6-Methoxy-7-benzofuranoxy and 6-methoxy-7-indolyloxy analogues of 2-[2-(2,6-Dimethoxyphenoxy)ethyl]aminomethyl-1,4-benzodioxane (WB4101):1 Discovery of a potent and selective α1D-adrenoceptor antagonist

Article abstract of DOI:10.1021/jm400867d

Previous results have shown that replacement of one of the two o-methoxy groups at the phenoxy residue of the potent, but not subtype-selective, α₁-AR antagonist (S)-WB4101 [(S)-1] by phenyl, or by ortho,meta-fused cyclohexane, or especially by ortho,meta-fused benzene preferentially elicits α_1D-AR antagonist affinity. Such observations inspired the design of four new analogues of 1 bearing, in lieu of the 2,6-dimethoxyphenoxy residue, a 6-methoxy-substituted 7-benzofuranoxy or 7-indolyloxy group or, alternatively, their corresponding 2,3-dihydro form. Of these new compounds, which maintain, rigidified, the characteristic ortho heterodisubstituted phenoxy substructure of 1, the S enantiomer of the dihydrobenzofuranoxy derivative exhibited the highest α_1D-AR antagonist affinity (pA₂ 9.58) with significant α_1D/ α_1A and α_1D/α_1B selectivity. In addition, compared both to α_1D-AR antagonists structurally related to 1 and to the well-known α_1D-AR antagonist BMY7378, this derivative had modest 5-HT_1A affinity and neutral α₁-AR antagonist behavior.

Full text of DOI:10.1021/jm400867d

Article
pubs.acs.org/jmc
6‑Methoxy-7-benzofuranoxy and 6‑Methoxy-7-indolyloxy Analogues
of 2‑[2-(2,6-Dimethoxyphenoxy)ethyl]aminomethyl-1,4-
benzodioxane (WB4101):1 Discovery of a Potent and Selective α1D-
Adrenoceptor Antagonist
Laura Fumagalli,† Marco Pallavicini,† Roberta Budriesi,# Cristiano Bolchi,† Mara Canovi,‡
Alberto Chiarini,# Giuseppe Chiodini,† Marco Gobbi,‡ Paola Laurino,§ Matteo Micucci,#
Valentina Straniero,† and Ermanno Valoti*,†
†Dipartimento di Scienze Farmaceutiche, Universita
̀
̀
degli Studi di Milano, via Mangiagalli 25, I-20133, Milano, Italy
di Bologna, via Belmeloro 6, I-40126 Bologna, Italy
#Dipartimento di Scienze Farmaceutiche, Universita
‡IRCCS - Istituto di Ricerche Farmacologiche ‘Mario Negri’, via La Masa 19, I-20156 Milano, Italy
§Department of Biological Chemistry, Weizman Institute of Science, IL-76100, Rehovot, Israel
S
* Supporting Information
ABSTRACT: Previous results have shown that replacement
of one of the two o-methoxy groups at the phenoxy residue of
the potent, but not subtype-selective, α1-AR antagonist (S)-
WB4101 [(S)-1] by phenyl, or by ortho,meta-fused cyclo-
hexane, or especially by ortho,meta-fused benzene preferen-
tially elicits α1D-AR antagonist affinity. Such observations
inspired the design of four new analogues of 1 bearing, in lieu
of the 2,6-dimethoxyphenoxy residue, a 6-methoxy-substituted
7-benzofuranoxy or 7-indolyloxy group or, alternatively, their
corresponding 2,3-dihydro form. Of these new compounds,
which maintain, rigidified, the characteristic ortho hetero-
disubstituted phenoxy substructure of 1, the S enantiomer of
the dihydrobenzofuranoxy derivative exhibited the highest α1D-AR antagonist affinity (pA2 9.58) with significant α1D/α1A and
α1D/α1B selectivity. In addition, compared both to α1D-AR antagonists structurally related to 1 and to the well-known α1D-AR
antagonist BMY7378, this derivative had modest 5-HT1A affinity and neutral α1-AR antagonist behavior.
In the course of several years, we have studied more than 50
enatiomeric pairs of analogues of 1 modified at the amino-
alkyloxy chain,5 at the benzodioxane,6−8 at the phenoxy
residue,7,9−11 or at two of these three fragments,4,9 finding
the potent and very selective α1A-AR antagonist (S)-33 and,
recently, the very potent and remarkably selective α1B-AR
antagonist (S)-48 (Chart 1,Table 1). The latter was obtained by
introducing a methoxyl substituent at the 8 position of
benzodioxane of (S)-1, while the former was obtained by
replacing the benzodioxane and the 2,6-dimethoxyphenoxy
moiety of (S)-1 with tetrahydronaphthodioxane and 2-
methoxy-1-naphthoxyl, respectively. Furthermore, the only
replacement of 2,6-dimethoxyphenoxy by 2-methoxy-1-naph-
thoxy without modifying the benzodioxane nucleus resulted in
the impressively potent α1D-AR antagonist (S)-5, whose α1B
and α1A antagonist affinities are very high but significantly lower
than that at the α1D-AR (Chart 1, Table 1).4
INTRODUCTION
■
The availability of potent and selective antagonists for each of
the three α1 adrenoceptor (α1-AR) subtypes remains a
demanding challenge. A recent review on the functional
characterization of α1-AR subtypes laments the lack of reliable
α1B- and α1D-AR antagonists without questionable selectivity in
functional tests and with no affinity at receptors other than α1-
ARs, such as 5-HT1A and α2-AR.2 The unavailability of truly
selective α1B-AR agonists and antagonists hampers studies on
the function of α1B-AR, thus making necessary the use of
knockout technology, while to investigate the responses
mediated by α1D-AR, the only pharmacological tool seems to
be 2 (BMY 7378) (Chart 1), a molecule which dates back to
1995 and is an antagonist also at the 5-HT1A and α2C
receptors.3 On the other hand, an attractive candidate for
structural modifications aimed at maintaining one of the three
antagonist activities while depressing the two others remains
(S)-1 [(S)-WB4101] (Chart 1), a molecule exhibiting
subnanomolar antagonist affinities at all the three subtypes
and consisting of two distinct rigid substructures connected by
a relatively flexible five-atom linear chain.3
Received: April 16, 2013
Published: July 31, 2013
© 2013 American Chemical Society
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Chart 1. Structures of 2, 30, (S)-1, and α1-AR Subtype-Selective Antagonists Related to (S)-1
Table 1. Antagonist Affinities, Expressed as pA2, of (S)-1,
(S)-3, (S)-4, and (S)-5 at α1- and α2-Adrenoceptors on
Isolated Rat Tissues, Namely Prostate (α1A), Spleen (α1B),
Thoracic Aorta (α1D), and Prostatic Vas Deferens (α2)
Chart 2. Target Benzofuranoxy and Indolyloxy Analogues of
1
a
pA2
α1A
α1B
α1D
α2
thoracic prostatic vas
compd prostate spleen
aorta
deferens
6.92
affinity ratios
2.1 (α1A 1.9 (α1A/
(S)-1 9.49
(S)-3 7.98
(S)-4 8.55
(S)-5 8.96
9.17 9.20
/
α1B) α1D
)
<5
5.59
<5
954 (α1A
/
245 (α1A
α1D
/
α1B)
)
9.58 7.93
6.23
<5
11 (α1B/ 45 (α1B/
α1A α1D
)
)
dihydro-6-methoxy-7-benzofuranoxyl is a conformationally
constrained mimic of the 2,6-dimethoxyphenoxy residue of 1.
9.69 10.68
52 (α1D
α1A
/
10 (α1D
α1B)
/
)
a
Data are taken from refs 4 and 8. pA2 values (n = 5−7) were
CHEMISTRY
■
calculated from Schild plots. The ratio of the potency (EC50) of
(−)-noradrenaline (α1A and α1D), phenylephrine (α1B), and clonidine
(α2), in the presence of the antagonist and in its absence, was
measured.
(S)- and (R)-1, necessary in the binding and functional tests as
reference compounds, are accessible, as previously reported,
from different unichiral synthons, such as (S)-isopropylidene
glycerol,5 (R)- and (S)-1,4-benzodioxane-2-carboxylic
acid,12−14 and the respective methyl esters.12,15 The enan-
tiomers of 4 were synthesized by N-alkylation of 6-methoxy-7-
(2-aminoethoxy)benzofuran (18) with (R)- and (S)-2-
mesyloxymethyl-1,4-benzodioxane,7,16 while the enantiomers
of 7, 8, and 9 were synthesized by N-alkylation of (S)- and (R)-
2-aminomethyl-1,4-benzodioxane7,17 with 6-methoxy-7-(2-
mesyloxyethoxy)indole (26), 6-methoxy-7-(2-mesyloxye-
thoxy)-2,3-dihydrobenzofuran (20), and N-Cbz-6-methoxy-7-
(2-bromoethoxy)-2,3-dihydroindole (29), respectively (Scheme
1). The enantiomers of 6 and 8 were isolated as hydrochlorides,
those of 9 as dihydrochlorides, and those of 7 as free amines.
The synthesis of the benzofuran and dihydrobenzofuran
building blocks, namely 18 and 20, is illustrated in Scheme 2.
o,m-Dimethoxyphenol was reacted with ethyl chloroacetate to
give the phenoxyacetate 10, which was hydrolyzed to the
corresponding carboxylic acid 11 and then converted into the
phenoxyacetyl chloride 12. The subsequent intramolecular
Friedel−Crafts yielded 13, whose OH was etherified with ethyl
chloroacetate to obtain the acetate 14, which was reduced to
the corresponding alcohol 15 and then mesylated. The mesyl
ester 16 was converted into the azide 17 and reduced to 18
with hydrazine. Hydrogenation of the intermediate 15 provided
the 2,3-dihydrobenzofuran 19, which was transformed into the
mesylate 20.
