C-3), 28.0

(dd, J = 11.9 Hz, C-1), 55.3 (q, C-11), 81.7 (ds, J = 229.2 Hz, C-2),

114.1 (d, C-7 and C-9), 127.3 (dd, J = 6.3 Hz, C-6 and C-10), 128.8

(ds, J = 21.2 Hz, C-5), 160.0 (s, C-8), 174.5 (s, C-4). ¹⁹F NMR (CDCl₃,

282 MHz): d ꢁ180.65 (not completely resolved ddd, 1F, J = 20.2 Hz

and 11.3 Hz, 2-CF). MS ESI^ꢁ(daughter ion experiment): m/z 210

(40) [M⁺], 190 (30), 146 (7), 132 (100), 63 (30). HRMS (ESI⁺)

5.7.1. trans-2-Fluoro-2-(4-triﬂuoromethyl phenyl)cyclo-

propane carboxylic acid (18d)

According to the general procedure^15,68trans-2-ﬂuoro-2-(4-tri-

ﬂuoromethylphenyl)cyclopropane carboxylic acid ethylester (14d)

(0.94 g, 3.39 mmol) was transferred into the corresponding carbox-

ylic acid. Recrystallization from cyclohexane/ethyl acetate gave

18d (yield: 0.79 g,92%) as colorless needles. Mp 117 °C (cyclohex-

ane/ethyl acetate). ¹H NMR (CDCl₃, 300 MHz): d 1.76 (ddd, 1H,

J = 7.4 Hz, 9.4 Hz and 10.9 Hz, H_B), 2.25 (ddd, 1H, J = 7.9 Hz,

9.4 Hz, and 2.9 Hz, H_X), 2.40 (ddd, 1H, J = 7.6 Hz, 7.6 Hz, and

20.3 Hz, H_A), 7.41 (dm, 2H, J = 8.2 Hz, C-6 and C-10), 7.66 (dm,

2 H, J = 8.2 Hz, C-7 and C-9), 10.33 (br s, 1H, 4-CO₂H). ¹³C NMR

(CDCl₃, 75 MHz): d 19.8 (dt, J = 10.9 Hz, C-3), 29.2 (dd, J = 11.6 Hz,

C-1), 80.7 (ds, J = 232.2 Hz, C-2), 123.3 (qs, J = 271.8 Hz, C-11),

124.7 (dd, J = 5.8 Hz, C-6 and C-10), 125.7 (qd, J = 4.0 Hz, C-7 and

C-9), 130.7 (qs, J = 31.2 Hz, C-8), 141.1 (ds, J = 21.7 Hz, C-5), 173.5

(s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ63.40 (s, 3F, 11-CF₃),

ꢁ190.02 (not completely resolved ddd, J = 18.4 Hz and 8.9 Hz, 2-

CF). GC (GC/MS, EI, as trimethylsilyl ester): m/z 320 (9) [M⁺], 305

(51), 265 (33), 230 (53), 211 (13), 202 (9), 183 (57), 173 (89),

145 (7), 133 (37), 115 (11), 73 (100), 55 (5), 45 (20). HRMS (ESI⁺)

C

₁₁H₁₁FO₃+ Na⁺calcd 233.0584, found 233.0597, C₁₁H₁₁FO₃ꢁH⁺:

calcd 209.0619, found 209.0630. C₁₁H₁₁FO₃(210.20): calcd C

62.85%, H 5.27%, found C 62.84% H 5.15%.

Data for 19f. Yield: 97 mg (19f/18f = 89:11, 10%). Mp 102 °C

(cyclohexane/ethyl acetate, 19f/18f = 89:11). ¹H NMR (CDCl₃,

300 MHz): d 1.80 (ddd, 1H, J = 18.2 Hz, 10.1 Hz, and 7.0 Hz, H_A),

1.86 (ddd, 1H, J = 13.7 Hz, 7.3 Hz, and 7.3 Hz, H_B), 2.47 (ddd, 1H,

J = 17.4 Hz, 10.0 Hz, and 7.5 Hz, H_X), 3.80 (s, 3H, 11-OCH₃), 6.86

(d, 2H, J = 8.5 Hz, 6-CH and 10-CH), 7.36 (dd, 2H, J = 8.6 Hz,

J_H,F= 1.7 Hz, 7-CH and 9-CH), 9.65 (br s, 1H, 4-CO₂H). ¹³C NMR

(CDCl₃, 75 MHz): d 17.4 (dt, J = 11.6 Hz, C-3), 27.2 (dd, J = 19.4 Hz,

C-1), 55.2 (q, C-11), 83.3 (ds, J = 221.0 Hz, C-2), 113.8 (d, C-7 and

C-9), 124.8 (ds, J = 20.2 Hz, C-5), 130.1 (dd, J = 3.3 Hz, C-6 and

C-10), 160.3 (ds, J = 2.7 Hz, C-8), 175.0 (s, C-4). ¹⁹F NMR (CDCl₃,

282 MHz): d ꢁ148.24 (m, 1F, 2-CF). MS (GCToF, EI, as trimethylsilyl

ester): m/z 282 (26) [M⁺], 267 (14), 262 (27), 247 (4), 239 (4), 227

(12), 223 (16), 209 (1), 208 (4), 207 (9), 195 (1), 193 (5), 192 (46),

190 (16), 189 (2), 177 (6), 174 (27), 173 (1), 165 (16), 161 (6), 159

(4), 149 (19), 146 (29), 145 (34), 136 (2), 135 (26), 131 (32), 130

(9), 121 (16), 115 (12), 109 (9), 103 (26), 102 (16), 96 (6), 89 (6),

78 (4), 77 (36), 76 (35), 73 (100), 64 (5), 63 (9), 55 (5), 51 (5), 47

(8), 45 (12). C₁₁H₁₁FO₃(210.20): calcd C 62.85% H 5.27%, found C

62.59% H 5.46%.

C

₁₁H₈F₄O₂+ Na⁺: calcd 271.0353, found 271.0359. HRMS (ESI^ꢁ)

₁₁H₇F₄O₂ꢁH⁺: calcd 247.0377, found 247.0386.

5.7.2. cis-2-Fluoro-2-(4-triﬂuoromethylphenyl)cyclopropane

carboxylic acid (19d)

According to the general procedure^15,68cis-2-ﬂuoro-2-(4-tri-

ﬂuoromethylphenyl)cyclopropane carboxylic acid ethylester

(15d) (0.75 g, 2.72 mmol) was transferred into the corresponding

carboxylic acid. Recrystallization from cyclohexane/ethyl acetate

gave 19d (yield: 0.61 g, 90%) as colorless needles. Mp 80 °C (cyclo-

hexane/ethyl acetate). ¹H NMR (CDCl₃, 300 MHz): d 1.92 (ddd, 1H,

J = 19.1 Hz, 10.2 Hz, and 7.4 Hz, H_A), 1.99 (ddd, 1H, J = 13.3 Hz,

7.6 Hz, and 7.6 Hz, H_B), 2.55 (ddd, 1H, J = 18.0 Hz, 10.2 Hz, and

7.7 Hz, H_X), 7.52 (dm, 2H, J = 8.4 Hz, 6-CH and 10-CH), 7.62 (dm,

2H, J = 8.8 Hz, 7-CH and 9-CH), 9.26 (br s, 1H, 4-CO₂H). ¹³C NMR

(CDCl₃, 75 MHz): d 17.4 (dt, J = 9.1 Hz, C-3), 28.0 (dd, J = 17.3 Hz,

C-1), 82.7 (ds, J = 222.7 Hz, C-2), 123.8 (q, J = 272.5 Hz, C-11),

125.2 (qd, J = 4.0 Hz, C-7 and C-9), 126.9 (dd, J = 5.7 Hz, C-6 and

C-10), 131.4 (qs, J = 33.3 Hz, C-8), 136.4 (ds, J = 20.8 Hz, C-5),

174.3 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ63.40 (s, 3F, 11-

CF₃), ꢁ156.57 (not completely resolved ddd, 1F, J = 19.8 Hz, 2-CF).

GC (GC/MS, EI, as trimethyl silyl ester): m/z 320 (4) [M⁺], 305

(12), 265 (9), 230 (19), 183 (18), 173 (41), 145 (7), 133 (16), 115

(6), 73 (100), 45 (13). HRMS (ESI^ꢁ) C₁₁H₈F₄O₂ꢁH⁺: calcd

247.0377, found 247.0390. C₁₁H₈F₄O₂(248.18): calcd C 53.24% H

3.25%, found C 50.49% H 3.11%.

5.7.4. cis- and trans-2-ﬂuoro-2-(3,4-dimethoxyphenyl)-

cyclopropanecarboxylic acids (18g and 19g)

According to the general procedure^15,68a mixture of cis and

trans-2-ﬂuoro-2-(3,4-dimethoxyphenyl)cyclopropanecarboxylic acid

ethylester (14g and 15g) (0.81 g, 3 mmol, 14g/15g = 1:1) was

transferred into the corresponding mixture of carboxylic acids

18g and 19g (yield: 0.72 g, 18g/19g = 1:1, 99%).

C₁₂H₁₃FO₄

(240.23): calcd C 60.00% H 5.45%, found C 59.79% H 5.45%. All spec-

troscopic data were taken from a 1:1 mixture of 18g and 19g.

Data for 18g. ¹H NMR (CDCl₃, 300 MHz): d 1.65 (dt, 1H,

J = 10.0 Hz, 9.2 Hz, and 6.8 Hz, H_B), 2.12 (ddd, 1H, J = 7.7 Hz,

10.0 Hz, and 2.8 Hz, H_X), 2.22 (ddd, 1H, J = 19.8 Hz, 7.1 Hz, and

7.5 Hz, H_A), 3.90 (2s, 6H, 11-OCH₃and 12-OCH₃), 6.83–7.06 (m,

3H, 6-CH, 9-CH and 10-CH), 8.65 (br s, 4-CO₂H). ¹³C NMR (CDCl₃,

75 MHz): d 18.8 (dt, J = 14.0 Hz, C-3), 28.0 (dd, J = 13.4 Hz, C-1),

55.8 and 55.9 (2q, C-11 and C-12), 81.7 (ds, J = 228.3 Hz, C-2),

109.6 (dd, J = 6.4 Hz, C-6), 111.1 (d, C-9), 118.0 (dd, J = 5.3 Hz, C-

10), 129.3 (d, J = 21.6 Hz, C-5), 149.2 (s, C-7), 149.6 (s, C-8), 174.5

(s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ180.67 (not completely re-

solved ddd, 1F, J = 18.7 Hz and 8.5 Hz, 2-CF). MS (GCToF, EI, as tri-

methyl silyl ester): m/z 313 (2), 312 (16) [M⁺], 297 (11), 292 (10),

277 (2), 257 (2), 253 (14), 238 (1), 223 (5), 220 (58), 204 (72), 195

(18), 189 (10), 176 (20), 165 (74), 161 (48), 149 (16), 145 (6), 133

(22), 131 (12), 115 (16), 103 (16), 92 (4), 89 (16), 77 (70), 73 (100),

63 (12), 51 (8), 47 (16).

