Stereoselective synthesis and structure-affinity relationships of bicyclic κ receptor agonists

DOI: 10.1039/b915180j

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Organic and Biomolecular Chemistry p. 212 - 225 (2010)

Update date:2022-08-05

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Authors:

Kracht, Daniel

Rack, Elisabeth

Schepmann, Dirk

Froehlich, Roland

Wuensch, Bernhard

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Article abstract of DOI:10.1039/b915180j

Reductive amination of the bicyclic ketone 4 led diastereoselectively to end-configured amines, which were transformed into the amides 7-10. The synthesis of the diastereomers 25 with an exo-configured amino moiety at position 6 was only successful after deactivation of both N-atoms of the 1,4-diazabicyclo[3.3.1]nonane system. The N-1-oxide 19 with an N-4-tosyl moiety was the crucial intermediate, which allows S_N2 substitution with NaN₃ under inversion of the configuration at position 6. Whereas the endo-configured pyrrolidine 7a (WMS-1302) revealed a κ receptor affinity of 73 nM, the exo-configured diastereomer 25a was almost inactive at the κ receptor (K_i > 1 μM). Replacement of the 3,4- dichlorophenylacetyl residue by other acyl and sulfonyl residues showed that it is essential for high κ affinity. The κ receptor affinities of the conformationally constrained pyrrolidines 7a and 25a were correlated with the dihedral angle N(pyrrolidine)-C-C-N(acetamide). A systematic conformational analysis of the potent but flexible κ agonist 2 showed that a dihedral angle of 168° (as in 25a) is energetically more disfavored than a dihedral angle of 58° (7a). However, even the conformation with a dihedral angle of 58° does not represent an energy minimum, which might explain the reduced K affinity of 7a. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b915180j

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PAPER

www.rsc.org/obc | Organic & Biomolecular Chemistry

Stereoselective synthesis and structure–afﬁnity relationships of bicyclic

j receptor agonists†

Daniel Kracht,^aElisabeth Rack,^aDirk Schepmann,^aRoland Fro¨hlich^band Bernhard Wu¨nsch*^a

Received 27th July 2009, Accepted 30th September 2009

First published as an Advance Article on the web 12th November 2009

DOI: 10.1039/b915180j

Reductive amination of the bicyclic ketone 4 led diastereoselectively to endo-conﬁgured amines, which

were transformed into the amides 7–10. The synthesis of the diastereomers 25 with an exo-conﬁgured

amino moiety at position 6 was only successful after deactivation of both N-atoms of the

1,4-diazabicyclo[3.3.1]nonane system. The N-1-oxide 19 with an N-4-tosyl moiety was the crucial

intermediate, which allows S_N2 substitution with NaN₃under inversion of the conﬁguration at position

6. Whereas the endo-conﬁgured pyrrolidine 7a (WMS-1302) revealed a k receptor afﬁnity of 73 nM, the

exo-conﬁgured diastereomer 25a was almost inactive at the k receptor (K_i> 1 mM). Replacement of the

3,4-dichlorophenylacetyl residue by other acyl and sulfonyl residues showed that it is essential for high

k afﬁnity. The k receptor afﬁnities of the conformationally constrained pyrrolidines 7a and 25a were

correlated with the dihedral angle N(pyrrolidine)–C–C–N(acetamide). A systematic conformational

analysis of the potent but ﬂexible k agonist 2 showed that a dihedral angle of 168^◦(as in 25a) is

energetically more disfavored than a dihedral angle of 58^◦(7a). However, even the conformation with a

dihedral angle of 58^◦does not represent an energy minimum, which might explain the reduced k afﬁnity

of 7a.

Dynorphine A^1,3), benzomorphans (e.g. ethylketocyclazocine^1,3),

Introduction

arylacetamides (e.g. the prototypical k agonist U-50 488⁴) and

the non-basic natural product salvinorin A.^5,6Monoacylated

ethylenediamines derived from the prototypical k agonist U-50 488

are of particular interest for this project.

The clinically used strong analgesics interact with the three

classical opioid receptors, which are termed m, k and d receptors.

Whereas activation of all three opioid receptor subtypes leads

to strong analgesia, the side effect proﬁles associated with the

three subtypes differ considerably. In view of their side effect

proﬁle, k agonists are of particular interest, because, in contrast to

m agonists, they cause minimal physical dependence, respiratory

depression and inhibition of gastrointestinal motility. In addition

to their analgesic effects in in vivo models, k agonists have

been shown to be potent neuroprotective and antihyperalgesic

agents. However, sedation, dysphoria and strong diuresis are

the most severe side effects associated with the application of

k agonists.¹

During the last few years, potent k agonists have been de-

scribed, which are derived from the lead compound U-50 488,

including annulated compounds,^7,8simpliﬁed ligands,^9,10as well

as heterocyclic analogues like 2-(aminomethyl)piperidines^11,12

and 2-(aminomethyl)piperazines.^13–15The (2R)-conﬁgured 2-

(aminomethyl)piperazine 1 (GR-89 696) belongs to the most active

k agonists with an IC₅₀-value of 0.018 nM^13–15(K_i= 0.36 nM,¹⁶

Fig. 1). Very recently, we have shown that the k receptor afﬁnity of

1 was exceeded by the (S,S)-conﬁgured pyrrolidinylethyl derivative

2 (K_i= 0.31 nM), bearing an additional CH₃-moiety at the C-2 side

chain.^16,17In both compounds, the k afﬁnity is strongly dependent

on the stereochemistry; in Fig. 1 the most active stereoisomers are

shown.

The 1,4-diacylated piperazine system of 1 and 2 represents

a rather rigid substructure. However, the axially oriented sub-

stituent in position 2¹⁷can rotate without hindrance around

the indicated axial bond. In order to investigate the preferred

orientation (bioactive conformation) of the pharmacophoric

pyrrolidine moiety of 1 and 2, conformationally constrained k

receptor agonists were designed. Herein, we report on the stere-

oselective synthesis and pharmacological evaluation of bicyclic

k receptor agonists of type 3. The 1,4-diazabicyclo[3.3.1]nonane

system of 3 results upon connection of the methyl residue

of 2 with the second piperazine N-atom. The orientation of

the basic amino group in position 6 can be adjusted by the

stereochemistry.

All three subtypes have already been cloned.²However,

X-ray crystal structures of the G-protein coupled membrane-

bound receptors showing the exact three dimensional orientation

of the ligand binding sites are not yet available. Therefore, for the

development of novel selective k agonists, lead compounds with

high k afﬁnity were selected.

Most of the described k agonists can be subdivided into

four compound classes:¹peptides (e.g. the physiological agonist

^aInstitut fu¨r Pharmazeutische und Medizinische Chemie der Univer-

sita¨t Mu¨nster, Hittorfstraße 58-62, D-48149 Mu¨nster, Germany. E-mail:

wuensch@uni-muenster.de; Fax: +49-251-8332144; Tel: +49-251-8333311

^bOrganisch-Chemisches Institut der Westfa¨lischen Wilhelms-Universita¨t

Mu¨nster, Corrensstr. 40, D-48149 Mu¨nster, Germany

† Electronic supplementary information (ESI) available: Further experi-

mental details. CCDC reference number 748563. For ESI and crystallo-

graphic data in CIF or other electronic format see DOI: 10.1039/b915180j

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Fig. 1 Design of conformationally constrained k agonists 3, with a deﬁned dihedral angle between the two pharmacophoric elements: pyrroline and

phenylacetamide.

In addition to the relative conﬁguration of the ﬁnal products,

the X-ray crystal structure also proves the reaction path of the

Results and discussion

reductive amination. The reducing agent NaBH(OAc)₃can only

attack the intermediate iminium ion from the exo-face, whereas

the endo-face is shielded by the larger bridge.

Chemistry

The synthesis of the ﬁrst series of k agonists started with the

bicyclic ketone 4, which has been prepared in four reaction

steps from ethyl piperazine-2-carboxylate.¹⁸Reductive amination

Although it is known from the literature that the dichloro-

phenylacetyl residue is optimal for binding at k receptors,¹it

was replaced by some similar residues (Scheme 2). Thus, the

N-benzyl moiety of pyrrolidine 5a was removed hydrogenolytically

to form the secondary amine 6a, which was directly converted

into the phenylacetyl (8a), benzoyl (9a) and tosyl (10a) derivatives.

The diethylamine 10b with an N-tosyl group was also prepared

by treatment of the benzyl derivative 5b with H₂, Pd/C and

subsequent tosylation.

For the synthesis of the diastereomeric amines with exo-

orientation of the amino group, ketone 4 should be reduced

diastereomerically and the resulting endo-alcohol should be

transformed into exo-amines by an inversion reaction. Indeed,

reduction of ketone 4 with LiBH₄in THF provided exclusively

the endo-alcohol 11 in 91% yield (Scheme 3). However, all

attempts to activate the OH-moiety with mesyl chloride or tosyl

chloride, even at low temperature, led to very fast decomposition

of the alcohol 11. Also, the direct reaction of 11 in a Mit-

sunobu inversion²⁰(PPh₃, diisopropyl azodicarboxylate (DIAD))

using different N-nucleophiles, like succinimide, phthalimide and

Zn(N₃)₂·(pyridine)₂complex,²¹failed due to fast decomposition.

Moreover, it was shown that alcohol 11 itself was also very

unstable. Storage in the refrigerator at 0 ^◦C under N₂for three days

led to a dark coloration of the compound and additional peaks in

the HPLC.

of ketone 4 with pyrrolidine and NaBH(OAc)₃provided di-

astereoselectively the endo-conﬁgured pyrrolidine 5a in 59% yield.

The corresponding dimethylamine 5c was prepared in the same

manner (38% yield). Unfortunately, the diethylamine 5b, as a

ring-opened pyrrolidine analogue, was not available by direct

reductive amination of ketone 4 with the secondary amine di-

ethylamine. Therefore, the diethylamine 5b was prepared stepwise.

First, reductive amination of ketone 4 with the primary amine

ethylamine and NaBH(OAc)₃led to the ethylamine 5d, which

was reductively alkylated with acetaldehyde and NaBH(OAc)₃to

afford the tertiary amine 5b (Scheme 1).

Hydrogenolytic removal of the N-benzyl protecting group of

5a–c provided the secondary amines 6a–c, which were directly

acylated, without puriﬁcation, using 3,4-dichlorophenylacetic acid

in the presence of dicyclohexylcarbodiimide (DCC), to form the

desired dichlorophenylacetamides 7a–c.

In order to prove the endo-conﬁguration of the ﬁnal products 7

unequivocally, an X-ray crystal structure analysis was performed.

For this purpose, pyrrolidine 7a was recrystallized from a mixture

of diethyl ether and acetonitrile to obtain colorless crystals which

were suitable for X-ray crystal structure analysis (Fig. 2). The

X-ray crystal structure clearly shows the endo-conﬁguration of

the pyrrolidine substituent at position 6. Both six-membered

heterocycles adopt the chair conformation and, moreover, the

dihedral angle between the pyrrolidine N-atom and the acetamide

N-atom could be determined to be 58.3^◦(see the Discussion of the

dihedral angle section).

