Modifications to five-substituted 3,3-diethyl-4,5-dihydro-2(3H)- Furanones en route to novel muscarinic receptor ligands

Article abstract of DOI:10.1007/s00044-010-9349-7

Lead lactone-based ligands with modest affinity for muscarinic receptors were modified based on structure- activity relationship data in the literature to provide a new series of 5-substituted 4,5-dihydro-2(3H)-furanones. The modifications included the addition of various nitrogencontaining heterocycles attached to substituted and unsubstituted aromatic rings. The target compounds were synthesized in modest yields and evaluated in preliminary muscarinic binding assays. A lactone-based ligand containing a diphenylmethylpiperazine moiety was identified as a nonselective muscarinic ligand with IC50 of 340 nM. The design of future ligands will be based, in part, on structure-activity data reported herein. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-010-9349-7

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:558–565
DOI 10.1007/s00044-010-9349-7
ORIGINAL RESEARCH
Modifications to five-substituted 3,3-diethyl-4,5-dihydro-2(3H)-
furanones en route to novel muscarinic receptor ligands
•
Richie R. Bhandare Daniel J. Canney
Received: 19 November 2009 / Accepted: 17 March 2010 / Published online: 6 April 2010
Ó Springer Science+Business Media, LLC 2011
Abstract Lead lactone-based ligands with modest affinity
for muscarinic receptors were modified based on structure–
activity relationship data in the literature to provide a new
series of 5-substituted 4,5-dihydro-2(3H)-furanones. The
modifications included the addition of various nitrogen-
containing heterocycles attached to substituted and unsub-
stituted aromatic rings. The target compounds were syn-
thesized in modest yields and evaluated in preliminary
muscarinic binding assays. A lactone-based ligand con-
taining a diphenylmethylpiperazine moiety was identified
as a nonselective muscarinic ligand with IC50 of 340 nM.
The design of future ligands will be based, in part, on
structure–activity data reported herein.
various disorders including overactive bladder, Alzheimer’s
disease, pain, cognitive impairment, drug addiction,
schizophrenia, and parkinson’s disease (Abrams et al., 2006;
Wess et al., 2007). To date, efforts to develop subtype
selective ligands for muscarinic acetylcholine receptors
(mAChRs) have been hampered by a lack of an X-ray crystal
structures of the proteins and the high degree of homology
among the receptor subtypes (Felder et al., 2000).
The pharmacophoric requirements for cholinergic
ligands have been reported by numerous investigators
based on structure–activity relationship (SAR) and/or
molecular modeling data of known muscarinic ligands. In
general, the models propose that the pharmacophoric ele-
ments that should be present in muscarinic ligands include:
(a) a quaternary ammonium group or its equivalent, (b) an
unshared pair of electrons that can mediate a H-bond,
(c) an appropriate distance between the H-bonding moiety
and the center of the positive charge, and (d) the presence
of a suitably located lipophilic/alkyl group (Beers and
Reich, 1970; Marriott et al., 1999; Peretto et al., 2007).
These fundamental requirements are useful when designing
muscarinic ligands but have provided little guidance in the
design of subtype selective compounds.