5.7.3. cis- and trans-2-ﬂuoro-2-(4-methoxyphenyl)cyclo-

propanecarboxylic acids (18f and 19f)

According to the general procedure^15,68a mixture of cis and

trans-2-ﬂuoro-2-(4-methoxyphenyl)cyclopropanecarboxylic acid

ethylester (14f and 15f) (1.06 g, 4.44 mmol, 14f/15f = 1:1) was

transferred into the corresponding mixture of carboxylic acids

16f and 17f (yield: 0.77 g, 18f/19f = 1:1, 83%). Subsequently, the

mixture of diasteromeres was separated by recrystallization from

cyclohexane/ethyl acetate giving diastereomerically pure 18f, a

mixed fraction (440 mg, 19f/18f = 70:30, 47%) and diastereomeri-

cally enriched 19f.

Data for 19g. ¹H NMR (CDCl₃, 300 MHz): d 1.84 (ddd, 1H,

J = 18.8 Hz, 10.0 Hz, and 7.2 Hz, H_A), 1.92 (ddd, 1H, J = 12.2 Hz,

7.2 Hz, and 7.2 Hz, H_B), 2.53 (ddd, 1H, J = 17.5 Hz, 10.0 Hz, and

7.5 Hz, H_X), 3.90 (2s, 6H, 11-OCH₃and 12-OCH₃), 6.83–7.06 (m,

3H, 6-CH, 9-CH and 10-CH), 8.65 (br s, 1H, 4-CO₂H). ¹³C NMR

Data for 18f. Yield: 225 mg (24%). Mp 112 °C (cyclohexane/ethyl

acetate). ¹H NMR (CDCl₃, 300 MHz): d 1.65 (ddd, 1H, J = 10.5 Hz,

9.2 Hz, and 6.9 Hz, H_B), 2.14 (ddd, 1H, J = 7.6 Hz, 9.6 Hz, and

2.2 Hz, H_X), 2.26 (ddd, 1H, J = 19.5 Hz, 7.3 Hz, and 7.3 Hz, H_A),

3.80 (s, 3H, 11-OCH₃), 6.91 (dm, 2H, J = 8.4 Hz, 6-CH and 10-CH),

(CDCl₃, 75 MHz):

d 17.4 (dd, J = 10.9 Hz, C-3), 27.4 (dd,

J = 17.6 Hz, C-1), 56.0 (q, C-11 and C-12), 83.5 (ds, J = 223.4 Hz,

C-2), 110.7 (d, C-9), 111.8 (dd, J = 3.3 Hz, C-6), 121.5 (dd, J = 4.9 Hz,

C-10), 125.2 (ds, J = 20.1 Hz,C-5), 148 (s, C-8), 150.0 (s, C-7),

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7161

173.7 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ148.72 (not com-

pletely resolved ddd, 1F, J = 18.3 Hz and 13.1 Hz, 2-CF). MS (GCToF,

EI, as trimethylsilyl ester): m/z 313 (2), 312 (17) [M⁺], 298 (2), 297

(11), 292 (10), 277 (2), 257 (6), 253 (18), 238 (1), 223 (4), 222 (28),

220 (96), 219 (2), 205 (22), 204 (70), 195 (21), 191 (22), 176 (26),

175 (25), 165 (96), 161 (74), 149 (16), 145 (6), 133 (22), 131 (12),

115 (15), 103 (15), 92 (4), 89 (13), 77 (93), 73 (100), 63 (12), 51 (9),

47 (16).

15), 35.2 (m, C-1), 80.3 (m, C-12), 80.6 (ds, J = 218.1 Hz, C-2),

124.1 (q, J = 272.6 Hz, C-11), 125.1 (qd, J = 3.1 Hz, C-7 and C-9),

126.5 (m, C-6 and C-10), 130.4 (qs, J = 33.3 Hz, C-8), 138.5 (m, C-

5), 155.5 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz, 298 K): d ꢁ63.25 (s,

1F, CF₃); ꢁ174.31 (br m, 0.67 F, 2-CF) and ꢁ177.3 1 (br m, 0.33F,

2-CF), signals of rotamers. ¹⁹F NMR (CDCl₃, 470 MHz, 328 K): d

ꢁ63.39 (s, 3F, 11-CF₃), ꢁ173.91 (br m, 1F, 2-CF). MS (GCToF, EI):

m/z 319 (0) [M⁺], 245 (2), 220 (3), 218 (11), 216 (11), 207 (2),

202 (4), 199 (44), 198 (94), 190 (16), 178 (9), 176 (20), 171 (16),

169 (5), 156 (1), 152 (4), 151 (18), 145 (8), 134 (3), 133 (12), 130

(30), 121 (10), 120 (4), 107 (1), 103 (7), 101 (7), 95 (2), 81 (1), 77

(3), 75 (7), 74 (12), 69 (1), 63 (1), 59 (14), 57 (100), 56 (36), 55

(14), 50 (8), 44 (63), 41 (76). C₁₅H₁₇F₄NO₂(319.30): calcd C

56.43% H 5.37% N 4.39%, found C 56.11% H 5.10% N 4.29%.

5.8. Curtius rearrangements

5.8.1. tert-Butyl trans-[2-ﬂuoro-2-(4-triﬂuoromethylphenyl)-

cyclopropyl]carbamate (20d)

According to the general procedure^15,68trans-2-ﬂuoro-2-(4-tri-

ﬂuoromethylphenyl)cyclopropane carboxylic acid (18d) (248 mg,

1 mmol) was transferred into the corresponding Boc-protected

amine. Silica gel column chromatography (10ꢄ 3 cm, pentane/

diethyl ether, 10:1) and subsequent recrystallization from petane

diethyl ether furnished 20d as a white solid (yield: 198 mg, 62%).

Mp 164–165 °C (pentane/diethyl ether). ¹H NMR (CDCl₃,

300 MHz, 298 K): d 1.40–1.67 (m, 2H, H_Band H_X), 1.46 (s, 9H, 13-

CH₃–15-CH₃), 3.02 (br s, 1H, H_A), 4.97 (br s, 1H, NH), 7.38 (d, 2H,

J = 8.1 Hz 6-CH and 10-CH), 7.62 (d, 2H, J = 8.2 Hz, 7-CH and 9-

CH). ¹H NMR (C₆D₆, 500 MHz, 298 K): d 0.86–0.99 (br m, 2H, H_B

and H_X), 1.44 (s, 9H, 13-CH₃–15-CH₃), 2.68 (br s, 1H, H_A), 4.42 (br

s, 1H, NH), 6.87 (d, 2H, J = 7.1 Hz 6-CH and 10-CH), 7.23 (d, 2H,

J = 7.8 Hz, 7-CH and 9-CH). ¹H NMR (C₆D₆, 500 MHz, 343 K): d

0.94–1.00 (m, 2H, H_Band H_X), 1.43 (s, 9H, 13-CH₃–15-CH₃), 2.69

(br s, 1H, H_A), 4.41 (br s, 1H, NH), 6.96 (d, 2H, J = 8.2, Hz 6-CH

and 10-CH), 7.29 (d, 2H, J = 8.1 Hz, 7-CH and 9-CH). ¹³C NMR

(CDCl₃, 75 MHz, 298 K): d 20.7 (m, C-3), 28.3 (q, C-13–C-15), 34.9

(m, C-1), 76.9 (m, C-12), 80.0 (m, C-2), 124.0 (q, J = 271.4 Hz, C-

11), 124.5 (m, C-6 and C-10), 125.5 (qd, J = 3.6 Hz, C-7 and C-9),

130.1 (m, C-8), 141.9 (m, C-5), 156.1 (s, C-4). ¹⁹F NMR (CDCl₃,

282 MHz, 298 K): d [ppm]: ꢁ62.92 (s, 3F, CF₃); ꢁ194.69 (br m,

0.83F, 2-CF) and ꢁ195.8 3 (br m, 0.17 F, 2-CF), signals of rotamers.

¹⁹F NMR (C₆D₆, 470 MHz, 298 K): d ꢁ62.40 (s, 3F, 11-CF₃); ꢁ194.93

(not completely resolved ddd, 0.81F, 2-CF) and ꢁ197.0 2 (br s, 0.19

F, 2-CF), signals of rotamers. ¹⁹F NMR (C₆D₆, 470 MHz, 343 K): d

ꢁ62.82 (s, 3F, 11-CF₃), ꢁ194.12 (br s, 1F, 2-CF). MS (GCToF, EI):

m/z 319 (0) [M⁺], 245 (1), 226 (1), 219 (5), 218 (5), 216 (4), 199

(4), 198 (59), 190 (8), 176 (11), 171 (11), 169 (5), 151 (18), 133

(8), 130 (17), 121 (8), 103 (6), 101 (5), 99 (4), 75 (4), 74 (3), 59

(7), 57 (55), 56 (60), 55 (24), 53 (8), 44 (100). C₁₅H₁₇F₄NO₂

(319.30): calcd C 56.43% H 5.37% N 4.39%, found C 56.16% H

5.34% N 4.25%.

