Factors influencing agonist potency and selectivity for the opioid δ receptor are revealed in structure - Activity relationship studies of the 4-[(n-substituted-4-piperidinyl)arylamino]-n,n-diethylbenzamides

Article abstract of DOI:10.1021/jm000427g

A study of the effect of transposition of the internal nitrogen atom for the adjacent benzylic carbon atom in δ-selective agonists such as BW373U86 (1) and SNC-80 (2) has been undertaken. It was shown that high-affinity, fully efficacious, and δ opioid re

Full text of DOI:10.1021/jm000427g

9
72
J . Med. Chem. 2001, 44, 972-987
F a ctor s In flu en cin g Agon ist P oten cy a n d Selectivity for th e Op ioid δ Recep tor
Ar e Revea led in Str u ctu r e-Activity Rela tion sh ip Stu d ies of th e
4
-[(N-Su bstitu ted -4-p ip er id in yl)a r yla m in o]-N,N-d ieth ylben za m id es
†
†
‡
†
†
J ames B. Thomas, Xavier M. Herault, Richard B. Rothman, Robert N. Atkinson, J ason P. Burgess,
†
‡
‡
#
#
S. Wayne Mascarella, Christina M. Dersch, Heng Xu, J udith L. Flippen-Anderson, Clifford F. George, and
F. Ivy Carroll*,†
Chemistry and Life Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709,
Clinical Psychopharmacology Section, NIDA Addiction Research Section, 5500 Nathan Shock Drive,
Baltimore, Maryland 21224, and Laboratory for the Structure of Matter, Naval Research Laboratory,
Building 35, Room 455, Overlook Avenue, Washington, D.C. 20375
Received October 2, 2000
A study of the effect of transposition of the internal nitrogen atom for the adjacent benzylic
carbon atom in δ-selective agonists such as BW373U86 (1) and SNC-80 (2) has been undertaken.
It was shown that high-affinity, fully efficacious, and δ opioid receptor-selective compounds
can be obtained from this transposition. In addition to the N,N-diethylamido group needed as
the δ address, the structural features identified to promote δ receptor affinity in the set of
compounds studied included a cis relative stereochemistry between the 3- and 4-substituents
in the piperidine ring, a trans-crotyl or allyl substituent on the basic nitrogen, the lack of a
2
-methyl group in the piperidine ring, and either no substitution or hydroxyl substitution in
the aryl ring not substituted with the N,N-diethylamido group. Structural features found to
be important for µ affinity include hydroxyl substitution in the aryl ring, the presence of a
2
-methyl group in a cis relative relationship to the 4-amino group as well as N-substituents
such as cyclopropylmethyl. It was also determined that µ receptor affinity could be increased
while maintaining δ receptor affinity, especially when hydroxyl-substituted compounds are
considered. Additionally, it was discovered that the somewhat lower µ/δ selectivities observed
for the piperidine compounds relative to the piperazine-based ligands appear to arise as a
consequence of the carbon-nitrogen transposition which imparts an overall lower δ and higher
µ affinity to the piperidine-based ligands. This higher affinity for the µ receptor, apparently
intrinsic to the piperidine-based compounds, suggests that ligands of this class will more easily
be converted to µ/δ combination agonists compared to the piperazine ligands such as 1. This is
particularly important since analogues of 1, which show both µ- and δ-type activity, are now
recognized as important for their strong analgesia and cross-canceling of many of the side
effects found in agonists operating exclusively from either the δ or µ opioid receptor.
In tr od u ction
peptide δ ligands over the past decade. Of these two
groups of compounds, naltrindole may be considered a
classical ligand for the opioid receptor since it contains
a tyramine-like substructure found in the tyrosine
residue of the endogenous ligands (enkephalins). The
former compounds have been referred to as nonclassical7
since their piperazine substructure represents a motif
not commonly associated with opioid binding com-
pounds.
The discovery of opioid analgesics that operate via δ
or κ opioid receptors as opposed to the µ opioid receptor,
which meditates the actions of morphine and its con-
geners, has been a goal of medicinal chemists for many
1
years. While morphine remains the painkiller of choice
for severe pain, the accompanying respiratory depres-
sion and addiction liability associated with its use
continue to drive the search for safer medications.
2
Much as the discovery of the non-peptide κ opioid
receptor-selective ligand U50,488 opened the door to
an explosion of research in this area during the 1980s,
These two sets of compounds influenced the area of δ
receptor research in different ways. The principal
impact of the diethylbenzamide compounds such as 1
and 2 was their introduction of novel structural concepts
by which δ selectivity could be realized. The impact of
3
the discovery of the N,N-diethylbenzamide agonists
4
5
BW373U86 (1) and SNC-80 (2) and the δ receptor-
selective antagonist naltrindole (NTI, 3)6 (Chart 1)
paved the way to the development of a variety of non-
the discovery of NTI (3) related not only to its δ
selectivity but also to the rationale behind its design.8
Portoghese successfully applied the message-address
concept of Schwyzer to opioid small-molecule ligands
by demonstrating that addition of a phenylalanine
mimic (the address unit of the enkephalins) to the
nonselective antagonist naltrexone resulted in a ligand
with δ selectivity. Research by other groups led to the
*
Corresponding author: Dr. F. Ivy Carroll, Chemistry and Life
9
Sciences, Research Triangle Institute, P.O. Box 12194, 3040 Cornwallis
Rd., Research Triangle Park, NC 27709. Tel: 919-541-6679. Fax: 919-
5
41-8868. E-mail: fic@rti.org.
†
Research Triangle Institute.
NIDA Addiction Research Section.
Naval Research Laboratory.
‡
#
1
0.1021/jm000427g CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/31/2001

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 973
Ch a r t 1
cent benzylic carbon. This line of investigation produced
not only high-affinity δ receptor-selective full agonists
but also information essential to better our understand-
ing of the fundamental elements governing ligand δ
receptor selectivity at the molecular level. In the present
article we relate our most recent findings derived from
this series of compounds. Preliminary results from some
of these studies have already been reported.1
2,13
Ch em istr y
Access to the required diarylanilinopiperidine system
found in the subject compounds 8 (Chart 1) utilized an
anionic aromatic nucleophillic substitution reaction be-
tween a given N-substituted 4-anilinopiperidine and the
butylated hydroxyanisole (BHA) ester of 4-fluorobenzoic
acid as the key step. This strategy, demonstrated by
2
8
Hattori and co-workers in the production of triaryl-
amines, proved to be robust and allowed for multiple
degrees of synthetic flexibility in the introduction of
molecular diversity from readily available starting
materials, piperidones and aniline derivatives. This
strategy is illustrated in the synthesis of the 2,5-dimethyl-
piperidine derivatives 16a -c as shown in Scheme 1.
The requisite dimethylpiperidones 12 and 13 were
prepared from ethyl 3-aminobutyrate (10) by treatment
with excess methyl methacrylate to give the isolable
intermediate 11 in 69% yield. This material was sub-
sequently converted to the piperidones in a one-pot
procedure involving cyclization of 11 by treatment with
sodium in refluxing xylenes, decarboxylation with 20%
HCl, and finally carbamate formation with di-tert-butyl
dicarbonate. From this reaction mixture 12 and 13 were
obtained in approximately equal proportions after flash
chromatography in 30% overall yield from 11. These
two 4-piperidones then underwent reductive amination
with aniline using titanium(IV) isopropoxide2
9,30
and
sodium borohydride to give intermediates 14a -c. The
diastereomers formed in this reaction were separated
at this point and carried forward independently. While
four diastereomers could arise in this reaction, only
introduction of the δ-selective agonist TAN-67 (4) and
the antagonist SB205588 (5).7 These two compounds
display simplified molecular structures relative to 3, but
both utilize Portoghese’s enkephalin Phe mimic concept
to promote δ receptor subtype selectivity.
,10
4
1
4a -c were isolated in synthetically useful quantities.
The allyl derivatives 15a -c were next prepared by
treating 14a -c with trifluoroacetic acid (TFA) to remove
the tert-butyloxycarbonyl group followed by alkylation
with allyl bromide in ethanol. Assembly of the di-
arylamine core, in 27-63% yields, was accomplished
by treating 15a -c with n-butyllithium in tetrahydro-
furan (THF) followed by combining with the BHA
ester of 4-fluorobenzoic acid. Removal of the BHA group
was accomplished by transesterification with refluxing
sodium methoxide in toluene/N-methylpyrrolidinone
followed by saponification of the methyl ester in ethanol
and water. The zwitterionic intermediates thus formed
were not isolated but instead converted directly into
N,N-diethylamides using benzotriazol-1-yloxytris(di-
methylamino)phosphonium hexafluorophosphate (BOP,
a.k.a. Castro’s reagent) and diethyl- and triethylamines
in a THF slurry to give 16a -c, respectively. Assignment
of the relative stereochemistry in compounds 16a -c was
accomplished by single-crystal X-ray analysis of final
products or of configurationally stable intermediates.
The relative stereochemistry of the cis-piperidone 13
was established by single-crystal X-ray analysis and
shown to be 2SR,5RS (Figure 1). The relative stereo-
chemistry of the other stereoisomer obtained (12) was
Additional discoveries important to this discussion
include two compounds that do not fall neatly into either
of the above categories. These are SB219825 (6), intro-
duced by Dondio and co-workers, and the peptido-
1
1
mimetic SL-3111 (7), discovered by Liao et al. The
former compound is particularly interesting because it
possesses structural elements of both the nonclassical
N,N-diethylbenzamide agonists as well as the classical
morphinan-based compounds and, therefore, represents
a unique molecular hybrid. The latter compound 7,
designed as a small-molecule peptidomimetic from cyclic
2
5
[
penacillamine ,penacillamine ]enkephalin (DPDPE), is
an intriguing δ opioid ligand since it is so strikingly
similar to 1 and 2 and yet possesses a structure-activity
(SAR) profile completely different from that of the
diethylbenzamides such as SNC-80 (2).
Recently, others, including our laboratory,12,13 have dis-
closed findings relating to the SAR of structures closely
1
4-27
related to the N,N-diethylbenzamides 1 and 2.
In
our discovery efforts in this field of δ opioid receptor
ligands, we have carried out SAR studies on compounds
of general structure 8, derived from transposition of the
internal nitrogen atom in compounds 2 with the adja-

9
74 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
Sch em e 1a
a
(
a) Methyl methacrylate, EtOH, HOAc; (b) sodium, xylenes, reflux then 20% HCl, reflux then di-tert-butyl dicarbonate, MeOH,
1
0% triethylamine, reflux; (c) Ti(Oi-Pr)4, aniline then NaBH4, EtOH; (d) TFA, CH2Cl2; (e) allyl bromide, EtOH, K2CO3; (f) n-BuLi, THF,
HMPA then 2,6-di-tert-butyl-4-methoxyphenyl 4-fluorobenzoate; (g) N-methylpyrrolidinone, NaOCH3, toluene then EtOH, H2O then Et2NH,
BOP, Et3N.
F igu r e 2. Results of the X-ray study on 14a drawn from
the experimentally determined coordinates with anisotropic
thermal parameters at the 20% probability level.
F igu r e 1. Results of the X-ray study on 13 drawn from
the experimentally determined coordinates with anisotropic
thermal parameters at the 20% probability level.
assumed to be trans. This assumption was verified in
the next step by single-crystal X-ray analysis of the
products obtained in the reductive alkylation reaction.
Thus, the cis-piperidone 13 provided predominantly 14a
(Figure 2), whereas the trans-piperidone provided pre-
dominantly 14b (Figure 3). Given that the stereocenters
in compounds 14a ,b are not disturbed during the
transformation of 14a ,b to 16a ,b, the relative stereo-
chemistry of 2SR,4RS,5SR and 2RS,4RS,5SR found for
F igu r e 3. Results of the X-ray study on 14b drawn from
the experimentally determined coordinates with anisotropic
thermal parameters at the 20% probability level.
1
4a ,b in Figures 2 and 3, respectively, will also be found
in products 16a ,b. The stereochemistry of compound 16c
was shown to be the 2RS,4SR,5SR isomer by single-
crystal X-ray analysis of its HCl salt (Figure 4).
Preparation of the monomethyl-substituted piperidine
derivatives used in this study proceeded in a manner
similar to that used for 16a -c. The representative
synthesis for all other compounds prepared for this
study is illustrated for compounds 20a ,b and 21 in
Scheme 2 starting from commercially available 1,3-
dimethyl-4-piperidone. Following reductive amination
with m-anisidine and titanium(IV) isopropoxide, the
diastereomers 17a ,b were separated and independently
coupled to the BHA ester of 4-fluorobenzoic acid to give
18a ,b. The yield for this reaction was observed to

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 975
Sch em e 2a
a
(a) Ti(Oi-Pr)4, aniline derivative then NaBH4, EtOH; (b) n-BuLi, THF, HMPA then 2,6-di-tert-butyl-4-methoxyphenyl 4-fluorobenzoate;
(c) N-methylpyrrolidinone, NaOCH3, toluene then EtOH, H2O; (d) Et2NH, BOP, Et3N; (e) PhOCOCl then KOH, i-PrOH, H2O; (f) allyl
bromide, EtOH, K2CO3; (g) BBr3, CHCl3.
to give 20a ,b in 35-60% yields from 19a ,b. Analogues
with free phenolic groups (21) were prepared from the
corresponding methyl ethers by treatment with boron
tribromide in chloroform. A preliminary account of the
synthesis of the optically pure compounds described
1
3
herein has been published.
Compound structures were based on elemental analy-
sis and proton and carbon NMR spectral analyses
including COSY and HMQC. The cis relative stereo-
chemistry of 19-34 was based on a large vicinal
coupling constant (J ) 13.0 Hz) between the H5 axial
and H4 protons that established the equatorial position
for the 4-diarylamine group and a correlation in the
NOESY spectrum between the H5 axial proton and the
F igu r e 4. Results of the X-ray study on 16c drawn from
the experimentally determined coordinates with anisotropic
thermal parameters at the 20% probability level.
3
4
-methyl group which places this group cis to the
-diarylamine group. Corroborating evidence for both
the relative (cis) and absolute (3S,4R) stereochemistries
of the most active enantiomer (-)-23a was obtained
through single-crystal X-ray analysis of the HCl salt of
depend on both the N-substituent as well as the relative
stereochemistry (cis or trans) in the piperidine 3,4-
position. Trans derivatives typically gave yields ap-
proximately one-third lower than cis derivatives. Also,
as might be expected, the N-methyl derivatives faired
better in this reaction than either N-allyl analogues or
Boc-protected derivatives presumably due to interaction
of n-BuLi with the latter N-substituents. Conversion of
the BHA ester to the N,N-diethylamide to give 19a ,b
was accomplished as described for the synthesis of 16a -
c. Preparation of a variety of N-substituent derivatives
(-)-23a (Figure 5).
Resu lts a n d Discu ssion
The radioligand binding data for the test compounds
16-34 illustrated in Chart 2 along with comparative
data for the prototypical N,N-diethylbenzamide δ recep-
tor-selective agonists BW373U86 (1) and SNC-80 (2)
are shown in Table 1. From the N-allyl compound
set of 20a ,b and 23a ,b it was clearly established that
with Kis of 22 and 11.9 nM, respectively, the 3,4-cis-
monomethyl compounds 20a and 23a possess superior
δ affinity relative to their similarly substituted trans
counterparts 20b and 23b with Kis of 379 and 126 nM.
The importance of the 3,4-cis stereochemical arrange-
ment to binding affinity is further elaborated in the
(illustrated for allyl) was accomplished in a two-pot
procedure, whereby 19a ,b were first treated with phenyl
chloroformate to form the carbamate which was not
isolated but directly hydrolyzed to the secondary amine
with potassium hydroxide in isopropyl alcohol. Follow-
ing purification of this material, N-substituent deriva-
tization proceeded under simple alkylation conditions

