Further optimization of the M5 NAM MLPCN probe ML375: Tactics and challenges

Article abstract of DOI:10.1016/j.bmcl.2014.11.082

This Letter describes the continued optimization of the MLPCN probe ML375, a highly selective M₅ negative allosteric modulator (NAM), through a combination of matrix libraries and iterative parallel synthesis. True to certain allosteric ligands, SAR was shallow, and the matrix library approach highlighted the challenges with M₅ NAM SAR within in this chemotype. Once again, enantiospecific activity was noted, and potency at rat and human M₅ were improved over ML375, along with slight enhancement in physiochemical properties, certain in vitro DMPK parameters and CNS distribution. Attempts to further enhance pharmacokinetics with deuterium incorporation afforded mixed results, but pretreatment with a pan-P450 inhibitor (1-aminobenzotriazole; ABT) provided increased plasma exposure.

Full text of DOI:10.1016/j.bmcl.2014.11.082

Bioorganic & Medicinal Chemistry Letters 25 (2015) 690–694
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Further optimization of the M5 NAM MLPCN probe ML375: Tactics
and challenges
Haruto Kurata b,c, Patrick R. Gentry b,c, Masaya Kokubo b,c, Hyekyung P. Cho a,b,c, Thomas M. Bridges a,b,c
,
Colleen M. Niswender a,b,c, Frank W. Byers a,b,c, Michael R. Wood a,b,c, J. Scott Daniels a,b,c
,
P. Jeffrey Conn a,b,c, Craig W. Lindsley a,b,c,d,
⇑
a Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
b Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical Center, Nashville, TN 37232, USA
c Vanderbilt Specialized Chemistry Center for Probe Development (MLPCN), Nashville, TN 37232, USA
d Department of Chemistry, Vanderbilt University, Nashville, TN 37232, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
This Letter describes the continued optimization of the MLPCN probe ML375, a highly selective M5 neg-
ative allosteric modulator (NAM), through a combination of matrix libraries and iterative parallel synthe-
sis. True to certain allosteric ligands, SAR was shallow, and the matrix library approach highlighted the
challenges with M5 NAM SAR within in this chemotype. Once again, enantiospecific activity was noted,
and potency at rat and human M5 were improved over ML375, along with slight enhancement in phys-
iochemical properties, certain in vitro DMPK parameters and CNS distribution. Attempts to further
enhance pharmacokinetics with deuterium incorporation afforded mixed results, but pretreatment with
a pan-P450 inhibitor (1-aminobenzotriazole; ABT) provided increased plasma exposure.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 27 October 2014
Revised 25 November 2014
Accepted 27 November 2014
Available online 13 December 2014
Keywords:
M5
Muscarinic receptor
Negative allosteric modulator
Matrix library
Pharmacokinetics
Of the five muscarinic acetylcholine receptors (mAChR subtypes
M1–M5), far less in known about the neurobiological roles of M5
due both to limited CNS expression (<2% of all mAChR protein in
rat brain and found exclusively in the ventral tegmental area
[VTA] on dopamine transporter [DAT]-expressing neurons and in
the substantia nigra pars compacta [SNc]) and the lack of highly
selective, in vivo probe molecules.1–10 Insight into the therapeutic
potential of M5 comes largely from genetic studies in M5-KO mice,
which exhibit reduced sensitivity to the rewarding effects of
cocaine and opiates.11–13 Recently, an association between an M5
SNP and an addictive phenotype was observed in man, directly
linking M5 to drug abuse and reward.14 To advance the M5 research
field, small molecule probes are required to recapitulate the
genetic data.
provided 1-(4-flurobenzoyl)-9b-phenyl-2,3-dihydro-1H-imidazo-
[2,1-a]isoindol-5(9bH)-one as an M5 negative allosteric modulator
(NAM) hit, 1 (Fig. 1).20 A limited chemical optimization effort affor-
ded ML375 (2), the first M5-selective NAM with favorable CNS
exposure (brain/plasma Kp = 1.8), moderate PK, high plasma pro-
tein binding (rat fu = 0.029, human fu = 0.013, rat brain fu = 0.003)
and enantiospecific activity (only the (S)-enantiomer of the 9b
p-Cl phenyl was active).20 Despite a major advance in the field,
due to weak potency at rat M5, coupled with high plasma protein
and brain homogenate binding, ML375 lacked the requisite free
drug exposure to serve as an in vivo tool compound.20 In this Let-
ter, we report on the continued optimization of our first-in-class
M5 NAM, and detail key tactics and noteworthy challenges en route
to an M5 NAM in vivo probe.
