Chiral, nonracemic (piperazin-2-yl)methanol derivatives with σ-receptor affinity

Article abstract of DOI:10.1016/j.bmc.2004.03.059

Starting with the proteinogenic amino acid (S)-serine a series of chiral nonracemic (piperazin-2-yl)methanols 3 with various N-4 substituents is described. The key step in the synthesis of 3 is the reaction of the chloroacetamide 5 with various primary am

Full text of DOI:10.1016/j.bmc.2004.03.059

Bioorganic & Medicinal Chemistry 12 (2004) 3299–3311
Chiral, nonracemic (piperazin-2-yl)methanol derivatives with
r-receptor affinity
a
Stephan Bedurftig and Bernhard Wunsch
b,
*
€
€
aPharmazeutisches Institut der Albert-Ludwigs-Universit€at Freiburg, Albertstraße 25, D-79104 Freiburg i. Br., Germany
bInstitut f€ur Pharmazeutische und Medizinische Chemie der Westf€alischen Wilhelms-Universit€at M€unster, Hittorfstraße 58––62,
D-48149 M€unster, Germany
Received 23 January 2004; accepted 26 March 2004
Available online 6 May 2004
Abstract—Starting with the proteinogenic amino acid (S)-serine a series of chiral nonracemic (piperazin-2-yl)methanols 3 with
various N-4 substituents is described. The key step in the synthesis of 3 is the reaction of the chloroacetamide 5 with various primary
amines to yield the diastereomeric bicyclic piperazinediones cis-6 and trans-6. The scope and limitation of this transformation is
thoroughly investigated. The r1- and r2-receptor affinities of the piperazines 3 are determined in receptor binding studies with
guinea pig brain and rat liver membrane preparations using [3H]-labeled (þ)-pentazocine and ditolylguanidine, respectively. It was
found, that an additional phenyl residue in the N-4 substituent is favorable to high r1-receptor affinity. In this series the p-meth-
oxybenzyl substituted piperazine 3d reveals the highest r1-receptor affinity (Ki ¼ 12:4 nM) with selectivity toward r2-, NMDA-,
j-opioid, and l-opioid receptors.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
play very high r1-receptor affinity (see Fig. 1). Recently,
we have reported on the synthesis and receptor binding
of enantiomerically pure 1,4-diazabicyclo[4.3.0]nonan-9-
ones.9 The synthesis of these ligands proceeded via 2-
(hydroxymethyl)piperazine intermediates 3 (see Fig. 1),
which are structurally related to the r1-ligands 1 and 2.
Therefore, the r-receptor affinity of the benzyl deriva-
tive 3c was investigated, which resulted in a considerable
r1-receptor affinity (see Table 2, entry 3). This result
encouraged a systematic structure–affinity relationship
study of hydroxymethyl substituted piperazine deriva-
tives 3. Scope and limitations of the synthesis of piper-
azines 3 is also included in this study and described in
this communication.
It is well accepted that r-receptors represent a unique
class of receptors in the central nervous system and the
periphery. The r-receptor is subdivided into r1- and r2-
receptor subtypes. Recently the r1-receptor of various
tissues and species has been cloned.1 The corresponding
amino acid sequence is not related to any known
mammalian receptor or even protein. The exact struc-
ture of the r1-receptor protein, the amino acid sequence
of the r2-receptor as well as a thorough understanding
of the physiological role of both r-receptor subtypes
still remain to be elucidated.2 However, it is well
established, that r-receptors are involved in several
physiological and pathophysiological events. Therefore,
ligands interacting with r-receptors possess a potential
as antipsychotics,3 antidepressants,4 anticocaine
agents,5;6 and antitumor agents.7
R
CH3
R
N
N
N
In the literature 1,4-disubstituted piperazine derivatives
are described as high affinity r-receptor ligands. Among
these piperazine derivatives compounds 18 and 25 dis-
H
N
Cl
N
N
OH
Cl
Keywords: Bicyclic piperazinediones; (Piperazin-2-yl)methanols; r1-
receptor ligands; r2-receptor ligands; Structure–affinity relationships.
* Corresponding author. Tel.: +49-251-8333311; fax: +49-251-32144;
e-mail: wuensch@uni-muenster.de
1
2
3
Figure 1. Comparison of new piperazine derivatives 3 with known
r-active ligands 1 and 2.
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.03.059

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S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
Table 1. Yield of the aminolysis of 5 and the subsequent LiAlH4
reduction
2. Chemistry
Starting with the methyl ester of (S)-serine (4ÆHCl) the
oxazolidine derivative 5 was obtained by acylation with
chloroacetyl chloride and subsequent condensation with
benzaldehyde dimethyl acetal (see Scheme 1).9 The dia-
stereomeric ratio cis-5/trans-5 is dependent on the
reaction conditions during acetalization with benzalde-
hyde dimethyl acetal.9 The diastereomeric mixture of 5
was reacted with various primary amines to yield the
bicyclic piperazinediones 6. The ratio of diastereomers
cis-6 and trans-6 corresponded with the cis/trans ratio of
5, since no epimerization occurred during aminolysis.
With exception of the tert-butyl derivative 6g, the
diastereomers cis-6, and trans-6 were separated by flash
chromatography and their relative configuration was
determined by NOE difference spectroscopy. The
stereodescriptors cis and trans are used to characterize
the arrangement of the protons in position 6 and 9 of the
bicyclic ring system.
Compound
Yield (%)
Compound
Yield (%)
6a
6b
6c
6d
6e
6f
89
95
95
69
90
58
93
86
86
3a
3b
3c
3d
3e
3f
44
74
57
73
82
74
55
53
71
6i
3i
6j
6k
3j
3k
group at the amino moiety (R-CH2-NH2: butan-1-
amine, benzylamine, 4-methoxybenzylamine, 2-phenyl-
ethylamine). Even cyclohexylamine with a branched
residue gave the bicyclic piperazinedione 6f in 58% yield.
However, tert-butylamine required boiling DMF for the
reaction with 5 to afford the tert-butyl derivative 6g in
only 3% yield. The electronically deactivated primary
aromatic amine aniline reacted with 5 in boiling DMF to
provide 6h in 9% yield. The products 6i–k demonstrate,
that primary amines substituted with additional func-
tional groups (primary alcohol, acetal) are also suc-
cessfully employed in this transformation.
In order to investigate the scope and limitations of this
key transformation various primary amines were reacted
with the chloroacetamide 5. Heating of an acetonitrile
solution of 5 and methylamine, the primary amine with
the smallest substituent attached to the NH2-group,
provided the bicyclic piperazinedione 6a in a total yield
of 89% (see Table 1). Comparable high yields were
obtained with primary amines bearing a methylene
Heating of the bicyclic piperazinediones 6 with an excess
10
of LiAlH4 afforded 1-benzyl-2-(hydroxymethyl)piper-
azines 3 bearing various substituents in position 4.
Thereby, both diastereomers cis-6 and trans-6 led to the
same product, respectively.
H3CO
N
O
H
H3CO
H2N
Cl
O
H
OH
(c) or
(d)
(a)
(b)
O
HCl
O
H
N
H
N
H3CO
N
O
H
O
H
O
H
.
N3
O
4 HCl
5
(b) or
(c)
(a)
O
N
H
O
N
5
+
H
R
R
N
O
O
O
4
N
N
O
H
O
H
2
6
O
O
N
O
1
7
+
7
cis-6m
trans-6m
CO2C2H5
H
O
9
H
H
N
N
(d)
(e)
H
cis-6a-k
trans-6a-k
H
N
N
OH
OH
(e)
3,6
R
a
b
c
d
e
f
g
h
i
CH3
R
CH2CH2CH2CH3
CH2C6H5
CH2C6H4-4-OCH3
CH2CH2C6H5
C6H11
C(CH3)3
C6H5
CH2CH2OH
CH2CH2CH2OH
CH2CH(OCH3)2
3m
3n
4
N
H
Scheme 2. Reagents and conditions: (a) NaN3, aetone, 56 ꢁC, 99%; (b)
NaBH4, CuSO4, CH3OH, rt, 76%; (c) H2, 1 bar, Pd/C, CH3OH, rt,
75%; (d) LiAlH4, THF, 66 ꢁC, 99%; (e) Br-CH2CO2Et, Na2CO3, THF,
66 ꢁC, 61%.
2
N
1
OH
3a-f, 3i-k
j
k
In order to obtain the ester substituted piperazine
derivative 3n the reaction sequence was changed. The
chloroacetyl derivative 5 was reacted with sodium azide
to afford the azidoacetyl substituted oxazolidine 7
(mixture of diastereomers), which was reduced and
Scheme 1. Reagents and conditions: (a) ClCH2COCl, NEt3, CH2Cl2,
1 h, ꢀ5 ꢁC, 1 h rt, 93%; (b) PhCH(OCH3)2, p-TolSO3H, toluene, 2 h,
110 ꢁC, 71%. (c) R-NH2, NEt3, CH3CN, 82 ꢁC, yields: see Table 1;
(d) R-NH2, NEt3, DMF, 153 ꢁC, yields: 6g 3%; 6h 9%; (e) LiAlH4,
THF, 66 ꢁC, yields: see Table 1.
11
cyclized with NaBH4/CuSO4 to yield the bicyclic
piperazinediones cis-6m and trans-6m (see Scheme 2). A

