8,9-Dihydroxy-1,2,3,11b-tetrahydrochromeno[4,3,2,-de]isoquinoline (dinoxyline), a high affinity and potent agonist at all dopamine receptor isoforms

Article abstract of DOI:10.1016/j.bmc.2004.01.008

The synthesis and preliminary pharmacological evaluation of 8,9-dihydroxy-1,2,3,11b-tetrahydrochromeno[4,3,2,-de]isoquinoline (5, now named dinoxyline) is described. This molecule was designed as a potential bioisostere that would conserve the essential elements of our β-phenyldopamine D ₁ pharmacophore (i.e., position and orientation of the nitrogen, hydroxyls, and phenyl rings). Previously, we have rigidified these elements using alkyl bridges, as exemplified in the dopamine D₁ full agonist molecules dihydrexidine (1) and dinapsoline (2). This approach has been modified and we now show that it is possible to tether these elements using an ether linkage. Preliminary pharmacology has revealed that 5 is a potent full D₁ agonist (K_0.5 <10 nM; EC₅₀=30 nM), but also has high affinity for brain D₂-like and cloned D₂ and D₃ receptors. Interestingly, whereas 1 and 2 and their analogues have only moderate affinity for the human D₄ receptor, 5 also has high affinity for this isoform. Moreover, although N-alkylation of 1 and 2 increases D₂ affinity, the N-allyl (15) and N-n-propyl (17) derivatives of 5 had decreased D₂ affinity. Therefore, 5 may be engaging different amino acid residues than do 1 and 2 when they bind to the D₂ receptor. This is the first example of a ligand with high affinity at all dopamine receptors, yet with functional characteristics similar to dopamine. These rigid ligands also will be useful tools to determine specific residues of the receptor transmembrane domains that are critical for agonist ligand selectivity for the D₄ receptor.

Full text of DOI:10.1016/j.bmc.2004.01.008

Bioorganic & Medicinal Chemistry 12 (2004) 1403–1412
8,9-Dihydroxy-1,2,3,11b-tetrahydrochromeno[4,3,2,-de]isoquinoline
(dinoxyline), a high affinity and potent agonist at all dopamine
receptor isoforms
Russell A. Grubbs,a Mechelle M. Lewis,b,y Connie Owens-Vance,a,y Elaine A. Gay,b
Amy K. Jassen,b Richard B. Mailmanb and David E. Nicholsa,*
aDepartment of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University,
West Lafayette, IN 47907, USA
bDepartments of Psychiatry, Pharmacology, and Medicinal Chemistry and Neuroscience Center,
University of North Carolina School of Medicine, Chapel Hill, NC 27599-7160, USA
Received 19 November 2003; revised 30 December 2003; accepted 12 January 2004
Abstract—The synthesis and preliminary pharmacological evaluation of 8,9-dihydroxy-1,2,3,11b-tetrahydrochromeno[4,3,2,-de]-
isoquinoline (5, now named dinoxyline) is described. This molecule was designed as a potential bioisostere that would conserve the
essential elements of our b-phenyldopamine D1 pharmacophore (i.e., position and orientation of the nitrogen, hydroxyls, and
phenyl rings). Previously, we have rigidified these elements using alkyl bridges, as exemplified in the dopamine D1 full agonist
molecules dihydrexidine (1) and dinapsoline (2). This approach has been modified and we now show that it is possible to tether
these elements using an ether linkage. Preliminary pharmacology has revealed that 5 is a potent full D1 agonist (K0.5 <10 nM;
EC50=30 nM), but also has high affinity for brain D2-like and cloned D2 and D3 receptors. Interestingly, whereas 1 and 2 and their
analogues have only moderate affinity for the human D4 receptor, 5 also has high affinity for this isoform. Moreover, although
N-alkylation of 1 and 2 increases D2 affinity, the N-allyl (15) and N-n-propyl (17) derivatives of 5 had decreased D2 affinity.
Therefore, 5 may be engaging different amino acid residues than do 1 and 2 when they bind to the D2 receptor. This is the first
example of a ligand with high affinity at all dopamine receptors, yet with functional characteristics similar to dopamine. These rigid
ligands also will be useful tools to determine specific residues of the receptor transmembrane domains that are critical for agonist
ligand selectivity for the D4 receptor.
# 2004 Elsevier Ltd. All rights reserved.
1. Introduction
channels. The D2 and D3 receptors vary in certain tissues
and species as a result of alternative splicing, and there
are interesting polymorphisms of the human D4 receptor
gene that have attracted great interest.6,7
The diverse physiological actions of dopamine are
mediated by at least five distinct G-protein coupled
receptors, the molecular biology of which has been
reviewed by numerous authors and in numerous
books.1ꢀ5 The D1-like receptor subtypes (D1 or D1A and
D5 or D1B) come from intron-less genes (albeit D5
pseudogenes exist), and the receptors typically couple to
the G proteins GS and Golf and activate adenylate
cyclase. The D2-like subfamily comes from three genes
(D2, D3, and D4) that are prototypic of G protein-coupled
receptors that inhibit adenylate cyclase and activate K+
Our major goal has been the development of isoform-
selective agonists, with a primary focus on drugs for the
D1 and D5 receptors, and a secondary one on D3 and
D4 selective agonists. We have been interested in drugs
that have particular characteristics that allow them to be
used for the structural elucidation of specific dopamine
receptor isoforms, and also as neuropharmacological
research tools. Thus, dihydrexidine (1) and other D1
agonists have been valuable research tools in studying
the roles of D1 receptors, both in vivo8,9 and in
vitro.10,11 These same drugs have clear and novel uses in
several neurological and psychiatric disorders.
* Corresponding author. Tel.: +76-5494-1461; fax: +76-5494-1414;
e-mail: drdave@pharmacy.purdue.edu
Current address: DarPharma, Inc., Chapel Hill NC 27514, USA
y
0968-0896/$ - see front matter # 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.01.008

1404
R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
For example, Parkinson’s disease (PD), a dopamine
degenerative disorder,12 still has ‘dopamine replace-
ment’ as the most widely used and accepted treatment.13
While the field has accepted for decades a crucial role
for D2-like receptors in the therapy of PD, recently our
group and others have shown the critical role of D1
receptor activation in the therapy of Parkinson’s dis-
ease.14ꢀ16 Thus, dihydrexidine (1), the first full D1
agonist, was used to provide the first demonstration
of the profound antiparkinsonian effects of full D1
agonists in primates resistant to l-DOPA or D2
agonists.14 Confirmatory results emerged from studies
of several drugs,17,18 including some developed by
Abbott Laboratories.19 Despite their efficacy, each of
these drugs was eliminated as a clinical agent by
bioavailability, tolerance, or seizure issues. Clearly, a
full D1 agonist without these side effects is likely to
have great utility, a view supported by numerous
recent studies that have elucidated new aspects of
basal ganglia circuitry and the role of D1-like
receptors.20,21
Other accessory rings such as thiophene have been sub-
stituted for the phenyl group of dihydrexidine, and 3
(A-86929) was shown to be a potent and selective D1
ligand.42 The geometry of the pharmacophore is defined
by a catechol ring that is close to planarity with the
accessory ring and a nitrogen atom that is 7 A away
from the meta-hydroxyl. Both 1 and 2 are rigid
compounds that have a limited range of low energy
conformations and meet the requirements of the pro-
posed pharmacophore.43,44 Conformational restriction
of dopaminergic pharmacophores also has been accom-
plished using isochromans, and compound 4 is a potent
and selective D3 agonist.45
The conformational restriction of dinapsoline (2) was
accomplished using a methylene linkage, which in fact is
somewhat difficult to construct. Using a bioisosteric
approach, it was hypothesized that an ether linkage
could be substituted for this methylene tether, antici-
pating that it might be easier to introduce the oxygen
than the methylene in 2, and that 5 (dinoxyline; DNX)
might possess useful and interesting dopaminergic
properties. This hypothesis was tested and the results
are presented here.