5.8.3. tert-Butyl trans-[2-ﬂuoro-2-(4-methoxyphenyl)cyclo-

propyl]carbamate (20f)

According to the general procedure^15,68trans-2-ﬂuoro-2-(4-

methoxyphenyl)cyclopropane carboxylic acid (18f) (0.190 g,

0.80 mmol) was transferred into the corresponding Boc-protected

amine. Silica gel column chromatography (20 ꢄ 3 cm, cyclohex-

ane/ethyl acetate, 10:1) and subsequent recrystallization from

cyclohexane/ethyl acetate furnished 20f as a white solid (yield:

161 mg, 71%). Mp 104 °C (cyclohexane/ethyl acetate). ¹H NMR

(CDCl₃, 300 MHz): d 1.35 (ddd, J = 21.8 Hz, 7.8 Hz, and 5.9 Hz, 1H,

H_A), 1.48 (s, 9H, 14-CH₃ꢁ16-CH₃), 1.44–1.54 (m, 1H, H_B), 2.93 (br

s, 1H, H_X), 3.81 (s, 3H, 11-OCH₃), 4.99 (br s, 1H, NH), 6.90 (d, 2H,

J = 8.2 Hz, 7-CH and 9-CH), 7.35 (dd, 2H, J = 7.8 Hz, 6-CH and 10-

CH). ¹³C NMR (CDCl₃, 75 MHz): d 19.2 (dt, J = 11.0 Hz, C-3), 28.3

(q, C-13–C-15), 33.0 (dd, J = 10.3 Hz, C-1), 55.3 (q, C-11), 80.2

(ms, C-2), 113.9 (d, C-7 and C-9), 128.0 (md, C-6 and C-10),

128.9-129.8 (ms, C-5), 156.4 (s, C-4) 159.7 (s, C-8). ¹⁹F NMR (CDCl₃,

282 MHz, 298 K): d ꢁ183.85 (not completely resolved ddd, 0.83F,

2-CF) and ꢁ185.7 7 (br m, 0.17 F, 2-CF), signals of rotamers. MS

(GCToF, EI): m/z 281 (<0.1) [M⁺], 225 (2), 205 (2), 188 (2), 180

(3), 164 (3), 161 (19), 160 (100), 159 (9), 146 (20), 145 (14), 144

(4), 133 (15), 130 (43), 119 (5), 118 (20), 117 (16), 116 (15), 103

(9), 92 (3), 91 (12), 90 (13), 89 (20), 79 (3), 77 (12), 65 (6), 63

(12), 57 (16), 56 (27), 55 (12), 51 (8), 44 (27), 41 (45). C₁₅H₂₀FNO₃

(281.33): calcd C 64.04% H 7.17% N 4.98%, found C 63.80% H 7.05%

N 4.95%.

5.8.4. tert-Butyl cis-[2-ﬂuoro-2-(4-methoxyphenyl)cyclo-

propyl]carbamate (21f)

According to the general procedure^15,68a mixture of cis-and

trans-2-ﬂuoro-2-(4-methoxyphenyl)cyclopropanecarboxylic acid

(0.440 g, 2.1 mmol, 19f/18f = 70:30) was transferred into the corre-

sponding Boc-protected amines. After silica gel column chroma-

tography (20 ꢄ 3 cm, cyclohexane/ethyl acetate, 10:1) a mixture

of both isomers was isolated as a white solid (yield: 404 mg, 21f/

20f = 70:30, 69%). Subsequently the diasteromeric mixture was

separated by recrystallization from cyclohexane/ethyl acetate to

give diasteromerically pure 21f (yield: 131 mg, 31% relating to

the ratio of 19f in the diastereomeric mixture of the reactand).

Mp 131 °C (cyclohexane/ethyl acetate). ¹H NMR (CDCl₃,

300 MHz): d 1.29–1.42 (m, 1H, H_B), 1.35 (s, 9H, 14-CH₃ꢁ16-CH₃),

1.72 (ddd, J = 21.4 Hz, 9.5 Hz and 9.5 Hz, 1H, H_A), 3.29 (m, 1H,

H_X), 3.82 (s, 3H, 11-OCH₃), 4.26 (br s, 1H, NH), 6.92 (d, 2H,

J = 8.3 Hz, 7-CH and 9-CH), 7.37–7.46 (m, 2H, 6-CH and 10-CH).

¹³C NMR (CDCl₃, 75 MHz): d 17.9–18.1 (mt, C-3), 28.2 (q, C-13–C-

15), 33.3–33.6 (md, C-1), 55.3 (q, C-11), 79.8 (s, C-12), 81.0 (ds,

J = 218.2 Hz, C-2), 113.8 (d, C-7 and C-9), 125.5 (ms, C-5), 129.5

(md, C-6 and C-10), 155.8 (s, C-4), 160.0 (ms, C-8). ¹⁹F NMR (CDCl₃,

282 MHz, 298 K): d ꢁ164.27 (br s, 0.76H, 2-CF) and ꢁ168.47 (br m,

0.24H, 2-CF), signals of rotamers. MS (GCToF, EI): m/z 281 (0) [M⁺],

226 (1), 225 (3), 205 (4), 188 (2), 180 (4), 164 (4), 161 (21), 160

5.8.2. tert-Butyl cis-[2-ﬂuoro-2-(4-triﬂuoromethylphenyl)-

cyclopropyl]carbamate (21d)

According to the general procedure^15,68cis-2-ﬂuoro-2-(4-tri-

ﬂuoromethylphenyl)cyclopropane carboxylic acid (19d) (310 mg,

1.25 mmol) was transferred into the corresponding Boc-protected

amine. Silica gel column chromatography (13ꢄ 3 cm, cyclohex-

ane/ethyl acetate, 20:1) and subsequent recrystallization from

pentane diethyl ether furnished 21d as a white solid (yield:

383 mg, 95%). Mp 168–170 °C (pentane/diethyl ether). ¹H NMR

(CDCl₃, 300 MHz, 298 K): d 1.27 (s, 9H, 13-CH₃–15-CH₃), 1.44–

1.56 (m, 1H, H_B), 1.86 (ddd, 1H, J = 8.4 Hz, 9.6 Hz, and 21.7 Hz,

H_A), 3.31 (ddd, 1H, J = 6.2 Hz, 9.9 Hz, and 15.3 Hz, H_X), 4.42 (br s,

1H, NH), 7.49 (dm, 2H, J = 8.5 Hz, C-6 and 10-CH), 7.64 (dm, 2H,

J = 8.2 Hz, 7-CH and 9-CH). ¹H NMR (CDCl₃, 500 MHz, 328 K): d

1.28 (s, 9H, 13-CH₃–15-CH₃), 1.43–1.51 (m, 1H, H_B), 1.85 (ddd,

1H, J = 8.6 Hz, 8.6 Hz, and 21.6 Hz, H_A), 3.31 (ddd, 1H, J = 7.7 Hz,

7.7 Hz, and 15.4 Hz, H_X), 4.34 (br s, 1H, NH), 7.49 (dm, 2H, J = 7.9

Hz, C-6 and 10-CH), 7.63 (dm, 2H, J = 8.2 Hz, 7-CH and 9-CH). ¹³C

NMR (CDCl₃, 125 MHz, 328 K): d 19.1 (m, C-3), 28.0 (q, C-13–C-

7162

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

(100), 159 (11), 152 (8), 146 (21), 145 (15), 144 (4), 133 (19), 130

(45), 119 (6), 118 (21), 117 (18), 116 (6), 103 (10), 102 (6), 92 (4),

91 (13), 90 (14), 89 (23), 74 (4), 77 (13), 65 (6), 63 (13), 57 (18), 56

(31), 55 (14), 51 (10), 44 (37), 41 (56). C₁₅H₂₀FNO₃(281.33): calcd

C 64.04% H 7.17% N 4.98%, found C 63.69% H 7.12% N 4.93%.

6-CH–10-CH and 12-CH–16-CH). ¹H NMR (C₆D₆, 600 MHz,

348 K): d 1.40 (s, 9H, 18-CH₃–20-CH₃), 1.76 (dd, 1H, J = 22.5 Hz

and 7.7 Hz, H_A), 1.99 (dd, 1H, J = 12.3 Hz and 8.4 Hz, H_B), 5.36 (br

s, 1H, NH), 6.82–7.16 (m, 6-CH–10-CH and 12-CH–16-CH). ¹³C

NMR (C₆D₆, 600 MHz, 343 K): d 23.9 (dt, J = 9.5 Hz, C-3), 28.5 (q,

C-18–C-20), 44.9 (ms, C-1), 79.4 (s, C-17), 84.5 (ds, J = 227.6 Hz,

C-2), 127.1, 127.8, 127.9, 128.0, 128.3, 128.9 (d, C-6–C-10 and

C-12–C-16), 135.1 (ds, J = 21.8 Hz, C-5), 138.8 (br s, C-11), 155.5

(br s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz, 298 K): d ꢁ170.90 (m,

0.71F, 2-CF) and ꢁ170.23 (br s, 0.29 F, 2-CF), signals of rotamers.

¹⁹F NMR (C₆D₆, 470 MHz, 298 K): d ꢁ170.32 (m, 0.93F, 2-CF) and

ꢁ170.23 (br s, 0.7 F, 2-CF), signals of rotamers. ¹⁹F NMR (C₆D₆,

564 MHz, 343 K): d ꢁ170.58 (br s, 1F, 2-CF). MS (GCToF, EI, in a

range from m/z 240 to 430) m/z 327 (0) [M⁺], 307 (1) [M⁺ꢁHF],

295 (3), 294 (1) [M⁺ꢁCH₂F], 273 (1), 272 (18), 271 (100)

[M⁺ꢁC₄H₇], 270 (15) [M⁺ꢁC₄H₈], 254 (12), 253 (41), 251 (75)

[271-HF], 248 (10). MS (GCToF, EI, in a range from m/z 40 to

430): m/z 327 (0) [M⁺], 272 (1), 271 (4), 270 (1), 251 (4), 228 (1),

227 (4), 226 (11), 224 (5), 208 (3), 207 (21), 206 (100), 204 (9),

191 (3), 180 (3), 179 (14), 178 (11), 176 (2), 150 (2), 133 (3), 130

(25), 122 (8), 105 (3), 104 (40), 103 (18), 102 (10), 101 (3), 89

(2), 78 (5), 77 (40), 76 (8), 75 (4), 73 (1), 56 (9), 51 (13), 41 (18).

