'Hybrid' benzofuran-benzopyran congeners as rigid analogs of hallucinogenic phenethylamines

Article abstract of DOI:10.1016/j.bmc.2008.04.030

Phenylalkylamines that possess conformationally rigidified furanyl moieties in place of alkoxy arene ring substituents have been shown previously to possess the highest affinities and agonist functional potencies at the serotonin 5-HT_2A recepto

Full text of DOI:10.1016/j.bmc.2008.04.030

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 6242–6251
‘Hybrid’ benzofuran–benzopyran congeners as rigid analogs
of hallucinogenic phenethylamines
Danielle M. Schultz,a Jennifer A. Prescher,a Stephanie Kidd,b Danuta Marona-Lewicka,b
David E. Nicholsb and Aaron Montea,*
aDepartment of Chemistry, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, WI 54601, USA
bDepartment of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences,
Purdue University, West Lafayette, IN 47907, USA
Received 11 April 2008; accepted 14 April 2008
Available online 6 May 2008
Abstract—Phenylalkylamines that possess conformationally rigidified furanyl moieties in place of alkoxy arene ring substituents
have been shown previously to possess the highest affinities and agonist functional potencies at the serotonin 5-HT2A receptor
among this chemical class. Further, affinity declines when both furanyl rings are expanded to the larger dipyranyl ring system.
The present paper reports the synthesis and pharmacological evaluation of a series of ‘hybrid’ benzofuranyl–benzopyranyl phen-
ylalkylamines to probe further the sizes of the binding pockets within the serotonin 5-HT2A agonist binding site. Thus, 4(a–b),
5(a–b), and 6 were prepared as homologs of the parent compound, 8-bromo-1-(2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b0]difuran-4-yl)-
2-aminopropane 2, and their affinity, functional potency, and intrinsic activity were assessed using cells stably expressing the rat
5-HT2A receptor. The behavioral pharmacology of these new analogs was also evaluated in the two-lever drug discrimination par-
adigm. Although all of the hybrid isomers had similar, nanomolar range receptor affinities, those with the smaller furanyl ring at the
arene 2-position (4a–b) displayed a 4- to 15-fold greater functional potency than those with the larger pyranyl ring at that position
(5a–b). When the furan ring of the more potent agonist 4b was aromatized to give 6, a receptor affinity similar to the parent difuranyl
compound 2 was attained, along with a functional potency equivalent to 2, 4a, and 4b. In drug discrimination experiments using rats
trained to discriminate LSD from saline, 4b was more than two times more potent than 5b, with the latter having a potency similar
to the classic hallucinogenic amphetamine 1 (DOB).
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
ethylamine agonists for this receptor,3,4 and we have been
interested in extending it to provide a more comprehen-
sive description of the key amino acid residues involved
in receptor binding and activation.5 As a member of the
type A G-protein coupled receptor (GPCR) family, we
Agonist activity at the serotonin 5-HT2A receptor appears
to be essential for the observed psychopharmacology of
psychedelic agents such as LSD, mescaline, psilocin,
and 5-MeO-DMT, compounds that exert unique and dra-
matic effects on certain aspects of consciousness.1 A key
aspect to understanding the unusual effects of psychedel-
ics is the study of the receptor–ligand interaction at the
molecular level and how it modulates second messenger
generation subsequent to receptor activation.
OCH3
O
O
O
NH2
CH3
NH2
NH2
CH3
R
Br
Br
Br
OCH3
O
2
1
3a R = H
b R = CH3
Recently, we have been particularly interested in experi-
mental validation of our h5-HT2A receptor homology
model.2 This model has proven to have predictive power
in designing simple conformationally constrained phen-
O
O
O
NH2
NH2
CH3
NH2
R
R
Br
Br
Br
Keywords: Phenethylamines; Hallucinogen; 5-HT receptor agonist; S-
tructure–activity relationship.
O
O
O
*
Corresponding author. Tel.: +1 608 785 8260; fax: +1 608 785
8281; e-mail: monte.aaro@uwlax.edu
4a R = H
b R = CH3
5a R = H
b R = CH3
6
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.04.030

D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
6243
OCH3
OCH3
reasoned that understanding this receptor would provide
general concepts that might extend across the GPCR field.