Previously, we have reported on the development of several
potent and selective M5 positive allosteric modulator (PAM) chem-
otypes,15–18 as well as the first highly M5 selective orthosteric
antagonist;19 however, DMPK properties were generally poor and
these efforts failed to produce in vivo probes. Last year we dis-
closed results from an M5 functional high-throughput screen that
The synthesis of novel analogs of ML375 required a simple two-
step synthesis involving condensation of ethylene diamine and an
appropriately substituted 2-benzoylbenzoic acid 3 (or heteroaro-
matic/cyclo(hetero)alkyl congener) to provide 4, followed by a
subsequent acylation reaction (Scheme 1) to deliver ML375
analogs 5–7.20,21 However, we quickly exhausted the commercial
analogs of 3. Fortunately, we were able to employ three synthetic
routes to access key intermediates 3 with either diverse substituents
or encompassing heterocycles.
⇑
Corresponding author.
E-mail address: craig.lindsley@vanderbilt.edu (C.W. Lindsley).
http://dx.doi.org/10.1016/j.bmcl.2014.11.082
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.

H. Kurata et al. / Bioorg. Med. Chem. Lett. 25 (2015) 690–694
691
heterocycles
F
Cl
alternate
amides
polar substiuents
O
O
limited
F
F
optimization
campaign
F
Cl
N
N
N
N
O
F
N
N
iterative
parallel
synthesis
O
O
1
2, ML375
hM5 IC50 = 3.49 µM
rM5 IC50 = 5.67 µM
r/h M1-M4 IC50s > 30 µM
hM5 IC50 = 300 nM
rM5 IC50 = 790 nM
r/h M1-M4 IC50s > 30 µM
O
heterocycles
polar substiuents
modification
expansion
Figure 1. Structures and mAChR activities of M5 NAM HTS hit 1, and the optimized MLPCN probe ML375 (2). Inset, optimization plan for ML375 to improve rat potency and
physiochemical/disposition properties. Potency values determined via a functional calcium mobilization assay in the presence of a fixed acetylcholine EC80 in recombinant
cells.20
and sp3-hybridized ring systems into the 9b position, while hold-
O
Ar (Het)
ing the 3,4-difluorobenzoyl moiety constant, to assess if we could
improve both physiochemical properties as well as hM5 potency.
Following Scheme 1, analogs 6 were rapidly prepared and
screened against hM5 (Table 2). Once again, SAR was shallow, with
all sp3-based systems, as well as heterocycles, devoid of hM5 activ-
ity. A similar pattern emerged for ethers between analog series 5
and 6, with 6c, the 4-OMe phenyl analog, superior potency (hM5
HO
O
H
N
O
(Het) Ar
Het
(Het) Ar
Het
N
N
a
b
Ar (Het)
R
N
R
R
Het
O
O
3
4
5-7
HO
O
O
IC50 = 1.3 lM), but insufficient to advance as an in vivo probe. As
O
BrZn
c or d
e
before, 6c possessed a lower clogP (4.21), which translated into
improved plasma free fraction (rat fu = 0.064, human fu = 0.037).
Interestingly, the addition of more sp3-character, in the form of
the cyclohexyl congener 6e, led to a higher clogP (5.2) and dimin-
ished free fraction (rat fu = 0.016, human fu = 0.008). In parallel, we
replaced the phenyl ring at the 9b position with the three regioiso-
meric pyridines, and all were not tolerated (hM5 IC50 >5 lM), as
were ring expansions and substitutions of the 1H-imidazo[2,
1-a]isoindol-5(9bH)-one core.