In order to stabilize alcohol 11, the N-benzyl group should be

replaced by an N-tosyl moiety. Unfortunately, the direct synthesis

of the sulfonamide 14 failed since the Dieckmann condensation

of the tosyl-protected piperazine derivative did not give the

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Scheme 1 The synthesized compounds are racemates; only one enantiomer is shown in this and the following schemes. Reagents and reaction conditions:

(a) R₂NH, NaBH(OAc)₃, THF, rt, 5a: 59%; 5c: 38%; 5d: 47%. (b) CH₃CH O, NaBH(OAc)₃, THF, 2 h, rt, 64%. (c) H₂, Pd/C, CH₃OH, rt. (d)

3,4-Dichlorophenylacetic acid, DCC, CH₂Cl₂, rt, 7a: 47%; 7b: 70%; 7c: 53%.

corresponding bicyclic product.¹⁸Therefore, an exchange of

the N-protecting group was performed. First, ketone 4 was

protected as dimethyl acetal 12. Hydrogenolytic removal of the

N-benzyl group and subsequent reaction with tosyl chloride

provided the sulfonamide 13, which was hydrolyzed with dilute

HCl to form the N-tosyl-protected ketone 14. Reduction of

14 with NaBH₄in methanol provided diastereomerically the

endo-conﬁgured alcohol 15 in 91% yield. In contrast to 11, alcohol

15 with the N-tosyl protecting group was considerably more

stable, and could be stored at 0 ^◦C for several months without

decomposition.

Furthermore, alcohol 15 could be reacted with mesyl chloride

and tosyl chloride to obtain the rather stable mesylate 16 and

tosylate 17 in 83 and 70% yields, respectively (Scheme 4).

Treatment of the endo-mesylate 16 with NaN₃in DMF at 80 ^◦C

led to two new products, whose mass spectra were in agreement

with the calculated molecular weights. Careful analysis of the ¹H

Fig. 2 X-Ray crystal structure of 7a, proving the endo-conﬁguration of

and ¹³C NMR spectra, however, revealed that the diastereomeric

the pyrrolidine substituent.

azides 18 had been formed instead of the desired exo-azide

21. Variation of the reaction conditions during the nucleophilic

substitution of mesylate 16, starting with tosylate 17, and even the

direct substitution of alcohol 15 via a Mitsunobu inversion (PPh₃,

DIAD, Zn(N₃)₂·(pyridine)₂complex), always led to the rearranged

azides 18.

This transformation is explained by a rearrangement of mesylate

16, which is outlined in Scheme 4. The rearrangement is driven by

the exact antiperiplanar orientation of the C-9–C-5 bond and the

C–O bond of the leaving group. The nitrogen atom at position

1, with its free electron pair, supports this rearrangement, and

the nitrogen atom of the sulfonamide at position 4 stabilizes the

intermediate carbenium ion A, which is ﬁnally trapped by the azide

nucleophile. The intermediate carbenium ion A also explains nicely

the formation of two diastereomeric azides 18a and 18b, since the

planar carbenium ion A can be attacked from both sides.

After elucidation of this process, we postulated that a similar

rearrangement is the reason for the instability of alcohol 11.

Scheme 2 Reagents and reaction conditions: (a) H₂, Pd/C, CH₃OH, rt.

(b) Phenylacetic acid, DCC, CH₂Cl₂, rt, 78%. (c) Benzoyl chloride, NEt₃,

CH₂Cl₂, rt, 48%. (d) Tosyl chloride, NEt₃, CH₂Cl₂, rt, 10a: 35%; 10b: 80%.

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Scheme 3 Reagents and reaction conditions: (a) LiBH₄, THF, -20 ^◦C, 91%. (b) CH₃OH, HC(OCH₃)₃, p-TosOH, reﬂux, 79%. (c) H₂, Pd/C, CH₃OH, rt,

then tosyl chloride, NEt₃, CH₂Cl₂, rt, 80%. (d) 2 M HCl, H₂O, reﬂux, 93%. (e) NaBH₄, CH₃OH, 0 ^◦C, 91%.

amino group. However, this side reaction is not detrimental, as

in the next reaction step the azide moiety was reduced with H₂

in the presence of Pd/C. Under these reaction conditions, both

functional groups, the N-oxide and the azide, were reduced and,

therefore, a mixture of 20 and 21 containing small amounts of the

starting N-oxide 19 was usually employed for this reaction step

(Scheme 5).

Hydrogenation of the mixture of azides 20 and 21 yielded the

primary amine 22, which was reductively alkylated without further

puriﬁcation. Reductive amination is the preferred method in this

reaction step, since alkyl halides react very fast with the bridgehead

tertiary amine to form quaternary ammonium ions. For the

synthesis of the diethylamine 23b, an excess of acetaldehyde in

the presence of NaBH(OAc)₃was used. However, succinaldehyde,

which was required for the synthesis of the pyrrolidine moiety,

Scheme 4 Reagents and reaction conditions: (a) Mesyl chloride or tosyl

was not commercially available. Therefore, succinaldehyde was

chloride, NEt₃, CH₂Cl₂, rt, 16: 83%; 17: 70%. (b) NaN₃, DMF, 80 ^◦C, 18a:

generated in situ upon hydrolysis of 2,5-dimethoxytetrahydrofuran

22%; 18b: 32%.

with dilute HCl.²³This procedure provided the exo-conﬁgured

pyrrolidine 23a in 36% yield, starting from the N-oxide 19.

Compared to the carbenium ion A, the analogous carbenium ion

formed from the N-benzyl-protected alcohol 11 is much better

stabilized by the N-benzyl moiety than the N-sulfonyl derivative

A. Therefore, its formation, together with subsequent uncontrolled

transformations, is generally favored.

In order to ﬁnalize the synthesis of the dichlorophenylac-

etamides 25, the tosyl protecting group was cleaved with Mg in

reﬂuxing methanol. The resulting secondary amines 24a and 24b

were subsequently acylated with dichlorophenylacetyl chloride

and NEt₃, to give the exo-conﬁgured bicyclic amines 25a and 25b

in 31% and 45% yield, respectively.

The observation that the reduction of the electron donating

properties of N-4 (compare the stability of alcohols 11 and 15)

leads to an at least slightly reduced rearrangement tendency

stimulated the idea to reduce the electron donating activity of N-1

as well, in order to suppress the unwanted rearrangement reaction

completely. For this purpose, the N-oxide 19 was prepared by

oxidation of tosylate 17 with m-chloroperbenzoic acid (MCPBA,

Scheme 5).²²Indeed, the S_N2 substitution of tosylate 19, bearing

electron withdrawing groups at both N-atoms, with NaN₃in DMF

To broaden the structure–k receptor afﬁnity relationships, the

tertiary amine (e.g. pyrrolidine) at position 6 was replaced by N-

containing substituents with modiﬁed basicity. For this purpose

N-heterocycles were annulated to the bicyclic framework. In

particular, the weakly basic quinoline 28 and the non-basic indole

31 were envisaged, synthesized and pharmacologically evaluated.

The key step in the synthesis of the weakly basic quinoline 28

was a Friedla¨nder quinoline synthesis²⁴of the bicyclic ketone

4 with 2-aminoacetophenone in boiling glacial acetic acid to

give the quinoline 26 in 73% yield (Scheme 6. ) Hydrogenolytic

removal of the N-benzyl group led to the secondary amine 27, and

attachment of the pharmacophoric dichlorophenylacetyl residue

was performed by coupling with dichlorophenylacetic acid and

DCC.

◦

at 150 C successfully gave the exo-conﬁgured azides 20 and 21.

Whereas azide 21 was isolated in 46% yield as the main product,

the N-oxide 20 could not be separated completely from the starting

tosylate 19. Performing this substitution reaction with microwave

irradiation resulted in a considerable reduction of the reaction

time from 20 h to 15 min. Obviously, during heating of the reaction

mixture in DMF to 150 ^◦C with an excess of NaN₃, reduction of

the N-oxide 20 occurred, directly forming azide 21 with a tertiary

A Fischer indole synthesis²⁵of the bicyclic ketone 4 with

p-methoxyphenylhydrazine in the presence of HCl provided the

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Scheme 5 Reagents and reaction conditions: (a) MCPBA, K₂CO₃, CH₂Cl₂, 73%. (b) NaN₃, DMF, 80 ^◦C, 21: 46%. (c) H₂, Pd/C, CH₃OH, rt.

(d) Succinaldehyde or CH₃CH O, NaBH(OAc)₃, THF, rt, 23a: 36%; 23b: 29%. (e) Mg, CH₃OH, reﬂux. (f) 3,4-Dichlorophenylacetyl chloride, NEt₃,

CH₂Cl₂, rt, 25a: 25%; 25b: 45%.

Scheme 6 Reagents and reaction conditions: (a) o-Aminoacetophenone, HOAc, reﬂux, 73%. (b) NH₄HCO₂, Pd/C, CH₃OH, reﬂux, 89%.

indole 29. After hydrogenolytic cleavage of the N-benzyl group,

the resulting secondary amine 30 was acylated with dichloro-

phenylacetic acid and DCC to give indole 31 in 54% yield.

(Scheme 7) In contrast to the other phenylacetamides, the indole

N-atom of 31 does not possess basic properties.

on the N-atom can never adopt the same conformation as the

pyrrolidine ring due to repulsion of the terminal methyl groups.

The data in Table

clearly show that the 3,4-

dichlorophenylacetyl residue and the endo-conﬁguration are es-

sential for a strong interaction with the binding site of the k

receptor. Exchange of this residue for a phenylacetyl (8a), benzoyl

(9a) or tosyl residue (10a, 10b) led to almost complete loss of

the k receptor afﬁnity. The change of the conﬁguration from

endo-conﬁgured amines 7 to exo-conﬁgured amines 25 also led to

inactive compounds. The quinoline and indole annulated bicyclic

compounds 28 and 31 did not interact signiﬁcantly with the

k receptor. It is assumed that the reduced (quinoline 28) or

eliminated (indole 31) basicity together with the planar geometry

around the N-atom are responsible for the reduced k receptor

afﬁnity.

In addition to the k receptor afﬁnity, the afﬁnity of the bicyclic

amines towards the other two classical opioid receptors, m and d,

as well as to the historically related s₁, s₂and NMDA receptors

were investigated in receptor binding studies with radioligands.

At a concentration of 1 mM the test compounds did not compete

Receptor binding studies

The k receptor afﬁnity of the bicyclic amines was determined in

competition experiments with the radioligand [³H]-U-69 593. In

the assay, membrane preparations of guinea pig brains were used

as receptor material. The non-speciﬁc binding was determined in

the presence of a large excess of non-tritiated U-69 593 (10 mM).¹⁶

In Table 1, the k receptor afﬁnities of the synthesized amines,

together with the k afﬁnities of some reference compounds, are

summarized. In our assay, the pyrrolidine derivative 7a has a K_i-

value of 73 nM. Whereas replacement of the pyrrolidine ring by a

dimethylamino group (7c) did not inﬂuence the k receptor afﬁnity,

the corresponding diethylamine shows a considerably reduced k

afﬁnity. This result is not surprising, since the two ethyl residues

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Scheme 7 Reagents and reaction conditions: (a) p-Methoxyphenylhydrazine HCl, EtOH, HCl, reﬂux, 28%. (b) H₂, Pd/C, CH₃OH, rt.

with respect to k receptor afﬁnity.²⁶Therefore, we assume that the

Table 1 k Receptor afﬁnities of the bicyclic compounds

additional basic N-atom of 7a is at least not exclusively responsible

for the reduced k afﬁnity.