S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
3301
O
receptor material. The r1-selective ligand [3H]-(þ)-pent-
azocine was employed as radioligand, and the nonspe-
cific binding was determined in the presence of a large
excess of haloperidol.14 Homogenates of rat liver served
as source for r2-receptors in the r2-assay. Since a r2-
selective radioligand is not available, the nonselective
radioligand [3H]-ditolylguanidine was employed in the
presence of an excess of nontritiated (þ)-pentazocine
(100 nM) for blocking the r1-receptors. Performing the
r2-assay in the presence of an excess of nontritiated
ditolylguanidine led to the nonspecific binding of the
radioligand.15;16 In order to determine receptor selec-
tivity the most promising compounds were screened for
their affinity at NMDA-, k-opioid, and l-opioid recep-
tors.17
O
H
CH3
N
N
O
O
O
CF3
OCH3
O
H
CH3
(a)
(b)
N
N
(R,S)-8
OH
O
O
CH3
O
3n
N
H
N
O
OCH3
CF3
5. Results and discussion
(R,R)-8
The r-receptor affinities of the (1-benzylpiperazin-2-
yl)methanols 3 are summarized in Table 2.
Scheme 3. Reagents and conditions: (a) (R)-Mosher’s acid chloride,
NEt3, DMAP, H2Cl2, 41 ꢁC; (b) (S)-Mosher’s acid chloride, NEt3,
DMAP, CH2Cl2, 41 ꢁC.
Piperazines with a small N-4 substituent (3a, R ¼ CH3,
entry 1) and functionalized N-4 residues (3i,j,k,n, entries
7–10) do not interact significantly with r1- and r2-
receptors. Larger aliphatic N-4 substituents, for exam-
ple, butyl (3b) and cyclohexyl (3f) residues, enhance the
r1-receptor affinity (entries 2 and 6). However, the
highest r1-receptor affinities were found for piperazines
with an additional aromatic residue in the N-4-sub-
stituent (entries 3–5). The number of methylene groups
between N-4 and the phenyl residue makes no difference
for the r1-receptor affinity, since the benzyl derivative 3c
(Ki ¼ 38:3 nM) and the 2-phenylethyl derivative 3e
(Ki ¼ 36:8 nM) reveal the same r1-receptor affinities
(entries 3 and 5). A further enhancement of the r1-
receptor affinity was achieved by introduction of a
methoxy residue in 4-position of the N-4 benzyl
substituent. The p-methoxybenzyl derivative 3d binds
with a Ki-value of 12.4 nM at r1-receptors being
three times more active than the benzyl derivative 3c
(entry 4).
mixture of cis-6m and trans-6m was heated with an
excess of LiAlH4 to yield the 1-benzyl-2-(hydroxy-
methyl)piperazine (3m) without substituent at N-4.
Alkylation12 of 3m with ethyl 2-bromoacetate furnished
the ester substituted piperazine derivative 3n.
3. Investigation of the enantiomeric purity
In order to determine the enantiomeric purity the ester
substituted piperazine derivative 3n was acylated with
(R)- and (S)-configured Mosher’s acid chloride [(R)-(ꢀ)-
and (S)-(þ)-3,3,3-trifluoro-2-methoxy-2-phenylpropion-
yl chloride]13 in the presence of triethylamine and
4-(dimethylamino)pyridine to yield the esters (R,S)-8
and (R,R)-8, respectively (see Scheme 3). The diaste-
reomeric composition of (R,S)-8 and (R,R)-8 was
determined by 19F NMR spectroscopy and HPLC. The
HPLC analysis was performed with a LiChrospnerꢂ 100
RP-18 endcapped column using methanol/H2O (75:25)
as eluent and UV-detection at 254 nm. The experiments
revealed a diastereomeric ratio of greater than 96.7:3.3.
Therefore, the enantiomeric purity of 3n is higher than
93.4% ee. Taking the enantiomeric purity of (S)-serine
(Sigma–Aldrich, 99%, 97% ee by GLC) into consid-
eration it can be concluded that no racemization had
occurred during the synthesis of (piperazin-2-yl)metha-
nol derivatives 3.
Generally, the r2-receptor affinities of the (2-hydroxy-
methyl)piperazines 3 are lower than their r1-receptor
affinities. The relationships between structure and r2-
receptor affinity correlate with the structure/r1-receptor
affinity relationships: Enhancement of r1-receptor
affinity leads to an increase of r2-receptor affinity.
However, the piperazines 3c–e binding with high affinity
at r1-receptors show the highest r1/r2-selectivity fac-
tors.
In Table 3 the NMDA-, k-opioid, and l-opioid receptor
affinities of piperazines 3 binding with high affinity
toward r1-receptors are shown. The residual binding of
the radioligand is given at a concentration of 10 lM of
the test compounds. In all cases the residual binding is
greater than 50% indicating IC50-values of at least
10 lM. These results lead to the conclusion that the
novel r1-receptor ligands described in this report display
high selectivity toward NMDA-, k-opioid, and l-opioid
receptors.
4. Receptor binding studies
The r-receptor affinities of the (piperazin-2-yl)metha-
nols 3a–f and 3i–n were determined in competition
experiments with radioligands. In the r1-assay, homo-
genates of guinea pig brain preparations were used as

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Table 2. r-receptor affinities of (1-benzylpiperazin-2-yl)methanols 3 heaving various substituents in position 4
R
N
H
N
OH
3
Entry
Compound
R
Kiꢁ SEM (3) (nM)
r1/r2-selectivity
r1 ([3H]-(þ)-pentazocine)
>10,000
r2 ([3H]-ditolyl-guanidine)
1
3a
3b
3c
3d
3e
3f
CH3
CH2CH2CH2CH3
CH2C6H5
>10,000
513 ꢁ 96
177 ꢁ 16
70.3 ꢁ 10
132 ꢁ 32
108 ꢁ 21
>10,000
>10,000
>10,000
>10,000
34.2 ꢁ 2.3
63.9 ꢁ 10.8
391 ꢁ 62.2
2
296 ꢁ 31
2
5
6
4
2
3
38.3 ꢁ 2.4
12.4 ꢁ 1.4
36.8 ꢁ 3.0
58.1 ꢁ 3.2
>10,000
4
CH2C6H4-4-OCH3
CH2CH2C6H5
C6H11
5
6
7
3i
CH2CH2OH
CH2CH2CH2OH
CH2CH(OCH3)2
CH2CO2C2H5
Haloperidol
8
3j
>10,000
>10,000
9
3k
3n
10
11
12
13
1578 ꢁ 203
2.20 ꢁ 0.31
164 ꢁ 47.4
265 ꢁ 32.0
16
Ditolylguanidine
BMY 14802
0.39
1.5
Table 3. Residual binding (%) of the respective radioligand at a test
compound concentration of 10 lM
Polarimeter 241 (Perkin–Elmer); 1.0 dm tube; concen-
tration c (g/100 mL); temperature 20 ꢁC. Elemental
analyses: Vario EL (Elementaranalysesysteme GmbH).
MS: MAT 312, MAT 8200, MAT 44, and TSQ
7000 (Finnigan); EI ¼ electron impact, CI ¼ chemical
ionization. High resolution MS (HRMS): MAT 8200
(Finnigan). IR: IR spectrophotometer 1605 FT-IR
(Perkin–Elmer). (br ¼ broad, m ¼ medium, s ¼ strong).
1H NMR (300 MHz), 13C NMR (75 MHz), 19F NMR
(282 MHz): Unity 300 FT NMR spectrometer (Varian),
d in ppm related to tetramethylsilane, coupling con-
stants are given with 0.5 Hz resolution; the assignments
of 13C and 1H NMR signals were supported by 2D
NMR techniques. HPLC: Gradientpump 2249 Phar-
macia, UV-detector VWM 2141 Pharmacia k ¼ 254 nm,
Integrator Chromatopac C-R6A Shimadzu, column:
LiChroCARTꢂ 250-4 Merck with LiChrospherꢂ 100
RP-18 endcapped, injection volume: 20 lL. The data of
compounds 5, 6b,c,k, 3b,c, and 3k are described in
Ref. 9.
Compound NMDA ([3H]-(þ)-
j ([3H]-U-
69593) (%)
l ([3H]-DAM-
GO) (%)
MK-801) (%)
3b
3c
3d
3e
3f
78
86
86
79
77
83
>100
84
79
>100
85
59
>100
90
90
52
98
3n
100
6. Conclusion
In summary the 4-methoxybenzyl piperazine 3d is the
most r1-active compound in this series. Whereas 3d has
only moderate selectivity toward r2-receptors (factor 6)
excellent selectivity with respect to NMDA-, -opioid,
and l-opioid receptors was found.
7. Experimental
7.2. (–)-(6S,9R)-4-Methyl-9-phenyl-8-oxa-1,4-diazabicy-
clo[4.3.0]nonane-2,5-dione (cis-6a) and (–)-(6S,9S)-4-
methyl-9-phenyl-8-oxa-1,4-diazabicyclo[4.3.0]nonane-
2,5-dione (trans-6a)
7.1. Chemistry, general
Unless otherwise noted, moisture sensitive reactions
were conducted under dry nitrogen. THF was distilled
from sodium/benzophenone ketyl prior to use. Petro-
leum ether used refers to the fraction boiling at 40–
60 ꢁC. Thin layer chromatography (TLC): Silica gel 60
F254plates (Merck). Flash chromatography (FC):18 Silica
gel 60, 0.040–0.063 mm (Merck); parentheses include:
diameter of the column (cm), eluent, fraction size (mL),
Rf . Melting points: melting point apparatus SMP 2
(Stuart Scientific), uncorrected. Optical rotation:
A solution of methylamine in ethanol (8 mol/L, 0.11 mL,
0.88 mmol) was added to a solution of 5 (cis-5/trans-
5 ¼ 30:70, 0.25 g, 0.88 mmol), and triethylamine
(0.12 mL, 0.88 mmol) in acetonitrile (50 mL) and the
mixture was heated to reflux for 96 h. Removal of the
solvent in vacuo followed by flash chromatography
(3 cm, ethyl acetate/ethanol 5:1, 5 mL) gave cis-6a, cis-
6a/trans-6a (yield 0.13 g, 60%) and trans-6a.

