Structure-affinity relationships of halogenated predicentrine and glaucine derivatives at D1 and D2 dopaminergic receptors: Halogenation and D1 receptor selectivity

Article abstract of DOI:10.1016/j.bmc.2005.03.022

Halogenation of the aporphine alkaloid boldine at the 3-position leads to increased affinity for rat brain D₁-like dopaminergic receptors with some selectivity over D₂-like receptors. A series of 3-halogenated and 3,8-dihalogenated (halogen = Cl, Br or I) derivatives of predicentrine (9-O-methylboldine) and glaucine (2,9-di-O-methylboldine) were prepared and assayed for binding at D₁ and D₂ sites. Halogenation of predicentrine led to strong increases in affinity for D₁-like receptors, while the affinities for D₂-like receptors were either practically unchanged or reduced three- to fourfold. Halogenated glaucine derivatives did not show any clear trend towards enhanced selectivity, and the affinities were poor and similar to or worse than the values previously recorded for glaucine itself. Together with earlier work on boldine derivatives, these results suggest that the 2-hydroxy group on the aporphine skeleton may determine a binding mode favoring D₁-like over D₂-like receptors, with enhanced affinity when the C-3 position is halogenated.

Full text of DOI:10.1016/j.bmc.2005.03.022

Bioorganic & Medicinal Chemistry 13 (2005) 3699–3704
Structure–affinity relationships of halogenated predicentrine
and glaucine derivatives at D1 and D2 dopaminergic
receptors: halogenation and D1 receptor selectivity
a
a
a
a,b,
*
´
´
Marcelo Asencio, Claudio Hurtado-Guzman, John J. Lopez, Bruce K. Cassels,
Philippe Protaisc,z and Abdeslam Chagraouic
aDepartment of Chemistry and Millennium Institute for Advanced Studies in Cell Biology and Biotechnology (CBB),
Faculty of Sciences, University of Chile, Casilla 653, Santiago, Chile
bProgramme of Molecular and Clinical Pharmacology, ICBM, Faculty of Medicine, University of Chile,
Santiago 7, Casilla 70.000, Chile
´ ´ ´
Laboratoire de Physiologie, Faculte de Medecine et de Pharmacie, Universite de Rouen, 7600 Rouen-cedex, Rouen, France
c
Received 4 February 2005; revised 11 March 2005; accepted 11 March 2005
Available online 11 April 2005
Abstract—Halogenation of the aporphine alkaloid boldine at the 3-position leads to increased affinity for rat brain D1-like dopa-
minergic receptors with some selectivity over D2-like receptors. A series of 3-halogenated and 3,8-dihalogenated (halogen = Cl, Br or
I) derivatives of predicentrine (9-O-methylboldine) and glaucine (2,9-di-O-methylboldine) were prepared and assayed for binding at
D1 and D2 sites. Halogenation of predicentrine led to strong increases in affinity for D1-like receptors, while the affinities for D2-like
receptors were either practically unchanged or reduced three- to fourfold. Halogenated glaucine derivatives did not show any clear
trend towards enhanced selectivity, and the affinities were poor and similar to or worse than the values previously recorded for glau-
cine itself. Together with earlier work on boldine derivatives, these results suggest that the 2-hydroxy group on the aporphine skel-
eton may determine a binding mode favoring D1-like over D2-like receptors, with enhanced affinity when the C-3 position is
halogenated.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
the previous classification into D1 (or D1-like) and D2
(or D2-like) receptors, positively or negatively coupled
to AC, is still widely used in preliminary studies.
Early pharmacological studies carried out on dopamine
(DA) receptors enabled these to be classified into two
major groups: D1, which activate the enzyme adenylate
cyclase (AC), and D2, which do not activate this enzyme
and were later shown to decrease its activity.1,2 Until
now, however, a total of five different molecular forms
of DA receptors have been described, originally based
on cloning studies. Cloned DA receptors include the
ꢀD1-likeꢁ D1 and D5, and the ꢀD2-likeꢁ D2 (which is ex-
pressed in a long and a short form), D3 and D4.3–8 In
spite of this diversity, and of the fact that alternative
transduction mechanisms have been demonstrated,9
Dopaminergic neurotransmission is intimately bound to
the physiopathology and treatment of neuropsychiatric
disorders, in particular schizophrenia and Parkinsonꢁs
disease (PD). For example, the discovery that L-DOPA
can alleviate the symptoms of patients with PD has been
an incentive for the search for many years of molecules
with similar pharmacological properties, that is, which
could afford similar benefits to those achieved with L-
DOPA. While attention was initially focussed on D2
receptor agonists, the pharmacology of D1 receptors
had been somewhat neglected, in part due to the lack
of specific ligands. This situation has been partly re-
verted with the discovery of the paradigmatic 1-phen-
ylbenzazepine antagonist SCH-23390 (1),10,11 and the
D1-selective tetracyclic agonists dihydrexidine (2) and
(S)-dinapsoline (3).12–14 These compounds have made
Keywords: Aporphines; Halogenated predicentrines; Halogenated gla-
ucines; Dopamine receptor affinities.