OCH3
Br
a
b
c
Br
We previously discovered that constraining the 2- and 5-
methoxy groups of prototypical, substituted phenethyl-
amine ligands such as 2,5-dimethoxy-4-bromoamphet-
amine (DOB) 1 into rigid heterocycles gave highly
potent compounds such as 2.6 These findings clearly
demonstrated that the methoxy groups adopted particu-
lar orientations upon binding to the 5-HT2A receptor,
presumably to direct their unshared electron pairs to-
ward polar complementary residues within the agonist
binding site, most likely serine residues S239 and
S159.2,5 We also had found that expanding the two het-
erocyclic rings to two, six-membered dihydropyran moi-
eties, as in 3, led to an almost 10-fold decrease in
activity, both in vitro and in vivo.7 The most reasonable
explanation for these findings was that the receptor
space around one, or both, of the oxygen atoms was ste-
rically constricted.
O
O
OH
Br
Br
7
9
8
OH
Br
O
O
O
Br
Br
d
e
Br
Br
O
O
Br
Br
10
11
12
Scheme 1. Reagents and conditions: (a) 1,2-dibromoethane, K2CO3,
acetone, reflux; (b) Br2, CH2Cl2, Fe; (c) B-bromo-9-BBN, CH2Cl2,
reflux 14 days; (d) 1,3-dibromopropane, K2CO3, acetone, reflux; (e) n-
butyllithium, THF, 0 °C.
mild demethylating agent was found to be highly effec-
tive, whereas the more reactive traditional reagents,
HBr, BBr3 and BCl3, were all found to cleave both of
the ether moieties of 9. Due to the moderately unstable
nature of phenol 10, after isolation, it was immediately
alkylated with 1,3-dibromopropane to afford the desired
diether 11. Finally, the simultaneous tandem ring-clo-
sure of 11 to yield key tricyclic intermediate 12 was read-
ily achieved using n-butyllithium.
This present study extends that earlier work, where now
the activity of the two isomeric pyrano/furano ‘hybrid’
analogues (4a–b vs 5a–b) is examined to determine
which, if either, of the oxygen atoms lies within a more
constrained steric area. Our virtual docking experiments
place the 2-oxygen atom downward in the binding cav-
ity, whereas the 5-oxygen atom is projected upward to-
ward the extracellular face of the receptor.3,5,8 These
observations suggest that the oxygen atom that is more
deeply embedded in the receptor might be the one that
has greater steric restriction around it. The present
experiments tested that hypothesis, and compared com-
pounds 4a and 4b with 5a and 5b, respectively, for affin-
ity and functional potency at the 5-HT2A receptor. We
also examined 4b and 5b for an LSD-like behavioral ef-
fect in rats. Because the lipophilic properties of these lat-
ter two compounds are virtually identical, any difference
in activity would be related to pharmacodynamic, rather
than pharmacokinetic effects. In addition, because it was
known that aromatization of the furan rings in 2 greatly
enhanced activity,9 we aromatized the furan ring of 4b
to afford 6 and examined the effect on receptor affinity
and potency.
With 12 in hand, formylation using dichloromethyl
methyl ether in the presence of a tin(IV) catalyst pro-
duced regioisomers 13 and 14 (Scheme 2). Separation
of these isomers by selective recrystallization and flash
column chromatography12 gave 13 and 14 in a 5:1 ratio,
respectively. Both aldehydes were then carried through
the parallel sequence of reactions shown in Scheme 2.
Thus, following condensation of the aldehydes with
nitromethane or nitroethane, the resulting nitroalkenes
15 and 16 were fully reduced in the presence of LiAlH4
to afford primary amines 17 and 18. Target compounds
4a–b and 5a–b were then produced in good yield by bro-
minating the remaining aromatic positions of 17 and 18,
respectively.
Aromatization of the furan ring of 4b was accomplished
using a method analogous to that employed by Parker
et al.9 As shown in Scheme 3, dihydrofuran 17b was pro-
tected as its N-trifluoroacetamide 19, brominated to
provide 20, and then oxidized using 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) to afford the pro-
tected intermediate 21. Deprotection in strong base gave
6, the final target molecule. The relatively minor
amounts of 14 obtained from the formylation reaction
in Scheme 2 precluded a parallel synthesis of aromatized
5b; fortunately, 4b proved to be the more potent isomer,
and its oxidized analog 6 sufficiently demonstrated the
effects of aromatization of the furan ring.