9
76 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
chemistry) provides an opportunity to assess the influ-
ence of an additional piperidine ring methyl group on
receptor binding affinity and ultimately on ligand
selectivity. Considering δ receptor affinity first, it is
found that methyl group substitution in the piperidine
ring R to the nitrogen and in a cis configuration relative
to the other two substituents (16a ) decreases δ receptor
affinity nearly 5-fold compared with compound 23a not
substituted in this manner. In compound 16b, with the
methyl group in a trans configuration, the affinity for
the δ receptor is decreased only 1.5-fold. Thus the
relative stereochemistry of a methyl substituent in the
2
-position on the piperidine ring can significantly impact
δ receptor affinity.
Compared to the selectivity found in compound 23a ,
methyl substitution in the piperidine 2-position is
observed to decrease δ selectivity overall. In compound
F igu r e 5. Results of the X-ray study on (-)-23a drawn from
the experimentally determined coordinates with anisotropic
thermal parameters at the 20% probability level.
1
6a , this results predominately from the nearly 5-fold
Ch a r t 2
loss of δ receptor affinity for 16a noted above since the
µ affinity decreases only 3-fold relative to 23a . This is
not the case for 16b with the additional methyl in the
trans relative configuration. In 16b the µ receptor
affinity is dramatically improved compared to either 16a
or 23a . Thus even though 16b shows relatively good
affinity for the δ receptor (Ki ) 19 nM), this does not
compete favorably with the 23-fold improvement in µ
receptor affinity relative to 16a and the compound is
not selective for the δ receptor. Such a dramatic impact
on µ receptor affinity is worthy of note since few other
single structural modifications in this study produced
this magnitude of change in binding affinity at any
opioid receptor. Overall, it is evident that a methyl
group in the 2-position of the piperidine ring of the
subject compounds, regardless of the configuration,
leads to compounds of lower δ affinity and selectivity.
However, since compounds with the highest affinity
(
16a ,b) for the δ receptor are also the ones possessing
a cis arrangement between the substituents in positions
and 4 of the piperidine ring, the 3,4-cis series, this
3
trend is apparently preserved in the presence of
a 2-methyl substituent. The observed effects of this
methyl group on δ affinity and µ/δ selectivity are in
general agreement with the findings of Knapp et al.31
in the SNC-80 series although the related piperidine
compounds are observed to display comparatively lower
δ affinity.
The general effect of aryl substitution on binding
affinity in the 3,4-cis series of compounds is available
from comparison of aryl methoxy, hydroxy, and unsub-
stituted compounds. Comparison of the 22 nM Ki value
of compound 20a (methoxy) with the 11.9 value for 23a
(unsubstituted) illustrates that methoxy substitution in
the aryl ring decreases binding affinity 2-fold for the δ
receptor. A comparison of the binding data for 20a
and 23a at the κ and µ receptor shows 2- and 4-fold
decreases, respectively. However, this same structural
feature also imparts about a 2-fold improvement in δ
receptor subtype selectivity. Overall, the methoxy sub-
stitution appears to decrease δ affinity but promote
selectivity. The hydroxy-substituted compounds 21 and
26 with Ki values of 1.85 and 2 nM, respectively, display
a 12- and 9-fold improvement in binding affinity at the
δ receptor relative to their methyl ethers (20a and 25).
However, in terms of selectivity, the significant increase
monomethylpiperidine compounds 19a , 22a , 27a , and
2
8a wherein a 3,4-cis arrangement provides compounds
of higher affinity for the δ receptor relative to corre-
sponding 3,4-trans compounds tested, 19b, 22b, 27b,
and 28b. Thus, the relative stereochemical position of
the 3-methyl group is critical to overall δ receptor
affinity.
Comparison of the data for 3-substituted monomethyl
compound 23a to that of the 2,5-dimethyl-substituted
compounds 16a ,b (all have the 3,4-cis relative stereo-

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 977
Ta ble 1. Radioligand Binding Results at the µ, δ, and κ Opioid Receptors for 4-[(N-Substituted-4-piperidinyl)arylamino]-N,N-
diethylbenzamides
Ki (nM ( SD)
3
a
δ [ H]DADLEb
3
κ [ H]U69,593c
3
compd
µ [ H]DAMGO
µ/δ
40
1030
74
κ/δ
1
2
1
1
1
1
1
2
2
2
2
2
2
2
, BW373U86
, SNC-80
36 ( 3.4
1614 ( 131
3895 ( 260
171 ( 15
9905 ( 448
>5917
3322 ( 269
5330 ( 605
4872 ( 541
126 ( 9
0.91 ( 0.05
1.57 ( 0.19
53 ( 4
18.8 ( 0.69
93 ( 6
141 ( 8.8
178 ( 9
NA
3535 ( 1841
2903 ( 310
1164 ( 76
6324 ( 369
>6061
6302 ( 1092
>7463
>7463
76.7 ( 4.6
>6061
>6061
3284 ( 299
8695 ( 978
3722 ( 556
1448 ( 196
>7463
1638 ( 166
>7463
2250
55
62
68
>43
35
>339
20
41
>132
6a
6b
6c
9a
9b
0a
0b
1
2a
2b
3a
3b
9
110
>42
19
240
13
68
9
6
102
13
>35
470
510
344
180
20
8
28
>180
>28
35
22 ( 1
379 ( 23
1.85 ( 0.24
45.6 ( 2.5
257 ( 7
11.9 ( 0.9
126 ( 5
139 ( 11.4
5.58 ( 0.31
7.0 ( 0.6
2.72 ( 0.62
18 ( 3
388 ( 13
1511 ( 40
1212 ( 132
1589 ( 86
>4854
2623 ( 307
3590 ( 285
938 ( 71
3252 ( 236
40.8 ( 7.8
160 ( 29
5341 ( 181
>6536
>6536
1260 ( 770
5685 ( 443
3785 ( 312
3387 ( 366
6425 ( 471
>6536
24
275
69
(
(
2
(
+)-23a
-)-23a
26
260
>1100
602
>414
82
120
>31
>210
>33
>210
>100
>497
170
200
>80
4
-)-24
2
2
2
2
2
2
2
3
3
3
3
3
5
6
2.00 ( 0.12
20 ( 3
193 ( 5
164 ( 12
2383 ( 225
>6061
7a
7b
8a
8b
9
0
1
2
3
36 ( 2
>7463
230 ( 11
36 ( 3
>7463
>7463
72 ( 6
>7463
80
252
94
95
>70
15.0 ( 0.6
36 ( 4
>7463
6020 ( 695
13459 ( 1715
>7463
68 ( 4
93 ( 4
4
a
[3
2
4
5
b
3
2
H]DAMGO [(D-Ala ,MePhe ,Gly-ol )enkephalin], tritiated ligand selective for the µ opioid receptor. [ H]DADLE [(D-Ala ,D-
5
c
3
3
Leu )enkephalin], tritiated ligand selective for the δ opioid receptor. [ H]U69,593 {[ H]-(5R,7R,8â)-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-
-oxaspiro[4.5]dec-8-yl]benzeneacetamide}, tritiated ligand selective for the κ opioid receptor.
1
in binding affinity for the δ receptor is insufficient to
offset the binding affinity increases found for µ and κ
receptors, and thus, the δ selectivity of 21 and 26
relative to the methoxy-substituted ligands 20a and 25
or the unsubstituted compounds 20a and 23a is dimin-
ished. These trends in receptor affinity modulation are
compound 24, not substituted in the aryl ring, showed
a binding affinity about 2.5-fold greater than the meth-
oxy-substituted compound 25. Indeed, this phenomenon
was observed for every N-substituent tested and is
discussed in more detail below.
Addition of a single methyl to the central carbon of
the allyl group provided the N-methallyl derivatives 29
and 30, which bind the δ receptor less effectively than
their allyl (20a and 23a ) counterparts. The prenyl
derivatives 31 and 32 possess two methyl groups at the
distal carbon of the allyl group and showed somewhat
lower affinity than the N-allyl compounds with Kis of
15 and 36 nM. However, this loss of affinity was only
one-half that observed for the N-methallyl derivatives
29 and 30. Compared with the more closely related
trans-crotyl derivatives, however, the prenyl compounds
display a 2-fold loss of affinity by the addition of a
second methyl group. Incorporation of a phenyl group
into the N-allyl substituent, in a trans geometric
relationship, provided the N-trans-cinnamyl derivatives
33 and 34 that also lacked good affinity for the δ
receptor. Indeed, of all the N-substituents tested, the
cinnamyl derivatives gave the lowest affinity observed
for the δ receptor. Assuming that high electron density
is a requirement in the N-substituent, then the relative
loss in affinity of about 6- and 4-fold, respectively, found
in 33 and 34 is likely to result from the increased size
since this was the most electron-rich substituent tested.
Relative to the allyl group the N-cyclopropylmethyl
substituent retains a degree of high electron density but
possesses an additional methylene group in what would
in agreement with those observed within the piperazine
series as related in several different studies5
,23,27
and
2
4
in other closely related studies of piperidine analogues.
To identify the effect on binding affinity associated
with changes to the N-substituent group of the more
selective compounds 20a and 23a , a series of “allyl-like”
compounds were tested along with the N-methyl inter-
mediates (19a , 22a ). With methyl as the N-substituent
(19a , 22a ) a significant loss of binding affinity relative
to the N-allyl compounds 20a and 23a was observed.
Thus, with Ki values of 141 and 45 nM, respectively, in
binding to the δ receptor, the N-methyl analogues 19a
and 22a showed a 6- and 4-fold loss, respectively, in
affinity compared to the N-allyl compounds 20a and
2
3a . The N-trans-crotyl derivative 24 with a Ki value
of 7 shows higher affinity and selectivity at the δ
receptor than similarly substituted allyl derivative 20a ,
showing that the addition of a distal methyl to the
N-allyl substituent can result in an increase in δ
receptor affinity and selectivity. The Ki values of 7 and
1
2
8 nM found for 24 and 25, respectively, represent a
-fold improvement for the aryl unsubstituted com-
pound 24 relative to 23a but only a 1.2-fold improve-
ment for the methoxy-substituted compound. In line
with the allyl derivatives seen earlier, the trans-crotyl

9
78 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
be the π cloud of the allyl substituent. In binding, the
N-cyclopropylmethyl compounds 27a and 28a displayed
a slight loss of binding affinity relative to the allyl
analogues 20a and 23a with Kis of 20 and 36 nM,
respectively, suggesting that N-substituents should be
2
sp hybridized between carbons 2 and 3 since the width
of the substituent appears to affect binding. Overall,
the data available from the N-substituent changes to
2
0a and 23a indicate that the binding site associated
with this region of the receptor prefers electron-rich
structures which is in accord with the findings of
Zhang27 and Furness in the SNC-80 series. Addition-
ally, the trans-crotyl group was found to provide
compounds of higher affinity and selectivity compared
with similarly substituted compounds possessing
allyl as the N-substituent. Overall, these data fall in
21
2
3
line with observations made in other piperazine and
F igu r e 6. K
i
s for 3,4-cis compounds at the δ receptor as a
piperidine2
4,26
related studies.
function of aryl substitution and N-substituent (group 1 )
unsubstituted aryl, group 2 ) methoxy-substituted aryl).
The optical isomers of 23a and 24 provided com-
pounds of higher affinity and δ receptor selectivity as
well as demonstrating a separation of activity between
the optical antipodes. As illustrated in Table 1, com-
parison of racemic 23a and its optical isomers reveals
that the high δ opioid binding affinity as well as the δ
receptor selectivity of the racemic mixture is due to (-)-
2
3a . With a Ki value of 5.5 nM, the (-)-isomer (-)-23a
is twice as potent as the racemic mixture (()-23a ,
whereas (+)-23a with a Ki value of 139 nM is 12-fold
less potent than (()-23a resulting in a 25-fold separa-
tion of binding affinity between the (-)- and (+)-
enantiomers. In terms of opioid receptor selectivity, (-)-
2
3a demonstrates a nearly 5-fold increase in δ versus
µ selectivity compared with the racemic material. This
increased δ selectivity is due in part to the increase in
δ receptor affinity and partly to a 2-fold decrease in
affinity for the µ receptor. Relative to the racemic
mixture or the (+)-23a isomer, (-)-23a shows a signifi-
cantly improved δ opioid binding affinity and δ selectiv-
ity. Since racemic 24 had greater affinity and selectivity
than did 23a , (-)-24 was prepared and evaluated.
Compound (-)-24 with a Ki of 2.7 nM had the highest
affinity for the δ receptor of all of the aryl unsubstituted
compounds tested. Compared with the racemic material,
F igu r e 7. Ratio of K for group 2 (methoxy-substituted aryl
ring) to group 1 (unsubstituted aryl ring) as a function of
N-substituent in the δ binding assay.
i
of ligand affinity modulation are revealed. The aryl
substituent (methoxy) is found to define broadly the
fundamental level of binding affinity achievable by a
given ligand while the N-substituent more narrowly
defines the ultimate binding affinity displayed by the
ligand. Stated another way, for any choice of N-sub-
stituent, the compound unsubstituted in the aryl ring
(-)-24 like (-)-23a displayed an improvement in δ
receptor binding affinity; however, unlike (-)-23a its δ
selectivity was somewhat diminished. Inspection of the
data for 24 and (-)-24 indicates that this change in
selectivity can be attributed to a much improved affinity
of (-)-24 for the µ receptor relative to the racemic
material. Thus, the 2.5-fold improvement in affinity for
the δ receptor shown by (-)-24 relative to the racemic
mixture is offset by an almost 4-fold increase affinity
for the µ receptor. Worthy of note is the observed impact
on δ selectivity resulting from the incorporation of this
single methyl group in the N-substituent.
(group 1) will bind with about twice the affinity as the
compound possessing a methoxy substituent in the aryl
ring (group 2), and this phenomenon is independent of
the N-substituent. Though this trend is visible by
inspection of Figure 6, it is more clearly revealed in
Figure 7 wherein the Ki ratios for the two groups are
compared as a function of the N-substituent. Remark-
ably, in this depiction, the ratio of Ki for the two groups
for any given N-substituent large (cinnamyl) or small
(methyl) is observed to remain nearly constant. Since
only the allyl and crotyl analogues with hydroxy-
substituted aryl rings were tested, a direct comparison
point-by-point for this series is not possible, but the data
available suggest that this trend appears to exist within
this series of compounds as well. Taken together, these
results indicate that the aryl substituent takes prece-
dence over the N-substituent for establishing the gross
δ receptor binding affinity available to a ligand of this
The overall affect of aryl substitution and N-substitu-
tion on δ affinity and selectivity as well as an interesting
trend was revealed by graphical analysis of the receptor
binding data obtained from the 3,4-cis series (Figure 6).
As discussed previously, the most potent and selective
compounds identified in this study were the 3,4-cis
compounds as represented by 23a . When the binding
affinities of the compounds of this series are plotted as
a function of aryl and N-substituent, two distinct levels