*
Corresponding author. Tel.: +56 2 271 3881; fax: +56 2 271 3888;
e-mail: bcassels@uchile.cl
z Deceased.
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.03.022

3700
M. Asencio et al. / Bioorg. Med. Chem. 13 (2005) 3699–3704
it possible to study the pharmacological effects on these
receptors and thus reconsider the potential use of D1
receptor agonists or antagonists in the treatment of neu-
ropsychiatric illnesses. Of particular current interest is
the blockade by such compounds of the reinstatement
of drug-seeking behaviour.15–17
OR
OH
H3CO
H3CO
H3CO
H3CO
H3CO
HO
N
N
H
H
OH
CH3
CH3
Cl
7 (glaucine: R = CH3)
6 (boldine)
12 (predicentrine: R = H)
H
Using radioligand displacement techniques ([3H]SCH
23390 for D1-like and [3H]raclopride for D2-like recep-
tors), the IC50 values of boldine for both major DA
receptor types were determined in rat striatal homoge-
nates and proved to be 0.4 lM for D1-like and 0.5 lM
for D2-like receptors, respectively. In similar experi-
ments, glaucine [(6aS)-1,2,9,10-tetramethoxyaporphine
(7)] showed 10-fold lower affinities for both major recep-
tor types. In vivo, both alkaloids elicited biochemical
and behavioural effects suggestive of DA receptor antag-
onism.22 In spite of the greater in vitro binding affinity
of boldine, its in vivo activities were weaker than those
of glaucine, which was interpreted as a result of its poor
access to the CNS, and can be related to its demonstra-
bly unfavourable pharmacokinetics.22,23
N
CH3
1 (SCH 23390)
OH
OH
HO
HO
H
H
H
N
N
H
H
3 (dinapsoline)
2 (dihydrexidine)
Among the diverse structural classes that have been
evaluated for dopaminergic activity, many are synthetic
and a few are natural aporphine alkaloids sharing the
5,6,6a,7-tetrahydro-4H-dibenzo[de,g]quinoline skeleton.18
The nonselective D1/D2 antagonist (6aS)-bulbocapnine
(4),19 the nonselective agonist (6aR)-apomorphine
(APO, 5)20 and some of its derivatives were among the
first pharmacological tools for the study of DA recep-
tors, and their use enabled the identification of a number
of structural features, which seem to affect their dopami-
nergic activities. Clinically, subcutaneous apomorphine
is used as an antiparkinsonian drug (Apokinonꢁ), and
a sublingual preparation has recently been marketed as
a treatment for male erectile dysfunction (Uprimaꢁ).
As halogenated boldine derivatives might be expected to
be more lipophilic and thus to have better absorption
and distribution properties, as well as being more stable
metabolically, several of these compounds were exam-
ined in the same in vitro binding models. These assays
showed that the affinities of 3-chloro- (8), 3-bromo-
(9), 3,8-dibromo- (10) and 3-iodoboldine (11) for D1-like
receptors are greater than that of boldine and rise with
the atomic number of the halogen, leading to significant
selectivity, especially for 3-bromo- and 3-iodoboldines.
In particular, 3-iodoboldine showed Ki values of 2 nM
for D1-like and 68 nM for D2-like receptors,
respectively.24
OH
O
H3CO
X
O
OH
OH
H3CO
HO
HO
H3CO
H
N
N
H
N
Y
CH3
CH3
H
CH3
8 (X = Cl; Y = H)
9 (X = Br; Y = H)
10 (X = Y = Br)
11 (X = I; Y = H)
4 (bulbocapnine)
5 (apomorphine)
A report on the ꢀneuroleptic-likeꢁ actions of bulbocap-
nine (4), its close (6aS) analogues corytuberine, boldine
(6) and glaucine (7),21 and the fact that boldine is readily
available in relatively large amounts prompted us to
study this alkaloid and some of its derivatives as dopa-
minergic ligands.
