Structure-activity relationships in 1,4-benzodioxan-related compounds. 6. Role of the dioxane unit on selectivity for α1-adrenoreceptor subtypes

Article abstract of DOI:10.1021/jm9910324

WB 4101-related benzodioxans 3-9 were synthesized, and their biological profiles at α₁-adrenoreceptor subtypes and 5-HT₁(A) serotoninergic receptors were assessed by binding assays in CHO and HeLa cells membranes expressing the human

Full text of DOI:10.1021/jm9910324

J . Med. Chem. 1999, 42, 2961-2968
2961
Str u ctu r e-Activity Rela tion sh ip s in 1,4-Ben zod ioxa n -Rela ted Com p ou n d s. 6.1
Role of th e Dioxa n e Un it on Selectivity for r1-Ad r en or ecep tor Su btyp es
Wilma Quaglia,† Maria Pigini,† Alessandro Piergentili,† Mario Giannella,† Gabriella Marucci,† Elena Poggesi,‡
Amedeo Leonardi,‡ and Carlo Melchiorre*,§
Department of Chemical Sciences, University of Camerino, Via S. Agostino 1, 62032 Camerino (MC), Italy, Research and
Development Division, Recordati S.p.A., Via Civitali 1, 20148 Milano, Italy, and Department of Pharmaceutical Sciences,
University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy
Received March 2, 1999
WB 4101-related benzodioxans 3-9 were synthesized, and their biological profiles at R1-
adrenoreceptor subtypes and 5-HT1A serotoninergic receptors were assessed by binding assays
in CHO and HeLa cells membranes expressing the human cloned receptors. Furthermore,
receptor selectivity of selected benzodioxan derivatives was further determined in functional
experiments in isolated rat vas deferens (R1A) and aorta (R1D) and guinea pig spleen (R1B), in
additional receptor binding assays in rat cortex membranes containing R2-adrenoreceptors and
5-HT2 serotoninergic receptors, and in rat striatum membranes containing D2 dopaminergic
receptors. An analysis of the results of receptor binding experiments for benzodioxan-modified
derivatives 3-9 showed high affinity and selectivity toward the R1a-adrenoreceptor subtype
for compounds 3-5 and 7 and a reversed selectivity profile for 9, which was a selective R1d
antagonist. Furthermore, the majority of structural modifications performed on the prototype
1 (WB 4101) led to a marked decrease in the affinity for 5-HT1A serotoninergic receptors, which
may have relevance in the design of selective R1A-adrenoreceptor antagonists. The exception
to these findings was the chromene derivative 8, which exhibited a 5-HT1A partial agonist profile.
In tr od u ction
antagonists bearing a benzodioxan moiety. Several
investigations were devoted to improving both affinity
and selectivity of 1.11-13 As a result, a variety of
analogues have been studied involving modification of
the benzodioxan ring, the amine function, or the (2,6-
dimethoxyphenoxy)ethyl moiety. Among these struc-
tural modifications performed on 1, the insertion of a
phenyl ring at the 3-position having a trans relationship
with the 2-side chain afforded phendioxan {trans-N-[2-
(2,6-dimethoxyphenoxy)ethyl]-2,3-dihydro-3-phenyl-1,4-
benzodioxin-2-methanamine, 2},14 which retained high
affinity for R1-adrenoreceptors while displaying only a
markedly reduced affinity for R2-adrenoreceptors. As an
overall result, the presence of a 3-phenyl unit as in 2
In recent years much effort has been directed toward
characterization of receptor systems, which are com-
prised usually of multiple subtypes. R1-Adrenoreceptors
do not represent an exception to the rule as they can be
divided into at least three subtypes, namely R1A (R1a),
R1B (R1b), and R1D (R1d), with upper and lower case
subscripts being used to designate the native or recom-
binant receptor, respectively.2-4 However, some func-
tional experiments indicate that an additional R1-
adrenoreceptor subtype may exist, which was named
R
1L-adrenoreceptor.5 Efforts to clone this receptor sub-
type have been unsuccessful so far.6 It has been sug-
gested that R1L-adrenoreceptors may represent a dif-
ferent affinity state of R1A-adrenoreceptors.7
The existence of multiple R1-adrenoreceptor subtypes
is a challenge to medicinal chemists to realize useful
drugs, which target only one receptor while not affecting
others. As a result, several relatively selective ligands
for R1-adrenoreceptors are now available.8 Whereas it
has been claimed that R1A-adrenoreceptor antagonists
can be useful in the treatment of benign prostatic
hyperplasia,9 a potential therapeutic use for either R1B
or R1D subtype antagonists has not been defined yet.
Benzodioxans represent one of the oldest and best-
known classes of R-adrenoreceptor antagonists whose
chemical structure incorporates a 1,4-benzodioxan-2-yl
moiety as the main feature.10 WB 4101 {N-[2-(2,6-
dimethoxyphenoxy)ethyl]-2,3-dihydro-1,4-benzodioxin-
2-methanamine, 1} is the prototype of R1-adrenoreceptor
determined a significant improvement in selectivity
toward R1-adrenoreceptors compared to the prototype
1. It should be emphasized, however, that the majority
of 1 analogues, including 2 and related compounds, were
not assayed to evaluate the affinity for the three R1-
adrenoreceptor subtypes. Most of these compounds were
tested only on the epididymal portion of the isolated rat
vas deferens,11-15 which proved to be a preparation
containing a mixture of R1A- and R1L-adrenoreceptors.16
Thus, the affinity for the three R1-adrenoreceptors was
not determined, which prevents drawing a relevant
conclusion on the structural features that determine
† University of Camerino.
‡ Recordati S.p.A.
§ University of Bologna.
10.1021/jm9910324 CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/13/1999

2962 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15
Quaglia et al.
Sch em e 1
Sch em e 2
selectivity for one R1-adrenoreceptor subtype relative to
the others. Mephendioxan, a p-tolyl analogue of phen-
dioxan, represents an exception as its enantiomers were
assayed at the three cloned R1-adrenoreceptor subtypes.