2. Results
2.1. Chemistry
It was envisioned that all target molecules 4–6 could be
prepared readily from their common tricyclic intermedi-
ate 12 (Scheme 1). This asymmetric pyrano/furano hy-
brid ring system required that the precursors of each
oxygen heterocycle (the respective bromoethyl and bro-
mopropyl ether moieties) be constructed independently,
as outlined in the scheme. Initially, para-methoxy phe-
nol 7 was alkylated with dibromoethane to provide
diether 8. (Our early attempts to build the larger pyran
ring first, by alkylating with 1,3-dibromopropane,
proved to be considerably less efficient.) Following
dibromination of 8, the aromatic methyl ether of 9
was selectively cleaved using B-bromo-9-BBN.10,11 This
2.2. Pharmacology
All new target compounds were assessed for their affin-
ity at the rat 5-HT2A receptor, using displacement of

6244
D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
O
O
O
O
NO2
NH2
b
H
c
d
4 a,b
R
R
O
O
O
17a R = H
b R = CH3
13
15a R = H
b R = CH3
a
12
O
O
O
O
NO2
NH2
b
H
c
d
5 a,b
R
R
O
O
O
14
16a R = H
b R = CH3
18a R = H
b R = CH3
Scheme 2. Reagents and conditions: (a) dichloromethyl methyl ether, SnCl4, CH2Cl2, 0 °C; (b) RCH2NO2, ammonium acetate, 80 °C; (c) LiAlH4,
THF, reflux; (d) Br2, AcOH.
O
O
O
H
N
H
N
CF3
NH2
CF3
b
a
O
O
Br
O
O
O
17b
19
20
O
H
c
N
CF3
d
6
O
Br
O
21
Scheme 3. Reagents and conditions: (a) ethyl trifluoroacetate, Et3N, THF, reflux; (b) AcOH, Br2, dioxane; (c) DDQ, toluene, reflux; (d) 5 M KOH,
MeOH.
[3H]ketanserin. In addition, functional potency and
Table 1. Analysis of biological activity at the rat 5-HT2A receptor
intrinsic activity were determined using the inositol
phosphate accumulation assay.13 The affinities and
potencies of the new compounds were compared with
the prototype dimethoxy compound, DOB 1, and its
rigidified difurano and dipyrano analogs, 2 and 3,
respectively. These data are presented in Table 1, along
with the clogP values of all compounds. Behavioral
pharmacology for new compounds 4b and 5b was as-
sessed using the two-lever drug discrimination para-
digm,14–18 and those results are presented in Table 2,
along with the comparative data for 1.
Drug clogP 5-HT2A Ki,
n
EC50
,
Intrinsic activity
n
nM (SEM)
nM (SEM) % 5-HT (SEM)
1
2.45
2.65
3.46
3.77
2.90
3.21
2.90
3.21
3.77
13 (6.0)
2
5
3
4
3
6
3
7
5
22 (3.8)
13 (1.9)
241 (46)
258 (45)
9.4 (1.2)
19 (1.9)
146 (30)
78 (11)
73 (5)
88 (4)
61 (9)
72 (2)
61 (6)
86 (7)
64 (12)
74 (8)
102 (6)
3
3
3
3
3
5
3
4
3
2
1.0 (0.12)
4.5 (0.76)
3.1 (0.55)
11 (1.4)
3a
3b
4a
4b
5a
5b
6
3.6 (0.73)
8.4 (0.35)
5.3 (0.57)
1.0 (0.12)
13 (1.9)
Ki values for [3H]ketanserin competition displacement assays in NIH-
3T3 cells expressing the rat 5-HT2A receptor and functional potency
for stimulating inositol phosphate accumulation in the same cells.
As seen in Table 1, the two new hybrid congeners, 4 and
5, as well as the dipyrano compounds 3,7 had approxi-
mately 4- to 5-fold lower affinity than the difurano ana-
log 2, suggesting that the smaller furan rings are better
tolerated by the receptor than the larger pyran rings.
There was no significant difference in receptor affinity
between 4 and 5. As we had previously observed with
the aromatization of 2,9,19 oxidation of the dihydrofuran
ring of 4b to give 6 increased receptor affinity nearly 4-
fold (compare Ki values of 4b and 6).
5b, and was nearly as potent as the difuranyl compound
2. Surprisingly, although the receptor affinities were
nearly the same for the dipyranyl compound 3b and
the smaller hybrid compound 4b, the latter was func-
tionally more than an order of magnitude more potent
than 3b in stimulating inositol phosphate accumulation.