Compound

k Afﬁnity [³H]-U-69 593 K_iSEM/nM^a

In Fig. 3, the dihedral angles (N(pyrrolidine)–C–C–

N(acetamide)) of the diastereomeric pyrrolidines 7a and 25a

are compared. The dihedral angle of the energetically most

favored conformer (MOE) of the almost inactive exo-conﬁgured

pyrrolidine 25a is 168^◦(Fig. 3). Originally, we were very interested

in this stereoisomer, since 25a is directly obtained by connecting

the free methyl group with the carbamate N-atom of the very

potent ﬂexible k agonist 2 (see Fig. 1).

7a (WMS-1302)

73 9.1

361 65

65 4.0

0%^b

10a

0%^b

10b

0%^b

23a

0%^b

23b

0%^b

25a

0%^b

25b

0%^b

16%^b

1%^b

2¹⁶

0.31 0.1

0.97 0.4

7.3 0.4

U-50 488

U-69 593

Naloxone

^aThe K_i-values were determined in three independent experiments (n = 3)

unless otherwise noted. ^bPercent inhibition at a concentration of 1 mM of

the test compound.

signiﬁcantly with the radioligands. Therefore the IC₅₀-values are

at least higher than 1 mM. This result indicates that the endo-

conﬁgured pyrrolidine, 7a and its dimethylamine analogue 7c,

are selective k agonists with minimal afﬁnity to the investigated

receptor systems.

Discussion of the dihedral angle

Compared with the lead compound 2, the most potent k agonist

of this series, the endo-conﬁgured pyrrolidine 7a (WMS-1302), is

about 200-fold less active (see Table 1). The reduction of the k

receptor afﬁnity may be due to (1) the additional basic bridgehead

N-atom in position 1 of the bicyclic system and/or (2) the ﬁxation

of the pyrrolidine ring in an unfavorable orientation.

Fig. 3 Dihedral angles of the diastereomeric pyrrolidines 7a and 25a.

In addition to the basic pyrrolidine system, the known k agonists

with an ethylenediamine substructure generally do not have a

further basic N-atom. Usually, additional N-atoms present in

potential k agonists are supplied with propionyl or methoxycar-

bonyl moieties.^13–16However, very recently we have demonstrated

that an additional basic N-atom is indeed tolerated by the k

receptor protein. In the quinoxaline compound class of k agonists,

secondary amines as well as methyl and benzyl amines even exceed

the corresponding propionyl and methoxycarbonyl derivatives

A systematic conformational analysis of N-protonated 2 was

performed by rotation of the pyrrolidinylethyl residue in 10^◦

intervals around the axially oriented C–C-bond (Fig. 4). Sub-

sequently, the resulting conformations were energy minimized

without changing the crucial dihedral angle N–C–C–N. The

energy proﬁle in Fig. 5 shows that a dihedral angle of 168^◦is

energetically disfavored. Therefore, the potent k agonist 2 probably

does not adopt a conformation similar to 25a at the k receptor.

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in Fig. 5, which reveals that the dihedral angle of 58^◦is close to

the energy minimum of 70^◦, but still differs slightly from it.

Conclusion

Starting from the very potent but ﬂexible k agonist 2, the

conformationally constrained stereoisomeric bicyclic amines 7 and

25 have been synthesized. Compared with the lead compound 2

(K_i= 0.31 nM), the k afﬁnity of the endo-conﬁgured pyrroli-

dine 7a (WMS-1302) and the exo-conﬁgured pyrrolidine 25a is

considerably reduced (K_i= 73 nM, K_i> 1 mM). It is assumed

that the relative orientation of the pharmacophoric elements, the

pyrrolidine ring and the dichlorophenylacetamide, determines the

interaction of the bicyclic ligands with the k receptor. Whereas a

dihedral angle of 168^◦(25a) is not tolerated by the k receptor, the

dihedral angle of 58^◦of 7a is closer to the bioactive conformation

of 2. The systematic conformational analysis of 2 revealed that the

dihedral angle of 58^◦is energetically favored compared to 168^◦,

but still differs from an energy minimum. This fact might explain

the reduced k receptor afﬁnity of the bicyclic pyrrolidine 7a.

Fig. 4 Superposition of the energy minimized conformations resulting

upon 10^◦rotation of the axially oriented pyrrolidinylethyl moiety of 2.

According to the X-ray crystal structure of the endo-conﬁgured

pyrrolidine 7a (WMS-1302), both six-membered heterocycles

adopt the chair conformation, which results in a dihedral angle of

58.3^◦(Fig. 3). Since the X-ray crystal structure is an energetically

favored conformation, at least in the solid state, it is possible that

7a reacts in this conformation with the k receptor protein. In

comparison with the exo-diastereomer 25a, the k afﬁnity of 7a

is increased, but reduced compared with the k afﬁnity of 2. So

we assume that the dihedral angle of 58^◦is closer to the dihedral

angle of the bioactive conformation of 2, but still is not optimal.

This assumption is supported by the energy proﬁle of 2 depicted

Experimental

General chemistry

Unless otherwise noted, moisture sensitive reactions were

conducted under dry nitrogen. THF was dried with

sodium/benzophenone and was freshly distilled before use. Thin

layer chromatography (tlc): silica gel 60 F₂₅₄plates (Merck). Flash

Fig. 5 Energy proﬁle resulting upon rotation of compound 2 with a proton at the pyrrolidine N-atom around the axially oriented C–C bond at position

3 (compare to Fig. 1).

218 | Org. Biomol. Chem., 2010, 8, 212–225

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chromatography (fc): silica gel 60, 40–64 mm (Merck); parentheses

include: diameter of the column, height of SiO₂column, fraction

size, eluent, R_fvalue. Melting point: melting point apparatus

SMP 3 (Stuart Scientiﬁc), uncorrected. MS: MAT GCQ (Thermo-

Finnigan); EI = electron impact, ESI = electrospray ionization.

IR: IR spectrophotometer 480Plus FT-ATR-IR (Jasco). ¹H NMR

(400 MHz), ¹³C NMR (100 MHz): Mercury-400BB spectrometer

(Varian); d in ppm relative to tetramethylsilane; coupling constants

are given with 0.5 Hz resolution. HPLC method 1: Merck Hitachi

Equipment; UV detector: L-7400; autosampler: L-7200; pump:

The reaction mixture was stirred at room temperature for 16 h,

then a saturated NaHCO₃solution (30 mL) was added and the

mixture extracted with CH₂Cl₂(3¥). The combined organic layers

were dried (Na₂SO₄), ﬁltered, and the solvent was removed in

vacuo. The residue was puriﬁed by ﬂash column chromatography

(∅ = 2 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 + 1%

NH₃, R_f= 0.20) to afford 165 mg (64%) of 5b as a colourless oil.

C₁₈H₂₉N₃(M_r= 287.5). ¹H NMR (CDCl₃): d [ppm] = 0.96 (t, J =

7.0 Hz, 6H, N(CH₂CH₃)₂, 1.60–1.69 (m, 1H, 7-H), 2.18–2.32 (m,

1H, 7-H or 6-H), 2.37–2.45 (m, 1H, 7-H or 6-H), 2.58 (d, J =

13.3 Hz, 1H, 9-H), 2.61–2.67 (m, 1H, 2-H or 3-H), 2.68–2.81 (m,

5H, 1H of 2-H or 3-H and N(CH₂CH₃)₂, 2.90 (s, 1H, 5-H), 2.92–

3.07 (m, 3H, 2¥ 8-H and 1H of 2-H or 3-H), 3.27–3.39 (m, 2H,

9-H and 1H of 2-H or 3-H), 3.90 (d, J = 14.1 Hz, 1H, PhCH₂N),

L-7100; degasser: L-7614; column: LiChrospher^ꢀ60 RP-select B

(5 mm), 250-4 mm; ﬂow rate: 1.00 mL/min; injection volume:

5.0 mL; detection at l = 210 nm; solvents: A: water with

0.05% (v/v) triﬂuoroacetic acid; B: acetonitrile with 0.05% (v/v)

triﬂuoroacetic acid: gradient elution: (A%): 0 min: 90%, 4 min:

90%, 29 min: 0%, 31 min: 0%, 31.5 min: 90%, 40 min: 90%. HPLC

method 2: Equipment: pump: HPLC pump 64 (Knauer); UV-

Detector: Variable Wavelength Monitor (Knauer); data acqui-

sition: D-2500 Chromato-Integrator (Merck Hitachi); injection

3.99 (d, J = 14.1 Hz, 1H, PhCH₂N), 7.19–7.37 (m, 5H, arom. H).

-1

IR (neat): n [cm ] = 735 and 700 (m, arom. out of plane). MS

(EI): m/z [%]: 287 (M, 55), 91 (PhCH₂, 86).

(1RS,5SR,6RS)-4-Benzyl-N,N -dimethyl-1,4-diazabicyclo-

[3.3.1]nonan-6-amine (5c). Under N₂atmosphere NaBH(OAc)₃

(318 mg, 1.5 mmol) was added to a solution of 4 (230 mg,

1.0 mmol), dimethylamine (2.5 mL of a 2 M solution in THF,

5.0 mmol) and acetic acid (60 mL, 1.0 mmol) in THF (10 mL).

The reaction mixture was stirred at room temperature for 14 h,

then a saturated NaHCO₃solution (20 mL) was added and the

mixture was extracted with CH₂Cl₂(3¥). The combined organic

layers were dried (Na₂SO₄), ﬁltered, and the solvent was removed in

vacuo. The residue was puriﬁed by ﬂash column chromatography

(∅ = 2 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 + 1%

triethylamine, R_f= 0.23) to afford 97 mg (38%) of 5c as a pale

yellow oil. C₁₆H₂₅N₃(M_r= 259.4). ¹H NMR (CDCl₃): d [ppm] =

1.70–1.81 (m, 1H, 7-H), 2.03–2.15 (m, 2H, 7-H and 6-H), 2.19 (s,

6H, N(CH₃)₂), 2.44 (ddd, J = 13.3/5.5/3.1 Hz, 1H, 2-H or 3-H),

2.55 (d, J = 13.3 Hz, 1H, 9-H), 2.68–2.76 (m, 1H, 2-H or 3-H), 2.85

(s, 1H, 5-H), 2.98–3.19 (m, 3H, 2¥ 8-H and 1H of 2-H or 3-H),

3.31–3.43 (m, 2H, 9-H and 1H of 2-H or 3-H), 3.98 (d, J = 14.1 Hz,

volume: 20.0 mL; stop time: 2 ¥ t_R; A: column: LiChroCART^ꢀ

250-4 with Superspher^ꢀ100 RP-18; solvent: methanol/water =

75:25 + 0.1% triethylamine; ﬂow rate: 0.6 mL/min; detection:

wavelength: 235 nm; B: column: LiChroCART^ꢀ250-4 with

Superspher^ꢀ100 RP-18; solvent: acetonitrile/water = 70:30 +

0.1% triethylamine; ﬂow rate: 1.0 mL/min; detection: wavelength:

254 nm; C: column: phenomenex Gemini 5 mm C18 100A, 250–

21.2 mm; solvent: methanol/water = 50:50 + 0.1% triethylamine;

ﬂow rate: 0.8 mL/min; detection: wavelength: 235 nm.