It turned out that, in binding experiments, (-)-(2S,3S)-
mephendioxan is a selective antagonist for R1a-adreno-
receptors.17
Sch em e 3
In the present study, our aim was to investigate
further the role of the dioxane unit and in particular of
the oxygens at positions 1 and 4 of 2 in the interaction
with the three different R1-adrenoreceptors. Further-
more, we wanted to verify whether benzodioxan-bearing
derivatives might allow us to understand the structural
requirements that differentiate the binding sites of R1-
adrenoreceptors and 5-HT1A serotoninergic receptors. It
is known that benzodioxans are effective ligands of
5-HT1A serotoninergic receptors as well.18 To this end,
we describe here the synthesis and the pharmacological
profile of compounds 3-8 related to both 1 and 2. Since
we demonstrated that opening of the dioxane ring of 1
did not result in a loss of R1-adrenoreceptor blocking
activity,11 we included in this study compound 9 to
verify whether the increased flexibility might allow a
better interaction with R1-adrenoreceptor subtypes lead-
ing hopefully to selectivity.
trans mixture (ratio 65:35) of the corresponding satu-
rated esters 15 and 16, which were separated by column
chromatography. The stereochemical relationship be-
tween the ester function at position 2 and the 3-phenyl
in 15 and 16 was deduced from the coupling constants
of the hydrogen atoms at the same positions. Thus, a
cis relationship was assigned to 15 since the coupling
constant (J ) 3.60 Hz) was lower than that found for
the corresponding trans isomer 16 (J ) 8.10 Hz). Basic
hydrolysis of 15 and 16 afforded acids 17 and 18,
respectively. These acids, in chloroform, were amidated
in the presence of Et3N and EtOCOCl with amine 1321
to give corresponding amides 19 and 20. Reduction of
19 and 20 with borane-methyl sulfide complex in dry
diglyme gave the corresponding amines 6 and 7.
Ch em istr y
The compounds used in the present investigation were
synthesized by standard procedures and characterized
1
by H NMR and elemental analysis.
Compounds 3,14 4, and 5 were synthesized by a
Mannich reaction of the corresponding ketones 10, 11,19
and 1220 with amine 1321 and paraformaldehyde (Scheme
1). This reaction afforded only one of the two possible
isomers. The stereochemical relationship between the
amino side chain and the phenyl ring in 4 and 5 was
deduced from the coupling constant of hydrogens at the
corresponding positions. A trans relationship was as-
signed to these compounds since their coupling con-
stants (J ) 11.64 Hz for 4 and J ) 11.90 Hz for 5) were
similar to the coupling constant observed previously for
3 (J ) 11.29 Hz),14 which has a trans relationship.
Isomers 6 and 7 were synthesized as shown in Scheme
2. Catalytic hydrogenation of ester 1422 afforded a cis/
Compound 8 was synthesized by reductive amination
of aldehyde 2123 with amine 1321 (Scheme 3).
The open analogue 9 was obtained following a similar
synthetic pathway described for amines 6 and 7 as
shown in Scheme 4. Thus, ester 22, which was synthe-
sized from 2-(benzyloxy)phenol and methyl chloroac-
etate, was hydrolyzed to the corresponding acid 23. The

SARs in 1,4-Benzodioxan-Related Compounds
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15 2963
Ta ble 1. Affinity Constants, Expressed as pKi (-log Ki), of 1,
3-9, and BMY-7378 for Human Recombinant
Sch em e 4
R1-Adrenoreceptor Subtypes and 5-HT1A Receptors and for Rat
Native R2, D2, and 5-HT2 Receptorsa
latter compound was transformed into amide 24, which
was reduced with borane to give the desired compound
9.
Biology
Bin d in g Exp er im en ts. The pharmacological profile
of compounds 3-9 was evaluated by receptor binding
assays using WB 4101 (1), 8-[2-[4-(2-methoxyphenyl)-
1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione
(BMY-7378), and 8-hydroxy-2-(di-n-propylamino)tetra-
lin (DPAT) as standard compounds. [3H]Prazosin was
used to label cloned human R1-adrenoreceptors ex-
pressed in Chinese hamster ovary (CHO) cells.24 Fur-
thermore, [3H]rauwolscine, [3H]spiperone, and [3H]-
ketanserin were used to label R2-adrenoreceptors in rat
cortex,25 D2 receptors in rat striatum,26 and 5-HT2A
receptors in rat cortex,27 respectively, whereas [3H]8-
hydroxy-2-(di-n-propylamino)tetralin was the radioli-
gand used to label cloned human 5-HT1A receptors
expressed in HeLa cells.28,29
pKi (nM),
cloned receptors
(human brain)
pKi (nM),
native receptors
(rat brain)
compd
R1a
R1b
R1d
5-HT1A
R2
7.83
D2
5-HT2
1
9.37
9.22
7.42 <6
8.06
6.78
8.49
7.14
9.33
6.42
8.0
9.29
7.93
6.37
6.88
6.86
7.28
6.95
8.68
6.73
7.36
6.83
6.76
6.84
8.08
7.93
9.43
8.47
6.91
<6
-
6.0
6.20
-
6.63
3
6.84
<6
d
4
-
5
6.11
6.45 <6
6
6.51
6.58
6.84
-
-
<6
-
-
-
-
7
<6
-
<6
-
8
9
9.27 10.17
6.15 8.89
<6 <6
-
-
BMYb
-
-
DPATc <6
6.08 <6
<6
F u n ction a l Stu d ies. Receptor subtype selectivity of
selected WB 4101-related benzodioxans was further
determined at R1-adrenoreceptors on different isolated
tissues using WB 4101 (1) and BMY-7378 as standard
compounds. R1-Adrenoreceptor subtype blocking activity
a
Equilibrium dissociation constants (Ki) were derived from IC50
values using the Cheng-Prusoff equation.35 The affinity estimates
were derived from displacement of [3H]prazosin, [3H]8-hydroxy-
2-(di-n-propylamino)tetralin, [3H]rauwolscine, [3H]ketanserin, and
[3H]spiperone binding for R1-adrenoreceptors, 5-HT1A receptors,
R2-adrenoreceptors, 5-HT2 receptors, and D2 receptors, respec-
tively. Each experiment was performed in triplicate. Ki values were
from 2 to 3 experiments, which agreed within (20%. b BMY, BMY-
was assessed by antagonism of (-)-noradrenaline-
30
induced contraction of prostatic vas deferens (R1A
)
or
7378. c DPAT, 8-hydroxy-2-(di-n-propylamino)tetralin. Not de-
termined.