The antagonist activity profile of (S)-5, discriminating α1D
relative to α1B- and α1A-ARs, focused our interest on the 2-
methoxy-1-naphthoxy group as a 2,6-dimethoxyphenoxy
substitute orienting to α1D antagonist affinity and prompted
us to optimize its interaction potential. Therefore, it seemed
proper to replace naphthalene with benzofuran or indole, which
are naphthalene isosteres and offer the additional chance of
disubstitution with heteroatoms at the benzene ring. In
particular, the substitution of the 2,6-dimethoxyphenoxy
portion of 1 with 6-methoxy-7-benzofuranoxy, compared to
that with 2-methoxy-1-naphthoxy, maintains the salient feature
of the 2-methoxy-1-naphthoxy derivative 5, that is the presence
of the o-methoxy-substituted aromatic bicycle but also the
phenoxy substructure ortho-disubstituted with two nonhydrox-
ylic HBA oxygens, which characterizes 1. This means that the
methoxybenzofuranoxy derivative 6 (Chart 2) is, at the same
time, an isostere of 5 and a rigidified analogue of 1.
Alternatively, the 6-methoxy-7-indolyloxy residue of compound
7 (Figure 2) is also isosteric to 2-methoxy-1-naphthoxy but the
two ortho heteroatoms of its phenoxy substructure, O and N,
have quite different character and interaction potential with the
binding site. To complete the investigation, it seemed
worthwhile to also consider the 2,3-dihydro-6-methoxy-7-
benzofuranoxy and 2,3-dihydro-6-methoxy-7-indolyloxy ana-
logues, 8 and 9, respectively (Chart 2), as we had contemplated
the 2-methoxytetrahydronaphthoxy derivative besides 5 in the
previous series of analogues of 14 and, moreover, because 2,3-
The synthesis of the indole and dihydroindole building
blocks, namely 26 and 29, is shown in Scheme 3. o,m-
Dimethoxybenzoic acid was converted into 6-methoxy-7-
hydroxyindole (24) in four steps according to slightly modified
literature procedures.18,19 The successive reaction with ethylene
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a
Scheme 1. Synthesis of the S Stereoisomers of Compounds 6−9
a
Reagents and conditions: (a) 2-Methylpropanol, 120 °C, 45 min, mw; (b) 3 N HCl/EtOH; (c) 2-methypropanol, 120 °C, 1 h, mw; (d) 2-
methylpropanol, 90 °C, 2 h, mw; (e) 3 N HCl/EtOH; (f) 2-methylpropanol, reflux, 18 h; (g) H2, Pd/C, MeOH, rt, 16 h; (h) 1.5 N HCl/EtOH.
a
Scheme 2. Synthesis of the Intermediates 18 and 19
a
Reagents and conditions: (a) Ethyl chloroacetate, NaH, THF/DMSO, rt, 15 h; (b) NaOH, MeOH, rt, 1 h; (c) oxalyl chloride, 60 °C, 1 h; (d)
AlCl3, dichloroethane, rt, 18 h, then 10% aqueous HCl; (e) potassium tert-butoxide, ethyl chloroacetate, THF/DMSO, rt, 4 h; (f) LiAlH4, THF,
reflux, 5 h; (g) MsCl, TEA, DCM, rt, 1 h; (h) NaN3, DMF/water, 90 °C, 1 h; (i) hydrazine hydrate, PdO, MeOH, reflux, 2 h; (j) H2, Pd/C, EtOH,
rt, 24 h.
a
Scheme 3. Synthesis of the Intermediates 26 and 29
a
Reagents and conditions: (a) DPPA, TEA, THF, EtOH, reflux, 4 h; (b) KOH, EtOH, water, reflux, 3 h; (c) BCl3, DCM, 0 °C then ClCH2CN,
dichloroethane, reflux, 3 h; (d) NaBH4, dioxane, 90 °C, 3 h; (e) ethylene carbonate, K2CO3, dioxane, 150 °C, 60 min mw; (f) MsCl, TEA, DCM, rt,
30 min; (g) H2, Pd/C, CH3COOH, rt, 16 h; (h) benzyl chloroformate, DCM, Py, 10 °C, 3 h; (i) 1,2-dibromoethane, NaH, THF/DMSO, reflux, 16
h.
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Table 2. Affinity Constants, Expressed as pKi (−log Ki, M) of (S)-1, (S)-5, and the Enantiomers of Compounds 6−9 for Cloned
Human α1-Adrenoceptor Subtypes and the 5-HT1A Receptor
a
b
pKi ( SE)
affinity ratios
compd group replacing 2,6-dimethoxyphenyl of 1
(S)-1
α1a
α1b
α1d
5-HT1A
α1a/α1b α1a/α1d α1a/5-HT1A
9.39 ( 0.06)
8.80 ( 0.09)
9.31 ( 0.02)
8.04 ( 0.07)
8.70 ( 0.03)
7.77 ( 0.05)
6.75 ( 0.04)
6.36 ( 0.05)
8.42 ( 0.09)
7.50 ( 0.05)
8.24 ( 0.04)
7.80 ( 0.07)
7.54 ( 0.12)
6.90 ( 0.06)
7.66 ( 0.01)
6.79 ( 0.05)
6.31 ( 0.11)
5.72 ( 0.13)
7.45 ( 0.8)
6.43 ( 0.09)
9.29 ( 0.11)
8.18 ( 0.13)
8.72 ( 0.14)
7.74 ( 0.09)
8.65 ( 0.10)
7.74 ( 0.08)
6.20 ( 0.10)
5.87 ( 0.10)
7.89 ( 0.10)
7.08 ( 0.04)
8.61 ( 0.04)
7.95 ( 0.06)
8.59 ( 0.08)
7.96 ( 0.15)
7.33 ( 0.07)
6.79 ( 0.08)
6.47 ( 0.09)
5.77 ( 0.18)
6.96 ( 0.07)
6.66 ( 0.11)
14.1
10.0
58.9
13.8
11.0
9.5
1.3
4.2
3.9
2.0
1.1
1.1
3.5
3.1
3.4
26.3
6.0
7.1
(S)-5
(S)-6
(R)-6
(S)-8
(R)-8
(S)-7
(R)-7
(S)-9
(R)-9
2-methoxy-1-naphthyl
6-methoxy-7-benzofuranyl
5.2
1.2
2,3-dihydro-6-methoxy-7-benzofuranyl
6-methoxy-7-indolyl
23.4
9.5
2.8
1.9
4.4
3.9
2,3-dihydro-6-methoxy-7-indolyl
9.3
28.8
6.9
11.7
a
b
Data of (S)-1 and (S)-3 are reported in ref 3. Antilog of ΔpKi.
Table 3. S Enantiomers of Compounds 6−9: Antagonist Affinities, Expressed as pA2, at α1A-, α1B-, α1D-AR on Isolated Rat
Tissues, and Inverse Agonism Expressed as Magnitude of Inhibition of Calcium-Induced Increase in the Resting Tension (IRT)
of Calcium-Depleted Guinea Pig Thoracic Aorta
a
pA2
α1A
α1B
α1D
α2
b
compd
prostate
prostatic vas deferens
spleen
thoracic aorta
prostatic vas deferens
inhibition of Ca2+-induced IRT (%)
(S)-6
(S)-8
(S)-7
(S)-9
8.71 ( 0.09)
7.88 ( 0.09)
7.88 ( 0.01)
8.44 ( 0.01)
8.26 ( 0.07)
7.47 ( 0.03)
8.31 ( 0.05)
8.03 ( 0.06)
8.68 ( 0.02)
8.49 ( 0.03)
7.77 ( 0.08)
9.08 ( 0.01)
9.01 ( 0.09)
9.58 ( 0.06)
8.52 ( 0.03)
8.62 ( 0.09)
6.55 ( 0.05)
6.63 ( 0.01)
6.09 ( 0.01)
6.05 ( 0.02)
0
0
25
100
a
pA2 values SE (n = 5−7) were calculated from Schild plots,23 constrained to a slope of −1.0, unless otherwise specified.24 pA2 is the positive value
of the intercept of the line derived by plotting log (DR-1) vs log[antagonist]. The log(DR-1) was calculated for least at three different antagonist
concentrations, and each was tested from three to five times. Dose-ratio (DR) values represent the ratio of the potency (EC50) of the agonist (α1A
and α1D: (−)-noradrenaline; α1B: phenylephrine; α2: clonidine) in the presence of the antagonist and in its absence. Parallelism of dose−response
b
curves was checked by linear regression, and the slopes were tested for significance (p < 0.05). Data are the percent decreases of the Ca2+ (1.8
mM)-induced IRT in the presence of the antagonist at 10 nM concentration, calculated assuming as a reference IRT the Ca2+ (1.8 mM)-induced
IRT in the absence of any agent. Data represent the mean SE from four to seven experiments.
carbonate gave the hydroxyethyl ether 25, which was mesylated
to 26. To prepare 29, the intermediate 24 was hydrogenated,
Cbz N-protected, and O-2-bromoethylated with dibromo-
ethane.
lower than that of (S)-1, though always less than by one pKi
unit at the α1-AR subtypes. Therefore, the selectivity profiles of
(S)-6 and (S)-8 substantially reproduce that of (S)-1 but with
more pronounced α1a versus α1b and α1d selectivity in the case
of (S)-6 and significantly improved α1a/5-HT1A and α1d/5-
HT1A selectivities in the case of (S)-8. Such a peculiarity of (S)-
8 becomes more evident in comparison with (S)-6 and (S)-5,
both conversely displaying 5-HT1A affinity closer to those at the
α1a- and α1d-AR. Another peculiarity distinguishes (S)-8 from
(S)-6 and (S)-5: its α1a/α1b/α1d selectivity profile is perfectly
superimposable to that of (S)-1, its α1d and α1a affinities being
nearly identical to each other as those of (S)-1, while both (S)-
6 and (S)-5 display lower affinity at α1d-AR than at α1a-AR.