HRMS (ESI⁺) C₂₀H₂₂FNO₂+ Na⁺: calcd 350.1527, found 350.1515.

Data for 21h. Yield: 210 mg (49% relating to the ratio of 19h in

the diastereomeric mixture of the reactand). Mp 128 °C (pentane/

diethyl ether). ¹H NMR (CDCl₃, 300 MHz, 298 K): d 1.28 (s, 9H,

18-CH₃ꢁ20-CH₃), 2.13 (br s, 1H, H_B), 2.27 (dd, 1H, J = 21.5 Hz and

7.8 Hz, H_A), 4.71 (br s, 1H, NH), 7.24–7.50 (m, 6-CH–10-CH and

12-CH–16-CH). ¹H NMR (C₆D₆, 600 MHz, 298 K): d 1.91 (s, 9H,

18-CH₃ꢁ20-CH₃), 2.00 (br s, 1H, H_B), 2.08–2.10 (m, 1H, H_A), 4.56

(br s, 1H, NH), 7.05–7.53 (m, 6-CH–10-CH and 12-CH–16-CH). ¹H

NMR (C₆D₆, 600 MHz, 348 K): d 1.20 (s, 9H, 18-CH₃ꢁ20-CH₃),

1.93 (br s, 1H, H_B), 2.06 (dd, 1H, J = 21.8 Hz and 8.2 Hz, H_A), 4.53

(br s, 1H, NH), 7.07–7.22 (m, C-7–C-9 and C-13–C-15), 7.35 (d,

2H, J = 7.5 Hz, 6-CH and 10-CH), 7.51 (d, 2H, J = 7.5 Hz, 12-CH and

16-CH). ¹³C NMR (C₆D₆, 600 MHz, 298 K): d 22.3 (mt, C-3), 27.2

(q, C-18–C-20), 43.8 (ms, C-1), 78.9 (s, C-17), 82.7 (ds,

J = 220.0 Hz, C-2), 125.6, 125.7, 126.4, 127.2, 127.4, 127.5, 127.6

(d, C-6–C-10 and C-12–C-16), 132.9 (ms, C-5), 136.6 (br s, C-11),

153.5 (br s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz, 298 K): d ꢁ172.52

(m, 0.37 F, 2-CF) and ꢁ173.28 (br s, 0.63F, 2-CF), signals of rota-

mers. MS (GCToF, EI, in the of m/z 240–390) m/z 327 (0) [M⁺],

320 (1), 307 (2), 306 (2), 295 (3), 294 (2), 273 (1), 272 (16), 271

(100), 270 (15), 254 (14), 253 (73), 252 (48), 251 (79), 248 (7).

MS (GCToF, EI, in the range of m/z = 0-390): m/z 327 (0), 272 (1),

271 (3), 270 (1), 251 (2), 232 (1), 227 (4), 226 (8), 224 (5), 208

(4), 207 (20), 206 (100), 204 (10), 191 (4), 179 (12), 176 (2), 165

(3), 156 (3), 133 (3), 130 (20), 122 (8), 120 (1), 105 (4), 104 (37),

103 (19), 102 (8), 101 (4), 89 (3), 78 (5), 77 (32), 76 (8), 75 (4),

63 (4), 56 (10), 51 (11), 41 (18). HRMS (ESI⁺) C₂₀H₂₂FNO₂+ Na⁺:

calcd 350.1527, found 350.1522.

5.8.5. tert-Butyl cis- and trans-[2-ﬂuoro-2-(3,4-dimethoxy-

phenyl)cyclopropyl]carbamate (20g and 21g)

According to the general procedure^15,68a mixture of cis-and

trans-2-ﬂuoro-2-(3,4-dimethoxyphenyl)cyclopropanecarboxylic acid

(0.77 g, 2.81 mmol, 19g/18g = 1:1) was transferred into the corre-

sponding Boc-protected amines. Silica gel column chromatography

(45 ꢄ 3 cm, pentane/diethyl ether, 4:1, then 3:1) furnished diaste-

reomerically pure products as white solids.

Data for 20g. Yield: 241 mg (55% relating to the ratio of 18g in

the diastereomeric mixture of the reactand). Mp 108 °C (cyclohex-

ane/ethyl acetate). ¹H NMR (CDCl₃, 300 MHz):

d 1.36 (ddd,

J = 21.8 Hz, 7.9 Hz, and 6.0 Hz, 1H, H_A), 1.48 (s, 9H, 14-CH₃ꢁ16-

CH₃), 1.45–1.54 (m, 1H, H_B), 2.96 (br s, 1H, H_X), 3.87 and (2s, 3H,

11-OCH₃and 12-OCH₃), 4.98 (br s, 1H, NH), 6.83–6.97 (m, 3H, 6-

CH, 9-CH and 10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 19.6 (dt,

J = 10.5 Hz, C-3), 28.3 (q, C-14–C-16), 33.3 (md, C-1), 55.9 (2q,

C-11 and C-12), 79.3 (ds, J = 220.6 Hz, C-2), 79.9 (s, C-13), 109.9

(dd, J = 5.9 Hz, C-6), 111.1 (d, C-9), 118.6 (md, C-10), 129.7 (ds,

J = 21.2 Hz, C-5), 149.1 (s, C-8), 149.3 (ds, J = 2.4 Hz, C-7), 156.3

(s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d ꢁ184.64 (br s, 0.82 F, 2-CF)

and ꢁ186.24 (br s, 0.18 F, 2-CF), signals of rotamers. MS (GCToF,

EI): m/z 311 (0) [M⁺], 235 (1), 210 (1), 190 (17), 174 (12) [M⁺-

(CH₃O)₂C₆H₃], 160 (45), 117 (6), 116 (2), 77 (4), 57 (25), 56 (52),

44 (100). C₁₆H₂₂FNO₄(311.35): calcd C 61.72% H 7.12% N 4.50%,

found C 61.61% H 7.14% N 4.41%.

Data for 21g. Yield: 240 mg (55% relating to the ratio of 19g in

the diastereomeric mixture of the reactand). Mp 135 °C (cyclohex-

ane/ethyl acetate).

¹H NMR (CDCl₃, 300 MHz): d 1.29–1.42 (m, 1H, H_B), 1.36 (s, 9H,

14-CH₃ꢁ16-CH₃), 1.73 (ddd, J = 8.1 Hz, 9.2 Hz, and 21.1 Hz, 1H, H_A),

3.27–3.32 (m, 1H, H_X), 3.89 and 3.90 (2s, 3H, 11-OCH₃and

12-OCH₃), 4.25 (br s, 1H, NH), 6.86–7.05 (m, 3H, 6-CH, 9-CH and

10-CH). ¹³C NMR (CDCl₃, 75 MHz): d 17.8–18.2 (mt, C-3), 28.2 (q,

C-14–C-16), 33.5–33.7 (md, C-1), 55.9 (2q, C-11 and C-12), 79.8

(s, C-13), 81.3 (ds, J = 218.0 Hz, C-2), 110.9 (d, C-9), 111.3–111.6

(md, C-6), 120.4 (md, C-10), 125.8 (ds, J = 18.9 Hz, C-5), 149.0 (s,

C-8), 149.6 (ms, C-7), 155.8 (s, C-4). ¹⁹F NMR (CDCl₃, 282 MHz): d

ꢁ163.93 (br s, 0.78 F, 2-CF) and ꢁ168.50 (br s, 0.22 F, 2-CF), signals

of rotamers. MS (GCToF, EI): m/z 311 (0) [M⁺], 235 (3), 210 (3), 190

(17), 174 (18), 160 (71), 117 (8), 116 (5), 77 (8), 57 (28), 56 (68), 44

(100). C₁₆H₂₂FNO₄(311.35): calcd C 61.72% H 7.12% N 4.50%, found

C 61.39% H 7.13% N 4.39%.

5.8.6. tert-Butyl cis- and trans-(2-ﬂuoro-1,2-diphenyl-

cyclopropyl)- carbamates (20h and 21h)

According to the general procedure^15,68a mixture of cis-and

trans-2-ﬂuoro-1,2-diphenylcyclopropanecarboxylic acid (0.83 g,

3.25 mmol, 18h/19h = 60:40) was transferred into the correspond-

ing Boc-protected amines. Silica gel column chromatography

(30 ꢄ 3 cm, pentane/diethyl ether, 20:1) furnished diastereomeri-

cally pure products as white solids and a mixed fraction (yield:

159 mg, 20h/21h = 33:67, 15%).

5.9. Synthesis of cyclopropylamine hydrochlorides

5.9.1. trans-2-Fluoro-2-(4-triﬂuoromethylphenyl)cyclo-

propylamine hydrochloride (7d)

According to the general procedure^15,68tert-butyl trans-[2-ﬂu-

oro-2-(4-triﬂuoromethylphenyl)cyclopropyl]carbamate

(20d)

Data for 20h. Yield: 442 mg (69% relating to the ratio of 18h in

the diastereomeric mixture of the reactand). Mp 108 °C (pentane/

diethyl ether). ¹H NMR (CDCl₃, 300 MHz, 298 K): d 1.43 (s, 9H,

18-CH–20-CH₃), 1.94 (dd, 1H, J = 21.0 Hz and 9.0 Hz, H_A), 2.30

(dd, 1H, J = 11.8 Hz and 8.4 Hz, H_B), 5.66 (br s, 1H, NH), 7.10–7.17

(m, 10H, 6-CH–10-CH and 12-CH–16-CH). ¹H NMR (C₆D₆,

600 MHz, 298 K): d 1.39 (s, 9H, 18-CH₃–20-CH₃), 1.76-1.81 (m,

1H, H_A), 1.96–1.99 (m, 1H, H_B), 5.39 (br s, 1H, NH), 6.80–7.12 (m,

(132 mg, 0.41 mmol) was transferred into the corresponding free

amine. Recrystallization from methanol/diethyl ether furnished

7d as a white solid (yield: 66 mg, 63%). Mp 165 °C (methanol/

diethyl ether, decomposition). ¹H NMR (methanol-d₄, 300 MHz):

d 1.90–2.00 (m, 2H, H_Aand H_B), 3.17–3.22 (m, 1H, H_X), 4.80 (br s,

3H, NH₂ꢀHCl), 7.60 (dm, 2H, J = 8.0 Hz, 5-CH and 9-CH), 7.75 (dm,

2H, J = 7.9 Hz, 6-CH and 8-CH). ¹³C NMR (methanol-d₄, 75 MHz):

d 18.9 (dt, J = 10.3 Hz, C-3), 33.4 (dd, J = 13.1 Hz, C-1), 78.9 (ds,

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7163

J = 220.3 Hz, C-2), 123.9 (ms, C-10), 126.9 (dd, J = 6.9 Hz, C-5 and C-

9), 127.1 (qd, J = 3.9 Hz, C-6 and C-8), 132.2 (qs, J = 32.9 Hz, C-7),

141.5 (ds, J = 20.7 Hz, C-4). ¹⁹F NMR (methanol-d₄, 282 MHz): d

ꢁ62.65 (s, 3F, 10-CF₃), ꢁ192.59 (m, 1F, 2-CF). MS ESI^ꢁ(daughter

ion experiment): m/z 220 (51) [M-–l^ꢁ], 203 (89), 200 (100), 183

(6), 180 (13), 131 (7). HRMS (ESI⁺) C₁₀H₁₀ClF₄NꢁCl^ꢁ: calcd

220.0749, found 220.0742. C₁₀H₁₀ClF₄N (255.64): calcd C 46.98%

H 3.94% N 5.48%, found C 46.25% H 3.78% N 5.46%.

