Design, synthesis, and structure - Activity relationships of alkylcarbamic acid aryl esters, a new class of fatty acid amide hydrolase inhibitors

Article abstract of DOI:10.1021/jm021119g

Fatty acid amide hydrolase (FAAH), an intracellular serine hydrolase enzyme, participates in the deactivation of fatty acid ethanolamides such as the endogenous cannabinoid anandamide, the intestinal satiety factor oleoylethanolamide, and the peripheral analgesic and anti-inflammatory factor palmitoylethanolamide. In the present study, we report on the design, synthesis, and structure-activity relationships (SAR) of a novel class of potent, selective, and systemically active inhibitors of FAAH activity, which we have recently shown to exert potent anxiolytic-like effects in rats. These compounds are characterized by a carbamic template substituted with alkyl or aryl groups at their O- and N-termini. Most compounds inhibit FAAH, but not several other serine hydrolases, with potencies that depend on the size and shape of the substituents. Initial SAR investigations suggested that the requirements for optimal potency are a lipophilic N-alkyl substituent (such as n-butyl or cyclohexyl) and a bent O-aryl substituent. Furthermore, the carbamic group is essential for activity. A 3D-QSAR analysis on the alkylcarbamic acid aryl esters showed that the size and shape of the O-aryl moiety are correlated with FAAH inhibitory potency. A CoMSIA model was constructed, indicating that whereas the steric occupation of an area corresponding to the meta position of an O-phenyl ring improves potency, a region of low steric tolerance on the enzyme active site exists corresponding to the para position of the same ring. The bent shape of the O-aryl moieties that best fit the enzyme surface closely resembles the folded conformations observed in the complexes of unsaturated fatty acids with different proteins. URB524 (N-cyclohexylcarbamic acid biphenyl-3-yl ester, 9g) is the most potent compound of the series (IC₅₀ = 63 nM) and was therefore selected for further optimization.

Full text of DOI:10.1021/jm021119g

2352
J . Med. Chem. 2003, 46, 2352-2360
Design , Syn th esis, a n d Str u ctu r e-Activity Rela tion sh ip s of Alk ylca r ba m ic Acid
Ar yl Ester s, a New Cla ss of F a tty Acid Am id e Hyd r ola se In h ibitor s
Giorgio Tarzia,† Andrea Duranti,† Andrea Tontini,† Giovanni Piersanti,† Marco Mor,*,‡ Silvia Rivara,‡
Pier Vincenzo Plazzi,‡ Chris Park,§ Satish Kathuria,§ and Daniele Piomelli§
Istituto di Chimica Farmaceutica e Tossicologica, Universita` degli Studi di Urbino Carlo Bo, Piazza del Rinascimento 6,
I-61029 Urbino, Italy, Dipartimento Farmaceutico, Universita` degli Studi di Parma, Parco Area delle Scienze 27/ A,
I-43100 Parma, Italy, and Department of Pharmacology, 360 MSII, University of California, Irvine, California 92697-4625
Received December 16, 2002
Fatty acid amide hydrolase (FAAH), an intracellular serine hydrolase enzyme, participates in
the deactivation of fatty acid ethanolamides such as the endogenous cannabinoid anandamide,
the intestinal satiety factor oleoylethanolamide, and the peripheral analgesic and anti-
inflammatory factor palmitoylethanolamide. In the present study, we report on the design,
synthesis, and structure-activity relationships (SAR) of a novel class of potent, selective, and
systemically active inhibitors of FAAH activity, which we have recently shown to exert potent
anxiolytic-like effects in rats. These compounds are characterized by a carbamic template
substituted with alkyl or aryl groups at their O- and N-termini. Most compounds inhibit FAAH,
but not several other serine hydrolases, with potencies that depend on the size and shape of
the substituents. Initial SAR investigations suggested that the requirements for optimal potency
are a lipophilic N-alkyl substituent (such as n-butyl or cyclohexyl) and a bent O-aryl substituent.
Furthermore, the carbamic group is essential for activity. A 3D-QSAR analysis on the
alkylcarbamic acid aryl esters showed that the size and shape of the O-aryl moiety are correlated
with FAAH inhibitory potency. A CoMSIA model was constructed, indicating that whereas
the steric occupation of an area corresponding to the meta position of an O-phenyl ring improves
potency, a region of low steric tolerance on the enzyme active site exists corresponding to the
para position of the same ring. The bent shape of the O-aryl moieties that best fit the enzyme
surface closely resembles the folded conformations observed in the complexes of unsaturated
fatty acids with different proteins. URB524 (N-cyclohexylcarbamic acid biphenyl-3-yl ester,
9g) is the most potent compound of the series (IC50 ) 63 nM) and was therefore selected for
further optimization.
In tr od u ction
The fatty acid ethanolamides (FAEs) constitute a
newly characterized family of lipid mediators,1 which
include the endogenous cannabinoid (endocannabinoid)
anandamide2 (arachidonoylethanolamide, 1, Figure 1),
the intestinal satiety factor oleoylethanolamide3 (OEA,
2, Figure 1), and the peripheral analgesic and anti-
inflammatory factor palmitoylethanolamide4 (PEA, 3,
Figure 1). The FAEs are normally present in mam-
malian organs and tissues, where their formation is
thought to be mediated through receptor-dependent
cleavage of N-acylphosphatidylethanolamine (NAPE), a
minor phospholipid component of cell membranes.5
After formation and release from cells, polyunsaturated
FAEs such as anandamide may be eliminated via a two-
F igu r e 1.
step process consisting of high-affinity transport into
cells,6 followed by intracellular degradation catalyzed
by the serine hydrolase, fatty acid amide hydrolase
(FAAH).7 On the other hand, saturated and monoun-
saturated FAEs such as OEA and PEA are not sub-
strates for transmembrane transport and their inacti-
vation may be exclusively mediated via FAAH-catalyzed
hydrolysis.6a,8
Various classes of FAAH inhibitors have been identi-
fied. Reversible inhibitors include endogenous com-
pounds such as 2-octyl-γ-bromoacetoacetate9 (4, Figure
2) as well as numerous synthetic agents containing
electrophilic carbonyls, such as trifluoromethyl ketones,
R-keto esters, and R-keto amides.10 Particularly promis-
ing within this group are the remarkably potent acyl
heterocycles developed by Boger and collaborators,11
* To whom correspondence should be addressed. Phone:
(0039) 0521-905063. Fax: (0039) 0521-905006. E-mail: mor@
ipruniv.cce.unipr.it.
† Universita` degli Studi di Urbino Carlo Bo.
‡ Universita` degli Studi di Parma.
§ University of California.
10.1021/jm021119g CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/10/2003

Alkylcarbamic Acid Aryl Esters
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12 2353
Ta ble 1. Inhibitor Potencies (IC50) of Test Compounds on
Fatty Acid Amide Hydrolase (FAAH) Activity
F igu r e 2.
among which 1-oxazolo[4,5-b]pyridin-2-yl ketones sub-
stituted with a C8-C12 unsaturated chain or with a
phenylalkyl chain of four to eight methylene units (e.g.,
compound 5, Figure 2) gave the best results. Irreversible
inhibitors comprise fatty acid sulfonyl fluorides or
fluorophosphonates such as hexadecanesulfonyl fluo-
ride12 (AM374, 6, Figure 2).
Although the pharmacological properties of ananda-
mide and other FAEs underscore the potential thera-
peutic interest of FAAH inhibition,5b,13 the development
of suitable clinical candidates from currently available
inhibitors may be difficult. The presence of a lipid-like
chain may confer to these compounds a number of
unfavorable biopharmaceutical properties, including low
water solubility, high plasma protein binding, and high
accumulation in fat tissues. Furthermore, the alkyl
chain also may limit the target selectivity of current
FAAH inhibitors by increasing their tendency to
bind to other endocannabinoid-metabolizing enzymes,
such as monoglyceride lipase14 and cannabinoid re-
ceptors.12a,b,15 Therefore, the design of potent and selec-
tive small-molecule inhibitors of FAAH remains an
essential step in the validation of this enzyme as a
therapeutic target.