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 979
less selective than compounds of group 2 (methoxy-
substituted). Indeed compounds of group 1 have greater
affinity for both µ and δ receptors than their methoxy-
substituted counterparts. The importance of this obser-
vation is made clear when one considers that piperazine-
based compounds such as 2 do not share such a behavior
between aryl methoxy-substituted and unsubstituted
compounds which strongly suggests that the transposi-
tion of the internal carbon and nitrogen atom funda-
mentally alters the overall conformation of the resulting
ligands and provides compounds that have an intrinsi-
cally higher affinity for the µ opioid receptor compared
with similarly substituted piperazine-based ligands.
To determine their effectiveness as δ receptor ago-
nists, a selected set of high-affinity compounds from
the binding assay were evaluated for their ability to
F igu r e 8. K
i
s for 3,4-cis compounds at the µ receptor as a
stimulate binding of the nonhydrolyzable GTP analogue,
function of aryl substitution and N-substituent (group 1 )
unsubstituted aryl, group 2 ) methoxy-substituted aryl).
35
[
S]GTP-γ-S, in guinea pig caudate membranes and
compared to the readily available, widely recognized full
agonist SNC-80 (2) (Table 2). Since the data was
obtained in a tissue preparation as opposed to receptors
expressed from cloned cell lines, parallel experiments
were performed utilizing combinations of the test ligand
and opioid receptor subtype-selective antagonists in
order to identify the receptor responsible for any ob-
served stimulation. These experiments were then com-
pared directly to the test ligand in the tissue preparation
alone, the “unblocked” condition. Under these condi-
tions, (+)-23a , which showed low radioligand binding
affinity at the δ receptor, displays no stimulation in the
unblocked case, whereas (-)-23a , which showed high
affinity at the δ receptor, exhibits an ED50 of 2508 nM
and an Emax value virtually identical to the full agonist
SNC-80 (2). In the combination experiments with opioid
receptor subtype-selective antagonists, (-)-23a was
observed to stimulate GTP binding only in the absence
of the δ-selective antagonist NTI indicating a δ receptor
series, while the N-substituent fine-tunes the Ki within
the parameters set by the aryl substituent. Considered
from a different perspective, as molecular probes of the
δ receptor binding domain, the highly organized data
obtained from the compounds of groups 1 and 2, as
depicted in Figure 6, reflect the presence of a well-
ordered region of highly specific requirements for bind-
ing. This is not the case for the µ receptor.
Graphical analysis of the µ binding data obtained for
the same compounds reveals that in contrast to the δ
assay analysis of Figure 6, no regular affinity profile,
based on either the nitrogen or aryl substituent, is
observed (Figure 8). This phenomenon arises because
for some of the N-substituents studied like the N-methyl
(19a and 22a ) or the N-cyclopropylmethyl (27a and 28a )
derivatives, very large differences in affinity between
the aryl methoxy-substituted and aryl-unsubstituted
compounds are observed. Thus, while the methoxy-
substituted derivatives (group 2) as a group do not bind
the µ receptor, some compounds unsubstituted in their
aryl ring (group 1), like 27a , are recognized by the µ
receptor and exhibit moderate binding affinity (Ki for
8
site of action. When combined with the µ-selective
3
2
antagonist CTAP or the κ-selective antagonist nor-
3
3
binaltorphimine (nor-BNI) the ED50 for (-)-23a was
found to double. This doubling does not appear to be
related to the test ligand since the phenomenon was also
observed for the standard δ agonist SNC-80 (2). Com-
pound (-)-24 with its N-trans-crotyl group displayed
greater potency in this assay (ED50 ) 1129 nM) than
did the allyl-substituted (-)-23a . This is not surprising
as (-)-24 had a higher affinity for the δ receptor
compared with (-)-23a . Compound (-)-24 was also
observed to retain full agonist activity and to operate
via the δ receptor as its stimulation occurred in the
presence of µ- and κ- but not δ-selective antagonists.
2
7a ) 160 nM). This fact has significant consequences
to the overall selectivity observed for a given ligand.
Comparison of the selectivity for compounds, 19a versus
2
2a and 27a versus 28a in Table 1, illustrates this
point. The δ versus µ selectivities for the cyclopropyl-
methyl-substituted compounds 27 and 28a , for example,
is 8 and >182, respectively; a striking difference con-
sidering the similarity of the two molecules. Inspection
of their δ receptor affinities of 20 and 36 nM, respec-
tively, which represents only a 1.8-fold difference dem-
onstrates that this is not the source of the large
difference in selectivities. However, comparison of the
µ affinities of 160 and >6536 nM for the same two
compounds, a difference of at least 40-fold, not only
illustrates the source of the divergence in selectivities
between groups 1 and 2 but also highlights the fact that
compounds of group 1 when appropriately substituted
on the nitrogen can effectively bind to the µ receptor.
The analyses of δ and µ affinity above provide a
rationale for the empirical observation addressed earlier
that compounds of group 1 (unsubstituted), on the
whole, possessed greater δ receptor affinity but were
The racemic phenolic derivatives 21 and 26 were by
far the most potent compounds seen in this assay with
ED50 values of 90.6 and 28.6 nM, respectively. This is
in line with the observation that they possessed the
highest affinity for the δ receptor of all of the compounds
tested. However, the ED50 values observed appear to
be lower than one would have suspected based on their
receptor affinity. The observed Emax of 98 obtained for
the allyl derivative 21 indicates partial agonist charac-
ter relative to SNC-80, while racemic 26 appears to be
a full agonist with an ED50 value of 28.6 nM and an
Emax of 121. In the functional assay, compounds 21 and
26 are observed to be δ-selective as evidenced by the

9
80 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
Ta ble 2. Apparent Functional ED50 and Emax Values of DAMGO, SNC-80, U69,593, and the Selected 4-[(N-Alkyl-3-methyl-4-
piperidinyl)phenylamino]-N,N-diethylbenzamides Using GTP-γ-S Binding Assays in Guinea Pig Caudate Membranes
unblocked condition
blocked with
20 nM NTId
blocked with
blocked with
6000 nM CTAP
6 nM nor-BNIe
f
compd
(nM ( SD)
a
DAMGO ED50
592 ( 105
123 ( 6
1850 ( 287
124 ( 6
509 ( 111
135 ( 7
a
DAMGO Emax
no stimulation
673 ( 108
131 ( 5
b
SNC-80 ED50
317 ( 54
142 ( 6
629 ( 71
143 ( 4
b
SNC-80 Emax
no stimulation
1980 ( 269
178 ( 8
c
U69,593 ED50
684 ( 74
177 ( 5
no stimulation
2142 ( 223
167 ( 6
c
U69,593 Emax
2
2
3a ED50
3a Emax
3500 ( 500
63 ( 5
no stimulation
3722 ( 1094
60 ( 7
2952 ( 440
91 ( 5
4667 ( 1937
55 ( 9
(
(
(
(
(
-)-23a , 3S,4R ED50
-)-23a , 3S,4R Emax
+)-23a , 3R,4S ED50
-)-24, 3S,4R ED50
-)-24, 3S,4R Emax
2508 ( 248
126 ( 5
no stimulation
no stimulation
3604 ( 837
85 ( 8
no stimulation
1129 ( 230
121 ( 7
1523 ( 605
116 ( 15
54.0 ( 14.5
79 ( 4
43.3 ( 12.1
120 ( 3
4709 ( 1364
116 ( 15
130 ( 23
87 ( 3
71.0 ( 16.5
129 ( 6
2
2
2
2
1 ED50
1 Emax
6 ED50
6 Emax
90.6 ( 32.4
98 ( 7
28.6 ( 12.5
121 ( 9
3591 ( 202.4
85 ( 14
1820 ( 361
195 ( 11
a
2
4
5
b
DAMGO [(D-Ala ,MePhe ,Gly-ol )enkephalin], agonist selective for the µ opioid receptor. SNC-80 ([(+)-4-[(RR)-R-(2S,5R)-4-allyl-2,5-
dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide), agonist selective for the δ opioid receptor. c U69,593 [(5R,7R,8â)-(-)-
N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]benzeneacetamide], agonist selective for the κ opioid receptor. Naltrindole (NTI),
antagonist selective for the δ opioid receptor. nor-Binaltorphimine (nor-BNI), antagonist selective for the κ opioid receptor. CTAP,
antagonist selective for the µ opioid receptor.
d
e
f
3
9- and 63-fold decreases in ED50 in the presence of NTI
changes to the amide alkyl substituents dramatically
affects ligand affinity implies a direct interaction of the
N,N-diethylamido group with the receptor and supports
the previous findings. Other important findings include
but only minor changes in ED50 when tested in combi-
nation with µ- and κ-selective antagonists. In direct
comparison to 23a the ED50 values of 90.6 and 28.6 nM
found for 21 and 26 represent 38- and 122-fold increases
in potency, respectively. These findings are important
when viewed in the light of the recent findings by
O’Neill et al.3 who demonstrated that the δ/µ combina-
tion agonists provide strong analgesia with simulta-
neous cross-canceling of some of the side effects pos-
sessed by highly specific µ or δ agonists. Taken together
with their high potency for both the µ and δ receptors,
the data from O’Neill et al. suggests that 21 and 26
could prove valuable as analgesics with reduced side
effects relative to compounds operating purely though
either the µ or δ opioid receptors.
3
7
the demonstration by Knapp et al. that the stereo-
chemistry of the benzyl carbon in 2 is the single most
important determinant of receptor selectivity and those
4
27
15
of Zhang and Barn who showed that the piperidine
methyl groups in 2 are not necessary for δ receptor
recognition. The studies of the piperidine compounds
2
4
presented herein and elsewhere illustrate additional
features influencing the behavior of the N,N-diethyl-
benzamide δ agonists.
For example, this study has shown that high-affinity,
fully efficacious, and δ opioid receptor-selective com-
pounds can be obtained from the transposition of the
internal nitrogen atom in BW373U86 (1) or SNC-80 (2)
with its adjacent benzylic carbon. In addition to the
N-(4-diethylcarboxamidophenyl) group needed for the
δ address and within the context of the examples
studied, the structural features found to promote δ
receptor affinity in this transposed class of δ agonist
were a cis relative stereochemistry between the 3- and
4-substituents in the piperidine ring, a trans-crotyl or
allyl substituent on the basic nitrogen, the lack of a
2-methyl group in the piperidine ring, and either no
substitution or hydroxyl substitution in the aryl ring
not substituted with the N,N-diethylcarboxamido group.
In contrast, hydroxyl substitution in the aryl ring, the
presence of a 2-methyl group in a cis relative relation-
ship to the 4-amino group as well as N-substituents such
as cyclopropylmethyl all appear to promote binding to
the µ opioid receptor while preserving affinity at the δ
receptor. Additionally it was found that the somewhat
lower selectivities observed for the piperidine com-
pounds relative to the piperazine-based ligands appear
to arise directly from the carbon-nitrogen transposition
which imparts an overall lower δ affinity and higher µ
affinity to the piperidine-based ligands. The fundamen-
tally higher affinity for the µ receptor intrinsic to the
piperidine-based compounds suggests that ligands of
Con clu sion s
The importance of the contribution made to the area
of δ receptor research by the discovery of the N,N-
diethylbenzamides 1 and 2 should not be understated
since such events occur infrequently. Their appearance
in the literature spawned the development of a multi-
tude of structurally related δ-selective ligands. A feature
held in common with other important breakthroughs
is that the N,N-diethylbenzamides 1 and 2 possessed a
unique structure relative to contemporaneous δ recep-
tor-selective ligands and thereby established a new
direction of discovery utilizing novel δ address moieties.
However, due to their novelty, it was not immediately
apparent which of the structural features present in
these ligands elicited δ selectivity since no other com-
pounds with similar structural features existed. Studies
performed over the past decade have provided evidence
for the mechanism by which the N,N-diethylbenzamido
substructure influences δ selectivity. For example,
Bishop et al.35 and Katsura et al. have clearly shown
that the N,N-diethylamido group serves as the δ address
moiety in 1 by demonstrating that δ selectivity is lost
upon moving this group from the para to the meta
36
3
6
position. The demonstration by Katsura et al. that