Het
R
O
Het
R
Ar (Het)
R
Het
EtO2C
O
9
8
3
O
Ar (Het)
HO
O
H
N
O
R
R
N
N
a
b
R
O
N
O
At a loss for a rational, singleton approach to build-in hM5
potency and improved physiochemical properties, we elected to
pursue a 3 Â 9 matrix library of analogs 7 to systematically evalu-
ate all the possible combinations of monomers that showed either
hM5 potency enhancement or improved physiochemical properties
(Table 3).22,23 While we have generated, on numerous occasions,
robust, tractable SAR within GPCR allosteric ligand chemotypes,
we have also reported on numerous accounts of chemotypes that
possess shallow or flat SAR,8–11,24 and this matrix library is an
example of the latter. Here, the clear stand-out was racemic
7B-6 (also referred to as VU0652483, hM5 IC50 = 517 nM,
pIC50 = 6.29 0.02), possessing a 3,4,5-trifluorobenzoyl amide and
a 3-methyl-4-methoxy phenyl moiety in the 9b position. Due to
the increased hM5 potency, we evaluated VU0652483 potency at
rat M5 and found submicromolar activity (rat M5 IC50 = 963 nM,
pIC50 = 6.02 0.04) as well. As all of the activity of ML375 resided
in the (S)-enantiomer, we resolved the enantiomers of
VU0652483 via chiral SFC to afford (S)-7B-6 (VU6000181) and
(R)-7B-6 (VU6000180); here again, the (R)-enantiomer was inac-
tive (Fig. 2) and the (S)-enantiomer, VU6000181, possessed all of
the M5 activity (hM5 IC50 = 264 nM, pIC50 = 6.58 0.03, rat M5
IC50 = 516 nM, pIC50 = 6.29 0.05), thus representing the most
potent M5 NAM reported to date and maintaining selectivity versus
O
3
4
5-7
HO
O
O
BrZn
EtO2C
c or d
e
O
R
O
9
8
3
Scheme 1. Reagents and conditions: (a) ethylene diamine, p-TSA, toluene (+1,4-
dioxane), reflux, Dean–Stark trap, or microwave irradiation 130-150 °C 4–77%; (b)
Ar(Het)COCl, CH2Cl2, DIPEA, 16–91%; (c) RMgX, THF, À65 °C to 0 °C or rt, 8–68%; (d)
R-H, AlCl3, PhNO2, rt, 41–88%; (e) (i) RCOCl, cat. Ni(acac)2, THF, rt, (ii) aq NaOH,
EtOH/THF, rt, 31–55%.
In the first round of library synthesis, we held the p-Cl 9b phe-
nyl moiety of ML375 constant, and scanned alternate amides
within a racemic core to provide analogs 5. Here, (Table 1) we
found that heterocycles were generally not tolerated (5i–l) in the
context of the p-Cl 9b phenyl core, but two amide congeners, the
4-isoproxyphenyl (5f) and the 3,4,5-trifluorophenyl (5g), displayed
submicromolar human M5 activity (hM5 IC50s of 790 nM and
610 nM, respectively), yet were less potent than racemic ML375
(5a, hM5 IC50 = 480 nM). Within a conserved series of ethers, hM5
potency, for example, M5 IC50s, was enhanced as steric bulk
increased—OMe (5d) < OEt (5e) < Oi-Pr (5f). Despite the lower
hM5 potency, 5d displayed a moderate improvement in clogP rel-
ative to 5a (4.6 vs 5.2), so we elected to evaluate how diminished
lipophilicity would impact plasma protein binding. While racemic
5a displayed high plasma protein binding (rat fu = 0.031, human
fu = 0.015), binding of 5f was slightly decreased (rat fu = 0.037,
human fu = 0.027). These findings then led us to pursue second
generation libraries where we aimed to incorporate polar, basic
M1–M4 (IC50s >30 l
M).20 Moreover, the clogP for VU6000181 (4.6)
was improved over ML375 (5.2), and this once again translated
into a slight improvement over ML375 (rat fu = 0.031, human
fu = 0.013, rat brain fu = 0.006). In addition, VU6000181 was highly
centrally penetrant (brain/plasma Kp = 2.7 at 0.25 h post-adminis-
tration), yet a high clearance compound in vitro (rat hepatic micro-
some CLINT = 332 mL/min/kg, predicted CLHEP = 57.8 mL/min/kg
and human hepatic microsome CLINT = 359 mL/min/kg, predicted
CLHEP = 19.8 mL/min/kg) and in vivo (rat CLp = 80 mL/min/kg, t1/2
= 65 min, Vss = 4.9 L/kg). The PK profile of VU6000181 rendered it
unsuitable as an in vivo probe.