d
31
thoracic aorta (R1D
)
and by antagonism of (-)-phe-
nylephrine-induced contraction of guinea pig spleen
(R1B).31 Finally, the agonist efficacy of 8 toward 5-HT1A
receptors was assessed by determining the induced
stimulation of [35S]GTPγS binding in cell membranes
from HeLa cells transfected with human cloned 5-HT1A
receptors32 using DPAT, 5-hydroxytryptamine, and
5-carboxamidotryptamine as reference compounds.
ergic receptors of compounds used in the present study
are shown in Table 1. To make relevant considerations
on structure-activity relationships, prototype 1 and the
reference compounds BMY-7378, a selective R1d-adreno-
receptor antagonist displaying also an even higher
affinity for 5-HT1A receptors, and DPAT, a selective
5-HT1A agonist, were included for comparison. By taking
as a starting point the prototype 1, it is possible to
observe how affinity and selectivity for R1-adrenorecep-
tor subtypes can be markedly affected by inserting in
the prototype structure a phenyl ring at position 3 and
(a) by replacing the oxygen atom at position 1 by a
carbonyl group, as in 3, (b) by replacing the oxygen
atoms at position 1 by a carbonyl function and at
position 4 by a sulfur atom, as in 4, or a methylene
group, as in 5, (c) by replacing the oxygen atom at
position 4 by a methylene group, affording 6 and 7, (d)
by replacing the oxymethylene moiety by a vinyl group,
as in 8, and (e) by opening the dioxane ring through
cleavage of the C2-C3 bond, as in 9.
Resu lts a n d Discu ssion
The main goal of this project was to synthesize
benzodioxan-like-bearing derivatives displaying an im-
proved R1-adrenoreceptor subtype selectivity relative to
the prototype WB 4101 (1). Furthermore, it was also
our aim to determine whether structural modifications
of 1 would discriminate between the binding sites of
5-HT1A serotoninergic receptors and R1-adrenoreceptors
while retaining hopefully the affinity for the latter ones.
The receptor affinities, expressed as pKi values, at
human cloned R1-adrenoreceptor subtypes and 5-HT1A
serotoninergic receptors and at native R2-adrenorecep-
tors, D2 dopaminergic receptors, and 5-HT2 serotonin-

2964 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15
Quaglia et al.
Ta ble 2. Agonist Efficacy ([35S]GTP Binding) of 8 on 5-HT1A
Serotoninergic Receptors in Comparison to DPAT, 5-HT, and
5-CTa
Ta ble 3. Antagonist Affinities, Expressed as Apparent pKb, of
1-3, 7, 9, and BMY-7378 at R1-Adrenoreceptors on Isolated Rat
Prostatic Vas Deferens (R1A) and Thoracic Aorta (R1D) and
a
Guinea Pig Spleen (R1B
)
binding [35S]GTP
pKb
compd
pD2
% max
compd
R1A
R1B
R1D
8
6.44
7.60
7.30
8.45
40
100
100
96
DPAT
5-HT
5-CT
1
2
3
7
9
9.36 ( 0.04
8.18 ( 0.08
7.88 ( 0.06
7.36 ( 0.04
8.39 ( 0.18
6.98 ( 0.09
8.21 ( 0.02
5.55 ( 0.06
6.05 ( 0.23
5.54 ( 0.04
7.87 ( 0.01
7.49 ( 0.09
8.60 ( 0.02
7.51 ( 0.04
6.98 ( 0.26
7.46 ( 0.05
9.37 ( 0.15
8.38 ( 0.07
a
DPAT, 8-hydroxy-2-(di-n-propylamino)tetralin; 5-HT, 5-hy-
droxytryptamine; 5-CT, 5-carboxamidotryptamine.
BMY-7378
a
Apparent pKb values ( SE were calculated according to
An analysis of the results shown in Table 1 reveals
that all compounds, with the exception of 3 and 9, were
weaker ligands at R1-adrenoreceptor subtypes relative
to 1. Furthermore, compounds 3-8 displayed a selectiv-
ity profile at R1-adrenoreceptors, which deserves com-
ment. The insertion of a phenyl ring in a trans rela-
tionship with the 2-side chain and the replacement of
an oxygen atom with a carbonyl group, leading to 3,
resulted in a marked drop in affinity at both R1b- and
R1d-adrenoreceptors (14- and 23-fold, respectively), while
not affecting the affinity at the R1a subtype. Further-
more, this structural modification caused a marked drop
in affinity for the other receptor systems investigated,
namely 89-, >68-, and >8-fold for 5-HT1A, R2, and D2
receptors, respectively, relative to 1. As an overall
result, 3 resulted as a potent and selective antagonist
for the R1a-adrenoreceptor subtype while displaying a
weak, if any, affinity for the other receptor systems.
Surprisingly enough, replacement of the oxygen at
position 1 of 3 by a sulfur atom or a methylene group,
affording 4 and 5, respectively, caused a significant
decrease in affinity for the three R1-adrenoreceptor
subtypes. This result does not parallel that found by
replacing the oxygen atom at position 4 of 1 by either a
sulfur or a methylene because the resulting analogues
were as active as the prototype.12,13 However, compound
7, which bears an oxygen atom at position 1 instead of
a carbonyl group as in 5, was only slightly less potent
than both 1 and 3 at R1a-adrenoreceptors. The decrease
in affinity observed for 8 at all R1-adrenoreceptor
subtypes in comparison to 1 and at R1a-adrenoreceptors
in comparison to 3, 5, and 7 clearly suggests that the
presence of a double bond alters the spatial orientation
of the molecule in such a way that the binding with the
adrenoreceptor is made difficult. Alternatively, the low
affinity displayed by 8 for R1-adrenoreceptors might
indicate that the oxygen at position 1 of 1 plays a role
in the binding process owing to its nonbonded electrons.
However, interestingly enough, unsaturated analogue
8 retained high affinity for 5-HT1A receptors and turned
out to be a partial agonist with an efficacy (pD2 ) 6.44),
that was only about 10-fold lower than that of full
agonists such as DPAT and 5-hydroxytryptamine as
shown in Table 2.
Arunlakshana and Schild33 with the following equation: pKb
)
-log Kb ) log(DR - 1) - log[B]. The log(DR - 1) was calculated
from 2 to 3 different antagonist concentrations, and each concen-
tration [B] of antagonist was tested four times. Dose-ratio (DR)
values represent the ratio of the potency of the agonist (EC50) in
the presence of the antagonist and in its absence.
oxygen-bearing ring, the presence of a phenyl ring at
position 3 in a trans relationship with the side chain at
position 2 imparts selective affinity for the R1a subtype
not only with regard to both R1b and R1d subtypes but
also with 5-HT1A, 5-HT2, R2, and D2 receptors as well.