In addition, D1 and D5 receptors play a crucial role in
the dopaminergic modulation of cognition and motor
behavior.22,23 For example, Goldman-Rakic and col-
leagues carried out elegant studies that have localized
the various message and proteins of the dopamine
receptors in various lamina of the primate prefrontal
cortex, and have demonstrated how working memory
performance is influenced by activation of D1-like
dopamine receptors in the prefrontal cortex.24ꢀ27 Similar
studies with D1 agonists in a number of tests of
cognitive function have determined their potential
utility.27,28 Indeed, a recent NIMH Consensus Sympo-
sium overwhelmingly voted drugs with D1 agonist
properties as the most promising future therapy for the
most difficult-to-treat aspects of schizophrenia (see
www.matrics.ucla.edu). There have also been extensive
studies on the importance of D1-like receptors for normal
hippocampal function.29,30 D1/D5 receptor agonists can
affect long-term potentiation (LTP) by inducing a pro-
tein synthesis-dependent late potentiation in the CA1
region of the hippocampus,31 and can increase the
magnitude of LTP in a synapse-specific and cAMP
dependent manner.32 Such data, coupled with other
related studies,33ꢀ36 suggest that dopamine D1/D5
receptor agonists (selective or non-selective) might have
therapeutic utility.37
2. Chemistry and pharmacology
The synthesis (Scheme 2) of 5 (dinoxyline) was based on
an alternative formal synthesis of dinapsoline (2)
described by Qandil et al..46 The biaryl bond of 10 was
constructed using the Miyaura–Suzuki47,48 cross-coupling
reaction and the ether linkage of 5 was generated by
phenol displacement of the isoquinoline nitro group. The
major modification from the Qandil synthesis involved
cyclization while the isoquinoline nucleus remained
unreduced and therefore did not require the previously-
needed protection and deprotection sequence.
As this brief review indicates, the essential role of D1-
like receptors in critical CNS processes makes it
imperative to develop drugs to study these functions,
also with an aim of improved clinical treatments. The
current model that led to the synthesis of the selective full
D1 agonists dihydrexidine (1)38 and dinapsoline (2),39 has
been referred to as the trans-b-phenyldopamine D1
agonist pharmacophore. The essential elements of this
pharmacophore include dopamine in the trans-b-
rotameric conformation with a b-accessory ring (typically
an aromatic ring).40 By contrast, apomorphine, an older
structurally rigid dopamine agonist, incorporates
dopamine in a trans-a-rotameric conformation and is a
partial agonist at the D1 receptor.41
The coupling partners 8 (Scheme 1) and 9 for the Suzuki
reaction were readily synthesized and required minimal
purification. Nitration of 4-bromoisoquinoline using
potassium nitrate and sulfuric acid, conditions described
previously by Osborn et al.49 for nitration of 5-bromoiso-
quinoline, gave 4-bromo-5-nitroisoquinoline (9) in excel-
lent yield. The borolane derivative 8 was obtained in
two steps: protection of 2,3-dimethoxyphenol (6) as the

R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
1405
genation of 14 was followed by treatment with boron
tribromide to obtain 17.
3. Pharmacology
In order to assess the receptor binding characteristics,
we first evaluated 5 and its N-alkyl analogues at rat
striatal D1 and D2 receptors. For comparison, we also
tested our first two full D1 agonist compounds, dihydrex-
idine (DHX, 1) and dinapsoline (DNS, 2). To generate a
more comprehensive pharmacological profile, we then
evaluated the affinity of 5 and its analogues at the
cloned dopamine receptors. Again, 1 and 2 were included
as reference compounds.
Scheme 1. (a) (i) NaH; (ii) ClCH2OCH3; (b) (i) n-BuLi; (ii) 2-iso-
propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.
methoxymethyl derivative 7,50 followed by lithiation51
and reaction with 2-isopropoxy-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (Scheme 1).
After obtaining the Suzuki coupling partners, the
synthesis of dinoxyline (5) was completed as shown in
Scheme 2. Suzuki coupling between 8 and 9 using con-
ditions described by Zoltewicz et al.48 gave 10 in high
yield. After isolation of 10 by column chromatography,
the methoxymethyl protecting group was hydrolyzed
with p-toluenesulfonic acid.52 The resulting nitrophenol
11 was isolated and treated with potassium carbonate in
DMF at 80 ꢁC to afford the tetracyclic chromenoiso-
quinoline 12.53 Reduction of the isoquinoline ring to
tetrahydroisoquinoline 13 was accomplished by catalytic
hydrogenation over platinum oxide in acetic acid con-
taining HCl.54 Boron tribromide was then used to cleave
the methoxy groups to obtain 5.
Finally, the functional profile of 5 and the two N-alkyl-
ated analogues was evaluated by assessing their ability
to modulate adenylate cyclase production using a
cAMP accumulation assay in rat striatal membranes
and in the cloned dopamine receptors. Activity at the D3
receptor was not evaluated because it is poorly coupled
in this assay system, and available assay systems (e.g.,
mitogenesis or MAP-K) are very indirect. The endo-
genous neurotransmitter dopamine was used to define
full agonist activity, and 1 and 2 were again included for
comparison.
4. Results and discussion
The N-allyl 15 and N-propyl 17 derivatives of 5 were
prepared from 13 as shown in Scheme 3.55 The tertiary
amine 14, was obtained by stirring 13 with potassium
carbonate and allyl bromide in acetone. Demethylation
of 14 with boron tribromide gave 15. Catalytic hydro-
The receptor binding characteristics of the new com-
pounds at rat striatal D1 and D2 receptors are presented
in Table 1 and Figures 1 and 2. At striatal D1-like
receptors, the parent compound 5 had high affinity
(K0.5=8.3 nM), similar to that observed with 1 and 2
ꢀ
ꢁ
Scheme 2. (a) Pd(PPh3)4, KOH, Bu4N+Cl , H2O, DME, reflux; (b) TsOH H2O, MeOH; (c) K2CO3, DMF, 80 C; (d) PtO2, AcOH, HCl, H2;
.
(e) BBr3, CH2Cl2, ꢀ78 ꢁC.
Scheme 3. (a) allyl bromide, acetone, K2CO3; (b) H2, Pd-C, EtOH; (c) BBr3, CH2Cl2.

1406
R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
Table 1. Binding affinities of 5 and analogues for striatal dopamine
receptorsa
dopamine receptors that affect isoform selectivity and
potency. These findings reinforce our previous conclusions
that substitutions on the pendant phenyl ring of either 1
or 2 can target the substituted molecule to different
receptor isoforms.
