Antimycobacterial activity of diphenylpyraline derivatives

Article abstract of DOI:10.1016/j.ejmech.2007.06.012

2-Substituted derivatives of diphenylpyraline and their 1-phenyl and 1-phenethyl analogues have been prepared in several steps from dihydropyridine-2(1H)-thiones. The structures of all new compounds have been confirmed by NMR spectroscopy. Their activity against Mycobacterium tuberculosis H₃₇Rv as well as their cytotoxicity against human cells (HEK-293) have been determined via in vitro assays. The antimycobacterial potency was in general increased by substitution in ring position 2. The most promising modifications were a 2-isopropyl derivative and a 1,2-diphenyl analogue.

Full text of DOI:10.1016/j.ejmech.2007.06.012

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 872e879
http://www.elsevier.com/locate/ejmech
Original article
Antimycobacterial activity of diphenylpyraline derivatives
*
Robert Weis , Johanna Faist, Ulrike di Vora, Klaus Schweiger, Barbara Brandner,
Andreas J. Kungl, Werner Seebacher
Institute of Pharmaceutical Sciences, Pharmaceutical Chemistry, Karl-Franzens-University, Universita¨tsplatz 1, A-8010 Graz, Austria
Received 6 December 2006; received in revised form 20 June 2007; accepted 21 June 2007
Available online 10 July 2007
Abstract
2-Substituted derivatives of diphenylpyraline and their 1-phenyl and 1-phenethyl analogues have been prepared in several steps from dihy-
dropyridine-2(1H )-thiones. The structures of all new compounds have been confirmed by NMR spectroscopy. Their activity against Mycobac-
terium tuberculosis H37Rv as well as their cytotoxicity against human cells (HEK-293) have been determined via in vitro assays. The
antimycobacterial potency was in general increased by substitution in ring position 2. The most promising modifications were a 2-isopropyl
derivative and a 1,2-diphenyl analogue.
Ó 2007 Elsevier Masson SAS. All rights reserved.
Keywords: 4-Alkoxypiperidine; Antimycobacterial activity; In vitro assay; Piperidin-4-ol; Synthesis
1. Introduction
antimycobacterial properties have not yet been reported.
Recently we published the synthesis of a number of
2-substituted derivatives of 1 [4]. This paper deals with
the preparation of some new analogues and with the in-
vestigation of the antimycobacterial activities of the so far
prepared 2-substituted diphenylpyraline derivatives. By com-
parison with the activity of 1 structureeactivity relationships
will be discussed.
Tuberculosis is the leading infectious cause of death to-
day afflicting more than 14 million and killing 1.7 million
people per year [1]. Due to the spreading of multi-drug re-
sistant strains new antimycobacterial and non-toxic drugs
are urgently needed [2]. The H1-antihistaminic agent diphe-
nylpyraline (1) has been proved to be far more active
against Mycobacterium tuberculosis than against Escherichia
coli and Staphylococcus aureus [3]. As outlined in Ref. [4]
many derivatives with different substitution on nitrogen or at
the aromatic ring system have been prepared, but their
2. Chemistry
Considering that enhanced lipophilicity was argued to in-
crease the antimycobacterial activity of H1-antihistamines
[3], we prepared 2-alkyl and 2-aryl derivatives of 1 as well
as the corresponding 1-phenyl analogues. Furthermore, some
1-phenethyl analogues of 1 were prepared. In contrast to the
syntheses of 2-unsubstituted diphenylpyraline derivatives
which have been summarized in Ref. [4] our method is based
on the conversion of easily available 4-amino-5,6-dihydropyr-
idine-2(1H)-thiones 2 and 3. The synthesis of 2-isopropyl and 2-
phenyl derivatives using this method has already been reported
[4]. Their 2,2-dimethyl analogues were prepared from the pyr-
idinethiones 2 and 13 [5] using slightly modified procedures.
Abbreviations: ATCC, American type culture collection; CC, Column
chromatography; CH3I, Iodomethane; CH2Cl2, Dichloromethane; DMAP, 4-
Dimethylaminopyridine; DMEM, Dulbecco‘s modified eagle medium; Ether,
Diethylether; EtOH, Ethanol; FCS, Fetal calf serum; HCl, Hydrochloride or
hydrogen chloride; HEK-293 cells, Human embryonic kidney 293 cells;
MABA, Microplate alamar blue assay; MeOH, Methanol; MIC, Minimum in-
hibitory concentration; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-
zolium bromide; NaOH, Sodium hydroxide; NMR, Nuclear magnetic
resonance; PBS, Phosphate-buffered saline; SDS, Sodium dodecylsulfate;
TAACF, Tuberculosis antimicrobial acquisition and coordinating facility.
* Corresponding author. Tel.: þ43 316 3805379; fax: þ43 316 3809846.
E-mail address: robert.weis@uni-graz.at (R. Weis).
0223-5234/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2007.06.012

R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
873
R3
N
Alkaline hydrolysis of 2 and 3 yielded the 4-hydroxy deriva-
R3
N
H
N
tives 4 and 5. The catalytic hydrogenation of 4 with Raney
nickel W-7 [6] afforded a mixture of the piperidinols cis-6
and trans-6, which were separated by column chromatography
[4]. By a similar procedure the piperidinol 7 was obtained
from 5. Since the methylation of 7 with iodomethane gave
quantitatively the quaternary salt 8, we converted cis-6,
trans-6 and 7 to their 1-methyl derivatives cis-9, trans-9 [4]
and 10 via a Leuckart reaction. The diphenylpyraline deriva-
tives cis-11, trans-11 [4] and 12 were obtained in good yields
by etherification with alkyl bromides (method A) in alkaline
medium (Scheme 1).
I
R2
R1
S
MeS
R2
R1
R2
R1
S
i
vi
OH
N(Me)2
N(Me)2
2,3,13-15
4,5
16-18
ii
vii
R3
N
H
R3
N
R2
R1
R2
R1
R4
R2
R1
N
iv
viii
The corresponding 1-phenyl substituted analogues were
prepared from 1-phenyl substituted 4-dimethylamino-pyridine-
thiones 13e15. The latter were obtained in a Dimroth rear-
rangement from 2-phenylimino-thiopyrane derivatives [7,8].