S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
3303
cis-6a (Rf ¼ 0:45): Colorless solid, mp 166–168 ꢁC (di-
trans-6d (Rf ¼ 0:60): Colorless solid, mp 160–162 ꢁC
ethyl ether), yield 0.056 g (26%). ½aꢂ ꢀ171.7 (c 0.34,
(diethyl ether), yield 0.008 g (1%). ½aꢂ þ9.2 (c 0.12,
589
589
CH2Cl2). C13H14N2O3 (246.27). HRMS: calcd 246.1004,
found 246.1000 (ꢀ0.4 ppm). MS (EI): m=z (%) ¼ 246 (M,
100), 231 (Mꢀmethyl, 1), 169 (Mꢀphenyl, 7), 141
(MꢀPhCHO, 24), 105 (PhCHO, 74), 91 (benzyl, 15). IR
(KBr): m (cmꢀ1) ¼ 2896 and 2889 (m, C–H), 1654 (s,
CH2Cl2). C20H20N2O4 (352.39). Calcd C 68.17, H 5.72,
N 7.95, found C 67.84, H 5.9, N 7.74. HRMS: calcd
352.1423, found 352.1431 (þ0.8 ppm). MS (EI): m=z
(%) ¼ 352 (M, 44), 231 (Mꢀ4-methoxybenzyl, 6), 121 (4-
methoxybenzyl, 100), 105 (PhCHO, 7), 91 (benzyl, 13).
IR (KBr): m (cmꢀ1) ¼ 2896 (w, C–H), 1671 (s, C@O),
1
C@O), 1441 (m, C–H), 750 and 699 (m, aryl-C–H). H
1
NMR (CDCl3): d ¼ 3:01 (s, 3H, CH3), 3.83 (d,
J ¼ 16:8 Hz, 1H, 3-H), 4.14 (t, J ¼ 8:2 Hz, 1H, 7-H),
4.25 (dd, J ¼ 16:6=1:7 Hz, 1H, 3-H), 4.40 (t, J ¼ 7:6 Hz,
1H, 6-H), 4.54 (dd, J ¼ 8:6=7:2 Hz, 1H, 7-H), 6.48 (s,
1H, 9-H), 7.34–7.41 (m, 3H, arom), 7.46–7.49 (m, 2H,
arom).
1437 (m, C–H), 757 and 699 (m, aryl-C–H). H NMR
(CDCl3): d ¼ 3:78 (d, J ¼ 16:9 Hz, 1H, 3-H), 3.81 (s,
3H, OCH3), 4.06 (d, J ¼ 17:3 Hz, 1H, 3-H), 4.29 (t,
J ¼ 8:1 Hz, 1H, 7-H), 4.43–4.53 (m, 2H, 6-H and 7-H),
4.53 (d, J ¼ 14:4 Hz, 1H, H3COPhCH2N), 4.66 (d,
J ¼ 14:0 Hz, 1H, H3COPhCH2N), 6.24 (s, 1H, 9-H),
6.88 (d, J ¼ 8:5 Hz, 2H, 30-H and 50-H [H3COPh]), 7.20
(d, J ¼ 8:5 Hz, 2H, 20-H and 60-H [H3COPh]), 7.26–7.30
(m, 3H, arom), 7.34–7.37 (m, 2H, arom).
trans-6a (Rf ¼ 0:37): Colorless solid, mp 162–164 ꢁC
(diethyl ether), yield 0.006 g (3%). ½aꢂ ꢀ54.8 (c 0.315,
589
CH2Cl2). C13H14N2O3 (246.27). HRMS: calcd 246.1004,
found 246.1005 (þ0.1 ppm). MS (EI): m=z (%) ¼ 246 (M,
100), 231 (Mꢀmethyl, 1), 169 (Mꢀphenyl, 13), 141
(MꢀPhCHO, 28), 105 (PhCHO, 66), 91 (benzyl, 17). IR
(KBr): m (cmꢀ1) ¼ 2901 and 2883 (m, C–H), 1668 (s,
7.4. (–)-(6S,9R)-9-Phenyl-4-(2-phenylethyl)-8-oxa-1,4-
diazabicyclo[4.3.0]nonane-2,5-dione (cis-6e) and (–)-
(6S,9S)-9-phenyl-4-(2-phenylethyl)-8-oxa-1,4-diazabicy-
clo[4.3.0]nonane-2,5-dione (trans-6e)
1
C@O), 1439 (m, C–H), 758 and 697 (m, aryl-C–H). H
NMR (CDCl3): d ¼ 3:07 (s, 3H, CH3), 3.84 (d,
J ¼ 17:0 Hz, 1H, 3-H), 4.26 (d, J ¼ 17:2 Hz, 1H, 3-H),
4.28 (t, J ¼ 6:6 Hz, 1H, 7-H), 4.45 (t, J ¼ 6:8 Hz, 1H, 7-
H), 4.49 (t, J ¼ 7:2 Hz, 1H, 6-H), 6.25 (s, 1H, 9-H),
7.33–7.41 (m, 5H, arom).
A solution of 5 (cis-5/trans-5 ¼ 30:70, 0.25 g, 0.88 mmol),
2-phenylethylamine (0.11 mL, 0.88 mmol) and triethyl-
amine (0.12 mL, 0.88 mmol) in acetonitrile (50 mL) was
heated to reflux for 48 h. Removal of the solvent in
vacuo followed by flash chromatography (3 cm, ethyl
acetate/ethanol 5:1, 7 mL) gave cis-6, cis-6e/trans-6e
(yield 0.243 g, 82%), and trans-6e.
7.3. (–)-(6S,9R)-4-(4-Methoxybenzyl)-9-phenyl-8-oxa-
1,4-diazabicyclo[4.3.0]nonane-2,5-dione (cis-6d) and
(+)-(6S,9S)-4-(4-methoxybenzyl)-9-phenyl-8-oxa-1,4-
diazabicyclo-[4.3.0]nonane-2,5-dione (trans-6d)
cis-6e (Rf ¼ 0:66): Pale yellow oil, yield 0.022 g (7%),
½aꢂ
ꢀ136.1 (c 1.08, CH2Cl2). C20H20N2O3 (336.39).
589
HRMS: calcd 336.1474, found 336.1475 (þ0.1 ppm).
MS (EI): m=z (%) ¼ 336 (M, 55), 245 (Mꢀbenzyl, 6), 231
(Mꢀphenylethyl, 15), 104 (PhCN, 100), 91 (benzyl, 21).
IR (film): m (cmꢀ1) ¼ 2886 (m, C–H), 1660 (s, C@O),
1449 (m, C–H), 1219 (m, C–O), 744 and 697 (m, aryl-C–
H). 1H NMR (CDCl3): d ¼ 2:91 (t, J ¼ 7:4 Hz, 2H,
PhCH2CH2N), 3.59 (dt, J ¼ 13:7=7:1 Hz, 1H,
PhCH2CH2N), 3.70 (d, J ¼ 16:5 Hz, 1H, 3-H), 3.79 (dt,
J ¼ 13:8=7:0 Hz, 1H, PhCH2CH2N), 4.04 (dd,
J ¼ 16:6=1:6 Hz, 1H, 3-H), 4.13 (‘t’, J ¼ 8:5 Hz, 1H, 7-
H), 4.35 (td, J ¼ 7:5=1:6 Hz, 1H, 6-H), 4.51 (dd,
J ¼ 8:6=7:4 Hz, 1H, 7-H), 6.45 (s, 1H, 9-H), 7.19–7.48
(m, 10H, arom).
A solution of 5 (cis-5/trans-5 ¼ 30:70, 0.25 g, 0.88 mmol),
4-methoxybenzylamine (0.11 mL, 0.88 mmol) and
triethylamine (0.12 mL, 0.88 mmol) in acetonitrile
(50 mL) was heated to reflux for 40 h. Removal of
the solvent in vacuo followed by flash chromato-
graphy (3 cm, ethyl acetate/ethanol 5:1, 5 mL) gave
cis-6d, cis-6d/trans-6d (yield 0.165 g, 53%), and
trans-6d.
cis-6d (Rf ¼ 0:73): Colorless solid, mp 124 ꢁC (diethyl
ether), yield 0.045 g (15%). ½aꢂ
ꢀ125.8 (c 0.545,
589
CH2Cl2). C20H20N2O4 (352.39). Calcd C 68.17, H 5.72,
N 7.95. Found C 67.9, H 5.75, N 7.56. HRMS: calcd
352.1423, found 352.1431 (þ0.8 ppm). MS (EI): m=z
(%) ¼ 352 (M, 51), 231 (Mꢀ4-methoxybenzyl, 10), 121
(4-methoxybenzyl, 100), 105 (PhCHO, 16), 91 (benzyl,
15). IR (KBr): (cmꢀ1) ¼ 2899 and 2837 (w, C–H), 1661
(s, C@O), 1441 (m, C–H), 757 and 699 (m, aryl-C–H).
1H NMR (CDCl3): d ¼ 3:79 (d, J ¼ 16:6 Hz, 1H, 3-H),
3.80 (s, 3H, OCH3), 4.05 (dd, J ¼ 16:7=1:7 Hz, 1H, 3-
H), 4.21 (t, J ¼ 8:2 Hz, 1H, 7-H), 4.41 (d, J ¼ 14:3 Hz,
1H, H3COPhCH2N), 4.45 (td, J ¼ 7:6=1:3 Hz, 1H, 6-H),
4.58 (dd, J ¼ 8:4=7:2 Hz, 1H, 7-H), 4.71 (d, J ¼ 14:4 Hz,
1H, H3COPhCH2N), 6.49 (s, 1H, 9-H), 6.87 (d,
J ¼ 8:9 Hz, 2H, 30-H and 50-H [H3COPh]), 7.19 (d,
J ¼ 8:9 Hz, 2H, 20-H and 60-H [H3COPh]), 7.33–7.40 (m,
3H, arom), 7.44–7.47 (m, 2H, arom).
trans-6e (Rf ¼ 0:55): Pale yellow oil, yield 0.002 g (1%),
½aꢂ
ꢀ20.3 (c 0.1, CH2Cl2). C20H20N2O3 (336.39).
589
HRMS: calcd 336.1474, found 336.1475 (þ0.1 ppm).
MS (EI): m=z (%) ¼ 336 (M, 67), 245 (Mꢀbenzyl, 8), 231
(Mꢀphenylethyl, 28), 104 (PhCN, 100), 91 (benzyl, 35).
IR (film): m (cmꢀ1) ¼ 2925 (m, C–H), 1671 (s, C@O),
1433 (m, C–H), 1227 (m, C–O), 750 and 699 (m, aryl-C–
H). 1H NMR (CDCl3): d ¼ 2:89–2.96 (m, 2H,
PhCH2CH2N), 3.63 (d, J ¼ 17:0 Hz, 1H, 3-H), 3.66 (dt,
J ¼ 13:4=7:0 Hz, 1H, PhCH2CH2N), 3.80 (dt,
J ¼ 13:5=6:9 Hz, 1H, PhCH2CH2N), 3.99 (br d,
J ¼ 17:0 Hz, 1H, 3-H), 4.23 (t, J ¼ 12:0 Hz, 1H, 7-H),
4.40 (ddd, J ¼ 12:2=6:8=1:2 Hz, 1H, 6-H), 4.41 (dd,
J ¼ 11:9=6:9 Hz, 1H, 7-H), 6.20 (s, 1H, 9-H), 7.19–7.39
(m, 10H, arom).