(1RS,5SR,6RS)-4-Benzyl-6-(pyrrolidin-1-yl)-1,4-diazabicyclo-

[3.3.1]nonane (5a). Under N₂atmosphere NaBH(OAc)₃(318 mg,

1.5 mmol) was added to a solution of 4 (230 mg, 1.0 mmol) and

pyrrolidine (90 mL, 1.1 mmol) in THF (10 mL). The reaction

mixture was stirred at room temperature for 14 h, then a saturated

NaHCO₃solution (20 mL) was added and the mixture was

extracted with CH₂Cl₂(3¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and the solvent was removed in vacuo.

The residue was puriﬁed by ﬂash column chromatography (∅ =

2 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 + 1%

dimethylethylamine, R_f= 0.29) to afford 168 mg (59%) of 5a

1H, PhCH₂N), 4.02 (d, J = 14.1 Hz, 1H, PhCH₂N), 7.17–7.38 (m,

-1

5H, arom. H). IR (neat): n [cm ] = 701 and 648 (m, arom. out of

plane). MS (EI): m/z [%] = 259 (M, 100), 91 (PhCH₂, 50).

(1RS,5SR,6RS)-4-Benzyl-N -ethyl-1,4-diazabicyclo[3.3.1]-

nonan-6-amine (5d). Under N₂atmosphere NaBH(OAc)₃

(636 mg, 3.0 mmol) was added to a solution of 4 (460 mg,

2.0 mmol) and ethylamine-HCl (245 mg, 3.0 mmol) in THF

(20 mL). The reaction mixture was stirred at room temperature

for 36 h, then a saturated NaHCO₃solution (30 mL) was added

and the mixture was extracted with CH₂Cl₂(3¥). The combined

organic layers were dried (Na₂SO₄), ﬁltered, and the solvent was

removed in vacuo. The residue was puriﬁed by ﬂash column

chromatography (∅ = 3 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH

9/1 + 1% NH₃, R_f= 0.17) to afford 242 mg (47%) of 5d as a pale

yellow oil. C₁₆H₂₅N₃(M_r= 259.4). ¹H NMR (CDCl₃): d [ppm] =

1.06 (t, J = 7.0 Hz, 3H, NHCH₂CH₃), 1.67–1.93 (m, 3H, 2H of

7-H or 6-H and NHCH₂CH₃), 2.39–2.47 (m, 1H, 7-H or 6-H),

2.53 (d, J = 13.3 Hz, 1H, 9-H), 2.55–2.62 (m, 2H, NHCH₂CH₃),

2.66 (ddd, J = 11.7/6.3/3.1 Hz, 1H, 2-H or 3-H), 2.69–2.77 (m,

1H, 2-H or 3-H), 2.82 (s, 1H, 5-H), 2.90–2.99 (m, 3H, 2¥ 8-H and

1H of 2-H or 3-H), 3.26–3.35 (m, 1H, 2-H or 3-H), 3.38 (d, J =

13.3 Hz, 1H, 9-H), 3.88 (d, J = 14.1 Hz, 1H, PhCH₂N), 3.93 (d, J =

as a pale yellow oil. C₁₈H₂₇N₃(M_r= 285.4). H NMR (CDCl₃):

d [ppm] = 1.67–1.76 (m, 5H, 7-H and N(CH₂CH₂)₂), 2.09–2.28

(m, 2H, 7-H and 6-H), 2.40–2.52 (m, 5H, 1H of 2-H or 3-H and

N(CH₂CH₂)₂), 2.66 (d, J = 13.3 Hz, 1H, 9-H), 2.75–2.82 (m, 1H,

2-H or 3-H), 2.84 (s, 1H, 5-H), 3.03–3.09 (m, 2H, 8-H), 3.13–3.22

(m, 1H, 2-H or 3-H), 3.27–3.40 (m, 2H, 9-H and 1H of 2-H or

3-H), 4.00 (d, J = 14.1 Hz, 1H, PhCH₂N), 4.08 (d, J = 14.1 Hz,

1H, PhCH₂N), 7.17–7.37 (m, 5H, arom. H). ¹³C NMR (CDCl₃):

d [ppm] = 23.2 (2C, N(CH₂CH₂)₂), 29.2 (1C, C-7), 46.8 (1C, C-2

or C-3), 50.8 (1C, C-2 or C-3), 51.5 (1C, C-9), 51.7 (1C, C-5), 52.0

(1C, C-8), 52.2 (2C, N(CH₂CH₂)₂), 60.2 (1C, PhCH₂N), 68.4 (1C,

C-6), 127.0 (1C, C-4_phenyl), 128.4 (2C, C-3_phenyl), 128.9 (2C, C-2_phenyl),

-1

140.6 (1C, C-1_phenyl). IR (neat): n [cm ] = 697 and 668 (m, arom.

out of plane). MS (EI): m/z [%] = 285 (M, 100), 194 (M–PhCH₂,

13), 91 (PhCH₂, 31).

(1RS, 5SR, 6RS) - 4 - Benzyl - N,N - diethyl - 1, 4 - diazabicyclo -

[3.3.1]nonan-6-amine (5b). Under N₂atmosphere NaBH(OAc)₃

(380 mg, 1.8 mmol) was added to a solution of 5d (240 mg,

0.9 mmol) and acetaldehyde (100 mL, 1.8 mmol) in THF (10 mL).

14.1 Hz, 1H, PhCH₂N), 7.19–7.35 (m, 5H, arom. H). IR (neat): n

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[cm^-1] = 3300 (br w, N-H), 737 and 695 (m, arom. out of plane).

MS (EI): m/z [%] = 259 (M, 55), 168 (M–PhCH₂, 5), 91 (PhCH₂,

82).

3.83 (d, J = 15.7 Hz, 0.58H, COCH₂Ar), 4.06 (d, J = 15.7 Hz,

0.58H, COCH₂Ar), 4.07–4.11 (m, 0.58H, NCH₂), 4.79 (s broad,

0.42H, 5-H), 7.05 (dd, J = 7.8/2.3 Hz, 0.58H, 6¢-H_{dichlorophenyl}), 7.14

(dd, J = 7.8/2.3 Hz, 0.42H, 6¢-H_{dichlorophenyl}), 7.30 (d, J = 2.3 Hz,

0.58H, 2¢-H_{dichlorophenyl}), 7.35 (dd, J = 7.8/2.3 Hz, 1H, 5¢-H_{dichlorophenyl}),

2-(3,4-Dichlorophenyl)-1-[(1RS,5SR,6RS)-6-(pyrrolidin-1-yl)-

1,4-diazabicyclo[3.3.1]nonan-4-yl]ethanone (7a). A solution of 5a

(135 mg, 0.47 mmol) containing 10% Pd/C (15 mg) in anhydrous

methanol (10 mL) was stirred under an atmosphere of hydrogen

at room temperature for 2 h. The reaction mixture was ﬁltered

through Celite, and the ﬁltrate was evaporated. The crude product

was dissolved in CH₂Cl₂(15 mL). Then, DCC (146 mg, 0.71 mmol)

and 3,4-dichlorophenylacetic acid (146 mg, 0.71 mmol) were

added. After 3 h the reaction mixture was washed with 1 M

NaOH. The organic layer was separated and the aqueous layer

was extracted with CH₂Cl₂(2¥). The combined organic layers

were dried (Na₂SO₄), ﬁltered, and concentrated in vacuo. The

residue was puriﬁed by column chromatography (∅ = 2 cm, l =

15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 with 1% NH₃, R_f=

0.51) to afford 84 mg (47%) o_◦f 7a as a colourless oil, which

gave a colourless solid (mp 144 C) upon standing in the fridge.

C₁₉H₂₅Cl₂N₃O (M_r= 382.3). ¹H NMR (CDCl₃): d [ppm] = 1.66–

1.83 (m, 6H, 2¥ 7-H and 4¥ N(CH₂CH₂)₂), 2.27–2.37 (m, 0.85H,

6-H), 2.40–2.49 (m, 2H, N(CH₂CH₂)₂), 2.51–2.58 (m, 0.15H, 6-

H), 2.65–2.78 (m, 2H, N(CH₂CH₂)₂), 2.83–2.94 (m, 2H, NCH₂),

2.97–3.22 (m, 4.15H, NCH₂), 3.28 (dd, J = 13.3/6.3 Hz, 0.85H,

NCH₂), 3.54 (td, J = 13.3/4.7 Hz, 0.85H, NCH₂), 3.68 (d, J =

15.7 Hz, 0.85H, COCH₂Ar), 3.72–3.83 (m, 0.45H, 0.15¥ 5-H and

0.30¥ COCH₂Ar), 3.77 (d, J = 15.7 Hz, 0.85H, COCH₂Ar), 4.09–

4.15 (m, 0.15H, NCH₂), 4.73 (s broad, 0.85H, 5-H), 7.05 (dd, J =

7.8/2.4 Hz, 0.15H, 6¢-H_{dichlorophenyl}), 7.15 (dd, J = 7.8/2.4 Hz, 0.85H,

6¢-H_{dichlorophenyl}), 7.30 (d, J = 2.4 Hz, 0.15H, 2¢-H_{dichlorophenyl}), 7.34

7.39 (d, J = 2.3 Hz, 0.42H, 2¢-H_{dichlorophenyl}). Ratio of rotational

-1

isomers 42:58. IR (neat): n [cm ] = 1634 (s, C O), 881 and 822

(w, arom. out of plane). MS (EI): m/z [%] = 383 (M, 2¥ ³⁵Cl, 97),

385 (M, ³⁵Cl/³⁷Cl, 60), 387 (M, 2¥ ³⁷Cl, 9). HPLC (Method 1):

t_R= 13.9 min, purity 96.5%.

2-(3,4-Dichlorophenyl)-1-[(1RS,5SR,6RS)-6-(dimethylamino)-

1,4-diazabicyclo[3.3.1]nonan-4-yl]ethanone (7c). A mixture of 5c

(90 mg, 0.35 mmol), 10% Pd/C (10 mg) and anhydrous methanol

(10 mL) was stirred under an atmosphere of hydrogen at room

temperature for 2 h. The reaction mixture was ﬁltered through

Celite, and the ﬁltrate was evaporated. The crude product was

dissolved in CH₂Cl₂(15 mL). Then, DCC (103 mg, 0.50 mmol)

and 3,4-dichlorophenylacetic acid (102 mg, 0.50 mmol) were

added. After 3 h the reaction mixture was washed with 1 M

NaOH. The organic layer was separated and the aqueous layer

was extracted with CH₂Cl₂(2¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and concentrated in vacuo. The residue

was puriﬁed by ﬂash column chromatography (∅ = 2 cm, l =

15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 with 1% NH₃, R_f=

0.42) to afford 66 mg (53%) of 7c as a colourless oil, which

gave a colourless solid (mp 95 ^◦C) upon standing in the fridge.