Test Ligand
D1-like K0.5 (nM)
D2-like K0.5 (nM)
Chlorpromazine
SCH23390
—
0.52c
0.92ꢂ0.12b
—
(ꢂ)-1 (DHX)
4.6ꢂ0.3b
5.9ꢂ0.7b
8.3ꢂ6.4
260ꢂ42
250ꢂ78
43ꢂ3b
31ꢂ4b
6.2ꢂ1.8
54ꢂ12
17ꢂ1
Previous studies with 1 had demonstrated that N-alkyl
substituents change the D1/D2 affinity profile such that
the resulting compounds have selectivity for various D2-,
rather than D1-like receptors.56,57 We synthesized the
N-allyl and N-n-propyl analogues of 5 and tested their
affinities at striatal D1 and D2 receptors (Table 1 and
Fig. 1). As was observed with 1, either an N-allyl or N-
n-propyl group on 5 reversed the D1/D2 affinity profile,
making these compounds 5- to 15-fold selective for D2
receptors, respectively. At D1-like receptors, addition of
either N-alkyl substituent caused a 40-fold decrease in
affinity (K0.5=260 nM and 250 nM for 15 and 17,
respectively), indicative of low steric tolerance in this
region of the D1-like receptors. At D2-like receptors,
addition of either N-alkyl substituent caused less than a
9-fold decrease in affinity (K0.5=54 nM and 17 nM for
15 and 17, respectively). Overall, the reversal in D1/D2
selectivity observed with the N-alkyl substituents can be
attributed to the substantial decrease in D1 binding
compared to the small decrease in D2 binding. Although
in the current work we did not resolve racemic 5 into its
enantiomers, the D1 full agonist pharmacophore we
have described has correctly predicted the absolute
configuration of all D1 full agonists (e.g., 1, 2, and 3).44
In the case of 5, this configuration would be 12aS,
homochiral with the active enantiomer shown for 2. In
addition, we have previously shown for 1 and 2 that the
same enantiomer possesses both the D1 and D2-like
activity, and it would be extremely surprising if this
were not also the case for 5 and its analogues.
(ꢂ)-2 (DNS)
(ꢂ)-5 (DNX)
(ꢂ)-15 (N-allyl-DNX)
(ꢂ)-17 (N-pr-DNX)
a The Hill slope nH for the antagonists was near unity, whereas those
for other compounds ranged from ꢃ0.9 for 15 and 17, to 0.65 for 1,
2, and 5. Data represent the mean and standard error from a mini-
mum of three independent assays.
b From Ghosh et al.39
c From Knoerzer et al.56
Figure 1. Representative competition binding curves for 5 (DNX) and
its N-alkyl analogues at D1-like receptors in rat striatal membranes.
The high-affinity, full agonist 1 (DHX) and the prototype antagonist
SCH23390 are included for comparison.
At the cloned dopamine receptors (Table 2) 5 had high
affinity at all of the dopamine receptor isoforms (K0.5
ranging from 1.0 nM to 3.9 nM) with the exception of
D2L (K0.5=86 nM). Compared to 1, the binding affinity
of 5 was similar at D1 and D5 receptors but was
approximately 15-fold higher at both D3 and D4 recep-
tors. It is particularly interesting that the introduction
of the oxygen tether into 5 leads to increased D4 affinity
and potency relative to 1 and 2.55,56 Similar to what was
observed in striatal homogenate, N-alkyl substituents
had dramatic effects on affinity, particularly for the D1-
like family of receptors. Consistent with proposed low
steric tolerance at D1-like receptors,40,44 N-alkyl sub-
stituents dramatically decreased affinity at D1 and D5
receptors. The most significant decrease was observed at
the D5 receptor (K0.5=1,500 nM and 570 nM for 15
and 17, respectively). At the D1 receptor, affinity was
decreased approximately 30- to 50-fold (K0.5=110 nM
and 190 nM for 15 and 17, respectively). At the D2-like
receptors, the N-alkyl substituents had very little effect
on affinity compared to 5. The N-allyl (15) substituent
decreased affinity less than 10-fold (K0.5=290 nM, 9.0
nM, and 6.3 nM for D2L, D3, and D4, respectively) and
the N-n-propyl (15) substituent had essentially no effect
(K0.5=98 nM, 0.93 nM, and 2.6 nM for D2L, D3, and
D4, respectively).
Figure 2. Representative competition binding curves for 5 (DNX) and
its N-alkyl analogues at D2-like receptors in rat striatal membranes.
The high-affinity, full agonist 1 (DHX) and the prototype antagonist
chlorpromazine are included for comparison.
(K0.5=4.6 nM and 5.9 nM, respectively). The affinity of
5 at striatal D2-like receptors was, however, surprisingly
high (K0.5=6.2 nM) and comparable to its D1-like affi-
nity. By contrast, both 1 and 2 had lower affinity
(K0.5=43 nM and 31 nM, respectively) at D2-like
receptors compared to D1-like receptors. Surprisingly,
despite the fact that 1, 2, and 5 all embody the same
pharmacophore (at least as defined for the D1 receptor),
the location and nature of the tethering moieties clearly
introduce subtle binding interactions within the different

R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
Table 2. Binding affinities of 5 and analogues for cloned dopamine receptorsa
1407
K0.5 (nM)ꢂSEM
Test Ligand
D1 (C-6)
D2L (C-6)
D3 (C-6)
D4 (CHO)
D5 (HEK)
Chlorpromazine
SCH23390
—
0.74ꢂ0.09b
—
0.86ꢂ0.03b
—
20ꢂ2
—
—
1.2ꢂ0.3
0.57ꢂ0.05c
2.2ꢂ0.4c
5.5ꢂ3c
(ꢂ)-1 (DHX)
180ꢂ21b
140ꢂ21d
86ꢂ19
15ꢂ3b
14ꢂ2
14ꢂ3
(ꢂ)-2 (DNS)
10ꢂ1
60ꢂ18
1.1ꢂ0.3
6.3ꢂ0.9
2.6ꢂ0.6
10ꢂ7
(ꢂ)-5 (DNX)
3.9ꢂ0.6
110ꢂ2
1.0ꢂ0.2
9.0ꢂ1.7
0.93ꢂ0.10
3.8ꢂ0.5
1500ꢂ550
570ꢂ66
(ꢂ)-15 (N-allyl-DNX)
290ꢂ40
(ꢂ)-17 (N-pr-DNX)
190ꢂ6
98ꢂ29
a The Hill slope nH for the antagonists was near unity, whereas those for other compounds ranged from 0.8–1 for 15 and 17, to 0.65–0.8 for 1, 2 and
5. Data represent the mean and standard error from a minimum of three independent assays.
b From Watts et al.10
c From Lewis et al.59
d From Ghosh et al.39
Table 3. Potency of 5 and analogues at dopamine receptorsa
EC50 (nM)ꢂSEM
Test Ligand
D1-like (striatum)
D1 (C6)
D2L (C6)
D4 (CHO)
D5 (HEK)
Dopamine
(ꢂ)-1 (DHX)
5000b
70b
530ꢂ260c
34ꢂ22c
20ꢂ3.2d
110ꢂ21d
550ꢂ120d
26ꢂ11
1800ꢂ680
1400ꢂ480
N.R.
110ꢂ18
12ꢂ4
(ꢂ)-2 (DNS)
30e
44ꢂ11c
9.7ꢂ2.2
12ꢂ6
(ꢂ)-5 (DNX)
87ꢂ14
N.R.
N.R.
8.6ꢂ3.2
610ꢂ200
760ꢂ220
52ꢂ16
(ꢂ)-15 (N-allyl-DNX)
>10 mM
99ꢂ9
170ꢂ120
25ꢂ17
N.R.
2600ꢂ970
(ꢂ)-17 (N-pr-DNX)
a Data represent the mean and standard error from a minimum of three independent assays. N.R.=No Response.
b From Brewster et al.38
c From Lewis et al.59
d From Watts et al.11
e From Ghosh et al.39
In the functional assays used to measure effects on
cAMP, 5 had high potency (EC50=8.6 nM to 52 nM)
and intrinsic activity equal to dopamine at all of the
cloned dopamine receptors tested (Table 3 and Fig. 3). It
was slightly less potent in striatal D1 receptor preparations
(EC50=87 nM). Whereas 5 was a potent full agonist at all
of the dopamine receptors, 1 and 2 displayed slightly
decreased potency at D2L (EC50=110 nM and 550 nM
for 1 and 2, respectively) and D4 receptors (EC50 ca.