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 981
this class will more easily be converted to µ/δ combina-
tion agonists relative to the piperazine ligands such as
(NMP; 40 mL) was added to freshly prepared sodium meth-
oxide (120 mmol) and heated at reflux for 4 h. After evapora-
tion of the toluene under reduced pressure, the residue was
1
which are now recognized as important for their strong
2
dissolved in a mixture of ethanol and H O (12:1, 150 mL) and
analgesia with diminished side effects relative to ago-
nists operating exclusively from either the δ or µ opioid
receptor.
heated at reflux for 1 h. After evaporation of the alcohol, the
residue was taken up in water (400 mL) and extracted with
hexanes (2 × 100 mL). The aqueous layer was made acidic
(
pH ) 1) with 10% HCl, saturated with NaCl and extracted
Exp er im en ta l Section
with a mixture of CH
drying over Na SO , the solvents were evaporated under
2
Cl
2
and THF (3:1, 5 × 200 mL). After
2
4
Melting points were determined on a Thomas-Hoover capil-
lary tube apparatus and are not corrected. Elemental analyses
were obtained by Atlantic Microlabs, Inc. and are within
reduced pressure. This material was then treated with diethyl-
amine (1.2 mL), BOP (a.k.a. Castro’s reagent) (5.0 g, 11.31
mmol) and triethylamine (4.2 mL) in THF (100 mL) for 30 min.
The reaction mixture was next diluted with ether (300 mL),
(
0.4% of the calculated values. All optical rotations were
determined at the sodium D-line using a Rudolph Research
washed with water (2 × 75 mL), saturated NaHCO
3
(75 mL)
1
Autopol III polarimeter (1-dm cell). H NMR were determined
and dried over Na SO providing a black oil following evapora-
2
4
on a Bruker Avance DPX-300 or Bruker AMX-500 spectrom-
eter using tetramethylsilane as an internal standard. Silica
gel 60 (230-400 mesh) was used for all column chromatogra-
phy. All reactions were followed by thin-layer chromatography
using Whatman silica gel 60 TLC plates and were visualized
by UV or by charring using 5% phosphomolybdic acid in
ethanol. All solvents were reagent grade. THF and diethyl
ether were dried over sodium benzophenone ketyl and distilled
prior to use.
tion of the solvents under reduced pressure. Chromatography
on silica gel using hexanes/ethyl acetate/ethanol/triethylamine
(
47:47:3:3) provided separation of all analogues prepared.
. Con ver sion fr om N-Meth ylp ip er id in e to Va r iou s N-
Alk ylp ip er id in e Der iva tives. The appropriate 4-[(N-methyl-
-piperidinyl)arylamino]-N,N-diethylbenzamide (10.82 mmol)
4
4
was treated with phenyl chloroformate (1.25 mL, 11.13 mmol)
in 1,2-dichloroethane (35 mL) at room temperature for 24 h.
The reaction was quenched with water and 30% NaOH then
3
3
2
5
[
H]DAMGO, DAMGO, and [ H][D-Ala ,D-Leu ]enkephalin
3 2 4
extracted with CHCl . After drying over Na SO and evapora-
were obtained via the Research Technology Branch, NIDA, and
were prepared by Multiple Peptide Systems (San Diego, CA).
tion of the solvents under reduced pressure, the crude product
was treated with methanol (100 mL), water (60 mL), 2-pro-
panol (50 mL) and 50% NaOH (30 mL) at reflux for 5 h. The
alcohols were evaporated under reduced pressure, and the
3
35
[
H]U69,593 and [ S]GTP-γ-S (s.a. ) 1250 Ci/mmol) were
obtained from DuPont New England Nuclear (Boston, MA).
U69,593 was obtained from Research Biochemicals Interna-
tional (Natick, MA). Levallorphan was a generous gift from
Kenner Rice, Ph.D., NIDDK, NIH (Bethesda, MD). GTP-γ-S
and GDP were obtained from Sigma Chemical Co. (St. Louis,
MO). The sources of other reagents are published.
aqueous layer was extracted with CHCl
3
/THF (3:1). After
drying with Na SO4, the solvents were evaporated under
2
reduced pressure. Chromatography of the crude residue on
silica gel using hexanes/ethyl acetate/ethanol/triethylamine
(
47:47:3) gave the N-demethylated material. This was dis-
solved in absolute ethanol (40 mL) and treated with the
appropriate alkyl bromide (2.54 mmol) and K CO (1.0 g, 7.24
Gen er a l P r oced u r es. 1. Red u ctive Alk yla tion . The
appropriate piperidone (92.68 mmol), aniline (or derivative)
2
3
(93.4 mmol) and titanium isopropoxide (35 mL, 117.7 mmol)
mmol) at room temperature for 24 h. After evaporation of the
ethanol under reduced pressure, the residue was chromato-
graphed on silica gel using hexanes/ethyl acetate/ethanol/
triethylamine (47:47:3) to provide the desired products.
were heated at 55 °C for 20 h under a nitrogen atmosphere.
The reaction mixture was allowed to cool and diluted with
ethanol (100 mL). Sodium borohydride (5.0 g, 131.6 mmol) was
then added, and the reduction was allowed to proceed at room
temperature for 4 h. The reaction was quenched by addition
of water and filtered over Celite, and the cake was washed
with ethanol. After evaporation of the filtrate under reduced
pressure, the white residue was taken up in ethyl acetate
and again filtered over Celite. This provided the 4-anilino-
piperidines as an oil after evaporation of the solvent under
reduced pressure. Chromatography on silica gel using ethyl
acetate in hexanes provided separation of all diastereomers
produced in this step. These compounds were then carried
forward independently throughout the subsequent reaction
steps.
5
. Clea va ge of Meth yl Eth er s. To a solution of compound
5 (0.500 g, 1.11 mmol) in dry CH Cl (25 mL) at -78 °C was
added BBr (0.524 mL, 5.55 mmol) dropwise over 5 min. The
reaction mixture was allowed to warm to room temperature
and then quenched with H O (25 mL). The aqueous layer was
extracted with CH Cl
(2 × 25 mL), the organic layers were
collected and dried (Na SO ), and the solvent was removed
under reduced pressure to yield crude product. This material
was purified by flash chromatography (50% (CHCl /MeOH/
NH OH, 80:18:2) in CHCl ) to afford 21 (375 mg, 78%) as an
off-white foam. Anal. (C26 ) C, H, N.
2
2
2
3
2
2
2
2
4
3
4
3
35 3 2
H N O
2
. Ar om a t ic Su b st it u t ion b et w een 4-An ilin op ip er i-
6. Rem ova l of ter t-Bu toxyca r bon yl P r otectin g Gr ou p s.
The appropriate Boc-protected piperidine (2.21 g, 7.27 mmol)
was dissolved in CH Cl (20 mL), and TFA (20 mL) was slowly
2 2
added. The reaction mixture was stirred for 1 h at room
temperature, and then the solvents were evaporated under
reduced pressure. The yellow oil was taken up in water (50
mL), and the aqueous phase was made basic (pH ) 14) with
d in es a n d 2,6-Di-ter t-bu tyl-4-m eth oxyp h en yl 4-F lu or o-
ben zoa te. The appropriate 4-anilinopiperidine (16.72 mmol)
was dissolved in dry THF (13 mL) and dry hexamethylphos-
phoramide (HMPA; 5 mL) and cooled to -42 °C. A 2.5 M
solution of n-butyllithium in hexanes (19.25 mol) was slowly
added, and the reaction mixture was kept at 0 °C for 1 h. The
reaction mixture was cannulated into a solution of 2,6-di-tert-
butyl-4-methoxyphenyl 4-fluorobenzoate (16.76 mmol) in dry
THF (13 mL) and dry HMPA (5 mL) at room temperature then
heated to 45-50 °C for 5 h. The reaction mixture was cooled
25% NaOH then extracted with CH
This residue was used directly in the alkylation step without
further purification.
2
Cl
2
/THF (3:1, 6 × 150 mL).
Eth yl 3-[N-(Meth yl 2-m eth ylp r op ion a te)a m in o]bu tyr -
a te (11). Ethyl 3-aminobutyrate (10; 50 g, 344 mmol), methyl
methacrylate (100 mL, 936 mmol), acetic acid (3.0 mL, 54.3
mmol), and ethanol (80 mL, 1.26 mol) were heated at reflux
for 16 h. The reaction mixture was allowed to cool and was
poured into a beaker containing ether (700 mL). A white
polymer of polymethyl methacrylate, formed in the reaction,
was washed with ether (2 × 100 mL). The organic phase was
4
then quenched with a solution of NH Cl and diluted with ether.
The aqueous layer was made basic (pH ) 14) with 25% NaOH
and extracted with ether (200 mL), and the ethereal layer was
4
washed with water three times. Drying with MgSO and
evaporation of the solvents under reduced pressure afforded
a crude brown oil. Chromatography on silica gel using ethyl
acetate in hexanes gave separation of all analogues prepared.
3
. Hydr olysis of BHA Ester s an d Con ver sion to N,N-Di-
washed with a saturated solution of NaHCO
3
(2 × 75 mL) and
eth ylben za m id e Der iva tives. 2,6-Di-tert-butyl-4-methoxy-
phenyl 4-[(N-substituted-4-piperidinyl)phenylamino]benzoate
with a saturated solution of NaCl (50 mL). After drying the
organic phase with MgSO and evaporation of the solvents and
excess methyl methacrylate under reduced pressure, a 75:25
4
(11.99 mmol) in toluene (150 mL) and N-methylpyrrolidinone

9
82 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
mixture of the diester and the starting amine (55.0 g, 69%)
was obtained as a yellow liquid. The mixture can be used as
such in the next reaction or can be further purified to give the
ized as its hydrochloride monohydrate salt obtained as previ-
1
ously described: H NMR (CD
3
OD) δ 1.16 (d, 3H, J ) 6.5 Hz),
1.17 (t, 3H, J ) 7.0 Hz), 1.17-1.25 (m, 3H), 1.39 (d, 3H, J )
5.6 Hz), 1.67-1.76 (m, 1H), 2.05-2.15 (m, 1H), 2.27 (d, 1H, J
) 13.7 Hz), 3.03 (t, 1H, J ) 12.5 Hz), 3.48 (q, 2H, J ) 7.1 Hz),
3.47-3.55 (m, 2H), 3.71 (dd, 1H, J ) 8.2 Hz, J ) 13.6 Hz),
3.94 (dd, 1H, J ) 6.2 Hz, J ) 13.6 Hz), 4.29 (dt, 1H, J ) 3.3
Hz, J ) 11.4 Hz), 5.60 (s, 1H), 5.64 (d, 1H, J ) 15.9 Hz), 5.94-
6.03 (m, 1H), 6.81 (d, 2H, J ) 8.7 Hz), 7.20 (d, 2H, J ) 7.5
Hz), 7.26 (d, 2H, J ) 8.7 Hz), 7.36 (t, 1H, J ) 7.4 Hz), 7.50 (d,
1
pure diester 11: H NMR (CDCl
1
(
3
) δ 1.13 (d, 3H, J ) 6.4 Hz),
.17 (d, 3H, J ) 6.9 Hz), 1.26 (t, 3H, J ) 7.1 Hz), 2.26-2.49
m, 2H), 2.58-2.70 (m, 2H), 2.29-2.91 (m, 1H), 3.08 (q, 1H,
J ) 6.4 Hz), 3.67 (s, 3H), 4.13 (q, 2H, J ) 7.1 Hz); C NMR
CDCl ) δ 14.0, 15.0, 20.0, 40.1, 41.5, 49.7, 49.9, 51.9, 60.1,
72.1, 176.0.
2RS,5RS)-1-(ter t-Bu toxycar bon yl)-2,5-dim eth yl-4-piper -
1
3
(
3
1
(
2H, J ) 7.7 Hz); 13C NMR (CD
OD) δ 13.9, 16.0, 17.9, 35.2,
id on e (12) a n d (2RS,5SR)-1-(ter t-Bu toxyca r bon yl)-2,5-
d im eth yl-4-p ip er id on e (13). Sodium (5.8 g, 252.2 mmol) in
xylenes (100 mL) was heated to 100 °C. The 75:25 mixture of
ethyl 3-[N-(methyl 2-methylpropionate)amino]butyrate (11)
and ethyl 3-aminobutyrate (55.0 g, 238.1 mmol) in xylenes (100
mL) was slowly added, and the heating was continued at reflux
for 2 h. The reaction mixture was allowed to cool, and the
xylenes were removed under reduced pressure to afford the
crude â-keto ester 3-(ethoxycarbonyl)-2,5-dimethyl-4-piperi-
done as a brown solid. The crude â-keto ester was dissolved
in 20% HCl (200 mL) and heated at reflux for 16 h. The
reaction mixture was allowed to cool, and water and HCl were
evaporated under reduced pressure to afford the crude 2,5-
dimethyl-4-piperidone hydrochloride as a brown solid. Methanol/
triethylamine 10% v/v (750 mL) was slowly added to the crude
piperidone hydrochloride. Di-tert-butyl dicarbonate (50.0 g,
3
37.5, 41.2, 44.9, 56.0, 57.8, 59.3, 59.9, 119.4, 127.1, 127.6,
128.8, 129.0, 129.6, 130.5, 131.2, 144.3, 151.7, 173.8. Anal.
(C27
H
38ClN
3
2
O‚H O) C, H, N.
4-[N-{(2RS,4SR,5SR)-N-Allyl-2,5-dim eth yl-4-piper idinyl}-
p h en yla m in o]-N,N-d ieth ylben za m id e (16c). Compound
1
6c was prepared according to the general procedures in 23%
yield starting from compound 14c. The product was character-
ized as its hydrochloride monohydrate salt obtained as a white
1
powder as previously described: H NMR (CD
3
OD) δ 1.16 (d,
3
1
1
H, J ) 6.5 Hz), 1.17 (t, 3H, J ) 7.0 Hz), 1.17-1.25 (m, 3H),
.39 (d, 3H, J ) 5.6 Hz), 1.67-1.76 (m, 1H), 2.05-2.15 (m,
H), 2.27 (d, 1H, J ) 13.7 Hz), 3.03 (t, 1H, J ) 12.5 Hz), 3.48
q, 2H, J ) 7.1 Hz), 3.47-3.55 (m, 2H), 3.71 (dd, 1H, J ) 8.2
Hz, J ) 13.6 Hz), 3.94 (dd, 1H, J ) 6.2 Hz, J ) 13.6 Hz), 4.29
dt, 1H, J ) 3.3 Hz, J ) 11.4 Hz), 5.60 (s, 1H), 5.64 (d, 1H, J
15.9 Hz), 5.94-6.03 (m, 1H), 6.81 (d, 2H, J ) 8.7 Hz), 7.20
d, 2H, J ) 7.5 Hz), 7.26 (d, 2H, J ) 8.7 Hz), 7.36 (t, 1H, J )
(
(
)
2
29.0 mmol) was added to the reaction mixture, and the
solution was heated to reflux for 2 h. The reaction mixture
was allowed to cool, and the solvents were evaporated under
reduced pressure. The crude product was dissolved in ether
(
13
7
1
1
1
.4 Hz), 7.50 (d, 2H, J ) 7.7 Hz); C NMR (CD OD) δ 13.9,
5.1, 16.9, 18.8, 36.2, 38.5, 42.9, 46.7, 56.9, 58.6, 59.9, 60.8,
17.4, 125.6, 127.8, 128.0, 129.1, 130.4, 132.0, 132.2, 144.4,
3
(
750 mL), washed with water (2 × 50 mL), and with a
saturated solution of NaCl (2 × 50 mL). After drying the
organic phase with MgSO , evaporation of the solvents under
53.6, 175.1. Anal. (C27
-[N-{(3SR,4RS)-N,3-Dim eth yl-4-piper idin yl}-3-m eth oxy-
p h en yla m in o]-N,N-d iet h ylb en za m id e (19a ). Compound
9a was prepared according to the general procedures in 53%
H
38ClN
3
O‚1.5H
2
O) C, H, N.
4
4
reduced pressure and chromatography on silica gel using
hexanes/ethyl acetate (80:20) as eluents, a 55:45 mixture of
cis (13) and trans (12) piperidones was obtained (16.37 g, 30%)
as a yellow liquid. Further chromatography afforded first the
cis-piperidone then the trans-piperidone. The spectral data for
1
yield starting from compound 17a . The product was character-
ized as its hydrochloride salt as a white powder obtained as
1
previously described: H NMR (CD
3
OD) δ 1.09-1.36 (m, 12H),
the cis-piperidone, obtained as a white solid, were the follow-
1
1.49-1.64 (m, 1H), 1.75-1.96 (m, 1H), 2.61-2.70 (m, 3H),
.06-3.13 (m, 1H), 3.30-3.60 (m, 4H), 3.76 (s, 3H), 4.30-4.45
m, 1H), 6.65 (s, 3H), 6.69-6.78 (m, 1H), 6.79-6.93 (m, 2H),
.20-7.37 (m, 3H). Anal. (C25 ‚1.25H O) C, H, N.
4-[N-{(3RS,4RS)-N,3-Dim eth yl-4-piper idin yl}-3-m eth oxy-
ing: H NMR (CDCl
3
) δ 0.94 (d, 3H, J ) 7.0 Hz), 1.04 (d, 3H,
3
(
J ) 6.6 Hz), 1.42 (s, 9H), 2.25 (dd, 1H, J ) 2.2 Hz, J ) 13.7
Hz), 2.53 (m, 1H, J ) 6.2 Hz), 2.68 (dd, 1H, J ) 6.8 Hz, J )
7
H
36ClN
3
O
2
2
1
4
4
3.6 Hz), 2.82 (t, 1H, J ) 12.6 Hz), 4.15-4.38 (m, 1H), 4.52-
13
.87 (m, 1H); C NMR (CDCl
3
) δ 10.9, 17.9, 28.0, 44.1, 45.3,
6.3, 48.8, 80.0, 154.0, 209.6; mp 57-59 °C. The spectral data
for the trans-piperidone, obtained as a yellow liquid, were the
following: H NMR (CDCl
p h en yla m in o]-N,N-d iet h ylb en za m id e (19b ). Compound
19b was prepared according to the general procedures in
50% yield starting from compound 17b. The product was char-
1
3
) δ 1.06 (d, 3H, J ) 7.1 Hz), 1.00
(
)
1
d, 3H, J ) 6.7 Hz), 1.47 (s, 9H), 2.09 (dd, 1H, J ) 3.6 Hz, J
acterized as its hydrochloride salt as a white powder obtained
1
15.3 Hz), 2.29-2.40 (m, 1H), 2.64 (dd, 1H, J ) 6.7 Hz, J )
as previously described: H NMR (CD
3
OD) δ 1.10-1.26
5.3 Hz), 3.46 (dd, 1H, J ) 5.2 Hz, J ) 13.8 Hz), 3.60 (dd, 1H,
(m, 9H), 1.75-2.40 (m, 3H), 2.84 (s, 3H), 2.88-3.04 (m, 1H),
3.12-3.28 (m, 1H), 3.34-3.58 (m, 6H), 3.80 (s, 3H), 4.10-4.22
(m, 1H), 6.66 (s, 1H), 6.73 (d, 1H, J ) 7.8 Hz), 6.82 (d, 2H,
J ) 8.6 Hz), 6.88 (d, 1H, J ) 7.9 Hz), 7.24 (d, 2H, J ) 8.6 Hz),
1
3
J ) 4.6 Hz, J ) 13.8 Hz), 4.38 (m, 1H, J ) 3.4 Hz); C NMR
CDCl ) δ 14.3, 19.9, 28.1, 43.3, 44.3, 46.2, 47.3, 79.9, 154.6,
11.2.
-[N-{(2SR,4RS,5SR)-N-Allyl-2,5-d im eth yl-4-p ip er id in -
yl}p h en yla m in o]-N,N-d ieth ylben za m id e (16a ). Compound
6a was prepared according to the general procedures in 11%
(
3
2
7
3
1
.36 (t, 1H, J ) 8.1 Hz); 13C NMR (CD
3
OD) δ 12.1, 16.2, 29.1,
5.3, 44.0, 55.4, 56.0, 58.9, 60.8, 115.9, 117.9, 127.8, 129.1,
31.6, 145.4, 151.5, 162.5, 173.9. Anal. (C25 ‚1.25H O)
4
H
36ClN
3
O
2
2
1
C, H, N.
yield starting from compound 14a . The product was character-
ized as its hydrochloride salt obtained as a white powder by
4-[N-{(3SR,4RS)-N-Allyl-3-m eth yl-4-piper idin yl}-3-m eth -
oxyp h en yla m in o]-N,N-d iet h ylb en za m id e (20a ). Com-
pound 20a was prepared according to the general procedures
in 32% yield starting from compound 17a . The product was
characterized as its hydrochloride salt as a white powder
addition of equimolar amounts of HCl, 1 M in ether, to an
1
ethereal solution of the benzamide: H NMR (CD
1
3
OD
)
δ 1.16-
.20 (m, 6H), 1.19 (d, 3H, J ) 7.3 Hz), 1.31 (d, 3H, J ) 6.3
Hz), 1.58-1.62 (m, 2H), 2.89-2.94 (m, 1H), 3.44-3.51 (m, 5H),
1
3
4
5
1
6
1
1
.73-3.79 (m, 1H), 3.97 (dd, 1H, J ) 6.1 Hz, J ) 13.6 Hz),
.39-4.43 (m, 1H), 5.64 (m, 1H), 5.67 (d, 1H, J ) 6.7 Hz),
.95-6.70 (m, 1H), 6.78 (d, 2H, J ) 6.8 Hz), 7.15 (dd, 2H, J )
Hz, J ) 8.4 Hz), 7.23 (d, 2H, J ) 8.8 Hz), 7.27 (t, 1H, J )
obtained as previously described: H NMR (CDCl ) δ 1.12 (d,
3
3H, J ) 6.0 Hz), 1.14-1.22 (m, 7H), 1.65 (q, 1H, J ) 10.9 Hz),
1.96 (t, 1H, J ) 10.9 Hz), 2.17 (d, 1H, J ) 10.7 Hz), 2.54 (s,
1H), 2.79-2.89 (m, 3H), 2.93-3.02 (m, 1H), 3.41 (s, 4H), 3.74
(s, 3H), 3.91 (d, 1H, J ) 12.1 Hz), 5.08 (d, 1H, J ) 9.8 Hz),
5.14 (d, 1H, J ) 17.1 Hz), 5.64-5.75 (m, 1H), 6.56 (s, 1H),
6.59 (d, 1H, J ) 7.5 Hz), 6.66 (d, 1H, J ) 7.5 Hz), 6.72 (d, 2H,
J ) 7.8 Hz), 7.18 (t, 1H, J ) 7.8 Hz), 7.22 (d, 2H, J ) 7.7 Hz);
.3 Hz), 7.41 (t, 2H, J ) 7.8 Hz); 13C NMR (CD
OD) δ 14.7,
3
5.9, 17.2, 20.1, 32.8, 36.5, 43.4, 47.5, 58.6, 59.0, 60.1, 62.9,
21.8, 129.2, 129.9, 131.2, 133.2, 148.4, 153.2, 176.2. Anal.
(
C
27
H
38ClN
3
O‚H
-[N-{(2RS,4RS,5SR)-N-Allyl-2,5-d im eth yl-4-p ip er id in -
yl}p h en yla m in o]-N,N-d ieth ylben za m id e (16b). Compound
6b was prepared according to the general procedures in 22%
yield starting from compound 14b. The product was character-
2
O) C, H, N.
1
3
4
C NMR (CDCl
3
) δ 13.4, 27.0, 30.2, 41.1, 54.2, 55.1, 58.6, 58.7,
61.5, 109.4, 113.2, 117.0, 119.7, 119.8, 127.5, 128.2, 129.4,
1
135.5, 147.1, 148.9, 160.3, 171.4. Anal. (C27
C, H, N.
H
38ClN
3
O
2
2
‚0.25H O)