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H. Kurata et al. / Bioorg. Med. Chem. Lett. 25 (2015) 690–694
Table 1
Structures and activities of analogs 5
Cl
O
Ar(Het)
N
N
O
5
a
a
Entry
Ar (Het)
hM5 IC50
0.48
(lM)
hM5 pIC50
Entry
Ar (Het)
hM5 IC50
0.61
(
lM)
hM5 pIC50
F
F
F
5a
6.32 0.03
5g
6.21 0.02
F
F
NMe2
F
5b
5c
>10
6.6
>5
5h
5i
>10
>10
>5
>5
MeO
5.18 0.16
N
OMe
OMe
N
F
5d
5e
1.8
5.74 0.08
6.07 0.05
5j
5.8
5.23 0.09
>5
N
N
OEt
0.85
5k
>10
F
N
F
Oi-Pr
5f
0.79
6.10 0.03
5l
>10
>5
a
hM5 pIC50 reported as average SEM from our calcium mobilization assay; n = 3.
Table 2
Structures and activities of analogs 6
O
N
N
F
F
R
O
6
a
a
Entry
R
hM5 IC50
5.5
(l
M)
hM5 pIC50
Entry
R
hM5 IC50
>10
(lM)
hM5 pIC50
6a
5.25 0.07
5.79 0.04
6g
6h
>5
>5
MeO
6b
1.6
>10
OMe
OMe
O
6c
1.3
5.88 0.01
>5
6i
6j
>10
>10
>5
>5
OPh
6d
>10
N
6e
6f
2.1
2.4
5.67 0.05
5.61 0.06
6k
6l
>10
>10
>5
>5
N
N
a
hM5 pIC50 reported as average SEM from our calcium mobilization assay; n = 3.
Previously, we productively utilized deuterium incorporation to
and provide target validation for M5 NAMs.26 In this instance, we
first pre-treated rats with an oral vehicle (10% tween 80 in 0.5%
MC in water), followed 1.5 h later by VU6000181 at 10 mg/kg, po
in 30% HPBCD in water (10 mg/mL). This control protocol revealed
a VU6000181 mean residence time (MRT) of 6.5 h, a Tmax of 2.8 h,
an AUC0–inf of 3660 (h ng/mL) and low oral bioavailability
(%F = 2.0). Pre-treatment of rats with a 56.6 mg/kg dose of ABT
PO (10% Tween 80 in 0.5% MC in water), followed 1.5 h later by
VU6000181 at 10 mg/kg, PO in 30% HPBCD in water (10 mg/mL),
provided a ꢀ5-fold increase in exposure (AUC0-inf of 17,700
(h ng/mL), %F = 9.5) relative to that in the vehicle pre-treated ani-
mals (Fig. 4). In addition, ABT pre-treatment afforded a ꢀ3-fold
overcome high clearance coupled with flat SAR in a series of mGlu3
NAMs,25 reducing rat in vitro and in vivo clearance by ꢀ50% and
affording an in vivo probe. Replacing the OCH3 moiety of
VU6000181 with a OCD3 moiety (10, VU6001005) did in fact
reduce human in vitro intrinsic clearance ꢀ5-fold (human
CLINT = 72.9 mL/min/kg) but provided negligible improvement to
rat intrinsic clearance, and thus, was not a productive path towards
an in vivo tool compound (Fig. 3).
Finally, we performed an in vivo PK study by predosing rats
with the pan-P450 inhibitor 1-aminobenzotriazole (ABT) in an
attempt to potentially achieve therapeutically relevant drug levels

H. Kurata et al. / Bioorg. Med. Chem. Lett. 25 (2015) 690–694
693
Table 3
F
F
F
F
H3CO
D3CO
Structures and activities of matrix library analogs 7
O
O
F
F
deuterium
installation
O
N
N
N
N
Ar2
Ar1
N
N
O
O
O
(S)-7B-6, VU6000181
human CLINT = 359 mL/min/kg
human CLHEP = 19.8 mL/min/kg
8, VU6001005
human CLINT = 72.9 mL/min/kg
mL/min/kg
7
human CLHEP = 16.3
Entry
Ar2
Ar1
rat CLINT
rat CLHEP = 57.8 mL/min/kg
= 332 mL/min/kg
A
B
C
rat CLINT
rat CLHEP = 55.8 mL/min/kg
= 275 mL/min/kg
F
F
F
O
F
Figure 3. The impact of deuterium incorporation into VU6000181 on human, but
not rat, intrinsic clearance determined in hepatic microsomes fortified with NADPH
(values represent means from one independent determination performed in
triplicate).