The cloning of rodent and human FAAH has revealed
the existence of a close structural relationship among
different mammalian forms of this enzyme and between
these and bacterial amidases. This homology is particu-
larly evident at the level of the amidase “signature
sequence”, a highly conserved domain enriched in
glycine and serine residues.7,16 Site-directed mutagen-
esis studies have shown that three serine residues
within this domain are essential for catalytic activity
(S217, S218, and S241), one of which (S241) may act as
nucleophile during the catalytic process. This nucleo-
philic serine may be activated by the lysine residue
K142 rather than through the Ser-His-Asp interaction
characteristic of other serine hydrolases.17
In the present study, we report on the synthesis of a
series of alkylcarbamic acid aryl esters (9), designed as
inhibitors of FAAH by progressive modification of the
structure of a known inhibitor of the serine hydrolase
acetylcholinesterase (AChE) (compound 19), and on the
biological activity of some other known carbamates
(compounds 7 and 20-27 in Table 1). We investigated
the importance for FAAH inhibition of the carbamate
group and the stereoelectronic properties of its N- and
the O-substituents. In particular, we evaluated the role
of the carbamate group by replacing it with isoster
groups. Moreover, carbamic acid esters having confor-

2354 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12
Tarzia et al.
aryl alcohols to isocyanatocyclohexane. Carbamate 11
was prepared by treatment of diimidazol-1-ylmethanone
(10) with biphenyl-3-ylamine,19 followed by cyclohex-
anol, and amide 13 from naphthalene-2-carboxylic acid
(12) via acyl chloride. The preparation of 16a -d in-
volved coupling of an iso(thio)cyanate with an appropri-
ate thiol or amine. Finally, the thiocarbamate 18 was
synthesized from thiophosgene (17), naphthalen-2-ol,
and cyclohexylamine.
F igu r e 3.
Sch em e 1a
Compounds 7 and 19-27 were purchased from Sigma-
Aldrich.
Resu lts a n d Discu ssion
We measured FAAH activity in rat brain membranes,
using [3H]anandamide as a substrate.18 Half-maximal
concentrations (IC50) for inhibition of FAAH activity by
compounds 9a -i, 11, 13, 16a -d , and 19-27 are re-
ported in Table 1. We first tested the AChE inhibitor
carbaryl (19) and its p-tolyl (20) and 2-naphthyl (21)
analogues. Only the latter analogue showed a weak
inhibitory activity, which was enhanced by introducing
more lipophilic alkyl residues on the carbamic nitrogen.
Thus, replacing the methyl group of 21 with a cyclohexyl
resulted in a 60-fold decrease in IC50 (compound 22).
Submicromolar potencies also were observed with the
n-butyl derivatives 7 and 23, whereas the very low
activity of 24 confirmed the essential role of the O-
substituent in FAAH inhibition. Importantly, unlike
carbaryl (19), which inhibited eel acetylcholinesterase
(AchE) activity with an IC50 of 3.1 µM, compounds 7
and 20-24 had no effect on the activities of this enzyme
or of horse-serum butyrylcholinesterase when tested at
concentrations as high as 30 µM (data not shown).
Furthermore, the compounds (1-100 µM) did not dis-
place the binding of [3H]WIN-55212-2 (10 nM) to rat
cerebellar CB1 receptors or human recombinant CB2
receptors and did not affect [3H]anandamide (100 nM)
transport in astrocytoma cells (data not shown).
Next, to examine the role of the carbamate function
in FAAH inhibition, we prepared several isosters of 22.
Both the ester 13 and the urea 16a were ineffective.
Furthermore, replacement of oxygen with sulfur (com-
pounds 16b-d , 18) also led to inactive analogues, with
the partial exception of the thiocarbamic acid S-naph-
thyl ester 16b. These results suggest that the carbamic
group is essential for inhibition of FAAH activity by this
series of compounds.
The hypothesis that guided our subsequent design
was that the FAAH inhibitory activity may be improved
by introducing aromatic substituents of defined shape
on the oxygen atom. We further assumed that this
moiety acted as a leaving group after the nucleophilic
attack of the S241 residue of FAAH on the carbonyl of
the inhibitors, resulting in enzyme carbamoylation.
Though direct evidence for this mechanism is still
needed, the findings that compound 7 inhibits FAAH
activity in a noncompetitive manner (Figure 4) and that
extensive dialysis (1 L/mL of sample, 16 h at 4 °C) does
not reverse inhibition (data not shown) support the
notion that these compounds interact irreversibly with
FAAH.
a
Reagents and conditions: (a) c-C6H11NCO, Et3N, toluene,
reflux, 8-24 h; (b1) biphenyl-3-ylamine, CH3CN, DMAP, reflux,
12 h; (b2) c-C6H11OH, reflux, 24 h; (c) (COCl)2, THF, 25 °C, 2 h;
(d) c-C6H11NH2, Et3N, CH2Cl2, 25 °C, 20 h; (e) Et3N, toluene,
reflux, 20 h for 16a ; t-BuOK, toluene, 50 °C, 15 min for 16b;
CH2Cl2, reflux, 14 h for 16c; 80-100 °C, 20 h for 16d ; (f1) sodium
naphthalen-2-olate, CHCl3, 25 °C, 1 h; (f2) c-C6H11NH2, 25 °C, 4
h.
mationally constrained O-aryl moieties, designed to
mimic the binding conformation of the FAEs chain,
allowed us to conduct a 3D-QSAR analysis of the steric
requirements of the carbamate group O-substituent.
We have recently shown that representative members
of this series (e.g., URB532, 7, Figure 3) are systemically
active inhibitors of FAAH activity.18 The fact that these
compounds exert profound anxiolytic-like effects in rats
suggests that they may provide candidates for the
development of innovative antianxiety medicines.18
Ch em istr y
The synthesis of compounds 9, 11, 13, 16, and 18 is
illustrated in Scheme 1. Cyclohexylcarbamic acid aryl
esters 9a -i were obtained by addition of the suitable
Comparison of the structures of compounds 7 and 22
provided a first insight into the shape requirements for
the O-substituent. A systematic conformational analysis

Alkylcarbamic Acid Aryl Esters
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12 2355
steric complementarity between the inhibitor and the
active site of the enzyme. This hypothesis was further
developed by supposing that the aryloxy group may
mimic the fatty acid chain of anandamide and other
FAEs (e.g., 1-3) by counterfeiting the arrangement of
the first 10-12 carbon atoms in the so-called “U-shaped”
conformation of these molecules.20
Accordingly, we conducted a systematic exploration
of the steric requirements of the aromatic O-substitu-
ents by synthesizing a series of carbamates in which
the shape of the O-residue was gradually modified,
while maintaining the cyclohexyl substituent on the
carbamic nitrogen. Starting from the phenyl and naph-
thyl derivatives 9a and 22, we prepared a series of
compounds with lipophilic groups potentially able to
occupy either a region of space antipodal to the carbam-
ate group (9e, 25, 26) or a region corresponding to the
meta position of the phenyl ring (9a -d ,f,g). The design
of these compounds took into consideration the possibil-
ity of calculating a 3D-QSAR model correlating steric
parameters with inhibitory potency after superposition
of their modeled structures.
F igu r e 4. Lineweaver-Burke analysis of the hydrolysis of
[3H]anandamide (1-100 µM) by rat brain membranes in the
absence (9) or presence (0) of compound 7 (1 µM). Results are
from one experiment, representative of five in which maximal
velocities (Vmax) for [3H]anandamide hydrolysis were 2271 (
477 pmol/(min‚mg) protein in control samples and 703 ( 188
pmol/(min‚mg) protein in the presence of compound 7 (p <
0.05). Michaelis-Menten constants (KM) were 9.3 ( 2.3 µM
in control samples and 10.2 ( 3.3 µM in the presence of
compound 7 (p > 0.05, Student’s t test; n ) 5).