Keywords Muscarinic receptors Á Lactone Á
Diphenylmethylpiperazine
Introduction
Muscarinic receptors belong to the superfamily of G-protein
coupled receptors and are classified into five receptor sub-
types (M1–M5). In general, M1, M3, and M5 receptor sub-
types are coupled via Gq like proteins; while M2 and M4
subtypes are coupled to Gi-proteins (Burstein et al., 1998;
Koch et al., 2005). Muscarinic receptors are widely dis-
tributed in the body where they are responsible for a variety
of important physiological functions. The receptors have
been targeted in drug discovery efforts for the treatment of
In recent years, molecular modeling and computational
approaches have been used also to aid in the design of
muscarinic ligands (Shapiro et al., 1992; Nordvall and
Hacksell, 1993; Peng et al., 2006; Johren and Holtje, 2002;
Ostopovici et al., 2007). For example, 3D molecular mod-
eling techniques and docking studies using a homology
model of bovine rhodopsin have revealed unique interac-
tions between acetylcholine (ACh) and the binding pockets
of M1–M5 receptors (Pedretti et al., 2006). Another study
involved docking analysis of muscarinic receptors (M1, M2,
and M5) using known agonists with the goal of using the
binding site geometry of the three receptors to design
R. R. Bhandare Á D. J. Canney (&)
Department of Pharmaceutical Sciences, School of Pharmacy,
Temple University, 3307 N. Broad St., Philadelphia,
PA 19140, USA
e-mail: canney@temple.edu
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559
Fig. 1 Structure of
representative lactone-based
leads reported previously
O
O
O
O
O
N
4
5
N
O
I
R
OH
3
subtype selective ligands (Vistoli et al., 2008). These mod-
eling studies and SAR data provide important information
with which to design novel muscarinic ligands. For example,
aromatic groups are reported to play a critical role in the
binding of ACh to muscarinic receptors in the modeling
studies discussed above (Nordvall and Hacksell, 1993; Peng
et al., 2006; Ostopovici et al., 2007). These interactions may
serve as auxiliary binding sites that contribute to increase
affinity and possibly increased selectivity for ligands with
appropriately positioned complimentary groups (Pedretti
et al., 2006).
O
HO
Scheme 1 Synthesis of precursors 4 and 5 (Ahungena and Canney,
1996)
COOH
NH2
Our interest in developing novel muscarinic receptor
ligands led to the design of lactone-based ligands using an
approach similar to that reported by Kaiser et al. (1992)
(Ahungena et al., 2003). Hence, a series of semi-rigid
muscarinic ligands were designed in which the lactone
oxygens serve as a H-bond acceptor moieties while dif-
ferent nitrogen-containing heterocycles provide the requi-
site cationic group (see below). Preliminary binding studies
indicate that several of the compounds were nonselective,
low affinity (IC50 = 1.81 and 1.56 lM for R = H and
i-propyl, respectively) muscarinic agonists (based on pre-
liminary in vivo data) (Ahungena et al., 2003) (Fig. 1).
In this work, molecular modifications to our lead lac-
tones have been made in order to increase receptor affinity.
SAR data and molecular modeling experiments in the
recent literature have been considered in the design of the
novel compounds. The ligands contain a H-bond accepting
moiety in the form of the lactone ring, a spacer (CH2 in the
present series), a cationic center in the form of nitrogen-
containing heterocycles, and aromatic groups (Ahungena
et al., 2003; Kozlowski et al., 2002; Ogino et al., 2003;
Lewis et al., 2008) (Fig. 2).
N
NH
NH
PPA, 180 °C
NH2
NH
7
6
Scheme 2 Synthesis of precursor
benzimidazole]
7
[2-(4-piperidinyl)-1H-
these molecular modifications on receptor affinity are
reported herein.
Chemistry
Precursors 4 and 5 were synthesized from olefinic acid 3 as
described previously (Scheme 1). Briefly epoxylacton-
ization of olefinic acid 3 afforded hydroxy lactone 5 while
iodolactonization of 3 provided iodolactone 4 in acceptable
yields (Ahungena and Canney, 1996).
Benzimidazole 7 served as an intermediate for the
synthesis of target compound 17 (Scheme 2) and was
prepared by treating 1,2-diamino benzene 6 with 4-piper-
idine carboxylic acid in presence of polyphosphoric acid
(PPA) (Orjales et al., 1995).
An important distinction between the newly designed
ligands and the lead lactones is the presence of substituted
or unsubstituted aromatic systems that provide opportuni-
ties for interactions with auxiliary binding sites. The syn-
thesis of the newly designed compounds and the effects of
Carbamate 13 (Scheme 3) was prepared by reacting
alcohol 5 with the commercially available 4-piperidyl-
benzenisocyanate in dry dichloromethane at room tem-
perature (Zhao, 2001).