Since it has been suggested that a dysfunction of the D1
receptor may be involved in the negative symptoms and
cognitive deficits observed in schizophrenia, and the
antipsychotic potential of D1 antagonists remains insuf-
ficiently explored,25–27 and it has recently been reported

M. Asencio et al. / Bioorg. Med. Chem. 13 (2005) 3699–3704
3701
that blockade of this receptor reduces the liability of re-
lapse into drug-seeking behaviour,15–17 it seems legiti-
mate to search for new D1-selective dopaminergic
Binding affinities were determined in rat striatal mem-
branes by means of competition binding assays versus
[3H]SCH 23390 (D1-like) or [3H]raclopride (D2-like),
and are summarized in Table 1. Replacement of the C-
3 hydrogen atom of predicentrine by bromine (13) raised
the affinity of this alkaloid for the [3H]SCH 23390-la-
belled site 20-fold while iodine (15) raised it 50-fold,
but the affinity for the [3H]raclopride-labelled site was
only doubled at most. Bromination on both C-3 and
C-8 (14) had a less marked effect, and comparison of
the 3-bromoderivatives of either boldine or predicen-
trine (9 and 13, respectively) with their 3,8-dibromo
counterparts (10 and 14) revealed two- to threefold de-
creases in affinity for both major receptor types. Thus,
an additional halogen atom at C-8 does not contribute
to DA receptor binding and seems to be a hindrance.
The similarity of these trends in both boldine and predi-
centrine derivatives suggests analogous binding modes.
In the case of 3-iodopredicentrine (15, Ki = 6 nM),
although this compound does not bind D1-like receptors
quite as strongly as 3-iodoboldine (11, Ki = 2 nM), it at-
tains much greater selectivity (140-fold) over D2-like
receptors.
antagonists
mechanisms.
with
possibly
novel
transduction
Considering the marked trends towards greater affinity
and selectivity observed in the halogenated boldine ana-
logues, and assuming that more favourable pharmacoki-
netics might be achieved by O-methylation of one or
both of the hydroxyl groups, which can be glucuroni-
dated in vivo, boldine was converted into predicentrine
(12, with the usual numbering scheme for aporphines)
and glaucine (7). A number of halopredicentrine and
haloglaucine derivatives were prepared, and their affini-
ties for D1-like and D2-like striatal receptors were deter-
mined using the same protocols as previously published
for the halogenated boldine derivatives.24
2. Results and discussion
Boldine (6) was extracted from Peumus boldus bark
using a previously described method,28 and O-methyl-
ated with diazomethane to afford glaucine (7) and predi-
centrine (12).29 Predicentrine and glaucine were
halogenated by adding N-halosuccinimides (NXS,
X = Cl, Br or I) to solutions of the alkaloids in trifluoro-
acetic acid, following a similar procedure to that used
earlier for boldine.24 NXS (1 M equiv) led in each in-
stance to the formation of the 3-halo derivative, while
the same reagents in excess produced the 3,8-dichloro
or dibromo but not the diiodo derivatives. The regiose-
lectivity of the halogenations was confirmed by HMQC/
HMBC NMR experiments.
Unlike the cases of boldine and predicentrine deriva-
tives, halogenation of glaucine at C-3 or C-3 and C-8
does not lead consistently to increased affinity for either
major receptor type. Although 3-bromo- (18) and 3-iodo-
glaucine (20) show a slight trend towards D1 selectivity
without significant loss of affinity, the very weakly bind-
ing 3-chloro- (16), 3,8-dichloro- (17) and 3,8-dibromo-
glaucine (19) exhibit no selectivity or even somewhat
lower affinity at [3H]SCH 23390-labelled sites than at
those labelled with [3H]raclopride. These observations
suggest that in this family of compounds the presence
of a hydroxyl group at C-2 favours both affinity and
selectivity for D1-like receptors.
Table 1. Inhibition of [3H]SCH 23390 or [3H]raclopride binding to rat
striatal binding sites by halogenated 1,2,9,10-tetraoxygenated apor-
phine derivatives
It has been speculated in the case of the boldine deriva-
tives that substitution at C-3 with halogen atoms of
increasing size might favour hydrophobic interactions
with a complementary region in the D1-like receptor,
particularly in the case of iodine, although enhanced
aromatic stacking interactions and some distortion of
the tetrahydropyridine ring might also increase receptor
binding.24 This now seems to be confirmed by the in-
crease in the D1 binding affinity for the halogenated
predicentrines. A systematic study of D1 receptor antago-
nism by ring D-substituted 11-hydroxyaporphines car-
ried out over a decade ago in the Lilly Research
Laboratories did not bring to light any analogues rival-
ing the affinity of 3-haloboldines or halopredicentrines
for these sites.30 The suggestion by the Lilly team that
a hydroxyl group at C-11 ꢀis critical for imparting affin-
ity for the D-1 receptorꢁ does not hold for our
compounds, and may be an indication that 2- and 11-
hydroxyaporphines bind to this receptor in different ori-
entations. An additional argument favouring this
hypothesis is the suggestion by Neumeyer and co-work-
ers, also based on 11-hydroxy compounds, that a hydr-
oxyl group at C-2 decreases aporphine affinity for
dopamine receptors,31,32 instead of increasing it as seen
when the boldine and predicentrine derivatives are
Compounds
Ki (nM) on specific binding
D2/D1 ratio
[3H]SCH 23390
[3H]raclopride
6
294a
2868a
60b
366a
2,831a
507b
739b
1345b
68b
1.2
1.0
8.5
15
7
8
9
49b
10
11
12
13
14
15
16
17
18
19
20
152b
2b
8.8
34
243
15
761
613
3.1
41
36
6
866
831
24
139
0.9
0.3
4.5
0.3
2.1
8566
27,794
522
7423
7958
2359
10,405
4514
35,074
2110
IC50 values were obtained from concentration–response curves with
n = 4 at each concentration using ORIGIN 5.0, and Ki values were cal-
culated using the Cheng and Prusoff equation,33 with KD(SCH 23390)
0.7 nM,34 and KD(raclopride) = 1.2 nM.35
a Data from Ref. 22.