Within this second set of compounds, greater inhibi-
tory potencies were obtained with those molecules that
had a bent shape. In particular, we observed the
strongest FAAH inhibition with the m-biphenyl deriva-
tive URB524 (9g), whose IC50 value (63 nM) indicates
a 36-fold increase in potency over the isomeric p-
biphenyl derivative 26. The comparison between 9e and
9f, 9c and 9d , and 9b and 25 is also suggestive of a
similar trend. While the O-phenyl derivative 9a was
almost inactive, we obtained compounds of moderate to
good inhibitory potency by substituting the meta posi-
tion of 9a with groups of suitable sizes (9b ,h ,g).
Importantly, the carbamates 9a -g, 25, and 26 did not
significantly interact with AChE or with cannabinoid-
related targets such as CB1 or CB2 cannabinoid recep-
tors and endocannabinoid transporter at concentrations
as high as 30 µM.
It is noteworthy that the m-biphenyl fragment of 9g
may be superposed to the first 10 carbons of the fatty
acid chain of arachidonic acid in the conformations
adopted by this compound when bound to various
proteins. The coordinates of such complexes are avail-
able through the Protein Data Bank.21 Figure 6 shows
the superposition of 9g on arachidonic acid in the
conformation the latter adopts when interacting with
human adipocyte lipid-binding protein,22 COX-1,23 and
COX-2.24 It should be noted that the two phenyl rings
of 9g can occupy regions of space corresponding to the
first two cis double bonds of arachidonic acid. A folded
conformation similar to that illustrated in Figure 5B
was found, together with other more straight conforma-
tions, for arachidonic acid in complex with human
serum albumin.25 Similar folded conformations also
were observed for oleic acid and other unsaturated fatty
acids bound to human fatty acid binding proteins
(FABP).26 These observations led us to consider the
m-biphenyl fragment as a putative bioisoster of the first
moiety of such chains, being able to reproduce the bent
shape of the first two cis-double bonds of the arachidonyl
chain.
F igu r e 5. (A) Representation of minimum energy conforma-
tions of 22 (green carbons) and 7 (white carbons, in gauche
and anti conformations) after superposition of the carbamate
group. (B) Superposition of the biphenyl moiety of 9i (orange
carbons) to the lipophilic chain of arachidonic acid, cocrystal-
lized with adipocyte lipid-binding protein (white carbons),
COX-1 (yellow carbons), or COX-2 (green carbons).
of the benzyloxyphenyl fragment of 7 revealed two
families of accessible conformers, mainly differing in the
torsion angle around the O-CH2 bond, with the two
phenyl rings in anti or in gauche conformation. Appar-
ently, the gauche conformation of 7 more closely re-
sembled the shape of the naphthyl derivative 23 when
the compounds were superimposed via their common
carbamate group (Figure 5A). This led us to hypothesize
that a bent shape of the carbamate O-substituent could
favor enzyme inhibition, possibly by allowing a greater

2356 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12
Tarzia et al.
Ta ble 2. Experimental and Observed pIC50 Values on FAAH
Activity Inhibition for the N-Alkylcarbamate Aryl Esters
Included in the 3D-QSAR Analysis
pIC50
compd
R1
R2
obsd
calcd
7
n-butyl
n-butyl
n-butyl
benzyloxyphenyl
6-bromonaphthalen-2-yl
4-fluorophenyl
2-naphthyl
phenyl
m-tolyl
6.41
6.12
4.94
6.49
5.42
6.09
5.27
6.76
5.45
5.48
6.58
7.20
5.64
6.73
6.48
5.81
4.99
6.22
5.41
5.94
5.55
6.31
6.13
5.49
6.89
6.98
5.55
6.83
23
24
22
9a
9b
25
9c
9d
9e
9f
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
p-tolyl
8-bromonaphthalen-2-yl
6-ethylnaphthalen-2-yl
(E)-4-styrylphenyl
(Z)-4-styrylphenyl
biphenyl-3-yl
9g
26
9h
biphenyl-4-yl
3-pentylphenyl
ploying, as the dependent variable, the inhibitory
potency expressed on a -log scale (pIC50). Only the
carbamate derivatives having a lipophilic N-substituent
and an aromatic O-substituent were included in the
analysis, since they represented a chemically homoge-
neous set with an initial standard deviation in pIC50
values of 0.67 units around a mean value of 6.06.
The superposition of the carbamate fragments and the
phenyl rings (see Experimental Section) led to a PLS
model with two latent variables endowed with ap-
preciable descriptive and predictive power (r2 ) 0.82, s
F igu r e 6. (A) Plot of the experimentally observed pIC50 data
vs those calculated by the 3D-QSAR CoMSIA model for the
14 compounds reported in Table 2. A PLS model with two
latent variables gave the following statistics: r2 ) 0.82, s )
0.32, q2
) 0.54. (B) 3D-QSAR graphical depiction of the
LOO
coefficients for the CoMSIA fields, calculated by PLS analysis
on the pIC50 values of the 14 compounds reported in Table 2.
All the compounds are represented as lines except 7 (white
carbons) and 9g (orange carbons), which are represented as
sticks. The colored volumes indicate the points where the
influence of the steric potential on pIC50 is more significant.
The color codes are the following: blue, very positive; green,
positive; yellow, negative (see Experimental Section).
) 0.32, q2
) 0.54) for the 14-compound set, whose
LOO
experimental and calculated pIC50 values are reported
in Table 2 and graphically plotted in Figure 6A.
The coefficients of the steric field are represented in
Figure 8 as isopotential surfaces. As can be observed
from the green and blue surfaces corresponding to a
positive and very positive correlation, respectively,
between steric occupancy and potency, two favorable
regions were detected by our model. The first (at the
top right of Figure 6B) was due to the lower mean pIC50
values observed for the N-butyl derivatives with respect
to the N-cyclohexyl ones. It should be noted that this
positive region would be much more relevant if the
compounds having small N-substituents (19-21) could
be included in the analysis, but this was precluded by
the fact that only one of them had a measurable IC50.
As a consequence, the importance of the N-substituent
is underestimated by our 3D-QSAR model, which,
however, was developed essentially to investigate the
O-substituent requirements. Indeed, a larger and deeper
favorable region was observed for this moiety, as il-
lustrated by the green and blue volumes at the bottom
of Figure 6B, indicating the presence of steric bulk,
positively correlated with inhibitory potency, around the
meta position of the proximal ring of the O-biphenyl
substituent. This region corresponds to the second ring
of the naphthyl system (especially the areas about its 7
and 8 positions) and of the distal phenyl of the styryl
substituent in its (Z)-configuration. It is reasonable to
assume the proximity of this region to the binding site
surface of FAAH, which would result in an improvement
of dispersion forces and/or lipophilic interaction between
We next replaced the aromatic O-substituent with
flexible alkyl chains. In the 2-acyloxazolopyridine series
of competitive FAAH inhibitors described by Boger and
collaborators,11 the introduction of an ω-phenylpentyl
group leads to one of the most potent inhibitors. By
contrast, in our series the presence of the same moiety
was detrimental to the inhibitory activity (see com-
pounds 27 and 9i). Together with their differences in
inhibition kinetics, these results support the notion that
the two classes of compounds inhibit FAAH through
separate mechanisms.
A further indication of the distinct SAR profile of the
N-alkylcarbamic acid aromatic esters described here is
the fact that compound 11, which has a bent shape like
9g but inverted N- and O-substituents, was inactive.
This suggests that the binding pockets of the two
moieties have specific stereoelectronic requirements.