Compared to (S)-6 and (S)-8, the N-analogues (S)-7 and
(S)-9 have modest and moderate affinities, respectively. In
particular, the dihydroindole derivative (S)-9 exhibits α1 and 5-
HT1A affinities a little lower than those of its dihydrobenzofur-
an analogue (S)-8, whereas a marked loss of affinity at all the
receptors is effected by the replacement of benzofuran with
indole as evidenced by comparing (S)-6 to (S)-7.
RESULTS AND DISCUSSION
■
Table 2 reports the binding affinities, expressed as pKi values
(−logKi, M), of the enantiomeric pairs of compounds 6−9 and,
as comparison terms, of (S)-1 and (S)-5 at the three cloned
human α1-AR subtypes and native 5-HT1A serotoninergic
receptor from rat hippocampus.
The affinities of the S enantiomers are always higher than
those of their antipodes, and the most considerable eudismic
indices are shown by 6, 8, and 9 at the three α1-AR subtypes.
A dividing line can be drawn between the benzofuran and
dihydrobenzofuran derivatives, (S)-6 and (S)-8, and the indole
and dihydroindole derivatives, (S)-7 and (S)-9, the former pair
exhibiting, at the four tested receptors, from high to moderate
affinities, always higher than those of the latter pair.
Furthermore, comparison of (S)-6 and (S)-8 with (S)-1
indicates that only the α1a- and the 5-HT1A affinities of (S)-6
are near to those of (S)-1, while the other affinity values are
In summary, the analysis of binding data indicates that
replacement of one of the two o-methoxy substituents of 1 with
benzo-condensed pyrrole or dihydropyrrole has a negative
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effect on the α1 and 5-HT1A affinities, which becomes severely
detrimental in particular when the 6-methoxy-7-indolyl residue
replaces, as in (S)-7, the 2,6-dimethoxyphenyl portion of (S)-1.
Quite different is the impact of furan and dihydrofuran benzo-
condensation, which allows the two ortho oxygens of (S)-1 to
be maintained: the affinities and the selectivity profiles of (S)-6
and (S)-8 are not so far from those of (S)-1 and (S)-5. This
notwithstanding, (S)-8 distinguishes itself from (S)-6, (S)-5,
and (S)-1 by its lower 5-HT1A affinity and from (S)-6 and (S)-5
by having identically high α1d and α1a affinities.
Table 4. Comparison of the Antagonists Affinities at α1-AR
Subtypes and of the Binding Affinity at the 5-HT1A Receptor
of (S)-6 and (S)-8, the Two New Benzofuranoxy Analogues
of 1, with Those of (S)-5, the Previously Reported
Naphthoxy Analogue of 1, and of the Literature α1D-AR
Antagonists 2 and 30
c
c
compd
α1A
α1B
α1D
α1D/α1A
α1D/α1B
5-HT1A
(S)-6
(S)-8
(S)-5
2
8.26
7.47
8.96
8.68
8.49
9.69
9.01
9.58
6
129
52
2
12
10
6
8.59
7.33
7.95
8.76
6.52
10.68
8.34
The functional assays were carried out only for the S
enantiomers. Their antagonist affinities at α1-AR subtypes and
α2-AR, expressed as pA2, are listed in Table 3. The blocking
activity was determined on different rat tissues: (a) by
antagonism of (−)-noradrenaline (NA)-induced contraction
of vas deferens prostatic portion (α1A-AR)20 and of thoracic
aorta (α1D-AR),21 (b) by antagonism to (−)-phenylephrine-
induced contraction of spleen (α1B-AR),21 (c) by antagonism to
clonidine-inhibited twitch responses of the field-stimulated
prostatic portion of vas deferens (α2-AR). Furthermore,
considering the demonstrated α1A-AR involvement in main-
taining prostate smooth muscle tone and the consequent
therapeutic potential of agents reducing the latter for LUTS,
the antagonist affinity was also evaluated in rat prostate.22
Inspection of the results reported in Table 3 reveals trends,
which can be summarized as follows: (a) all the compounds
exhibit high α1/α2 selectivity; (b) the α1 antagonist affinities are
always high (pA2 > 8) with the exception of the α1A antagonist
affinities of (S)-8 and (S)-7 and of the α1B antagonist affinity of
the latter; (c) the maximum antagonist activities (subnanomo-
lar pA2) are shown by the two benzofuran and dihydrobenzo-
furan derivatives, (S)-6 and (S)-8, at the α1D-AR and by the
dihydroindole derivative (S)-9 at the α1B-AR. The most
interesting behavior is that of the dihydrobenzofuran (S)-8,
which is a very potent (pA2 = 9.58) and significantly selective
(α1D/α1A = 50−130 and α1D/α1B = 12) α1D-AR antagonist.
Matching of binding with functional tests indicates
substantial divergences: all the α1B and α1D antagonist affinities
are higher than the respective α1b and α1d binding affinities,
while the α1A antagonist affinity, compared to the α1a binding
affinity, decreases in the benzofuran and dihydrobenzofuran
derivatives and increases in the two N-analogues. An analogous
behavior to benzofuran and dihydrobenzofuran (S)-6 and (S)-8
was exhibited by the 2-methoxy-1-naphthoxy derivative (S)-5,4
the α1B and α1D but not the α1A antagonist affinities of which
are remarkably higher than the corresponding binding affinities.
In Table 4, the α1D-AR selectivities of (S)-5, (S)-6, and (S)-8
resulting from such a trend are compared with those of two
literature α1D-AR selective antagonists, 30 (SNAP 8719)25
(Chart 1) and 2,3,26 which is commercially available. Also in
Table 4, the 5-HT1A binding affinities are reported. The
compound (S)-8 shows the highest α1D-AR antagonist affinity,
associated with intermediate α1D-AR selectivity between 2 and
30 and, similarly to the latter, with about 200-fold lower 5-
HT1A binding affinity.
a
a
a
6.94
7.55
6.7b
25
b
30
5.4
8.8b
2500
126
a
b
c
pA2 values taken from ref 26. pKB values taken from ref 25. Antilog
of ΔpA2 or of ΔpKB.
ortho mono- and disubstituted phenoxy analogues of WB4101
we have previously studied only for their binding affinity.10,11 In
fact, frequent discrepancies between binding and functional
tests have demonstrated poor prediction of activity by binding
tests making comparison of these compounds with those
hazardous. However, on the basis of the whole set of data that
we previously reported, we can reasonably state that ortho
disubstitution at the phenoxy moiety is strictly required for high
binding and antagonist α1-affinity probably because of
stabilization of a properly extended conformation of the
molecule and a properly oriented phenoxy moiety. The
involvement of the two ortho substituents both in intra-
molecular (H-bond between O and NH+ and/or hampered
rotation of phenoxyl) and binding interactions is conceivable.
Limiting the analysis to (S)-1 and to the analogues, whose α1-
AR antagonist activities we have determined,4 we notice that
from high to very high α1-AR antagonist activities are associated
with the o-dimethoxy substitution at the phenoxyl or,
alternatively, with the o-methoxy substitution combined with
the presence of an aromatic ring, fused at the ortho and meta
positions of phenoxyl or ortho linked, or of a heteroalicycle,
condensed at the same positions and with the heteroatom
superimposable on the oxygen of one of the two methoxy
groups of 1 (Figure 1). When this pattern of ortho-
disubstitution at the phenoxy residue was abandoned, as in
the 2-methoxyphenoxy analogues bearing a phenyl in meta or
in para position or in the 2-methoxytetrahydronaphthoxy
analogue,4 we observed a significant decrease or loss of
antagonist activity. Hence, provided the ortho-disubstitution at
the phenoxyl, the α1-AR subtype selectivity is then achieved by
modifying the benzodioxane portion. In particular, as shown in
Figure 1, the 8-methoxylation of benzodioxane of (S)-1 results
in a selective α1B-AR antagonist,8 while a selective α1A-AR
antagonist is obtained by fusing a cyclohexane ring at the 6 and
7 positions of the benzodioxane of (S)-5.4 On the other hand, a
significant α1D-AR selectivity is just shown by (S)-5, whose only
modification, with respect to (S)-1, is the replacement of one of
the two o-methoxy groups by a fused benzene ring.4 Moreover,
α1D-AR-oriented activities, though with lower subtype
selectivity, was also found for the analogues of (S)-1 in which
2,6-dimethoxyphenoxyl is replaced by 2-methoxy-5,6,7,8-
tetrahydronaphthoxyl or 2-methoxy-6-phenylphenoxyl.4 These
data indicate that the mere presence of an additional ring ortho-
linked to phenoxyl or ortho-meta fused to it benefits the α1D-
AR antagonist activity, and such a suggestion is confirmed by
the activity profile of the present compounds (Figure 1). These
exhibit high and generally prevalent α1D-AR antagonist activity
As previously for 1 and some of its derivatives and by the
same semiquantitative assay, we verified if these antagonists
behave as inverse agonists.4,8 The results, reported in Table 3,
indicate that (S)-6 and (S)-8 are neutral antagonists, thus
differentiating them from (S)-7 and (S)-9 but also from (S)-1
and (S)-5.