SAR of Piperidinyl-Based Diethylbenzamides
-[N-{(3RS,4RS)-N-Allyl-3-m eth yl-4-piper idin yl}-3-m eth -
oxyp h en yla m in o]-N,N-d iet h ylb en za m id e (20b ). Com-
pound 20b was prepared according to the general procedures
in 18% yield starting from compound 17b. The product was
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 983
2
0
4
recrystallized from an ethyl acetate/methanol mixture: [R]
-204° (c 1.01, MeOH). Anal. (C26 ‚HCl) C, H, N.
D
35 3 2
H N O
(+)-4-[N-{(3R,4S)-N-Allyl-3-m eth yl-4-piper idin yl}ph en yl-
a m in o]-N,N-d ieth ylben za m id e [(+)-23a ]. This compound
characterized as its hydrochloride salt as a white powder
was prepared from (+)-cis-3-methyl-4-N-phenyl-4-piperidin-
1
13,38
obtained as previously described: H NMR (CD
3
OD) δ 1.12-
amine
according to the general procedures in 28% yield.
1
3
2
5
(
1
.25 (m, 9H), 1.78-2.00 (m, 1H), 2.03-2.30 (m, 2H), 2.84-
The product was characterized as its hydrochloride salt as a
2
0
.02 (m, 1H), 3.10-3.27 (m, 1H), 3.38-3.55 (m, 7H), 3.73 (dd,
H, J ) 7.0 Hz), 3.70 (s, 3H), 4.11-4.28 (m, 1H), 5.56 (s, 1H),
.61 (d, 1H, J ) 5.6 Hz), 5.82-6.02 (m, 1H), 6.66 (s, 1H), 6.73
white powder obtained as previously described: [R]
+203°
D
(c 1.07, MeOH). Anal. (C26
35 3 2
H N O ‚HCl) C, H, N.
4
-[N-{(3RS,4RS)-N-Allyl-3-m eth yl-4-piper idin yl}ph en yl-
d, 1H, J ) 7.9 Hz), 6.82 (d, 2H, J ) 8.6 Hz), 6.85-6.90 (m,
H), 7.23 (d, 2H, J ) 8.5 Hz), 7.36 (t, 1H, J ) 8.1 Hz); 13
NMR (CD OD) δ 12.1, 16.2, 28.9, 35.2, 53.0, 55.9, 58.4, 59.1,
0.2, 112.5, 115.9, 117.9, 121.9,126.9, 127.5, 128.2, 129.0,
31.7, 145.6, 151.4, 162.6, 173.8. Anal. (C27 ‚H O)
a m in o]-N,N-d ieth ylben za m id e (23b). Compound 23b was
prepared according to the general procedures in 38% yield
starting from compound 17d . The product was characterized
as its hydrochloride salt as a white powder obtained as
C
3
6
1
1
H
38ClN
3
O
2
2
previously described: H NMR (CD OD) δ 1.10-1.26 (m, 9H),
3
C, H, N.
1.74-1.96 (m, 1H), 1.98-2.29 (m, 2H), 2.88-01 (m, 1H), 3.10-
3.22 (m, 1H), 3.35-3.61 (m, 7H), 3.73 (d, 2H, J ) 7.3 Hz), 4.20
(dt, 1H, J ) 3.4 Hz, J ) 11.5 Hz), 5.55 (s, 1H), 5.61 (d, 1H,
J ) 5.4 Hz), 5.85-6.03 (m, 1H), 6.78 (d, 2H, J ) 8.8 Hz), 7.19
(d, 2H, J ) 7.8 Hz), 7.23 (d, 2H, J ) 8.8 Hz), 7.34 (t, 1H, J )
4
-[N-{(3SR,4RS)-N-Allyl-3-m eth yl-4-p ip er id in yl}-3-h y-
d r oxyp h en yla m in o]-N,N-d ieth ylben za m id e (21). Com-
pound 21 was prepared according to the general procedures
in 18% yield starting from compound 17a . The product was
7.4 Hz), 7.51 (t, 2H, J ) 7.6 Hz); 13C NMR (CD
OD) δ 11.9,
13.9, 16.2, 28.9, 35.2, 52.9, 58.3, 59.1, 60.1, 117.0, 126.8,
27.6, 127.8, 129.0, 130.7, 131.2, 144.1, 151.8, 173.9. Anal.
O‚0.25H O) C, H, N.
4-[N-{(3SR,4RS)-N-Crotyl-3-methyl-4-piperidinyl}phenyl-
characterized as its hydrochloride salt as a white powder
3
1
obtained as previously described: H NMR (CDCl
3
) δ 7.19 (d,
1
(
2
1
2
1
H, J ) 8.5 Hz), 7.09 (m, 1H), 6.65-6.50 (m, 5H), 5.82 (m,
C
26
H
36ClN
3
2
H), 3.78 (m, 2H), 3.88 (d, 1H, J ) 8.7 Hz), 3.42 (br. 4H), 3.03-
.81 (m, 4H), 2.54 (br., 1H), 2.22 (d, 1H, J ) 9.6 Hz), 1.99 (t,
H, J ) 11.5 Hz), 1.66 (q, 1H, J ) 12.1 Hz), 1.25-1.15 (m, 7
a m in o]-N,N-d ieth ylben za m id e (24). Compound 24 was
prepared according to the general procedures in 22% yield
starting from compound 17c. The product was characterized
1
3
Hz), 1.08 (d, 3H, J ) 6.9 Hz); C NMR (CDCl
3
) δ 172.3, 158.1,
49.8, 146.5, 135.0 (br.), 129.9, 129.2, 128.0, 126.8, 120.2,
18.3, 116.3, 113.0, 61.9, 58.9, 58.5, 54.3, 43.0 (br.), 30.5, 30.0,
2.0, 13.9 (br.). Anal. (C26 ‚HCl‚EtOH) C, H, N.
-[N-{(3SR,4RS)-N,3-Dim et h yl-4-p ip er id in yl}p h en yl-
1
1
2
as its hydrochloride salt as a white solid obtained as previously
1
H
35
N
3
O
2
described: H NMR (CD
3
OD) δ 1.09-1.30 (m, 9H), 1.49-1.60
(
m, 1H), 1.72-1.89 (m, 4H), 2.85-3.20 (m, 2H), 3.35-3.57 (m,
4
7
6
H), 3.60-3.88 (m, 2H), 4.35-4.47 (m, 1H), 5.58-5.70 (m, 1H),
.00-6.15 (m, 1H), 6.74-6.86 (m, 2H), 7.09-7.48 (m, 7H);
a m in o]-N,N-d ieth ylben za m id e (22a ). Compound 22a was
prepared according to the general procedures in 61% yield
starting from compound 17c. The product was characterized
1
3
C NMR (CD OD) δ 12.4, 13.7, 18.3, 25.6, 30.3, 53.2, 53.3,
3
5
4.5, 56.3, 57.5, 57.6, 60.2, 119.1, 119.4, 120.1, 127.4,
as its hydrochloride salt as a white powder obtained as
1
128.4, 128.8, 130.7, 136.9, 140.0, 146.1, 150.9, 173.8 Anal.
O‚1.5H O) C, H, N.
previously described: H NMR (CD
3
OD) δ 1.07-1.38, 6.80 (d,
(
C
27
H
38ClN
3
2
2
H, J ) 8.3 Hz), 7.14 (d, 2H, J ) 7.7 Hz), 7.26 (t, 3H, J ) 7.5
13
(-)-4-[N-{(3S,4R)-N-Crotyl-3-methyl-4-piperidinyl}phenyl-
Hz), 7.40 (t, 2H, J ) 7.4 Hz); C NMR (CD
3
OD) δ 12.2, 25.6,
0.4, 44.5, 55.7, 56.0, 60.2, 119.4, 127.4, 128.8, 130.7, 130.8,
46.1, 150.8, 173.8. Anal. (C24 O‚H O) C, H, N.
-[N-{(3RS,4RS)-N,3-Dim et h yl-4-p ip er id in yl}p h en yl-
a m in o]-N,N-d ieth ylben za m id e [(-)-24]. This compound
3
1
was prepared from (-)-cis-3-methyl-4-N-phenyl-4-piperidin-
H
34ClN
3
2
amine1
3,38
according to the general procedures in 33% yield.
4
The product was characterized as its hydrochloride salt as an
a m in o]-N,N-d ieth ylben za m id e (22b). Compound 22b was
prepared according to the general procedures in 59% yield
starting from compound 17d . The product was characterized
2
0
off-white foam obtained as previously described: [R]
c 1.04, MeOH). Anal. (C27 O‚HCl‚0.5H O) C, H, N.
-[N-{(3SR,4RS)-N-Cr ot yl-3-m et h yl-4-p ip er id in yl}-3-
D
-204°
(
H
37
N
3
2
4
as its hydrochloride salt as a white powder obtained as
1
m eth oxyp h en yla m in o]-N,N-d ieth ylben za m id e (25). Com-
pound 25 was prepared according to the general procedures
in 22% yield starting from compound 17a . The product was
characterized as its hydrochloride salt as a white powder
previously described: H NMR (CD
3
OD) δ 1.10-1.25 (m, 12H),
1
1
8
7
.76-2.28 (s, 3H), 2.99 (t, 1H, J ) 12.5 Hz), 3.12-3.29 (m,
H), 3.31-3.58 (m, 7H), 4.12-4.29 (m, 1H), 6.78 (d, 2H, J )
.8 Hz), 7.18 (d, 2H, J ) 7.3 Hz), 7.22 (d, 2H, J ) 8.8 Hz),
.33 (t, 1H, J ) 7.4 Hz), 7.48 (t, 2H, J ) 7.5 Hz); 13C NMR
obtained as previously described: 1H NMR (CDCl
H, J ) 6.6 Hz), 1.12 (d, 3H, J ) 6.9 Hz), 1.13-1.20 (m, 7H),
) δ 1.11 (d,
3
3
1
1
3
6
(
CD
3
OD) δ 16.1, 29.0, 35.3, 43.8, 55.3, 58.7, 60.7, 116.9,
27.3, 127.8, 129.1, 130.7, 131.2, 144.0, 152.0, 173.9. Anal.
O‚1.25H O) C, H, N.
-[N-{(3SR,4RS)-N-Allyl-3-m eth yl-4-piper idin yl}ph en yl-
.58-1.71 (m, 4H), 1.92 (t, 1H, J ) 11.7 Hz), 2.14 (d, 1H, J )
1.6 Hz), 2.54 (s, 1H), 2.75-2.94 (m, 4H), 3.41 (s, 4H), 3.73 (s,
H), 3.86-3.93 (m, 1H), 5.41-5.47 (m, 1H), 5.52-5.59 (m, 1H),
.55 (t, 1H, J ) 2.1 Hz), 6.59 (d, 1H, J ) 7.3 Hz), 6.63-6.68
1
(C
24
H
34ClN
3
2
4
a m in o]-N,N-d ieth ylben za m id e (23a ). Compound 23a was
prepared according to the general procedures in 43% yield
starting from compound 17c. The product was characterized
(
m, 1H), 6.72 (d, 2H, J ) 8.7 Hz), 7.17 (dt, 1H, J ) 3.6 Hz,
13
J ) 8.0 Hz), 7.22 (d, 2H, J ) 8.7 Hz); C NMR (CDCl
3
) δ 13.5,
7.6, 27.0, 30.2, 41.1, 54.0, 54.6, 55.1, 58.7, 60.7, 109.4, 113.2,
19.7, 127.5, 127.9, 128.2, 129.4, 147.2, 148.9, 160.3, 171.4.
‚0.25H O) C, H, N.
-[N-{(3SR,4RS)-N-Cr ot yl-3-m et h yl-4-p ip er id in yl}-3-
1
1
as its hydrochloride salt as a white powder obtained as
1
previously described: H NMR (CDCl
(
3
) 1.08-1.24 (m, 9H), 1.54
Anal. (C28
H
40ClN
3
O
2
2
d, 1H, J ) 13.9 Hz), 1.82 (q, 1H, J ) 12.1 Hz), 2.90 (s, 1H),
4
3
6
5
7
.09 (t, 1H, J ) 12.0 Hz), 3.33-3.52 (m, 7H), 3.75 (d, 2H, J )
.6 Hz), 4.39 (d, 1H, J ) 11.9 Hz), 5.59 (d, 1H, J ) 4.9 Hz),
.62 (s, 1H), 5.96-6.04 (m, 1H), 6.81 (d, 2H, J ) 8.1 Hz),
.23 (d, 2H, J ) 7.8 Hz), 7.26 (d, 1H, J ) 7.5 Hz), 7.40 (t, 2H,
h yd r oxyp h en yla m in o]-N,N-d ieth ylben za m id e (26). Com-
pound 26 was prepared according to the general procedures
in 78% yield starting from compound 25. The product was
characterized as its hydrochloride salt as an off-white foam
1
3
J ) 7.5 Hz); C NMR (CDCl
5
1
3
) δ 14.7, 15.5, 16.6, 27.9, 32.7,
5.8, 58.6, 60.1, 63.0, 121.8, 129.3, 129.7, 129.9, 131.1, 131.2,
33.0, 133.1, 148.5, 153.1, 176.1. Anal. (C26 O‚0.25H O)
1
obtained as previously described: H NMR (CDCl
3
) δ 7.19 (d,
2
(
4
H, J ) 8.6 Hz), 7.09 (t, 1H, J ) 7.8 Hz), 6.62 (m, 3H), 6.50
m, 2H), 5.54 (m, 2H), 3.88 (m, 1H), 3.42 (br., 4H), 2.85 (m,
H
36ClN
3
2
C, H, N.
H), 2.53 (br., 1H), 2.20 (m, 1H), 1.92 (t, 1H, J ) 11.3 Hz),
13
(
-)-4-[N-{(3S,4R)-N-Allyl-3-m eth yl-4-piper idin yl}ph en yl-
1.65 (m, 4H), 1.18 (m, 8H), 1.07 (d, 3H, J ) 6.9 Hz);
C
a m in o]-N,N-d ieth ylben za m id e [(-)-23a ]. This compound
3
NMR (CDCl ) δ 171.9, 157.9, 149.5, 145.8, 129.4, 129.0,
was prepared from (-)-cis-3-methyl-4-N-phenyl-4-piperidin-
127.5, 127.0, 125.7, 119.7, 117.3, 116.2, 112.7, 60.7, 58.5,
58.1, 53.6, 41.5 (br.), 29.9, 26.4, 17.6, 13.4 (br.), 12.9. Anal.
1
3,38
amine
according to the general procedures in 31% yield.
The product was characterized as its HCl salt which was
(C27
H
35
N
3
O
2
2
‚1.5HCl‚0.75H O) C, H, N.