The correlation between molecular shape and FAAH
inhibitor potency was tested by 3D-QSAR methods. A
number of key compounds characterized by variations
of their steric (and not electrostatic or lipophilic) fea-
tures were selected, and only the correlation between
steric field and biological activity was investigated. A
3D-QSAR analysis was performed by partial least
squares (PLS) regression on the comparative molecular
similarity index analysis (CoMSIA) steric field27 em-

Alkylcarbamic Acid Aryl Esters
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12 2357
in hertz (Hz). IR spectra were obtained on a Shimadzu FT-
8300 or a Nicolet Atavar spectometer. Absorbances are re-
ported as ν (cm-1). Elemental analyses were performed on a
Carlo Erba analyzer. All products had satisfactory (within (0.4
of theoretical values) C, H, N analyses results.
Gen er a l P r oced u r e for th e Syn th esis of Cycloh exyl-
ca r ba m ic Acid Ar yl Ester s (9a -e,g-i). To a stirred mixture
of the suitable aryl alcohol 8a -e,g-i (0.5 mmol) in toluene (3
mL), Et3N (3 mg, 0.004 mL, 0.03 mmol) and c-C6H11NCO (69
mg, 0.07 mL, 0.55 mmol) were added. After refluxing the
reactants for 5 h, a further amount of c-C6H11NCO (34 mg,
0.035 mL, 0.27 mmol) was added, and the mixture again
reacted for 3 h [9g, 19 h; in the case of 9a ,b a third addition
of c-C6H11NCO (34 mg, 0.035 mL, 0.27 mmol) was necessary;
overall, these reactions required 24 h; in the case of 9e, the
the enzyme and the inhibitor. Thus, the O-aromatic
moiety, which is hypothesized to serve as a leaving
group in the reaction leading to enzyme carbamoylation,
would exert its effect on inhibitory potency at an early
recognition stage of the process.
We observed a small region with moderately negative
coefficients, represented by the yellow surface at the
bottom left of Figure 6B, opposite the point of attach-
ment of the phenyl ring to the carbamate group. It
indicates that longer straight fragments can be accom-
modated at the binding pocket in a less efficient manner
than the folded ones. The most relevant example is
represented by p-biphenyl derivative 26, whose potency
is much lower than that of its m-biphenyl isomer 9g.
We interpret the CoMSIA coefficients to indicate the
existence of a large cavity with a curved shape in the
active site of enzyme, where suitable O-substituents can
be accommodated, so that the interaction of their
carbonyl group with the active serine of the enzyme is
facilitated. This result further highlights the similarity
between the m-biphenyl moiety and the conformation
of arachidonic acid bound to FABP (Figure 6), strength-
ening the initial hypothesis that FAEs bind to FAAH
in a folded conformation, at least for the first 10 carbon
atoms. We cannot exclude, however, that the fatty acyl
chain of anandamide and the O-substituent of our
carbamate esters are docked to different binding pockets
within the FAAH active site. The availability of FAAH
3D coordinates, which were published for a covalent
adduct of the enzyme with O-methylarachidonyl fluo-
rophosphonate (MAFP)28 while the present manuscript
was under review, may help to resolve this issue. It is
worth noting that in this crystal the arachidonyl chain
of the inhibitor takes a turn after its first double bond
and is flanked by aromatic residues interacting with the
first two double bonds, which may be mimicked by the
two phenyl rings in compound 9g.
initial mixture was refluxed 8 h, no further addition of c-C6H11
-
NCO being necessary], then cooled, and concentrated. Purifi-
cation of the residue by column cromatography (cyclohexane/
EtOAc 9:1 for 9a ,b,h ; 8:2 for 9i; 85:15 for 9c; 95:5 for 9g;
CH2Cl2 for 9d ,e) and recrystallization gave 9a -e,g-i.
Cycloh exylca r ba m ic Acid P h en yl Ester (9a ). White
needles. Yield: 73% (80 mg). Mp: 137 °C (MeOH) (lit. 128-
1
30 °C from 50% EtOH).33 MS (EI): m/z 219 (M+), 94 (100). H
NMR (CDCl3): δ 1.20-2.05 (m, 10H), 3.57 (m, 1H), 4.91 (br s,
1H), 7.11-7.40 (m, 5H) ppm. The IR spectrum is in agreement
with literature.33 Anal. (C13H17NO2) C, H, N.
Cycloh exylca r ba m ic Acid m -Tolyl Ester (9b). White
needles. Yield: 87% (101 mg). Mp: 117-118 °C (MeOH). MS
1
(EI): m/z 233 (M+), 107 (100). H NMR (CDCl3): δ 1.18-2.05
(m, 10H), 2.35 (s, 3H), 3.57 (m, 1H), 4.90 (br s, 1H), 6.91-7.02
(m, 3H), 7.23 (t, 1H) ppm. IR (KBr): 3305, 1744, 1709 cm-1
Anal. (C14H19NO2) C, H, N.
.
Cycloh exylca r ba m ic Acid 8-Br om on a p h th a len -2-yl Es-
ter (9c). Yellow needles. Yield: 66% (115 mg). Mp: 170-171
°C (MeOH). MS (EI): m/z 348 (M+), 114 (100). 1H NMR
(CDCl3): δ 1.18-2.09 (m, 10H), 3.63 (m, 1H), 5.03 (br d, 1H),
7.26-7.99 (m, 6H) ppm. IR (KBr): 3316, 1737, 1708 cm-1
Anal. (C17H18BrNO2) C, H, N.
.
Cycloh exylca r ba m ic Acid 6-Eth yln a p h th a len -2-yl Es-
ter (9d ). White needles. Yield: 74% (110 mg). Mp: 162-164
°C (MeOH). MS (EI): m/z 297 (M+), 157 (100). 1H NMR
(CDCl3): δ 1.17-2.07 (m, 13H), 2.81 (q, 2H), 3.61 (m, 1H), 4.97
(br d, 1H), 7.22-7.79 (m, 6H) ppm. IR (CHCl3): 3440, 1732
cm-1. Anal. (C19H23NO2) C, H, N.
In conclusion, we have characterized a new class of
FAAH inhibitors, namely, alkylcarbamic acid aryl es-
ters, and demonstrated that their inhibitory potency can
be improved by shape modulation of the aromatic
O-substituent. The marked anxiolytic-like properties of
these compounds18 should encourage further investiga-
tions of their SAR. Indeed, a systematic structural
modulation of the biphenyl derivative 9g is currently
underway in our laboratories.
(E)-Cycloh exylca r b a m ic Acid 4-St yr ylp h en yl E st er
(9e). White crystals. Yield: 86% (138 mg). Mp: 165-166 °C
1
(MeOH). MS (EI): m/z 321 (M+), 196 (100). H NMR (CDCl3):
δ 1.22-2.05 (m, 10H), 3.56 (m, 1H), 4.91 (br d, 1H), 7.03 (d,
1H, J ) 16.7), 7.12 (d, 1H, J ) 16.7), 7.13 (d, 2H), 7.26-7.52
(m, 7H) ppm. IR (CHCl3): 3440, 1736, 963 cm-1. Anal. (C21H23
NO2) C, H, N.
-
Cycloh exylca r ba m ic Acid Bip h en yl-3-yl Ester (9g).
White crystals. Yield: 97% (143 mg). Mp: 141-143 °C
1
(MeOH). MS (EI): m/z 170 (100). H NMR (CDCl3): δ 1.22-
Exp er im en ta l Section
2.06 (m, 10H), 3.59 (m, 1H), 4.94 (br d, 1H), 7.12-7.61 (m,
9H) ppm. IR (CHCl3): 3440, 1733 cm-1. Anal. (C19H21NO2) C,
H, N.
(a ) Ch em ica ls, Ma ter ia ls, a n d Meth od s. All reagents and
compounds 7 and 19-27 were purchased from Sigma-Aldrich
with the exception of 8c,29 8d ,30 8e,31 8h ,32 and biphenyl-3-
ylamine,19 whose preparation is reported in the literature.