C₁₇H₂₃Cl₂N₃O (M_r= 356.3). ¹H NMR (CDCl₃): d [ppm] = 1.66–

1.75 (m, 1H, 7-H), 1.77–1.85 (m, 1H, 7-H), 2.19–2.25 (m, 0.76H,

6-H), 2.27 (m, 6¥ 0.24H, N(CH₃)₂), 2.30 (m, 6¥ 0.76H, N(CH₃)₂),

2.64–2.70 (m, 0.24H, 6-H), 2.81–2.92 (m, 2H, NCH₂), 2.97–3.22

(m, 4.24H, NCH₂), 3.33 (dd, J = 13.3/6.3 Hz, 0.76H, NCH₂), 3.54

(td, J = 13.3/4.7 Hz, 0.76H, NCH₂), 3.67 (d, J = 15.7 Hz, 0.76H,

COCH₂Ar), 3.74 (d, J = 15.7 Hz, 0.76H, COCH₂Ar), 3.78 (s

broad, 0.24H, 5-H), 3.81 (d, J = 15.7 Hz, 0.24H, COCH₂Ar), 3.90

(d, J = 15.7 Hz, 0.24H, COCH₂Ar), 4.06–4.11 (m, 0.24H, NCH₂),

4.81 (s broad, 0.76H, 5-H), 7.06 (dd, J = 7.8/2.3 Hz, 0.24H, 6¢-

H_{dichlorophenyl}), 7.11 (dd, J = 7.8/2.3 Hz, 0.76H, 6¢-H_{dichlorophenyl}), 7.32

(d, J = 2.3 Hz, 0.24H, 2¢-H_{dichlorophenyl}), 7.35 (d broad, J = 7.8 Hz, 1H,

(d, J = 7.8 Hz, 1H, 5¢-H_{dichlorophenyl}), 7.44 (d, J = 2.3 Hz, 0.85H, 2¢-

-1

H_{dichlorophenyl}). Ratio of rotational isomers 85:15. IR (neat): n [cm ] =

1632 (s, C O), 881 and 821 (w, arom. out of plane). MS (EI): m/z

[%] = 381 (M, 2¥ ³⁵Cl, 100), 383 (M, ³⁵Cl/³⁷Cl, 63), 385 (M, 2¥

³⁷Cl, 9). HPLC (Method 1): t_R= 14.7 min, purity 98.9%. X-ray

crystal structure analysis:^27–30see the ESI.†

2-(3,4-Dichlorophenyl)-1-[(1RS,5SR,6RS)-6-(diethylamino)-

1,4-diazabicyclo[3.3.1]nonan-4-yl]ethanone (7b). A solution of 5b

(150 mg, 0.52 mmol) containing 10% Pd/C (15 mg) in anhydrous

methanol (10 mL) was stirred under an atmosphere of hydrogen

at room temperature for 2 h. The reaction mixture was ﬁltered

through Celite, and the ﬁltrate was evaporated. The crude product

was dissolved in CH₂Cl₂(15 mL). Then DCC (206 mg, 1.0 mmol)

and 3,4-dichlorophenylacetic acid (205 mg, 1.0 mmol) were

added. After 3 h the reaction mixture was washed with 1 M

NaOH. The organic layer was separated and the aqueous layer

was extracted with CH₂Cl₂(2¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and concentrated in vacuo. The residue

was puriﬁed by ﬂash column chromatography (∅ = 2 cm, l =

15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 with 1% NH₃, R_f=

0.44) to afford 140 mg (70%) of 7b as a colourless oil, which

5¢-H_{dichlorophenyl}), 7.44 (d, J = 2.3 Hz, 0.76H, 2¢-H_{dichlorophenyl}). Ratio

-1

of rotational isomers 76:24. IR (neat): n [cm ] = 1631 (s, C O),

874 and 811 (w, arom. out of plane). MS (ESI): m/z [%] = 356

(MH, 2¥ ³⁵Cl, 100), 358 (MH, ³⁵Cl/³⁷Cl, 60), 360 (MH, 2¥ ³⁷Cl, 9).

HPLC (Method 1): t_R= 13.9 min, purity 97.2%.

(1RS,5SR,6RS)-4-Benzyl-1,4-diazabicyclo[3.3.1]nonan-6-ol

(11). Under N₂atmosphere lithium borohydride (2 M solution

in THF, 4.0 mL, 8.0 mmol) was added slowly to a solution of 4

(461 mg, 2.0 mmol) in dry methanol (15 mL) at -20 ^◦C. After

1 h the reaction mixture was acidiﬁed by addition of 1 M aq.

HCl. The resulting mixture was warmed to rt and stirred for 2 h.

Then, saturated NaHCO₃solution was added (pH 8–9) and the

mixture was extracted with CH₂Cl₂(3¥). The combined organic

layers were dried (Na₂SO₄), ﬁltered, and the solvent was removed

in vacuo. The residue was puriﬁed by ﬂash column chromatography

(∅ = 3 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 + 1% NEt₃, R_f=

0.32) to afford 422 mg (91%) of 11 as a colourless oil. C₁₄H₂₀N₂O

◦

gave a colourless solid (mp 147 C) upon standing in the fridge.

C₁₉H₂₇Cl₂N₃O (M_r= 384.4). ¹H NMR (CDCl₃): d [ppm] = 0.88–

0.97 (m, 6¥ 0.42H, N(CH₂CH₃)₂), 1.02 (t, J = 7.0 Hz, 6¥ 0.58H,

N(CH₂CH₃)₂), 1.63–1.77 (m, 2H, 7-H), 1.96–2.10 (m, 0.58H, 6-H),

2.47–2.67 (m, 4H, N(CH₂CH₃)₂), 2.78–3.25 (m, 7H, 6.58¥ NCH₂

and 0.42¥ 6-H), 3.34 (dd, J = 13.3/6.3 Hz, 0.42H, NCH₂), 3.51–

3.73 (m, 1.84H, 0.42¥ NCH₂, 0.84¥ COCH₂Ar and 0.58¥ 5-H),

(M_r= 232.3). H NMR (CDCl₃): d [ppm] = 1.83–2.02 (m, 2H,

7-H), 2.42–2.53 (m, 2H, NCH₂), 2.57 (s broad, 1H, OH), 2.72

(dtd, J = 14.1/5.5/1.6 Hz, 1H, NCH₂), 2.79 (s broad, 1H, 5-H),

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2.86–3.00 (m, 3H, NCH₂), 3.30 (ddd, J = 13.3/8.6/6.3 Hz, 1H,

NCH₂), 2.75 (dt, J = 14.1/2.3 Hz, 1H, NCH₂), 3.71 (s broad, 1H,

(CH₂Cl₂/MeOH 9/1 with 1% NH₃)] to afford 164 mg (73%) of 19

as a colourless solid, mp 162 ^◦C. C₂₁H₂₆N₂O₆S₂(M_r= 466.6). ¹H

NMR (CDCl₃): d [ppm] = 2.23–2.39 (m, 2H, 7-H), 2.42 (s, 3H,

ArCH₃), 2.45 (s, 3H, ArCH₃), 3.07–3.15 (m, 1H, 9-H), 3.19–3.31

(m, 1H, 2-H or 3-H), 3.34 (d, J = 13.3 Hz, 1H, 9-H), 3.43–3.58

(m, 2H, 1¥ 8-H and 1H of 2-H or 3-H), 3.62–3.70 (m, 1H, 8-

H), 3.72–3.83 (m, 1H, 2-H or 3-H), 3.93 (dd, J = 14.9/7.0 Hz,

1H, 2-H or 3-H), 4.61 (s, 1H, 5-H), 4.67–4.76 (m, 1H, 6-H), 7.30

(d, J = 8.6 Hz, 2H, 3¢-H_tosylate, 5¢-H_tosylate), 7.36 (d, J = 8.6 Hz,

2H, 3¢-H_tosylate, 5¢-H_tosylate), 7.70 (d, J = 8.6 Hz, 2H, 2¢-H_tosylate, 6¢-

H_tosylate), 7.84 (d, J = 8.6 Hz, 2H, 2¢-H_tosylate, 6¢-H_tosylate). ¹³C NMR

(CDCl₃): d [ppm] = 21.8, 22.0 (2C, ArCH₃), 28.9 (1C, C-7), 42.0

(1C, C-2 or C-3), 53.0 (1C, C-5), 66.4 (1C, C-2 or C-3), 66.6 (1C,

C-8), 66.8 (1C, C-9), 73.1 (1C, C-6), 127.4 (2C, C-2_tosylate, C-6_tosylate),

128.4 (2C, C-2_tosylate, C-6_tosylate), 130.3 (2C, C-3_tosylate, C-5_tosylate), 130.5

6-H), 3.90 (d, J = 14.1 Hz, 1H, PhCH₂N), 3.96 (d, J = 14.1 Hz,

-1

1H, PhCH₂N), 7.20–7.33 (m, 5H, arom. H). IR (neat): n [cm ] =

3317 (m br, O-H), 739 and 696(m, arom. out of plane). MS (EI):

m/z [%] = 232 (M, 100), 141 (M–PhCH₂, 97), 91 (PhCH₂, 45).

4-Tosyl-1,4-diazabicyclo[3.3.1]nonan-6-one (14). A solution of

13 (930 mg, 2.5 mmol) was heated to reﬂux in 2 M aqueous HCl

(50 mL) under N₂atmosphere. After 14 h the reaction mixture was

cooled to room temperature, made alkaline with KOH solution

and extracted with CH₂Cl₂(3¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered and the solvent was removed in vacuo.

The residue was puriﬁed by ﬂash column chromatography [∅ =

3 cm, V = 10 mL, CH₂Cl₂/MeOH 9.5/0.5 → 9/1, R_f= 0.55

(CH₂Cl₂/MeOH 9/1)] to afford 685 mg (93%) of 14 as a colourless

solid, mp 129 ^◦C. C₁₄H₁₈N₂O₃S (M_r= 294.4). ¹H NMR (CDCl₃):

d [ppm] = 1.94–2.05 (m, 1H, 7-H), 2.17–2.25 (m, 1H, 7-H), 2.39

(s, 3H, ArCH₃), 3.00 (d, J = 14.1 Hz, 1H, 9-H), 3.05–3.14 (m, 4H,

NCH₂), 3.34–3.47 (m, 2H, NCH₂), 3.52–3.59 (m, 1H, NCH₂),

(2C, C-3_tosylate, C-5_tosylate), 132.9 (1C, C-1_tosylate), 136.3 (1C, C-1_tosylate),

-1

144.8 (1C, C-4_tosylate), 145.8 (1C, C-4_tosylate). IR (neat): n [cm ] =

1343 (s, N-O), 1157 (s, S O), 812 (m, arom. out of plane). MS

(ESI): m/z [%] = 467 (M + H, 23), 489 (M + Na, 24), 933 (2M +

H, 100). HPLC (Method 1): t_R= 18.8 min, purity 98.2%.