5-CH and 9-CH). ¹³C NMR (methanol-d₄, 75 MHz): d 16.3 (dt,

J = 14.4 Hz, C-3), 32.6 (dd, J = 22.9 Hz, C-1), 56.2 (q, C-10), 80.1

(ds, J = 220.0 Hz, C-2), 115.9 (d, C-6 and C-8), 123.9 (ds,

J = 20.6 Hz, C-4), 132.9 (dd, J = 2.2 Hz, C-5 and C-9), 163.1 (ds,

J = 2.3 Hz, C-7). ¹⁹F NMR (methanol-d₄, 282 MHz): d ꢁ155.36 (not

completely resolved ddd, 1F, J = 21.1 Hz and 11.1 Hz, 2-CF). MS

ESI⁺(daughter ion experiment): m/z 182 (35) [MꢁCl^ꢁ], 165 (83)

[182-NH₃], 162 (29) [182-HF], 153 (71) [182-CHO], 145 (15)

[162-NH₃], 139 (9), 135 (20) [165-HF], 119 (4) [139-HF], 117 (6)

[145-CO], 115 (4) [145-CH₂O], 91 (7) [C₇H₇^þ], 30 (100) [CH₂O⁺].

HRMS (ESI⁺) C₁₀H₁₃ClFNOꢁCl^ꢁ: calcd 182.0976, found 182.0978.

5.9.2. cis-2-Fluoro-2-(4-triﬂuoromethylphenyl)cyclopropyl-

amine hydrochloride (10d)

According to the general procedure^15,68tert-butyl cis-[2-ﬂuoro-

2-(4-triﬂuoromethylphenyl)cyclopropyl]carbamate (21d) (155 mg,

0.48 mmol) was transferred into the corresponding free amine.

Recrystallization from methanol/diethyl ether furnished 10d as a

white solid (yield: 100 mg, 81%). Mp 156 °C (methanol/diethyl

ether, decomposition). ¹H NMR (methanol-d₄, 300 MHz): d 1.90–

2.11 (m, 2H, H_Band H_A), 3.46 (ddd, 1H, J = 14.4 Hz, 10.2 Hz, and

6.3 Hz, H_X), 4.79 (s, 3H, NH₂ꢀHCl), 7.80–7.87 (m, 4H, 5-CH–9-CH).

¹³C NMR (methanol-d₄, 75 MHz): d 16.5 (dt, J = 12.4 Hz, C-3), 33.3

(dd, J = 20.5 Hz, C-1), 79.9 (ds, J = 220.7 Hz, C-2), 123.8 (q,

J = 272.5 Hz, C-10), 127.5 (qd, J = 4.2 Hz, C-8 and C-6), 131.2 (dd,

J = 4.0 Hz, C-5 and C-9), 133.6 (qs, J = 33.1 Hz, C-7), 136.5 (ds,

J = 21.5 Hz, C-4). ¹⁹F NMR (methanol-d₄, 282 MHz): d ꢁ62.82 (s,

3F, 10-CF₃), ꢁ163.41 (not completely resolved ddd, 1F, J = 21.1 Hz

and 12.7 Hz, 2-CF). MS (direct injection, EI): m/z 257/255 (0/0)

[M⁺], 219 (21), 218 (27), 198 (100), 183 (5), 171 (16), 151 (23),

130 (34), 121 (5), 103 (6), 74 (31), 73 (5), 54 (3). HRMS (ESI⁺):

5.9.5. trans-2-Fluoro-2-(3,4-dimethoxyphenyl)cyclopropyl-

amine hydrochloride (7g)

According to the general procedure^15,68tert-butyl trans-[2-ﬂu-

oro-2-(3,4-dimethoxyphenyl)cyclopropyl]carbamate (20g) (156 mg,

0.5 mmol) was transferred into the corresponding free amine.

Recrystallization from methanol/diethyl ether furnished 7g as a

white solid (yield: 90 mg, 77%). Mp 155 °C (methanol/diethyl

ether, decomposition). ¹H NMR (methanol-d₄, 300 MHz): d 1.73–

1.81 (m, 2H, H_Aand H_B), 3.00–3.05 (m, 1H, H_X), 3.84 and 3.86

(2s, 3H, 10-OCH₃and 11-OCH₃), 4.77 (s, 3H, NH₂ꢀHCl), 6.98–7.10

(m, 3H, 5-CH, 8-CH and 9-CH). ¹³C NMR (methanol-d₄, 75 MHz):

d 17.5 (dt, J = 17.5 Hz, C-3), 32.3 (dd, J = 10.7 Hz, C-1), 56.8 and

57.0 (2q, C-10 and C-11), 79.6 (ds, J = 218.4 Hz, C-2), 112.3 (dd,

J = 3.3 Hz, C-5), 113.2 (d, C-8), 121.1 (dd, J = 5.2 Hz, C-9), 128.9

(ds, J = 19.7 Hz, C-4), 151.0 (s, C-7), 151.9 (ds, J = 3.2 Hz, C-6). ¹⁹F

NMR (methanol-d₄, 282 MHz): d ꢁ181.26 (m, 1F, 2-CF). MS ESI⁺

(daughter ion experiment): m/z 212 (21) [M⁺ꢁHCl], 192 (100),

161 (6). HRMS (ESI⁺) C₁₁H₁₅ClFNO₂ꢁCl^ꢁ: calcd 212.1081, found

212.1080.

C

₁₀H₁₀ClF₄NꢁCl^ꢁ: calcd 220.0749, found 220.0742. C₁₀H₁₀ClF₄N

(255.64): calcd C 46.98% H 3.94% N 5.48%, found C 46.62% H

3.95% N 5.43%.

5.9.3. trans-2-Fluoro-2-(4-methoxyphenyl)cyclopropylamine

hydrochloride (7f)

5.9.6. cis-2-Fluoro-2-(3,4-dimethoxyphenyl)cyclopropylamine

hydrochloride (10g)

According to the general procedure^15,68tert-butyl trans-[2-ﬂu-

oro-2-(4-methoxyphenyl)cyclopropyl]carbamate (20f) (132 mg,

0.41 mmol) was transferred into the corresponding free amine.

Recrystallization from methanol/diethyl ether furnished 7f as a

white solid (yield: 84 mg, 94%). Mp 166 °C (methanol/diethyl

ether, decomposition). ¹H NMR (methanol-d₄, 300 MHz): d 1.69–

1.82 (m, 2H, H_Aand H_B), 2.97-3.02 (m, 1H, H_X), 3.81 (s, 3H, 10-

OCH₃), 4.91 (s, 3H, NH₂ꢀHCl), 6.98 (d, 1H, J = 8.1 Hz, 6-CH and 8-

CH), 7.43 (dd, 1H, J = 8.7 Hz, J_H,F= 1.3 Hz, 5-CH and 9-CH). ¹³C

NMR (methanol-d₄, 75 MHz): d 17.4 (dt, J = 15.1 Hz, C-3), 32.1

(dd, J = 10.5 Hz, C-1), 56.2 (q, C-10), 79.4 (ds, J = 218.9 Hz, C-2),

115.5 (d, C-6 and C-8), 128.3 (ds, J = 19.8 Hz, C-4), 129.8 (ds,

J = 4.4 Hz, C-5 and C-9), 162.3 (ds, J = 2.5 Hz, C-7). ¹⁹F NMR (meth-

anol-d₄, 282 MHz): d ꢁ181.05 (not completely resolved ddd, 1F,

J = 19.4 Hz and 15.4 Hz, 2-CF). MS ESI⁺(daughter ion experiment):

m/z 182 (5) [M-Cl^ꢁ], 162 (100) [182-HF], 147 (53) [162-CH₃], 132

(23) [162-CH₂O], 131 (28) [162-CH₃O], 130 (14) [147-NH₃], 119

According to the general procedure^15,68tert-butyl cis-[2-ﬂuoro-

2-(3,4-methoxyphenyl)cyclopropyl]carbamate

(21g)

(35 mg,

0.11 mmol) was transferred into the corresponding free amine.