This result may have relevance for the development of
new WB 4101-related compounds having high affinity
and high specificity for R1a-adrenoreceptors. Another
interesting finding was the observation that opening the
dioxane ring, as in 9, markedly increased the affinity
toward R1d-adrenoreceptors. Consequently, open ana-
logue 9 may represent a lead for the design of ligands
selective for this receptor subtype.
Compounds 3, 7, and 9 were selected for further
pharmacological investigation in functional experi-
ments, and the results are shown in Table 3 in com-
parison with those obtained with prototypes 1 and 2 and
the reference compound BMY-7378. Although lower, the
antagonist affinity displayed by 3 and 9 had a trend
similar to that found in binding assays. On the contrary,
these data did not confirm the selectivity for the R1a
subtype found for 7 in the binding assays.
Exp er im en ta l Section
Ch em istr y. Melting points were taken in glass capillary
tubes on a Bu¨chi SMP-20 apparatus and are uncorrected. IR
and H NMR spectra were recorded on Perkin-Elmer 297 and
1
Varian VXR 300 instruments, respectively. Chemical shifts are
reported in parts per million (ppm) relative to tetramethylsi-
lane (TMS), and spin multiplicities are given as s (singlet), br
s (broad singlet), d (doublet), dd (double doublet), t (triplet),
br t (broad triplet), dt (double triplet), q (quartet), or m
(multiplet). Although the IR spectral data are not included
(because of the lack of unusual features), they were obtained
for all compounds reported and were consistent with the
assigned structures. The elemental compositions of the com-
pounds agreed to within (0.4% of the calculated values. When
the elemental analyses are not included, crude compounds
were used in the next step without further purification.
Chromatographic separations were performed on silica gel
columns (Kieselgel 40, 0.040-0.063 mm; Merck) by flash
chromatography.
tr a n s-2-P h en yl-3-[[[2-(2,6-d im et h oxyp h en oxy)et h yl]-
a m in o]m eth yl]th ioch r om a n -4-on e Hyd r och lor id e (4). A
solution of 1119 (0.51 g, 2.12 mmol), 1321 hydrochloride (0.35
g, 1.50 mmol), paraformaldehyde (0.2 g, 6.66 mmol), and
concentrated HCl (0.05 mL) in absolute EtOH (2 mL) was
heated at reflux for 6 h. The resulting mixture was left at 0
°C overnight. The solid was filtered and crystallized from
2-PrOH: 0.4 g (55% yield); mp 150-152 °C; 1H NMR (DMSO)
Opening the dioxane ring gave 9, which was a very
potent ligand at R1-adrenoreceptors while retaining also
high affinity for 5-HT1A receptors, although the affinity
for the latter was 22-174-fold lower than that at the
former ones. This structural modification also resulted
in an inversion of the selectivity profile as 9 was more
potent at R1d-adrenoreceptors than at both R1a and R1b
subtypes.
A most intriguing finding of the present investigation
was the observation that, whatever the kind of the

SARs in 1,4-Benzodioxan-Related Compounds
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15 2965
δ 2.91 (m, 1, 3-H), 3.11-3.53 (m, 4, CH2NCH2), 3.75 (s, 6,
OCH3), 3.98-4.24 (m, 2, CH2O), 5.15 (d, J ) 11.64 Hz, 1, 2-H),
6.67-8.12 (m, 12, ArH), 8.52 (br s, 1, NH, exchangeable with
with Et2O to give 19: 0.37 g (72% yield); mp 123-125 °C; Rf
0.09; 1H NMR (CDCl3) δ 3.0-3.70 (m, 5, NCH2, 3-H and 4-H),
3.71 (s, 6, OCH3), 3.84-4.12 (m, 2, CH2O), 4.73 (d, J ) 2.44
Hz, 1, 2-H), 6.50-7.27 (m, 12, ArH), 7.43 (br t, 1, NH,
exchangeable with D2O).
D2O), 9.25 (br s, 1, NH, exchangeable with D2O). Anal. (C26H27
-
NO4S‚HCl‚0.5H2O) C, H, N, S.
tr a n s-3-P h en yl-2-[[[2-(2,6-d im et h oxyp h en oxy)et h yl]-
a m in o]m eth yl]-1-tetr a lon e Hyd r och lor id e (5). This was
synthesized from 1220 (0.43 g, 1.93 mmol) following the
procedure described for 4. After evaporation of the solvent, the
residue was dissolved in 2 N NaOH and extracted with
chloroform. Removal of dried solvent gave an oil, which was
purified by column chromatography. Eluting with cyclohex-
ane-acetone (7:3) afforded 5 as the free base: 1H NMR (CDCl3)
δ 2.45 (br s, 1, NH, exchangeable with D2O), 2.57-2.81 (m, 3,
CHNCH2), 2.94 (m, 2, CHN and 2-H), 3.06-3.35 (m, 2, 4-H),
3.5 (dt, J ) 11.90 and 3.96 Hz, 1, 3-H), 3.79 (s, 6, OCH3), 3.99
(t, 2, CH2O), 6.50-8.11 (m, 12, ArH).
tr a n s-3-P h en yl-2-[[[2-(2,6-d im et h oxyp h en oxy)et h yl]-
a m in o]m eth yl]ch r om a n e Oxa la te (7). A solution of 10 M
BH3‚CH3SCH3 (0.06 mL) in dry diglyme (1 mL) was added
dropwise at room temperature to a solution of 20 (0.26 g, 0.60
mmol) in dry diglyme (12 mL) with stirring under a stream of
dry nitrogen with exclusion of moisture. When the addition
was completed, the reaction mixture was heated at 120 °C for
8 h. After cooling at 0 °C, excess borane was destroyed by
cautious dropwise addition of MeOH (5 mL). The resulting
mixture was left to stand overnight at room temperature,
cooled at 0 °C, treated with HCl gas for 10 min, and then
heated at 120 °C for 4 h. Removal of the solvent under reduced
pressure gave a residue, which was dissolved in water. The
aqueous solution was basified with NaOH pellets and ex-
tracted with CHCl3. Removal of dried solvent gave a residue,
which was purified by column chromatography. Eluting with
cyclohexanes-EtOAc-EtOH (8:1.5:0.5) afforded 7 as the free
The free base was transformed into the hydrochloride salt,
which was crystallized from 2-PrOH/Et2O: 0.3 g (48% yield);
mp 161-163 °C; 1H NMR (DMSO) δ 2.67-3.54 (m, 7, CH2-
NCH2, 2-H, 3-H, and 4-H), 3.75 (s, 6, OCH3), 4.04 (m, 2, CH2O),
6.68-8.07 (m, 12, ArH), 8.53 (br s, 1, NH, exchangeable with
1
D2O), 9.59 (br s, 1, NH, exchangeable with D2O). Anal. (C27H29
-
base: 0.18 g (72% yield); Rf 0.29; H NMR (CDCl3) δ 1.64 (br
NO4‚HCl) C, H, N.