4.11 (s, 1H, 5-H), 7.27 (d, J = 8.6 Hz, 2H, 3¢-H_tosylate, 5¢-H_tosylate),

-1

(1RS,5SR,6SR)-6-Azido-4-(4-methylphenylsulfonyl)-1,4-diaza-

bicyclo[3.3.1]nonane (21). Under N₂atmosphere, a mixture of

19 (233 mg, 0.5 mmol) and sodium azide (325 mg, 5.0 mmol)

in dry DMF (10 mL) was heated to 80 ^◦C. Since a conversion

was not observed after 16 h, the reaction mixture was heated to

150 ^◦C. After additional 20 h the reaction mixture was cooled to rt,

diluted with 2 M NaOH and extracted with small portions of ethyl

acetate (6¥). The combined organic layers were dried (Na₂SO₄),

ﬁltered, and the solvent was removed in vacuo. The residue was

puriﬁed by ﬂash column chromatography (∅ = 3 cm, V = 10 mL,

CH₂Cl₂/MeOH 9.5/0.5, R_f= 0.35) to afford 74 mg (46%) of 21

as a colourless oil. C₁₄H₁₉N₅O₂S (M_r= 321.4). ¹H NMR (CDCl₃):

d [ppm] = 1.56 (dd, J = 15.2/4.2 Hz, 1H, 7-H), 2.10–2.22 (m, 1H,

7-H), 2.42 (s, 3H, ArCH₃), 2.64 (d, J = 14.2 Hz, 1H, 9-H), 2.75

(dd, J = 14.7/6.3 Hz, 1H, 8-H), 2.95–3.06 (m, 1H, 2-H or 3-H),

3.09–3.25 (m, 4H, 2¥ 2-H or 3-H, 1¥ 8-H and 1¥ 9-H), 3.42–3.54

(m, 2H, 1¥ 2-H or 3-H and 6-H), 4.04 (s broad, 1H, 5-H), 7.31

(d, J = 7.9 Hz, 2H, 3¢-H_tosylate, 5¢-H_tosylate), 7.68 (d, J = 7.9 Hz,

2H, 2¢-H_tosylate, 6¢-H_tosylate). ¹³C NMR (CDCl₃): d [ppm] = 21.8 (1C,

ArCH₃), 24.9 (1C, C-7), 40.7 (1C, C-2 or C-3), 46.6 (1C, C-9), 47.9

(1C, C-8), 48.0 (1C, C-6), 49.8 (1C, C-2 or C-3), 59.1 (1C, C-5),

7.60 (d, J = 8.6 Hz, 2H, 2¢-H_tosylate, 6¢-H_tosylate). IR (neat): n [cm ] =

1715 (s, C O), 1160 (s, S O), 809 (m, arom. out of plane). MS

(EI): m/z [%] = 294 (M, 9), 139 (M–SO₂C₆H₄CH₃, 100). HPLC

(Method 1): t_R= 11.5 min, purity 99.9%.

(1RS,5SR,6RS)-4-Tosyl-1,4-diazabicyclo[3.3.1]nonan-6-ol (15).

Under N₂atmosphere, sodium borohydride (330 mg, 8.7 mmol)

was added in small portions to an ice-cooled solution of 14

(642 mg, 2.2 mmol) in dry methanol (50 mL). After 1 h at 0 ^◦C the

reaction was terminated by addition of 1 M aq. HCl. The resulting

mixture was warmed to rt and stirred for an additional 0.5 h. Then,

saturated NaHCO₃solution was added (pH 8–9) and the mixture

was extracted with CH₂Cl₂(3¥). The combined organic layers

were dried (Na₂SO₄), ﬁltered, and the solvent was removed in

vacuo. The residue was puriﬁed by ﬂash column chromatography

[∅ = 3 cm, V = 10 mL, CH₂Cl₂/MeOH 9.5/0.5 → 9/1, R_f= 0.39

(CH₂Cl₂/MeOH 9/1)] to afford 589 mg (91%) of 15 as a colourless

solid, mp 159 ^◦C. C₁₄H₂₀N₂O₃S (M_r= 296.4). ¹H NMR (CDCl₃):

d [ppm] = 1.70–1.82 (m, 1H, 7-H), 1.87–1.95 (m, 1H, 7-H), 2.41

(s, 3H, ArCH₃), 2.68 (d, J = 14.1 Hz, 1H, 9-H), 2.77–2.83 (m, 1H,

NCH₂), 2.84–3.10 (m, 4H, NCH₂), 3.29 (ddd, J = 13.3/7.0/3.1 Hz,

1H, NCH₂), 3.43–3.55 (m, 1H, NCH₂), 3.76–3.85 (m, 2H, 5-H,

6-H), 7.30 (d, J = 8.6 Hz, 2H, 3¢-H_tosylate, 5¢-H_tosylate), 7.71 (d, J =

127.4 (2C, C-2_tosylate, C-6_tosylate), 130.1 (2C, C-3_tosylate, C-5_tosylate), 135.9

-1

(1C, C-1_tosylate), 144.0 (1C, C-4_tosylate). IR (neat): n [cm ] = 2094 (s,

8.6 Hz, 2H, 2¢-H_tosylate, 6¢-H_tosylate). The signal for the proton of the

N N N), 1159 (s, S O), 815 (m, arom. out of plane). MS (ESI):

m/z [%] = 322 (MH, 27), 665 (M + Na, 100). HPLC (Method 1):

t_R= 15.7 min, purity 95.5%.

-1

OH group could not be detected. IR (neat): n [cm ] = 3200 (br w,

O-H), 1153 (s, S O), 822 (m, arom. out of plane). MS (EI): m/z

[%] = 296 (M, 19), 141 (M–SO₂C₆H₄CH₃, 100). HPLC (Method

(1RS,5SR,6SR)-6-(Pyrrolidin-1-yl)-4-(4-methylphenylsulfonyl)-

1,4-diazabicyclo[3.3.1]nonan-6-amine (23a). A mixture of 19

(513 mg, 1.1 mmol) and sodium azide (143 mg, 2.2 mmol) in

dry DMF (3 mL) was heated by microwave irradiation in a

sealed microwave reaction vial (300 W max. power, 150 ^◦C max.

temperature, 3.0 bar max. pressure, time program 5-10-5 min,

cooling on). Then, the reaction mixture was diluted with 2 N

NaOH and extracted with small portions of ethyl acetate (6¥).

The combined organic layers were dried (Na₂SO₄), ﬁltered, and the

solvent was removed in vacuo. The crude product was dissolved

in anhydrous MeOH (15 mL), 10% Pd/C (30 mg) was added

and the resulting slurry was stirred under an atmosphere of

1): t_R= 11.6 min, purity 99.1%.

(1RS,5RS,6SR)-1-Oxy-4-tosyl-1,4-diazabicyclo[3.3.1]nonan-

6-yl toluene-4-sulfonate (19). Under N₂atmosphere, 3-

chloroperoxybenzoic acid (70%, 130 mg, 0.53 mmol) was added

to an ice-cooled mixture of 17 (217 mg, 0.48 mmol) and K₂CO₃

(166 mg, 1.20 mmol) in CH₂Cl₂(20 mL). After 1 h at 0 ^◦C, water

was added. The organic layer was separated and the aqueous layer

was extracted with CH₂Cl₂(2¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and the solvent was removed in vacuo. The

crude product was puriﬁed by ﬂash column chromatography [∅ =

2 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 with 1% NH₃, R_f= 0.22

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hydrogen at room temperature for 2 h. The reaction mixture was

ﬁltered through Celite, and the ﬁltrate was evaporated. The crude

product was dissolved in THF (15 mL), and, under N₂atmosphere,

NaBH(OAc)₃(630 mg, 3.0 mmol) and succinaldehyde (172 mg,

2.0 mmol, obtained as described in ref. 23 upon hydrolysis of

2,5-dimethoxytetrahydrofuran) were added. The reaction mixture

was stirred at room temperature for 16 h. Then, 0.1 M NaOH

was added and the mixture was extracted with CH₂Cl₂(3¥). The

combined organic layers were dried (Na₂SO₄), ﬁltered and the

solvent was removed in vacuo. The residue was puriﬁed by ﬂash

column chromatography (∅ = 3 cm, l = 15 cm, V = 10 mL,

CH₂Cl₂/MeOH 9/1, R_f= 0.28) to afford 137 mg (36%) of 23a as

129.9 (2C, C-3_tosylate, C-5_tosylate), 136.8 (1C, C-1_tosylate), 143.5 (1C, C-

-1

4_tosylate)_.IR (neat): n [cm ] = 1157 (s, S O), 814 (m, arom. out of

plane). MS (ESI): m/z [%] = 352 (MH, 100). HPLC (Method 1):

t_R= 11.4 min, purity 96.6%.

2-(3,4-Dichlorophenyl)-1-[(1RS,5SR,6SR)-6-(pyrrolidin-1-yl)-

1,4-diazabicyclo[3.3.1]non-4-yl]ethanone

(25a). Magnesium

(turnings, 90 mg, 3.75 mmol) was added to a solution of 23a

(130 mg, 0.37 mmol) in MeOH (10 mL), and the mixture was

heated to reﬂux. After 2 h, additional magnesium (turnings,

90 mg, 3.75 mmol) was added, and the mixture was again

heated to reﬂux for 2 h and cooled to rt. Then HCl (gas)

was bubbled through the reaction mixture until the insoluble

material had dissolved. The resulting solution was concentrated

in vacuo. The residue was dispersed in CH₂Cl₂(15 mL) and

3,4-dichlorophenylacetyl chloride (827 mg, 3.7 mmol) and

triethylamine (1.0 mL, 7.2 mmol) were added. After 16 h at rt

the reaction mixture was washed with 1 M NaOH. The organic

layer was separated, and the aqueous layer was extracted with

CH₂Cl₂(2¥). The combined organic layers were dried (Na₂SO₄),

ﬁltered, and concentrated in vacuo. The residue was puriﬁed by

column chromatography (∅ = 3 cm, l = 15 cm, V = 10 mL,

CH₂Cl₂/MeOH 9/1 with 1% NH₃, R_f= 0.25) to afford 35 mg

(25%) of 25a as a colourless oil. C₁₉H₂₅Cl₂N₃O (M_r= 382.3).

¹H NMR (CDCl₃): d [ppm] = 1.64–1.83 (m, 5H, 1¥ 7-H and

4¥ N(CH₂CH₂)₂), 1.86–1.99 (m, 1H, 1¥ 7-H), 2.43–2.49 (m,

1H, 6-H), 2.52–2.61 (m, 2.9H, N(CH₂CH₂)₂), 2.62–2.72 (m,

2.55H, 1.1¥ N(CH₂CH₂)₂, 0.45¥ 8-H and 1¥ 9-H), 2.78 (dd, J =

14.1/5.5 Hz, 0.55H, 8-H), 3.02 (dd, J = 14.1/6.5 Hz, 0.55H, 2-H

or 3-H), 3.09 (dd, J = 14.3/7.0 Hz, 0.45H, 2-H or 3-H), 3.21–3.46

(m, 3H, 2¥ 2-H or 3-H and 1¥ 8-H), 3.53–3.62 (m, 3H, 0.55¥ 2-H

or 3-H, 0.45¥ 5-H, 1¥ 9-H, 1¥ COCH₂Ar), 3.68–3.73 (m, 1H,

COCH₂Ar), 3.86 (dd, J = 14.3/7.0 Hz, 0.45H, 2-H or 3-H), 4.36

(s broad, 0.55H, 5-H), 7.04–7.08 (m, 1H, 6¢-H_{dichlorophenyl}), 7.32 (d

broad, J = 2.0 Hz, 1H, 2¢-H_{dichlorophenyl}), 7.36 (d, J = 8.3 Hz, 0.45H,

5¢-H_{dichlorophenyl}), 7.37 (d, J = 8.3 Hz, 0.55H, 5¢-H_{dichlorophenyl}). Ratio