In contrast to their 1-unsubstituted analogues 2 and 3, com-
pounds 13e15 were stable against caustic soda. The replace-
ment of the 4-dimethylamino group by a hydroxy group
failed. However, their methoiodides 16e18 were successfully
hydrolyzed to the dihydropyridin-4(1H )-ones 19e21. Hydro-
genation of 19 and 20 with Raney nickel W-2 [9] afforded
the cis and trans configurated piperidin-4-ols 22 and 23, which
were separated by column chromatography [4]. When com-
pound 21 was treated that way, a large excess of catalyst was
required. Better results were obtained by the use of the more
active Raney nickel W-7. When the 1,2-diphenyl compound
20 was treated with that catalyst, the dihydropyridine ring
was cleaved and high amounts of a pentanol derivative were
formed [4]. But when its 2,2-dimethyl analogue 21 was stirred
at 70 ꢀC in an inert-gas atmosphere with Raney nickel W-7 the
methylthio group was selectively removed giving 25. Under
hydrogen pressure the same reaction afforded the piperidinol
24 in good yields. The latter was readily converted to ether
28 with bromodiphenylmethane (method A). However, the
cis and trans forms of compounds 22 and 23 were e in order
to circumvent N-substitution e rather etherified with diphenyl-
methanol (method B) to give the cis and trans forms of 26 and
27 [4].
OH
OH
H
H
O
6,7,29
9,10,22-24,30,32,38
19-21, 25
v
v
iii
R3
R2
N
R3
N
Me
Me
I
R2
R1
N
Me
Me
R1
OCH(Ph)2
1,11,12,26-28,31,33
OCH(Ar)2
H
H
H
OH
8
34-37
Ar = 4-chlorophenyl
R4
R1
H
iPr
Me
R2
H
H
Me
R3
Me
H
Compound
--
--
--
--
--
--
--
--
--
1,34,38
2,4,cis-6
3,5,7
H
H
iPr
H
iPr
H
iPr
Me
H
trans-6
Me
Me
Me
cis-9,cis-11,cis-35
trans-9,trans-11
10,12
13,16,19,cis-22,cis-26
14,17,20,cis-23,cis-27
15,18,21,24,28
Me
iPr
Ph
Me
H
H
Me
Ph
Ph
Ph
--
MeS
MeS
MeS
--
--
H
--
--
--
iPr
Ph
Me
H
H
Me
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
--
19
20
21
The 1-phenethyl derivative 31 was prepared in two steps
from commercially available 4-piperidinol (29), whereas its 2-
isopropyl analogue cis-33 was obtained from cis-6. The piperi-
dinols 29 and cis-6 were treated with phenethyl bromide in
aprotic solvent giving the corresponding 1-alkyl derivatives 30
and cis-32 in good yields. The formation of a quaternary
Me
iPr
Ph
Me
H
trans-22,trans-26
trans-23,trans-27
25
29
H
H
Ph(CH2)2
Ph(CH2)2
30,31,36
cis-32,cis-33,cis-37
1
iPr
H
by-product was not observed in the H NMR spectrum of the
reaction mixture. Compounds 31 and cis-33 were afforded
by etherification of 30 and cis-32 with diphenylmethanol
(method B).
Since higher lipophilicity has been argued to increase the
antimycobacterial activity of diphenylpyraline derivatives
[3], selected bis-(4-chlorophenyl) analogues 34, cis-35, 36
and cis-37 have been prepared by reaction of the corresponding
piperidinols 38, cis-9, 30, and cis-32 with bis-(4-chlorophenyl)-
methanol (method B).
Scheme 1. Reagents and reaction conditions: (i) NaOH, 60e110 ꢀC, 24e72 h;
(ii) Raney nickel W-7, ethanol, 45 psi (H2), 20e50 ꢀC, 48e96 h; (iii) CH3I,
CHCl3, rt, 1 h; (iv) HCOOH, CH2O, 100 ꢀC or Ph(CH2)2Br, K2CO3, 110 ꢀC,
16 h; (v) method A: (Ph)2CHBr, K2CO3, 140 ꢀC, 3e16 h; method B:
(Ph)2CHOH or (Ar)2CHOH, p-toluene sulfonic acid, PhMe, 130e140 ꢀC,
6e18 h; (vi) CH3I, CHCl3, rt, 16e18 h; (vii) NaOH, 100 ꢀC, 2 h; (viii) Raney
nickel W-2 or W-7, ethanol, 30e45 psi (H2), rt, 6e16 h.
achieved by the method which is outlined in Ref. [4].
Through-space interactions were observed from protons in
ring position 4 or 6 to axial protons or protons of axial methyl
groups in ring position 2. For all newly synthesized 2-substituted
The assignment of most of the signals in the NMR spectra
and the structural elucidation of the new compounds were

874
R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
compounds chair conformation was deduced from those NOEs
and w-couplings in their NMR spectra.
activity, and the 2,4-trans isomer trans-27 (trans-27: 75% in-
hib.) was even the most active of the screened compounds.
Replacement of the 1-methyl groups of compounds 1 and
cis-11 by a 1-phenethyl group led to scarcely active analogues
(31, cis-33: ꢁ8% inhib.).
3. Pharmacology
The 2-unsubstituted bis-(4-chlorophenyl) derivatives 34
and 36 (34, 36: ꢂ56% inhib.) were far more active than their
analogues 1 and 31 indicating the remarkable positive influ-
ence of the chloro substitution. However, this observation
was not transferable to the 2-substituted bis-(4-chlorophenyl)
derivatives cis-35 and cis-37 (Table 1).
3.1. Antimycobacterial activity
The antimycobacterial activities were determined as micro-
plate assays using M. tuberculosis H37Rv (ATCC 27294)
within the tuberculosis antimicrobial acquisition and coordi-
nating facility (TAACF) screening program by means of the
microplate alamar blue assay (MABA) [13].
For diphenylpyraline (1) a maximum dose of 75 mg daily
for oral application has been documented [10]. In our cyto-
toxicity assay we determined a LC50 of 107.59 mg/ml for 1
(Table 1). Of the more active compounds the 2-isopropyl
derivatives cis-11 and trans-27 showed comparable cyto-
toxicity (cis-11: LC50 of 98.06 mg/ml, trans-27: LC50 of
111.67 mg/ml), whereas all of the more potent bis-(4-chloro-
phenyl) analogues 34e36 were distinctly more toxic (34e36:
LC50 ꢁ 25.46 mg/ml).
3.2. Cytotoxicity
Cytotoxicity was determined indirectly in a microplate as-
say using HEK-293 cells (human embryonic kidney 293 cells).
4. Results and discussion
5. Conclusion
For diphenylpyraline (1) the MIC (minimum inhibitory
concentration) of 64 mg/ml against M. tuberculosis H37Ra
has been published [3]. In our screening the antimycobacterial
activity was determined at a concentration of 6.25 mg/ml
against M. tuberculosis H37Rv. At this concentration diphenyl-
pyraline caused only 5% inhibition. Dimethylation or the in-
sertion of an isopropyl group trans to the benzhydryloxy
group in ring position 2 only slightly improved the activity
(12, trans-11: ꢁ18% inhib.), whereas the activity of the
2,4-cis isomer cis-11 was remarkable (cis-11: 68% inhib.).