Fig. 2 General structural
features of the newly designed
ligands
O
Piperazine,
Piperidine or
N containing heterocycles
R
O
CH2
Aromatic moiety
Cationic Center
Hydrogen bond
acceptor
Linker
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Med Chem Res (2011) 20:558–565
Scheme 3 Synthesis of
carbamate 13 from lactone 5
and commercially available
1-(4-isocyanatophenyl)
piperidine
O
O
N
O
C N
O
C
O
O
N
NH
13
O
HO
5
CH2Cl2
RT
O
O
Scheme 4 Synthesis of target
compounds 8–12, 14–22 from
iodolactone 4
R
R
2
3
O
O
N
N
R
R
1
N
4
NH
17
R1 = N: 8-12, 14-16, 19
O
R1 = C: 18
THF Reflux
20 amine
O
O
4
O
N
N
21
N
O
20
O
N
N
O
22
Table 1 Preliminary binding data (% inhibition at 10 lM) for lac-
tone-based compounds containing phenyl piperazines and piperidines
Compounds 8–12, 14–22 were prepared as shown in
Scheme 4 using precursor 4. Hence, displacement of the
iodine of lactone 4 by secondary amines under refluxing
conditions (48 h) afforded the target ligands in 7–40% yield
(Ahungena et al., 2003; Ahungena and Canney, 1996).
O
R3
R2
O
R1
R4
N
Results
Compound # R1 R2
R3
R4
% Specific inhibition
A series of substituted furanones were prepared in modest
yields using well precedented literature routes. The lactone-
based ligands reported herein have pharmacophoric features
in common but differ in potentially important ways. Com-
pounds 8–12, 14–16, and 19 share a lactone ring coupled to
phenyl piperazines containing a variety of electron with-
drawing (NO2, CN) or electron donating (OCH3, OH) aro-
matic substituents. Compound 20 is an unsubstituted
diphenylpiperazine. Compound 17 has a piperidine nitrogen
and benzimidazole nitrogens as potential cationic centers.
Compounds 18, 21, and 22 are similar in that each com-
pound has only one nitrogen capable of forming a cationic
center. Compounds 13 and 22 have additional opportunities
for H-bond formation in their carbamate and amide moie-
ties. Compound 13 is unique within the present series of
ligands as its nitrogen-containing heterocycle is on the
opposite side of the aromatic group.
8
N
N
N
N
N
N
N
N
C
N
H
H
H
H
H
OCH3 26
9
H
CN
NO2
H
18
18
16
32
9
10
11
12
14
15
16
18
19
H
H
OCH3
H
H
H
OCH3
H
H
H
OH
H
7
OH
H
H
46
68
31
H
H
CN
H
H
Bold value indicates % specific inhibition of more than 20%
For details regarding the evaluation of results, see ‘‘Experimental’’
section
Preliminary binding studies performed for the test
compound at 10 lM revealed that both piperidine and
piperazine containing compounds exhibited affinity for
muscarinic receptors. Piperazines 8, 12, and 19 and pipe-
ridinyl phenyl carbamate 13 inhibited [3H]-QNB binding to
rat cerebral cortex membranes by 26–32%. Piperazine 16,
piperidine (benzimidazole) 17, and 1,2,3,4-tetrahydroiso-
quinoline 21 were inhibitors of specific binding also with
Binding studies were preformed at CEREP using rat
cerebral cortex membranes as per a previously published
method (Richards, 1990). Preliminary data presented in
Tables 1 and 2 represent the percent inhibition of specific
binding of radioligand at a single concentration (10 lM) of
test compound.
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Med Chem Res (2011) 20:558–565
561
Molecular modifications to a series of lactone-based mus-
carinic leads were made in an effort to increase affinity.
The original lead lactones contained various substituted
amines and amine containing heterocycles and were found
to have IC50 values in 1–2 lM. The compounds reported
herein differ from the leads in that all possess substituted or
unsubstituted aromatic rings. The electronic nature of
substituents on the test compounds vary from electron
donating groups (e.g., 16; OH) to strong electron with-
drawing groups (e.g., 10; NO2). The position of the func-
tional groups was varied also (e.g., 8, 12, and 14).
Generally, the % inhibition data provided herein is inter-
preted as follows: the baseline for % inhibition is consid-
ered -20 to 20% and compounds in this range are
considered to be inactive; compounds in the range 20–49%
are considered marginally active; while compounds
exhibiting [50% inhibition are considered active and
warrant further study.