of rotational isomers 55:45. ¹³C NMR (CDCl₃): d [ppm] = 23.5

(0.9 C, N(CH₂CH₂)₂), 23.6 (1.1C, N(CH₂CH₂)₂), 26.1 (0.45C,

C-7), 26.5 (0.55C, C-7), 39.1 (0.45C, COCH₂Ar), 39.8 (0.45C, C-2

or C-3), 40.2 (0.55C COCH₂Ar), 42.0 (0.55C, C-2 or C-3), 44.7

(0.55C, C-5), 46.9 (0.55C, C-9), 47.4 (0.45C, C-9), 47.6 (0.45C,

C-8), 47.7 (0.55C, C-8), 47.8 (0.45C, C-5), 49.9 (0.45C, C-2 or

C-3), 50.0 (0.55C, C-2 or C-3), 51.9 (1.1C, N(CH₂CH₂)₂), 52.0

(0.9C, N(CH₂CH₂)₂), 61.5 (0.55C, C-6), 64.0 (0.45C, C-6), 128.3

(0.45C, C-6_phenyl), 128.6 (0.55C, C-6_phenyl), 130.4 (0.45C, C-5_phenyl),

130.5 (0.55C, C-5_phenyl), 130.8 (0.45C, C-2_phenyl), 130.9 (0.45C,

C-4_phenyl), 131.0 (0.55C, C-4_phenyl), 131.1 (0.55C, C-2_phenyl), 132.5

(1C, C-3_phenyl), 135.0 (0.55C, C-1_phenyl), 135.3 (0.45C, C-1_phenyl),

a colourless oil. C₁₈H₂₇N₃O₂S (M_r= 349.5). H NMR (CDCl₃):

d [ppm] = 1.60 (d broad, J = 15.7 Hz, 1H, 7-H), 1.71–1.80 (m,

4H, N(CH₂CH₂)₂), 1.94–2.06 (m, 1H, 7-H), 2.41 (s, 3H, ArCH₃),

2.48–2.68 (m, 7H, 6-H, 1¥ 8-H, 1¥ 9-H and N(CH₂CH₂)₂), 2.94–

3.03 (m, 1H, 1¥ 2-H or 3-H), 3.13–3.28 (m, 3H, 2¥ 2-H or 3-H

and 1¥ 8-H), 3.44 (d, J = 13.3 Hz, 1H, 9-H), 3.49–3.58 (m, 1H,

1¥ 2-H or 3-H), 3.70 (s broad, 1H, 5-H), 7.29 (d, J = 7.8 Hz, 2H,

3¢-H_tosylate, 5¢-H_tosylate), 7.68 (d, J = 7.8 Hz, 2H, 2¢-H_tosylate, 6¢-H_tosylate).

-1

IR (neat): n [cm ] = 1157 (s, S O), 815 (m, arom. out of plane).

MS (ESI): m/z [%] = 350 (MH, 100). HPLC (Method 1): t_R

11.4 min, purity 96.6%.

(1RS,5SR,6SR)-N,N-Diethyl-4-(4-methylphenylsulfonyl)-1,4-

diazabicyclo[3.3.1]nonan-6-amine (23b). mixture of 19

(233 mg, 0.5 mmol) and sodium azide (325 mg, 5.0 mmol)

in dry DMF (3 mL) was heated by microwave irradiation in

a sealed microwave reaction vial (300 W max. power, 150 ^◦C

max. temperature, 3.0 bar max. pressure, time program 5-10-

5 min, cooling on). Then, the reaction mixture was diluted with

2 M NaOH and extracted with small portions of ethyl acetate

(6¥). The combined organic layers were dried (Na₂SO₄), ﬁltered,

and the solvent was removed in vacuo. The crude product was

dissolved in anhydrous MeOH (10 mL), 10% Pd/C (15 mg) was

added and the resulting slurry was stirred under an atmosphere

of hydrogen at room temperature for 1 h. The reaction mixture

was ﬁltered through Celite, and the ﬁltrate was evaporated. The

crude product was dissolved in THF (10 mL), and, under N₂

atmosphere, NaBH(OAc)₃(160 mg, 0.75 mmol) and acetaldehyde

(43 mL, 0.75 mmol) were added. The reaction mixture was stirred at

room temperature for 16 h. Then 0.1 M NaOH was added and the

mixture was extracted with CH₂Cl₂(3¥). The combined organic

layers were dried (Na₂SO₄), ﬁltered and the solvent was removed in

vacuo. The residue was puriﬁed by ﬂash column chromatography

(∅ = 2 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1, R_f= 0.32)

to afford 51 mg (29%) of 23b as a pale yellow oil. C₁₈H₂₉N₃O₂S

(M_r= 351.5). H NMR (CDCl₃): d [ppm] = 0.96 (t, J = 7.0 Hz,

170.3 (0.55C, COCH₂Ar), 170.4 (0.45C, COCH₂Ar). IR (neat): n

6H, N(CH₂CH₃)₂, 1.58 (dd, J = 15.7/2.4 Hz, 1H, 7-H), 1.86–1.98

(m, 1H, 7-H), 2.41 (s, 3H, ArCH₃), 2.56 (d, J = 13.3 H, 1H, 9-H),

2.63–2.69 (m, 1H, 8-H), 2.64 (q, J = 7.0 Hz, 4H, N(CH₂CH₃)₂,

2.89–2.98 (m, 2H, 1¥ 2-H or 3-H and 6-H), 3.09–3.25 (m, 3H, 2¥

2-H or 3-H and 1¥ 8-H), 3.37 (d, J = 13.3 Hz, 1H, 9-H), 3.46–

3.55 (m, 1H, 1¥ 2-H or 3-H), 3.64 (s broad, 1H, 5-H), 7.28 (d, J =

-1

[cm ] = 1634 (s, C O), 877 and 824 (w, arom. out of plane). MS

(EI): m/z [%] = 381 (M, 2¥ ³⁵Cl, 100), 383 (M, ³⁵Cl/³⁷Cl, 65), 385

(M, 2¥ ³⁷Cl, 11). HPLC (Method 1): t_R= 13.6 min, purity 97.5%.

2-(3,4-Dichlorophenyl)-1-[(1RS,5SR,6SR)-6-(diethylamino)-

1,4-diazabicyclo[3.3.1]nonan-4-yl]ethanone (25b). Magnesium

(turnings, 30 mg, 1.25 mmol) was added to a solution of 23b

(40 mg, 0.11 mmol) in MeOH (10 mL), and the mixture was heated

to reﬂux. After 2 h, additional magnesium (turnings, 30 mg,

1.25 mmol) was added, and the mixture was again heated to reﬂux

for 2 h and cooled to rt. Then, HCl (gas) was bubbled through

7.8 Hz, 2H, 3¢-H_tosylate, 5¢-H_tosylate), 7.68 (d, J = 7.8 Hz, 2H, 2¢-H_tosylate

6¢-H_tosylate). ¹³C NMR (CDCl₃): d [ppm] = 11.8 (2C, NCH₂CH₃),

21.8 (1C, ArCH₃), 23.2 (1C, C-7), 40.4 (1C, C-2 or C-3), 43.2 (2C,

NCH₂CH₃), 46.9 (1C, C-9), 48.4 (1C, C-5), 48.8 (1C, C-8), 50.5

(1C, C-2 or C-3), 57.9 (1C, C-6), 127.4 (2C, C-2_tosylate, C-6_tosylate),

222 | Org. Biomol. Chem., 2010, 8, 212–225

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the reaction mixture until the insoluble material had dissolved.

The resulting solution was concentrated in vacuo. The residue

was dispersed in CH₂Cl₂(10 mL) and 3,4-dichlorophenylacetyl

chloride (246 mg, 1.1 mmol) and triethylamine (310 mL, 2.2 mmol)

were added. After 16 h at rt the reaction mixture was washed

with 1 M NaOH. The organic layer was separated, and the

aqueous layer was extracted with CH₂Cl₂(2¥). The combined

organic layers were dried (Na₂SO₄), ﬁltered, and concentrated

in vacuo. The residue was puriﬁed by column chromatography

(∅ = 2 cm, l = 15 cm, V = 10 mL, CH₂Cl₂/MeOH 9/1 with 1%

NH₃, R_f= 0.31) to afford 19 mg (45%) of 25b as a colourless oil.

tion of 29 (80 mg, 0.24 mmol) containing 10% Pd/C (10 mg)

in anhydrous methanol (10 mL) was stirred under an atmosphere

of hydrogen at room temperature for 4 h. The reaction mixture was

ﬁltered through Celite, and the ﬁltrate was evaporated. The crude

product (30) was dissolved in CH₂Cl₂(10 mL), then DCC (74 mg,

0.36 mmol) and 3,4-dichlorophenylacetic acid (74 mg, 0.36 mmol)

were added. After 3 h, 1M NaOH was added to the reaction

mixture, the organic layer was separated, and the aqueous layer

was extracted with CH₂Cl₂(2¥). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and concentrated in vacuo. The residue

was puriﬁed by ﬂash column chromatography (∅ = 2 cm, l =

15 cm, V = 10 mL, CH₂Cl₂/MeOH 9.5/0.5, R_f= 0.20) to afford

54 mg (54%) of 31 as a colourless solid, mp 221 ^◦C. C₂₂H₂₁Cl₂N₃O₂

C₁₉H₂₇Cl₂N₃O (M_r= 384.3). H NMR (CDCl₃): d [ppm] = 0.96

(t, J = 7.0 Hz, 3.6H, N(CH₂CH₃)₂), 0.99 (t, J = 7.0 Hz, 2.4H,

N(CH₂CH₃)₂), 1.63–1.93 (m, 2H, 7-H), 2.55–2.83 (m, 7H, 4¥

N(CH₂CH₃)₂, 6-H, 1¥ 9-H, 1¥ 8-H), 2.94–3.04 (m, 1H, 2-H or

3-H), 3.11–3.36 (m, 3H, 2¥ 2-H or 3-H and 1¥ 8-H), 3.39–3.76

(m, 4H, 0.6¥ 2-H or 3-H, 0.4¥ 5-H, 1¥ 9-H, COCH₂Ar), 3.90

(dd, J = 14.5/6.2 Hz, 0.4H, 2-H or 3-H), 4.29 (s broad, 0.6H,

5-H), 7.03–7.09 (m, 1H, 6¢-H_{dichlorophenyl}), 7.32 (d broad, J = 2.0 Hz,

1H, 2¢-H_{dichlorophenyl}), 7.36 (d, J = 8.3 Hz, 0.4H, 5¢-H_{dichlorophenyl}), 7.37

(M_r= 430.3). H NMR (CDCl₃): d [ppm] = 2.94–3.02 (m, 1H,

NCH₂), 3.03–3.12 (m, 1H, NCH₂), 3.18–3.37 (m, 4H, NCH₂), 3.50

(d, J = 15.7 Hz, 1H, 1-H), 3.59 (d, J = 15.7 Hz, 1H, 1-H), 3.81 (s,

3¥ 0.12H, OCH₃), 3.81 (s, 3¥ 0.88H, OCH₃), 3.93 (d, J = 16.4 Hz,

0.88H, COCH₂Ar), 3.95 (d, J = 16.4 Hz, 0.12H, COCH₂Ar), 4.37

(d, J = 16.4 Hz, 0.12H, COCH₂Ar), 3.41 (d, J = 16.4 Hz, 0.88H,

COCH₂Ar), 4.64 (s broad, 0.12H, 6-H), 5.55 (s broad, 0.88H, 6-

H), 6.84 (dd, J = 9.4/2.3 Hz, 1H, 9-H), 6.87 (d, J = 2.3 Hz, 1H,

11-H), 7.05 (dd, J = 8.6/1.6 Hz, 0.88H, 6¢-H_{dichlorophenyl}), 7.15 (d

broad, J = 8.6 Hz, 0.12H, 6¢-H_{dichlorophenyl}), 7.18–7.32 (m, 3H, 8-H,

(d, J = 8.3 Hz, 0.6H, 5¢-H_{dichlorophenyl}), Ratio of rotational isomers

-1

60:40. IR (neat): n [cm ] = 1636 (s, C O), 870 and 824 (w, arom.