Likewise, in the 1-phenyl series the 2,4-cis analogue cis-26
(cis-26: 36% inhib.) was more active than its 2,4-trans isomer
trans-26 and the 2,2-dimethyl analogue 28 (trans-26, 28: ꢁ7%
inhib.). Both 1,2-diphenyl substituted diphenylpyraline deriva-
tives cis-27 and trans-27 exhibited good antimycobacterial
This paper reports the synthesis and the screening of
the antimycobacterial activity of new analogues of diphenyl-
pyraline. The majority of its 2-substituted derivatives and its
bis-(4-chlorophenyl) analogues showed improved activity
against M. tuberculosis H37Rv. The most active chloro com-
pounds displayed high cytotoxicity. However, the 2-isopropyl
derivative of diphenylpyraline and its 1,2-diphenyl analogue
exhibited markedly increased antimycobacterial activity and
similar cytotoxicity compared to diphenylpyraline. These com-
pounds have potential as leads for a future study.
6. Experimental protocols
6.1. Instrumentation and chemicals
Melting points were measured using melting point appara-
tus Dr. Tottoli (Buchi 510) or on a digital melting point ap-
¨
Table 1
Antimycobacterial activity (alamar blue assay) and cytotoxicity of 4-alkoxy-
piperidines 1e37
paratus Electrothermal IA 9200 and are uncorrected. The
refractive indices were measured on a Abbe refractometer
(Carl Zeiss). IR spectra were measured by infrared spectrom-
eter system 2000 FT (Perkin-Elmer) in KBr discs; frequen-
cies are reported in cmꢃ1. NMR spectra were measured on
a Varian Gemini 200 or a Varian Inova 400 (298 K) using
5 mm tubes; TMS resonance was used as internal standard.
1H NMR (200 MHz or 400 MHz) and 13C NMR (50 MHz
Compound
%Inhibition
6.25 mg/ml
Cytotoxicity
(LC50) (mg/ml)
Diphenylpyraline HCl (1)
5
68
12
18
36
7
107.59
98.06
69.44
104.67
69.38
97.06
77.82
111.67
65.08
14.93
62.80
25.46
17.92
17.26
76.45
>576
cis-11
trans-11
12
cis-26
trans-26
cis-27
trans-27
28
1
or 100 MHz) spectra are reported in ppm, H and 13C reso-
39
75
3
nances were assigned using 1H,1H- and 1H,13C-correlation
spectra. Microanalyses were done at the Microanalytical Lab-
oratory at the Institute of Physical Chemistry, Vienna using
EA 1108 CHNS-O apparatus (Carlo Erba). Hydrogenations
were performed in an Erlenmeyer flask at atmospheric pres-
sure or in a Parr hydrogenation apparatus shaker type 3911.
Column chromatography (CC): silica gel 60 (Merck),
31
cis-33
34
8
0
65
74
56
0
cis-35
36
cis-37
Isoniazid (INH)
>99
˚
0.063e0.200 mm, poreediameter 60 A, column diameter

R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
875
30e40 mm, layer thickness 300e700 mm, rate of flow: 2 ml/
min. TLC: plates (Merck) silica gel 60 F254. Analyses indi-
cated by the symbols of the elements were within ꢄ0.4%
of the theoretical values.
piperidinol distilled in vacuo. The distillate was recrystal-
lized. Yield: 2.24 g (87%); m.p. (EtOH/H2O) ¼ 78 ꢀC; bp:
66 ꢀC/0.2 mbar; IR (KBr) 3254, 2930, 2843, 1452, 1364,
1
1260, 1146, 1117, 1072 cmꢃ1; H NMR (400 MHz, CDCl3)
d 1.10 (s, 3H, CH3ax), 1.13 (t, J ¼ 12.3 Hz, 1H, 3-Hax),
1.16 (s, 3H, CH3eq), 1.23 (dddd, J ¼ 13.0, 12.3, 10.0,
4.7 Hz, 1H, 5-Hax), 1.84 (ddd, J ¼ 12.3, 4.3, 2.0 Hz, 1H,
3-Heq), 1.90e1.98 (m, 1H, 5-Heq), 2.81 (ddd, J ¼ 13.4,
12.3, 2.9 Hz, 1H, 6-Hax), 2.96 (ddd, J ¼ 13.4, 4.7, 2.7 Hz,
1H, 6-Heq), 3.80e3.88 (m, 1H, 4-Hax) ppm; 13C NMR
(100 MHz, CDCl3) d 24.47 (CH3ax), 32.64 (CH3eq), 36.53
(C-5), 40.01 (C-6), 47.70 (C-3), 51.17 (C-2), 66.22 (C-4) ppm;
Anal. C7H15NO (C, H, N).
6.2. Syntheses
6.2.1. Dihydropyridin-4-ones 19, 20, 21, 25
The preparation of compounds 19 and 20 has already been
reported [8].
6.2.1.1. 2,2-Dimethyl-6-methylthio-1-phenyl-2,3-dihydropyri-
din-4(1H )-one (21). Compound 18 (8.04 g (20 mmol)) [7]
was refluxed in 100 ml 2 M NaOH for 2 h. The aqueous
phase was extracted with toluene repeatedly. The extract
was washed twice with H2O, dried with Na2SO4, evaporated
in vacuo, and the residue was recrystallized. Yield: 4.44 g
(89%); m.p. (EtOH) ¼ 158 ꢀC; IR (KBr) 2975, 1618, 1505,
1390, 1289, 1142, 1104, 768, 698 cmꢃ1; NMR: 1H NMR
(200 MHz, CDCl3) d 1.25 (s, 6H, (CH3)2), 2.22 (s, 3H,
SCH3), 2.58 (s, 2H, 3-H), 5.20 (s, 1H, 5-H), 7.21e7.45 (m,
5H, aromatic H) ppm; 13C NMR: (50 MHz, CDCl3)
d 15.95 (SCH3), 25.51 ((CH3)2), 50.46 (C-3), 60.89 (C-2),
95.30 (C-5), 128.88, 128.97, 130.81, 139.19 (aromatic C),
167.12 (C-6), 188.50 (C-4) ppm; Anal. C14H17NOS (C, H,
N, S).
6.2.2.2. (RS )-(ꢄ)-4-Hydroxy-1,1,2,2-tetramethylpiperidinium
iodide (8). To a solution of 1.29 g (10 mmol) of 7 in
50 ml of CHCl3, 1.42 g (10 mmol) of CH3I were added
dropwise. The reaction mixture was stirred for 6 h at
room temperature, then the solvent was removed in vacuo.
The residue was triturated with ethyl acetate, filtered with
suction and recrystallized. Yield: 1.40 g (98%); m.p.