Table 2 Preliminary binding data (% inhibition at 10 lM) for lac-
tone-based compounds 13, 17, 20–22
O
O
R2 R1
Compound # R2
R1
% Specific inhibition
13
31
O
C
N
N
H
O
17
20
46
97
N
N
NH
With these limitations in mind, the binding data for this
set of aromatic heterocycles suggest that the position of the
substituent may hold precedent over the electronic nature.
For example, the ortho substituted compounds 12 (32%),
16 (46%), and 19 (31%) were marginally active and were
the only compounds in Table 1 to inhibit the binding by
more than 30%. The corresponding derivatives with sub-
stituents at the para position (9, 10, and 15) were inactive
(7–18%). Introduction of an additional hydrogen bond
acceptor in the form of a carbamate in 13 did not improve
activity. A comparison of the % inhibition for piperazine
11 with that for piperidine 18 reveals an improvement in
activity. These results suggest that further evaluation of
piperidine containing lactones is warranted. The addition of
an imidazole ring in 17 resulted in marginal activity (46%).
These results may suggest that the phenyl ring (without the
imidazole) of 18 (68%) is better able to p–p stacking
interaction with aromatic residues in the receptor pocket
(additional work is required to test this hypothesis). Fusing
the piperidine with an aromatic ring in 21 did not improve
the activity and the introduction of an additional H-bond
acceptor group (amide carbonyl) in 22 proved deleterious
to binding. Of all the test compounds assayed, diphe-
nylmethylpiperazine 20 was found to inhibit specific
binding by 97% at 10 lM. Further evaluation to determine
the IC50 value revealed 20 to be the highest affinity lac-
tone-based ligand identified in this series (IC50 = 340 nM).
The affinity of ligand 20 (IC50 = 340 nM) is improved
compared to our previously reported ligands (IC50s of
1–2 lM). The data reported herein confirm that the lactone
nucleus is a useful scaffold for the design of muscarinic
ligands and indicate that the addition of appropriately
positioned aromatic substituents can improve affinity. The
% inhibition studies reported herein suggest that further
structural modification to these lactone derivatives may
N
N
21
22
44
N
5
N
N
O
Bold value indicates % specific inhibition of more than 20%
For details regarding the evaluation of results, see ‘‘Experimental’’
section
percent inhibition values ranging from 44 to 46%. In the
present series of lactones, compounds 18 and 20 exhibited
the highest % inhibition values (68 and 97%, respectively).
Compound 20 was chosen for further evaluation and a full
binding curve was generated. The IC50 of biphenylmeth-
ylpiperazine 20 was determined to be 340 nM. Based on
the guidelines suggested for interpretation of these data, the
remaining piperazines 9, 10, 11, 14, 15, and 22 (amide)
were considered inactive.
Discussion
The test compounds were prepared based on literature
procedures and evaluated in preliminary binding assays.
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Med Chem Res (2011) 20:558–565
provide high affinity compounds that could be used in
future efforts to develop subtype selective ligands. Com-
pounds 18 and 20 will serve as leads in future efforts to
design higher affinity muscarinic ligands.
L’EVESCAULT, France using rat cerebral cortex mem-
branes expressing muscarinic receptor subtypes M1–M5.
The competitive binding assays were performed according
to the previously reported method (Richards, 1990). The
assays were done in duplicate and are presented as supplied
by CEREP. Briefly, [3H]-QNB (0.05 nM) and the test
compound (10 lM) were incubated with rat cerebral cortex
membranes for 90 min at room temperature. Following
incubation, the reaction was terminated by filtration.
Atropine (1 lM) was used to determine non-specific
binding. The bound radioactivity was measured with
scintillation counter. For interpretation of this type of
preliminary data, CEREP suggests the following guide-
lines: 50% inhibition or higher represent significant effects
(i.e., 50% is a common cut-off value for further investi-
gation; determination of IC50 or EC50 values from con-
centration response curves). Results showing an inhibition
between 20 and 50% indicate weak to moderate effects;
inhibition less than 20% are considered inactive.