1,400 nM for 1 and no activity detected for 2).
response for 15) compared to 5 (EC50=12 nM). In
terms of efficacy, 15 was a weak partial agonist at all the
dopamine receptors tested except for D4, where it had
significant efficacy. In contrast, 17 retains near full agonist
activity at all cloned receptors except the D5 (Fig. 3).
Taken together, this preliminary structure–activity
information about 5 and its N-allyl and N-n-propyl
substituted analogues should prove useful in the design
Addition of N-alkyl substituents to 5 produced dramatic
effects on functional effects in terms of adenylate cyclase
activity. Both the N-allyl (15) and N-n-propyl (17) sub-
stituents lost all agonist activity at striatal D1-like
receptors. At cloned D1 receptors, the N-allyl (15) and
N-n-propyl (17) substituents significantly decreased
potency (EC50=610 nM and 760 nM, respectively)
compared to the parent compound 5 (EC50=8.6 nM).
At D2L receptors, the N-allyl substituent (15) markedly
attenuated agonist activity (EC50 >10 mM), whereas the
N-n-propyl derivative (17) had only slightly decreased
potency (EC50=99 nM) compared to 5 (EC50=26 nM)
at this receptor. At D4 receptors, the N-allyl (15) sub-
stituent slightly decreased potency (EC50=170 nM)
whereas the N-propyl (17) substituent, by contrast,
slightly increased potency (17 EC50=25 nM) compared
to the parent compound (5 EC50=52 nM). At D5
receptors, both N-alkyl substituents dramatically
decreased potency (EC50=2600 nM for 17 and no
Figure 3. Maximal stimulation or inhibition of cAMP accumulation
produced by 5 (DNX) and its N-alkyl analogues at D1-like and D2-like
receptors. Compounds were evaluated in rat striatal tissue (D1-like) or
in cells expressing the cloned receptors (monkey D1 stably expressed in
C-6 glioma, rat D2L stably expressed in C-6 glioma, human D4 stably
expressed in CHO, or human D5 transiently expressed in HEK 293).
Emax values were determined from full dose-response curves. Data
represent meanꢂSEM from at least two experiments. *=significantly
different from effects of dopamine (P<0.05).

1408
R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
of new dopamine agonists by guiding our ability to target
specific receptor isoforms.
dried (MgSO4), filtered, and concentrated under
vacuum. After Kugelrohr distillation (90–100 ꢁC, 0.3
atm), 24.6 g (84%) of a clear oil was obtained: 1H
NMR: (300 MHz, CDCl3): d 6.97 (t, 1H, J=8.7 Hz);
6.79 (dd, 1H, J=7.2, 1.8 Hz); 6.62 (dd, 1H, J=6.9, 1.2
Hz); 5.21 (s, 2H); 3.87 (s, 3H); 3.85 (s, 3H); 3.51 (s, 3H).
CIMS m/z: 199 (M+H+, 50%); 167 (M+H+-CH3OH,
100%). Anal. cald (C10H14O4): C, H, N.
5. Conclusions
The current work demonstrates yet another approach to
tethering the b-phenyldopamine pharmacophore to
afford potent and useful new dopamine receptor ago-
nists. Although our initial hypothesis was that 5 would
possess dopamine D1/D5 selectivity, surprisingly, we
obtained a potent agonist with activity at all of the
dopamine receptor isoforms. The subtle differences in
isoform selectivity and potency for substituted derivatives
of 1, 2, and 5 should be extremely useful information in
conjunction with docking studies of these ligands within
homology models of the receptors, to identify key residues
that are differentially engaged in the different receptors
by these structurally similar rigid analogues. Compound
5 and its analogues also may represent the first drugs
that can be considered true high affinity dopamine
replacements, and as such may have interesting biological
properties.
6.1.3. 2-(3,4-Dimethoxy-2-methoxymethoxyphenyl)-4,4,5,5-
tetramethyl[1,3,2]dioxaborolane (8). The MOM-pro-
tected phenol 7 (10 g, 0.0505 mol) was dissolved in 1000
mL of dry diethyl ether and cooled to ꢀ78 ꢁC. A solu-
tion of n-butyl lithium in hexane (22.2 mL of 2.5 M,
0.0555 mol) was then added by syringe. The cooling
bath was removed and the solution was allowed to
warm to room temperature. While stirring the solution
at room temperature for 2 h, a yellow precipitate
formed. The mixture was cooled to ꢀ78 ꢁC, and 2-iso-
propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(15
mL, 0.080 mol) was added by syringe. The cooling bath
was removed after 2 h. Stirring was continued for four
hours at room temperature. The mixture was then
poured into 300 mL of water and extracted with diethyl
ether (3ꢄ300 mL), dried (Na2SO4), and concentrated to
a yellow oil (12.37g, 76%) that was used without further
6. Experimental
6.1. Chemistry
1
purification; H NMR: (300 MHz, CDCl3): d 7.46 (d,
1H, J=8.4 Hz); 6.69 (d, 1H, J=8.4 Hz); 5.15 (s, 2H);
3.87 (s, 3H); 3.83 (s, 3H); 1.327 (s, 12H).
6.1.1. General procedures. All reagents were commer-
cially available and were used without further purification,
unless otherwise indicated. Dry THF and diethyl ether
were obtained by distillation from benzophenone-
sodium under nitrogen immediately before use. Column
chromatography was carried out using silica gel 60 (230-
400 mesh). J.T. Baker flexible thin layer chromato-
graphy sheets (silica gel IB2-F) were used to monitor
reactions. Melting points were determined using a Thomas-
Hoover apparatus and are uncorrected. 1H NMR spectra
were recorded using a 300 MHz Bruker ARX-300 NMR
spectrometer. Chemical shifts are reported in d values
ppm relative to an internal reference (0.03%, v/v) of
tetramethylsilane (TMS) in CDCl3, except where noted.
Chemical ionization mass spectra (CIMS) using iso-
butane as a carrier gas were obtained with a Finnigan
4000 spectrometer. Elemental analyses were performed
by the Purdue University Microanalysis Laboratory. All
the reactions were carried out under an inert atmo-
sphere of argon.
6.1.4. 4-Bromo-5-nitroisoquinoline (9). Potassium nitrate
(5.34 g, 0.052 mol) was added to 20 mL of concentrated
sulfuric acid and slowly dissolved by careful heating.
The resulting solution was added dropwise to a solution
of 4-bromoisoquinoline (10 g, 0.048 mol) dissolved in 40
mL of concentrated sulfuric acid at 0 ꢁC. After removal
of the cooling bath, the solution was stirred for 1 h at
room temperature. The reaction mixture was then
poured onto crushed ice (400 g) and made basic with
ammonium hydroxide. The resulting yellow precipitate
was collected by filtration and the filtrate was extracted
with diethyl ether (3ꢄ500 mL), dried (Na2SO4), and
concentrated to give a yellow solid that was combined
with the initial precipitate. Recrystallization from
methanol gave 12.1 g (89%) of slightly yellow crystals:
1
mp 172–174 C; H NMR: (300 MHz, CDCl3): d 9.27 (s,
1H); 8.87 (s, 1H); 8.21 (dd, 1H, J=6.6, 1.2 Hz); 7.96
(dd, 1H, J=6.6, 1.2 Hz); 7.73 (t, 1H, J=7.5 Hz). CIMS
m/z: 253 (M+H+, 100%); 255 (M+H++2, 100%).