SAR analysis of these activity data would require the
knowledge of the antagonist affinities of the wide number of
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Figure 1. SAR milestones in the optimization of the hit compound (S)-1.
independently from the aromatic or nonaromatic nature of the
heterocycle fused at the 5 and 6 positions of the 2-
methoxyphenoxyl and from the HBA properties of its
heteroatom (cf., benzofuran oxygen and indole nitrogen). In
this set of α1D-AR antagonists, the highest activity and the
maximum α1D selectivity of (S)-8 would be due to the fact that
only 6-methoxydihydrobenzofuran, among all the methoxylated
bicycle systems replacing 2,6-dimethoxyphenoxyl and prefer-
entially increasing the α1D antagonist affinity, is a properly
rigidified analogue of this portion of 1, maintaining its
electronic features and interaction potential unchanged.
challenge is to have a deeper insight into the alternating nature
between inverse agonism and neutral antagonism of these
molecules, a dualism which should be reconsidered because the
present-day concept of pharmacological efficacy at seven-
transmembrane receptors is that all ligands with affinity have
some form of efficacy and modify the receptor behavior.27
According to these new models, the effects of both agonists and
antagonists depend on their preferential interactions with, and
stabilization of, a particular conformational state of the
receptor, out of the different states the receptor may assume
depending on the biological system. Thus, the discrepancies
observed in this and previous studies4,8 are not surprising,
taking into account that, with binding assays, we are measuring
the compound’s affinity for the antagonist binding site on
recombinant α1-AR overexpressed in CHO cells, whereas
functional assays provide the compound’s potency in
preventing a specific agonist-induced effect in native tissues.
CONCLUSION
■
We identified an analogue of 1, (S)-8, which is a potent and
selective α1D-AR antagonist. Such a subtype selectivity was
achieved simply by rigidifying the 2,6-dimethoxyphenoxyl
substructure in the 2,3-dihydro-6-methoxy-7-benzofuranoxy
system of (S)-8. In a lower degree, α1D selectivity is also
shown by the methoxybenzofuranoxy and methoxyindolyloxy
analogues, (S)-6 and (S)-7. Furthermore, (S)-8 stands out for
being a neutral antagonist and having modest 5-HT1A binding
affinity, markedly lower than that of (S)-6 and the 2-
methoxynaphthoxy analogue (S)-5. Compared to 2, which is
reported as the most reliable α1D-AR antagonist and which acts
as an inverse agonist,2,3 and to 30, the most α1D-AR selective
antagonist,25 (S)-8 is significantly more potent and displays a
high α1D-AR selectivity, intermediate between those of 2 and
30.
EXPERIMENTAL SECTION
■
Chemistry. 1H NMR spectra were recorded, operating at 300 MHz
and 13C NMR at 75 MHz. Chemical shifts are given in parts per
million relative to residual solvent (CHCl3 or DMSO) as internal
standard. Optical rotations were determined by a Jasco P-1010
polarimeter. Melting points were measured on a Buchi melting point
apparatus and are uncorrected. Thermal analyses were performed on
2−5 mg samples in closed pans at 5 °C/min using a DSC 2010 (TA
Instruments). Elemental analyses (CHN) are within 0.40% of
theoretical values. Purifications were performed using KP-Sil 32−63
μm 60 Å cartridges and Merck silica gel (particle size 40−63 μm). The
results of elemental analyses indicated that the purity of all tested
compounds was higher than 95%.
Further advancements in the field of 2-aminomethyl-1,4-
benzodioxanes as α1-AR antagonists might include designing
new derivatives by replacing the 2,6-dimethoxyphenoxy moiety
with other aromatic heterobicyclic systems as well as by
hybridizing the most productive modification at the benzodiox-
ane substructure, namely replacement with tetrahydronaph-
thodioxane,4 with those at the phenoxy moiety such as the
here-described ortho-meta fusion with heterocycles. Moreover,
the moderate 5-HT1A selectivity of ortho monosubstituted
analogues of 1 we have previously observed in binding
experiments10 deserves further investigation and might be
matter for development of new 5-HT1A selective ligands.
However, at the present stage of our research, the major
Ethyl (2,3-Dimethoxyphenoxy)acetate (10). A solution of (2,3-
dimethoxy)phenol (16.95 mL, 130 mmol) in THF/DMSO (10 mL/
10 mL) was added dropwise to a suspension of NaH (3.26 g, 136
mmol) in THF/DMSO (10 mL/10 mL) under nitrogen atmosphere
at 0 °C. After 30 min, ethyl chloroacetate (15.4 mL, 143 mmol) was
added dropwise. The reaction mixture was stirred at room temperature
for 15 h and then quenched in a cooled solution of 10% HCl (50 mL).
The aqueous layer was extracted with dichloromethane (3 × 30 mL).
The organic phases were combined, washed with water (2 × 50 mL),
dried, and concentrated to give 30.86 g (98.8%) of 10 as an orange oil:
1H NMR (CDCl3): δ 1.23 (t, 3H), 3.80 (s, 3H), 3.85 (s, 3H), 4.19 (q,
2H), 4.64 (s, 2H), 6.45 (d, 1H), 6.57 (d, 1H), 6.90 (dd, 1H).
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1
(2,3-Dimethoxyphenoxy)acetic Acid (11). A 10% NaOH
aqueous solution (300 mL) was added to a solution of 10 (30.86 g,
128 mmol) in methanol at 20 °C. After 1 h, methanol was removed
under vacuum, and the residue was treated with 10% HCl (100 mL)
and extracted with dichloromethane (3 × 30 mL). The organic phases
were combined, washed with water, dried, and concentrated to give
24.47 g (90.1%) of 11 as a white solid: mp 103.3 °C. 1H NMR
(CDCl3) δ 3.88 (s, 3H), 3.92 (s, 3H), 4.70 (s, 2H), 6.59 (d, 1H), 6.68
(d, 1H), 7.01 (t, 1H).
(100%) of 17 as an orange oil: H NMR (CDCl3) δ 3.61 (m, 2H),
3.91 (s, 3H), 4.44 (m, 2H), 6.69 (s, 1H), 6.92 (d, 1H), 7.21 (d, 1H),
7.54 (s, 1H).
6-Methoxy-7-(2-aminoethoxy)benzofuran (18). Hydrazine
hydrate (4.6 mL, 94.8 mmol) was added dropwise to a refluxing
mixture of 17 (2.21 g, 9.5 mmol) and PdO (50 mg) in methanol (20
mL). The reaction was refluxed for 2 h. After cooling at room
temperature, PdO was removed by filtration and the solvent
evaporated. The residue was treated with dichloromethane (20 mL)
and 10% HCl (45 mL). The aqueous layer was separated, washed with
dichloromethane three times, made alkaline (pH 12) with NaOH, and
extracted with ethyl acetate (4 × 20 mL). The organic phases were
combined, dried, and concentrated to give 1.33 g (67.9%) of 18 as a
(2,3-Dimethoxyphenoxy)acetyl Chloride (12). Oxalyl chloride
(97.3 mL, 1.15 mol) was added dropwise to 11 (24.47 g, 115 mmol) at
0 °C. The reaction mixture was heated at 60 °C for 1 h and then
1
concentrated to give 26.52 g (100%)of 12 as a yellow oil: H NMR
1
(CDCl3) δ 3.86 (s, 6H), 5.00 (s, 2H), 6.53 (d, 1H), 6.67 (d, 1H), 6.97
(t, 1H).
yellow oil: H NMR (CDCl3) δ 1.63 (s, 2H), 3.00 (t, 2H), 3.91 (s,
3H), 4.32 (t, 2H), 6.69 (s, 1H), 6.91 (d, 1H), 7.20 (d, 1H), 7.53 (s,
7-Hydroxy-6-methoxy-3-oxo-2,3-dihydrobenzofuran (13).
Under nitrogen, aluminum chloride (30.67 g, 230 mmol) was added
to a solution of 12 (26.52 g, 115 mmol) in dichloroethane (120 mL)
at 0 °C. The reaction mixture was stirred for 18 h at room temperature
and then quenched in cooled 10% HCl (200 mL). The suspension was
filtered, and the resultant solid crude product was crystallized from
methanol (110 mL) to give 11.60 g (53.4%) of 13 as a light yellow
1H).
6-Methoxy-7-(2-hydroxyethoxy)-2,3-dihydrobenzofuran
(19). Pd/C (5%, 1.4 g) was added to a solution of 15 (6.09 g, 29.3
mmol) in absolute ethanol (200 mL). The mixture was vigorously
shaken under hydrogen at room temperature for 24 h. Afterward, the
catalyst was removed by filtration and the filtrate concentrated to give
6.15 g (100%) of 19 as a yellow oil: 1H NMR (CDCl3) δ 3.12 (t, 2H),
3.72 (t, 2H), 3.83 (s, 3H), 4.19 (t, 2H), 4.60 (t, 2H), 6.40 (d, 1H),
6.80 (d, 1H).
6-Methoxy-7-(2-mesyloxyethoxy)-2,3-dihydrobenzofuran
(20). Obtained as a crude product from 19 (5.3 g, 25.2 mmol) as
described for 16. Crystallization from isopropyl ether/isopropyl
alcohol (9:1) gave pure 20 (5.8 g, 80%) as a white solid: H NMR
(CDCl3) δ 3.06 (s, 3H), 3.09 (t, 2H), 3.75 (s, 3H), 4.34 (t, 2H), 4.52
1
solid: mp 218.0 °C. H NMR (DMSO-d6) δ 3.88 (s, 3H), 4.74 (s,
2H), 6.81 (d, 1H), 7.08 (d, 1H), 9.29 (s, 1H, exchangeable with D2O).