s, 1, NH, exchangeable with D2O), 2.52-3.13 (m, 7, CH2NCH2,
3-H and 4-H), 3.82 (s, 6, OCH3), 4.09 (m, 2, CH2O), 4.36 (m, 1,
2-H), 6.52-7.40 (m, 12, ArH).
The free base was transformed into the oxalate salt and
crystallized from EtOH/Et2O. The melting point was indefinite;
fusion started at 103 °C and was complete at 159-161 °C.
Anal. (C26H29NO4‚H2C2O4) C, H, N.
cis-3-P h en yl-2-[[[2-(2,6-d im eth oxyp h en oxy)eth yl]a m i-
n o]m eth yl]ch r om a n e Oxa la te (6). This was synthesized
from 19 (0.37 g, 0.85 mmol) following the procedure described
for 7. Eluting with cyclohexanes-EtOAc-EtOH (8:1.2:0.8)
afforded 6 as the free base: 0.17 g (48% yield); Rf 0.20; 1H
NMR (CDCl3) δ 2.60-3.48 (m, 8, CH2NCH2, 3-H, 4-H, and NH,
exchangeable with D2O), 3.80 (s, 6, OCH3), 4.11 (m, 2, CH2O),
4.52 (m, 1, 2-H), 6.52-7.34 (m, 12, ArH).
The free base was transformed into the oxalate salt and
crystallized from 2-PrOH. The melting point was indefinite;
fusion started at 120 °C and was complete at 154-156 °C.
Anal. (C26H29NO4‚H2C2O4) C, H, N.
2-P h en yl-3-[[[2-(2,6-d im eth oxyp h en oxy)eth yl]a m in o]-
m eth yl]-3-ch r om en e Oxa la te (8). A 2.03 M solution of HCl
gas in EtOH (1.67 mL) was added to a solution of 1321
hydrochloride (2.0 g, 10.14 mmol) and 2123 (0.4 g, 1.69 mmol)
in EtOH (13 mL), followed by the addition of NaBH3CN (0.09
g, 1.35 mmol) and molecular sieves (4 Å). The mixture was
stirred at room temperature for 15 h, then acidified at pH 1
with 2 N HCl, filtered, and evaporated. The residue was taken
up with water and basified with 6 N KOH and the mixture
extracted with Et2O. After drying, the solvent was evaporated
and the residue purified by column chromatography. Eluting
with EtOAc gave 8 as the free base: 0.35 g (50% yield); 1H
NMR (CDCl3) δ 2.10 (br s, 1, NH, exchangeable with D2O),
2.98 (m, 2, NCH2), 3.30 (br s, 2, CH2N), 3.82 (s, 6, OCH3), 4.17
(m, 2, CH2O), 5.95 (br s, 1, CHd), 6.54-7.46 (m, 13, ArH and
2-H).
cis- a n d tr a n s-3-P h en ylch r om a n -2-ca r b oxylic Acid
Eth yl Ester s (15 a n d 16). Ester 1422 (1.1 g, 3.74 mmol) in
AcOH (9.35 mL) was hydrogenated over 10% Pd on charcoal
(0.074 g) for 10 h at 70 °C and 50 psi of pressure. Following
catalyst removal, the solution was diluted with water and
extracted with Et2O. The extracts were washed with 2 N
NaOH and water. Removal of dried solvent gave an oil, which
was purified by column chromatography eluting with cyclo-
hexanes-EtOAc (98:2). The trans isomer 16 eluted first: 0.22
g (21% yield); Rf 0.21; 1H NMR (CDCl3) δ 0.99 (t, 3, CH3), 3.10
(m, 2, 4-H), 3.42 (m, 1, 3-H), 4.01 (q, 2, CH2), 4.7 (d, J ) 8.10
Hz, 1, 2-H), 6.87-7.40 (m, 9, ArH).
The second fraction was the cis isomer 15: 0.41 g (39%
1
yield); mp 99-101 °C; Rf 0.16; H NMR (CDCl3) δ 1.09 (t, 3,
CH3), 3.04-3.38 (two dd, 2, 4-H), 3.72 (m, 1, 3-H), 4.09 (m, 2,
CH2), 4.89 (d, J ) 3.60 Hz, 1, 2-H), 6.90-7.35 (m, 9, ArH).
tr a n s-3-P h en ylch r om a n -2-ca r boxylic Acid (18). A mix-
ture of 16 (0.22 g, 0.78 mmol) and 2 N NaOH (3.1 mL) was
stirred at room temperature for 40 h. The mixture was
extracted with CHCl3, and the aqueous layer was acidified with
concentrated HCl. Extraction with CHCl3, followed by wash-
ing, drying, and evaporation of the extracts, gave 18: 0.18 g
1
(91% yield); mp 172-173 °C; H NMR (CDCl3) δ 3.10 (m, 2,
4-H), 3.52 (q, 1, 3-H), 4.82 (d, J ) 6.7 Hz, 1, 2-H), 6.35 (br s,
1, COOH, exchangeable with D2O), 6.90-7.40 (m, 9, ArH).
cis-3-P h en ylch r om a n -2-ca r boxylic Acid (17). This was
synthesized from 15 (0.41 g, 1.45 mmol) following the proce-
1
dure described for 18: 0.3 g (81% yield); mp 193-195 °C; H
NMR (CDCl3) δ 3.09 (dd, 1, 4-H), 3.45 (dd, 1, 4-H), 3.79 (m, 1,
3-H), 4.50 (br s, 1, COOH, exchangeable with D2O), 4.90 (d, J
) 3.01 Hz, 1, 2-H), 6.93-7.34 (m, 9, ArH).