(EtOH) ¼ 295 ꢀC; IR (KBr) 3363, 2941, 1473, 1416, 1160,
1067, 1055 cmꢃ1
;
1H NMR (400 MHz, CDCl3) d 1.36
(s, 3H, CH3eq), 1.39 (s, 3H, CH3ax), 1.63e1.73 (m, 1H,
5-Hax), 1.80 (dd, J ¼ 14.5, 9.5 Hz, 1H, 3-Hax), 1.84e1.97
(m, 2H, 3-Heq, 5-Heq), 2.94 (s, 3H, NCH3eq), 3.02 (s, 3H,
NCH3ax), 3.43 (dt, J ¼ 13.4, 4.6 Hz, 1H, 6-Heq), 3.49e3.67
(m, 1H, 6-Hax), 3.79e3.88 (m, 1H, 4-Hax), 4.99 (d,
J ¼ 4.0 Hz, 1H, OH) ppm; 13C NMR (100 MHz, CDCl3)
d 22.31 (CH3ax), 23.86 (CH3eq), 29.13 (C-5), 41.47 (C-3),
46.67 (NCH3ax), 47.75 (NCH3eq), 58.61 (C-6), 61.33 (C-4),
69.61 (C-2) ppm; Anal. C9H20INO (C, H, I, N).
6.2.1.2. 2,2-Dimethyl-1-phenyl-2,3-dihydropyridin-4(1H )-one
(25). Raney nickel W-7 (15 g) was added to a stirred solu-
tion of 3.71 g (15 mmol) of 21 in 50 ml of EtOH. The mix-
ture was refluxed at 70 ꢀC on an oil-bath for 72 h. The
catalyst was filtered off and the filtrate was evaporated.
The residue was triturated with CHCl3 and filtered. The sol-
vent was evaporated and the residue was recrystallized.
Yield: 2.62 g (86%); m.p. (heptane) ¼ 133 ꢀC; IR (KBr)
3050, 2967, 1637, 1572, 1488, 1429, 1365, 1296, 781,
6.2.2.3. (RS )-(ꢄ)-1,2,2-Trimethylpiperidin-4-ol (10). Formic
acid (85%) (4.0 g (75 mmol)) were added to 1.92 g
(15 mmol) of 7 at 0 ꢀC. The mixture was slowly warmed
until solution was obtained. Then 1.5 g (18 mmol) of a
37% aqueous solution of CH2O was added at room temper-
ature. The mixture was heated on a steam bath until the
generation of CO2 ceased. The solution was cooled, acidi-
fied with concentrated HCl and evaporated. The oily residue
was dissolved in 2 ml H2O, alkalified with a 25% solution
of NaOH and extracted three times with ether. The com-
bined organic layers were dried over Na2SO4. The solvent
was removed and the piperidinol distilled in vacuo. For
characterization purposes a part of the pure colourless oil
was treated with an equivalent amount of HCl in EtOH.
The solvent was evaporated and the residue recrystallized
giving the hydrochloride of 10 as white crystals. Yield:
1.81 g (84%); m.p. (HCl, EtOH/ethyl acetate) ¼ 208 ꢀC;
refractive index n2D0 (base): 1.4835 (Ref. [12]: 1.4804); IR
(HCl, KBr) 3264, 2938, 2680, 1467, 1396, 1382, 1348,
1204, 1162, 1065, 1024 cmꢃ1; NMR (base): 1H NMR
(400 MHz, CDCl3) d 0.94 (s, 3H, CH3ax), 1.16 (s, 3H,
CH3eq), 1.39 (t, J ¼ 11.9 Hz, 1H, 3-Hax), 1.53 (qd,
J ¼ 12.2, 4.6 Hz, 1H, 5-Hax), 1.75 (ddd, J ¼ 11.9, 4.2,
770, 709 cmꢃ1; H NMR (200 MHz, DMSO-d6) d 1.20 (s,
1
6H, (CH3)2), 2.44 (s, 2H, 3-H), 4.90 (d, J ¼ 7.7 Hz, 1H,
5-H), 7.17 (d, J ¼ 7.7 Hz, 1H, 6-H), 7.22e7.44 (m, 5H,
aromatic H) ppm; 13C NMR: (50 MHz, DMSO-d6) d 24.51
((CH3)2), 50.22 (C-3), 59.04 (C-2), 98.38 (C-5), 127.40,
128.05, 129.09, 142.68 (aromatic C), 152.20 (C-6), 190.70
(C-4) ppm; Anal. C13H15NO (C, H, N).
6.2.2. Piperidin-4-ols cis-6, trans-6, 7, 8, cis-9, trans-9, 10,
cis-22, trans-22, cis-23, trans-23, 24, 29, 30, 32, 38
The preparation of compounds cis-6, trans-6, cis-9, trans-
9, cis-22, trans-22, cis-23, trans-23 has already been re-
ported [4]. Compounds 29 and 38 have been purchased
from Aldrich.
6.2.2.1. (RS )-(ꢄ)-2,2-Dimethylpiperidin-4-ol (7). A solution
of 3.15 g (20 mmol) of 5 [11] in 200 ml of EtOH was shaken
at 50 ꢀC at 45 psi for 48 h with 15 g of freshly prepared
Raney nickel W-7. After filtration the solvent was evapo-
rated. The residue was dissolved in CHCl3, filtered, washed
with H2O and dried. The solvent was removed and the

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R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
2.4 Hz, 1H, 3-Heq), 1.91e1.98 (m, 1H, 5-Heq), 2.23 (s, 3H,
NCH3), 2.45 (td, J ¼ 12.2, 3.1 Hz, 1H, 6-Hax), 2.66 (ddd,
J ¼ 12.2, 4.6, 3.4 Hz, 1H, 6-Heq), 3.76e3.85 (m, 1H, 4-
Hax) ppm; 13C NMR (100 MHz, CDCl3) d 16.00 (CH3ax),
29.40 (CH3eq), 35.43 (C-5), 37.07 (NCH3), 48.41 (C-3),
49.14 (C-6), 54.13 (C-2), 66.15 (C-4) ppm; Anal.
C8H18ClNO (C, H, Cl, N).
aluminium oxide) and 1.10 g (8 mmol) of K2CO3 were
heated in 80 ml bromobenzene at 180 ꢀC on an oil-bath
for 18 h. The solvent was evaporated and the residue acid-
ified. Excess alkyating agent was removed with ether
(50 ml). The aqueous solution was made alkaline and ex-
tracted with CH2Cl2. The organic layer was dried and evap-
orated. The residue was purified by column chromatography
(toluene/MeOH ¼ 4:1) over silica gel giving pure cis-32.