Further, aromatization of the furan ring of 4b to give 6
had virtually no effect on potency, although receptor
affinity was enhanced. Comparison of 3a with 3b, 4a
with 4b, and 5a with 5b also shows that the addition
When functional potency was examined (see EC50 values
in Table 1), 4b had about 4-fold higher potency in stim-
ulating inositol phosphate accumulation, compared to

D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
Table 2. Results from substitution tests in LSD-trained rats
6245
Drug
Dose
N
% D
% SDL
ED50 (95% CL)
lmol/kg
1.06
mg/kg
lmol/kg
mg/kg
1
0.25
0.38
0.50
0.80
1.21
1.61
13
10
14
46
40
36
29
50
89
0.35
(0.27–0.46)
(0.82–1.36)
4b
5b
0.09
0.17
0.35
0.25
0.50
1.00
12
11
12
0
0
0
33
54
83
0.14
(0.08–0.23)
0.38
(0.24–0.60)
0.17
0.35
0.69
0.50
1.00
2.00
12
12
10
17
0
10
41
80
0.40
(0.26–0.61)
1.16
(0.77–1.75)
0
All drugs were injected 30 min before tests. N, number of rats used for tests. % D, the percentage of rats with disrupted behavior. % SDL, the
percentage of rats that selected the drug-appropriate lever. If the drug was one that completely substituted for the training drug, the method of
Litchfield and Wilcoxon20 was used to determine the ED50 and 95% confidence interval (95% CL).
of the alpha methyl slightly enhances intrinsic activity in
this series, confirming the earlier conclusions drawn by
Parrish et al.8
Although this conclusion is not as evident in the affinity
data, it is clearly apparent when functional potency is
assessed. Indeed, because affinity simply measures how
tightly the ligand binds to the receptor, measures of
functional potency better reflect general complementar-
ity between the agonist and the receptor.
The drug discrimination (DD) paradigm routinely has
been used in our laboratory as a screen for evaluating
the behavioral activity and hallucinogenic potential of
newly synthesized molecules.14–16 This assay system
models human hallucinogenic effects by examining the
LSD-like discriminative stimulus properties produced
in animals.17,18 Thus, compounds 1, 4b, and 5b were
evaluated in the two-lever DD assay using a group of
rats trained to discriminate the effects of ip injections
of saline from those of D-lysergic acid N,N-diethylamide
(LSD) tartrate (0.08 mg/kg; 186 nmol/kg) (Table 2). As
can be seen in Table 2, 4b has nearly three times the
in vivo potency of 5b, whereas the ED50s for 1 and 5b
are not significantly different from each other.
Intrinsic activity also is increased slightly by addition of
the alpha-methyl to the side chain (compare 3a with 3b,
4a with 4b, and 5a with 5b). We previously reported a
similar result for other substituted hallucinogenic phen-
alkylamines.8 Although there is no definitive explana-
tion for this observation, our virtual docking studies8
prompt us to speculate that the alpha-methyl may have
favorable van der Waals interactions with a residue in
transmembrane helix 6. Although aromatization of the
furan rings of 2 leads to the most potent simple pheneth-
ylamine type agonists presently known,9,19 aromatiza-
tion of the furan ring of 4b to 6 had a slight, albeit
non-significant, effect on intrinsic activity. It should be
noted, however, that this aromatization did increase
receptor affinity nearly 4-fold.
3. Discussion
Previously, we demonstrated that when the two meth-
oxy groups of 1 are constrained into dihydrofuran rings,
as in 2, both receptor affinity and functional potency are
significantly increased.9 In a prior study, we also had
shown that expansion of both furan rings to the larger,
six-membered pyrans led to a nearly 10-fold loss of affin-
ity and in vivo behavioral activity, although compounds
3 were still significantly more potent than the flexible
prototype 1.7 In this report, new compounds 4–6 further
support those earlier observations and confirm the prop-
er orientation of the arene oxygen lone pair electrons for
optimal activity at the 5-HT2A receptor.
Of the new compounds reported here, those with the
smaller O-heterocycle (furan) at the 2-position of the
aryl ring (4a, 4b, and 6) clearly have higher affinities
and functional potencies than those with the smaller
O-heterocycle (furan) at the 5-position (5a and 5b).
These findings support our primary current hypothesis
that the 5-HT2A receptor is more tolerant of steric bulk
in the region that interacts with the 5-oxygen function.