tr a n s-3-P h en ylch r om an -2-car boxylic Acid [2-(2,6-Dim e-
t h oxyp h en oxy)et h yl]a m id e (20). Ethyl chlorocarbonate
(0.079 g, 0.708 mmol) was added dropwise to a stirred and
cooled (0 °C) solution of 18 (0.18 g, 0.708 mmol) and Et3N
(0.072 g, 0.708 mmol) in CHCl3 (10 mL), followed after 30 min
by the addition of a solution of 1321 (0.14 g, 0.708 mmol) in
CHCl3 (5 mL). The resulting reaction mixture was stirred for
4 h at room temperature and then washed with 2 N HCl, 2 N
NaOH, and finally water. Removal of dried solvent gave an
oil, which was purified by column chromatography. Eluting
with cyclohexanes-EtOAc (8:2) gave 20 as an oil: 0.26 g (85%
The free base was transformed into the oxalate salt, which
was crystallized from EtOH: mp 162-163 °C; 1H NMR
(DMSO) δ 3.22 (m, 2, CH2N), 3.47-3.89 (m, 2, NCH2), 3.75 (s,
6, OCH3), 4.11 (t, 2, CH2O), 6.09 (s, 1, CHd), 6.64-7.60 (m,
13, ArH and 2-H), 9.20 (br s, 1, NH, exchangeable with D2O).
Anal. (C26H27NO4‚H2C2O4) C, H, N.
2-(Ben zyloxy)p h en oxya cetic Acid Meth yl Ester (22).
A mixture of 2-(benzyloxy)phenol (3 g, 14.98 mmol), methyl
chloroacetate (1.63 g, 14.98 mmol), and K2CO3 (2.07 g, 14.98
mmol) in dry acetone (100 mL) was refluxed for 8 h. After
cooling, the solid was filtered and the solvent was evaporated.
The residue was dissolved in Et2O and washed with 2 N
NaOH. Removal of dried solvent gave 22 as an oil: 1.91 g (47%
yield); 1H NMR (DMSO) δ 3.70 (s, 3, OCH3), 4.82 (s, 2, OCH2-
CO), 5.12 (s, 2, OCH2Ph), 6.85-7.60 (m, 9, ArH).
1
yield); Rf 0.11; H NMR (CDCl3) δ 3.07 (t, 2, NCH2), 3.48 (m,
2, 4-H), 3.61 (q, 1, 3-H), 3.80 (s, 6, OCH3), 4.01 (t, 2, CH2O),
4.73 (d, J ) 6.02 Hz, 1, 2-H), 6.55-7.32 (m, 12, ArH), 7.50 (br
t, 1, NH, exchangeable with D2O).
cis-3-P h en ylch r om a n -2-ca r boxylic Acid [2-(2,6-Dim e-
th oxyp h en oxy)eth yl]a m id e (19). This was synthesized from
17 (0.3 g, 1.18 mmol) following the procedure described for
20. Removal of dried solvent gave an oil, which was triturated

2966 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15
Quaglia et al.
2-(Ben zyloxy)p h en oxya cetic Acid (23). A mixture of 22
(1.91 g, 7.01 mmol) and 2 N NaOH (10 mL) was stirred at 70
°C for 30 min. The cooled mixture was extracted with CHCl3,
and the aqueous layer was acidified with concentrated HCl.
Extraction with CHCl3, followed by washing, drying, and
evaporation of the extracts, gave a solid, which was crystallized
and normetaepinephrine hydrochloride (1 µM) were added to
prevent neuronal and extraneuronal uptake of (-)-noradrena-
line. The spleen strips were placed under 1-g resting tension
and equilibrated for 1 h. The cumulative concentration-
response curves to (-)-noradrenaline were measured iso-
metrically and obtained at 45-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; then a
new concentration-response curve to the agonist was con-
structed.
1
from cyclohexane: 1.5 g (83% yield); mp 90-91 °C; H NMR
(CDCl3) δ 4.69 (s, 2, OCH2CO), 5.16 (s, 2, OCH2Ph), 6.90-7.49
(m, 10, ArH and COOH, exchangeable with D2O).
2-(Ben zyloxy)p h en oxya cetic Acid [2-(2,6-Dim eth oxy-
p h en oxy)eth yl]a m id e (24). This was synthesized from 23
(0.66 g, 2.56 mmol) following the procedure described for 20.
The oil residue was purified by column chromatography.
Eluting with cyclohexanes-EtOAc (75:25) gave 24: 0.87 g
Ra t Aor ta . This tissue (from rats of 250-300 g) was used
to assess R1D-adrenoreceptor antagonist potency.31 Thoracic
aorta was cleaned from extraneous connective tissue and
placed in Krebs solution of the following composition (mM):
NaCl, 118.4; KCl, 4.7; CaCl2, 1.9; MgSO4, 1.2; NaHCO3, 25.0;
NaH2PO4, 1.2; glucose, 11.7. Cocaine hydrochloride (0.1 µM)
and (()-propranolol hydrochloride (1 µM) were added to
prevent the neuronal uptake of (-)-noradrenaline and to block
â-adrenoreceptors, respectively. Two helicoidal strips (15 mm
× 3 mm) were cut from each aorta beginning from the end
most proximal to the heart. The endothelium was removed by
rubbing with filter paper: the absence of acetylcholine (100
µM)-induced relaxation to preparations contracted with (-)-
noradrenaline (1 µM) was taken as an indicator that vessel
was denuded successfully. Vascular strips were then tied with
surgical thread and suspended in a jacketed tissue bath
containing Tyrode solution. Strips were secured at one end to
Plexiglas hooks and connected to a transducer for monitoring
changes in isometric contraction. After at least a 1-h equilibra-
tion period under an optimal tension of 1 g, cumulative (-)-
noradrenaline concentration-response curves were recorded
at 30-min intervals, the first two being discarded and the third
one taken as control. The antagonist was allowed to equilibrate
with the tissue for 30 min before the generation of the fourth
cumulative concentration-response curve to (-)-noradrena-
line.
1
(78% yield); H NMR (CDCl3) δ 3.58 (q, 2, NCH2), 3.76 (s, 6,
OCH3), 4.08 (t, 2, CH2O), 4.57 (s, 2, OCH2CO), 5.09 (s, 2, OCH2-
Ph), 6.50-7.44 (m, 12, ArH), 7.90 (br t, 1, NH, exchangeable
with D2O).