Experimental
Chemical methods
Proton magnetic resonance spectra (1H NMR) were mea-
sured in CDCl3 on a Bruker WM-400 MHz instrument,
data are presented as follows: chemical shift in parts per
million (ppm) on the d scale relative to internal tetra-
methylsilane (TMS) (coupling constant(s) in hertz). The
following abbreviations are used to denote signal patterns:
s = singlet, d = doublet, t = triplet, m = multiplet.
Elemental analyses were performed by Atlantic Micolabs,
Inc., Atlanta, GA, and were within 0.4% of the theoret-
ical values. All TLC was run using Silicycle precoated
60-F-254 silica plates (0.25 mm) with dichloromethane in
methanol (9:1) solvent system and the components were
visualized with iodine vapor and/or UV-light. Extractive
workups culminated in washing the organic layer with
brine, drying over MgSO4, and evaporating the solvent at
reduced pressure on a rotary evaporator. Flash column
chromatography was carried out on Silia-P flash silica gel
(40–63 lm) using methanol (0–3%) in dicloromethane
solvent system. Preparative TLC was performed on Silia-
plate TLC plates (particle size 1000 lm) using methanol
(8%) in dichloromethane mobile phase (HPLC grade).
HPLC analysis was performed using a Gilson 215 reversed
phase chromatographic system equipped with a Sepax
GP-C18 (21.2 9 100 mm 5 lm column) and a UV–Vis
detector. The purity was analyzed using two mobile phases
in 10–90% acetonitrile in water solvent gradient containing
0.1% formic acid (method A) and; 10–90% methanol in
water solvent gradient containing 0.1% trifluroacetic acid
(method B). The purity of compounds 10, 12–22 was found
to be [95%. Elemental analyses were performed on com-
pounds 8, 9, and 11 and were found to be in acceptable
range ( 0.4%). LC–MS (ESI) analyses were done on an
Agilent technologies 1200 series instrument using 95%
acetonitrile in water solvent system. Compounds 4, 5, and 7
were prepared as described previously and spectro-
scopic data were identical to reported data (Ahungena and
Canney, 1996; Orjales et al., 1995).
Chemistry
General procedure for compounds 8–12, 14–22
Iodomethyl lactone 4 (1 Eq) and the appropriate secondary
amine (5 Eq) in anhydrous tetrahydrofuran (THF; 35 ml)
was stirred at reflux under a nitrogen atmosphere for 48 h.
After 48 h, the mixture was filtered (when appropriate),
concentrated under reduced pressure and the residue was
dissolved in dichloromethane and purified by flash silica
gel chromatography using methanol (0–3%) in dichloro-
methane.
General procedure for compound 13
To a solution of hydroxymethyl lactone 5 (1 Eq) in anhy-
drous dichloromethane (5 ml) was added 1-(4-isocyana-
tophenyl) piperidine (1 Eq) in dichloromethane (5 ml) with
stirring. The reaction was stirred overnight, filtered, and the
residue chromatographed on silica gel using methanol (1%)
in dichloromethane.
3,3-Diethyl-4,5-dihydro-5-(4-[4-methoxyphenyl]piperazi-
nylmethyl)-2(3H)-furanone (8) Pale yellow solid. Yield:
31.33%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.88–0.96
(m, 6H), 1.59–1.65 (m, 4H), 1.88–1.94 (m, 1H), 2.04–2.09
(m, 1H), 2.57–2.79 (m, 6H), 3.06–3.09 (m, 4H), 3.74 (s,
3H), 4.56–4.60 (m, 1H), 6.81–6.89 (m, 4H). Elemental
analysis: calcd for C20H30N2O3: C, 69.33; H, 8.73; N, 8.09.
Found: C, 69.11; H, 8.81; N, 8.01%.