Yield: 3.19 g (69%); m.p.: 160e162 ꢀC; IR (KBr) 2966,
2937, 2631, 1456, 1418, 1399, 1068, 1050, 753,
703 cmꢃ1; NMR: 1H NMR: (400 MHz, CDCl3) d 0.86,
0.91 (2d, J ¼ 6.7 Hz, 6H, 2CH3), 1.18 (dt, J ¼ 11.7,
11.2 Hz, 1H, 3-Hax), 1.53 (dtd, J ¼ 12.2, 11.0, 4.2 Hz, 1H,
5-Hax), 1.85 (dddd, J ¼ 11.7, 4.3, 2.8, 2.3 Hz, 1H, 3-Heq),
1.88e1.94 (m, 1H, 5-Heq), 2.01e2.19 (m, 3H, 2-Hax, OH,
CH(CH3)2), 2.42 (ddd, J ¼ 12.4, 12.0, 2.5 Hz, 1H, 6-Hax),
2.65e2.78 (m, 3H, PhCH2, NCH), 2.82e2.91 (m, 1H,
NCH), 3.06 (ddd, J ¼ 12.0, 3.8, 3.0 Hz, 1H, 6-Heq), 3.53e
3.62 (m, 1H, 4-Hax), 7.16 (d, J ¼ 7.4 Hz, 2H, o-Ph-H),
7.18 (t, J ¼ 7.4 Hz, 1H, p-Ph-H), 7.28 (t, J ¼ 7.4 Hz, 2H,
m-Ph-H) ppm; 13C NMR: (100 MHz, CDCl3) d 15.41,
20.09 (2CH3), 27.32 (CH(CH3)2), 31.01 (PhCH2), 33.38
(C-3), 34.63 (C-5), 50.86 (C-6), 53.53 (NCH2), 63.07
(C-2), 69.78 (C-4), 125.87, 128.34, 128.58, 140.69 (aromatic
C) ppm; Anal. C16H26ClNO$0.3H2O (C, H, Cl, N).
6.2.2.4.
(RS )-(ꢄ)-2,2-Dimethyl-1-phenylpiperidin-4-ol
(24). Freshly prepared Raney nickel W-7 (15 g) was added
to a solution of 2.47 g (10 mmol) of 21 in 50 ml of EtOH.
The mixture was shaken at room temperature at 45 psi for
16 h and sucked off through a sintered-glass filter. The residue
was thoroughly washed with EtOH and the filtrate was con-
centrated in vacuo. The residue was dissolved in CH2Cl2 and
H2O. The organic layer was washed once with H2O and dried
with Na2SO4. The solvent was evaporated and the residue was
treated with an equivalent amount of HCl in EtOH. The sol-
vent was evaporated and the residue recrystallized. Yield:
2.03 g (83%); m.p. (HCl, EtOH/ethyl acetate) ¼ 236 ꢀC; IR
(KBr) 3341, 2925, 1490, 1377, 1138, 1072, 1028, 778,
709 cmꢃ1; NMR (base): 1H NMR: (400 MHz, CDCl3)
d 1.01 (s, 3H, CH3ax), 1.08 (s, 3H, CH3eq), 1.46 (d,
J ¼ 5.1 Hz, 1H, OH), 1.58 (dd, J ¼ 12.3, 11.6 Hz, 1H,
3-Hax), 1.62 (tdd, J ¼ 12.0, 11.2, 4.1 Hz, 1H, 5-Hax), 1.88
(ddd, J ¼ 12.3, 4.4, 2.0 Hz, 1H, 3-Heq), 2.01e2.08 (m, 1H,
5-Heq), 2.95 (dt, J ¼ 12.0, 4.1 Hz, 1H, 6-Heq), 3.34 (td,
J ¼ 12.0, 2.7 Hz, 1H, 6-Hax), 3.92e4.01 (m, 1H, 4-Hax),
7.08e7.27 (m, 5H, aromatic H) ppm; 13C NMR: (100 MHz,
CDCl3) d 18.48 (CH3ax), 31.56 (CH3eq), 36.42 (C-5), 46.59
(C-6), 49.43 (C-3), 55.29 (C-2), 66.73 (C-4), 124.45, 127.90,
149.61 (aromatic C) ppm; Anal. C13H20ClNO (C, H, Cl, N).
6.2.3. Analogues of diphenylpyraline 11, 12, 26e28, 31,
33e37
The preparation of compounds cis-11, trans-11, cis-26,
trans-26, cis-27 and trans-27 has already been reported [4].
6.2.3.1. General procedure for the synthesis of 12 and 28. The
piperidinols 10, 24 (10 mmol), benzhydrylbromide (10 mmol)
and K2CO3 (5 mmol) were stirred on an oil-bath at 140 ꢀC.
The mixture was cooled and benzene (50 ml) was added.
The inorganic salts were dissolved in H2O (10 ml). The layers
were separated in a separatory funnel. The aqueous layer was
extracted once with benzene (10 ml). The combined organic
layers were washed twice with H2O, dried and evaporated.
The residue was purified by column chromatography
(CH2Cl2/toluene ¼ 3:1) over silica gel. Their hydrochlorides
were afforded by treatment with equivalent amounts of
a 1 M solution of HCl in ether. Crystallizing products were
sucked off. Alternatively the solvent was evaporated and the
residue recrystallized.
6.2.2.5. (RS )-(ꢄ)-1-Phenethylpiperidin-4-ol (30). Piperidin-
4-ol (29). (1.0 g (10 mmol)), 3.7 g (20 mmol) of 2-phenethyl
bromide (deacidified with basic aluminium oxide) and 0.7 g
(5 mmol) of K2CO3 were refluxed over night in 50 ml of dry
toluene. The solvent was evaporated and the residue acidified.
Excess alkyating agent was removed with ether (30 ml). The
aqueous solution was made alkaline and extracted with ether.
The organic layer was dried and evaporated giving pure 30.
Yield: 1.95 g (95%); m.p.: 95e97 ꢀC (Ref. [14] 95.5e
98.5 ꢀC); IR (KBr) 3158, 2949, 2812, 1497, 1472, 1454,
1373, 1345, 1248, 1120, 1068, 1016, 773, 748, 698 cmꢃ1
;
NMR: 1H NMR: (400 MHz, CDCl3) d 1.58e1.67 (m, 2H,
3-Hax, 5-Hax), 1.87e1.95 (m, 2H, 3-Heq, 5-Heq), 2.20 (br t,
J ¼ 9.9 Hz, 2H, 2-Hax, 6-Hax), 2.55e2.60 (m, 2H, NCH2),
2.77e2.82 (m, 2H, PhCH2), 2.82e2.89 (m, 2H, 2-Heq,
6-Heq), 2.97 (br s, 1H, OH), 3.64e3.71 (m, 1H, 4-Hax),
7.18e7.27 (m, 5H, aromatic H) ppm; 13C NMR: (100 MHz,
CDCl3) d 33.88 (PhCH2), 34.53 (C-3, C-5), 51.08 (C-2, C-
6), 60.46 (NCH2), 67.96 (C-4), 125.99, 128.35, 128.66,
140.39 (aromatic C) ppm; Anal. C13H19NO (C, H, N).