N-[2-[2-(Ben zyloxy)ph en oxy]eth yl]-N-[2-(2,6-dim eth oxy-
p h en oxy)et h yl]a m in e Oxa la t e (9). This was synthesized
from 24 (0.85 g, 1.94 mmol) following the procedure described
for 7. The oil residue was purified by column chromatography.
Eluting with a dried mixture of EtOAc-33% NH4OH (200:0.6)
gave 9 as the free base: 0.3 g (37% yield); 1H NMR (CDCl3) δ
2.62 (br s, 1, NH, exchangeable with D2O), 2.98 (t, 2, CH2N),
3.11 (t, 2, CH2N), 3.80 (s, 6, OCH3), 4.09-4.26 (dt, 4, OCH2
and CH2O), 5.10 (s, 2, OCH2Ph), 6.51-7.48 (m, 12, ArH).
The free base was transformed into the oxalate salt, which
was crystallized from 2-PrOH. The melting point was indefi-
nite; fusion started at 120 °C and was complete at 140-142
°C. Anal. (C25H29NO5‚H2C2O4) C, H, N.
Biology. F u n ction a l An ta gon ism in Isola ted Tissu es.
Male Sprague-Dawley rats and guinea pigs (Charles River,
Italy) were killed by cervical dislocation under ketamine
anesthesia, and the organs required were isolated, freed from
adhering connective tissue, and set up rapidly under a suitable
resting tension in 15-mL organ baths containing physiological
salt solution kept at appropriate temperature (see below) and
aerated with 5% CO2:95% O2 at pH 7.4. Concentration-
response curves were constructed by cumulative addition of
agonist. The concentration of agonist in the organ bath was
increased approximately 5-fold at each step, with each addition
being made only after the response to the previous addition
had attained a maximal level and remained steady. Contrac-
tions were recorded by means of a force displacement trans-
ducer (FT.03 Grass and 7003 Basile) connected to a four-
channel pen recorder (Battaglia-Rangoni KV 380). In addition
parallel experiments in which tissues did not receive any
antagonist were run in order to check any variation in
sensitivity.
Ra t Va s Defer en s P r osta tic P or tion . This tissue (from
rats of 200-230 g) was used to assess R1A-adrenergic antago-
nism.30 Prostatic portions of 2-cm length were mounted under
300-350-g tension at 37 °C in Tyrode solution of the following
composition (mM): NaCl, 130.0; KCl, 2.0; CaCl2‚2H2O, 1.8;
MgCl2, 0.89; NaHCO3, 25.0; NaH2PO4‚2H2O, 0.42; glucose, 5.6.
Cocaine hydrochloride (0.1 µM) was added to the Tyrode to
prevent the neuronal uptake of (-)-noradrenaline. The prepa-
rations were equilibrated for 60 min with washing every 20
min. After the equilibration period, tissues were primed two
times by addition of 10 µM noradrenaline. After another
washing and equilibration period of 60 min, a noradrenaline
concentration-response curve was constructed (basal re-
sponse). The antagonist was allowed to equilibrate with the
tissue for 30 min; then a new concentration-response curve
to the agonist was obtained. (-)-Noradrenaline solutions
contained 0.05% Na2S2O5 to prevent oxidation.
Ra d ioliga n d Bin d in g Assa ys. 1. Na tive Recep tor s.
Binding studies on native R2-adrenoreceptors, 5-HT2A sero-
toninergic receptors, and D2 dopaminergic receptors were
carried out in membranes of rat cerebral cortex (R2 and
25,27
5-HT2A
)
and striatum (D2).26 Male Sprague-Dawley rats
(200-300 g; Charles River, Italy) were killed by cervical
dislocation, and different tissues were excised immediately
frozen, and stored at -70 °C until use. For R2 and 5-HT2A
membrane preparations, cerebral cortex were homogenized (2
× 20 s) in 50 volumes of cold Tris-HCl buffer, pH 7.4, using a
Politron homogenizer (speed 7). Homogenates were centrifuged
at 49000g for 10 min, resuspended in 50 volumes of the same
buffer, incubated at 37 °C for 15 min, and centrifuged and
resuspended two more times. The final pellets were suspended
in 100 volumes of Tris-HCl buffer, pH 7.4, containing 10 µM
pargiline and 0.1% ascorbic acid. Membranes were incubated
in a final volume of 1 mL for 30 min at 25 °C with 0.5-1.5
nM [3H]rauwolscine (R2-adrenoreceptors) or for 20 min at 37
°C with 0.7-1.3 nM [3H]ketanserin (5-HT2A serotoninergic
receptors), in the absence or presence of competing drugs. For
D2 membrane preparations, rat striata were homogenized (2
× 20 s) in 30 volumes of cold Tris-HCl buffer, pH 7.4, using a
Politron homogenizer (speed 7) and centrifuged at 49000g for
10 min. The final pellets were suspended in 200 volumes of
Tris-HCl incubation buffer containing 10 µM pargiline, 0.1%
ascorbic acid, and the following saline concentrations: NaCl,
120 mM; KCl, 5 mM; CaCl2, 2 mM; MgCl2, 1 mM, and then
membranes were incubated for 15 min at 37 °C with 0.2-0.6
nM [3H]spiperone. Nonspecific binding was determined in the
presence of 10 µM phentolamine (R2-adrenoreceptors), 2 µM
ketanserin (5-HT2A serotoninergic receptors), and 1 µM (+)-
butaclamol (D2 dopaminergic receptors). The incubation was
stopped by addition of ice-cold Tris-HCl buffer and rapid
filtration through 0.2% poly(ethylenimine)-pretreated What-
man GF/B or Schleicher & Schuell GF52 filters. The filters
were then washed with ice-cold buffer, and the radioactivity
retained on the filters was counted by liquid scintillation
spectrometry.