Recrystallization from methanol/diethyl ether furnished 10g as a

white solid (yield: 26 mg, 84%). Mp 156 °C (methanol/diethyl

ether, decomposition). ¹H NMR (methanol-d₄, 300 MHz): d 1.74

(ddd, 1H, J = 9.3 Hz, 9.3 Hz, and 5.9 Hz, H_B), 1.89 (ddd, 1H,

J = 19.3 Hz, 9.9 Hz, and 9.3 Hz, H_A), 3.37 (ddd, 1H, J = 13.4 Hz,

10.0 Hz, and 5.9 Hz, H_X), 3.87 and 3.92 (2s, 3H, 10-OCH₃or 11-

OCH₃), 3.92 (s, 3H, 10- or 11-OCH₃), 4.88 (s, 3H, NH₂ꢀHCl), 7.08

(dm, 1H, J = 8.2 Hz, 8-CH), 7.21 (dd, 1H, J = 8.2 Hz, J_H,F= 2.2 Hz, 9-

CH), 7.25 (m, 1H, 5-CH). ¹³C NMR (methanol-d₄, 75 MHz): d 16.3

(dt, J = 12.8 Hz, C-3), 32.7 (dd, J = 22.7 Hz, C-1), 56.8 and 57.0 (2q,

C-10 and C-11), 57.0 (q, C-10 or C-11), 80.4 (ds, J = 221.3 Hz, C-

2), 113.2 (d, C-8), 114.6 (d, C-5), 124.4 (d, C-9), 124.3 (ds,

J = 17.7 Hz, C-4), 151.1 (s, C-7), 152.6 (ms, C-6).¹⁹F NMR (metha-

nol-d₄, 282 MHz): d ꢁ155.88 (m, 1F, 2-CF). MS ESI⁺(daughter ion

experiment): m/z 212 (2) [M–Cl^ꢁ], 192 (100), 165 (8). HRMS

(ESI⁺) C₁₁H₁₅ClFNO₂ꢁClꢁ: calcd 212.1081, found 212.1081.

(10)

C

[147-CHO],

118

(6)

[147-CH₂O].

HRMS

(ESI⁺)

₁₀H₁₃ClFNOꢁCl^ꢁ: calcd 182.0976, found 182.0913.

5.9.4. cis-2-Fluoro-2-(4-methoxyphenyl)cyclopropylamine

5.9.7. cis-( )-2-Fluoro-1,2-diphenylcyclopropylamine

hydrochloride (7h)

hydrochloride (10f)

According to the general procedure^15,68tert-butyl cis-[2-ﬂuoro-

2-(4-methoxyphenyl)cyclopropyl]carbamate (21f) (74 mg, 0.26 mmol)

was transferred into the corresponding free amine. Recrystalliza-

tion from methanol/diethyl ether furnished 10f as a white solid

(yield: 55 mg, 96%). Mp 156 °C (methanol/diethyl ether, decompo-

sition). ¹H NMR (methanol-d₄, 300 MHz): d 1.71 (ddd, 1 H,

J = 9.4 Hz, 9.4 Hz, and 5.8 Hz, H_B), 1.88 (ddd, 1H, J = 19.2 Hz,

9.9 Hz, and 9.0 Hz, H_A), 3.36 (ddd, 1H, J = 13.7 Hz, 10.1 Hz, and

5.9 Hz, H_X), 3.84 (s, 3H, 10-OCH₃), 4.89 (s, 3H, NH₂ꢀHCl), 7.06 (d,

1H, J = 8.6 Hz, 6-CH and 8-CH), 7.59 (dd, 1H, J = 8.7 Hz, J_H,F= 1.8 Hz,

According to the general procedure^15,68tert-butyl cis-[2-ﬂuoro-

1,2-diphenylcyclopropyl]carbamate (20h) (164 mg, 0.5 mmol) was

transferred into the corresponding free amine. Recrystallization

from methanol/diethyl ether furnished 7h as a white solid (yield:

132 mg, 99%). Mp 155 °C (methanol/diethyl ether, decomposition).

¹H NMR (methanol-d₄, 300 MHz): d 2.21 (dd, 1H, J = 23.6 Hz and

9.8 Hz, H_A), 2.64 (dd, 1H, J = 13.3 Hz and 9.8 Hz, H_B), 4.77 (br s,

3H, NH₂ꢀHCl), 7.23–7.30 (m, 10H, 4-CH–9-CH and 11-CH–15-CH).

¹³C NMR (methanol-d₄, 75 MHz): d 20.4 (dt, J = 11.0 Hz, C-3), 45.5

7164

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

(ds, J = 11.4 Hz, C-1), 83.7 (ds, J = 225.6 Hz, C-2), 128.2, 129.6,

130.3, 130.4, 130.8 (d, C-5– C-9, C-11–C-15), 133.3 (s, C-10),

133.9 (ds, J = 22.4 Hz, C-4). ¹⁹F NMR (methanol-d₄, 282 MHz): d

ꢁ175.28 (dd, 1F, J = 22.0 Hz and 13.3 Hz, 2-CF). MS ESI⁺(daughter

ion experiment): m/z 228 (20) [MꢁCl^ꢁ], 211 (23), 208 (100), 191

(12), 133 (5). HRMS (ESI⁺) C₁₅H₁₅ClFNꢁCl^ꢁ: calcd 228.1183, found

228.1186.

( h, k, l), [(sinh)/k] = 0.59 Å^ꢁ1, 3934 independent (R_int= 0.045)

and 3339 observed reﬂections [I P 2r(I)], 365 reﬁned parameters,

R = 0.089, wR²= 0.283, two almost identical molecules in the asym-

metric unit, CF₃-groups heavily disordered, reﬁned with split posi-

tions, max. residual electron density 0.47 (ꢁ0.28) e Å^ꢁ3, hydrogens

calculated and reﬁned as riding atoms.

5.10.4. X-ray crystal structure analysis for 19f

5.9.8. trans-( )-2-Fluoro-1,2-diphenylcyclopropylamine

hydrochloride (10h)

Formula

0.60 ꢄ 0.30 ꢄ 0.20 mm, a = 14.976(1), b = 5.783(1), c = 12.932(1) Å,

b = 112.90(1)°, V = 1031.7(2) Å³, _calc= 1.353 g cm^ꢁ3= 0.933 mm^ꢁ1

empirical absorption correction (0.605 6 T 6 0.835), Z = 4, mono-

clinic, space group P2₁/c (No. 14), k = 1.54178 Å, T = 293 K, and

scans, 12037 reﬂections collected ( h, k, l), [(sinh)/

k] = 0.59 Å^ꢁ1, 1789 independent (R_int= 0.037) and 1671 observed

C

₁₁H₁₁FO₃,

M = 210.20,

colorless

crystal

According to the general procedure^15,68tert-butyl trans-(2-ﬂu-

oro-1,2-diphenylcyclopropyl)carbamate (21h) (80 mg, 0.24 mmol)

was transferred into the corresponding free amine. Recrystalliza-

tion from methanol/diethyl ether furnished 10h as a white solid

(yield: 62 mg, 96%). Mp 143 °C (methanol/diethyl ether, decompo-

sition). ¹H NMR (methanol-d₄, 300 MHz): d 2.26–2.39 (m, 2H, H_A

and H_B), 4.79 (br s, 3H, NH₂ꢀHCl), 7.47–7.79 (m, 10H, 5-CH–9-CH

and 11-CH–15-CH). ¹³C NMR (methanol-d₄, 75 MHz): d 20.6 (dt,

J = 11.5 Hz, C-3), 45.4 (ds, J = 17.3 Hz, C-1), 82.7 (ds, J = 224.2 Hz,

C-2), 130.6, 130.8, 130.9, 131.2, 131.4, 132.4 (d, C-5 – C-9, C-11 –

C-15), 133.3 (ms, C-10), 133.9 (ds, J = 1.9 Hz, C-4). ¹⁹F NMR (meth-

anol-d₄, 282 MHz): d ꢁ158.43 (dd, 1F, J = 18.2 Hz and 12.6 Hz, 2-

CF). MS ESI⁺(daughter ion experiment): m/z 228 (39) [MꢁCl^ꢁ],

211 (19), 208 (100), 191 (8), 133 (5), 106 (8), 105 (33), 104 (90).

HRMS (ESI⁺) C₁₅H₁₅ClFNꢁCl^ꢁ: calcd 228.1183, found 228.1176.

q

,

l

,

x

u

reﬂections [I P 2r(I)], 138 reﬁned parameters, R = 0.042,

wR²= 0.135, max. residual electron density 0.13 (ꢁ0.12) e Å^ꢁ3

,

hydrogen calculated and reﬁned as riding atoms.

5.10.5. X-ray crystal structure analysis for 20d

Formula

0.30 ꢄ 0.15 ꢄ 0.01 mm, a = 13.647(1), b = 11.542(1), c = 10.039(1) Å,

b = 93.79(1)°, V = 1577.8(2) Å³, _calc= 1.344 g cm^ꢁ3= 1.048 mm^ꢁ1

empirical absorption correction (0.744 6 T 6 0.990), Z = 4, mono-

clinic, space group P2₁/c (No. 14), k = 1.54178 Å, T = 223 K, and

scans, 8932 reﬂections collected ( h, k, l), [(sinh)/k]

= 0.59 Å^ꢁ1, 2465 independent (R_int= 0.074) and 1471 observed

C₁₅H₁₇F₄NO₂,

M = 319.30,

colorless

crystal

q

,

l

,

x

u

5.10. X-ray structures

reﬂections [I P 2r(I)], 216 reﬁned parameters, R = 0.063,

Datasets were collected with Nonius KappaCCD diffractometers,

in the case of Mo-radiation equipped with a rotating anode gener-

ator. Programs used: data collection COLLECT,⁶⁹data reduction

Denzo-SMN⁷⁰, absorption correction SORTAV⁷¹and Denzo⁷², struc-

ture solution SHELXS-97,⁷³structure reﬁnement SHELXL-97,⁷⁴

graphics SCHAKAL.⁷⁵

wR²= 0.152, CF₃-groups disordered, reﬁned with split positions,

max. residual electron density 0.19 (ꢁ0.15) e Å^ꢁ3, hydrogen at N1

from difference fourier map, other calculated and reﬁned as riding

atoms.