=
b Data from Ref. 24.

3702
M. Asencio et al. / Bioorg. Med. Chem. 13 (2005) 3699–3704
compared with the C-2-methoxylated, C-3 or C-3/C-8
halogenated glaucines. Furthermore, our compounds
seem to be relatively insensitive to structural modifica-
tion on the C-11-unsubstituted ring D.
ascorbic acid (Tris–ions buffer), and the suspension
was treated as described above.
4.2. Radioligand binding assays
Although additional synthetic work is clearly necessary,
together with more detailed studies on their pharmaco-
logical actions, we postulate that 2-hydroxyaporphines
bearing a hydrophobic substituent at C-3 may represent
a template for the development of novel, potent D1-like
dopaminergic ligands showing good selectivity as far as
D2-like receptors are concerned. Future research should
determine if such compounds may prove useful for the
discovery of novel inhibitors of the reinstatement of
drug-seeking behaviour or of a new series of atypical
antipsychotics with reduced adverse effects.
For [3H]SCH 23390 binding experiments, a 100 lL ali-
quot of freshly prepared striatal membrane suspension
(100 lg of protein) was incubated for 1 h at 25 ꢂC with
100 lL of Tris buffer containing [3H]SCH 23390
(0.25 nM final concentration) and 800 lL of Tris–Mg
buffer containing the required drugs. Nonspecific bind-
ing was determined in the presence of 30 lM SK&F
38393 and represented around 2–3% of total binding.
For [3H]raclopride binding experiments, a 200 lL ali-
quot of freshly prepared striatal membrane suspension
(200 lg of protein) was incubated for 1 h at 25 ꢂC with
200 lL of Tris–ions buffer containing [3H]raclopride
(0.5 nM final concentration) and 400 lL of Tris–ions
buffer containing the drug being investigated. Nonspe-
cific binding was determined in the presence of 50 lM
apomorphine and represented ꢀ5–7% of total binding.
In both cases, incubations were stopped by addition of
3 mL of ice-cold buffer (Tris–Mg buffer or Tris–ions buf-
fer, as appropriate) followed by rapid filtration through
Whatman GF/B filters. Tubes were rinsed with 3 mL of
ice-cold buffer. After the filters had been dried, radioac-
tivity was counted in 4 mL BCS scintillation liquid at an
efficiency of 45%. Filter blanks corresponded to approxi-
mately 0.5% of total binding and were not modified by
the drugs.
3. Conclusions
Our results demonstrate that the aporphine skeleton is a
fruitful scaffold for the construction of potent dopamine
receptor ligands with selectivity for D1/D5 over D2-like
receptors. Specifically, introduction of a halogen atom
at C-3 of predicentrine [(6aS)-2-hydroxy-1,9,10-trimeth-
oxyaporphine] results in compounds that bind to D1-like
receptors with low nanomolar affinities, and up to 140
times better than their binding affinities for D2-like
receptors. These results are in contrast with earlier work
indicating that 2,11-dihydroxyaporphines show weak
affinity for dopamine receptors, and suggest that 2-hydr-
oxy- and 11-hydroxyaporphines may interact with
them in different orientations. Considering that the par-
ent (6aS)-aporphines boldine (6) and glaucine (7) block
dopamine receptors in vivo, the close structural congen-
ers described here, particularly 13 and 15, may be inter-
esting leads for the development of useful drugs acting
via dopamine receptor antagonism.