3304
S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
7.5. (–)-(6S,9R)-4-Cyclohexyl-9-phenyl-8-oxa-1,4-diaza-
bicyclo[4.3.0]nonane-2,5-dione (cis-6f) and (–)-(6S,9S)-4-
cyclohexyl-9-phenyl-8-oxa-1,4-diazabicyclo[4.3.0]nonane-
2,5-dione (trans-6f)
1.54 (s, 9 ꢃ 0.17H, CH3) trans), 4.06–4.08 (m, 2H, 3-H),
4.22 (dd, J ¼ 8:5=7:3 Hz, 1H, 7-H), 4.36 (t, J ¼ 7:2 Hz,
1H, 6-H), 4.49 (dd, J ¼ 8:3=7:2 Hz, 1H, 7-H), 6.37 (s,
0.17H, 9-H trans), 6.48 (s, 0.83H, 9-H cis), 7.36–7.41 (m,
3H, arom), 7.45–7.49 (m, 2H, arom).
A
solution of
5
(cis-5/trans-5 ¼ 30:70, 0.254 g,
0.89 mmol), cyclohexylamine (0.10 mL, 0.89 mmol), and
triethylamine (0.12 mL, 0.89 mmol) in acetonitrile
(50 mL) was heated to reflux for 96 h. Removal of the
solvent in vacuo followed by flash chromatography
(3 cm, ethyl acetate/ethanol 5:1, 5 mL) gave cis-6f, cis-6f/
trans-6f (yield 0.115 g, 41%), and trans-6f.
7.7. (–)-(6S,9R)-4,9-Diphenyl-8-oxa-1,4-diazabicyclo-
[4.3.0]nonane-2,5-dione (cis-6h) and (–)-(6S,9S)-
4,9-diphenyl-8-oxa-1,4-diazabicyclo[4.3.0]nonane-2,5-
dione (trans-6h)
A solution of 5 (cis-5/trans-5 ¼ 90:10, 0.50 g, 1.76 mmol),
aniline (0.16 mL, 1.76 mmol), and triethylamine
(0.25 mL, 1.76 mmol) in DMF (30 mL) was heated to
reflux for 24 h. The reaction mixture was concentrated in
vacuo. The residue was dissolved in CH2Cl2 (15 mL), the
solution was washed with HCl (0.5 N, 2 ꢃ 10 mL),
NaOH (0.5 N, 2 ꢃ 10 mL) and water (10 mL), dried with
Na2SO4, and evaporated. Purification of the residue by
flash chromatography (3 cm, ethyl acetate/petroleum
ether 7:3, 10 mL) gave cis-6h and trans-6h.
cis-6f (Rf ¼ 0:80): Colorless solid, mp 154 ꢁC, yield
0.043 g (15%). ½aꢂ
ꢀ130.3 (c 0.44, CH2Cl2).
589
C18H22N2O3 (314.38). Calcd C 68.77, H 7.05, N 8.91,
found C 68.36, H 7.39, N 8.66. MS (EI): m=z (%) ¼ 314
(M, 100), 231 (Mꢀcyclohexyl, 20), 105 (PhCHO, 36), 82
(cyclohexyl, 10). IR (KBr): m (cmꢀ1) ¼ 2929 and 2856 (m,
C–H), 1652 (s, C@O), 1444 (m, C–H), 741 and 698 (m,
1
aryl-C–H). H NMR (CDCl3): d ¼ 1:05–1.19 (m, 1H,
cyclohexyl), 1.32–1.49 (m, 4H, cyclohexyl), 1.68–1.73
(m, 3H, cyclohexyl), 1.83–1.87 (m, 2H, cyclohexyl), 3.89
(d, J ¼ 16:5 Hz, 1H, 3-H), 4.02 (dd, J ¼ 16:5=1:5 Hz,
1H, 3-H), 4.22 (t, J ¼ 8:3 Hz, 1H, 7-H), 4.37–4.60 (m,
1H, NCHcyclohexyl), 4.41 (td, J ¼ 7:3=1:4 Hz, 1H, 6-H),
4.55 (dd, J ¼ 8:5=7:3 Hz, 1H, 7-H), 6.49 (s, 1H, 9-H),
7.36–7.43 (m, 3H, arom), 7.47–7.50 (m, 2H, arom).
cis-6h (Rf ¼ 0:52): Pale yellow solid, mp 104–108 ꢁC,
yield 0.041 g (8%). ½aꢂ
ꢀ157.8 (c 0.225, CH2Cl2).
589
C18H16N2O3 (308.34). HRMS: calcd 308.1161, found
308.1162 (þ0.1 ppm). MS (EI): m=z (%) ¼ 308 (M, 59),
231 (Mꢀphenyl, 3), 105 (PhCHO, 100), 91 (benzyl, 32),
77 (phenyl, 51). IR (KBr): m (cmꢀ1) ¼ 2924 (m, C–H),
1677 (s, C@O), 1445 (m, C–H), 742 and 698 (m, aryl-C–
trans-6f (Rf ¼ 0:69): Colorless solid, mp 151 ꢁC, yield
0.005 g (2%). ½aꢂ
ꢀ34.8 (c 0.25, CH2Cl2).
1
589
H). H NMR (CDCl3): d ¼ 4:21 (d, J ¼ 16:1 Hz, 1H, 3-
C18H22N2O3(314.38). Calcd C 68.77, H 7.05, N 8.91,
found C 68.27, H 7.27, N 8.66. MS (EI): m=z (%) ¼ 314
(M, 100), 237 (Mꢀphenyl, 7), 231 (Mꢀcyclohexyl, 17),
105 (PhCHO, 29), 82 (cyclohexyl, 14). IR (KBr): m
(cmꢀ1) ¼ 2929 and 2856 (m, C–H), 1667 (s, C@O), 1435
(m, C–H), 757 and 698 (m, aryl-C–H). 1H NMR
(CDCl3): d ¼ 1:07–1.13 (m, 1H, cyclohexyl), 1.26–1.48
(m, 4H, cyclohexyl), 1.62–1.87 (m, 5H, cyclohexyl), 3.90
(d, J ¼ 17:1 Hz, 1H, 3-H), 3.98 (d, J ¼ 17:1 Hz, 1H, 3-H),
4.25 (t, J ¼ 7:3 Hz, 1H, 7-H), 4.38–4.49 (m, 2H, 6-H
and NCHcyclohexyl), 4.42 (t, J ¼ 7:0 Hz, 1H, 7-H), 6.25
(s, 1H, 9-H), 7.26–7.30 (m, 2H, arom), 7.34–7.38 (m, 3H,
arom).
H), 4.39 (dd, J ¼ 11:6=10:3 Hz, 1H, 7-H), 4.56–4.62 (m,
2H, 6-H and 7-H), 4.69 (dd, J ¼ 16:2=1:3 Hz, 1H, 3-H),
6.58 (s, 1H, 9-H), 7.28–7.35 (m, 3H, arom), 7.38–7.47
(m, 5H, arom), 7.51–7.54 (m, 2H, arom).
trans-6h (Rf ¼ 0:28): Pale yellow, viscous oil, yield
0.005 g (1%), ½aꢂ ꢀ47.3 (c 0.23, CH2Cl2). C18H16N2O3
589
(308.34). HRMS: calcd 308.1161, found 308.1162
(þ0.1 ppm). MS (EI): m=z (%) ¼ 308 (M, 100), 231
(Mꢀphenyl, 2), 105 (PhCHO, 3), 77 (phenyl, 2). IR
(film): m (cmꢀ1) ¼ 2935 (m, C–H), 1684 (s, C@O), 1434
(m, C–H), 756 and 698 (m, aryl-C–H). 1H NMR
(CDCl3): d ¼ 4:22 (d, J ¼ 16:4 Hz, 1H, 3-H), 4.39 (t,
J ¼ 9:2 Hz, 1H, 7-H), 4.50 (dd, J ¼ 9:2=7:0 Hz, 1H, 7-
H), 4.67 (ddd, J ¼ 9:5=7:0=0:9 Hz, 1H, 6-H), 4.68 (dd,
J ¼ 16:4=0:9 Hz, 1H, 3-H), 6.33 (s, 1H, 9-H), 7.30–7.35
(m, 4H, arom), 7.40–7.48 (m, 6H, arom).
7.6. (6S,9R) and (6S,9S)-4-tert-butyl-9-phenyl-8-oxa-1,4-
diazabicyclo[4.3.0]nonane-2,5-dione (cis/trans-6g)
A solution of 5 (cis-5/trans-5 ¼ 90:10, 0.10 g, 0.35 mmol),
tert-butylamine (37 lL, 0.35 mmol) and triethylamine
(50 lL, 0.35 mmol) in DMF (20 mL) was heated to reflux
for 72 h. Removal of the solvent in vacuo followed by
flash chromatography (2 cm, ethyl acetate/petroleum
ether 1:1, 3 mL) provided 6g (cis-6g/trans-6g ¼ 83:17).
7.8. (–)-(6S,9R)-4-(2-Hydroxyethyl)-9-phenyl-8-oxa-1,4-
diazabicyclo[4.3.0]nonane-2,5-dione (cis-6i) and (–)-
(6S,9S)-4-(2-hydroxyethyl)-9-phenyl-8-oxa-1,4-diazabi-
cyclo[4.3.0]-nonane-2,5-dione (trans-6i)
A solution of 5 (cis-5/trans-5 ¼ 90:10, 0.50 g, 1.76 mmol),
2-aminoethanol (0.11 mL, 1.76 mmol), and triethyl-
amine (0.25 mL, 1.76 mmol) in acetonitrile (100 mL) was
heated to reflux for 30 h. Removal of the solvent in
vacuo followed by flash chromatography (4 cm, ethyl
acetate/ethanol 5:1, 15 mL) gave cis-6i, cis-6i/trans-6i
(yield 0.088 g, 18%), and trans-6i.
cis-6g/trans-6g (Rf ¼ 0:67): Colorless solid, mp 118–
123 ꢁC, yield 0.003 g (3%). C16H20N2O3 (288.35). MS
(EI): m=z (%) ¼ 288 (M, 100), 273 (Mꢀmethyl, 9), 231
(Mꢀtert-butyl, 35), 105 (PhCHO, 45), 91 (benzyl, 23),
57 (tert-butyl, 37). IR (KBr): m (cmꢀ1) ¼ 2925 (m, C–H),
1661 (s, C@O), 1443 (m, C–H), 756 and 699 (m, aryl-C–
H). 1H NMR (CDCl3): d ¼ 1:48 (s, 9 ꢃ 0.83H, CH3) cis),