Solvents were RP grade unless otherwise indicated. Purifica-
tion of the crude materials obtained from the reactions,
affording the desired products, was carried out by flash column
chromatography on silica gel (Kieselgel 60, 0.040-0.063 mm,
Merck). TLC analyses were performed on precoated silica gel
on aluminum sheets (Kieselgel 60 F254, Merck). Melting points
were determined on a Bu¨chi SMP-510 capillary melting point
apparatus and are uncorrected. The structure of the unknown
Cycloh exylca r ba m ic Acid 3-P en tylp h en yl Ester (9h ).
White crystals. Yield: 98% (142 mg). Mp: 94-95 °C (petro-
leum ether). MS (EI): m/z 289 (M+), 164 (100). 1H NMR
(CDCl3): δ 0.89 (t, 3H), 1.18-2.05 (m, 16H), 2.60 (t, 2H), 3.57
(m, 1H), 4.88 (br d, 1H), 6.93-7.27 (m, 4H) ppm. IR (KBr):
3306, 1743, 1705 cm-1. Anal. (C18H27NO2) C, H, N.
Cycloh exylca r ba m ic Acid 5-P h en ylp en tyl Ester (9i).
White needles. Yield: 80% (115 mg). Mp: 55-56 °C (Et2O/
1
petroleum ether). MS (EI): m/z 289 (M+), 146 (100). H NMR
(CDCl3): δ 1.09-1.96 (m, 16H), 2.62 (t, 2H), 3.49 (m, 1H), 4.04
(t, 2H), 4.53 (br s, 1H), 7.16-7.28 (m, 5H) ppm. IR (CHCl3):
3442, 1703 cm-1. Anal. (C18H27NO2) C, H, N.
Syn th esis of (Z)-Cycloh exylcar bam ic Acid 4-Styr ylph e-
n yl Ester (9f). A stirred mixture of benzyltriphenylphospho-
nium chloride (16.8 g, 43.3 mmol), 4-hydroxybenzaldehyde
(5.28 g, 43.3 mmol), DBU (6.8 g, 45 mmol), and CH3CN (67
mL) was refluxed for 4 h and concentrated. Purification of the
1
compounds was unambiguously assessed by MS, H NMR, IR,
and elemental analysis. EI-MS spectra (70 eV) were recorded
with a Fisons Trio 1000 spectrometer. Only molecular ions
(M+) and base peaks are given. 1H NMR spectra were recorded
on a Bruker AC 200 spectrometer. Chemical shifts (δ scale)
are reported in parts per million (ppm) relative to the central
peak of the solvent. Coupling constants (J values) are given

2358 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12
Tarzia et al.
1
residue by column cromatography (cyclohexane/EtOAc 85:15)
gave pure E-stilben-4-ol (2 g) and a 1:1 (NMR)34 mixture of Z-
and E-stilben-4-ols (0.456 g, 2.33 mmol). This was dissolved
in toluene (13 mL), and Et3N (0.014 g, 0.019 mL, 0.14 mmol)
and c-C6H11NCO (0.32 g, 0.33 mL, 2.57 mmol) were added. The
mixture was refluxed under stirring for 3 h, cooled, and
concentrated. Purification of the residue by column cromatog-
raphy (cyclohexane/EtOAc 85:15) gave the desired product
along with a substantial amount of 9e. Recrystallization gave
9f (105 mg) as a white solid. Mp: 131-133 °C (EtOH/H2O).
aqueous EtOH).36 MS (EI): m/z 284 (M+), 143 (100). H NMR
(CDCl3): δ 1.02-2.18 (m, 11H), 4.31 (m, 1H), 6.02 (d, 1H), 7.30
(dd, 1H), 7.55 (m, 1H), 7.64 (d, 1H), 7.75-7.95 (m, 4H) ppm.
IR (KBr): 3331, 3192, 1598 cm-1. Anal. (C17H20NS) C, H, N.
Syn th esis of Cycloh exyld ith ioca r ba m ic Acid Na p h -
th a len -2-yl Ester (16d ). A stirred mixture of naphthalene-
2-thiol (15b) (125 mg, 0.78 mmol) and c-C6H11NCS (14b) (110
mg, 0.11 mL, 0.78 mmol) was heated at 80-100 °C in a sealed
tube for 20 h, cooled, and filtered. Recrystallization gave 16d
as a white solid. Yield: 46% (108 mg). Mp: 118-122 °C
(toluene/n-pentane). MS (EI): m/z 301 (M+), 160 (100). 1H
NMR (CDCl3): δ 0.97-1.94 (m, 10H), 4.38 (m, 1H), 6.54 (br s,
1H), 7.56-7.66 (m, 3H), 7.89-8.00 (m, 3H), 8.13 (s, 1H) ppm.
IR (KBr): 3337, 1580 cm-1. Anal. (C17H19NS2) C, H, N.
1
MS (EI): m/z 321 (M+), 196 (100). H NMR (CDCl3): δ 1.19-
2.04 (m, 10H), 3.54 (m, 1H), 4.88 (br d, 1H), 6.54 (d, 1H, J )
12.2), 6.60 (d, 1H, J ) 12.2), 6.98 (d, 2H), 7.24 (m, 7H) ppm.
IR (CHCl3): 3440, 1736 cm-1. Anal. (C21H23NO2) C, H, N.
Syn th esis of Bip h en yl-3-yl Ca r ba m ic Acid Cycloh exyl
Ester (11). To a stirred solution of biphenyl-3-ylamine (90 mg,
0.53 mmol) in CH3CN (2 mL), diimidazol-1-ylmethanone (10)
(345 mg, 2.13 mmol) and DMAP (12 mg, 0.1 mmol) were added.
After the mixture was refluxed for 14 h, c-C6H11OH (800 mg,
0.84 mL, 8 mmol) was added. The mixture reacted under reflux
for 24 h and then was cooled and concentrated. Purification
of the residue by column cromatography (cyclohexane/EtOAc
9:1) and recrystallization gave 11 as a white solid. Yield: 55%
(86 mg). Mp: 127-129 °C (EtOH). MS (EI): m/z 295 (M+), 141
Syn th esis of Cycloh exylth ioca r ba m ic Acid O-Na p h -
th a len -2-yl Ester (18). To a stirred solution of C(S)Cl2 (17)
(57 mg, 0.038 mL, 0.5 mmol) in CHCl3 (2 mL), sodium
naphthalen-2-olate [obtained as a sticky solid by adding
naphthalen-2-ol (72 mg, 0.5 mmol) to a solution of Na (0.11
mg, 0.5 mmol) in dry MeOH (1 mL), stirring the mixture for
0.5 h, evaporating the solvent, and drying the residue] was
added (exothermic reaction). After stirring the reactants at
room temperature for 1 h, c-C6H11NH2 (99 mg, 0.11 mL, 1
mmol) was added (exothermic reaction). The mixture reacted
at room temperature for 4 h and then was concentrated. H2O
was cautiously added to the residue, and the mixture was
extracted with EtOAc. The combined organic layers were dried
(Na2SO4) and concentrated. Purification of the residue by
column chromatography (cyclohexane/EtOAc 9:1) and recrys-
tallization gave 18 as a light-yellow, garlic-smelling solid.
Yield: 60% (86 mg). Mp: 154-155 °C (EtOH). MS (EI): m/z
1
(100). H NMR (CDCl3): δ 1.30-2.03 (m, 10H), 4.78 (m, 1H),
6.66 (br s, 1H), 7.31-7.47 (m, 6H), 7.59-7.70 (m, 3H) ppm.
IR (KBr): 3320, 1725, 1689 cm-1. Anal. (C19H21NO2) C, H, N.