Data from the in vivo behavioral studies using the drug
discrimination paradigm, where rats are trained to dis-
criminate LSD from saline, are also consistent with
these conclusions. Thus, analog 4b, which had a 4-fold
higher functional potency than 5b, proved to be nearly
three times more potent than 5b in this in vivo assay. Be-
cause 4 and 5 have essentially identical pharmacokinetic
properties (compare clogP values in Table 1), as well as
similar affinities and intrinsic activities, the in vivo po-
tency seems to be primarily attributable to the func-
tional potency of the ligand, and thus to a highly
complementary agonist–receptor interaction. Nonethe-
less, 5b, where the 2-oxygen is incorporated into a pyran
ring and the 5-oxygen into a furan ring, still produced a
On the basis of virtual docking studies, we have hypoth-
esized that the 5-HT2A receptor has less steric tolerance
around the oxygen moiety that projects downward into
the receptor than the one projected toward the extracel-
lular face of the receptor.2 Those virtual docking studies
are supported by our recent mutagenesis experiments
and indicate that the 5-oxygen of 1 projects upward, to-
ward the extracellular face of the receptor, whereas the
2-oxygen projects downward into the receptor binding
cavity.5 In the present study, a comparison of the activ-
ities of 4 and 5 further supports this hypothesis.

6246
D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
discriminative stimulus effect similar to that of 1. It
should be noted that the loss of potency of 5b, when
compared with 4b, was not as dramatic as was observed
earlier for compounds 3, where both oxygen atoms are
incorporated into larger pyran rings.7
Facility. All solvents (acetone, diethyl ether, CH2Cl2,
THF, ethyl acetate, hexanes, acetic acid, and toluene)
were obtained from Fisher Scientific and used as re-
ceived. Most inorganic reagents, along with 4-methoxy-
phenol, 1,3-dibromopropane, 1,2-dibromoethane, 1.0 M
B-bromo-9-BBN in CH2Cl2, dichloromethyl methyl
ether, DDQ, ethyl trifluoroacetate, nitromethane, and
nitroethane were used as received from Sigma–Aldrich.
The high potency and intrinsic activity of compounds
with an extended aromatic system, that is, 6, suggests
that they are also closely complementary to the agonist
binding site of the receptor. Because the endogenous
agonist ligand, serotonin, is based on a bicyclic aromatic
indole nucleus, we speculate that the aromatic furan
rings better mimic the indole system and provide a more
extensive p–p stacking partner for an aromatic residue
within the receptor. Furthermore, the differences in
hydrophobicity between 4b, 5b, and 6 are most likely
so small as to not contribute significantly to the different
in vivo activities of these agents; rather, the primary fac-
tors influencing activity and potency in this class appear
to be the steric–electronic effects of the heterocyclic moi-
eties of the 2 and 5 positions.
4.2. Synthesis of 13
4.2.1. 1-(2-Bromoethoxy)-4-methoxybenzene (8)21.
A
solution of 7 (10.1 g, 81.3 mmol) dissolved in acetone
(100 mL) was added over a 12 h period to a mixture of
1,2-dibromoethane (35 mL, 0.41 mol), finely powdered
K2CO3 (35 g, 0.25 mol) and acetone (300 mL) at reflux.
The reaction was held at reflux for 125 h before the
K2CO3 was removed by filtration. After solvent removal
in vacuo, the remaining residue was combined with
CH2Cl2, washed with 2.5 M NaOH, 1 M HCl, and
brine, and dried over anhydrous MgSO4. Evaporation
of the volatiles in vacuo yielded an orange solid that
was treated with a 10% CH2Cl2–90% hexanes solution
(100 mL) to precipitate the dimeric material present.
Following filtration, the filtrate was evaporated in vacuo
and recrystallized from EtOAc/hexanes to yield 8.42 g
(44.8%) of 8 as translucent sheet-like crystals (mp 50–
In conclusion, we have demonstrated that the different
regioisomeric O-heterocycles in this homologous series
of phenethylamines are not equally well accommodated
by the receptor. In particular, we have shown that the
steric space around the 2-oxygen appears to be more
constrained than around the 5-position, as seen when
comparing the potencies of 4b with 5b. Future struc-
ture-activity relationship work probing the extent of
these different spatial size constraints is warranted and
is currently underway in our laboratories.
1
51 °C) with a H NMR spectrum identical to that re-
ported by Pomilio and Tettamanzi.21 Low-resolution
ESIMS, m/z (rel intensity) 136, 151, 178.