6.2.3.1.1. (RS )-(ꢄ)-4-Benzhydryloxy-1,2,2-trimethylpiperi-
dine (12). Compound 10 (1.43 g (10 mmol)), 2.53 g
(10 mmol) of benzhydrylbromide and 0.71 g (5 mmol)
K2CO3 gave after 3 h a resinous residue. Upon treatment
with ethereal HCl the hydrochloride of 12 was obtained. Yield:
1.75 g (56%); m.p. (HCl, EtOH/ether) ¼ 160 ꢀC; IR (HCl,
KBr) 3029, 2953, 1494, 1473, 1454, 1093, 741, 698 cmꢃ1
;
1
NMR (base): H NMR (400 MHz, DMSO-d6) d 0.75 (s, 3H,
CH3ax), 1.05 (s, 3H, CH3eq), 1.38 (dd, J ¼ 12.4, 10.4 Hz, 1H,
3-Hax), 1.47 (dtd, J ¼ 11.7, 11.0, 4.4 Hz, 1H, 5-Hax), 1.75
(ddd, J ¼ 12.4, 4.0, 1.8 Hz, 1H, 3-Heq), 1.82e1.86 (m, 1H,
5-Heq), 2.07 (s, 3H, NCH3), 2.23 (td, J ¼ 11.8, 2.7 Hz, 1H,
6.2.2.6. (2RS,4SR)-(ꢄ)-2-Isopropyl-1-phenethylpiperidin-4-ol
(cis-32). Compound cis-6 (2.28 g (16 mmol)), 5.88 g
(32 mmol) of 2-phenethyl bromide (deacidified with basic

R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
877
6-Hax), 2.52 (dt, J ¼ 11.8, 4.4 Hz, 1H, 6-Heq), 3.43e3.50 (m,
1H, 4-Hax), 5.61 (s, 1H, OCH), 7.18e7.39 (m, 10H, aromatic
H) ppm; 13C NMR (100 MHz, DMSO-d6): 16.33 (CH3ax),
28.28 (CH3eq), 32.18 (C-5), 36.81 (NCH3), 45.06 (C-3),
48.25 (C-6), 53.30 (C-2), 70.96 (C-4), 79.07 (OCH), 126.45,
126.49, 126.93, 126.94, 128.07, 128.09, 143.10, 143.25 (aro-
matic C) ppm; Anal. C21H27NO$0.2H2O (C, H, N).
(PhCH2), 50.91 (C-2, C-6), 60.46 (NCH2), 72.12 (C-4),
80.11 (OCH), 126.03, 127.06, 127.31, 128.30, 128.37,
128.68, 140.23, 142.80 (aromatic C) ppm; Anal. C26H30ClNO
(C, H, N).
6.2.3.2.2. (2RS,4SR)-(ꢄ)-4-Benzhydryloxy-2-isopropyl-1-
phenethylpiperidine (cis-33). Compound cis-32 (0.50 g
(2 mmol)), 1.11 g (6 mmol) of benzhydrol and 0.48 g
(2.5 mmol) toluene-4-sulfonic acid monohydrate in 100 ml
of toluene gave a residue, from which cis-33 was obtained
upon purification with CC over silica gel (toluene; toluene/
MeOH ¼ 49:1). Yield: 0.89 g (98%); m.p. (HCl): 147 ꢀC; IR
(HCl, KBr) 2967, 2334, 1494, 1455, 1421, 1399, 1100,
6.2.3.1.2. (RS )-(ꢄ)-4-Benzhydryloxy-2,2-dimethyl-1-phenyl-
piperidine (28). Compound 24 (2.05 g (10 mmol)), 2.53 g
(10 mmol) of benzhydrylbromide and 0.71 g (5 mmol)
K2CO3 gave after 12 h a resinous residue. Upon treatment
with ethereal HCl the hydrochloride of 28 was obtained.
Yield: 1.83 g (49%); m.p. (HCl, EtOH/ether) 214 ꢀC; IR
(base, KBr) 2968, 2941, 1596, 1492, 1453, 1070, 740,
701 cmꢃ1; NMR (base): 1H NMR (400 MHz, CDCl3)
d 0.90 (s, 3H, CH3ax), 1.08 (s, 3H, CH3eq), 1.75 (dd,
J ¼ 12.5, 10.2 Hz, 1H, 3-Hax), 1.71e1.80 (m, 1H, 5-Hax),
1.87e1.94 (m, 1H, 3-Heq), 2.00e2.07 (m, 1H, 5-Heq),
2.97e3.04 (m, 1H, 6-Heq), 3.14 (td, J ¼ 11.4, 2.8 Hz, 1H,
6-Hax), 3.66e3.73 (m, 1H, 4-Hax), 5.55 (s, 1H, OCH),
7.03e7.37 (m, 15H, aromatic H) ppm; 13C NMR
(100 MHz, CDCl3) d 20.05 (CH3ax), 30.24 (CH3eq), 33.01
(C-5), 46.06 (C-3), 46.36 (C-6), 55.23 (C-2), 71.60 (C-4),
80.24 (OCH), 124.31, 126.97, 127.00, 127.22, 127.77,
127.80, 128.24, 142.78, 142.99, 149.66 (aromatic C) ppm;
Anal. C26H29NO (C, H, N).
1
1076, 752, 702 cmꢃ1; NMR: H NMR: (400 MHz, CDCl3)
d
0.84, 0.89 (2d, J ¼ 6.5 Hz, 6H, 2CH3), 1.31 (q,
J ¼ 11.4 Hz, 1H, 3-Hax), 1.61 (dtd, J ¼ 12.5, 12.2, 4.1 Hz,
1H, 5-Hax), 1.88e1.94 (m, 1H, 3-Heq), 1.95e2.02 (m, 1H,
5-Heq), 2.04e2.12 (m, 2H, 2-Hax, CH(CH3)2), 2.31 (ddd,
J ¼ 12.5, 12.3, 12.0 Hz, 1H, 6-Hax), 2.61e274 (m, 3H,
NCH, PhCH2), 2.80e2.88 (m, 1H, NCH), 3.04 (ddd,
J ¼ 12.0, 4.1, 3.5 Hz, 1H, 6-Heq), 3.31e3.39 (m, 1H, 4-Hax),
5.58 (s, 1H, OCH), 7.13e7.38 (m, 15H, aromatic H) ppm;
13C NMR: (100 MHz, CDCl3) d 15.55, 20.12 (2CH3), 27.54
(CH(CH3)2), 30.46 (C-3), 31.09 (PhCH2), 31.50 (C-5), 50.84
(C-6), 53.47 (NCH2), 63.16 (C-2), 74.92 (C-4), 80.03
(OCH), 125.88, 127.08, 127.10, 127.27, 127.32, 128.30,
128.33, 128.37, 128.63, 140.80, 142.73, 142.95 (aromatic
C) ppm; Anal. C29H36ClNO$0.2H2O (C, H, Cl, N).