out of plane). MS (EI): m/z [%] = 383 (M, 2¥ ³⁵Cl, 100), 385

(M, ³⁵Cl/³⁷Cl, 53), 387 (M, 2¥ ³⁷Cl, 8). HPLC (Method 1): t_R

5¢-H_{dichlorophenyl}and 2¢-H_{dichlorophenyl}), 8.35 (s broad, 1H, NH). Ratio of

-1

14.1 min, purity 95.6%.

rotational isomers 88:12. IR (neat): n [cm ] = 3205 (m broad, N-

H), 1632 (s, C O), 786, 777 and 740 (m, arom. out of plane). MS

5-[2-(3,4-Dichlorophenyl)acetyl]-12-methyl-1,2,3,4,5,6-hexa-

hydro-2,6-methano-[1,4]diazocino[6,7-b]quinoline (28). A solu-

tion of 27 (130 mg, 0.55 mmol), 3,4-dichlorophenylacetic acid

(169 mg, 0.83 mmol) and DCC (170 mg, 0.83 mmol) in CH₂Cl₂

(20 mL) was stirred at rt for 14 h. Then, the reaction mixture

was washed with a saturated solution of NaHCO₃. The organic

layer was separated, and the aqueous layer was extracted with

CH₂Cl₂(2¥). The combined organic layers were dried (Na₂SO₄),

ﬁltered, and concentrated in vacuo. The residue was puriﬁed by

ﬂash column chromatography [∅ = 3 cm, l = 15 cm, V =

15 mL, CH₂Cl₂/MeOH 9.5/0.5, R_f= 0.56 (CH₂Cl₂/MeOH

9/1)] to afford 173 mg (74%) of 28 as a colourless solid, mp

108 ^◦C. C₂₃H₂₁Cl₂N₃O (M_r= 426.3). ¹H NMR (CDCl₃): d [ppm] =

2.46–2.55 (m, 0.78H, NCH₂), 2.53 (s, 3¥ 0.22H, CH₃), 2.56 (s, 3¥

0.78H, CH₃), 2.80–2.86 (m, 0.22H, NCH₂), 2.90–2.97 (m, 0.22H,

NCH₂), 3.05–3.13 (m, 1H, NCH₂), 3.18–3.48 (m, 3H, NCH₂), 3.63

(d, J = 15.7 Hz, 0.22H, COCH₂Ar), 3.68 (d, J = 15.7 Hz, 0.22H,

COCH₂Ar), 4.06–4.19 (m, 2.56H, 1¥ 1-H, 0.78¥ COCH₂Ar, 0.78¥

NCH₂), 4.37 (d, J = 15.7 Hz, 0.78H, COCH₂Ar), 4.44 (d, J =

18.0 Hz, 1H, 1-H), 5.03 (s broad, 0.78H, 6-H), 5.96 (s broad,

0.22H, 6-H), 7.04 (dd, J = 8.6/2.3 Hz, 0.22H, 6¢-H_{dichlorophenyl}), 7.18–

7.28 (m, 1.22H, 0.78¥ 6¢-H_{dichlorophenyl}, 0.22¥ 2¢-H_{dichlorophenyl}and 0.22¥

5¢-H_{dichlorophenyl}), 7.41 (d, J = 7.8 Hz, 0.78H, 2¢-H_{dichlorophenyl}), 7.50–

7.59 (m, 1.78, 1¥ 10-H and 0.78¥ 5¢-H_{dichlorophenyl}), 7.63 - 7.71 (m,

1H, 9-H), 7.95–8.04 (m, 1.78H, 1¥ 11-H and 0.78¥ 8-H), 8.10–8.15

(EI): m/z [%] = 429 (M, 2¥ ³⁵Cl, 30), 431 (M, ³⁵Cl/³⁷Cl, 16), 433

(M, 2¥ ³⁷Cl, 3). HPLC (Method 1): t_R= 19.4 min, purity 98.5%.

Receptor binding studies

Materials and general procedures. Guinea pig brains were

commercially available (Harlan-Winkelmann, Germany). Ho-

mogenizer: Elvehjem Potter (B. Braun Biotech International).

Centrifuge: high-speed cooling centrifuge model Sorvall RC-5C

plus (Thermo Finnigan). Filter: Printed Filtermat Type B (Perkin

Elmer), pre-soaked in 0.5% aqueous polyethylenimine for 2 h at

rt before use. The ﬁltration was carried out with a MicroBeta

FilterMate-96 Harvester (Perkin Elmer). The scintillation analysis

was performed using Meltilex (Type A) solid scintillator (Perkin

Elmer). The solid scintillator was melted on the ﬁltermat at a

temperature of 95 ^◦C for 5 min. After solidiﬁcation of the scintil-

lator at rt, the scintillation was measured using a MicroBeta Trilux

scintillation analyzer (Perkin Elmer). The counting efﬁciency was

20%.

Membrane preparation for the j assay (modiﬁed according to ref.

16). Five guinea pig brains were homogenized with the potter

(500–800 rpm, 10 up-and-down strokes) in 6 volumes of cold

0.32 M sucrose. The suspension was centrifuged at 1200 ¥ g for

10 min at 4 ^◦C. The supernatant was separated and centrifuged at

23 500 ¥ g for 20 min at 4 ^◦C. The pellet was resuspended in 5–6

volumes of buffer (50 mM TRIS, pH 7.4), and centrifuged again

(m, 0.22H, 8-H). Ratio of rotational isomers 78:22. IR (neat): n

-1

[cm ] = 1634 (s, C O), 1499 (m, C C), 756 and 737 (m, arom.

out of plane). MS (ESI): m/z [%] = 426 (MH, 2¥ ³⁵Cl, 86), 428

(MH, ³⁵Cl/³⁷Cl, 55), 873 (2M + Na, 4¥ ³⁵Cl, 81), 875 (2M + Na,

3¥ Cl/1¥ Cl, 100), 877 (2M + Na, 2¥ Cl/2¥ Cl, 48). HPLC

(Method 1): t_R= 18.9 min, purity 97.6%.

◦

at 23 500 ¥ g (20 min, 4 C). This procedure was repeated twice.

The ﬁnal pellet was resuspended in 5–6 volumes of buffer, the

protein concentration was determined according to the method

of Bradford³¹, using bovine serum albumin as the standard, and

subsequently the preparation was frozen (-80 ^◦C) in 1.5 mL

portions containing about 1.5 mg protein mL^-1.

5-[(3,4-Dichlorophenyl)acetyl]-10-methoxy-2,3,4,5,6,7-hexa-

hydro-2,6-methano-1H-[1,4]diazocino[6,7-b]indole (31). A solu-

This journal is

The Royal Society of Chemistry 2010

Org. Biomol. Chem., 2010, 8, 212–225 | 223

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Performing of the j assay (modiﬁed according to ref. 16).

The test was performed with the radioligand [³H]-U-69 593

(55 Ci mmol^-1, Amersham, Little Chalfont, UK). The thawed

membrane preparation (about 75 mg of the protein) was incubated

with various concentrations of test compounds, 1 nM [³H]-U-

69’593, and TRIS-MgCl₂-buffer (50 mM, 8 mM MgCl₂, pH 7.4) in

a total volume of 200 mL for 150 min at 37 ^◦C. The incubation was

terminated by rapid ﬁltration through the pre-soaked ﬁltermats

using a cell harvester. After washing each well ﬁve times with

300 mL of water, the ﬁltermats were dried at 95 ^◦C. Subsequently,

the solid scintillator was placed on the ﬁltermat and melted at

95 ^◦C. After 5 min, the solid scintillator was allowed to solidify at

room temperature. The bound radioactivity trapped on the ﬁlters

was counted in the scintillation analyzer. The non-speciﬁc binding

was determined with 10 mM unlabelled U-69 593. The K_d-value of

U-69 593 is 0.69 nM.³²

Molecular modelling. The conformational analysis was per-

formed with force ﬁeld MMFF94x of the Molecular Mod-

elling Program MOE (molecular operating environment), version

2008.10 (Chemical Computing Group AG).

Acknowledgements

This work was performed within the International Research Train-

ing Group “Complex Functional Systems in Chemistry: Design,

Synthesis and Applications” in collaboration with the University

of Nagoya. Financial support of this IRTG by the Deutsche

Forschungsgemeinschaft is gratefully acknowledged. Thanks are

also due to Dr W. Englberger, Gru¨nenthal GmbH, Aachen, for the

determination of the d receptor afﬁnity of some bicyclic amines.

References

Membrane preparation for the l assay (modiﬁed according to ref.

16). Five guinea pig brains were homogenized with the potter

(500–800 rpm, 10 up-and-down strokes) in 6 volumes of cold

0.32 M sucrose. The suspension was centrifuged at 1200 ¥ g for

10 min at 4 ^◦C. The supernatant was separated and centrifuged at

23 500 ¥ g for 20 min at 4 ^◦C. The pellet was resuspended in 5–6

volumes of buffer (50 mM TRIS, pH 7.4), and centrifuged again

1 (a) D. I. C. Scopes, Drugs Future, 1993, 18, 933–947; (b) U. Holzgrabe,

C. Nachtsheim, T. Siener, S. Drohsin and W. Brandt, Pharmazie, 1997,

52, 4–22.

2 (a) K. Yasuda, K. Raymor, H. Kong, C. D. Breder, J. Takeda, T. Reisine

and G. I. Bell, Proc. Natl. Acad. Sci. U. S. A., 1993, 90, 6736–6740; (b) Y.

Chen, A. Mestek, J. Liu, J. A. Hurley and L. Yu, Mol. Pharmacol., 1993,

44, 8–12.

3 D. C. Horwell, Drugs Future, 1988, 13, 1061–1071.

4 B. R. de Costa, W. D. Bowen, S. B. Hellewell, C. George, R. B. Rothman,

A. A. Reid, J. M. Walker, A. E. Jacobson and K. C. Rice, J. Med. Chem.,

1989, 32, 1996–2002.

◦

at 23 500 ¥ g (20 min, 4 C). This procedure was repeated twice.

The ﬁnal pellet was resuspended in 5–6 volumes of buffer, the

protein concentration was determined according to the method

of Bradford³¹using bovine serum albumin as the standard, and

subsequently the preparation was frozen (-80 ^◦C) in 1.5 mL

portions containing about 1.5 mg protein mL^-1.

5 B. L. Roth, K. Baner, R. Westkaemper, D. Siebert, K. C. Rice, S.

Steinberg, P. Ernsberger and R. B. Rothman, Proc. Natl. Acad. Sci.

U. S. A., 2002, 99, 11934–11939.

6 D. Siebert, J. Pharmacol., 1994, 43, 53–56.

7 J. P. Freeman, E. T. Michalson, S. V. D’Andrea, L. Baczynskyj, P. F.

VonVoigtla¨nder, R. A. Lahti, M. W. Smith, C. F. Lawson, T. A. Scahill,

S. A. Mizsak and J. Szmuszkovicz, J. Med. Chem., 1991, 34, 1891–

1896.

Performing of the l assay (modiﬁed according to ref. 16).

The test was performed with the radioligand [³H]-DAMGO

(51 Ci mmol^-1, Perkin Elmer LAS). The thawed membrane

preparation (about 75 mg of the protein) was incubated with

various concentrations of test compounds, 3 nM [³H]-DAMGO,

and TRIS-MgCl₂-PMSF-Buffer (50 mM, 8 mM MgCl₂, pH 7.4) in