Anal. (C9H5BrN2O2) C, H, N.
6.1.2. 1,2-Dimethoxy-3-(methoxymethoxy)benzene (7). A
stirring suspension of sodium hydride was prepared by
adding 1000 mL of dry THF to 7.06 g (0.18 mol) of
sodium hydride (60% dispersion in mineral oil) under
an argon atmosphere at 0 ꢁC. To the suspension, neat
2,3-dimethoxyphenol (23.64 g, 0.153 mol) was added
with a syringe. The resulting mixture was allowed to
warm to room temperature and stir for 2 h. The black
solution was cooled to 0 ꢁC and 13.2 mL (14 g, 0.173
mol) of chloromethyl methyl ether was slowly added by
syringe. The solution was allowed to reach room temp-
erature and stirred for an additional 8 h. The yellow
mixture was concentrated to an oil that was dissolved in
1000 mL of diethyl ether. The resulting solution was
washed with water (500 mL), 2N NaOH (3ꢄ400 mL),
6.1.5. 4-(3,4-Dimethoxy-2-methoxymethoxyphenyl)-5-nitro-
isoquinoline (10). Pinacol boronate ester 8 (5.56 g,
0.0172 mol), isoquinoline 9 (3.36 g, 0.0143 mol), and 1.0
g (6 mol%) of Pd(PPh3)4 were suspended in 100 mL of
dimethoxyethane (DME). Potassium hydroxide (3.6 g,
0.064 mol), and 0.46
g
(10 mol%) of tetra-
butylammonium bromide were dissolved in 14.5 mL of
water and were added to the DME mixture. The result-
ing suspension was degassed for 30 min with argon and
then heated at reflux for 4 h. The resulting black solu-
tion was allowed to cool to room temperature, poured
into 500 mL of water, extracted with diethyl ether

R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
1409
(3ꢄ500 mL), dried (Na2SO4), and concentrated. The
product was then purified by column chromatography
(silica gel, 50% ethyl acetate:hexane) giving 5.29 g of
yellow crystals (80%); mp 138–140 ꢁC; 1H NMR:
(300 MHz, CDCl3): d 9.33 (s, 1H); 8.61 (s, 1H); 8.24 (dd,
1H, J=7.2, 0.9 Hz); 8.0 (dd, 1H, J=6.3, 1.2 Hz); 7.67
(t, 1H, J=7.8 Hz); 7.03 (d, 1H, J=9.6 Hz); 6.81 (d, 1H,
J=8.1 Hz); 4.86 (d, 1H, J=6 Hz); 4.70 (d, 1H, J=5.4 Hz);
3.92 (s, 3H); 3.89 (s, 3H); 2.613 (s, 3H). CIMS m/z: 371
(M+H+, 100%). Anal. calcd (C19H18N2O6) C, H, N.
extracted into diethyl ether (3ꢄ250 mL), dried
(Na2SO4), and concentrated. The resulting oil (0.997 g,
99%) was used without further purification: H NMR:
1
(300 MHz, CDCl3): d 7.10 (t, 1H, J=7.5 Hz); d 7.00 (d,
1H, J=8.4 Hz); d 6.78 (m, 2H); d 6.60 (d, 1H, J=9 Hz); d
4.10 (s, 2H); d 3.84 (m, 8H); d 2.93 (t, 1H, J=12.9 Hz).
6.1.9. 8,9-Dihydroxy-1,2,3,11b-tetrahydrochromeno[4,3,2-
de]isoquinoline hydrobromide (5). Crude 13 (0.834 g, 3.0
mmol) was dissolved in 50 mL of anhydrous dichloro-
methane. The solution was cooled to ꢀ78 ꢁC and 15.0
mL of a boron tribromide solution (1.0 M in dichloro-
methane) was slowly added. The solution was stirred
overnight, while the reaction slowly warmed to room
temperature. Then, after cooling the solution to ꢀ78 ꢁC,
50 mL of methanol was slowly added to quench the
reaction. The solution was then concentrated to dry-
ness. Methanol (50 mL) was added and the solution was
concentrated. This process was repeated three times.
The resulting brown solid was treated with activated
charcoal, filtered through Celite, and recrystallized from
ethanol as yellow crystals (0.72 g, 72%): mp 298–302 ꢁC
6.1.6. 2,3-Dimethoxy-6-(5-nitroisoquinolin-4-yl)phenol (11).
After dissolving isoquinoline 10 (5.285 g, 0.014 mol) in
200 mL of methanol by gentle heating, p-toluene-
sulfonic acid monohydrate (8.15 g, 0.043 mol) was
added in several portions. Stirring was continued for
four h at room temperature. After completion of
the reaction (monitored by TLC), the solution was made
basic by adding saturated sodium bicarbonate. The pro-
duct was then extracted with dichloromethane (3ꢄ250
mL), dried (Na2SO4), and concentrated. The resulting
yellow solid (4.65 g, 98%) was used directly in the next
reaction. An analytical sample was recrystallized from
methanol: mp 170–174 ꢁC; 1H NMR: (300 MHz,
CDCl3): d 9.33 (s, 1H); 8.62 (s, 1H); 8.24 (dd, 1H,
J=7.2, 0.9 Hz); 7.99 (dd, 1H, J=6.3, 1.2 Hz); 7.67 (t,
1H, J=7.8 Hz); 6.96 (d, 1H, J=8.7 Hz); 6.59 (d, 1H,
J=8.7 Hz); 5.88 (bs, 1H); 3.94 (s, 3H); 3.92 (s, 3H).
CIMS m/z: 327 (M+H+, 100%). Anal. calcd
(C17H14N2O5) C, H, N.
1
dec; H NMR: (300 MHz, D2O): d 7.12 (t, 1H, J=9
Hz); 6.88 (d, 1H, J=7.5 Hz); 6.83 (d, 1H, J=7.5 Hz);
6.46 (d, 1H, J=6 Hz); 6.40 (d, 1H, J=6 Hz); 4.20 (q,
2H, J=15 Hz); 4.07 (m, 1H); 3.93 (m, 1H); 2.91 (t,
.
1H, J=12 Hz). Anal. calcd (C15H14BrNO3 H2O) C, H,
N.
6.1.10. N-Allyl-8,9-dimethoxy-1,2,3,11b-tetrahydrochro-
meno[4,3,2-de]isoquinoline (14). The tetrahydroisoquino-
line 13 (1.273 g, 4.5 mmol) was dissolved in 150 mL of
acetone. Potassium carbonate (0.613 g, 4.5 mmol) and
0.4 mL (4.6 mmol) of allyl bromide were added. The
reaction was stirred at room temperature for 4 h. The
mixture was then filtered and the filtered solids washed
several times with ether. The filtrate was concentrated
and purified by flash chromatography (silica gel, 50%
ethyl acetate:hexane) to afford 1.033 g (71%) of a yel-
6.1.7. 8,9-Dimethoxychromeno[4,3,2-de]isoquinoline (12).
Phenol 11 (4.65 g, 0.014 mol) was dissolved in 100 mL
of dry DMF. The solution was degassed with argon for
thirty min. Potassium carbonate (5.80 g, 0.042 mol) was
added to the yellow solution in one portion. After
heating the mixture at 80 ꢁC for 1 h, the mixture had
turned brown and no more starting material remained.