9
84 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
-[N-{(3SR,4RS)-N-Cyclopr opylm eth yl-3-m eth yl-4-piper -
Thomas et al.
4
pound 30 was prepared according to the general procedures
in 19% yield starting from compound 17a . The product was
characterized as its hydrochloride salt as a white solid obtained
id in yl}p h en yla m in o]-N,N-d ieth ylben za m id e (27a ). Com-
pound 27a was prepared according to the general procedures
in 21% yield starting from compound 17c. The product was
1
as previously described: H NMR (CDCl
3
) δ 1.13 (d, 3H, J )
1
characterized as its free base: H NMR (CDCl
3
) δ 0.08-0.09
6.9 Hz), 1.15-1.20 (m, 7H), 1.60-1.68 (m, 1H), 1.69 (s, 3H),
1.92 (t, 1H, J ) 11.7 Hz), 2.10 (d, 1H, J ) 10.9 Hz), 2.52 (s,
1H), 2.66-2.75 (m, 2H), 2.79 (d, 1H, J ) 10.4 Hz), 2.84 (d,
1H, J ) 13.0 Hz), 3.41 (s, 4H), 3.74 (s, 3H), 3.91 (dt, 1H, J )
3.9 Hz, J ) 10.9 Hz), 4.78 (s, 1H), 4.83 (s, 1H), 6.57 (s, 1H),
6.60 (d, 1H, J ) 7.9 Hz), 6.66 (dd, 1H, J ) 2.3 Hz, J ) 8.2 Hz),
(
9
2
m, 2H), 0.31-0.50 (m, 2H), 0.66-0.82 (m, 1H), 1.07-1.18 (m,
H), 1.58 (dq, 1H, J ) 3.7 Hz, J ) 12.4 Hz), 1.86-2.04 (m,
H), 2.14-2.23 (m, 2H), 2.50 (s, 2H), 2.91 (d, 2H, J ) 11.1
Hz), 3.27-3.48 (m, 4H), 3.84 (dt, 1H, J ) 4.0 Hz, J ) 8.0 Hz),
6
.60 (d, 2H, J ) 8.7 Hz), 6.99 (d, 2H, J ) 7.3 Hz), 7.07 (t, 1H,
J ) 7.3 Hz), 7.16 (d, 2H, J ) 8.7 Hz), 7.24 (t, 2H, J ) 7.5 Hz);
6.72 (d, 2H, J ) 8.5 Hz), 7.19 (t, 1H, J ) 8.1 Hz), 7.23 (d, 2H,
1
3
13
C NMR (CDCl
8.5, 58.8, 63.4, 118.0, 124.6, 127.0, 127.5, 129.0, 129.8, 145.3,
49.3, 171.4. Anal. (C27 O) C, H, N.
-[N-{(3RS,4RS)-N-Cyclopr opylm eth yl-3-m eth yl-4-piper -
3
) δ 3.4, 4.1, 8.3, 13.5, 27.0, 29.9, 39.1, 54.1,
J ) 8.5 Hz); C NMR (CDCl ) δ 13.2, 13.3, 20.5, 27.1, 30.3,
3
5
1
41.3, 54.3, 55.1, 58.5, 58.9, 65.1, 109.4, 112.1, 113.4, 119.6,
119.9, 127.5, 128.2, 129.4, 143.3, 147.2, 149.0, 160.3, 171.4.
37 3
H N
Anal. (C28
H
40ClN
3
O
2
2
‚0.25H O) C, H, N.
4
id in yl}p h en yla m in o]-N,N-d ieth ylben za m id e (27b). Com-
pound 27b was prepared according to the general procedures
in 7% yield starting from compound 17d . The product was
4-[N-{(3SR,4SR)-N-P renyl-3-methyl-4-piperidinyl}phenyl-
a m in o]-N,N-d ieth ylben za m id e (31). Compound 31 was
prepared according to the general procedures in 24% yield
starting from compound 17c. The product was characterized
1
characterized as its free base: H NMR (CDCl
2
6
)
1
4
3
) 0.10-0.15 (m,
H), 0.49-0.58 (m, 2H), 0.81-0.89 (m, 1H), 1.06 (d, 3H, J )
.1 Hz), 1.18 (t, 6H, J ) 6.7 Hz), 1.72 (dq, 1H, J ) 4.0 Hz, J
as its hydrochloride salt as a white solid obtained as previously
1
described: H NMR (CD
3
OD) δ 1.11-1.30 (m, 9H), 1.52-1.60
12.6 Hz), 1.89-1.99 (m, 3H), 2.15-2.21 (m, 3H), 3.11 (d,
(m, 1H), 1.70-1.80 (m, 1H), 1.80 (s, 3H), 1.87 (s, 3H), 2.90 (s,
1H), 3.06 (dt, 1H, J ) 2.5 Hz, J ) 12.8 Hz), 3.32-3.52 (m,
7H), 3.73 (d, 2H, J ) 7.8 Hz), 4.23-4.30 (m, 1H), 5.32 (t, 1H,
J ) 7.9 Hz), 6.80 (d, 2H, J ) 8.7 Hz), 7.15 (d, 2H, J ) 7.3 Hz),
H, J ) 10.3 Hz), 3.16 (d, 1H, J ) 10.3 Hz), 3.39-3.53 (m,
H), 3.76-3.83 (m, 1H), 6.72 (d, 2H, J ) 7.0 Hz), 7.15-7.22
1
3
(
m, 4H), 7.26-7.31 (m, 1H), 7.41-7.47 (m, 2H); C NMR
7.23-7.38 (m, 3H), 7.42 (t, 2H, J ) 7.6 Hz); 13C NMR (CD -
(CDCl
3
) 4.5, 4.6, 8.7, 13.8, 17.3, 30.7, 36.0, 54.3, 62.0, 62.6,
4.2, 116.7, 126.8, 127.2, 128.9, 130.6, 130.8, 145.0, 152.3,
74.0. Anal. (C27 O‚0.25H O) C, H, N.
-[N-{(3SR,4RS)-N-Cyclopr opylm eth yl-3-m eth yl-4-piper -
id in yl}-3-m eth oxyp h en yla m in o]-N,N-d ieth ylben za m id e
28a ). Compound 28a was prepared according to the general
3
6
1
OD) δ 12.3, 13.5, 18.6, 25.6, 26.2, 30.3, 53.1, 56.0, 56.4, 57.3,
H
37
N
3
2
119.6, 128.6, 128.7, 130.6, 130.7, 146.1, 146.6, 150.8, 173.7.
4
Anal. (C28
H
40ClN
3
2
O‚1.25H O) C, H, N.
4-[N-{(3SR,4RS)-N-P r en yl-3-m et h yl-4-p ip er id in yl}-3-
m eth oxyp h en yla m in o]-N,N-d ieth ylben za m id e (32). Com-
pound 32 was prepared according to the general procedures
in 20% yield starting from compound 17a . The product was
characterized as its hydrochloride salt as a white solid obtained
(
procedures in 13% yield starting from compound 17a . The
product was characterized as its hydrochloride salt as a white
1
solid obtained as previously described: H NMR (CDCl
-
3
) δ
1
0.02-0.01 (m, 2H), 0.36-0.46 (m, 2H), 0.69-0.82 (m, 1H),
as previously described: H NMR (CDCl ) δ 1.12 (d, 3H, J )
3
1
2
3
.02-1.19 (m, 10H), 1.55-1.73 (m, 1H), 1.87-2.11 (m, 2H),
.13-2.30 (m, 2H), 2.51 (s, 1H), 2.94 (d, 2H, J ) 10.6 Hz),
.29-3.45 (m, 4H), 3.69 (s, 3H), 3.82-3.91 (m, 1H), 6.50-6.70
7.0 Hz), 1.14-1.22 (t, 7H), 1.61 (s, 3H), 1.67 (dd, 1H, J ) 3.8
Hz, J ) 12.3 Hz), 1.70 (s, 3H), 1.95 (t, 1H, J ) 11.0 Hz), 2.17
(dd, 1H, J ) 2.1 Hz, J ) 11.4 Hz), 2.54 (s, 1h), 2.81 (d, 1H,
J ) 11.2 Hz), 2.82-2.86 (m, 3H), 3.42 (s, 4H), 3.74 (s, 3H),
3.92 (dt, 1H, J ) 4.0 Hz, J ) 8.1 Hz), 5.18 (t, 1H, J ) 6.7 Hz),
6.56 (t, 1H, J ) 2.0 Hz), 6.60 (dd, 1H, J ) 1.6 Hz, J ) 7.9 Hz),
6.66 (dd, 1H, J ) 2.3 Hz, J ) 8.2 Hz), 6.73 (d, 2H, J ) 8.5 Hz),
1
3
(
1
1
m, 5H), 7.10-7.22 (m, 3H); C NMR (CDCl
3
) δ 3.5, 4.1, 8.3,
3.5, 26.8, 30.1, 54.1, 55.1, 58.6, 58.8, 63.4, 109.4, 113.3, 119.6,
19.9, 127.6, 128.2, 129.5, 147.1, 148.9, 160.3, 171.4. Anal.
‚0.25H O) C, H, N.
-[N-{(3RS,4RS)-N-Cyclopr opylm eth yl-3-m eth yl-4-piper -
id in yl}-3-m eth oxyp h en yla m in o]-N,N-d ieth ylben za m id e
28b). Compound 28b was prepared according to the general
(C
28
H
40ClN
3
O
2
2
1
3
4
7.18 (t, 1H, J ) 8.1 Hz), 7.23 (d, 2H, J ) 8.5 Hz);
NMR (CDCl ) δ 13.5, 17.9, 25.7, 27.0, 30.2, 42.3, 54.1, 55.1,
56.0, 58.7, 58.9, 109.4, 113.2, 119.7, 121.4, 127.5, 128.2, 129.4,
C
3
(
procedures in 8% yield starting from compound 17b. The
product was characterized as its hydrochloride salt as a white
134.7, 147.2, 148.9, 160.3, 171.4. Anal. (C29
C, H, N.
H
42ClN
3
O
2
2
‚1.5H O)
1
powder obtained as previously described: H NMR (CD
3
OD) δ
4-[N-{(3SR,4RS)-N-Cin n a m yl-3-m eth yl-4-p ip er id in yl}-
p h en yla m in o]-N,N-d ieth ylben za m id e (33). Compound 33
was prepared according to the general procedures in 15% yield
starting from compound 17c. The product was characterized
as its hydrochloride salt as a white solid obtained as previously
0
1
7
2
.35-0.49 (m, 2H), 0.74 (d, 2H, J ) 7.6 Hz), 1.02-1.31 (m,
0H), 1.81-2.01 (m, 1H), 2.08-2.29 (m, 2H), 3.00 (d, 3H, J )
.0 Hz), 3.11-3.30 (m, 1H), 3.34-3.52 (m, 4H), 3.57-3.74 (m,
H), 3.77 (s, 3H), 4.09-4.28 (m, 1H), 6.67 (s, 1H), 6.74 (d, 1H,
J ) 8.0 Hz), 6.84 (d, 2H, J ) 8.5 Hz), 6.85-6.89 (m, 1H), 7.23
described: H NMR (CD OD) δ 1.10-1.22 (m, 6H), 1.24 (d, 3H,
1
3
1
3
(
d, 2H, J ) 8.3 Hz), 7.36 (t, 1H, J ) 8.0 Hz); C NMR (CD
3
-
J ) 7.3 Hz), 1.58 (d, 1H, J ) 14.0 Hz), 1.82 (q, 1H, J ) 12.5
Hz), 2.88-2.98 (s, 1H), 3.13 (t, 1H, J ) 12.3 Hz), 3.35-3.57
(m, 7H), 3.91 (d, 2H, J ) 7.2 Hz), 4.39 (d, 1H, J ) 12.3 Hz),
6.30-6.39 (m, 1H), 6.81 (d, 2H, J ) 8.5 Hz), 6.92 (d, 1H, J )
15.7 Hz), 7.24 (d, 3H, J ) 8.3 Hz), 7.32-7.43 (m, 7H), 7.51 (d,
OD) δ 5.1, 6.6, 12.1, 16.3, 28.8, 35.1, 53.2, 55.9, 58.7, 59.3, 62.8,
1
1
12.5, 115.9, 117.9, 122.0, 128.1, 129.0, 131.8, 145.7, 151.4,
62.6, 173.8. Anal. (C28 ‚0.75H O) C, H, N.
-[N-{(3SR,4RS)-N-Meth a llyl-3-m eth yl-4-p ip er id in yl}-
H
40ClN
3
O
2
2
4
2H, J ) 7.2 Hz); 13C NMR (CD
OD) δ 11.0, 14.0, 24.2, 29.0,
p h en yla m in o]-N,N-d ieth ylben za m id e (29). Compound 29
was prepared according to the general procedures in 20% yield
starting from compound 17c. The product was characterized
3
51.9, 54.9, 56.4, 59.1, 116.1, 118.1, 125.9, 126.8, 127.3, 128.4,
128.7, 129.2, 129.3, 135.3, 140.7, 144.7, 149.7, 172.3. Anal.
as its hydrochloride salt as a white solid obtained as previously
(C32
H
40ClN
3
O‚1.5H
2
O) C, H, N.
1
described: H NMR (CD
J ) 7.3 Hz), 1.58 (d, 1H, J ) 14.0 Hz), 1.81-1.88 (m, 1H),
3
OD) 1.10-1.19 (m, 6H), 1.22 (d, 3H,
4
-[N-{(3SR,4RS)-N-Cin n a m yl-3-m eth yl-4-p ip er id in yl}-
3
-m eth oxyph en ylam in o]-N,N-dieth ylben zam ide (34). Com-
1
6
.89 (s, 3H), 2.92 (s, 1H), 3.09-3.18 (m, 1H), 3.35-3.55 (m,
H), 3.65 (d, 1H, J ) 12.5 Hz), 3.79 (d, 1H, J ) 13.6 Hz), 4.38
pound 34 was prepared according to the general procedures
in 14% yield starting from compound 17a . The product was
characterized as its hydrochloride salt as a white solid obtained
(
d, 1H, J ) 12.2 Hz), 5.26 (s, 1H), 5.35 (s, 1H), 6.81 (d, 2H,
J ) 8.7 Hz), 7.16 (d, 2H, J ) 7.4 Hz), 7.22-7.44 (m, 3H), 7.49-
as previously described: 1H NMR (CDCl
3
) δ 1.14-1.24 (m,
0H), 1.71 (dq, 1H, J ) 3.6 Hz, J ) 12.4 Hz), 2.03 (t, 1H, J )
0.9 Hz), 2.26 (d, 1H, J ) 9.6 Hz), 2.57 (s, 1H), 2.89 (d, 1H,
1
3
7
5
1
.53 (m, 2H); C NMR (CD
4.9, 56.3, 57.4, 63.8, 119.8, 122.8, 127.2, 128.7, 128.9, 130.5,
30.7, 136.0, 146.2, 150.7, 173.7. Anal. (C27 O‚H O)
3
OD) δ 12.2, 13.5, 21.5, 25.6, 30.3,
1
1
H
38ClN
3
2
J ) 11.5 Hz), 2.93 (d, 1H, J ) 9.7 Hz), 3.03 (dd, 1H, J ) 6.8
Hz, J ) 13.5 Hz), 3.14 (dd, 1H, J ) 6.0 Hz, J ) 13.6 Hz), 3.42
(s, 4H), 3.75 (s, 3H), 3.95 (dt, 1H, J ) 4.0 Hz, J ) 8.4 Hz),
6.22 (dt, 1H, J ) 6.6 Hz, J ) 15.8 Hz), 6.50 (d, 1H, J ) 15.8
C, H, N.
-[N-{(3SR,4RS)-N-Meth a llyl-3-m eth yl-4-p ip er id in yl}-
-m eth oxyph en ylam in o]-N,N-dieth ylben zam ide (30). Com-
4
3