Syn t h esis of N-Cycloh exyl-2-n a p h t h a len -2-yla cet a -
m id e (13). To a stirred, cooled (0 °C) solution of naphthalene-
2-carboxylic acid (12) (186 mg, 1 mmol) in dry THF (3.3 mL)
under N2 atmosphere, (COCl)2 (508 mg, 0.35 mL, 4 mmol) was
added. The mixture was stirred at room temperature for 2 h
and then concentrated. The residue was dissolved in CH2Cl2
(3.3 mL), and then Et3N (283 mg, 0.39 mL, 2.8 mmol) and
c-C6H11NH2 (131 mg, 0.15 mL, 1.3 mmol) in a minimal amount
of CH2Cl2, were added. The mixture reacted at room temper-
ature for 20 h and then was concentrated. Purification of the
residue by column cromatography (cyclohexane/EtOAc 7:3) and
recrystallization gave 13 as white needles. Yield: 33% (88 mg).
Mp: 185-186 °C (EtOAc). MS (EI): m/z 267 (M+), 168 (100).
1H NMR (CDCl3): δ 0.89-1.86 (m, 10H), 3.73 (s and m, 3H),
5.26 (br s, 1H), 7.35-7.87 (m, 7H) ppm. IR (KBr): 3285, 1640
cm-1. Anal. (C18H21NO) C, H, N.
Syn th esis of 1-Cycloh exyl-3-n aph th alen -2-ylu r ea (16a).35
A stirred mixture of naphthalen-2-ylamine (15a ) (143 mg, 1
mmol), c-C6H11NCO (14a ) (138 mg, 0.14 mL, 1.1 mmol), Et3N
(5 mg, 0.07 mL, 0.05 mmol), and toluene (5 mL) was refluxed
for 20 h. Two further amounts of 14a (69 mg, 0.07 mL, 0.55
mmol) were added during this period, after 5 and 3 h,
respectively. The mixture was then cooled and concentrated.
Purification of the residue by column chromatography (cyclo-
hexane/EtOAc 85:15) and recrystallization gave 16a as a white
solid. Yield: 30% (80 mg). Mp: 204 °C (MeOH) (lit. 204-205
°C).35 Anal. (C17H20N2O) C, H, N.
Syn th esis of Cycloh exylth ioca r ba m ic Acid S-Na p h -
th a len -2-yl Ester (16b).36 To a stirred solution of t-BuOK (2.1
mg, 0.018 mmol) and naphthalene-2-thiol (15b) (300 mg, 1.875
mmol) in toluene (0.6 mL), c-C6H11NCO (14a ) (235 mg, 0.24
mL, 1.875 mmol) in toluene (0.6 mL) was added dropwise at
50 °C during 5 min. The mixture was stirred at the same
temperature for 15 min and then cooled and filtered. Recrys-
tallization gave 16b as a white solid. Yield: 60% (318 mg).
Mp: 153 °C (EtOH). MS (EI): m/z 159, 115 (100). 1H NMR
(CDCl3): δ 0.98-1.96 (m, 10H), 3.75 (m, 1H), 5.29 (br s, 1H),
7.50-7.62 (m, 3H), 7.83-7.90 (m, 4H), 8.09 (s, 1H) ppm. IR
(KBr): 3294, 1643 cm-1. Anal. (C17H19NOS) C, H, N.
Syn th esis of 1-Cycloh exyl-3-n a p h th a len -2-ylth iou r ea
(16c). To a stirred solution of naphthalen-2-ylamine (15a ) (143
mg, 1 mmol) in CH2Cl2 (2 mL), c-C6H11NCS (14b) (141 mg,
0.14 mL, 1 mmol) was added. The mixture was stirred at room
temperature for 5 h, refluxed for 14 h, cooled, and concen-
trated. Purification of the residue by column cromatography
(CH2Cl2) and recrystallization gave 16c as white solid. Yield:
51% (145 mg). Mp: 165-167 °C (EtOH) (lit. 172 °C from
1
144, 115 (100). H NMR (CDCl3): δ 1.22-2.22 (m, 10H), 4.14
(m, 1H), 6.64 and 6.84 (1H),37 7.24-7.32 (m, 1H), 7.46-7.54
(m, 3H), 7.79-7.90 (m, 3H) ppm. IR (Nujol): 3212, 1623 cm-1
Anal. (C17H19NOS) C, H, N.
.
(b) P h a r m a cology. Cell fractions were prepared from brain
homogenates, and membrane FAAH activity was assayed
using anandamide[ethanolamine-3H] (American Radiolabeled
Chemicals, ARC (St. Louis, Missouri), 60 Ci/mmol) as a
substrate.18 [3H]Anandamide transport assays were conducted
in human astrocytoma cells, preincubating cells with inhibitors
for 10 min at 37 °C, prior to exposure to [3H]anandamide for
4 min.8 CB1 and CB2 binding assays were conducted in rat
cerebellar membranes (27000g) and CB2-overexpressing CHO
cells (purchased from Receptor Biology-Perkin-Elmer, Welle-
sley, MA), respectively, using [3H]WIN-55212-2 (NEN-Dupont,
Boston, MA, 40-60 Ci/mmol, 10 nM) as a ligand.18 Cholinest-
erase assays were conducted with a commercial kit (Sigma,
St. Louis, MO), using purified enzymes (electric eel acetylcho-
linesterase type V-S and horse-serum cholinesterase, both from
Sigma, St. Louis, MO) and following vendor’s instructions.
(c) Molecu la r Mod elin g. Molecular models were built by
applying the standard tools in Sybyl, version 6.6 (Tripos Inc.,
1699 South Hanley Rd, Louis, MO, 63144). Their geometries
were optimized by energy minimization, employing the Merck
molecular force field 94s (MMFF94s),38 implemented in Sybyl.
Conformational analysis was performed by systematic scan-
ning of the rotatable bonds and energy minimization to a
gradient of 0.01 kcal mol-1 Å-1. The conformations giving the
highest intersection volume with the template structure were
employed for compound alignment in the following analysis.
For 3D-QSAR analysis, minimum energy conformations of the
compounds were aligned by a rigid root-mean-square (rms) fit
of the five atoms in the carbamate fragment and the six carbon
atoms in the closer phenyl ring, employing 9g as a template
structure. For compounds 7 and 9f, the centroid of the distal
phenyl ring was also superposed to that of 9g. The CoMSIA27
modules of Sybyl were employed for the quantitative structure-
activity study. The CoMSIA steric field was calculated within
a lattice with a grid resolution of 2 Å, whose extension was at
least 4 Å beyond every molecular boundary in all directions.
An sp3 carbon was taken as the probe atom. Regression
analyses were performed using the PLS39 algorithm in Sybyl.
The cross-validation technique with the leave-one-out (LOO)

Alkylcarbamic Acid Aryl Esters
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12 2359
procedure40 was applied to calculate q2LOO as a rough estimate
of the predictive power and to choose the optimal number of
latent variables. Variables with an energy standard deviation
lower than 2 kcal/mol were discarded to minimize the influence
of noisy columns and to speed the computation. The final non-
cross-validated analyses were derived with the number of
(11) (a) Boger, D. L.; Sato, H.; Lerner, A. E.; Hedrick, M. P.; Fecik,
R. A.; Miyauchi, H.; Wilkie, G. D.; Austin, B. J .; Patricelli, M.
P.; Cravatt, B. F. Exceptionally potent inhibitors of fatty acid
amide hydrolase: The enzyme responsible for degradation of
endogenous oleamide and anandamide. Proc. Natl. Acad. Sci.
U.S.A. 2000, 97, 5044-5049. (b) Boger, D. L.; Miyauchi, H.;
Hedrick, M. P. R-Keto Heterocycle Inhibitors of Fatty Acid Amide
Hydrolase: Carbonyl Group Modification and R-Substitution.
Bioorg. Med. Chem. Lett. 2001, 11, 1517-1520.
(12) (a) Deutsch, D. G.; Lin, S.; Hill, W. A. G.; Morse, K. L.; Salehani,
D.; Arreaza, G.; Omeir, R. L.; Makriyannis, A. Fatty Acid
Sulphonyl Fluorides Inhibit Anandamide Metabolism and Bind
to the Cannabinoid Receptor. Biochem. Biophys. Res. Commun.