After cooling to room temperature, 200 mL of water
was added. The aqueous layer was extracted with di-
chloromethane (3ꢄ500 mL), which was washed with
water (3ꢄ500 mL), dried (Na2SO4), and concentrated.
A white powder (3.65 g 92%) was obtained that was
used in the next reaction without further purification.
An analytical sample was recrystallized from ethyl
1
low oil that was used without further purification: H
NMR: (300 MHz, CDCl3): d 7.15 (t, 1H, J=9 Hz); 7.04
(d, 1H, J=9 Hz); 6.83 (m, 2H); 6.65 (d, 1H, J=6 Hz);
5.98 (m, 1H); 5.27 (m, 2H); 4.10 (m, 3H); 3.95 (s, 3H);
3.86 (s, 3H); 3.46 (d, 1H, J=15 Hz); 3.30 (d, 2H, J=6
Hz); 2.56 (t, 1H, J=12 Hz).
ꢁ
1
acetate:hexane: mp 195–196 C; H NMR: (300 MHz,
CDCl3): d 9.02 (s, 1H); 8.82 (s, 1H); 7.87 (d, 1H, J=8.7
Hz); 7.62 (m, 3H); 7.32 (dd, 1H, J=6.0, 1.5 Hz); d 6.95
(d, J=9.6 Hz); 3.88 (s, 3H); d 3.82 (s, 3H). CIMS m/z:
280 (M+H+, 100%). Anal. calcd(C17H13NO3) C, H, N.
HRCIMS m/z: Calc’d: 280.0974; Found: 280.0975.
6.1.11. N-Allyl-8,9-dihydroxy-1,2,3,11b-tetrahydrochrom-
eno[4,3,2-de]isoquinoline (15). The N-Allylamine 14
(0.625 g, 1.93 mmol) was dissolved in 50 mL of di-
chloromethane. The solution was cooled to ꢀ78 ꢁC and
10.0 mL of a boron tribromide solution (1.0 M in di-
chloromethane) was slowly added. The solution was
stirred overnight, while the reaction slowly warmed to
room temperature. After cooling the solution to ꢀ78 ꢁC,
50 mL of methanol was slowly added to quench the
reaction. The reaction was then concentrated to dry-
ness. Methanol (50 mL) was added and the solution was
concentrated. This process was repeated three times.
Recrystallization of the brown solid from ethanol gave
6.1.8. 8,9-Dimethoxy-1,2,3,11b-tetrahydrochromeno[4,3,2-
de]isoquinoline (13). Platinum (IV) oxide (200 mg) was
added to a solution containing 50 mL of acetic acid and
isoquinoline 12 (1.0 g, 3.5 mmol). After adding 2.8 mL
of concentrated HCl, the mixture was shaken for 24 h
under 60 psi H2 in a Parr hydrogenator. When the
reaction was complete the green solution was filtered
through Celite to remove the catalyst, and most of the
acetic acid was removed by rotary evaporation. The
remaining acid was neutralized using a saturated
sodium bicarbonate solution, and the product was
0.68 g (61%) of a white solid: mp 251–253 ꢁC dec; H
1
NMR: (300 MHz, D2O): d 10.55 (s, 1H); 10.16 (s, 1H);
8.61 (t, 1H, J=9 Hz); 8.42 (d, 1H, J=9 Hz); 8.31 (d,
1H, J=9 Hz); 7.87 (d, 1H, J=9 Hz); 7.82 (d, 1H, J=9

1410
R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
Hz); 7.36 (q, 1H, J=9 Hz); 6.89 (m, 2H); 6.85 (d, 1H,
J=15 Hz); 5.58 (m, 3H); 5.28 (m, 2H); 3.76 (d, 1H, J=3
Hz). Anal. calcd(C18H18BrNO3): C, H, N. HRCIMS m/
z: Calc’d: 295.1208; Found: 295.1214.
functional activity at D1-like and D2-like receptors, as
described previously,10,59,60 utilizing both rat striatum
and cell lines expressing the various receptor subtypes.
D1 and D5 binding affinities were evaluated in the same
manner, essentially as described in Watts et al.10 for rat
striatum and Lewis et al.59 for cell line assays. D2-like
receptor binding and functional assays were performed
essentially as described previously.60
6.1.12. N-n-Propyl-8,9-dimethoxy-1,2,3,11b-tetrahydro-
chromeno[4,3,2-de]isoquinoline (16). The N-Allyl amine
14 (1.033 g, 3.2 mmol) was dissolved in 50 mL of etha-
nol. Palladium (10% dry weight; 0.103 g) was then
added. The mixture was shaken for 3 h under 60 psi H2
in a Parr hydrogenator. After TLC showed the absence
of starting material, the mixture was filtered through
Celite and concentrated to give 0.95 g (91%) of an oil
For radioligand binding studies at dopamine receptors
in membranes prepared from rat striatum, receptors
were labeled with 0.3 nM [3H]-SCH23390 (for D1-like)
or 0.07 nM [3H]-spiperone (for D2-like) with 100 nM
ketanserin to mask 5-HT2 receptors. Total binding was
defined in the absence of test ligand and nonspecific
binding was defined by the addition of 1 mM SCH23390
(for D1-like) or 1 mM chlorpromazine (for D2-like). Test
ligands were incubated with membranes (150–200 mg
protein/assay tube) for 15 min prior to harvesting by
vacuum filtration.
1
that was used without further purification: H NMR:
(300 MHz, CDCl3): d 7.15 (t, 1H, J=7.2 Hz); 7.04 (d,
1H, J=8.1 Hz); 6.84 (t, 2H, J=7.5 Hz); 6.65 (d, 1H,
J=8.4 Hz); 4.07 (m, 2H); 3.95 (s, 3H); 3.86 (s, 3H); 3.71
(q, 1H, J=5.1 Hz); 3.42 (d, 2H, J=15.6 Hz); 2.62 (m,
2H); 2.471 (t, J=10.5 Hz); 1.69 (h, 2H, J=7.2 Hz); 0.98
(t, 3H, J=7.5 Hz). CIMS m/z: 326 (M+H+, 100%).
6.1.13. N-n-Propyl-8,9-dihydroxy-1,2,3,11b-tetrahydro-
chromeno[4,3,2-de]isoquinoline (17). The N-propyl
amine 16 (0.90 g, 2.8 mmol) was dissolved in 200 mL of
dichloromethane and cooled to ꢀ78 ꢁC. In a separate
250 mL round bottom flask, 125 mL of dry dichloro-
methane was cooled to ꢀ78 ꢁC, and 1.4 mL (14.8 mmol)
of BBr3 was added by syringe. The BBr3 solution was
then transferred using a cannula to the flask containing
the solution of 16. The reaction was stirred overnight,
while slowly warming to room temperature. After cool-
ing the solution to ꢀ78 ꢁC, 50 mL of methanol was
slowly added to quench the reaction. The reaction
was then concentrated to dryness. Methanol (50 mL)
was added and the solution was concentrated. This
process was repeated three times. The resulting tan solid
was suspended in hot isopropyl alcohol. Slowly cooling
to room temperature resulted in a fine yellow pre-
cipitate. The solid was collected by filtration (0.66 g,
Radioligand binding studies were also carried out in
membranes prepared from cell lines expressing the
cloned receptors (monkey D1, rat D2L, or rat D3 stably
expressed in C-6 glioma; human D4 stably expressed in
CHO; human D5 transiently transfected into HEK 293
cells using Lipofectamine, following the manufacturer’s
recommended guidelines). Receptors were labeled with
either 0.3 or 1.0 nM [3H]-SCH23390 (for D1 and D5,
respectively) or 0.07 nM [3H]-spiperone (for D2-like).