4.3. General chemical procedures
Melting points were determined on a Reichert–Jung
Galen III Kofler hot stage. Optical rotations were deter-
mined with a Schmidt–Haensch Polartronic electronic
polarimeter. NMR spectra were recorded in CDCl3
using a Bruker AMX 300 instrument, operating at
300.13 MHz (1H) or 75.48 MHz (13C). Assignments
were confirmed by HMQC and HMBC NMR experi-
ments carried out using the standard Bruker software,
inv4gstp and inv4gslplrnd, respectively. Electron impact
mass spectra (70 eV) were recorded with a Hewlett–
Packard Mass Spectra Acta 5973 instrument.
4. Experimental
4.1. Binding assays: materials
[3H]SCH 23390 and [3H]raclopride were purchased from
New England Nuclear. Binding experiments were per-
formed on Wistar rat (Charles River, France) striatal
membranes. Each striatum was homogenized in 2 mL
of ice-cold Tris–HCl buffer (50 mM, pH = 7.4 at
22 ꢂC) with a Polytron (4 s, maximal scale) and immedi-
ately diluted with Tris buffer. The homogenate was cen-
trifuged either twice ([3H]SCH 23390 binding
experiments) or four times ([3H]raclopride binding
experiments) at 20,000g for 10 min at 4 ꢂC with resus-
pension in the same volume of Tris buffer between cen-
trifugations. For [3H]SCH 23390 binding experiments,
the final pellet was resuspended in Tris buffer containing
5 mM MgSO4, 0.5 mM EDTA, and 0.02% ascorbic acid
(Tris–Mg buffer), and the suspension was briefly soni-
cated and diluted to a protein concentration of 1 mg/
mL. For [3H]raclopride binding experiments, the final
pellet was resuspended in Tris buffer containing
120 mM NaCl, 5 mM KCl, 1 mM CaCl2 and 0.1%
4.4. Preparation of predicentrine (12) and glaucine (7)
Boldine (6), isolated from Peumus boldus (boldo) bark
and crystallized in CHCl3 as the 1:1 complex with this
solvent, was methylated with diazomethane in MeOH–
Et2O and the higher Rf products (7 and 12) were sepa-
rated from unreacted boldine and isolated by column
chromatography on silica gel 60 (Merck), eluting with
EtOAc–MeOH 9:1.29
4.5. General halogenation procedure
A solution of the appropriate aporphine (7 or 12) (1 g)
in TFA (20 mL) was treated with N-halosuccinimide (1
or 2 M equiv depending upon whether the mono- or
dihalogenated product was desired) at room tempera-
ture (20 ꢂC). After 2 h stirring, the mixture was poured
into cold water (100 mL), the aqueous solution was

M. Asencio et al. / Bioorg. Med. Chem. 13 (2005) 3699–3704
3703
adjusted to pH 8–9 with concd NH3, extracted with
CHCl3 (5 · 50 mL) and subjected to column chromato-
graphy on silica gel 60 (Merck), eluting with EtOAc to
isolate the halogenated derivatives. The yields, melting
points, 1H NMR, mass spectral data and elemental anal-
yses are presented below.
4.5.6. 3-Bromoglaucine (18). Obtained in 58% yield; hyd-
robromide (H2O) mp > 225 ꢂC (decomp.); base
18
1
½aꢁ +127 (c 0.3, EtOH); H NMR d 2.49 (3H, s, N–
D
CH3), 3.68 (3H, s, 1-O-CH3), 3.87 (3H, s, 2-O-CH3),
3.89 (3H, s, 9-O-CH3), 3.89 (3H, s, 10-O-CH3), 6.74
(1H, s, 8-H), 7.90 (1H, s, 11-H); MS m/z (rel. abund.
%) 435 (87)/433 (89) (M)+ꢀ, 434 (100)/432 (90)
(MꢂH)+, 420 (54)/418 (60) (MꢂCH3)+, 404 (32)/402
(30) (MꢂOCH3)+, 392 (1)/390 (16) (MꢂCH3N@CH2)+ꢀ,
354 (45) (MꢂBr)+. Anal. Calcd for C21H24BrNO4ÆHBrÆ
H2O: C, 47.30; H, 5.10; N, 2.63. Found: C, 47.45; H,
5.39; N, 2.57.