S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
3305
cis-6i (Rf ¼ 0:39): Colorless solid, mp 132–134 ꢁC, yield
trans-6j (Rf ¼ 0:27): Colorless, viscous oil, yield 0.040 g
(11%). ½aꢂ ꢀ33.3 (c 0.725, CH2Cl2). C15H18-
0.318 g (65%). ½aꢂ
ꢀ177.9 (c 0.945, CH2Cl2).
589
589
C14H16N2O4 (276.29). Calcd C 60.86, H 5.84, N 10.14,
found C 60.49, H 5.68, N 9.84. MS (EI): m=z (%) ¼ 276
(M, 60), 245 ( MꢀCH2OH, 9), 231 (MꢀCH2CH2OH, 5),
199 (Mꢀphenyl, 6), 105 (PhCHO, 73), 91 (benzyl, 33).
IR (KBr): m (cmꢀ1) ¼ 3442 (br, OH), 2926 (m, C–H),
1663 (s, C@O), 1456 (m, C–H), 1226 (m, C–O), 756 and
N2O4(290.32). Calcd C 62.06, H 6.25, N 9.65, found C
61.92, H 6.33, N 9.37. MS (EI): m=z (%) ¼ 290 (M, 7),
259 ( MꢀCH2OH, 1), 245 (MꢀCH2CH2OH, 1), 231
(MꢀCH2CH2CH2OH, 1), 213 (Mꢀphenyl, 3), 105
(PhCHO, 27), 91 (benzyl, 15), 77 (phenyl, 16). IR (film):
m (cmꢀ1) ¼ 3420 (br, OH), 2926 (m, C–H), 1668 (s,
C@O), 1444 (m, C–H), 1233 (m, C–O), 1054 (m, C–OH),
758 and 699 (m, aryl-C–H). 1H NMR (CDCl3): d ¼ 1:73
(br s, 1 H, OH), 1.81 (‘quint’, J ¼ 6:0 Hz, 2H, NCH2-
CH2CH2OH), 3.57–3.72 (m, 4H, NCH2CH2CH2OH),
3.84 (d, J ¼ 16:9 Hz, 1H, 3-H), 4.26 (dd, J ¼
16:9=1:3 Hz, 1H, 3-H), 4.28 (t, J ¼ 8:9 Hz, 1H, 7-H), 4.45
(dd, J ¼ 8:9=7:0 Hz, 1H, 7-H), 4.52 (td, J ¼ 7:0=1:3 Hz,
1H, 6-H), 6.26 (s, 1H, 9-H), 7.33–7.40 (m, 5H, arom).
1
697 (m, aryl-C–H). H NMR (CDCl3): d ¼ 2:65 (br s,
1H, OH), 3.39–3.47 (m, 1H, CH2CH2OH), 3.66–3.78
(m, 3H, CH2CH2OH), 3.97 (d, J ¼ 16:5 Hz, 1H, 3-H),
4.18 (dd, J ¼ 8:1=7:3 Hz, 1H, 7-H), 4.35 (dd,
J ¼ 16:5=1:7 Hz, 1H, 3-H), 4.42 (td, J ¼ 7:3=1:7 Hz, 1H,
6-H), 4.50 (t, J ¼ 8:1 Hz, 1H, 7-H), 6.45 (s, 1H, 9-H),
7.30–7.39 (m, 3H, arom), 7.42–7.45 (m, 2H, arom).
trans-6i (Rf ¼ 0:25): Pale yellow, viscous oil, yield
0.051 g (10%). ½aꢂ ꢀ64.3 (c 1.43, CH2Cl2). C14H16N2O4
589
(276.29). Calcd C 60.86, H 5.84, N 10.14, found C 60.34,
H 5.55, N 9.79. MS (EI): m=z (%) ¼ 276 (M, 34), 245
(MꢀCH2OH, 7), 231 (MꢀCH2CH2OH, 4), 199
(Mꢀphenyl, 11), 105 (PhCHO, 55), 91 (benzyl, 33). IR
(film): m (cmꢀ1) ¼ 3444 (br, OH), 2944 (m, C–H), 1668 (s,
C@O), 1451 (m, C–H), 1231 (m, C–O), 1070 (m, C–OH),
756 and 692 (m, aryl-C–H). 1H NMR (CDCl3): d ¼ 2:20
(br s, 1H, OH), 3.38–3.49 (m, 1H, CH2CH2OH), 3.74–
3.84 (m, 3H, CH2CH2OH), 3.93 (d, J ¼ 17:1 Hz, 1H, 3-
H), 4.24 (t, J ¼ 9:0 Hz, 1H, 7-H), 4.34 (dd,
J ¼ 16:9=1:4 Hz, 1H, 3-H), 4.41 (t, J ¼ 9:0 Hz, 1H, 7-
H), 4.49 (td, J ¼ 9:0=1:4 Hz, 1H, 6-H), 6.23 (s, 1H, 9-H),
7.30–7.40 (m, 5H, arom).
7.10. (2R,4S)- and (2S,4S)-Methyl 3-(azidoacetyl)-2-
phenyl-1,3-oxazolidine-4-carboxylate (cis-7/trans-7)
A solution of 5 (cis-5/trans-5 ¼ 90:10, 1.84 g, 6.48 mmol),
and sodium azide (1.265 g, 19.5 mmol) in acetone
(150 mL) was heated to reflux for 16 h. The solvent was
removed under reduced pressure. The residue was dis-
solved in diethyl ether (30 mL), washed with a half-sat-
urated solution of NaCl (30 mL) and the organic layer
was separated. The aqueous layer was extracted with
diethyl ether (3 ꢃ 20 mL). The organic layers were
combined, dried with Na2SO4, and concentrated in
vacuo. The residue was characterized without further
purification and was converted into 6m.
7.9. (–)-(6S,9R)-4-(3-Hydroxypropyl)-9-phenyl-8-oxa-
1,4-diazabicyclo[4. 3.0]nonane-2,5-dione (cis-6j) and (–)-
(6S,9S)-4-(3-hydroxypropyl)-9-phenyl-8-oxa-1,4-diazabi-
cyclo[4.3.0]-nonane-2,5-dione (trans-6j)
cis-7/trans-7: Pale yellow, viscous oil, yield 1.881 g
(99%). C13H14N4O4 (290.28). MS (EI): m=z (%) ¼ 248
(MꢀN3, 95), 234 (MꢀCH2N3, 51), 206 (MꢀCOCH2N3,
79), 148 (2-phenyl-1,3-oxazolidine, 26), 105 (PhCHO,
68). MS (CI): m=z (%) ¼ 307 (MþNH3, 100), 291 (MHþ,
23). IR (film): m (cmꢀ1) ¼ 2954 (m, C–H), 2108 (s, N3),
1745 (s, C@O ester), 1666 (s, C@O amide), 1434 (s, C–
H), 1370 and 1213 (m, C–O), 733 and 701 (s, aryl-C–H).
1H NMR (CDCl3): d ¼ 3:36 (d, J ¼ 15:9 Hz, 1H,
CH2N3), 3.56 (d, J ¼ 15:9 Hz, 1H, CH2N3), 3.83 (s,
3 ꢃ 0.9H, OCH3 cis), 3.84 (s, 3 ꢃ 0.1H, OCH3 it trans),
4.09–4.16 (m, 1H, 5-H), 4.29 (dd, J ¼ 9:5=7:0 Hz, 1H, 5-
H), 4.90 (dd, J ¼ 10:2=7:1 Hz, 1H, 4-H), 6.00 (br s,
0.1H, 2-H trans), 6.25 (s, 0.7H, 2-H cis rotamer 1), 6.51
(s, 0.2H, 2-H, cis rotamer 2), 7.35–7.50 (m, 4H, arom),
7.67–7.75 (m, 1H, arom).
A
solution of
5
(cis-5/trans-5 ¼ 90:10, 0.362 g,
1.28 mmol), 3-aminopropan-1-ol (0.10 mL, 1.28 mmol),
and triethylamine (0.18 mL, 1.28 mmol) in acetonitrile
(75 mL) was heated to reflux for 36 h. Removal of the
solvent in vacuo followed by flash chromatography
(4 cm, ethyl acetate/ethanol 5:1, 10 mL) gave cis-6j, cis-
6j/trans-6j (yield 0.034 g, 9%), and trans-6j.
cis-6j (Rf ¼ 0:39): Colorless solid, mp 107–108 ꢁC, yield
0.246 g (66%). ½aꢂ ꢀ243.6 (c 0.515, CH2Cl2). C15H18
589
N2O4 (290.32). Calcd C 62.06, H 6.25, N 9.65, found C
61.76, H 6.31, N 9.50. MS (EI): m=z (%) ¼ 290 (M, 69),
259 (MꢀCH2OH, 2), 245 (MꢀCH2CH2OH, 3), 231
(MꢀCH2CH2CH2OH, 4), 213 (Mꢀphenyl, 8), 105
(PhCHO, 100), 77 (phenyl, 25). IR (KBr):
m
7.11. (–)-(6S,9R)-9-Phenyl-8-oxa-1,4-diazabicyclo-
[4.3.0]nonane-2,5-dione (cis-6m) and (–)-(6S,9S)-9-
phenyl-8-oxa-1,4-diazabicyclo[4.3.0]nonane-2,5-dione
(trans-6m)
(cmꢀ1) ¼ 3433 (br, OH), 2882 (m, C–H), 1665 (s, C@O),
1449 (m, C–H), 1223 (m, C–O), 1056 (m, C–OH), 748
and 700 (m, aryl-C–H). 1H NMR (CDCl3): d ¼ 1:77
(‘quint’, J ¼ 6:0 Hz, 2H, NCH2CH2CH2OH), 2.75 (br s,
1H, OH), 3.49–3.66 (m, 4H, NCH2CH2CH2OH), 3.84
(d, J ¼ 16:6 Hz, 1H, 3-H), 4.17 (dd, J ¼ 8:2=7:8 Hz, 1H,
7-H), 4.24 (dd, J ¼ 16:6=1:7 Hz, 1H, 3-H), 4.43 (td,
J ¼ 7:6=1:6 Hz, 1H, 6-H), 4.53 (dd, J ¼ 8:2=7:3 Hz, 1H,
7-H), 6.48 (s, 1H, 9-H), 7.36–7.40 (m, 3H, arom), 7.45–
7.48 (m, 2H, arom).
(a) Reductive cyclization with NaBH4/CuSO4 following
Ref. 11: NaBH4 (82 mg, 2.16 .mmol) was added to a
stirred and cooled (ꢀ5 ꢁC) suspension of CH3OH
(70 mL) and CuSO4 (0.010 g, 0.065 mmol). Then a
solution of cis-7/trans-7 (cis-7/trans-7 ¼ 90:10, 1.882 g,
6.48 mmol) dissolved in CH3OH (20 mL) was added

3306
S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
dropwise. Subsequently NaBH4 (163 mg, 4.32 mmol)
was added in five portions within 1 h. It was allowed to
warm to room temperature and the reaction mixture
was stirred for 24 h. The mixture was filtered through a
pad of Celiteꢂ AFA and the filtrate was concentrated in
vacuo. Flash chromatography of the residue (6 cm, ethyl
acetate/ethanol 5:1, 15 mL) yielded cis-6m, cis-6m/trans-
6m (yield 0.412 g, 27%) and trans-6m.
chromatography (2 cm, ethanol, 5 mL, Rf ¼ 0:17) and
gave 3a as a colorless solid, mp 86.5–87 ꢁC, yield 0.114 g
(44%). ½aꢂ
þ25.5 (c 0.55, CH2Cl2). C13H20N2O
589
(220.31). Calcd C 70.87, H 9.15, N 12.72, found C 70.68,
H 9.39, N 12.70. MS (EI): m=z (%) ¼ 220 (M, 1), 189
(MꢀCH2OH, 100), 98 (MꢀCH2OHꢀbenzyl, 9), 91
(benzyl, 55). MS (CI): m=z (%) ¼ 221 (MHþ, 100), 189
(MꢀCH2OH, 14). IR (KBr): m (cmꢀ1) ¼ 3390 (br, OH),
2937 (m, C–H), 2800 (s, C–H), 1450 (m, C–H), 735 and
1
cis-6m (Rf ¼ 0:38): Colorless solid, mp 174–176 ꢁC, yield
698 (m, aryl-C–H). H NMR (CDCl3): d ¼ 2:27 (s, 3H,
0.668 g (44%). ½aꢂ
ꢀ244.1 (c 0.37, CH3OH).
CH3), 2.27–2.31 (m, 1H, 5-H, or 6-H), 2.40–2.56 (m, 3H,
3-H, 5-H, and 6-H), 2.61–2.70 (m, 2H, 2-H, and 3-H),
2.90–2.98 (m, 1H, 6-H or 5-H), 3.41 (d, J ¼ 13:4 Hz, 1H,
PhCH2N), 3.60 (dd, J ¼ 11:3=2:4 Hz, 1H, CH2OH),
4.02 (d, J ¼ 13:4 Hz, 1H, PhCH2N), 4.06 (dd, J ¼
11:3=4:0 Hz, 1H, CH2OH), 7.22–7.33 (m, 5H, arom).
The signal for the proton of the OH group could not be
detected. 13C NMR (CDCl3): d ¼ 46:1 (1C, C3), 50.1
and 54.5 (2C, C-5, C-6), 57.97 (1C, C-3), 57.99 (1C,
NCH2Ph), 59.0 (1C, C-2), 61.9 (1C, CH2OH), 127.1 (1C,
C-40), 128.3 (2C, C-30 and C-50), 128.8 (2C, C-20 and C-
60), 138.4 (1C, C-10).
589
C12H12N2O3 (232.24). Calcd C 62.06, H 5.21, N 12.06,
found C 61.84, H 5.26, N 11.90. MS (EI): m=z (%) ¼ 232
(M, 100), 155 (Mꢀphenyl, 11), 105 (PhCHO, 86), 91
(benzyl, 15), 77 (phenyl, 18). IR (KBr): m (cmꢀ1) ¼ 3244
(br, NH), 2845 (m, C–H), 1667 (s, C@O), 1454 (m, C–
H), 744 and 698 (m, aryl-C–H). 1H NMR (CDCl3):
d ¼ 3:94 (dd, J ¼ 16:9=4:3 Hz, 1H, 3-H), 4.20 (dd,
J ¼ 16:5=1:6 Hz, 1H, 3-H), 4.22 (t, J ¼ 7:9 Hz, 1H, 7-
H), 4.42 (td, J ¼ 7:5=1:6 Hz, 1H, 6-H), 4.53 (t,
J ¼ 7:8 Hz, 1H, 7-H), 6.48 (br s, 1H, NH), 6.52 (s, 1H,
9-H), 7.36–7.43 (m, 3H, arom), 7.47–7.50 (m, 2H,
arom).
trans-6m(Rf ¼ 0:29) (contains 5% cis-6m): Colorless
solid, mp 218–219 ꢁC, yield 0.079 g (5%). ½aꢂ ꢀ63.1 (c
7.13. (+)-[(2R)-1-Benzyl-4-(4-methoxybenzyl)piperazin-
2-yl]methanol (3d)
589
0.535, CH3OH). C12H12N2O3 (232.24). Calcd C 62.06, H
5.21, N 12.06, found C 62.33, H 5.09, N 12.22. MS (EI):
m=z (%) ¼ 232 (M, 89), 155 (Mꢀphenyl, 11), 105
(PhCHO, 100), 91 (benzyl, 22), 77 (phenyl, 28). IR
(KBr): m (cmꢀ1) ¼ 3317 (br, NH), 2871 (m, C–H), 1666
(s, C@O), 1434 (m, C–H), 764 and 698 (m, aryl-C–H).
1H NMR (CDCl3): d ¼ 3:91 (dd, J ¼ 16:9=4:7 Hz, 1H,
3-H), 4.16 (d, J ¼ 17:1 Hz, 1H, 3-H), 4.26 (t, J ¼ 8:9 Hz,
1H, 7-H), 4.43 (dd, J ¼ 8:8=7:0 Hz, 1H, 7-H), 4.50 (br t,
J ¼ 7:5 Hz, 1H, 6-H), 6.27 (s, 1H, 9-H), 6.31 (br s, 1H,
NH), 7.33–7.40 (m, 5H, arom).
Under N2 LiAlH4 powder (0.236 g, 6.2 mmol) was added
to a stirred solution of 6d (mixture of cis/trans isomers,
0.219 g, 0.62 mmol) in THF (50 mL). The reaction mix-
ture was heated to reflux for 72 h. Under N2 atmosphere
and cooling (ice bath) water (0.5 mL), 3 N NaOH
(0.5 mL), and again water (0.5 mL) were successively
added. The suspension was heated to reflux for 30 min.
After the mixture was cooled to room temperature, the
precipitate was filtered off, and the solvent removed
under reduced pressure. The residue was dissolved in
CH2Cl2 (15 mL) and the solution was washed with 1 N
NaOH (2 ꢃ 7 mL) and brine (7 mL). The aqueous layer
was extracted with CH2Cl2 (3 ꢃ 10 mL). The organic
layers were combined, dried with Na2SO4 and concen-
trated in vacuo. Purification of the residue by flash
chromatography (2 cm, ethyl acetate, 5 mL, Rf ¼ 0:21)
furnished 3d as a pale yellow oil, yield 0.149 g (73%).
(b) Catalytic hydrogenation: Pd/C (10%, 0.20 g) was
a solution of cis-7/trans-7 (cis-7/trans-
added to
7 ¼ 30:70, 2.12 g, 6.91 mmol) in CH3OH (60 mL). The
suspension was stirred under a H2 atmosphere (balloon)
at room temperature for 8 h. The mixture was filtered
through a pad of Celiteꢂ AFA and the filtrate was
concentrated in vacuo. Flash chromatography (6 cm,
ethyl acetate/ethanol 5:1, 20 mL) of the residue
yielded cis-6m/trans-6m as a colorless solid, yield 1.21 g
(75%).
½aꢂ
þ30.7 (c 0.59, CH2Cl2). C20H26N2O2 (326.44).
589
Calcd C 73.59, H 8.03, N 8.58, found C 73.41, H 8.59, N
7.90. MS (EI): m=z (%) ¼ 295 (MꢀCH2OH, 25), 121 (4-
methoxybenzyl, 100), 91 (benzyl, 21). MS (ESI): m=z
(%) ¼ 327 (MHþ, 100). IR (film): m (cmꢀ1) ¼ 3385 (br,
OH), 2934 (m, C–H), 2810 (m, C–H), 1453 (m, C–H),
740 and 699 (m, aryl-C–H). 1H NMR (CDCl3):
d ¼ 2:32–2.40 (m, 1H, 5-H or 6-H), 2.42–2.51 (m, 2H, 5-
H and 6-H), 2.58–2.67 (m, 3H, 2-H and 3-H), 2.92–3.00
(m, 1H, 6-H or 5-H), 3.42 (s, 2H, H3COPhCH2N), 3.47
(d, J ¼ 13:5 Hz, 1H, PhCH2N), 3.58 (br d, J ¼ 10:9 Hz,
1H, CH2OH), 3.80 (s, 3H, OCH3), 3.97 (d, J ¼ 13:5 Hz,
1H, PhCH2N), 4.05 (br d, J ¼ 10:8 Hz, 1H, CH2OH),
6.85 (d, J ¼ 8:5 Hz, 2H, 30-H and 50-H [H3COPh]), 7.20
(d, J ¼ 8:7 Hz, 2H, 20-H and 60-H [H3COPh]), 7.21–7.32
(m, 5H, arom). The signal for the proton of the OH
group could not be detected. 13C NMR (CDCl3):
d ¼ 49:8 and 52.4 (2C, C-5, C-6), 55.2 (1C, OC3), 55.9
7.12. (+)-[(2R)-1-Benzyl-4-methylpiperazin-2-yl]metha-
nol (3a)
Under N2 LiAlH4 powder (0.45 g, 11.8 mmol) was added
to a stirred solution of 6a (mixture of cis/trans isomers,
0.292 g, 1.18 mmol) in THF (50 mL). The reaction mix-
ture was heated to reflux for 87 h. Under N2 atmosphere
and cooling (ice bath) water (0.5 mL), 3 N NaOH
(0.5 mL), and again water (0.5 mL) were successively
added. The suspension was refluxed for 30 min. After
the mixture was cooled to room temperature, the pre-
cipitate was filtered off and the solvent removed under
reduced pressure. The residue was purified by flash