Binding studies
The target compounds 8–22 were evaluated in radioligand
binding assays performed by CEREP, 86600 CELLE
3,3-Diethyl-4,5-dihydro-5-(4-[4-cyanophenyl]piperazinylm-
ethyl)-2(3H)-furanone (9) Pale yellow liquid. Yield:
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Med Chem Res (2011) 20:558–565
563
15.78%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.80–0.90
(m, 6H), 1.53–1.61 (m, 4H), 1.83–1.88 (m, 1H), 1.99–2.04
(m, 1H), 2.49–2.71 (m, 6H), 3.24–3.26 (m, 4H), 4.49–4.55
(m, 1H), 6.76–6.80 (d, 2H), 7.41–7.44 (d, 2H). Elemental
analysis: calcd for C20H27N3O2: C, 70.35; H, 7.97; N,
12.31. Found: C, 70.07; H, 8.03; N, 12.11%.
HPLC analysis: [95% purity using two different mobile
phases.
3,3-Diethyl-4,5-dihydro-5-(4-[4-hydroxyphenyl]piperazi-
nylmethyl)-2(3H)-furanone (15) Pale yellow solid. Yield:
1
7.79%. H NMR: {CDCl3, 400 MHz, d (ppm)} 0.85–0.92
(m, 6H), 1.55–1.62 (m, 4H), 1.82–1.88 (m, 1H), 2.01–2.06
(m, 1H), 2.54–2.81 (m, 6H), 3.02–3.05 (m, 4H), 4.55–4.62
(m, 1H), 6.71 (d, 2H), 6.78 (d, 2H). LC–MS (ESI)
(m/z) 333.0 (M ? H)?. HPLC analysis:[95% purity using
two different mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[4-nitrophenyl]piperazinylm-
ethyl)-2(3H)-furanone (10) Pale yellow liquid. Yield:
25.97%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.87–0.97
(m, 6H), 1.59–1.66 (m, 4H), 1.89–1.94 (m, 1H), 2.05–2.10
(m, 1H), 2.56–2.78 (m, 6H), 3.37–3.42 (m, 4H), 4.55–4.61
(m, 1H), 6.77–6.82 (d, 2H), 8.07–8.12 (d, 2H). LC–MS
(ESI) (m/z) 362.3 (M ? H)?. HPLC analysis:[95% purity
using two different mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[2-hydroxyphenyl]piperazi-
nylmethyl)-2(3H)-furanone (16) Pale yellow liquid. Yield:
18.38%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.89–0.97
(m, 6H), 1.62–1.67 (m, 4H), 1.88–1.94 (m, 1H), 2.07–2.12
(m, 1H), 2.60–2.78 (m, 6H), 2.88–2.90 (m, 4H), 4.57–4.64
(m, 1H), 6.83–6.88 (m, 1H), 6.93–6.95 (m, 1H), 7.05–7.09
(m, 1H), 7.14–7.17 (m, 1H). LC–MS (ESI) (m/z) 333.3
(M ? H)?. HPLC analysis: [95% purity using two dif-
ferent mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[4-phenyl]piperazinylmethyl)-
2(3H)-furanone (11) Pale yellow solid. Yield: 22.02%.
1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.89–0.98 (m, 6H),
1.60–1.66 (m, 4H), 1.90–1.96 (m, 1H), 2.06–2.11 (m, 1H),
2.58–2.80 (m, 6H), 3.14–3.21 (m, 4H), 4.57–4.63 (m, 1H),
6.85 (t, 1H), 6.92 (d, 2H), 7.26 (t, 2H). Elemental analysis:
calcd for: C19H28N2O2: C, 72.12; H, 8.92; N, 8.85. Found:
C, 72.40; H, 9.13; N, 8.65%.