4.5.1. 3-Bromopredicentrine (13). Obtained in 55% yield;
hydrobromide (H2O) mp 192–193 ꢂC (decomp.); base
18
D
1
½aꢁ +109 (c 0.60, EtOH); H NMR d 2.54 (3H, s, N–
CH3), 3.63 (3H, s, 1-O-CH3), 3.90 (3H, s, 10-O-CH3),
3.93 (3H, s, 9-O-CH3), 6.79 (1H, s, 8-H), 7.89 (1H, s,
11-H); MS m/z (rel. abund. %) 421 (79)/419 (81) (M)+ꢀ,
420 (100)/418 (87) (MꢂH)+, 406 (50)/404 (52) (MꢂCH3)+,
390 (32)/388 (29) (MꢂOCH3)+, 379 (15)/377 (16)
(MꢂCH3N@CH2)+ꢀ, 340 (26) (MꢂBr)+. Anal. Calcd
for C20H22BrNO4ÆHBrÆ0.5H2O: C, 47.08; H, 4.74; N,
2.75. Found: C, 46.85; H, 5.17; N, 2.67.
4.5.7. 3,8-Dibromoglaucine (19). Obtained in 47% yield;
(hydrobromide) mp 203–205 ꢂC (H2O/i-PrOH); base
18
D
1
½aꢁ +155 (c 0.3, EtOH); H NMR d 2.57 (3H, s, N–
CH3), 3.71 (3H, s, 1-O-CH3), 3.91 (3H, s, 2-O-CH3),
3.92 (3H, s, 9-O-CH3), 3.94 (3H, s, 10-O-CH3), 7.93
(1H, s, 11-H); MS m/z (rel. abund. %) 515 (44)/513
(79)/511 (44) (M)+ꢀ, 514 (61)/512 (100)/510 (51)
(MꢂH)+, 500 (22)/498 (44)/496 (20) (MꢂCH3)+, 484
(13)/482 (24)/480 (13) (MꢂOCH3)+, 472 (9)/470 (20)/
468 (16) (MꢂCH3N@CH2)+ꢀ, 434 (48)/432 (50)
(MꢂBr)+. Anal. Calcd for C21H23Br2NO4ÆHBrÆ
0.5H2OÆ0.5C3H8O: C, 43.15; H, 4.94; N, 2.29. Found:
C, 43.21; H, 4.50; N, 2.42.
4.5.2. 3,8-Dibromopredicentrine (14). Obtained in 24%
18
D
yield; base mp 189–190 ꢂC (EtOH); ½aꢁ +127 (c 0.25,
1
CHCl3); H NMR d 2.58 (3H, s, N–CH3), 3.62 (3H, s,
1-O-CH3), 3.90 (3H, s, 9-O-CH3), 3.92 (3H, s, 10-O-
CH3), 7.92 (1H, s, 11-H); MS m/z (rel. abund. %) 501
(35)/499 (74)/497 (38) (M)+ꢀ, 500 (58)/498 (100)/496
(49) (MꢂH)+, 486 (14)/484 (34)/482 (20) (MꢂCH3)+,
470 (10)/468 (20)/466 (14) (MꢂOCH3)+, 458 (6)/456
(13)/454 (11) (MꢂCH3N@CH2)+ꢀ, 420 (26)/418 (27)
(MꢂBr)+. Anal. Calcd for C20H21Br2NO4ÆHClÆ3H2O:
C, 40.74; H, 4.79; N, 2.38. Found: C, 40.45; H, 4.18;
N, 2.42.
4.5.8. 3-Iodoglaucine (20). Obtained in 26% yield; hydro-
1
chloride (H2O) mp 160–162 ꢂC; H NMR d 2.56 (3H, s,
N–CH3), 3.72 (3H, s, 1-O-CH3), 3.92 (3H, s, 2-O-CH3),
3.93 (3H, s, 9-O-CH3), 3.93 (3H, s, 10-O-CH3), 6.78 (1H,
s, 8-H), 7.94 (1H, s, 11-H); MS m/z (rel. abund. %) 481
(100) (M)+ꢀ, 480 (83) (MꢂH)+, 466 (53) (MꢂCH3)+, 450
(27) (MꢂOCH3)+, 438 (10) (MꢂCH3N@CH2)+ꢀ, 354
(24) (MꢂI)+. Anal. Calcd for C21H24INO4ÆHClÆ5.5H2O:
C, 40.89; H, 5.88; N, 2.27. Found: C, 40.32; H, 5. 57; N,
2.27.
4.5.3. 3-Iodopredicentrine (15). Obtained in 49% yield;
hydrochloride (H2O) mp > 225 ꢂC; 1H NMR d 2.57
(3H, s, N–CH3), 3.61 (3H, s, 1-O-CH3), 3.91 (3H, s, 9-
O-CH3), 3.94 (3H, s, 10-O-CH3), 6.79 (1H, s, 8-H),
7.90 (1H, s, 11-H); MS m/z (rel. abund. %) 467 (100)
(M)+ꢀ, 466 (90) (MꢂH)+, 452 (41) (MꢂCH3)+, 436 (27)
(MꢂOCH3)+, 425 (MꢂH3N@CH2)+ꢀ, 340 (22) (MꢂI)+.