F
a
a
a
hM5 IC50
(l
M) hM5 IC50
(l
M) hM5 IC50
4.1
(lM)
OEt
O
1
2
3
4
3.2
>30
>30
1.3
3.3
2.4
1.0
1.9
1.1
3.2
O
O
OMe
>30
F
OMe
5
6
7
8
9
5.5
1.2
2.7
2.0
1.3
1.4
0.51
0.7
1.6
0.9
3.3
1.3
1.3
6.4
2.2
Cl
OMe
Me
F
OMe
Cl
OMe
Me
OMe
Figure 4. Oral plasma pharmacokinetics of VU6000181 in the absence (blue) or
presence (red) of ABT pre-treatment in rats (male, Sprague-Dawley). ABT pre-
treatment improved exposure ꢀ5-fold and maximum concentrations ꢀ3-fold.
a
hM5 IC50 data, n = 1; hM5 IC50 for 7B-6, n = 6, pIC50 = 6.29 0.02.
Figure 2. Structures and M5 functional assay concentration–response-curves (CRCs) obtained in the presence of a fixed acetylcholine EC80 in recombinant cells. (A) rat M5
CRCs of racemic VU0652483, the active (S)-enantiomer, VU6000181 and the inactive (R)-enantiomer, VU6000180; (B) human M5 CRCs of racemic VU0652483, the active (S)-
enantiomer, VU6000181 and the inactive (R)-enantiomer, VU6000180; (C) structures of VU0652483, VU6000181, VU6000180.

694
H. Kurata et al. / Bioorg. Med. Chem. Lett. 25 (2015) 690–694
18. Gentry, P. R.; Kokubo, M.; Bridges, T. M.; Byun, N.; Cho, H. P.; Smith, E.; Hodder,
increase in Cmax (plasma = 2.0
on the a brain/plasma Kp (2.7), projected Cmax levels in brain in
l
M, ꢀ62 nM unbound) and, based
P. S.; Niswender, C. M.; Daniels, J. S.; Conn, P. J.; Lindsley, C. W.; Wood, M. R. J.
Med. Chem. 2014, 57, 7804.
19. Gentry, P. R.; Kokubo, M.; Bridges, T. M.; Cho, H. P.; Smith, E.; Chase, P.; Hodder,
P. S.; Utley, T. J.; Rajapakse, A.; Byers, F.; Niswender, C. M.; Morrison, R. D.;
Daniels, J. S.; Wood, M. R.; Conn, P. J.; Lindsley, C. W. ChemMedChem 2014, 9,
1677.
20. Gentry, P. R.; Kokubo, M.; Bridges, T. M.; Kett, N. R.; Harp, J. M.; Cho, H. P.;
Smith, E.; Chase, P.; Hodder, P. S.; Niswender, C. M.; Daniels, S. J.; Conn, P. J.;
Wood, M. R.; Lindsley, C. W. J. Med. Chem. 2013, 56, 9351.
the presence of ABT would be ꢀ5.4 M (ꢀ32 nM unbound). Thus,
l
ABT pretreatment may serve as a viable strategy to increase levels
of VU6000181 for future fMRI and addiction studies to test selec-
tive M5 inhibition hypotheses.
In summary, we reported on the continued optimization of the
MLPCN probe ML375, a highly selective M5 NAM, through a combi-
nation of matrix libraries and iterative parallel synthesis. While
SAR can be highly tractable for certain allosteric ligands, this chem-
otype was a clear example of ‘flat’ or ‘shallow’ SAR, wherein an
matrix library was critical in identifying a productive lead com-
pound, VU6000181, with improved activity at rat M5 and disposi-
tion relative to ML375. Attempts to improve PK by deuterium
21. Synthesis of VU6000181. To a suspension of Mg (936 mg, 38.5 mmol) and
iodine (5 mg) in THF (2 mL) was added a part of a solution of 4-bromo-2-
methylanisole (7.39 g, 36.8 mmol) in THF (9 mL) at ambient temperature. After
initiating the reaction, a solution of 4-bromo-2-methylanisole diluted with THF
(19 mL) was added dropwise to the mixture diluted with THF (10 mL). After
the mixture was allowed to stir at ambient temperature for 2 h, resulting
Grignard reagent was added to a suspension of phthalic anhydride 8 (5.18 g,
35.0 mmol) in THF (50 mL) at À65 °C. The mixture was allowed to stir for 2.5 h
as temperature was elevated up to 0 °C. The reaction was quenched with cold
water and the aqueous layer was separated. The organic layer was extracted
incorporation substantially impacted only human in vitro CLINT
,
but ABT pre-treatment significantly increased exposure in rats,
potentially affording a strategy to achieve target validation for
selective M5 inhibition. Efforts continue, and work is in progress
to pharmacologically probe M5 neurobiology and therapeutic
potential with small molecules.