3,3-Diethyl-4,5-dihydro-5-(2-[4-piperidinyl]benzimidazo-
lylmethyl)-2(3H)-furanone (17) Pale yellow solid. Yield:
10.15%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.85–0.96
(m, 6H), 1.57–1.65 (m, 4H), 1.86–2.28 (m, 9H), 2.51–2.64
(m, 2H), 2.88–3.09 (m, 3H), 4.52–4.58 (m, 1H), 7.15–7.25
(m, 2H), 7.51–7.54 (m, 2H). LC–MS (ESI) (m/z) 356.0
(M ? H)?. HPLC analysis: [95% purity using two dif-
ferent mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[2-methoxyphenyl]piperaz-
inylmethyl)-2(3H)-furanone (12) Pale yellow liquid. Yield:
17.04%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.89–0.97
(m, 6H), 1.60–1.65 (m, 4H), 1.88–1.91 (m, 1H), 2.05–2.10
(m, 1H), 2.60–2.81 (m, 6H), 3.08 (m, 4H), 3.85 (s, 3H),
4.58–4.62 (m, 1H), 6.84–7.01 (m, 4H). LC–MS (ESI) (m/
z) 347.3 (M ? H)?. HPLC analysis: [95% purity using
two different mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[4-phenyl]piperidinylmeth-
yl)-2(3H)-furanone (18) Pale yellow liquid. Yield:
23.74%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.93–1.01
(m, 6H), 1.63–1.69 (m, 4H), 1.81–1.95 (m, 5H), 2.09–2.14
(m, 1H), 2.23–2.29 (m, 2H), 2.51 (m, 1H), 2.64–2.67 (m,
2H), 3.05 (d, 11.2 Hz, 1H), 3.19 (d, 12.4 Hz, 1H),
4.62–4.63 (m, 1H), 7.22–7.34 (m, 5H). LC–MS (ESI) (m/
z) 316.3 (M ? H)?. HPLC analysis: [95% purity using
two different mobile phases.
(4-Piperidinylphenyl)-1-carbamic acid 3,3-diethyl-4,5-
dihydro-2(3H)-furanone methylester (13) Pale yellow solid.
1
Yield: 52.66%. H NMR: {CDCl3, 400 MHz, d (ppm)}
0.89–0.97 (m, 6H), 1.52–1.72 (m, 10H), 1.90–1.95 (m,
1H), 2.06–2.11 (m, 1H), 3.07–3.10, 4.12–4.16 (m, 1H),
4.38–4.42 (m, 1H), 4.61–4.67 (m, 1H), 6.57 (s, 1H), 6.89
(d, 2H), 7.22–7.23 (m, 2H). LC–MS (ESI) (m/z) 376.2
(M ? H)?. HPLC analysis: [95% purity using two dif-
ferent mobile phases.
3,3-Diethyl-4,5-dihydro-5-(4-[2-cyanophenyl]piperazinylm-
ethyl)-2(3H)-furanone (19) Pale yellow liquid. Yield:
15.80%. 1H NMR: {CDCl3, 400 MHz, d (ppm)} 0.85–0.93
(m, 6H), 1.55–1.61 (m, 4H), 1.84–1.90 (m, 1H), 2.01–2.06
(m, 1H), 2.57–2.80 (m, 6H), 3.14–3.21 (m, 4H), 4.52–4.57
(m, 1H), 6.93–6.97 (m, 2H), 7.41–7.45 (m, 1H), 7.49 (dd, 8
and 4 Hz, 1H). LC–MS (ESI) (m/z) 342.2 (M ? H)?.
HPLC analysis: [95% purity using two different mobile
phases.
3,3-Diethyl-4,5-dihydro-5-(4-[3-methoxyphenyl]piperazi-
nylmethyl)-2(3H)-furanone (14) Pale yellow liquid.
1
Yield: 40.54%. H NMR: {CDCl3, 400 MHz, d (ppm)}
0.87–0.96 (m, 6H), 1.58–1.64 (m, 4H), 1.88–1.93 (m, 1H),
2.03–2.08 (m, 1H), 2.55–2.76 (m, 6H), 3.12–3.18 (m, 4H),
3.76 (s, 3H), 4.56–4.59 (m, 1H), 6.38–6.53 (m, 3H),
7.12–7.16 (t, 1H). LC–MS (ESI) (m/z) 347.3 (M ? H)?.
123

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Acknowledgments The authors are grateful to Temple University
(D. J. C.; Grant-in-Aid of Research) and the Dean’s office, Temple
University School of Pharmacy, for generous financial support and to
Dr. Magid Abou-Gharbia and Rogelio Martinez (Moulder Center for
Drug Discovery Research) for access to instrumentation and helpful
discussions regarding this work. R. R. B is thankful to Dr. Schaf-
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