Anal. Calcd for C20H22INO4ÆHClÆ1.5H2O: C, 45.26; H,
4.94; N, 2.64. Found: C, 45.07; H, 5.26; N, 2.65.
Acknowledgements
This research was funded by the Presidential Chair in
Science (B.K.C., Chile, 1996), and by ICM grant No.
P99-031-F. An exchange program between France and
Chile (ECOS/CONICYT) and scholarships to M.A.
from CONICYT and the French Embassy made this
work possible. The principal author is grateful to the
Alexander von Humboldt Foundation (Germany) for
a generous donation of equipment.
4.5.4. 3-Chloroglaucine (16). Obtained in 24% yield; base
18
D
1
(i-PrOH) mp 121–122 ꢂC; ½aꢁ +111 (c 0.6, CHCl3); H
NMR d 2.56 (3H, s, N–CH3), 3.73 (3H, s, 1-O-CH3),
3.90 (3H, s, 9-O-CH3), 3.93 (3H, s, 2-O-CH3), 3.95
(3H, s, 10-O-CH3), 6.78 (1H, s, 8-H), 7.97 (1H, s,
11H); MS m/z (rel. abund. %) 391 (32)/389 (98) (M)+ꢀ,
390 (50)/388 (100) (MꢂH)+, 376 (22)/374 (58) (41)
(MꢂCH3)+, 360 (12)/358 (58) (MꢂOCH3)+, 354 (30)
(MꢂCl)+, 331 (13) (MꢂCH3N@CH2)+ꢀ.
References and notes
1. Kebabian, J. W.; Calne, D. B. Nature 1979, 277, 93.
2. Stoof, J. C.; Kebabian, J. W. Life Sci. 1984, 35, 2281.
3. Bunzow, J. R.; Van Tol, H. H. M.; Grandy, D. K.; Albert,
P.; Salon, J.; Christie, M.; Machida, C. A.; Neve, K. A.;
Civelli, O. Nature 1988, 336, 783.
4. Giros, B.; Sokoloff, P.; Martres, M.-P.; Riou, J.-F.;
Emorine, L.-J.; Schwartz, J.-C. Nature 1989, 342, 923.
5. Dearry, A.; Gingrich, J. A.; Falardeau, P.; Fremeau, R.
T., Jr.; Bates, M. D.; Caron, M. G. Nature 1990, 347, 72.
6. Sokoloff, P.; Giros, B.; Martres, M.-P.; Bouthenet, M.-L.;
Schwartz, J.-C. Nature 1990, 347, 146.
4.5.5. 3,8-Dichloroglaucine (17). Obtained in 27% yield;
18
D
hydrochloride (Et2O) mp 205–206 ꢂC; base ½aꢁ +129
1
(c 0.2, AcOEt); H NMR d 2.50 (3H, s, N–CH3), 3.65
(3H, s, 1-O-CH3), 3.85 (3H, s, 2-O-CH3), 3.86 (3H, s,
9-O-CH3), 3.88 (3H, s, 10-O-CH3), 7.83 (1H, s, 11-H);
MS m/z (rel. abund. %) 427 (12)/425 (62)/423 (89)
(M)+ꢀ, 426 (25)/424 (84)/422 (100) (MꢂH)+, 412 (7)/
410 (38)/408 (59) (MꢂCH3)+, 396 (4)/394 (21)/392 (31)
(MꢂOCH3)+, 390 (20)/388 (53) (MꢂCl)+, 384 (28)/382
(17)/380 (28) (MꢂCH3N@CH2)+ꢀ.

3704
M. Asencio et al. / Bioorg. Med. Chem. 13 (2005) 3699–3704
7. Van Tol, H. H. M.; Bunzow, R. R.; Guan, H. C.;
Sunahara, R. K.; Seeman, P.; Niznik, H. B.; Civelli, O.
Nature 1991, 350, 610.
20. Goldman, M. E.; Kebabian, J. W. Mol. Pharmacol. 1984,
25, 18.
´
21. Zetler, G. Arch. Int. Pharmacodyn. Ther. 1988, 296,
8. Sunahara, R. K.; Guan, H. C.; OꢁDowd, B. F.; Seeman,
P.; Laurier, L. G.; Ng, G.; George, S. R.; Torchia, J.; Van
Tol, H. H. M.; Niznik, H. B. Nature 1991, 350, 614.
9. Kilts, J. D.; Connery, H. S.; Arrington, W. G.; Lewis, M.
M.; Lawler, C. P.; Oxford, G. S.; OꢁMalley, K. L.; Todd,
R. D.; Blake, B. L.; Nichols, D. E.; Mailman, R. B. J.
Pharmacol. Exp. Ther. 2002, 301, 1179.