Ethyl (6-Methoxy-3-oxo-2,3-dihydro-7-benzofuranoxy)-
acetate (14). Under nitrogen, a solution of potassium tert-butoxide
(8.67 g, 77.3 mmol) in anhydrous THF (75 mL) and DMSO (55 mL)
was added dropwise to 13 (11.6 g, 64.4 mmol), previously dissolved in
the same solvent mixture, at 0 °C. Subsequently, ethyl chloroacetate
(7.60 mL, 70.8 mmol) was added. The reaction mixture was stirred at
room temperature for 4 h. THF was removed under vacuum. The
residue was quenched in cooled 10% HCl (200 mL) and extracted
twice with dichloromethane (2 × 100 mL). The combined organic
phases were washed, in the following order, with 10% NaOH aqueous
solution (2 × 100 mL), 10% HCl (100 mL), and water (2 × 100 mL),
dried, and concentrated. The solid residue was crystallized from
ethanol to give 12.43 g (72.4%) of 14 as a light yellow solid: mp 83.3
°C. 1H NMR (CDCl3) δ 1.25 (t, 3H), 3.93 (s, 3H), 4.22 (q, 2H), 4.62
(s, 2H), 4.80 (s, 2H), 6.69 (d, 1H), 7.37 (d, 1H).
6-Methoxy-7-(2-hydroxyethoxy)benzofuran (15). Under ni-
trogen atmosphere at 0 °C, a solution of 14 (12.43 g, 46.7 mmol) in
anhydrous THF was added to a suspension of LiAlH4 (5.31 g, 140.1
mmol) in anydrous THF. The reaction mixture was refluxed for 5 h
and then cooled to 0 °C. A 10% HCl (20 mL) solution was added
dropwise, and then dichloromethane (50 mL) was added. The organic
phase was separated, washed with 10% HCl (2 × 100 mL) and with
brine (2 × 100 mL), dried, and concentrated to give a residue, which
was purified by flash chromatography on silica gel (eluent:
cyclohexane/ethyl acetate 80:20) to obtain 2.5 g (25.7%) of 15 as a
yellow oil: 1H NMR (CDCl3) δ 3.13 (s, 1 H, exchangeable with D2O),
3.81 (t, 2H), 3.93 (s, 3H), 4.39 (t, 2H), 6.71 (s, 1H), 6.92 (d, 1H),
7.24 (d, 1H), 7.55 (s, 1H).
6-Methoxy-7-(2-mesyloxyethoxy)benzofuran (16). Mesyl
chloride (0.93 mL, 12.0 mmol) was added dropwise to a solution of
15 (2.50 g, 12.0 mmol) and triethylamine (1.71 mL, 12.0 mmol) in
dichloromethane (20 mL) at 0 °C. The reaction mixture was stirred at
room temperature for 1 h, and then dichloromethane (30 mL) was
added. The resulting mixture was washed, in sequence, with 10% HCl
(3 × 40 mL) and with brine (2 × 40 mL). The organic phase was
separated, dried, and concentrated to give 2.87 g of crude product,
which was crystallized from isopropyl ether/isopropyl alcohol (6:1; 35
mL) to give 2.71 g (78.8%) of 16 as white solid: mp 51.6 °C. 1H NMR
(CDCl3) δ 3.14 (s, 3H), 3.91 (s, 3H), 4.60 (m, 4H), 6.71 (s, 1H), 6.91
(d, 1H), 7.23 (d, 1H) 7.54 (s, 1H).
6-Methoxy-7-(2-azidoethoxy)benzofuran (17). Sodium azide
(8.09 g, 123.1 mmol) was added to a solution of 16 (2.71g, 9.5 mmol)
in DMF/water (2:1, 75 mL). The reaction mixture was heated at 90
°C and, after 1 h, cooled to room temperature and extracted with
dichloromethane (3 × 20 mL). The organic phases were combined,
washed with brine (6 × 30 mL), dried, and concentrated to give 2.21 g
1
(t, 2H), 4.53 (t, 2H), 6.32 (d, 1H), 6.77 (d, 1H).
O-Ethyl N-(2,3-Dimethoxyphenyl)carbamate (21). Under
nitrogen atmosphere at 0 °C, a THF solution of diphenylphosphoryl
azide (19.6 mL, 90.8 mmol), ethanol (55 mL), and triethylamine (12.7
mL, 90.8 mmol) were added, in sequence, to a solution of 2,3-
dimethoxybenzoic acid (16.55 g, 90.8 mmol) in anhydrous THF. After
refluxing for 4 h, THF was removed and the residue was taken up by
ethyl acetate (100 mL), washed with 10% aqueous solution of Na2CO3
(2 × 100 mL) and with brine (2 × 100 mL), dried, and concentrated.
The resulting residue was purified by flash chromatography on silica
gel (eluent: cyclohexane/ethyl acetate; 9:1) to obtain 15.74 g (76.9%)
of 21 as a white solid: mp 45.1 °C. 1H NMR (CDCl3) δ 1.33 (t, 3H),
3.86 (s, 6H), 4.23 (q, 2H), 6.61 (d, 1H), 7.02 (t, 1H), 7.23 (m, 1H),
7.78 (m, 1H).
2,3-Dimethoxyaniline (22). A solution of compound 21 (15.74 g,
69.9 mmol) in ethanol was added to a suspension of KOH (11.76 g,
209.6 mmol) in ethanol (56 mL) and water (14 mL) at 10 °C. After
refluxing for 3 h, the solvent was evaporated and the resulting residue
was treated with dichloromethane (100 mL) and cooled 10% HCl
(100 mL). The aqueous layer was separated, washed with dichloro-
methane (2 × 50 mL), made alkaline with 30% NaOH, and then
extracted with dichloromethane (2 × 70 mL). The organic phases
were combined, washed with 10% NaOH (2 × 50 mL), brine (2 × 50
mL), dried and concentrated to give 10.64 g (99.4%) of 22 as a yellow
1
oil. H NMR (CDCl3) δ 3.82 (s, 6H), 6.35 (dd, 1H), 6.40 (dd, 1H),
6.85 (t, 1H).
2-Amino-3-hydroxy-4-methoxy-α-chloroacetophenone (23).
Under nitrogen atmosphere at 0 °C, a solution of 22 (10.64 g, 69.5
mmol) in dichloroethane (50 mL) was added dropwise to a 1 M
solution of BCl3 in dichloromethane (278 mL). Subsequently, a
solution of chloroacetonitrile (5.3 mL, 83.4 mmol) in dichloroethane
was added. After refluxing for 3 h, the reaction mixture was poured
into cooled phosphate buffer (18 g/L NaH2PO4, 72 g/L gNaHPO4),
and the separated aqueous layer was extracted with ethyl acetate (2 ×
200 mL). The combined organic phases were washed with phosphate
buffer (2 × 200 mL) and brine (2 × 200 mL), dried, and concentrated.
Flash chromatography on silica gel (eluent: cyclohexane/ethyl acetate;
8:2) of the resulting residue afforded 7.48 g (50%) of 23 as a yellow
1
solid: mp 122.0 °C. H NMR (CDCl3) δ 3.92 (s, 3H), 4.63 (s, 2H),
5.15 (br s, 1H), 6.31 (d, 1H), 7.24 (d, 1H).
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6-Methoxy-7-hydroxyindole (24). NaBH4 (1.80 g, 47.58 mmol)
was added to a solution of 23 (7.48 g, 29.7 mmol) in dioxane (150
mL) and water (15 mL) at 0 °C. The reaction mixture was heated at
90 °C for 3 h and then cooled to room temperature and concentrated.
The resulting residue was treated with cooled 10% HCl (100 mL) and
dichloromethane. The aqueous layer was separated and extracted with
dichloromethane (50 mL). The combined organic phases were washed
with 10% HCl (2 × 50 mL) and then with brine (50 mL) and dried.
to 0 °C. Aqueous HCl (10%, 15 mL) and diethyl ether (80 mL) were
added. The aqueous phase was separated and extracted with diethyl
ether (2 × 80 mL). The organic phases were combined, washed with
brine (2 × 70 mL), dried, and concentrated to give 3.87 g of crude
product, which was purified by flash chromatography on silica gel
(eluent cyclohexane/ethyl acetate, 9.1) to yield 2.22 g of 29 as a
colorless oil: H NMR (CDCl3) δ 2.93 (t, 2H), 3.48 (t, 2H), 3.83 (s,
3H), 4.10 (t, 2H), 4.31 (t, 2H), 5.23 (s, 2H), 6.60 (d, 1H), 6.84 (d,
1H), 7.31−7.44 (m, 5H).
1
1
Solvent removal afforded 3.20 g (66.4%) of 24 as a yellow oil: H
NMR (CDCl3) δ 3.94 (s, 3H), 5.72 (s, 1H), 6.47 (m, 1H), 6.85 (d,
1H), 7.13 (m, 2H), 8.24 (br s, 1H).