5.10.6. X-ray crystal structure analysis for 20g

Formula

0.60 ꢄ 0.15 ꢄ 0.03 mm, a = 10.934(1), b = 13.227(1), c = 10.156(1) Å,

V = 1603.1(2) Å³, _calc= 1.290 g cm^ꢁ3= 0.833 mm^ꢁ1, empirical

absorption correction (0.635 6 T 6 0.975), Z = 4, orthorhombic,

C

₁₆H₂₂FNO₄,

M = 311.35,

colorless

crystal

5.10.1. X-ray crystal structure analysis for 18d

Formula

0.40 ꢄ 0.35 ꢄ 0.15 mm, a = 23.478(1), b = 7.074(1), c = 14.505(1)

Å, b = 118.19(1)°, V = 2123.3(3) Å³, _calc= 1.553 g cm^ꢁ3

= 1.354

mm^ꢁ1, empirical absorption correction (0.613 6 T 6 0.823), Z = 8,

monoclinic, space group C2/c (No. 15), k = 1.54178 Å, T = 223 K,

C₁₁H₈F₄O₂,

M = 248.17,

colorless

crystal

q

, l

q

,

l

space group Pca2₁(No. 29), k = 1.54178 Å, T = 223 K, x and u scans,

5796 reﬂections collected ( h, k, l), [(sinh)/k] = 0.59Å^ꢁ1, 1873

independent (R_int= 0.037) and 1756 observed reﬂections

x

and u scans, 6490 reﬂections collected ( h, k, l), [(sinh)/k]

[I P 2r

(I)], 207 reﬁned parameters, R = 0.038, wR²= 0.103, Flack

= 0.60 Å^ꢁ1, 1891 independent (R_int= 0.030) and 1748 observed

parameter 0.5(3), max. residual electron density 0.14

(-0.15) e Å^ꢁ3, hydrogen at N1 from difference fourier map, other

calculated and reﬁned as riding atoms.

reﬂections [I P 2r(I)], 155 reﬁned parameters, R = 0.057,

wR²= 0.153, max. residual electron density 0.54 (ꢁ0.39) e Å^ꢁ3

,

hydrogens calculated and reﬁned as riding atoms.

5.10.7. X-ray crystal structure analysis for 20h

5.10.2. X-ray crystal structure analysis for 18f

Formula

C

₂₀H₂₂FNO₂ꢀ C₅H₁₂

, M = 399.53, colorless crystal

Formula

0.30 ꢄ 0.20 ꢄ 0.10 mm, a = 5.528(1), b = 7.348(1), c = 25.592(1) Å,

b = 94.91(1)°, V = 1035.7(2) Å³, _calc= 1.348 g cm^ꢁ3= 0.929 mm^ꢁ1

empirical absorption correction (0.768 6 T 6 0.913), Z = 4, mono-

clinic, space group P2₁/c (No. 14), k = 1.54178 Å, T = 293 K, and

scans, 6736 reﬂections collected ( h, k, l), [(sinh)/k]

= 0.59 Å^ꢁ1, 1772 independent (R_int= 0.037) and 1611 observed

C₁₁H₁₁FO₃,

M = 210.20,

colorless

crystal

0.35 ꢄ 0.35 ꢄ 0.30 mm, a = 25.168(1), c = 10.039(1) Å, V = 9834.6(8) Å³,

q

_calc= 1.079 g cm^ꢁ3= 0.577 mm^ꢁ1, empirical absorption correc-

, l

q

,

l

,

tion (0.824 6 T 6 0.846), Z = 16, tetragonal, space group I4₁/a (No.

88), k = 1.54178 Å, T = 223 K, and u scans, 44,801 reﬂections col-

lected ( h, k, l), [(sinh)/k] = 0.59Å^ꢁ1

4405 independent

(R_int= 0.042) and 3897 observed reﬂections [I P 2 (I)], 240 reﬁned

x

,

u

r

parameters, R = 0.063, wR²= 0.208, disordered solvent molecule re-

ﬁned with geometrical constraints, max. residual electron density

0.37 (ꢁ0.26) e Å^ꢁ3, hydrogen at N1 from difference fourier map,

other calculated and reﬁned as riding atoms.

reﬂections [I P 2r(I)], 139 reﬁned parameters, R = 0.043,

wR²= 0.136, max. residual electron density 0.17 (ꢁ0.14) e Å^ꢁ3

,

hydrogen calculated and reﬁned as riding atoms.

5.10.3. X-ray crystal structure analysis for 19d

5.10.8. X-ray crystal structure analysis for 21h

Formula

0.25 ꢄ 0.25 ꢄ 0.20 mm, a = 5.534(1), b = 10.323(1), c = 22.474(1) Å,

= 81,77(1), b = 89.29(1),

= 76.55(1)°, V = 1235.5(3) Å³, q_calc

1.334 g cm^ꢁ3= 1.164 mm^ꢁ1

empirical absorption correction

(0.760 6 T 6 0.801), Z = 4, triclinic, space group P1bar (No. 2),

k = 1.54178 Å, T = 223 K, and u scans, 11,148 reﬂections collected

C

₁₁H₈F₄O₂,

M = 248.17,

colorless

crystal

Formula

0.30 ꢄ 0.15 mm, a = 10.846(1), b = 16.590(1), c = 10.086(1) Å,

b = 101.85(1)°, V = 1776.1(3) Å³, _calc= 1.224 g cm^ꢁ3= 0.696 mm^ꢁ1

empirical absorption correction (0.768 6 T 6 0.903), Z = 4, mono-

clinic, space group P2₁/c (No. 14), k = 1.54178 Å, T = 223 K, and u

scans, 14,110 reﬂections collected ( h, k, l), [(sinh)/k] = 0.59 Å^ꢁ1

C

₂₀H₂₂FNO₂, M = 327.39, colorless crystal 0.40 ꢄ

a

c

=

q

,

l

,

l

,

x

,

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

7165

16. Rosen, T. C.; Yoshida, S.; Fröhlich, R.; Kirk, K. L.; Haufe, G. J. Med. Chem. 2004, 47,

5860–5871.

17. Palfreyman, M. G.; Bey, P.; Sjoerdsma, A. Essays Biochem. 1987, 23, 28–81.

18. Zreika, M.; McDonald, I. A.; Bey, P.; Palfreyman, M. G. J. Neurochem. 1984, 43,

448–454.

19. Lyles, G. A.; Marshall, C. M. S.; McDonald, I. A.; Bey, P.; Palfreyman, M. G.

Biochem. Pharmacol. 1987, 36, 2847–2853.

20. (a) Alvernhe, G.; Laurent, A.; Haufe, G. Synthesis 1987, 562–564; (b) Haufe, G.;

Alvernhe, G.; Laurent, A.; Ernet, T.; Goj, O.; Kröger, S.; Sattler, A. Org. Synth.

1999, 76, 159–168.

21. Ernet, T.; Haufe, G. Tetrahedron Lett. 1996, 37, 7251–7252.

22. Hruschka, S.; Fröhlich, R.; Kirsch, P.; Haufe, G. Eur. J. Org. Chem. 2007, 141–148.

23. Fuller, R. W.; Molly, B. B. The effect of aliphatic ﬂuorine on amine drugs. In

Biochemistry Involving Carbon–Fluorine Bonds; Filler, R., Ed.; ACS Symposium

Series; American Chemical Society: Washington, 1976; Vol. 28, pp 77–98.

24. (a) Zheng, R.; Blanchard, J. S. Biochemistry 2000, 39, 16244–16251; (b) Cox, C.

D.; Breslin, M. J.; Whitman, D. B.; Coleman, P. J.; Garbaccio, R. M.; Fraley, M. E.;

Zrada, M. M.; Buser, C. A.; Walsh, E. S.; Hamilton, K.; Lobell, R. B.; Tao, W.;

Abrams, M. T.; South, V. J.; Huber, H. E.; Kohl, N. E.; Hartman, G. D. Bioorg. Med.

Chem. Lett. 2007, 17, 2697–2702.

3113 independent (R_int= 0.033) and 2959 observed reﬂections

[I P 2r

(I)], 224 reﬁned parameters, R = 0.038, wR²= 0.105, max.

residual electron density 0.18 (ꢁ0.15) e Å^ꢁ3, hydrogen at N1 from

difference fourier map, other calculated and reﬁned as riding atoms.

5.10.9. X-ray crystal structure analysis for 7h

Formula

0.35 ꢄ 0.30 ꢄ 0.25 mm, a = 12.233(1), b = 9.498(1), c = 11.404(1) Å,

b = 95.02(1)°, V = 1319.9(2) Å³, _calc= 1.327 g cm^ꢁ3= 0.282 mm^ꢁ1

empirical absorption correction (0.908 6 T 6 0.933), Z = 4, mono-

clinic, space group P2₁/c (No. 14), k = 0.71073 Å, T = 198 K, and

scans, 6987 reﬂections collected ( h, k, l), [(sinh)/k]

= 0.59 Å^ꢁ1, 2327 independent (R_int= 0.037) and 2072 observed

C

₁₅H₁₅FN⁺Cl^ꢁ,

M = 263.73,

colorless

crystal

q

,

l

,

x

u

reﬂections [I P 2r(I)], 172 reﬁned parameters, R = 0.030,

wR²= 0.079, max. residual electron density 0.23 (ꢁ0.24) e Å^ꢁ3

,

hydrogen calculated and reﬁned as riding atoms.

25. Hyla-Kryspin, I.; Grimme, S.; Hruschka, S.; Haufe, G. Org. Biomol. Chem.,

submitted for publication.

26. Smart, B. E. J. Fluorine Chem. 2001, 109, 3–11.

27. Smart, B. E. In Characteristics of C–F Systems; Banks, R. E.; Smart, B. E.; Tatlow, J.

C.; Eds.; Organoﬂuorine Chemistry. Principles and Commercial Applications;

Plenum Press: New York, 1994; pp 57–88.

CCDC 642246–642254 contain the supplementary crystallo-

graphic data for this paper. These data can be obtained free of

charge at www.cam.ac.uk/conts/retrieving.html [or from Cam-

bridge Crystallographic Data Centre, 12 Union Road, Cambridge

CB2 1EZ, UK; fax: (internat.) +44(1223)336-033, E-mail:

deposit@ccdc.cam.ac.uk].

28. Silverman, R. B. J. Biol. Chem. 1983, 258, 14766–14769.

29. Silverman, R. B. Acc. Chem. Res. 1995, 28, 335–342.

30. Paech, C.; Salach, J. I.; Singer, T. P. J. Biol. Chem. 1980, 255, 2700–2704.

31. Silverman, R. B.; Yamasaki, R. B. Biochemistry 1984, 23, 1322–1332.

32. Kang, G. I.; Hong, S. K. Arch. Pharm. Res. 1990, 13, 82–96.

33. Silverman, R. B.; Cesarone, J. M.; Lu, X. J. Am. Chem. Soc. 1993, 115, 4955–4961.

34. Zhong, B.; Silverman, R. B. J. Am. Chem. Soc. 1997, 119, 6690–6691.

35. Mitchell, D. J.; Nikolic, D.; Rivera, E.; Sablin, S. O.; Choi, S.; van Breemen, R. B.;

Singer, T. P.; Silverman, R. B. Biochemistry 2001, 40, 5447–5456.