255.
22. Asencio, M.; Delaquerriere, B.; Cassels, B. K.; Speisky,
`
H.; Comoy, E.; Protais, P. Pharmacol. Biochem. Behav.
1999, 62, 7.
´
23. Jimenez, I.; Speisky, H. Phytother. Res. 2000, 14, 254.
24. Sobarzo-Sanchez, E. M.; Arbaoui, J.; Protais, P.; Cassels,
´
B. K. J. Nat. Prod. 2000, 63, 480.
10. Billard, W.; Ruperto, V.; Crosby, G.; Iorio, L. C.; Barnett,
A. Life Sci. 1984, 35, 1885.
11. OꢁBoyle, K. M.; Waddington, J. L. Eur. J. Pharmacol.
1984, 98, 433.
25. Okubo, Y.; Suhara, T.; Suzuki, K.; Kobayashi, K.; Inoue,
O.; Terasaki, O.; Someya, Y.; Sassa, T.; Sudo, Y.;
Matsushima, E.; Iyo, M.; Tateno, Y.; Toru, M. Nature
1997, 385, 634.
12. Ghosh, D.; Snyder, S. E.; Watts, V. J.; Mailman, R. B.;
Nichols, D. E. J. Med. Chem. 1996, 39, 549.
13. Doll, M. K.-H.; Nichols, D. E.; Kilts, J. D.; Prioleau, C.;
Lawler, C. P.; Lewis, M. M.; Mailman, R. B. J. Med.
Chem. 1999, 42, 935.
14. Sit, S.-Y.; Xie, K.; Jacutin-Porte, S.; Taber, M. T.;
Gulwadi, A. G.; Korpinen, C. D.; Burris, K. D.; Molski,
T. F.; Ryan, E.; Xu, C.; Wong, H.; Zhu, J.; Krishnanan-
than, S.; Gao, Q.; Verdoorn, T.; Johnson, G. J. Med.
Chem. 2002, 45, 3660.
26. Peacock, L.; Gerlach, J. Biol. Psychiat. 2001, 50, 501.
27. Kapur, S.; McClelland, R. A.; VanderSpek, S. C.;
Wadenberg, M. L.; Baker, G.; Nobrega, J.; Zipursky, R.
B.; Seeman, P. Neuroreport 2002, 13, 831.
28. Speisky, H.; Cassels, B. K.; Lissi, E. A.; Videla, L. A.
Biochem. Pharmacol. 1991, 41, 1575.
29. (a) Tschesche, R.; Welzel, P.; Legler, G. Tetrahedron Lett.
1965, 445; (b) Asencio, M.; Cassels, B. K.; Speisky, H. Bol.
´
Soc. Chil. Quım. 1993, 38, 331.
30. Schaus, J. M.; Titus, R. D.; Foreman, M. M.; Mason, N.
R.; Truex, L. L. J. Med. Chem. 1990, 33, 600.
31. Neumeyer, J. L.; Reischig, D.; Arana, G. W.; Campbell,
A.; Baldessarini, R. J.; Kula, N. S.; Watling, K. J. J. Med.
Chem. 1983, 26, 516.
15. Eiler, W. J. A., II; Seyoum, R.; Foster, K. L.; Mailey, C.;
June, H. L. Synapse 2003, 48, 45.
16. Khroyan, T. V.; Platt, D. M.; Rowlett, J. K.; Spealman,
R. D. Psychopharmacol 2003, 168, 124.
17. Anderson, S. M.; Bari, A. A.; Pierce, R. C. Psychophar-
macol 2003, 168, 132.
32. Cox, R. F.; Neumeyer, J. L.; Waszczak, B. L. J.
Pharmacol. Exp. Ther. 1988, 247, 355.
18. Neumeyer, J. L.; Arana, G. W.; Ram, V. J.; Baldessarini,
R. J. In Dopamine Receptor Agonists; Carlsson, A.,
Nilsson, J. L. G., Eds.; Swedish Pharmaceutical: Stock-
holm, 1983; pp 11–24.
19. Miller, R. J.; Kelly, P. H.; Neumeyer, J. L. Eur. J.
Pharmacol. 1976, 35, 77.
33. Cheng, Y. C.; Prusoff, W. H. Biochem. Pharmacol. 1973,
22, 3099–3108.
34. Schulz, D. W.; Stanford, E. J.; Wyrick, S. W.; Mailman,
R. B. J. Neurochem. 1985, 45, 1601–1611.
¨
35. Kohler, C.; Hall, H.; Ogren, S. O.; Gawell, L. Biochem.
Pharmacol. 1985, 34, 2251–2259.