(S)-2-[((2-(6-Methoxy-7-benzofuranoxy)ethyl)amino)-
methyl]-1,4-benzodioxane Hydrochloride [(S)-6]. A mixture of
(R)-2- mesyloxymethyl-1,4-benzodioxane (713 mg, 3.14 mmol) and
18 (650 mg, 3.14 mmol) in 2-methylpropanol (5 mL) was subjected
to microwave irradiation for 45 min (120 °C, 100 W). After cooling
the reaction mixture to room temperature, the solvent was evaporated
and the resultant residue taken up in dichloromethane (20 mL) and
washed with 10% aqueous NaHCO3 (3 × 20 mL) and with brine (2 ×
20 mL). The organic phase was dried and concentrated to give a
residue, which was purified by chromatography on silica gel (eluent:
dichloromethane/methanol/triethylamine; 98:2:1), yielding 373 mg of
(S)-2-[((2-(6-methoxy-6-benzofuranoxy)ethyl)amino)methyl]-1,4-
6-Methoxy-7-(2-hydroxyethoxy)indole (25). A mixture of 24
(3.20 g, 19.6 mmol), ethylene carbonate (1.72 g, 19.61 mmol), and
K2CO3 (2.7 g, 19.61 mmol) in dioxane (10 mL) was subjected to
microwave irradiation for 60 min (150 °C, 150 W). The reaction
mixture was cooled to room temperature, and dichloromethane (50
mL) and water (100 mL) were added. The organic phase was
separated and washed with 10% HCl (3 × 50 mL). The aqueous layer
was extracted with dichloromethane (50 mL) again, and the two
organic phases were combined and washed with water (2 × 50 mL),
dried, and concentrated. The resulting residue was purified by flash
chromatography on silica gel (eluent cyclohexane/ethyl acetate, 6:4)
to give 1.61 g (34.9%) of 25 as a red oil: 1H NMR (CDCl3) δ 3.20 (br
s, 1H, exchangeable with D2O), 3.91 (m, 5H), 4.27 (m, 2H), 6.47 (m,
1H), 6.84 (d, 1H), 7.11 (m, 1H), 7.31 (d, 1H), 8.90 (br s, 1H,
exchangeable with D2O).
25
benzodioxane as a colorless oil: [α]D = −16.1 (c 1, CHCl3). The
amine was dissolved in ethanol (4 mL), and 3 N ethanolic HCl (2 mL)
was added. The solvent was removed, and the resulting crude product
was treated with ethyl acetate (3 mL) to give a suspension, which was
cooled to 0 °C and filtered, yielding 172 mg (42%, based on the
starting amount of secondary amine) of (S)-6 as a white solid: mp
123.7 °C; [α]D25 = −39.4 (c 1, ethanol). 1H NMR (DMSO-d6) δ 3.43
(m, 4H), 3.84 (s, 3H), 4.10 (m, 1H), 4.42 (m, 3H), 4.68 (m, 1H), 6.89
(m, 5H), 7.06 (d, 1H), 7.32 (d, 1H), 7.88 (m, 1H), 9.35 (br s, 2H,
exchangeable with D2O); 13C NMR (DMSO-d6) δ 47.29, 47.37, 57.57,
65.58, 69.2, 70.01, 107.56, 107.62, 110.71, 116.38, 117.85, 118.08,
122.43, 123.57, 132.84, 142.57, 143.42, 146.42, 147.52, 149.55. Anal.
(C20H22ClNO5) C, H, N, Cl.
6-Methoxy-7-(2-mesyloxyethoxy)indole (26). Mesyl chloride
(1.15 g, 10.0 mmol) was added dropwise to a solution of 25 (1.61 g,
7.8 mmol) and triethylamine (1.4 mL, 10.0 mmol) in dichloromethane
(15 mL) at 0 °C. The reaction mixture was stirred at room
temperature for 30 min, and then dichloromethane (20 mL) and 10%
HCl (20 mL) were added. The aqueous layer was extracted with
dichloromethane (2 × 20 mL). The organic phases were combined,
washed with 10% HCl (2 × 20 mL) and water (2 × 20 mL), dried, and
1
concentrated to give 2.15 g (97.0%) of 26 as a dark oil: H NMR
(R)-2-[((2-(6-Methoxy-7-benzofuranoxy)ethyl)amino)-
methyl]-1,4-benzodioxane Hydrochloride [(R)-6]. Obtained from
(CDCl3) δ 3.05 (s, 3H), 3.91 (s, 3H), 4.46 (m, 2H), 4.54 (m, 2H),
6.46 (m, 1H), 6.83 (d, 1H), 7.15 (m, 1H), 7.31 (d, 1H), 8.87 (br s,
1H, exchangeable).
(S)-2-mesyloxymethyl-1,4-benzodioxane (707 mg, 2.9 mmol) and 18
25
(600 mg, 2.9 mmol) as described for (S)-6: mp 124.2 °C; [α]D
=
+37.9 (c 1, ethanol. 1H NMR identical to that of (S)-6. Anal.
(C20H22ClNO5) C, H, N, Cl. (R)-2-[((2-(6-Methoxy-6-
benzofuranoxy)ethyl)amino)methyl]-1,4-benzodioxane (free amine):
6-Methoxy-7-hydroxy-2,3-dihydroindole (27). Pd/C (5%,
580 mg) was added to a solution of 26 (2.94 g, 18.0 mmol) in acetic
acid (50 mL), and the mixture was vigorously shaken under hydrogen
atmosphere at room temperature for 16 h. Afterward, the catalyst was
removed by filtration and the filtrate concentrated. The residue was
treated with dichloromethane (120 mL) and 10% aqueous NaHCO3
(80 mL). The aqueous layer was separated and extracted with
dichloromethane (2 × 50 mL). The organic phases were combined,
dried, and concentrated to give 2.78 g (94%) of 27 as a brown solid:
mp 106.6 °C. 1H NMR (CDCl3) δ 2.99 (t, 2H), 3.59 (t, 2H), 3.83 (s,
3H), 6.30 (d, 1H), 6.63 (d, 1H).
25
[α]D = +15.9 (c 1, CHCl3).
(S)-2-[((2-(6-Methoxy-7-indolyloxy)ethyl)amino)methyl]-1,4-
benzodioxane [(S)-7]. A mixture of (S)-2-aminomethyl-1,4-
benzodioxane (672 mg, 4.1 mmol) and 26 (1.16 g mg, 4.1 mmol)
in 2-methylpropanol (5 mL) was subjected to microwave irradiation
for 1 h (120 °C, 100 W). The reaction mixture was cooled to room
temperature and concentrated; the resultant residue was taken up in
dichloromethane (20 mL) and washed with10% aqueous NaHCO3 (3
× 20 mL) and with brine (2 × 20 mL). The organic phase was dried
and concentrated and the residue purified by chromatography on silica
gel (eluent: dichloromethane/methanol; 9:1), yielding 584 mg (40%)
N-Cbz-6-methoxy-7-hydroxy-2,3-dihydroindole (28). Benzyl
chloroformate (2.9 mL, 20.2 mmol) in dichloromethane (5 mL) was
added dropwise to a solution of 27 (2.28 g, 16.8 mmol) in
dichloromethane (50 mL) and pyridine (6.7 mL) at 0 °C. The
reaction mixture was stirred at 10 °C for 3 h and then allowed to reach
room temperature. Dichloromethane (50 mL) was added, and the
resulting mixture was quenched in 10% aqueous NaHCO3. The
organic phase was separated, washed with 10% aqueous NaHCO3 (80
mL) and then with brine (2 × 50 mL), and finally dried. The resulting
dark solution was decolorized over charcoal by stirring for 30 min,
filtered, and concentrated to give 4.77 g of crude product, which was
crystallized from ethyl acetate to give 4.30 g (85.5%) of 28 as a white
25
of (S)-7 as a light pink solid: mp 120.5 °C; [α]D = −20.3 (c 1,
CHCl3). 1H NMR (CDCl3) δ 2.50 (br s, 1H, exchangeable with D2O),
3.05 (m, 4H), 3.91 (s, 3H), 4.00 (dd, 1H), 4.29 (m, 3H), 4.44 (m,
1H), 6.43 (d, 1H), 6.90 (m, 5H), 7.10 (d, 1H), 7.29 (d, 1H), 10.15 (br
s, 1H, exchangeable with D2O); 13C NMR (DMSO-d6) δ 49.83, 49.93,
57.94, 66.79, 72.94, 73.37, 102.01, 102.05, 108.80, 115.60, 117.56,
117.76, 121.75, 122.01, 125.27, 125.63, 131.24, 133.95, 143.78, 146.93.
Anal. (C20H22N2O4) C, H, N.
(R)-2-[((2-(6-Methoxy-7-indolyloxy)ethyl)amino)methyl]-1,4-
benzodioxane [(R)-7]. Obtained from (R)-2-aminomethyl-1,4-
benzodioxane (726 mg, 4.4 mmol) and 26 (1.25 g, 4.4 mmol) as
1
solid: mp 135.0 °C. H NMR (CDCl3) δ 3.01 (t, 2H), 3.86 (s, 3H),
4.05 (t, 2H), 5.27 (s, 2H), 6.60 (s, 2H), 7.41−7.26 (m, 5H) 10.94 (s,
1H).
25
1
described for (S)-7: mp 122 °C; [α]D = +17.6 (c 1, CHCl3). H
NMR identical to that of (S)-7. Anal. (C20H22N2O4) C, H, N.
(S)-2-[((2-(6-Methoxy-2,3-dihydro-7-benzofuranoxy)ethyl)-
amino)methyl]-1,4-benzodioxane Hydrochloride [(S)-8]. A
mixture of (S)-2-aminomethyl-1,4-benzodioxane (691 mg, 4.2
mmol) and 20 (721 mg, 2.5 mmol) in 2-methylpropanol (4 mL)
was subjected to microwave irradiation for 2 h (90 °C, 40 W). The
N-Cbz-6-methoxy-7-(2-bromoethoxy)-2,3-dihydroindole
(29). A solution of 28 (3.78 g, 12.6 mmol) in THF/DMSO (19 mL/
19 mL) was added dropwise to a suspension of NaH (757 mg, 31.5
mmol) in THF/DMSO (2 mL/2 mL) under nitrogen atmosphere at 0
°C. After 15 min, 1,2-dibromoethane (3.3 mL, 37.9 mmol) was added
dropwise. The reaction mixture was refluxed for 16 h and then cooled
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reaction mixture was cooled to room temperature and concentrated.