4.2.2.
1,4-Dibromo-2-(2-bromoethoxy)-5-methoxyben-
zene (9). Bromine (21.8 g, 0.137 mol) in CH2Cl2
(50 mL) was added dropwise to a mixture of 8 (14.9 g,
64.6 mmol) dissolved in CH2Cl2 (500 mL) with a cata-
lytic amount of Fe filings. The reaction continued for
24 h before the mixture was washed with 3 M NaOH,
3 M HCl, and brine. The organic phase was dried over
MgSO4 and the solvent was removed in vacuo to give
an orange solid that was recrystallized from EtOAc/hex-
anes to yield 21.5 g (85.3%) of 9 as off-white crystals: mp
4. Experimental
4.1. Chemistry
All reactions were carried out under an inert atmosphere
unless otherwise indicated. Melting points were deter-
mined using a Thomas-Hoover capillary melting point
apparatus and are uncorrected. Thin-layer chromatog-
raphy (TLC) was performed using Baker-flex silica gel
plastic-backed plates with fluorescent indicator, devel-
oping with CH2Cl2, and visualizing under UV light.
1H NMR spectra were obtained using a 300 MHz Bru-
ker AC-300 or a 300 MHz Bruker ARX-300 NMR spec-
trometer with TMS as the internal standard.
Abbreviations used in NMR analyses are as follows:
64–65 °C. 1H NMR (CDCl3)
d 3.66 (t, 2, Ar-
OCH2CH2Br, J = 6.4 Hz), 3.87 (s, 3, ArOCH3), 4.30
(t, 2, ArOCH2CH2Br, J = 6.4 Hz), 7.11 (s, 1, ArH),
7.17 (s, 1, ArH). Low-resolution EIMS, m/z 386/388/
390 (M+), 309, 281. Anal. Calcd for C9H9Br3O2: C,
27.80; H, 2.31. Found: C, 27.69; H, 2.08.
4.2.3. 2,5-Dibromo-4-(2-bromoethoxy)phenol (10).
A
br = broad,
s = singlet,
d = doublet,
t = triplet,
1.0 M B-Br-9-BBN (522 mL, 0.522 mol) was added
dropwise to a solution of 9 (45.0 g, 0.116 mol) in CH2Cl2
(1 L). The reaction continued for 14 days before the vol-
atiles were removed in vacuo to give a yellow colored oil
(that emitted white fumes). The oil was stirred under N2
for 2 h until the white fumes subsided, and the oil was
taken up in Et2O (500 mL) and brought to 0 °C. Etha-
nolamine (37.9 mL, 1.2 equiv relative to B-Br-9-BBN)
was added to precipitate the B-Br-9-BBN adduct, and
this solid was removed by filtration, washing thoroughly
with Et2O. Solvent was removed from the filtrate in va-
cuo to yield a yellow oil that was taken up in CH2Cl2
and washed with 3 M HCl and 3 M NaOH. The basic
extracts were acidified with 12 M HCl, and the solution
q = quartet, p = pentet, m = multiplet, and Ar = aro-
matic. GC–MS analyses were obtained using a Varian
3800 GC coupled to a Varian Saturn 2000 ion trap
MS. Infrared spectra were recorded on a Midac Pros-
pect FT-IR spectrometer. Elemental analyses were per-
formed by Quantitative Technologies, Inc. (QTI) of
Whitehouse, NJ, USA, and reported values are within
0.4% of the calculated values. High-resolution mass
spectrometry was performed with a Perkin-Elmer Voy-
ager matrix-assisted laser desorption ionization time-
of-flight (MALDI-TOF) mass spectrometer located in
the Biophysics Instrumentation Facility at the Univer-
sity of Wisconsin-Madison Biophysics Instrumentation

D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
6247
was extracted with CH2Cl2. The organic fractions were
combined, washed once with brine, dried over MgSO4,
and solvent removal in vacuo gave a yellow oil. The
crude oil was purified by dry column flash chromatogra-
phy22 on silica gel (eluting with CH2Cl2) to yield 29.5 g
(73.7%) of 10 as a fine white powder: mp 106–107 °C. IR
(NaCl, cmꢀ1) 3437, 3054, 2986, 1266. 1H NMR (CDCl3)
d 3.65 (t, 2, ArOCH2CH2Br, J = 6.4 Hz), 4.27 (t, 2, Ar-
OCH2CH2Br, J = 6.4 Hz), 5.29 (s, 1, ArOH), 7.07 (s, 1,
ArH), 7.28 (s, 1, ArH). Low-resolution EIMS, m/z 372/
374/376 (M+), 295, 267. Anal. Calcd for C8H7Br3O2: C,
25.63; H, 1.86. Found: C, 25.80; H, 1.64.