6.2.3.2. General procedure for the synthesis of 31, 33e37. To
a solution of the corresponding piperidinol in toluene, toluene-
4-sulfonic acid monohydrate and diphenylmethanol or bis-4-
(chlorophenyl)methanol were added. The flask was fitted
with a Dean-Stark trap and the mixture was refluxed with stir-
ring over night at 140 ꢀC. The water formed during the reac-
tion was removed by introducing dry molecular sieves
(0.4 nm) in the trap. The mixture was cooled and washed
with 1 M NaOH and once with water. The organic layer was
dried with Na2SO4 and the solvent removed in vacuo. Excess
diarylmethanol was removed by CC over silica gel. Fractions
containing the diphenylpyraline analogue were collected and
the solvent removed in vacuo. The residue was redissolved
in acetone and a 2 M solution of hydrogen chloride in ether
was added. The precipitate was sucked off and washed with
a mixture of acetone and ether.
6.2.3.2.1. (RS )-(ꢄ)-4-Benzhydryloxy-1-phenethylpiperidine
(31). Compound 30 (0.82 g (4 mmol)), 1.84 g (10 mmol) of
diphenylmethanol and 1.90 g (10 mmol) toluene-4-sulfonic
acid monohydrate in 200 ml of toluene gave a residue from
which 31 was obtained upon purification with CC over silica
gel (toluene/MeOH ¼ 49:1). Yield: 1.45 g (89%); m.p.
(HCl): 254e258 ꢀC; IR (HCl, KBr) 3424, 2942, 2487, 1599,
1493, 1455, 1086, 1058, 755, 743, 700 cmꢃ1; NMR: 1H
NMR: (400 MHz, CDCl3) d 1.72e1.81 (m, 2H, 3-Hax,
5-Hax), 1.87e1.95 (m, 2H, 3-Heq, 5-Heq), 2.17e2.26 (m, 2H,
2-Hax, 6-Hax), 2.54e2.59 (m, 2H, NCH2), 2.76e2.86 (m,
4H, 2-Heq, 6-Heq, PhCH2), 3.43e3.49 (m, 1H, 4-Hax), 5.53
(s, 1H, OCH), 7.18e7.36 (m, 15H, aromatic H) ppm; 13C
NMR: (100 MHz, CDCl3) d 31.17 (C-3, C-5), 33.67
6.2.3.2.3.
(RS )-(ꢄ)-4-(Bis-(4-chlorophenyl)methoxy)-1-
methylpiperidine (34). 1-Methylpiperidin-4-ol (38) (0.46 g
(4 mmol)), 3.04 g (12 mmol) of bis-(4-chlorophenyl)methanol
and 0.96 g (5 mmol) toluene-4-sulfonic acid monohydrate in
200 ml of toluene gave a residue, from which 34 was obtained
upon purification with CC over silica gel (toluene/
MeOH ¼ 39:1). Yield: 1.12 g (72%); m.p. (HCl): 116e
118 ꢀC; IR (HCl, KBr) 2957, 2418, 1489, 1089, 1069, 1014,
818, 796 cmꢃ1
;
NMR: 1H NMR: (400 MHz, CDCl3)
d 1.66e1.76 (m, 2H, 3-Hax, 5-Hax), 1.81e1.89 (m, 2H,
3-Heq, 5-Heq), 2.05e2.15 (m, 2H, 2-Hax, 6-Hax), 2.24 (s, 3H,
NCH3), 2.63e2.71 (m, 2H, 2-Heq, 6-Heq), 3.34e3.42 (m,
1H, 4-Hax), 5.44 (s, 1H, OCH), 7.22e7.30 (m, 8H, aromatic
H) ppm; 13C NMR: (100 MHz, CDCl3) d 31.42 (C-3, C-5),
46.20 (NCH3), 53.17 (C-2, C-6), 72.28 (C-4), 78.81 (OCH),
128.29, 128.58, 133.29, 140.96 (aromatic C) ppm; Anal.
C19H22Cl3NO (C, H, Cl, N).
6.2.3.2.4. (2RS,4SR)-(ꢄ)-4-(Bis-(4-chlorophenyl)methoxy)-
2-isopropyl-1-methylpiperidine (cis-35). Compound cis-9
(0.63 g (4 mmol)), 1.27 g (5 mmol) of bis-(4-chlorophenyl)-
methanol and 0.95 g (5 mmol) toluene-4-sulfonic acid
monohydrate in 200 ml of toluene gave a residue, from which
cis-35 was obtained upon purification with CC over silica gel
(toluene/MeOH ¼ 9:1). Yield: 1.65 g (96%); m.p. (HCl):
239e240 ꢀC; IR (HCl, KBr) 2969, 2598, 2515, 1490, 1411,
1089, 1052, 1014, 823, 797 cmꢃ1
;
NMR: 1H NMR:
(400 MHz, CDCl3) d 0.84, 0.86 (2d, J ¼ 7.3 Hz, 6H, 2CH3),
1.29 (q, J ¼ 11.7 Hz, 1H, 3-Hax), 1.60 (qd, J ¼ 12.4, 3.9 Hz,
1H, 5-Hax), 1.60e1.66 (m, 1H, 2-Hax), 1.80e1.86 (m, 1H,
3-Heq), 1.87e1.94 (m, 1H, 5-Heq), 1.95e2.07 (m, 2H, 6-Hax,

878
R. Weis et al. / European Journal of Medicinal Chemistry 43 (2008) 872e879
CH(CH3)2), 2.17 (s, 3H, NCH3), 2.88 (ddd, J ¼ 11.7, 4.0,
3.2 Hz, 1H, 6-Heq), 3.23e3.32 (m, 1H, 4-Hax), 5.49 (s, 1H,
OCH), 7.22e7.32 (m, 8H, aromatic H) ppm; 13C NMR:
M. tuberculosis H37Rv (ATCC 27294) in BACTEC 12B me-
dium using a broth microdilution assay, the microplate alamar
blue assay (MABA) [13]. Isoniazid (INH) was used as
standard.
(100 MHz, CDCl3)
d
14.88, 19.97 (2CH3), 27.77
(CH(CH3)2), 30.20 (C-3), 31.94 (C-5), 41.68 (NCH3), 55.63
(C-6), 66.99 (C-2), 75.18 (C-4), 78.76 (OCH), 128.31,
128.34, 128.58, 128.63, 133.28, 133.32, 140.87, 141.08 (aro-
matic C) ppm; Anal. C22H28Cl3NO (C, H, Cl, N).