The residue was taken up in dichloromethane (30 mL) and washed
with 10% aqueous NaHCO3 (3 × 20 mL) and with brine (2 × 20 mL).
The organic phase was dried and concentrated, and the residue was
purified by chromatography on silica gel (eluent: ethyl acetate),
yielding 488 mg of (S)-2-[((2-(6-methoxy-2,3-dihydro-7-
benzofuranoxy)ethyl)amino)methyl]-1,4-benzodioxane as a colorless
oil: [α]D25 = −22.6 (c 1, CHCl3). The secondary amine was dissolved
in ethanol (4 mL), and 3 N ethanolic HCl (3 mL) was added. The
solvent was removed and the resulting crude product treated with
refluxing ethyl acetate. After cooling to 0 °C, the precipitate was
isolated by filtration, yielding 470 mg (87%, based on the starting
amount of secondary amine) of (S)-8 as a white solid: mp 160.0 °C;
α1d AR-subtypes, and 5-HT1A serotoninergic receptor with in vitro
binding studies, (b) by determining the α1-AR subtypes and α2-AR
blocking activity of the S enantiomers on different rat tissues, and (c)
by evaluating the inverse agonist activity of the S enantiomers as an
inhibition of calcium-induced increase in the resting tension (IRT) of
calcium-depleted guinea pig thoracic aorta.
α1-AR binding studies were carried out in membranes derived from
Chinese Hamster Ovary (CHO) cells expressing α1-AR subtypes were
incubated for 30 min at 25 °C in Tris HCl, 50 mM (pH = 7.7,
containing 10 μM pargyline and 0.1% ascorbic acid) with 0.5 nM
[3H]prazosin, in the absence or presence of different concentrations of
the tested compounds. Prazosin, 1 μM, was used to determine
nonspecific binding. 5-HT1A receptor binding studies were carried out
in crude membrane preparations from rat hippocampus, which were
incubated for 30 min at 25 °C in Tris HCl (50 mM, pH = 7.7,
containing 10 μM pargyline and 4 mM CaCl2) with 1 nM [3H]-8-OH-
DPAT, in the absence or presence of different concentrations of the
tested compounds. 5-HT, 1 μM, was used to determine nonspecific
binding. Incubation was stopped by rapid filtration through GF/B fiber
filters.
25
1
[α]D = −34.0 (c 1, ethanol). H NMR (DMSO-d6) δ 3.08 (t, 2H),
3.43 (m, 4H), 3.72 (s, 3H), 4.10 (m, 1H), 4.20 (t, 2H), 4.40 (m, 1H),
4.57 (t, 2H), 4.68 (m, 1H), 6.48 (d, 1H), 6.89 (m, 5H), 9.28 (br s, 1H,
exchangeable with D2O), 9.7 (br s, 1H, exchangeable with D2O); 13C
NMR (DMSO-d6) δ 29.53, 47.10, 47.47, 56.80, 65.56, 68.32, 69.96,
73.14, 105.18, 117.85, 117.92, 118.07, 120.16, 122.01, 122.43, 131.70,
142.56, 143.41, 152.55, 152.66. Anal. (C20H24ClNO5) C, H, N, Cl.
(R)-2-[((2-(6-Methoxy-2,3-dihydro-7-benzofuranoxy)ethyl)-
amino)methyl]-1,4-benzodioxane Hydrochloride [(R)-8]. Ob-
tained from (R)-2-aminomethyl-1,4-benzodioxane (500 mg, 3.0
mmol) and 20 (865 mg, 3.0 mmol) as described for (S)-8: mp
Saturation curves were analyzed using the one-site binding equation
built into GraphPad Prism, giving IC50 values with the relative
standard errors. Affinity constants were expressed as pKi (−log Ki
values, calculated using the Cheng and Prusoff equation).
25
1
158.3 °C; [α]D = +29.9 (c 1, ethanol). H NMR identical to that of
(S)-6. Anal. (C20H24ClNO5) C, H, N, Cl. (R)-2-[((2-(6-Methoxy-2,3-
dihydro-7-benzofuranoxy) ethyl)amino)methyl]-1,4-benzodioxane
Functional antagonism was determined on different tissues from
Male Sprague−Dawley rats (Charles River, Italy). The required organ
were isolated, freed from adhering connective tissue, and set up rapidly
under resting tension in an organ bath (15 mL) containing
physiological salt solution kept at appropriate temperature (see
below) and gassed with 95% O2 and 5% CO2 at pH 7.4.
Concentration−response curves were constructed by cumulative
addition of agonist before and after incubation with antagonist.
Parallel experiments in which tissues did not receive any antagonist
were run to check any variation in sensitivity.
25
(free amine): [α]D = +19.5 (c 1, CHCl3).
(S)-2-[((2-(6-Methoxy-2,3-dihydro-7-indolyloxy)ethyl)-
amino)methyl]-1,4-benzodioxane Dihydrochloride [(S)-9]. A
mixture of (S)-2-aminomethyl-1,4-benzodioxane (1.13 g, 6.82 mmol)
and 29 (1.39 g, 3.41 mmol) in 2-methylpropanol (8 mL) was refluxed
for 18 h. The solvent was evaporated and the resultant residue taken
up in dichloromethane (35 mL) and washed with 10% aqueous
NaHCO3 (3 × 25 mL) and then with brine (3 × 20 mL). The organic
phase was dried and concentrated and the residue purified by
chromatography on silica gel (eluent: ethyl acetate), yielding 950 mg
of (S)-2-[((2-(N-Cbz)-(6-methoxy-2,3-dihydro-7-indolyloxy)ethyl)-
Prostates (from rats of 200−250 g) were used to assess α1A-
adrenoceptor antagonist activity.22 Before the concentration curves
were started, tissues were exposed to (−)-noradrenaline at a
concentration of 1.0 μM. A minimum response of 0.5 g of tension
was required for the tissue to be used for concentration−response
curves. After a 90 min time period, a cumulative response curve to
(−)-noradrenaline was constructed. After completion of the
concentration−response curve, the tissue was washed for 90 min,
and the antagonist was added and incubated for 30 min before a
second cumulative concentration−response curve was obtained.
The vas deferens prostatic portion (from rats of 200−250 g) was
used to assess α1A-adrenoceptor antagonist activity.20 Desipramine
hydrochloride (0.01 μM) was present in the organ bath solution to
prevent the neuronal uptake of (−)-noradrenaline. Contraction−
response curves for isotonic contractions in response to (−)-nora-
drenaline were recorded at 30 min intervals, the first one being
discarded and the second one taken as control. After the incubation
with antagonist for 30 min, a third dose−response curve was obtained.
α2-Adrenoreceptor antagonist activity was determined also on vas
deferens prostatic portions. Propranolol hydrochloride (1 μM) and
desipramine hydrochloride (0.01 μM) were present in the organ bath
solution throughout the experiments to block β-adrenoreceptors and
to prevent the neuronal uptake of (−)-noradrenaline, respectively. A
first clonidine concentration−response curve, taken as control, was
obtained cumulatively. The antagonist was allowed to equilibrate with
the tissue for 30 min before obtaining a second dose−response curve.
Spleens (from rats of 250−300 g) were used to assess α1B-
adrenoceptor antagonist activity.21 Desipramine hydrochloride (0.01
μM) and propranolol hydrochloride (1 μM) were added to the organ
bath solution to prevent the neuronal uptake of (−)-noradrenaline and
to block β-adrenoreceptors, respectively. The cumulative concen-
tration−response curves to phenylephrine were measured isometrically
and obtained at 30 min intervals, the first one being discarded and the
second one taken as control. The antagonist was allowed to equilibrate
with the tissue for 30 min, and then a new concentration−response
curve to the agonist was constructed.
25
amino)methyl]-1,4-benzodioxane as a colorless oil: [α]D = −19.6
(c 1, CHCl3). The secondary amine was dissolved in methanol (70
mL), and 5% Pd/C (82 mg) was added. The reaction mixture was
stirred under hydrogen atmosphere for 2 h. Afterward the catalyst was
removed by filtration and the solvent evaporated. The resulting residue
was taken up in dichloromethane (30 mL), washed with NaHCO3 (2
× 15 mL), dried, and concentrated to give 660 mg of (S)-2-[((2-(6-
methoxy-2,3-dihydro-7-indolyloxy)ethyl)amino)methyl]-1,4-benzo-
25
dioxane: [α]D = −23.6 (c 1, CHCl3). The diamine was dissolved in
ethanol (1 mL), and 1.5 N ethanolic HCl (5 mL) was added. The
resulting mixture was heated at 50 °C for 10 min and then stirred at 0
°C for 1 h. The suspension was filtered, obtaining 650 mg (82%, based
on the starting amount of secondary amine) of (S)-9 as a white solid:
mp 238 °C; [α]D25= −46.3 (c 1, methanol). H NMR (DMSO-d6)
1
3.11 (t, 2H), 3.34 (dd, 1H), 3.38−3.50 (m, 2H), 3.59 (dd, 1H), 3.68
(t, 2H), 3.81 (s, 3H), 4.11 (dd, 1H), 4.42−4.48 (m, 3H), 4.77−4.82
(m, 1H), 6.84−6.95 (m, 4H), 7.01 (d, 1H), 7.08 (d, 1H), 9.50 (br s,
1H, exchangeable with D2O); 13C NMR (DMSO-d6) δ29.37, 46.11,
47.62, 48.02, 57.25, 65.54, 68.84, 69.87, 113.85, 117.82, 117.98,
118.15, 121.11, 122.41, 128.75, 131.56, 138.19, 142.54, 143.42, 151.94.