36. Vintém, A. P.; Price, N. T.; Silverman, R. B.; Ramsay, R. R. Bioorg. Med. Chem.

2005, 13, 3487–3495.

37. Schmidt, D. M. Z.; McCafferty, D. G. Biochemistry 2007, 46, 4408–4416.

38. Yang, M.; Culhane, J. C.; Szewczuk, L. M.; Jalili, P.; Ball, H. L.; Machius, M.; Cole,

P. A.; Yu, H. Biochemistry 2007, 46.

39. Gooden, D. M.; Schmidt, D. M. Z.; Pollock, J. A.; Kabadi, A. M.; McCafferty, D. G.

Bioorg. Med. Chem. Lett. 2008, 18, 3047–3051.

40. Kang, G. I.; Hong, S. K. Arch. Pharm. Res. 1988, 11, 292–300.

41. Hoffmann, R.; Stohrer, W. P. J. Am. Chem. Soc. 1971, 93, 6941–6948.

42. Clark, T.; Spitznagel, G. W.; Klose, R.; Schleyer, P. v. R. J. Am. Chem. Soc. 1984,

106, 4412–4419.

43. Zeiger, D. N.; Liebman, J. F. J. Mol. Struct. 2000, 556, 83–94.

44. Dolbier, W. R., Jr.; Battiste, M. A. Chem. Rev. 2003, 103, 1071–1098.

45. Paris, L. C.; Klug, J. T.; Mann, C. K. J. Org. Chem. 1974, 39, 3488–3494.

46. Newton-Vinson, P. In Flavins and Flavoproteins; Ghisla, S.; Kroneck, P.;

Macheroux, P.; Sund, H.; Eds.; Agency for Scientiﬁc Publications: Berlin,

1999; pp 431–434.

47. Erdem, S.; Karahan, Ö.; Yildiz, I.; Yelekci, K. Org. Biomol. Chem. 2006, 4, 646–

658.

48. Binda, C.; Li, M.; Hubálek, F.; Restelli, N.; Edmondson, D. E.; Mattevi, A. Proc.

Natl. Acad. Sci. U.S.A. 2003, 100, 9750–9755.

49. Sayre, L. M.; Singh, M. P.; Kokil, P. B.; Wang, F. J. Org. Chem. 1991, 56, 1353–

1355.

50. Walker, W. H.; Hemmerich, P.; Massey, V. Helv. Chim. Acta 1967, 50, 2269–

2279.

51. Binda, C.; Hubálek, F.; Li, M.; Herzig, Y.; Sterling, J.; Edmondson, D. E.; Mattevi,

A. J. Med. Chem. 2004, 47, 1767–1774.

52. De Colibus, L.; Li, M.; Binda, C.; Lustig, A.; Edmondson, D. E.; Mattevi, A. Proc.

Natl. Acad. Sci. U.S.A. 2005, 102, 12684–12689.

53. Li, M.; Binda, C.; Mattevi, A.; Edmondson, D. E. Biochemistry 2006, 45, 4775–

4784.

Acknowledgments

This work was partially supported by the DFG as a contribu-

tion from the Sonderforschungsbereich 424, the International

NRW Graduate School of Chemistry, the Intramural Research

Funds of NIDDK, NIH, and the research grant of Tottoti Prefec-

tural Government, Japan. We thank Professor Dale E. Edmond-

son, Emory University, Atlanta, Georgia, USA, for the kind

donation of recombinant human mitochondrial MAO A and B,

Professor Klaus Müller, F. Hoffmann La Roche Ltd, Basel, Switzer-

land and Dr. Thomas Krämer, Bayer Schering Pharma for mea-

surements of pK_a, and logD values, and Prof. Norbert Straeter,

University of Leipzig for his help concerning the structure of

the binding pocket of MAO A.

References

1. Floris, G.; Agro, A. F. In Amine Oxidases, in Encyclopedia of Biological Chemistry;

Lennarz, W.; Lane, M.; Modrich, P.; Dixon, J.; Carafoli, E.; Exton, J.; Cleveland,

D.; Eds.; Academic Press: New York, 2004; Vol. 1, pp 85–89.

2. Edmondson, D. E.; Mattevi, E.; Binda, C.; Li, M.; Hubálek, F. Curr. Med. Chem.

2004, 11, 1983–1993.

3. Fowler, J. S.; Logan, J.; Volkow, N. D.; Wang, G.-J.; MacGregor, R. R.; Ding, Y.-S.

Methods 2002, 27, 263–277.

4. Singer, T. P.; von Korff, R. W.; Murphy, D. L. In Monoamine Oxidase: Structure

Function and Altered Functions; Academic Press: New York, 1979.

5. Macleod, A. D.; Counsell, C. E.; Ives, N.; Stowe, R. Cochrane Database of

Systematic

Reviews

2005,

Art.

No.

CD004898.

DOI:

10.1002/

14651858.CD004898.pub2;

http://www.mrw.interscience.wiley.com/

cochrane/clsysrev/articles/CD004898/frame.html.

6. Riederer, P.; Danielczyk, W.; Grünblatt, E. Neurotoxicology 2004, 25, 271–277.

7. Boomsma, F.; Derkx, F. H.; van den Meiracker, A. H.; Man in’t Veld, A. J.;

Schalekamp, M. A. Clinical Science 1995, 88, 675–679.

8. Obata, T. Life Science 2006, 79, 417–422. and therein cited references.

9. Tripton, K. F.; Boyce, S.; O’Sullivan, J.; Davey, G. P.; Healy, J. Curr. Med. Chem.

2004, 11, 1965–1982.

10. Youdim, M. B. H.; Edmondson, D.; Tipton, K. F. Nat. Rev. Neurosci. 2006, 7, 295–

309.

11. Petersen, T.; Papakostas, G. I.; Posternak, M. A.; Kant, A.; Guyker, W. M.;

Iosifescu, D. V.; Yeung, A. S.; Nierenberg, A. A.; Fava, M. J. Clin. Psychopharmacol.

2005, 25, 336–341.

12. Rosen, T. C.; Yoshida, S.; Kirk, K. L.; Haufe, G. ChemBioChem 2004, 5, 1033–

1043.

13. Yoshida, S.; Rosen, T. C.; Meyer, O. G. J.; Sloan, M. J.; Ye, S.; Haufe, G.; Kirk, K. L.

Biorg. Med. Chem. 2004, 12, 2645–2652.

14. Ye, S.; Yoshida, S.; Fröhlich, R.; Haufe, G.; Kirk, K. L. Bioorg. Med. Chem. 2005, 13,

2489–2499.

15. Yoshida, S.; Meyer, O. G. J.; Rosen, T. C.; Haufe, G.; Ye, S.; Sloan, M. J.; Kirk, K. L. J.

Med. Chem. 2004, 47, 1796–1806.

54. Edmondson, D. E.; Binda, C.; Mattevi, A. Arch. Biochem. Biophys. 2007, 464, 269–

276.

55. Geha, R. M.; Rebrin, I.; Chen, K.; Shih, J. C. J. Biol.Chem. 2001, 276, 9877–9882.

56. Miller, J. R.; Edmondson, D. E. Biochemistry 1999, 38, 13670–13683.

57. Walkers, M. C.; Edmondson, D. E. Biochemistry 1994, 33, 7088–7098.

58. Nandigama, R. K.; Edmondson, D. E. Biochemistry 2000, 39, 15258–15265.

59. Husain, M.; Edmondson, D. E.; Singer, T. P. Biochemistry 1982, 21, 595–600.

60. Böhm, H.-J.; Banner, D.; Bendels, S.; Kansy, M.; Kuhn, B.; Müller, K.; Obst-

Sander, U.; Stahl, M. ChemBioChem 2004, 5, 637–643. and references cited

therein.

61. See also: Akyüz, A.; Erdem, S. S.; Edmondson, D. E. J. Neural Trans. 2007, 114,

693–698.

62. Newton-Vinson, P.; Hubalek, F.; Edmondson, D. E. Protein Expr. Purif. 2000, 20,

334.

63. Li, M.; Hubálek, F.; Newton-Vinson, P.; Edmondoson, D. E. Protein Expr. Purif.

2002, 24, 154.

64. Houslay, M. D.; Tipton, K. F. Biochem. J. 1973, 135, 735.

65. Bradford, M. M. Anal. Biochem. 1976, 72, 248.

66. Kitz, R.; Wilson, I. B. J. Biol. Chem. 1962, 237, 3245.

67. Eckes, L.; Hanack, M. Synthesis 1978, 217–219.

7166

S. Hruschka et al. / Bioorg. Med. Chem. 16 (2008) 7148–7166

68. Meyer, O. G. J.; Fröhlich, R.; Haufe, G. Synthesis 2000, 1479–1490.

69. Nonius, B. V., Program for Data Collection, 1998.

70. Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307–326.

71. Blessing, R. H. Acta Cryst. 1995, A51, 33–37; Blessing, R. H. J. Appl. Cryst. 1997,

30, 421–426.

72. Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta Cryst. 2003, A59, 228–

234.

73. Sheldrick, G. M. Acta Cryst. 1990, A46, 467–473.

74. Sheldrick, G. M. Program for Structure Reﬁnement; Universität Göttingen, 1997.

75. Keller, E. Graphics Program; Universität Freiburg, 1997.

Article Doi

Fluorinated phenylcyclopropylamines. Part 5: Effects of electron-withdrawing or -donating aryl substituents on the inhibition of monoamine oxidases A and B by 2-aryl-2-fluoro-cyclopropylamines

DOI: 10.1016/j.bmc.2008.06.048

Source and publish data:

Authors:

Article abstract of DOI:10.1016/j.bmc.2008.06.048

Full text of DOI:10.1016/j.bmc.2008.06.048

Products guided by the article

R&D Labs maybe for 1070382-47-6

Relevant to this article

Hot Product