6.3.2. Cytotoxicity
The cytotoxic properties of all diphenylpyraline analogues
were detected indirectly via cell proliferation of a HEK-293
cell line using a colorimetric assay based on the reduction of
MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide) to a coloured formazan product by proliferating
cells [15]. HEK-293 cells were seeded in 96-well plates at
a density of 12 000 cells/well in 180 ml DMEM (Dulbecco‘s
modified eagle medium) supplemented with 10% FCS (fetal
calf serum) and incubated at 37 ꢀC and 5% CO2. After 48 h
100 ml of the medium were carefully removed from each
well and substituted by an equal volume of fresh medium.
Then various concentrations of the hydrochlorides of the
test compounds in 20 ml of an aseptically filtered mixture
of 17% glycerine, 33% DMSO and 50% water were added
(as negative controls, the corresponding solutions free of
compounds were used). After incubation for 72 h 100 ml of
the medium were carefully removed from each well and
20 ml of DMEM and 13 ml MTT reagent (5 mg MTT/ml
PBS) were added to each well. The plates were shaken for
30 s at 120 rpm and incubated for 3 h. The resulting forma-
zan dye was solubilised with 100 ml of a solution of 10%
SDS (sodium dodecylsulfate) in 0.01 M aqueous hydrochloric
acid. The plates were shaken at 170 rpm for 30 min, sealed
with lab film and stored until complete solubilization of
the purple formazan crystals. Finally the plates were shaken
at 180 rpm for 30 min. The absorbance was measured spec-
trophotometrically on a Fluostar Galaxy (BMG LABTECH)
at a sample wavelength of 544 nm and a reference wave-
length of 640 nm. To obtain the LC50 values of the com-
pounds, their concentrations were plotted against the
absorbance and fitted to a sigmoidal curve with the Boltz-
mann equation using the program Microcal Origin. INH
was used as standard.
6.2.3.2.5. (RS )-(ꢄ)-4-(Bis-(4-chlorophenyl)methoxy)-1-phe-
nethylpiperidine (36). Compound 30 (0.82 g (4 mmol)),
2.53 g (10 mmol) of bis-(4-chlorophenyl)methanol and
0.95 g (5 mmol) toluene-4-sulfonic acid monohydrate in
200 ml of toluene gave a residue, from which 36 was obtained
upon purification with CC over silica gel (toluene/
MeOH ¼ 9:1). Yield: 1.83 g (96%); m.p. (HCl): 207e
208 ꢀC; IR (HCl, KBr) 2940, 2404, 1489, 1090, 1066, 1015,
819, 795, 753, 698 cmꢃ1; NMR: 1H NMR: (400 MHz,
CDCl3) d 1.70e1.81 (m, 2H, 3-Hax, 5-Hax), 1.88e1.97 (m,
2H, 3-Heq, 5-Heq), 2.23e2.33 (m, 2H, 2-Hax, 6-Hax), 2.60 (t,
J ¼ 8.0 Hz, 2H, NCH2), 2.82 (t, J ¼ 8.0 Hz, 2H, PhCH2),
2.79e2.87 (m, 2H, 2-Heq, 6-Heq), 3.41e3.48 (m, 1H, 4-Hax),
5.45 (s, 1H, OCH), 7.18e7.31 (m, 13H, aromatic H) ppm;
13C NMR: (100 MHz, CDCl3) d 30.80 (C-3, C-5), 33.34
(PhCH2), 50.60 (C-6), 60.21 (NCH2), 71.96 (C-4), 78.91
(OCH), 126.14, 128.23, 128.40, 128.60, 128.63, 133.34,
139.78, 140.81 (aromatic C) ppm; Anal. C26H28Cl3NO (C,
H, Cl, N).
6.2.3.2.6. (2RS,4SR)-(ꢄ)-4-(Bis-(4-chlorophenyl)methoxy)-
2-isopropyl-1-phenethylpiperidine (cis-37). Compound cis-32
(0.50 g (2 mmol)), 1.52 g (6 mmol) of bis-(4-chlorophenyl)-
methanol and 0.48 g (2.5 mmol) toluene-4-sulfonic acid
monohydrate in 100 ml of toluene gave a residue, from which
cis-37 was obtained upon purification with CC over silica gel
(toluene/MeOH ¼ 49:1). Yield: 0.98 g (94%); m.p. (HCl):
223e224 ꢀC; IR (HCl, KBr) 2967, 2508, 1490, 1399, 1089,
1071, 1014, 822, 799, 751, 701 cmꢃ1; NMR: 1H NMR:
(400 MHz, CDCl3) d 0.84, 0.89 (2d, J ¼ 6.4 Hz, 6H, 2CH3),
1.28 (td, J ¼ 11.5, 11.2 Hz, 1H, 3-Hax), 1.58 (dddd, J ¼ 12.3,
12.1, 11.2, 4.2 Hz, 1H, 5-Hax), 1.83e1.89 (m, 1H, 3-Heq),
1.89e1.96 (m, 1H, 5-Heq), 2.04e2.13 (m, 2H, 2-Hax,
CH(CH3)2), 2.30 (td, J ¼ 12.3, 2.2 Hz, 1H, 6-Hax), 2.61e
2.74 (m, 3H, NCH, PhCH2), 2.79e2.90 (m, 1H, NCH),
3.01e3.08 (m, 1H, 6-Heq), 3.25e3.34 (m, 1H, 4-Hax), 5.50
(s, 1H, OCH), 7.12e7.33 (m, 13H, aromatic H) ppm; 13C
NMR: (100 MHz, CDCl3) d 15.52, 20.12 (2CH3), 27.51
(CH(CH3)2), 30.43 (C-3), 31.15 (PhCH2), 31.49 (C-5), 50.76
(C-6), 53.47 (NCH2), 63.13 (C-2), 75.20 (C-4), 78.70
(OCH), 125.93, 128.32, 128.35, 128.40, 128.59, 128.63,
133.29, 133.33, 140.74, 140.87, 141.09 (aromatic C) ppm;
Anal. C29H34Cl3NO$0.2H2O (C, H, Cl, N).
Acknowledgements
Antimycobacterial data were provided by the TAACF
through a research and development contract with the U.S.
National Institute of Allergy and Infectious Diseases.
References
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WHO information, http://www.who.int/mediacentre/factsheets/fs104/en/,
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6.3. Biological tests
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1755e1757.
[3] W. Meindl, Arch. Pharm. (Weinheim, Ger.) 322 (1989) 493e497.
[4] R. Weis, A.J. Kungl, W. Seebacher, Tetrahedron 59 (2003) 1403e1411.
[5] G. Zigeuner, K. Schweiger, Monatsh. Chem. 107 (1976) 1361e1367.
[6] H. Adkins, H.R. Billica, J. Am. Chem. Soc. 70 (1948) 695e698.
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6.3.1. Antimycobacterial activity
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