Anal. (C20H26Cl2N2O4) C, H, N, Cl.
(R)-2-[((2-(6-Methoxy-2,3-dihydro-7-indolyloxy)ethyl)-
amino)methyl]-1,4-benzodioxane Dihydrochloride [(R)-9]. Ob-
tained from (R)-2-aminomethyl-1,4-benzodioxane (812 mg g, 4.92
mmol) and 29 (1.0 g, 2.46 mmol) as described for (S)-9: mp 238 °C;
25
1
[α]D = +44.60 (c 1, methanol). H NMR identical to that of (S)-9.
Anal. (C20H26Cl2N2O4) C, H, N, Cl. (R)-2-[((2-(6-Methoxy-2,3-
dihydro-7-indolyloxy)ethyl)amino)methyl]-1,4-benzodioxane (free
25
amine): [α]D = +23.2 (c 1, CHCl3).
Biology. According to previously reported procedures,4,8 the
pharmacological profile of compounds 6−9 was assessed: (a) by
measuring the affinities of both the S and R enantiomers for α1a, α1b,
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Thoracic aortas (from rats of 250−300 g) were used to assess α1D
-
related compounds: new, subtype-selective α1-adrenoreceptor antag-
onists (or inverse agonists?). J. Med. Chem. 2006, 49, 7140−7149.
(5) Villa, L.; Valoti, E.; Villa, A. M.; Pallavicini, M.; Ferri, V.; Iuliano,
E.; Brunello, N. Molecular properties of the WB4101 enantiomers and
of its chiral methyl derivatives for α1-adrenoceptor recognition.
Farmaco 1994, 49, 587−606.
(6) Valoti, E.; Pallavicini, M.; Villa, L.; Pezzetta, D. Synthesis of
homochiral 5- and 8-substituted 2-[((2-(2,6-dimethoxyphenoxy)-
ethyl)amino)methyl]-1,4-benzodioxanes and electrophoretic determi-
nation of their enantiomeric excess. J. Org. Chem. 2001, 66, 1018−
1025.
(7) Bolchi, C.; Catalano, P.; Fumagalli, L.; Gobbi, M.; Pallavicini, M.;
Pedretti, A.; Villa, L.; Vistoli, G.; Valoti, E. Structure-affinity studies for
a novel series of homochiral naphtho and tetrahydronaphtho
analogues of α1 antagonist WB-4101. Bioorg. Med. Chem. 2004, 12,
4937−4951.
(8) Fumagalli, L.; Pallavicini, M.; Budriesi, R.; Gobbi, M.; Straniero,
V.; Zagami, Michael; Chiodini, g.; Bolchi, C.; Chiarini, A.; Micucci, M.;
Valoti, E. Affinity and activity profiling of unichiral 8-substituted 1,4-
benzodioxane analogues of WB4101 reveals a potent and selective α1B-
adrenoceptor antagonist. Eur. J. Med. Chem. 2012, 58, 184−191.
(9) Ferri, V.; Pallavicini, M.; Piccini, D.; Valoti, E.; Villa, L.; Brunello,
N.; Racagni, G. Synthesis, Binding affinities for α-adrenoceptor and
eudismic analysis of chiral benzodioxane derivatives and their chiral
opened analogues. Farmaco 1988, 49, 1153−1163.
adrenoceptor antagonist activity.21 Desipramine hydrochloride (0.01
μM)) and propranolol hydrochloride (1 μM) were added to the organ
bath solution to prevent the neuronal uptake of (−)-noradrenaline and
to block β-adrenoreceptors, respectively. Two helicoid strips were cut
in strips from each aorta of about 1.5 cm length. The endothelium was
removed by rubbing with filter paper: the functional loss of endothelial
cells was confirmed by the absence of the relaxing response to
acetylcholine. After an at least 1 h equilibration period under an
optimal tension of 1 g, cumulative (−)-noradrenaline dose−response
curves were recorded, the first two being discarded and the third one
taken as a control. The antagonist was allowed to equilibrate with the
tissue for 30 min before the generation of a fourth cumulative dose−
response curve with (−)-noradrenaline.
The guinea pig thoracic aorta was used to assess the activity of α1-
antagonist as inverse agonist.4,28 Aortic strips were isolated and
cleaned as previously described and placed in an organ bath containing
the Krebs solution maintained at 37 °C of the following composition
(mM): NaCl, 118; KCl, 4.75; CaCl2, 1.8; MgCl2, 1.2; NaHCO3, 25.0;
KH2PO4, 1.2; glucose, 11. Tissues were equilibrated for 1 h under an
optimal tension of 1 g, and the effect of a single dose of
(−)-noradrenaline (1 μM) was recorded. During 1 h of wash in
Ca2+-free Krebs solution containing EDTA (0.1 mM), the agonist was
applied and washed with Ca2+-free solution until no contraction was
elicited, indicating depletion of internal Ca2+ stores sensitive to NA.
After incubation with the antagonist for 30 min, addition of Ca2+ (1.8
mM) induced an increase in the resting tension (IRT). The magnitude
of the inhibition was expressed as a percent decrease of the reference
IRT, namely of the IRT induced by calcium (1.8 mM) in the absence
of any agent.
(10) Fumagalli, L.; Bolchi, C.; Colleoni, S.; Gobbi, M.; Moroni, B.;
Pallavicini, M.; Pedretti, A.; Villa, L.; Vistoli, G.; Valoti, E. QSAR study
for a novel series of ortho monosubstituted phenoxy analogues of α1-
adrenoceptor antagonist WB4101. Bioorg. Med. Chem. 2005, 13,
2547−2559.
(11) Pallavicini, M.; Fumagalli, L.; Gobbi, M.; Bolchi, C.; Colleoni, S.;
Moroni, B.; Pedretti, A.; Rusconi, C.; Vistoli, G.; Valoti, E. QSAR
study for a novel series of ortho disubstituted phenoxy analogues of α1-
adrenoceptor antagonist WB4101. Eur. J. Med. Chem. 2006, 41, 1025−
1040.
(12) Bolchi, C.; Fumagalli, L.; Moroni, B.; Pallavicini, M.; Valoti, E. A
short entry to enantiopure 2-substituted 1,4-benzodioxanes by efficient
resolution methods. Tetrahedron: Asymmetry 2003, 14, 3779−3885.
(13) Bolchi, C.; Pallavicini, M.; Fumagalli, L.; Marchini, N.; Moroni,
B.; Rusconi, C.; Valoti, E. Highly efficient resolutions of 1,4-
benzodioxane-2-carboxylic acid with para substituted 1-phenylethyl-
amines. Tetrahedron: Asymmetry 2005, 16, 1639−1643.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR and 13C NMR spectra and elemental analysis results
for the final compounds 6−9. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Phone: +39 02 50319334; fax +39 02 50319359; e-mail:
ermanno.valoti@unimi.it.
■
(14) Marchini, N.; Bombieri, G.; Artali, R.; Bolchi, C.; Pallavicini, M.;
Valoti, E. Influence of (S)-1-phenylethylamine para substitution on the
resolution of ( )-1,4-benzodioxane-2-carboxylic acid: A crystallo-
graphic, theoretical and morphologic approach. Tetrahedron: Asymme-
try 2005, 16, 2099−2106.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This research was supported by the Universita
Milan and by the University of Bologna.
■
̀
degli Studi of
(15) Bolchi, C.; Pallavicini, M.; Fumagalli, L.; Rusconi, C.; Binda, M.;
Valoti, E. Resolution of 2-substituted benzodioxanes by entrainment.
Tetrahedron: Asymmetry 2007, 18, 1038−1041.
ABBREVIATIONS USED
(16) Pallavicini, M.; Valoti, E.; Villa, L.; Piccolo, O. Synthesis of (R)-
and (S)-isopropylidene glycerol. Tetrahedron: Asymmetry 1994, 5, 5−8.
(17) Bolchi, C.; Pallavicini, M.; Fumagalli, L.; Ruggeri, P.; Valoti, E.
Diastereomeric 2-aminomethyl-1,4-benzodioxane mandelates: Phase
diagrams and resolution. Tetrahedron: Asymmetry 2013, 24, 796−800.
(18) White, J. D.; Yager, K. M.; Yakura, T. Synthetic studies of the
pyrroloquinoline nucleus of the makaluvamine alkaloids. Synthesis of
the topoisomerase II inhibitor makaluvamine D. J. Am. Chem. Soc.
1994, 116, 1831−1838.
(19) Dharmasena, P.; Oliveira-Campos, A. M. R.; Queiroz, M. J. R.
P.; Shannon, P. V. R. Anti-tumour heterocycles. Part 12. The synthesis
of new hydroxypyrrolocarbazoles and hydroxypyridocarbazoles. J.
Chem. Res., Miniprint 1996, 316−363.
(20) Elze, M.; Boer, R.; Sander, K. H.; Kolossa, N. Vasodilatation
elicited by 5-HT1A receptor agonists in constant-pressure-perfused
kidney is mediated by blockade of α1A-adrenoreceptors. Eur. J.
Pharmacol. 1991, 202, 33−44.
(21) Ko, F. N.; Guh, J. H.; Yu, S. M.; Hou, Y. S.; Wu, Y. C.; Teng, C.
M. (−)-Discretamine, a selective α1D-adrenoreceptor antagonist,
■
AR, adrenoreceptor; Cbz, carbobenzyloxy; DCM, dichloro-
methane; DPPA, diphenylphosphoryl azide; HBA, hydrogen
bond acceptor; IRT, increase in resting tension; LUTS, lower
urinary tract symptoms; MsCl, mesyl chloride; SAR, structure−
activity relationship; TEA, triethylamine
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