1997, 231, 217-221. (b) Deutsch, D. G.; Omeir, R.; Arreaza, G.;
Salehani, D.; Prestwich, G. D.; Huang, Z.; Howlett, A. Methyl
Arachidonyl Fluorophosphonate: A Potent Irreversible Inhibitor
of Anandamide Amidase. Biochem. Pharmacol. 1997, 53, 255-
260. (c) De Petrocellis, L.; Melck, D.; Ueda, N.; Maurelli, S.;
Kurahashi, Y.; Yamamoto, S.; Marino, G.; Di Marzo, V. Novel
Inhibitors of Brain, Neuronal, and Basophilic Anandamide
Amidohydrolase. Biochem. Biophys. Res. Commun. 1997, 231,
82-88.
latent variables corresponding to the first maximum q2
LOO
value, or before nonsignificant increase of q2
(i.e., <0.05).
LOO
No filter was applied to the dependent variables in this case.
The contour volumes of the 3D-QSAR model, represented in
Figure 6B, correspond to the following cutoff values for the
product of the PLS coefficients and the standard deviation of
the steric potential: (blue) >+0.05, (green) >+0.01, (yellow)
<-0.01, (red) <-0.05.
Ack n ow led gm en t. This work was supported by
MIUR (Ministero dell’Istruzione, dell’Universita` e della
Ricerca), Universities of Parma and Urbino, and the
National Institute of Drug Abuse (to D.P.). The CCE
(Centro di Calcolo Elettronico) and CIM (Centro Inter-
facolta` Misure) of the University of Parma are gratefully
acknowledged for supplying the Sybyl software license.
(13) Bisogno, T.; De Petrocellis, L.; Di Marzo, V. Fatty Acid Amide
Hydrolase, an Enzyme with Many Bioactive Substrates. Possible
Therapeutic Implications. Curr. Pharm. Des. 2002, 8, 533-547.
(14) Dinh, T. P.; Carpenter, D.; Leslie, F. M.; Freund, T. F.; Katona,
I.; Sensi, S. L.; Kathuria, S.; Piomelli, D. Brain monoglyceride
lipase participating in endocannabinoid inactivation. Proc. Natl.
Acad. Sci. U.S.A. 2002, 99, 10819-10824.
Refer en ces
(15) (a) Fernando, S. R.; Pertwee, R. G. Evidence that methyl
arachidonyl fluorophosphonate is an irreversible cannabinoid
receptor antagonist. Br. J . Pharmacol. 1997, 121, 1716-1720.
(b) Edgemond, W. S.; Greenberg, M. J .; McGinley, P. J .; Muth-
ians, S.; Campbell, W. B.; Hillard, C. J . Synthesis and Charac-
terization of Diazomethylarachidonyl Ketone: An Irreversible
Inhibitor of N-Arachidonylethanolamide Amidohydrolase. J .
Pharmacol. Exp. Ther. 1998, 286, 184-190.
(16) (a) Cravatt, B. F.; Giang, D. K.; Mayfield, S. P.; Boger, D. L.;
Lerner, R. A.; Gilula, N. B. Molecular characterization of an
enzyme that degrades neuromodulatory fatty-acid amides. Na-
ture (London) 1996, 384, 83-87. (b) Kobayashi, M.; Fujiwara,
Y.; Goda, M.; Komeda, H.; Shimizu, S. Identification of Active
Sites in Amidase: Evolutionary Relationship between Amide
Bond- and Peptide Bond-Cleaving Enzymes. Proc. Natl. Acad.
Sci. U.S.A. 1997, 94, 11986-11991.
(17) (a) Patricelli, M. P.; Lovato, M. A.; Cravatt, B. F. Chemical and
Mutagenic Investigations of Fatty Acid Amide Hydrolase: Evi-
dence for a Family of Serine Hydrolases with Distinct Catalytic
Properties. Biochemistry 1999, 38, 9804-9812. (b) Patricelli, M.
P.; Cravatt, B. F. Clarifying the Catalytic Roles of Conserved
Residues in the Amidase Signature Family. J . Biol. Chem. 2000,
275, 19177-19184.
(18) Kathuria, S.; Gaetani, S.; Fegley, D.; Valin˜o, F.; Duranti, A.;
Tontini, A.; Mor, M.; Tarzia, G.; La Rana, G.; Calignano, A.;
Giustino, A.; Tattoli, M.; Palmery, M.; Cuomo, V.; Piomelli, D.
Modulation of Anxiety through Blockade of Anandamide Hy-
drolysis. Nat. Med. 2003, 9, 76-81.
(19) Leung, W.-Y.; Mao, F.; Haugland, R. P.; Klaubert, D. H.
Lipophilic Sulfophenylcarbocyanine Dyes: Synthesis of a New
Class of Fluorescent Cell Membrane Probes. Bioorg. Med. Chem.
Lett. 1996, 6, 1479-1482.
(20) (a) Reggio, P. H.; Traore, H. Conformational requirements for
endocannabinoid interaction with the cannabinoid receptors, the
anandamide transporter and fatty acid amidohydrolase. Chem.
Phys. Lipids 2000, 108, 15-35. (b) Barnett-Norris, J .; Guarnieri,
F.; Hurst, D. P.; Reggio, P. H. Exploration of Biologically
Relevant Conformations of Anandamide, 2-Arachidonylglycerol,
and Their Analogues Using Conformational Memories. J . Med.
Chem. 1998, 41, 4861-4872.
(1) Fowler, C. J .; J onsson, K.-O.; Tiger, G. Fatty acid amide
hydrolase: biochemistry, pharmacology, and therapeutic pos-
sibilities for an enzyme hydrolyzing anandamide, 2-arachi-
donoylglycerol, palmitoylethanolamide, and oleamide. Biochem.
Pharmacol. 2001, 62, 517-526 and refs 1-4 therein.
(2) Devane, W. A.; Hanusˇ, L.; Breuer, A.; Pertwee, R. G.; Stevenson,
L. A.; Griffin, G.; Gibson, D.; Mandelbaum, A.; Etinger, A.;
Mechoulam, R. Isolation and Structure of a Brain Constituent
That Binds to the Cannabinoid Receptor. Science 1992, 258,
1946-1949.
(3) Rodr´ıguez de Fonseca, F.; Navarro, M.; Go´mez, R.; Escuredo,
L.; Nava, F.; Fu, J .; Murillo-Rodr´ıguez, E.; Giuffrida, A.; LoV-
erme, J .; Gaetani, S.; Kathuria, S.; Gall, C.; Piomelli, D. An
anorexic lipid mediator regulated by feeding. Nature (London)
2001, 414, 209-212.
(4) (a) Calignano, A.; La Rana, G.; Giuffrida, A.; Piomelli, D. Control
of pain initiation by endogenous cannabinoids. Nature (London)
1998, 394, 277-281. (b) Lambert, D. M.; Vandevoorde, S.;
J onsson, K.-O.; Fowler, C. J . The Palmitoylethanolamide Fam-
ily: A New Class of Anti-inflammatory Agents? Curr. Med.
Chem. 2002, 9, 663-674.
(5) See the following for a review. (a) Schmid, H. H.; Schmid, P. C.;
Natarajan, V. The N-acylation-phosphodiesterase pathway and
cell signaling. Chem. Phys. Lipids 1996, 80, 133-142. (b)
Piomelli, D.; Giuffrida, A.; Calignano, A.; Rodrı´guez de Fonseca,
F. The endocannabinoid system as a target for therapeutic drugs.
Trends Pharmacol. Sci. 2000, 21, 218-224.
(6) (a) Di Marzo, V.; Fontana, A.; Cadas, H.; Schinelli, S.; Cimino,
G.; Schwartz, J .-C.; Piomelli, D. Formation and inactivation of
endogenous cannabinoid anandamide in central neurons. Nature
(London) 1994, 372, 686-691. (b) Beltramo, M.; Stella, N.;
Calignano, A.; Lin, S. Y.; Makriyannis, A.; Piomelli, D. Func-
tional Role of High-Affinity Anandamide Transport, as Revealed
by Selective Inhibition. Science 1997, 277, 1094-1097.