S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
3307
(1C, C-3), 58.0 (1C, NCH2Ph), 58.5 (1C, C-2), 62.2 (1C,
CH2OH), 62.5 (1C, H3COPhCH2N), 113.7 (2C, C-30
and C-50 [H3COPh]), 127.1 (1C, C-40 [bn]), 128.3 (2C, C-
30 and C-50 [bn]), 128.8 (2C, C-20 and C-60 [bn]), 129.6
(1C, C-10 [H3COPh]), 130.3 (2C, C-20 and C-60
[H3COPh]), 138.6 (1C, C-10 [bn]), 158.8 (1C, C-40
[H3COPh]).
sively added. The suspension was heated to reflux for
30 min. After the mixture was cooled to room temper-
ature, the precipitate was filtered off, and the solvent
removed under reduced pressure. The residue was dis-
solved in CH2Cl2 (15 mL) and the solution was washed
with 1 N NaOH (2 ꢃ 7 mL) and brine (7 mL). The
aqueous layer was extracted with CH2Cl2 (3 ꢃ 10 mL).
The organic layers were combined, dried with Na2SO4
and concentrated in vacuo. Purification of the residue by
flash chromatography (2 cm, ethyl acetate/ethanol, 5:1,
5 mL, Rf ¼ 0:30) furnished 3f as a viscous oil, which
solidified in a refrigerator, mp 63–65 ꢁC, yield 0.099 g
7.14. (+)-[(2R)-1-Benzyl-4-(2-phenylethyl)piperazin-2-
yl]methanol (3e)
(74%). ½aꢂ
þ14.1 (c 0.50, CH2Cl2). C18H28N2O
589
Under N2 LiAlH4 powder (0.268 g, 7.1 mmol) was added
to a stirred solution of 6e (mixture of cis/trans isomers,
0.237 g, 0.71 mmol) in THF (50 mL). The reaction mix-
ture was heated to reflux for 72 h. Under N2 atmosphere
and cooling (ice bath) water (0.5 mL), 3 N NaOH
(0.5 mL) and again water (0.5 mL) were successively
added. The suspension was heated to reflux for 30 min.
After the mixture was cooled to room temperature, the
precipitate was filtered off, and the solvent removed
under reduced pressure. The residue was dissolved in
CH2Cl2 (15 mL) and the solution was washed with 1 N
NaOH (2 ꢃ 7 mL) and brine (7 mL). The aqueous layer
was extracted with CH2Cl2 (3 ꢃ 10 mL). The organic
layers were combined, dried with Na2SO4 and concen-
trated in vacuo. Purification of the residue by flash
chromatography (3 cm, ethyl acetate, 10 mL, Rf ¼ 0:24)
furnished 3e as a pale yellow, viscous oil, yield 0.178 g
(288.43). Calcd C 74.96, H 9.78, N 9.71, found C 74.34,
H 10.36, N 9.43. MS (EI): m=z (%) ¼ 257 (MꢀCH2OH,
100), 175 (MꢀC6H10ꢀCH2OH, 11), 166 (Mꢀben-
zylꢀCH2OH, 12), 91 (benzyl, 52), 83 (cyclohexyl, 8). MS
(CI): m=z (%) ¼ 289 (MHþ, 100). IR (film):
m
(cmꢀ1) ¼ 3372 (br, OH), 2927 and 2852 (s, C–H), 2811
(m, CO–H), 1451 (m, C–H), 1155 (m, C–OH), 737 and
1
698 (m, aryl-C–H). H NMR (CDCl3): d ¼ 1:15–1.26
(m, 5H, cyclohexyl), 1.60–1,64 (m, 1H, 4-Hcyclohexyl),
1.77–1.86 (m, 4H, cyclohexyl), 2.23–2.31 (m, 1H,
NCHcyclohexyl), 2.44–2.54 (m, 2H, 5-H and 6-H), 2.59–
2.67 (m, 2H, 2-H and 5-H or 6-H), 2.74–2.81 (m, 2H, 3-
H), 2.94–3.02 (m, 1H, 6-H or 5-H), 3.47 (d, J ¼ 13:2 Hz,
1H, PhCH2N), 3.62 (dd, J ¼ 11:4=2:5 Hz, 1H, CH2OH),
3.95 (d, J ¼ 13:6 Hz, 1H, PhCH2N), 4.13 (dd,
J ¼ 11:4=2:7 Hz, 1H, CH2OH), 7.21–7.32 (m, 5H,
arom). The signal for the proton of the OH group could
not be detected. 13C NMR (CDCl3): d ¼ 26:0 (2C, C-3,
and C-5 cyclohexyl), 26.4 (1C, C-4 cyclohexyl), 28.8 and
28.9 (2C, C-2, and C-6 cyclohexyl), 48.8 and 50.6 (2C,
C-5, C-6), 52.8 (1C, C-3), 58.4 (1C, NCH2Ph), 58.6 (1C,
C-2), 63.0 (1C, CH2OH), 63.7 (1C, C-1 cyclohexyl),
127.2 (1C, C-4 arom), 128.5 (2C, C-3 and C-5
arom), 129.1 (2C, C-2 and C-6 arom), 138.8 (1C, C-1
arom).
(82%). ½aꢂ
þ15.5 (c 0.545, CH2Cl2). C20H26N2O
589
(310.44). Calcd C 77.38, H 8.44, N 9.02, found C 76.67,
H 8.37, N 8.75. MS (EI): m=z (%) ¼ 279 (MꢀCH2OH,
100), 219 (Mꢀbenzyl, 38), 189 (MꢀbenzylꢀCH2OH,
25), 91 (benzyl, 56). MS (ESI): m=z (%) ¼ 311 (MHþ,
100). IR (film): m (cmꢀ1) ¼ 3366 (br, OH), 2942 (m, C–H),
2810 (m, CO–H), 1452 (m, C–H), 1152 (m, C–OH), 737
1
and 697 (m, aryl-C–H). H NMR (CDCl3): d ¼ 2:42–
2.51 (m, 2H, 5-H and 6-H), 2.56–2.68 (m, 5H, 2-H, 3-H,
5-H, or 6-H and NCH2CH2Ph), 2.75–2.83 (m, 3H, 3-H
and NCH2CH2Ph), 2.95–3.00 (m, 1H, 6-H or 5-H), 3.45
(d, J ¼ 13:3 Hz, 1H, PhCH2N), 3.61 (dd, J ¼
11:5=2:1 Hz, 1H, CH2OH), 4.00 (d, J ¼ 13:0 Hz, 1H,
PhCH2N), 4.08 (dd, J ¼ 11:3=2:8 Hz, 1H, CH2OH),
7.18–7.33 (m, 10H, arom). The signal for the proton of
the OH group could not be detected. 13C NMR (CDCl3):
d ¼ 33:5 (1C, NCH2CH2Ph), 50.0 and 52.6 (2C, C-5, C-
6), 56.3 (1C, C-3), 58.0 (1C, NCH2Ph), 58.7 (1C, C-2),
60.3 (1C, NCH2CH2Ph), 62.2 (1C, CH2OH), 126.1 and
127.1 (2 C, 2 ꢃ C-4 arom), 128.3 and 128.4 (4C, 2 ꢃ C-3
and 2 ꢃ C-5 arom), 128.6 and 128.8 (4C, 2 ꢃ C-2 and
2 · C-6 arom), 138.4 and 140.0 (2C, 2 ꢃ C-1 arom).
7.16. (+)-[(2R)-1-Benzyl-4-(2-hydroxyethyl)piperazin-2-
yl]methanol (3i)
To a stirred solution of 1 M LiAlH4 in Et2O (15.1 mL,
15.1 mmol) and THF (10 mL) was added dropwise a
solution of 6i (mixture of cis/trans isomers, 0.417 g,
1.51 mmol) in THF (30 mL) under N2 atmosphere. The
mixture was heated to reflux for 96 h. Under N2 atmo-
sphere and cooling (ice bath) water (0.4 mL), 3 N NaOH
(0.4 mL) and again water (0.4 mL) were successively
added. The suspension was heated to reflux for 30 min.
After the mixture was cooled to room temperature,
the precipitate was filtered off, and the solvent removed
under reduced pressure. Purification of the residue by
flash chromatography (3 cm, ethanol, 7 mL, Rf ¼ 0:25)
gave 3i as a pale yellow, viscous oil, yield 0.210 g (55%).
7.15. (+)-[(2R)-1-Benzyl-4-cyclohexylpiperazin-2-
yl]methanol (3f)
½aꢂ
þ30.0 (c 0.415, CH2Cl2). C14H22N2O2 (250.34).
589
Under N2 LiAlH4 powder (0.176 g, 4.64 mmol) was
added to a stirred solution of 6f (mixture of cis/trans
isomers, 0.146 g, 0.464 mmol) in THF (30 mL). The
reaction mixture was heated to reflux for 72 h. Under N2
atmosphere and cooling (ice bath) water (0.5 mL), 3 N
NaOH (0.5 mL) and again water (0.5 mL) were succes-
HRMS: calcd 250.1681, found 250.1682 (þ0.1 ppm),
HRMS: calcd for MꢀCH2OH (C13H19N2O) 219.1497,
found 219.1497 (þ/ꢀ0 ppm). MS (EI): m=z (%) ¼ 219
(MꢀCH2OH, 46), 174 (benzylpiperazine, 6), 128
(MꢀbenzylꢀCH2OH, 11), 91 (benzyl, 100). MS (CI):
m=z (%) ¼ 251 (MHþ, 100). IR (film): m (cmꢀ1) ¼ 3375