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 985
Hz), 6.59 (s, 1H), 6.62 (d, 1H, J ) 7.9 Hz), 6.68 (dd, 1H, J )
mL), bestatin (100 µg/mL), leupeptin (40 µg/mL), and chymo-
statin (20 µg/mL). Incubations were initiated by the addition
of 750 µL of the prepared membrane preparation containing
0.2 mg/mL of protein and proceeded for 2 h at 25 °C. The ligand
was displaced by 10 concentrations of test drug, in triplicate,
2×. Nonspecific binding was determined using 20 µM leval-
1
8
7
2
1
.9 Hz, J ) 8.0 Hz), 6.74 (d, 2H, J ) 8.6 Hz), 7.20 (t, 2H, J )
.0 Hz), 7.25 (d, 2H, J ) 8.6 Hz), 7.30 (t, 2H, J ) 7.6 Hz),
1
3
.36 (t, 2H, J ) 7.4 Hz); C NMR (CDCl ) δ 13.5, 17.6,
3
7.0, 30.2, 41.1, 54.0, 54.6, 55.1, 58.7, 60.7, 109.4, 113.2, 119.7,
27.5, 127.9, 128.2, 129.4, 147.2, 148.9, 160.3, 171.4. Anal.
3
(
C
33
H
42ClN
3
O
2
‚H
Sin gle-Cr ysta l X-r a y Diffr a ction An a lysis of 13, 14a ,b,
6c, a n d 23a . 13: C12
2
O) C, H, N.
lorphan. Under these conditions, the ED50 of [ H]DAMGO
binding was 2.65 nM. Brandel cell harvesters were used to
filter the samples over Whatman GF/B filters, which were
presoaked in wash-buffer (ice-cold 10 mM Tris-HCl, pH 7.4).
1
H
21NO
3
(0.36 × 0.18 × 0.13 mm), tri-
clinic space group P 1h ; a ) 5.912(1), b ) 9.499(1), c ) 12.353(1)
3
3
2
5
Å; R ) 70.63(1), â ) 86.66(1), γ ) 89.35(1)°; V ) 653.3(1) Å ,
[ H][D-Ala ,D-Leu ]enkephalin binding proceeded as fol-
lows: 12- × 75-mm polystyrene test tubes were prefilled with
100 µL of the test drug which was diluted in BB, followed by
50 µL of a salt solution containing choline chloride (2 M, final
-
3
-1
Z ) 2, Fcalc ) 1.16 mg mm , µ ) 0.08 mm ; F(000) ) 248,
1
694 unique data, R
4a : C18
space group C2/c; a ) 30.164(4), b ) 6.944(1), c ) 22.976(4) Å;
1
) 0.046 for 1398 observed data.
1
28 2 2
H N O
(0.722 × 0.08 × 0.06 mm), monoclinic
2
concentration of 100 mM), MnCl (1 M, final concentration of
3
-3
â ) 128.96(1)°; V ) 3742.6(9) Å , Z ) 8, Fcalc ) 1.08 mg mm
,
3.0 mM), and, to block µ sites, DAMGO (2000 nM, final
-
1
3 2
µ ) 0.55 mm ; F(000) ) 1328, 1680 unique data, R
1
) 0.077
concentration of 100 nM), followed by 100 µL of [ H][D-Ala ,D-
5
for 1478 observed data.
Leu ]enkephalin in the protease inhibitor cocktail. Incubations
were initiated by the addition of 750 µL of the prepared
membrane preparation containing 0.41 mg/mL of protein and
proceeded for 2 h at 25 °C. The ligand was displaced by 10
concentrations of test drug, in triplicate, 2×. Nonspecific
binding was determined using 20 µM levallorphan. Under
1
4b: C18
H
28
N
2
O
2
(0.74 × 0.72 × 0.08 mm), orthorhombic
space group Pbca; a ) 12.328(2), b ) 12.298(3), c ) 24.583(4)
3
-3
Å; V ) 3727.2(13) Å , Z ) 8, Fcalc ) 1.08 mg mm , µ ) 0.56
-
1
mm ; F(000) ) 1328, 2609 unique data, R ) 0.070 for 1797
1
observed data.
3
2
5
+
-
these conditions the ED50 of [ H][D-Ala ,D-Leu ]enkephalin
binding was 1.7 nM. Brandel cell harvesters were used to filter
the samples over Whatman GF/B filters, which were presoaked
in wash buffer (ice-cold 10 mM Tris-HCl, pH 7.4).
1
6c: C27
space group P2
Å; â ) 99.11(1)°; V ) 2516.7(5) Å , Z ) 4; F(000) ) 984, 3290
H
38
N
3
O ‚Cl (0.64 × 0.38 × 0.07 mm), monoclinic
1
/n; a ) 7.150(1), b ) 21.455(2), c ) 16.616(2)
3
unique data, R
3a : C26
space group P2
1
) 0.071 for 2187 observed data.
3
+
-
[ H]U69,593 binding proceeded as follows: 12- × 75-mm
2
H
36
N
3
O
5
‚Cl (0.09 × 0.21 × 0.68 mm), monoclinic
polystyrene test tubes were prefilled with 100 µL of the test
drug which was diluted in BB, followed by 50 µL of BB,
1
; a ) 6.901(1), b ) 8.799(1), c ) 20.990(2) Å;
3
-3
â ) 96.94(1)°; V ) 1265.3(2) Å , Z ) 2, Fcalc ) 1.16 mg mm
,
3
-
1
followed by 100 µL of [ H]U69,593 in the standard protease
µ ) 1.49 mm ; F(000) ) 476, 2077 unique data, R ) 0.040
1
inhibitor cocktail with the addition of captopril (1 mg/mL in
for 1737 observed data.
0
.1 N acetic acid containing 10 mM 2-mercaptoethanol to give
Data were collected using Cu KR radiation (Mo KR for 13)
on an automated Bruker P4 diffractometer equipped with an
incident beam monochromator (Bruker SMART 1K CCD with
Gobel mirrors in the incident beam for 14a ). All crystals
remained stable throughout data collection. Corrections were
applied for Lorentz, polarization, and absorption effects (face
corrected absorption was applied to the data for 23a ). The
structures were solved by direct methods and refined with the
aid of the SHELXTLplus system of programs (Sheldrick, 1997,
a final concentration of 1 µg/mL). Incubations were initiated
by the addition of 750 µL of the prepared membrane prepara-
tion containing 0.4 mg/mL of protein and proceeded for 2 h at
2
5 °C. The ligand was displaced by 10 concentrations of test
drug, in triplicate, 2×. Nonspecific binding was determined
3
using 1 µM U69,593. Under these conditions the ED50 of [ H]-
U69,593 binding was 4.48 nM. Brandel cell harvesters were
used to filter the samples over Whatman GF/B filters, which
were presoaked in wash buffer (ice-cold 10 mM Tris-HCl, pH
442). The full-matrix least-squares refinement on F2 values
#
7
.4) containing 1% PEI.
included atomic coordinates and anisotropic thermal param-
eters for all non-H atoms. H atoms were included using a
riding model [coordinate shifts of C applied to attached H
atoms, C-H distances set to 0.96, and N-H distances set to
.90 Å, H angles idealized, Uiso(H) set to 1.2-1.5Ueq(C)]. Final
difference maps were featureless. The X-ray results provided
relative stereochemistry for the racemates of 13, 14a ,b, and
6c and absolute configuration for 23a . Coordinates for all
compounds have been deposited with the Crystallographic
Data Centre, Cambridge CB2 1EW, England.
Op ioid Bin d in g Assa ys. µ Binding sites were labeled using
H][D-Ala -MePhe ,Gly-ol ]enkephalin ([ H]DAMGO) (2.0 nM,
s.a. ) 45.5 Ci/mmol), and δ binding sites were labeled using
H][D-Ala ,D-Leu ]enkephalin (2.0 nM, s.a. ) 47.5 Ci/mmol)
using rat brain membranes prepared as follows. Rat mem-
branes were prepared each assay day using a partially thawed,
frozen rat brain which was polytroned in 10 mL/brain of ice-
cold 10 mM Tris-HCl, pH 7.0. Membranes were then centri-
fuged twice at 30000g for 10 min each centrifugation. After
the second centrifugation, the membranes were prepared each
assay day using a partially thawed, frozen guinea pig brain
which was polytroned in 20 mL/brain of ice-cold 10 mM Tris-
HCl, pH 7.0. The membranes were then centrifuged twice at
For all three assays, the filtration step proceeded as fol-
lows: 4 mL of the wash buffer was added to the tubes, rapidly
filtered, and was followed by two additional wash cycles. The
tritium retained on the filters was counted, after an overnight
extraction into ICN Cytoscint cocktail, in a Taurus beta
counter at 44% efficiency.
0
[35S]GTP -γ-S F u n ct ion a l Assa ys. [ S]GTP-γ-S binding
35
1
3
9
was determined as described previously. Guinea pig caudate
membranes (10 µg) were suspended in 500 µL of buffer
containing 50 mM Tris-HCl, pH 7.4, 100 mM NaCl, 10 mM
[3
2
4
5
3
MgCl , 1 mM EDTA, 1 mM DTT, 100 µM GDP, 0.1% BSA,
2
35
0.05 nM [ S]GTP-γ-S, and 10 µM test drugs. The reaction was
initiated by the addition of membranes and terminated after
3 h by the addition of 3 mL of cold (4 °C) 10 mM Tris-HCl, pH
7.4, followed by rapid vacuum filtration through Whatman
GF/B filters. The filters were then washed twice with 5 mL
of cold 10 mM Tris-HCl, pH 7.4. Bound radioactivity was
counted using a Taurus (Micromedic) liquid scintillation
counter at 98% efficiency. Nonspecific binding was determined
in the presence of 40 µM GTP-γ-S. Assays were performed in
triplicate, and each experiment was performed three times.
3
2
5
[
3
5
The percent stimulation in the [ S]GTP-γ-S binding was
3
0000g for 10 min each centrifugation. After the second
centrifugation, the membranes were resuspended in 85 mL/
calculated according to the following formula: [(S - B)/B] ×
3
5
100, where B is the basal level of [ S]GTP-γ-S binding and
35
brain of 25 °C 50 mM Tris-HCl, pH 7.4.
S is the stimulated level of [ S]GTP-γ-S binding. The results
are mean ( SD from three experiments with triplicate
determinations.
3
[
H]DAMGO binding proceeded as follows: 12- × 75-mm
polystyrene test tubes were prefilled with 100 µL of the test
drug which was diluted in binding buffer (BB: 10 mM Tris-
HCl, pH 7.4, containing 1 mg/mL BSA), followed by 50 µL of
BB, and 100 µL of [ H]DAMGO in a protease inhibitor cocktail
10 mM Tris-HCl, pH 7.4, which contained bacitracin (1 mg/
Da ta An a lysis. The data of two ligand binding experiments
were pooled and fit, using MLAB-PC, to the two-parameter
logistic equation for the best-fit estimates of the IC50 and slope
3
(
i
factor. The K values were then determined using the equation