Test ligands were incubated with membranes (10-40 mg
protein) for 15 min prior to harvesting by vacuum
filtration.
Functional potency was measured as follows. D1-like
functional assays were done as described in Watts et
al.10 using broken cell membranes from both rat stria-
tum and cell lines, followed by RIA to determine cAMP
levels. For D1-like receptors, adenylate cyclase activity
was determined in membranes prepared from frozen rat
striatal tissue. For cloned receptors expressed in cells,
adenylate cyclase activity was measured in whole cell
preparations (for D2L and D4) or membranes (for
D1A and D5). Tissue samples (20 mg protein for striatal
tissue or 10–20 mg protein/well for cell membranes)
were incubated with 100 mM HEPES (pH 7.4),
100 mM NaCl, 4 mM MgCl2, 2 mM EDTA, 500 mM
isobutyl methylxanthine, 0.01% ascorbic acid, 10 mM
pargyline, 2 mM ATP, 5 mM GTP, 20 mM phospho-
creatine, 5 units of creatine phosphokinase, and test
ligand. After incubating for 15 min at 30 ꢁC, the reac-
tion was terminated by addition of 0.1 N HCl. The
concentrations of accumulated cAMP were assessed by
radioimmunoassay.
63%): mp 259–264 ꢁC dec; H NMR: (300 MHz, D2O):
1
d 7.16 (t, 1H, J=9 Hz); 6.97 (d, 1H, J=12 Hz); 6.83 (d,
1H, J=9 Hz); 6.55 (d, 1H, J=9 Hz); 6.46 (d, 1H, J=9
Hz); 4.45 (d, 1H, J=15 Hz); 4.10 (m, 3H); 3.17 (q, 2H,
J=6 Hz); 3.04 (t, 1H, J=9 Hz); 1.73 (q, 2H, J=9 Hz); 0.90
(t, 3H, J=6 Hz). Anal. calcd(C18H20BrNO3) C, H, N.
6.2. Pharmacology methods
6.2.1. Materials. [3H]-SCH23390 (specific activity ꢅ70
Ci/mmol) was synthesized according to the method of
Wyrick et al.58 [3H]-Spiperone (specific activity=65-140
Ci/mmol) was purchased from Amersham (Piscataway,
NJ). Dihydrexidine (1) and dinapsoline (2) were syn-
thesized according to published methods.39,56 Chlor-
promazine HCl was a gift from SmithKline Beecham
and other ligands were purchased from Research Bio-
chemicals, Inc. (Natick, MA). Antibodies were pur-
chased from Advanced Magnetics (Cambridge MA). All
reagents and supplies for cell culture were obtained
from known commercial sources.
6.2.3. Data and statistical analyses. Receptor binding
data were analyzed using algorithms in Prism 3.03
(GraphPad, Inc, San Diego, CA). The data were fit to a
sigmoidal curve with variable slope to provide a slope
coefficient. Final affinity data are expressed as K0.5 by
correcting the experimentally-derived IC50 values for
radioligand concentration using the one-site Cheng–
Prusoff equation.61
6.2.2. Receptor bindingand functional assays. Novel
compounds were evaluated for binding affinity and

R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
1411
For functional assays, data were expressed as fmol/mg
protein. Dose–response curves were plotted as a per-
centage of the maximal dopamine response versus log
concentration of test ligand. Data were analyzed as a
sigmoidal curve with variable slope (GraphPad Prism)
to determine EC50 and Emax. Competition curves were
analyzed by nonlinear regression to determine estimates
for K0.5 and Hill slope (nH). For each receptor, efficacy
data (i.e., Emax) for 5 and its analogues were compared
to the full agonist dopamine using an unpaired Student’s
t-test to determine statistical significance. A p<0.01 was
considered significant (as denoted by * in Fig. 3).
11. Watts, V. J.; Lawler, C. P.; Gonzales, A. J.; Zhou, Q. Y.;
Civelli, O.; Nichols, D. E.; Mailman, R. B. Synapse 1995,
21, 177.
12. Jenner, P. Neurology 1995, 45, S6.
13. Wolters, E. C.; Tissingh, G.; Bergmans, P. L.; Kuiper,
M. A. Neurology 1995, 45, S28.
14. Taylor, J. R.; Lawrence, M. S.; Redmond, D. E., Jr.; Els-
worth, J. D.; Roth, R. H.; Nichols, D. E.; Mailman, R. B.
Eur. J. Pharmacol. 1991, 199, 389.
15. Mailman, R. B.; Nichols, D. E.; Lewis, M. M.; Blake, B. L.;
and Lawler, C. P. In Dopamine Receptor Subtypes: from
Basic Science to Clinical Application; Jenner, P. and Demir-
demar, R. Eds.; IOS Stockton Press: New York, 1998; p 64.
16. Mailman, R. B.; Nichols, D. E. Trends Pharmacol. Sci.
1998, 19, 255.
17. Goulet, M.; Madras, B. K. J. Pharmacol. Exp. Ther. 2000,
292, 714.
18. Gnanalingham, K. K.; Hunter, A. J.; Jenner, P.; Mars-
den, C. D. Psychopharmacology (Berl.) 1995, 117, 287.
19. Williams, M.; Wright, S.; Lloyd, G. K. Trends Pharmacol.
Sci. 1997, 18, 307.
20. Huang, X.; Lawler, C. P.; Lewis, M. M.; Nichols, D. E.;
Mailman, R. B. Int. Rev. Neurobiol. 2001, 48, 65.
21. Mailman, R.; Huang, X.; Nichols, D. E. Curr. Opin.
Investig. Drugs 2001, 2, 1582.
22. Huntley, G. W.; Morrison, J. H.; Prikhozhan, A.; Seal-
fon, S. C. Brain Res. Mol. Brain Res. 1992, 15, 181.
23. Rappaport, M. S.; Sealfon, S. C.; Prikhozhan, A.; Hunt-
ley, G. W.; Morrison, J. H. Brain Res. 1993, 616, 242.
24. Lidow, M. S.; Elsworth, J. D.; Goldman-Rakic, P. S. J.
Pharmacol. Exp. Ther. 1997, 281, 597.
Elemental analysis data
Compd
%C
%H
%N
Calcd Found Calcd Found Calcd Found
5
7
9
10
11
12
15
17
50.87 51.18 4.55 4.31
60.59 60.93 7.12 7.16
42.72 42.59 1.99 1.76
61.62 61.66 4.90 4.81
62.57 62.18 4.32 4.38
73.11 72.85 4.69 4.40
57.46 56.82 4.82 4.80
57.16 56.78 5.33 5.26
3.82 3.95
NA NA
11.07 10.87
7.56 7.49
8.58 8.35
5.02 4.86
3.72 3.61
3.70 3.65
25. Lidow, M. S.; Wang, F.; Cao, Y.; Goldman-Rakic, P. S.
Synapse 1998, 28, 10.
Acknowledgements
26. Muly, E. C., III; Szigeti, K.; Goldman-Rakic, P. S. J.
Neurosci. 1998, 18, 10553.
27. Castner, S. A.; Williams, G. V.; Goldman-Rakic, P. S.
Science 2000, 287, 2020.
28. Granon, S.; Passetti, F.; Thomas, K. L.; Dalley, J. W.;
Everitt, B. J.; Robbins, T. W. J. Neurosci. 2000, 20, 1208.
29. Laurier, L. G.; O’Dowd, B. F.; George, S. R. Brain Res.
Mol. Brain Res. 1994, 25, 344.