3308
S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
(br, OH), 2943 and 2820 (m, C–H), 1446 (m, C–H), 1151
(m, C–OH), 738 and 700 (m, aryl-C–H). 1H NMR
(CDCl3): d ¼ 2:30 (td, J ¼ 11:6=2:4 Hz, 1H, 5-H or 6-H),
2.39 (td, J ¼ 11:6=2:6 Hz, 1H, 6-H or 5-H), 2.51–2.57 (m,
3H, 3-H and NCH2CH2OH), 2.60–2.68 (m, 2H, 2-H and
5-H or 6-H), 2.79 (ddd, J ¼ 10:6=2:8=1:8 Hz, 1H, 3-H),
2.89 (ddd, J ¼ 11:6=5:1=2:5 Hz, 1H, 6-H or 5-H), 3.35 (d,
J ¼ 13:1 Hz, 1H, PhCH2N), 3.58 (dd, J ¼ 11:3=2:4 Hz,
1H, CH2OH), 3.63 (t, J ¼ 5:3 Hz, 2H, NCH2CH2OH),
3.99 (dd, J ¼ 11:3=4:0 Hz, 1H, CH2OH), 4.07 (d,
J ¼ 13:1 Hz, 1H, PhCH2N), 7.24–7.36 (m, 5H, arom).
The signals for the protons of the OH groups could not
be detected. 13C NMR (CDCl3): d ¼ 50:3 and 52.3 (2C,
C-5, C-6), 55.3 (1C, C-3), 57.90 (1C, NCH2Ph), 57.93
(1C, NCH2CH2OH), 59.5 (1C, NCH2CH2OH), 59.8
(1C, C-2), 61.2 (1C, CH2OH), 127.2 (1C, C-40), 128.4
(2C, C-30 and C-50), 128.8 (2C, C-20 and C-60), 138.2 (1C,
C-10).
7.18. (+)-[(2R)-1-Benzylpiperazin-2-yl]methanol (3m)
Three LiAlH4 pellets (2.353 g, 61.9 mmol) were added to
a stirred solution of 6m (mixture of cis/trans isomers,
1.346 g, 5.8 mmol) in THF (200 mL). The suspension
was heated to reflux for 96 h. Under N2 atmosphere and
cooling (ice bath) water (2 mL), 3 N NaOH (2.0 mL),
and again water (2 mL) were successively added. The
suspension was heated to reflux for 30 min. After the
mixture was cooled to room temperature, the precipitate
was filtered off, and the solvent removed under reduced
pressure. The residue was characterized without further
purification and was converted into 3n.
Compound 3m: Pale yellow solid, yield 1.196 g (>99%).
C12H18N2O (206.29). MS (EI): m=z (%) ¼ 175
(MꢀCH2OH, 81), 91 (benzyl, 100). MS (CI): m=z
(%) ¼ 207 (MHþ, 100). IR (film): m (cmꢀ1) ¼ 3362 (br, O–
H), 2943 (s, C–H), 2814 (s, OCH3), 1454 (m, C–H), 1128
(m, C–OH), 737 and 700 (m, aryl-C–H). 1H NMR
(CDCl3): d ¼ 2:24–2.32 (m, 1H, 3-H, 5-H, or 6-H), 2.44–
2.50 (m, 1H, 2-H, 3-H, 5-H, or 6-H), 2.75–2.81 (m, 1H,
2-H, 3-H, 5-H, or 6-H), 2.84–2.91 (m, 2H, 2-H, 3-H, 5-
H, or 6-H), 2.98–3.06 (m, 2H, 3-H, 5-H, or 6-H), 3.35 (d,
J ¼ 13:5 Hz, 1H, PhCH2N), 3.58 (dd, J ¼ 11:1=2:7 Hz,
1H, CH2OH), 4.03 (dd, J ¼ 11:4=3:8 Hz, 1H, CH2OH),
4.06 (d, J ¼ 13:8 Hz, 1H, PhCH2N), 7.23–7.37 (m, 5H,
arom). The signals for the protons of the OH group and
the NH group could not be detected.
7.17. (–)-[(2R)-1-Benzyl-4-(3-hydroxypropyl)piperazin-
2-yl]methanol (3j)
To a stirred solution of 1 M LiAlH4 in Et2O (5.3 mL,
5.3 mmol) and THF (10 mL) was added dropwise a
solution of 6j (mixture of cis/trans isomers, 0.154 g,
0.53 mmol) in THF (30 mL) under N2 atmosphere. The
mixture was heated to reflux for 96 h. Under N2 atmo-
sphere and cooling (ice bath) water (0.2 mL), 3 N NaOH
(0.2 mL) and again water (0.2 mL) were successively
added. The suspension was heated to reflux for 30 min.
After the mixture was cooled to room temperature, the
precipitate was filtered off, and the solvent removed
under reduced pressure. Purification of the residue by
flash chromatography (2 cm, ethanol, 5 mL, Rf ¼ 0:27) fur-
nished 3j as a colorless, viscous oil, yield 0.074 g (53%).
7.19. (+)-Ethyl 2-[(3R)-4-benzyl-3-(hydroxymethyl)-
piperazin-1-yl]acetate (3n)
Na2CO3 (1.01 g, 9.54 mmol) and ethyl bromoacetate
(1.1 mL, 9.54 mmol) were added to a stirred solution of
3m (1.968 g, 9.54 mmol) in THF (180 mL). The reaction
mixture was heated to reflux for 17 h. After the mixture
was cooled to room temperature, Na2CO3 was filtered
off, and the solvent removed under reduced pressure.
Flash chromatography of the residue (6 cm, ethyl ace-
tate/acetone, 8:2, 20 mL, Rf ¼ 0:31) afforded 3n as a
½aꢂ þ34.8 (c 0.775, CH2Cl2). C15 H24N2O2 (264.37).
589
HRMS: calcd for MꢀCH2OH (C14H21N2O) 233.1654,
found 233.1652 (ꢀ0.2 ppm). MS (EI): m=z (%) ¼ 264 (M,
1), 233 (MꢀCH2OH, 100), 174 (benzylpiperazine, 8), 142
(MꢀbenzylꢀCH2OH, 82), 91 (benzyl, 62). MS (CI): m=z
(%) ¼ 265 (MHþ, 100), 233 (MꢀCH2OH, 13). IR (film): m
(cmꢀ1) ¼ 3377 (br, OH), 2943 and 2817 (m, C–H), 1452
(m, C–H), 1148 (m, C–OH), 740 and 700 (m, aryl-C–H).
1H NMR (CDCl3): d ¼ 1:71 (‘quint’, J ¼ 5:6 Hz, 2H,
NCH2CH2CH2OH), 2.18 (td, J ¼ 10:1=2:3 Hz, 1H, 5-H
or 6-H), 2.33 (td, J ¼ 10:6=2:8 Hz, 1H, 6-H or 5-H), 2.44
(dd, J ¼ 11:2=9:0 Hz, 1H, 3-H), 2.57–2.61 (m, 3H, 2-H
and NCH2CH2CH2OH), 2.71–2.75 (m, 1H, 5-H or 6-H),
2.82–2.89 (m, 2H, 3-H and 6-H or 5-H), 3.28 (d,
viscous oil; yield 1.699 g (61%), ½aꢂ
ꢀ12.2 (c 1.045,
589
CH2Cl2). C16H24N2O3 (292.38). Calcd C 65.73, H 8.27, N
9.58, found C 64.95, H 8.23, N 9.38. MS (EI): m=z
(%) ¼ 292 (M, 1), 261 (MꢀH2OH, 71), 219
(MꢀCO2C2H5, 9), 170 (261ꢀbenzyl, 100), 91 (benzyl,
47). MS (CI): m=z (%) ¼ 293 (MHþ, 100). IR (film): m
(cmꢀ1) ¼ 3418 (br, O–H), 2937 (m, C–H), 2816 (m, C–H),
1747 (s, C@O), 1455 (m, C–H), 1168 (s, C–OH), 748 and
700 (m, aryl-C–H). 1H NMR (CDCl3): d ¼ 1:27 (t,
J ¼ 7:2 Hz, 3H, OCH2CH3), 2.37–2.53 (m, 2H, 5-H and
6-H), 2.63–2.73 (m, 3H, 2-H, 3-H, and 5-H or 6-H), 2.79–
2.83 (m, 1H, 2-H), 2.95 (ddd, J ¼ 11:3=6:1=2:6 Hz, 1H,
6-H or 5-H), 3.14 (d, J ¼ 16:5 Hz, 1H, NCH2CO2Et),
3,21 (d, J ¼ 16:8 Hz, 1H, NCH2CO2Et), 3.43 (d,
J ¼ 13:3 Hz, 1H, PhCH2N), 3.60 (dd, J ¼ 11:4=2:4 Hz,
1H, CH2OH), 4.02 (d, J ¼ 13:2 Hz, 1H, PhCH2N), 4.06
(dd, J ¼ 11:5=4:0 Hz, 1H, CH2OH), 4.19 (q, J ¼ 7:2 Hz,
2H, OCH2CH3), 7.23 –7.32 (m, 5H, arom). The signal for
the proton of the OH group could not be detected. 13C
NMR (CDCl3): d ¼ 14:2 (1C, OCH2CH3), 49.8 and 52.4
(2C, C-5, C-6), 55.5 (1C, C-2), 57.9 (1C, PhCH2N), 59.0
J ¼ 13:2 Hz, 1H, PhCH N), 3.54 (dd, J ¼ 11:6=2:5 Hz,
2
1H, CH2OH), 3.79 (t, J ¼ 5:2 Hz, 2H, NCH2CH2-
CH2OH), 3.98 (dd, J ¼ 11:2=4:2 Hz, 1H, CH2OH), 4.06
(d, J ¼ 13:3 Hz, 1H, PhCH2N), 7.23–7.35 (m, 5H, arom).
The signals for the protons of the OH groups could
not be detected. 13C NMR (CDCl3): d ¼ 27:2 (1C,
NCH2CH2CH2OH), 50.4 and 50.7 (2C, C-5, C-6), 55.5
(1C, C-3), 57.9 (1C, NCH2Ph), 58.4 (1C, NCH2CH2-
CH2OH), 60.1 (1C, C-2), 60.9 (1C, CH2OH), 64.0
(1C, NCH2CH2CH2OH), 127.2 (1C, C-40), 128.4 (2C,
C-30 and C-50), 128.8 (2C, C-20 and C-60), 138.2 (1C,
C-10).