9
86 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6
Thomas et al.
3
5
K
i
) IC50/(1 + [L]/K
d
). The data of three [ S]GTP-γ-S assays
(17) Carson, J . R.; Carmosin, R. J .; Fitzpatrick, L. J .; Reitz,
A. B.; J etter, M. C. Preparation of 4-[aryl(piperidin-4-yl)]amino-
benzamides which bind to the delta-opioid receptor. WO
were pooled and fit to a one-site binding model for the best-fit
3
9
estimates of ED50 and Emax
.
9
933806, 1999.
(
18) Cottney, J .; Rankovic, Z.; Morphy, J . R. Synthesis of novel
analogues of the delta opioid ligand SNC-80 using REM resin.
Bioorg. Med. Chem. Lett. 1999, 9, 1323-1328.
Ack n ow led gm en t . This work was supported by
the National Institute on Drug Abuse, Grant DA09045,
and by the Office of Naval Research. The authors
acknowledge Robert B. Horel’s expert technical assist-
ance.
(
19) Dondio, G.; Ronzoni, S.; Petrillo, P. Non-peptide δ opioid agonists
and antagonists. Exp. Opin. Ther. Patents 1997, 7, 1075-1098.
20) Dondio, G.; Ronzoni, S.; Petrillo, P. Non-peptide δ opioid agonists
and antagonists (Part II). Exp. Opin. Ther. Patents 1999, 9,
(
3
53-374.
(
21) Furness, M. S.; Zhang, X.; Coop, A.; J acobson, A. E.; Rothman,
R. B.; Dersch, C. M.; Xu, H.; Porreca, F.; Rice, K. C. Probes
for narcotic receptor-mediated phenomena. 27. Synthesis and
pharmacological evaluation of selective delta-opioid receptor
agonists from 4-[(alphaR)-alpha-(2S,5R)-4-substituted-2,5-di-
methyl-1-piperazinyl-3-methoxybenzyl]-N,N-diethylbenzamides
and their enantiomers. J . Med. Chem. 2000, 43, 3193-3196.
22) Pelcman, B.; Roberts, E. Preparation of 4-aminopiperidines with
analgesic effect. WO 9828270, 1998.
Su p p or tin g In for m a tion Ava ila ble: Crystal data, struc-
tural refinement analysis, atomic coordinates, bond lengths,
bond angles, anisotropic displacement parameters, hydrogen
coordinates, and isotropic displacement parameters of 13,
1
4a ,b, 16c, and (-)-23a . This material is available free of
charge via the Internet at http://pubs.acs.org.
(
(
Refer en ces
23) Plobeck, N.; Delorme, D.; Wei, Z.-Y.; Yang, H.; Zhou, F.; Schwarz,
P.; Gawell, L.; Gagnon, H.; Pelcman, B.; Schmidt, R.; Yue, S.-
Y.; Walpole, C.; Brown, W.; Zhou, E.; Labarre, M.; Payza, K.;
St-Onge, S.; Kamassah, A.; Morin, P.-E.; Projean, D.; Ducharme,
J .; Roberts, E. New diarylmethylpiperazines as potent and
selective nonpeptidic delta opioid receptor agonists with in-
creased In vitro metabolic stability [In Process Citation]. J . Med.
Chem. 2000, 43, 3878-3894.
(
1) Aldrich, J . V. Analgesics. In Burger’s Medicinal Chemistry and
Drug Discovery; Wolff, M. E., Ed.; J ohn Wiley & Sons: New
York, 1996; Vol. 3.
(
2) Williams, M.; Kowaluk, E. A.; Arneric, S. P. Emerging molecular
approaches to pain therapy. J . Med. Chem. 1999, 42, 1481-500.
3) Von Voigtlander, P. F.; Lahti, R. A.; Ludens, J . H. U-50,488H:
A selective and structurally novel nonmu (kappa) opioid agonist.
J . Pharmacol. Exp. Ther. 1983, 224, 7-12.
(
(24) Podlogar, B. L.; Poda, G. I.; Demeter, D. A.; Zhang, S.-P.; Carson,
J . R.; Neilson, L. A.; Reitz, A. B.; Ferguson, D. M. Synthesis and
evaluation of 4-(N,N-diarylamino)piperidines with high selec-
tivity to the delta-opioid receptor: a combined 3D-QSAR and
ligand docking study [In Process Citation]. Drug Des. Discov.
(
4) Chang, K. J .; Rigdon, G. C.; Howard, J . L.; McNutt, R. W. A
novel potent and selective nonpeptidic delta opioid receptor
agonist, BW373U86. J . Pharmacol. Exp. Ther. 1993, 267,
8
52-857.
(
5) Calderon, S. N.; Rothman, R. B.; Porreca, F.; Flippen-Anderson,
J . L.; McNutt, R. W.; Xu, H.; Smith, L. E.; Bilsky, E. J .; Davis,
P.; Rice, K. C. Probes for narcotic receptor mediated phenomena.
2
000, 17, 34-50.
(
25) Thomas, J . B.; Atkinson, R. N.; Rothman, R. B.; Burgess, J . P.;
Mascarella, S. W.; Dersch, C. M.; Xu, H.; Carroll, F. I. 4-[(8-
Alkyl-8-azabicyclo[3.2.1]octyl-3-yl)-3-arylanilino]-N,N-diethyl-
benzamides: high affinity, selective ligands for the delta opioid
receptor illustrate factors important to antagonist activity [In
Process Citation]. Bioorg. Med. Chem. Lett. 2000, 10, 1281-1284.
26) Wei, Z.-Y.; Brown, W.; Takasaki, B.; Plobeck, N.; Delorme, D.;
Zhou, F.; Yang, H.; J ones, P.; Gawell, L.; Gagnon, H.; Schmidt,
R.; Yue, S.-Y.; Walpole, C.; Payza, K.; St-Onge, S.; Labarre, M.;
Godbout, C.; J akob, A.; Butterworth, J .; Kamassah, A.; Morin,
P.-E.; Projean, D.; Ducharme, J .; Roberts, E. N,N-Diethyl-4-
1
9. Synthesis of (+)-4-[(RR)-R-(2S,5R)-4-allyl-2,5-dimethyl-1-
piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC 80):
A highly selective, nonpeptide δ opioid receptor agonist. J . Med.
Chem. 1994, 37, 2125-2128.
(
6) Portoghese, P. S.; Sultana, M.; Takemori, A. E. Design of
peptidomimetic delta opioid receptor antagonists using the
message-address concept. J . Med. Chem. 1990, 33, 1714-1720.
7) Dondio, G.; Ronzoni, S.; Eggleston, D. S.; Artico, M.; Petrillo,
P.; Petrone, G.; Visentin, L.; Farina, C.; Vecchietti, V.; Clarke,
G. D. Discovery of a novel class of substituted pyrrolooctahydro-
isoquinolines as potent and selective δ opioid agonists, based
on an extension of the message-address concept. J . Med. Chem.
(
(
(
phenylpiperidin-4-ylidenemethyl)benzamide: A novel, excep-
tionally selective, potent delta opioid receptor agonist with oral
bioavailability and its analogues [In Process Citation]. J . Med.
Chem. 2000, 43, 3895-3905.
1
997, 40, 3192-3198.
(
8) Portoghese, P. S. An approach to the design of receptor-type-
selective non-peptide antagonists of peptidergic receptors:
δ
(27) Zhang, X.; Rice, K. C.; Calderon, S. N.; Kayakiri, H.; Smith,
L.; Coop, A.; J acobson, A. E.; Rothman, R. B.; Davis, P.; Dersch,
C. M.; Porreca, F. Probes for narcotic receptor mediated
phenomena. 26. Synthesis and biological evaluation of diaryl-
methylpiperazines and diarylmethylpiperidines as novel, non-
peptidic delta opioid receptor ligands. J . Med. Chem. 1999, 42,
5455-5463.
(28) Hattori, T.; Satoh, T.; Miyano, S. Convenient synthesis of triaryl-
amines via ester-mediated nucleophilic aromatic substitution.
Synthesis 1996, 514-518.
(29) Mattson, R. J .; Pham, K. M.; Leuck, D. J .; Cowen, K. A. An
improved method for reductive alkylation of amines using
titanium(IV) isopropoxide and sodium cyanoborohydride. J . Org.
Chem. 1990, 55, 2552-2554.
opioid antagonists. J . Med. Chem. 1991, 34, 1757-1762.
(
9) Schwyzer, R. ACTH: A short introductory review. Ann. N. Y.
Acad. Sci. 1977, 247, 3-26.
(
10) Kamei, J .; Saitoh, A.; Ohsawa, M.; Suzuki, T.; Misawa, M.;
Nagase, H.; Kasuya, Y. Antinociceptive effects of the selective
nonpeptidic δ-opioid receptor agonist TAN-67 in diabetic mice.
Eur. J . Pharmacol. 1995, 276, 131-135.
(
11) Liao, S.; Alfaro-Lopez, J .; Shenderovich, M. D.; Hosohata, K.;
Lin, J .; Li, X.; Stropova, D.; Davis, P.; J ernigan, K. A.; Porreca,
F.; Yamamura, H. I.; Hruby, V. J . De novo design, synthesis,
and biological activities of high-affinity and selective non-peptide
agonists of the delta-opioid receptor. J . Med. Chem. 1998, 41,
4
767-4776.
(
12) Thomas, J . B.; Herault, X. M.; Rothman, R. B.; Burgess,
J . P.; Mascarella, S. W.; Xu, H.; Horel, R. B.; Dersch, C. M.;
Carroll, F. I. (()-4-[(N-Allyl-cis-3-methyl-4-piperidinyl)phenyl-
amino]-N,N-diethylbenzamides display selective binding for
the delta opioid receptor. Bioorg. Med. Chem. Lett. 1999, 9,
(
30) Abdel-Magid, A. F.; Carson, K. G.; Harris, B. D.; Maryanoff,
C. A.; Shah, R. D. Reductive amination of aldehydes and
ketones with sodium triacetoxyborohydride. studies on direct
and indirect reductive amination procedures. J . Org. Chem.
1
996, 61, 3849-3862.
3
053-3056.
(
31) Knapp, R. J .; Santoro, G.; De Leon, I. A.; Lee, K. B.; Edsall, S.
A.; Waite, S.; Malatynska, E.; Varga, E.; Calderon, S. N.; Rice,
K. C.; Rothman, R. B.; Porreca, F.; Roeske, W. R.; Yamamura,
H. I. Structure-activity relationships for SNC80 and related
compounds at cloned human delta and mu opioid receptors. J .
Pharmacol. Exp. Ther. 1996, 277, 1284-1291.
32) Kramer, T. H.; Shook, J . E.; Kazmierski, W.; Ayres, E. A.; Wire,
W. S.; Hruby, V. J .; Burks, T. F. Novel peptidic mu opioid
antagonists: Pharmacologic characterization in vitro and in vivo.
J . Pharmacol. Exp. Ther. 1989, 249, 544-551.
(
13) Thomas, J . B.; Atkinson, R. N.; Herault, X. M.; Rothman, R. B.;
Mascarella, S. W.; Dersch, C. M.; Xu, H.; Horel, R. B.; Carroll,
F. I. Optically pure (-)-4-[(N-allyl-3-methyl-4-piperidinyl)phenyl-
amino]-N,N-diethylbenzamide displays selective binding and full
agonist activity for the δ opioid receptor. Bioorg. Med. Chem.
Lett. 1999, 9, 3347-3350.
(
(
14) Thomas, J . B.; Mascarella, S. W.; Carroll, F. I. Novel opiate
compounds, methods of making and methods of use. WO
9
9/45925, 1999.
(
15) Barn, D. R.; Bom, A.; Cottney, J .; Caulfield, W. L.; Morphy, J .
R. Synthesis of novel analogues of the delta opioid ligand SNC-
(
33) Portoghese, P. S.; Lipkowski, A. W.; Takemori, A. E. Binaltorph-
imine and nor-binaltorphimine, potent and selective κ-opioid
receptor antagonists. Life Sci. 1987, 40, 1287-1292.
8
1
0 using AlCl3-promoted aminolysis. Bioorg. Med. Chem. Lett.
999, 9, 1329-1334.
(
16) Boyd, R. E.; Carson, J . R.; Codd, E. E.; Gauthier, A. D.; Neilson,
L. A.; Zhang, S.-P. Synthesis and binding affinities of 4-diaryl-
aminotropanes, a new class of delta opioid agonists. Bioorg. Med.
Chem. Lett. 2000, 10, 1109-1111.
(34) O’Neill, S. J .; Collins, M. A.; Pettit, H. O.; McNutt, R. W.; Chang,
K. J . Antagonistic modulation between the delta opioid agonist
BW373U86 and the mu opioid agonist fentanyl in mice. J .
Pharmacol. Exp. Ther. 1997, 282, 271-277.

SAR of Piperidinyl-Based Diethylbenzamides
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 6 987
(
35) Bishop, M. J .; McNutt, R. W.; Bubacz, D. G.; Collins, M. A.;
Pettit, H. O.; Chang, K.-J . DPI3290: A mixed delta/mu opioid
agonist analgesic with reduced side effects.
(38) Van Bever, W. F. M.; Niemegeers, C. J . E.; J anssen, P. A. J .
Synthetic analgesics. Synthesis and pharmacology of the
diastereoisomers of N-(3-methyl-1-(2-phenylethyl)-4-piperidyl)-
N-phenylpropanamide and N-(3-methyl-1-(1-methyl-2-phenyl-
ethyl)-4-piperidyl)-N-phenylpropanamide. J . Med. Chem. 1974,
17, 1047-1051.
(
36) Katsura, Y.; Zhang, X.; Homma, K.; Rice, K. C.; Calderon, S.
N.; Rothman, R. B.; Yamamura, H. I.; Davis, P.; Flippen-
Anderson, J . L.; Xu, H.; Becketts, K.; Foltz, E. J .; Porreca, F.
Probes for narcotic receptor-mediated phenomena. 25. Synthesis
and evaluation of N-alkyl-substituted (alpha-piperazinylbenzyl)-
benzamides as novel, highly selective delta opioid receptor
agonists. J . Med. Chem. 1997, 40, 2936-2947.
(39) Partilla, J . S.; Carroll, F. I.; Thomas, J . B.; Rice, K. C.;
Zimmerman, D. M.; Rothman, R. B. Opioid peptide receptor
studies. 13. Characterization of opioid antagonists with the
35S]GTP-γ-S binding assay. Analgesia 1999, 4, 27-32.
[
(
37) Knapp, R. J .; Waite, S.; Landsman, R.; Santoro, G.; De Leon, I.
A.; Malatynska, E.; Varga, E.; Nagase, H.; Calderon, S. N.; Rice,
K.; et al. Efficacy of peptide and nonpeptidic agonists at the
cloned human delta opioid receptor. Proc. West. Pharmacol. Soc.
1
995, 38, 141-143.
J M000427G