30. Choi, W. S.; Machida, C. A.; Ronnekleiv, O. K. Brain
Res. Mol. Brain Res. 1995, 31, 86.
The authors gratefully acknowledge support for this
work by NIH research grants MH42705 and MH40537,
and training grants. Drs. Mailman and Nichols have a
significant financial interest in DarPharma Inc., Chapel
Hill, NC, the company that currently holds license
rights to dinoxyline and its analogues. The interpretation
and discussion in this article are those of the authors
alone and do not reflect the views of DarPharma Inc,
Purdue University, or the University of North Carolina
at Chapel Hill.
31. Huang, Y. Y.; Kandel, E. R. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 2446.
32. Otmakhova, N. A.; Lisman, J. E. J. Neurosci. 1996, 16,
7478.
33. Otmakhova, N. A.; Lisman, J. E. J. Neurosci. 1998, 18,
1270.
References and notes
1. Sunahara, R. K.; Seeman, P.; Van Tol, H. H.; Niznik,
H. B. Br. J. Psychiatry Suppl. 1993, 31.
34. Kusuki, T.; Imahori, Y.; Ueda, S.; Inokuchi, K. Neurore-
port 1997, 8, 2037.
2. Sibley, D. R.; Monsma, F. J., Jr.; Shen, Y. Int. Rev. Neuro-
biol. 1993, 35, 391.
3. Ogawa, N. Acta Med. Okayama 1995, 49, 1.
4. Missale, C.; Nash, S. R.; Robinson, S. W.; Jaber, M.;
Caron, M. G. Physiol. Rev. 1998, 78, 189.
5. Neve, K. A.; Neve, R. L. The Dopamine Receptors;
Humana Press: Totowa NJ, 1997.
6. Okuyama, Y.; Ishiguro, H.; Nankai, M.; Shibuya, H.;
Watanabe, A.; Arinami, T. Mol. Psychiatry 2000, 5, 64.
7. Paterson, A. D.; Sunohara, G. A.; Kennedy, J. L. Neuro-
psychopharmacology 1999, 21, 3.
35. Swanson-Park, J. L.; Coussens, C. M.; Mason-Parker,
S. E.; Raymond, C. R.; Hargreaves, E. L.; Dragunow, M.;
Cohen, A. S.; Abraham, W. C. Neuroscience 1999, 92,
485.
36. Yang, S. N. Neurosci. Lett. 1999, 270, 87.
37. Bach, M. E.; Barad, M.; Son, H.; Zhuo, M.; Lu, Y. F.;
Shih, R.; Mansuy, I.; Hawkins, R. D.; Kandel, E. R.
Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 5280.
38. Brewster, W. K.; Nichols, D. E.; Riggs, R. M.; Mottola,
D. M.; Lovenberg, T. W.; Lewis, M. H.; Mailman, R. B.
J. Med. Chem. 1990, 33, 1756.
8. Arnsten, A. F.; Cai, J. X.; Murphy, B. L.; Goldman-
Rakic, P. S. Psychopharmacology (Berl) 1994, 116, 143.
9. Schneider, J. S.; Sun, Z. Q.; Roeltgen, D. P. Brain Res.
1994, 663, 140.
10. Watts, V. J.; Lawler, C. P.; Gilmore, J. H.; Southerland,
S. B.; Nichols, D. E.; Mailman, R. B. Eur. J. Pharmacol.
1993, 242, 165.
39. Ghosh, D.; Snyder, S. E.; Watts, V. J.; Mailman, R. B.;
Nichols, D. E. J Med.Chem. 1996, 39, 549.
40. Nichols, D. E. In Dopamine Receptors; Kaiser, C., Keba-
bian, J. W. Eds.; American Chemical Society: Washington,
D.C., 1983; p 201.
41. Andersen, P. H.; Jansen, J. A. Eur. J. Pharmacol. 1990,
188, 335.

1412
R. A. Grubbs et al. / Bioorg. Med. Chem. 12 (2004) 1403–1412
42. Michaelides, M. R.; Hong, Y.; DiDomenico, S., Jr; Bay-
burt, E. K.; Asin, K. E.; Britton, D. R.; Lin, C. W.;
Shiosaki, K. J. Med. Chem. 1997, 40, 1585.
43. Brewster, W. K.; Nichols, D. E.; Watts, V. J.; Riggs,
R. M.; Mottola, D.; Mailman, R. B. J. Med. Chem. 1995,
38, 318.
44. Mottola, D. M.; Laiter, S.; Watts, V. J.; Tropsha, A.;
Wyrick, S. D.; Nichols, D. E.; Mailman, R. B. J. Med.
Chem. 1996, 39, 285.
53. Tsuji, K.; Nakamura, K.; Konishi, N.; Okumura, H.;
Matsuo, M. Chem. Pharm. Bull.(Tokyo) 1992, 40, 2399.
54. Liu, L.; Lin, Y.; Wang, C.; Lin, M.; Yen, S.; Chen, H.
Chem. Pharm. Bull. (Tokyo) 1996, 40, 2399.
55. Qandil, A. M.; Lewis, M. M.; Jassen, A.; Leonard, S. K.;
Mailman, R. B.; Nichols, D. E. Bioorg. Med. Chem. 2003,
11, 1451.
56. Knoerzer, T. A.; Watts, V. J.; Nichols, D. E.; Mailman,
R. B. J. Med. Chem. 1995, 38, 3062.
45. Pugsley, T. A.; Davis, M. D.; Akunne, H. C.; MacKenzie,
R. G.; Shih, Y. H.; Damsma, G.; Wikstrom, H.; Whetzel,
S. Z.; Georgic, L. M.; Cooke, L. W. J. Pharmacol. Exp.
Ther. 1995, 275, 1355.
46. Qandil, A. M.; Ghosh, D.; Nichols, D. E. J. Org. Chem.
1999, 64, 1407.
47. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
48. Zoltewicz, J.; Maier, N.; Lavieri, S.; Ghivirgia, I.;
Abboud, K. Tetrahedron 1997, 53, 5379.
49. Osborn, A.; Schofield, K.; Short, L. J. Chem. Soc. 1956,
157, 4191.
57. Watts, V. J.; Lawler, C. P.; Knoerzer, T.; Mayleben,
M. A.; Neve, K. A.; Nichols, D. E.; Mailman, R. B. Eur.
J. Pharmacol. 1993, 239, 271.
58. Wyrick, S. D.; McDougald, D. L.; Mailman, R. B.
J. Label. Comp. Radiopharm. 1986, 23, 685.
59. Lewis, M. M.; Watts, V. J.; Lawler, C. P.; Nichols, D. E.;
Mailman, R. B. J. Pharmacol. Exp. Ther. 1998, 286,
345.
60. Mottola, D. M.; Kilts, J. D.; Lewis, M. M.; Connery,
H. S.; Walker, Q. D.; Jones, S. R.; Booth, R. G.; Hyslop,
D. K.; Piercey, M.; Wightman, R. M.; Lawler, C. P.;
Nichols, D. E.; Mailman, R. B. J. Pharmacol. Exp. Ther.
2002, 301, 1166.
50. Harvey, R.; Cortez, C.; Ananthanarayan, T.; Schmolka,
S. J. Org. Chem. 1988, 53, 3936.
51. Townsend, C.; Bloom, L. Tetrahedron Lett. 1981, 22, 3923.
52. Toth, J.; Hamann, P.; Fuchs, P. J. Org.Chem. 1988, 53,
4694.
61. Cheng, Y.; Prusoff, W. H. Biochem. Pharmacol. 1973, 22,
3099.