S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
3309
(1C, C-3), 59,3 (1C, NCH2CO2Et), 60.7 (1C,
OCH2CH3), 61.5 (1C, CH2OH), 127.2 (1C, C-40), 128.4
(2C, C-30 and C-50), 128.9 (2C, C-20 and C-60), 138.1 (1C,
C-10), 170.2 (1C, C@O).
2H, arom). 19F NMR (CDCl3): d ¼ ꢀ71:80 (s, 3F, CF3,
2.7% intensity), ꢀ71.83 (s, 3F, CF3, 97.3% intensity).
HPLC:
MeOH/H2O ¼ 75: 25, 0.8 mL/min.
t((R,S)-8) ¼ 49 min,
t((R,R)-8) ¼ 47.1 min,
7.20. (2S)-{[(2R)-1-Benzyl-4-(ethoxycarbonylmethyl)pip-
erazin-2-yl]methyl}-3,3,3-trifluoro-2-methoxy-2-phenyl-
propionate [(R,S)-8]
8. Receptor binding studies
8.1. General
A solution of 3n (33 mg, 0.114 mmol), triethylamine
(15 lL, 0.114 mmol), 4-(dimethylamino)pyridine (14 mg,
0.114 mmol) and (R)-(ꢀ)-3,3,3-trifluoro-2-methoxy-2-
phenylpropionyl chloride (20 lL, 0.108 mmol) in CH2Cl2
(5 mL) was heated to reflux for 7 h. After the mixture was
cooled to room temperature, the mixture was washed
with a saturated solution of NaHCO3 (5 mL) and water
(5 mL). The organic layer was dried (Na2SO4) and
evaporated in vacuo. About 15 mg of the residue was
Homogenizer: PotterꢂS (B. Braun Biotech Interna-
tional). Ultraturrax: Euroturraxꢂ T20 (Ika Labortech-
nik). Centrifuge: High speed cooling centrifuge model
J2-HS (Beckman). Filter: Whatman glass fiber filters GF/
B, presoaked in 0.5% polyethylenimine in water for 2 h at
4 ꢁC before use. Filtration was performed with a Brandel
24-well cell harvester. Scintillation cocktail: Rotiscint
Eco Plus (Roth). Liquid scintillation analyzer: TriCarb
2100 TR (Canberra Packard), counting efficiency 66%.
All experiments were carried out in triplicates. IC50 val-
ues were determined in competition experiments with at
least six concentrations of test compounds and were
calculated with the program GraphPad Prismꢂ 3.0
(GraphPad Software) by nonlinear regression analysis.
Ki values were calculated according to Cheng and Prus-
off.19 The Ki values are given as mean value ꢁ SEM from
three independent experiments.
1
investigated by H and 19F NMR and by HPLC, the
remainder was purified by flash chromatography (1 cm,
petroleum ether/ethyl acetate 3:7, 1 mL, Rf ¼ 0:52) to
provide (R,S)-8. C26H31F3N2O5 (508.54). 1H NMR
(CDCl3): d ¼ 1:25 (t, J ¼ 7:2 Hz, 3H, OCH2CH3), 2.32–
2.47 (m, 3H, 3-H, 5-H and/or 6-H), 2.63–2.81 (m, 3H, 2-
H, 3-H, 5-H, and/or 6-H), 2.86–2.88 (m, 1H, 2-H, 3-H, 5-
H, or 6-H), 3.12 (d, J ¼ 16:8 Hz, 1H, NCH2CO2Et), 3.18
(d, J ¼ 16:8 Hz, 1H, NCH2CO2Et), 3.35 (d, J ¼ 13:5 Hz,
1H, PhCH2N), 3.55 (s, 3H, OCH3), 3.95 (d, J ¼ 13:4 Hz,
1H, PhCH2N), 4.16 (q, J ¼ 7:1 Hz, 2H, OCH2CH3), 4.57
(br d, J ¼ 4:8 Hz, 2H, CH2OC@O), 7.22–7.27 (m, 5H,
arom), 7.35–7.40 (m, 3H, arom), 7.52–7.55 (m, 2H,
arom). 19F NMR (CDCl3): d ¼ ꢀ71:80 (s, 3F, CF3,
96.7% intensity), ꢀ71.83 (s, 3F, CF3, 3.3% intensity).
8.2. r1-Receptor binding assay
For the r1-assay guinea pig brain membranes were pre-
pared as described in Ref. 20. The test was performed
with the radioligand [3H]-(þ)-pentazocine (1036 GBq/
mmol; NENe Life Science Products). The thawed
membrane preparation (about 150 lg of protein) was
incubated with various concentrations of the test com-
pound, 3 nM [3H]-(þ)-pentazocine, and buffer (50 mM
Tris–HCl, pH 7.4) in a total volume of 500 lL for 120 min
at 37 ꢁC. The incubation was terminated by rapid filtra-
tion through Whatman GF/B filters using a cell har-
vester. After washing four times with 2 mL of cold buffer
3 mL of scintillation cocktail were added to the filters.
After at least 8 h bound radioactivity trapped on the fil-
ters was counted in a liquid scintillation analyzer. Non-
specific binding was determined with 10 lM haloperidol.
HPLC:
t((R,S)-8) ¼ 49 min,
t((R,R)-8) ¼ 47.1 min,
MeOH/H2O .¼ 75:25, 0.8 mL/min.
7.21. (2R)-{[(2R)-1-Benzyl-4-(ethoxycarbonylmethyl)pip-
erazin-2- yl]methyl}-3,3,3-trifluoro-2-methoxy-2-phenyl-
propionate [(R,R)-8]
A solution of 3n (30 mg, 0.103 mmol), triethylamine
(14 lL, 0.103 mmol), 4-(dimethylamino)pyridine (13 mg,
0.103 mmol) and (S)-(þ)-3,3,3-trifluoro-2-methoxy-2-
phenylpropionyl chloride (18 lL, 0.098 mmol) in CH2Cl2
(5 mL) was heated to reflux for 7 h. After the mixture was
cooled to room temperature, the reaction solution was
washed with a saturated solution of NaHCO3 (5 mL) and
water (5 mL). The organic layer was dried (Na2SO4) and
evaporated in vacuo. About 14 mg of the residue was
8.3. r2-Receptor binding assay
1
investigated by H and 19F NMR and by HPLC, the
For the r2-assay rat liver membranes were prepared as
described in Ref. 20. The membrane preparation (about
60 lg of protein) was incubated with 3 nM [3H]-ditolyl-
guanidine (2220 GBq/mmol, American Radiolabeled
Chemicals, Inc.) and different concentrations of test
compounds in buffer (50 mM Tris–HCl, pH 8.0) in the
presence of 100 nM (þ)-pentazocine. The total volume
was 250 lL. The incubation (120 min, 25 ꢁC) was stopped
by addition of 2 mL of ice-cold buffer (10 mM Tris–HCl,
pH 8.0) followed by rapid filtration through presoaked
Whatman GF/B filters using a cell harvester. After the
sample was washed three times with 2 mL of cold buffer,
a total volume of 3 mL of scintillation cocktail was added
remainder was purified by flash chromatography (1 cm,
petroleum ether/ethyl acetate 3:7, 1 mL, Rf ¼ 0:52) to
provide (R,R)-8. C26H31F3N2O5 (508.54). 1H NMR
(CDCl3): d ¼ 1:25 (t, J ¼ 7:2 Hz, 3H, OCH2CH3), 2.33–
2.46 (m, 3H, 3-H, 5-H and/or 6-H), 2.64–2.74 (m, 2H,
2-H, 3-H, 5-H, and/or 6-H), 2.79 –2.87 (m, 2H, 2-H,
3-H, 5-H, and/or 6-H), 3.12 (d, J ¼ 16:5 Hz, 1H,
NCH2CO2Et), 3.17 (d, J ¼ 16:4 Hz, 1H, NCH2CO2Et),
3.30 (d, J ¼ 13:7 Hz, 1H, PhCH2N), 3.55 (s, 3H, OCH3),
3.94 (d, J ¼ 13:2 Hz, 1H, PhCH2N), 4.16 (q, J ¼ 7:1 Hz,
2H, OCH2CH3), 4.56 (br s, 2H, CH2OC@O), 7.22–7.27
(m, 5H, arom), 7.36–7.41 (m, 3H, arom), 7.51–7.55 (m,

3310
S. Bed€urftig, B. W€unsch / Bioorg. Med. Chem. 12 (2004) 3299–3311
to the filters. After at least 8 h bound radioactivity
trapped on the filters was counted in a liquid scintillation
analyzer. Nonspecific binding was determined with
10 lM nonradiolabeled ditolylguanidine.
of scintillation cocktail were added to the filters. After at
least 8 h bound radioactivity trapped on the filters was
counted in a liquid scintillation analyzer. Nonspecific
binding was determined with 1 lM naloxone.17
8.4. Investigation of the affinity for the phencyclidine
binding site of the NMDA receptor
Acknowledgements
For the NMDA-assay pig brain membrane preparations
were used as receptor material. The test was performed
with the radioligand [3H]-(þ)-MK-801 (832.5GBq/mmol;
NENe Life Science Products). The thawed membrane
preparation (about 100 lg of the protein) was incubated
with various concentrations of test compounds, 2 nM
[3H]-(þ)-MK-801, and buffer (5mM Tris–acetate, 1 mM
EDTA, pH 7.5) in a total volume of 500 lL for 90min at
25ꢁC. The incubation was terminated by rapid filtration
through presoaked Whatman GF/C filters (1% polyethy-
lenimine in water for 3 h at 4 ꢁC) using a cell harvester.
After washing four times with 2 mL of cold buffer 3 mL of
scintillation cocktail were added to the filters. After at
least 8 h bound radioactivity trapped on the filters was
counted in a liquid scintillation analyzer. Nonspecific
binding was determined with 10lM (þ)-MK-801.17
Financial support of this work by the Deutsche Fors-
chungsgemeinschaft and the Fonds der Chemischen Industrie
is gratefully acknowledged. Thanks are also due to the
Degussa AG, Janssen-Cilag GmbH, and Bristol-Myers
Squibb for donation of chemicals and reference compounds.
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