(7) See the following for
a review. Deutsch, D. G.; Ueda, N.;
Yamamoto, S. The fatty acid amide hydrolase (FAAH). Prostag-
landins Leukotrienes Essent. Fatty Acids 2002, 66, 201-210.
(8) Piomelli, D.; Beltramo, M.; Glasnapp, S.; Lin, S. Y.; Goutopoulos,
A.; Xie, X. Q.; Makriyannis, A. Structural determinants for
recognition and translocation by the anandamide transporter.
Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 5802-5807.
(9) Patricelli, M. P.; Patterson, J . E.; Boger, D. L.; Cravatt, B. F.
An Endogenous Sleep-Inducing Compound Is a Novel Competi-
tive Inhibitor of Fatty Acid Amide Hydrolase Bioorg. Med. Chem.
Lett. 1998, 8, 613-618.
(21) Berman, H. M.; Westbrook, J .; Feng, Z.; Gilliland, G.; Bhat, T.
N.; Weissig, H.; Shindyalov, I. N.; Bourne, P. E. The Protein Data
Bank. Nucleic Acids Res. 2000, 28, 235-242.
(10) (a) Koutek, B.; Prestwich, G. D.; Howlett, A. C.; Chin, S. A.;
Salehani, D.; Akhavan, N.; Deutsch, D. G. Inhibitors of Arachi-
donoyl Ethanolamide Hydrolysis. J . Biol. Chem. 1994, 269,
22937-22940. (b) Patterson, J . E.; Ollmann, I. R.; Cravatt, B.
F.; Boger, D. L.; Wong, C.-H.; Lerner, R. A. Inhibition of
Oleamide Hydrolase Catalyzed Hydrolysis of the Endogenous
Sleep-Inducing Lipid cis-9-Octadecenamide. J . Am. Chem. Soc.
1996, 118, 5938-5945. (c) Boger, D. L.; Sato, H.; Lerner, A. E.;
Austin, B. J .; Patterson, J . E.; Patricelli, M. P.; Cravatt, B. F.
Trifluoromethyl Ketone Inhibitors of Fatty Acid Amide Hydro-
lase: A Probe of Structural and Conformational Features
Contributing to Inhibition. Bioorg. Med. Chem. Lett. 1999, 9,
265-270.
(22) LaLonde, J . M.; Levenson, M. A.; Roe, J . J .; Bernlohr, D. A.;
Banaszak, L. J . Adipocyte Lipid-Binding Protein Complexed with
Arachidonic Acid. Titration Calorimetry and X-ray Crystal-
lographic Studies. J . Biol. Chem. 1994, 269, 25339-25347.
(23) Malkowski, M. G.; Ginell, S. L.; Smith, W. L.; Garavito, R. M.
The Productive Conformation of Arachidonic Acid Bound to
Prostaglandin Synthase. Science 2000, 289, 1933-1937.
(24) Kiefer, J . R.; Pawlitz, J . L.; Moreland, K. T.; Stegeman, R. A.;
Gierse, J . K.; Hood, W. F.; Stevens, A. M.; Goodwin, D. C.;
Rowlinson, S. W.; Marnett, L. J .; Stallings, W. C.; Kurumbail,
R. G. Structural insights into the stereochemistry of the cy-
clooxygenase reaction. Nature (London) 2000, 405, 97-101.

2360 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 12
Tarzia et al.
(25) Petitpas, I.; Gruene, T.; Bhattacharya, A. A.; Curry, S. Crystal
Structures of Human Serum Albumin Complexed with Monoun-
saturated and Polyunsaturated Fatty Acids. J . Mol. Biol. 2001,
314, 955-960.
(26) Balendiran, G. K.; Schnutgen, F.; Scapin, G.; Borchers, T.;
Xhong, N.; Lim, K.; Godbout, R.; Spener, F.; Sacchettini, J . C.
Crystal Structure and Thermodynamic Analysis of Human Brain
Fatty Acid-Binding Protein. J . Biol. Chem. 2000, 275, 27045-
27054.
(27) (a) Klebe, G.; Abraham, U.; Mietzner, T. Molecular Similarity
Indices in a Comparative Analysis (CoMSIA) of Drug Molecules
To Correlate and Predict Their Biological Activity. J . Med. Chem.
1994, 37, 4130-4146. (b) Klebe, G.; Abraham, U. Comparative
Molecular Similarity Index Analysis (CoMSIA) To Study Hy-
drogen-Bonding Properties and To Score Combinatorial Librar-
ies. J . Comput.-Aided Mol. Des. 1999, 13, 1-10.
(28) Bracey, M. H.; Hanson, M. A.; Masuda, K. R.; Stevens, R. C.;
Cravatt, B. F. Structural Adaptations in a Membrane Enzyme
That Terminates Endocannabinoid Signaling. Science 2002, 298,
1793-1796.
(29) Snyckers, F.; Zollinger, H. Stereochemistry of the σ-Complex
Intermediate in Sterically Hindered Electrophilic Aromatic
Substitutions. Helv. Chim. Acta 1970, 53, 1294-1305.
(30) Buu-Ho¨ı, Ng. Ph.; Royer, R.; Eckert, B.; J acquignon, P. Carci-
nogenic Nitrogen Compounds. Part XIII.* Benzacridines, Ben-
zocarbazoles, and Related Compounds Bearing Ethyl and Propyl
Groups. J . Chem. Soc. 1952, 4867-4869.
(31) Brown, B. R.; Cummings, W.; Somerfield, G. A. Polymerisation
of Flavans. Part I. The Condensation of Methoxybenzyl Alcohols
with Phenols. J . Chem. Soc. 1957, 3757-3761.
(32) Alles, G. A.; Icke, R. N.; Feigen, G. A. Some Analogs of Synthetic
Tetrahydrocannabinol. J . Am. Chem. Soc. 1942, 64, 2031-2035.
(33) Butula, I.; Cˇ urkovic´, Lj.; Prosˇtenik, M. V.; Vela, V.; Zorko, F.
Reactions with 1-Chlorocarbonylbenzotriazole: II. Synthesis of
Carbamic Acid Esters and Related Compounds. Synthesis 1977,
704-706.
(34) The signals at 7.02 (d, J ) 6.3) and 6.84 (d, J ) 6.3) ppm were
attributed to (E)-stilben-4-ol. Those at 7.14 (d, J ) 8.8) and 6.69
(d, J ) 8.8) ppm were attributed to the (Z)-isomer, and the rest
of the spectrum is consistent with the proposed structure.
(35) Urban´ski, T.; Skowron´ska-Serafinowa, B.; Zylowski, J . Naph-
thylamidinourea and Its Reactions with Amines. Rocz. Chem.
1959, 33, 1377-1382.
(36) Brown, E. L.; Campbell, N. Studies in Qualitative Organic
Analysis. Identification of Alkyl Halides, Amines and Acids. J .
Chem. Soc. 1937, 1699-1701.
(37) The NH proton appears to be split into two broad doublets,
possibly because of tautomeric forms involving the C(S)-N bond.
(38) Halgren, T. A. Merck Molecular Force Field. I. Basis, Form,
Scope, Parametrization, and Performance of MMFF94*. J .
Comput. Chem. 1996, 17, 490-519.
(39) Wold, S.; Ruhe, A.; Wold, H.; Dunn, W. J . The Covariance
Problem in Linear Regression. The Partial Least Squares (PLS)
Approach to Generalized Inverses. SIAM J . Sci. Stat. Comput.
1984, 5, 735-743.
(40) Cramer, R. D., III.; Bunce, J . D.; Patterson, D. E. Crossvalida-
tion, Bootstrapping, and Partial Least Squares Compared with
Multiple Regression in Conventional QSAR Studies. Quant.
Struct.-Act. Relat. 1988, 7, 18-25.
J M021119G