with
1 N NaOH aqueous solution and the combined aqueous layer was
acidified with 2 N HCl solution. The aqueous layer was extracted with ethyl
acetate twice and the combined organic layer was washed with brine and dried
over magnesium sulfate. The filtrate was evaporated under reduced pressure.
The residue was triturated with ethyl acetate/diethyl ether to give compound 3
as a white powder (5.61 g, 59% yield). To a solution of compound 3 (1.0 g,
3.7 mmol) and para-toluene sulfonic acid monohydrate (10 mg) in PhMe
(8 mL) and 1,4-dioxane (8 mL) was added ethylenediamine (0.50 mL,
7.4 mmol) at ambient temperature. The resulting white suspension was
subjected to microwave irradiation at 150 °C for 30 min. After removing
insoluble material, the filtrate was concentrated. The procedure above was
repeated twice more and the three portions were combined and purified on
silica gel using hexane/ethyl acetate as an eluent. Crude product was triturated
with diethyl ether to give compound 4 as an off-white powder (1.69 g, 52%
yield). To a solution of compound 4 (500 mg, 1.70 mmol) in dichloromethane
(8 mL) was added DIPEA (0.74 mL, 4.25 mmol) and 3,4,5-trifluorobenzoyl
chloride (0.33 mL, 2.55 mmol) at ambient temperature. After stirring for
30 min, cold NaHCO3-aq was added to the mixture which was extracted with
dichloromethane twice. The combined organic layer was concentrated under
reduced pressure and the residue was purified on silica gel using hexane/ethyl
acetate as an eluent. Crude product was triturated with diethyl ether/hexane to
yield compound 7B-6 as a white powder (491 mg, 64% yield). Chiral resolution
by SFC (Agilent 1260, Column: LUX cellulose-3, Column dimensions:
10 Â 250 mm, Co-solvent: MeOH, Modifier: none, Gradient Profile: 10%
isocratic, Flow Rate: 15 mL/min, Backpressure: 100, Column temperature: 40
degrees, retention time: 2.814 min, dated on July 30th) followed by
concentration afforded (S)-7B-6 (VU6000181) as a white powder. 1H NMR
(400.1 MHz, DMSO-d6): 7.89 (d, J = 7.4 Hz, 1H), 7.80-7.78 (m, 1H), 7.71–7.57
(m, 4H), 7.03 (dd, J = 8.5, 2.5 Hz, 1H), 6.91 (d, J = 8.5 Hz, 1H), 6.86 (d, J = 2.5 Hz,
1H), 4.11–3.99 (m, 2H), 3.84–3.80 (m, 4H), 3.22–3.15 (m, 1H). 13C NMR
(100.6 MHz, DMSO-d6):171.88, 165.56, 158.26, 150.99 (dd, J = 249, 9.8 Hz),
147.01, 140.76 (dt, J = 252, 15.6 Hz), 133.87, 133.68 (q, J = 6.1 Hz), 132.84,
131.18, 130.35, 129.48, 128.74, 126.61, 125.75, 124.18, 113.29 (dd, J = 16.5,
Acknowledgments
Vanderbilt is a member of the MLPCN and houses the Vander-
bilt Specialized Chemistry Center for Accelerated Probe Develop-
ment. This work was supported by the NIH/MLPCN Grant U54
MH084659 (C.W.L.), the Vanderbilt Department of Pharmacology
and William K. Warren, Jr. who funded the William K. Warren, Jr.
Chair in Medicine (to C.W.L.).
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