Gu in ea P ig Sp leen . This tissue (from guinea pigs of 250-
300 g) was employed to determine R1B-adrenoreceptor antago-
nist potency.31 The spleen was removed and bisected longitu-
dinally into two strips which were suspended in tissue baths
containing Krebs solution of the following composition (mM):
NaCl, 120.0; KCl, 5.5; CaCl2, 2.5; MgCl2, 1.2; NaHCO3, 20.0;
NaH2PO4, 1.2; glucose, 11.7. Cocaine hydrochloride (0.1 µM)

SARs in 1,4-Benzodioxan-Related Compounds
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 15 2967
2. Clon ed Recep tor s. Binding to cloned human R1-adreno-
receptor subtypes was performed in membranes from CHO
(chinese hamster ovary) cells transfected by electroporation
with DNA expressing the gene encoding each R1-adrenorecep-
tor subtype. Cloning and stable expression of the human R1-
adrenoreceptor gene was performed as previously described.24
CHO cell membranes (30 µg of protein) were incubated in 50
mM Tris-HCl, pH 7.4, with 0.1-0.4 nM [3H]prazosin, in a final
volume of 1.02 mL for 30 min at 25 °C, in the absence or
presence of competing drugs (1 pM-10 µM). Nonspecific
binding was determined in the presence of 10 µM phentola-
mine. The incubation was stopped by addition of ice-cold Tris-
HCl buffer and rapid filtration through 0.2% poly(ethylenimine)-
pretreated Whatman GF/B or Schleicher & Schuell GF52
filters. Genomic clone G-21 coding for the human 5-HT1A
receptor is stably transfected in a human cell line (HeLa).28
HeLa cells were grown as monolayers in Dulbecco’s modified
Eagle’s medium (DMEM), supplemented with 10% fetal calf
serum and gentamicin (100 µg/mL), 5% CO2 at 37 °C. Cells
were detached from the growth flask at 95% confluence by a
cell scraper and were lysed in ice-cold Tris (5 mM) and EDTA
(5 mM) buffer (pH 7.4). Homogenates were centrifuged at
40000g × 20 min, and pellets were resuspended in a small
volume of ice-cold Tris 5 (mM) and EDTA 5 (mM) buffer (pH
7.4), immediately frozen, and stored at -70 °C until use. On
the experimental day, cell membranes were resuspended in
binding buffer: 50 mM Tris-HCl (pH 7.4), 2.5 mM MgCl2, 10
µM pargiline.29 Membranes were incubated in a final volume
of 1 mL for 30 min at 30 °C with 0.7-1.4 nM [3H]8-OH-DPAT,
in the absence or presence of competing drugs. Nonspecific
binding was determined in the presence of 10 µM 5-HT. The
incubation was stopped by addition of ice-cold Tris-HCl buffer
and rapid filtration through 0.2% poly(ethylenimine)-pre-
treated Whatman GF/B or Schleicher & Schuell GF52 filters.
Stim u la tion of [35S]GTP γS Bin d in g a t Clon ed 5-HT1A
Ser oton in er gic Recep tor s. The effects of compound 8 tested
with [35S]GTPγS binding were evaluated according to the
method of Stanton and Beer32 with minor modifications. On
the experimental day, cell membranes from HeLa cells trans-
fected with human cloned 5-HT1A serotoninergic receptors,
prepared as above-described, were resunspended in buffer
containing 20 mM HEPES, 3 mM MgSO4, and 120 mM NaCl
(pH 7.4). The membranes were incubated with 30 µM GDP
and decreasing concentrations of test drugs (from 100 µM to
0.1 nM) or decreasing concentrations of 5-HT, from 100 µM to
0.1 nM (reference curve), for 20 min at 30 °C in a final volume
of about 0.5 mL. Samples were then transferred to ice, added
with [35S]GTPγS (150-250 pM), and then incubated for a
further 30 min at 30 °C. Nonspecific binding was determined
in the presence of 10 µM GTPγS. The incubation was stopped
by addition of ice-cold HEPES and rapid filtration on Schle-
icher & Schuell GF52 filters, using a Brandel cell harvester.
The filters were washed three times with a total of 5 mL of
the same buffer. Radioactivity was counted by liquid scintil-
lation spectrometry at efficiency >90%. All assays were carried
out in triplicate on 2-3 separate sessions.
radioligand. pKi values (Table 2) are the mean ( SE of 2-3
separate experiments performed in triplicate.
Stimulation of [35S]GTPγS binding induced by the com-
pounds tested was expressed as percent increase in binding
above the basal value, being the maximal stimulation observed
with 5-HT taken as 100%. The concentration-response curve
of the agonistic activity was analyzed by the nonlinear curve-
fitting program Allifit.34 The maximal stimulation of [35S]-
GTPγS binding (Emax) achieved for each drug and the concen-
tration required to obtain 50% of Emax (pD2 value) were
evaluated.
Ack n ow led gm en t. This work was supported by
grants from the University of Camerino, University of
Bologna, and MURST.
Refer en ces
(1) For parts 4 and 5, see refs 15 and 17, respectively.
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Da ta An a lysis. In functional studies responses were ex-
pressed as percentage of the maximal contraction observed in
the agonist concentration-response curve taken as a control.
The agonist concentration-response curves were analyzed by
pharmacological computer programs. pKb values were calcu-
lated according to Arunlakshana and Schild33 by the formula:
pKb ) log([B]/(DR - 1)), where B is the antagonist concentra-
tion and the dose ratio (DR) is the ratio of the potency of the
agonist (EC50) in the presence of the antagonist and in its
absence. DR values were obtained for 2-3 different antagonist
concentrations, and each concentration was tested four times.
Binding data were analyzed using the nonlinear curve-
fitting program Allfit.34 Scatchard plots were linear in all
preparations. All pseudo-Hill coefficients (nH) were not sig-
nificantly different from unity (p > 0.05). Equilibrium inhibi-
tion constants (Ki) were derived from the Cheng-Prusoff
equation:35 Ki ) IC50/(1 + L/Kd), where L and Kd are the
concentration and the equilibrium dissociation constant of the
(11) (a) Melchiorre, C.; Giardina`, D.; Gallucci, P.; Brasili, L. Struc-
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pancy by Cyclic and Open Analogues of WB 4101. J . Pharm.
Pharmacol. 1982, 34, 683-644. (b) Giardina`, D.; Angeli, P.;
Brasili, L.; Gulini, U.; Melchiorre, C.; Strappaghetti, G. Syn-
thesis and R-Blocking Activity of Some Cyclic and Opened
Analogues of WB 4101. Eur. J . Med. Chem. 1984, 19, 411-414.
(12) Melchiorre, C.; Brasili, L.; Giardina`, D.; Pigini, M.; Strappa-
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1,4-benzoxathian: a New Antagonist with High Potency and
Selectivity Toward R1-Adrenoreceptors. J . Med. Chem. 1984, 27,
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(13) Pigini, M.; Brasili, L.; Giannella, M.; Giardina`, D.; Gulini, U.;
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