EtOAc/hexanes to afford 3.91 g (40.6%) of pure 13.
The remaining oil, containing both 13 and 14,was sub-
jected to silica gel flash chromatography (eluting with
95% CH2Cl2/5% hexane) to afford 14, the first to elute,
as a yellow solid: mp 72–73 °C. IR (NaCl, cmꢀ1) 3053,
2986, 1265. 1H NMR (CDCl3) d 1.96 (p, 2, Ar-
OCH2CH2CH2), 2.79 (t, 2, ArOCH2CH2CH2,
J = 6.5 Hz), 3.45 (t, 2, ArOCH2CH2, J = 8.8 Hz), 4.22
(t, 2, ArOCH2CH2CH2, J = 5.2 Hz), 4.55 (t, 2, Ar-
OCH2CH2, J = 8.8 Hz), 6.70 (s, 1, ArH), 10.47 (s, 1,
ArCHO). Low-resolution EIMS, m/z (rel intensity) 204
(M+, 100). Anal. Calcd for C12H12O3: C, 70.57; H,
5.92. Found: C, 70.36; H, 6.08.
4.2.4. 1,4-Dibromo-2-(2-bromoethoxy)-5-(3-bromo-pro-
poxy)benzene (11). In a manner analogous to the prepara-
tion of 8, 10 (17.5 g, 46.6 mmol) was alkylated with 1,3-
dibromopropane to give 18.3 g (79.0%) of 11 as white nee-
dle-like crystals: mp 67–68 °C. 1H NMR (CDCl3) d 2.34
The second to elute, 13, was isolated as a bright yellow
solid: mp 71–72 °C. IR (NaCl, cmꢀ1) 3054, 2986, 1264.
1H NMR (CDCl3) d 1.96 (p, 2, ArOCH2CH2CH2),
3.11 (t, 2, ArOCH2CH2CH2), superimposed upon 3.17
(t, 2, ArOCH2CH2, J = 8.7 Hz), 4.11 (t, 2, Ar-
OCH2CH2CH2, J = 5.1 Hz), 4.65 (t, 2, ArOCH2CH2,
J = 8.4 Hz), 6.92 (s, 1, ArH), 10.37 (s, 1, ArCHO).
Low-resolution EIMS, m/z (rel intensity) 204 (M+,
100). Anal. Calcd for C12H12O3: C, 70.57; H, 5.92.
Found: C, 70.47; H, 5.98.
(p,
2,
ArOCH2CH2CH2Br),
3.64
(t,
2,
ArOCH2CH2CH2Br), superimposed upon 3.67 (t, 2, Ar-
OCH2CH2Br), 4.10 (t, 2, ArOCH2CH2CH2Br,
J = 5.7 Hz), 4.27 (t, 2, ArOCH2CH2Br, J = 6.3 Hz), 7.17
(s, 1, ArH), 7.28 (s, 1, ArH). Low-resolution EIMS, m/z
492/494/496 (M+), 107. Anal. Calcd for C11H12Br4O2:
C, 26.65; H, 2.42. Found: C, 26.85; H, 2.20.
4.3. Synthesis of 4a and 5a
4.2.5. 3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromene (12).
Diether 11 (17.6 g, 35.5 mmol) was dissolved in anhy-
drous THF (75 mL) and cooled to 0 °C before the drop-
wise addition of 10 M n-butyllithium in hexanes
(10.9 mL, 109 mmol). The reaction was held at 0 °C
for 4 h before being quenched with H2O (10 mL). Sol-
vent removal in vacuo gave a red oil that was taken
up in Et2O and washed with H2O and brine. The organic
phase was dried over MgSO4 and the solvent was re-
moved in vacuo to afford a red oil that was recrystallized
from EtOAc/hexanes to yield 4.3 g (69%) of 12 as orange
4.3.1.
9-[(E)-2-Nitroethenyl]-3,6,7,8-tetrahydro-2H-
furo[2,3-g]chromene (15a). Aldehyde 13 (1.37 g,
6.69 mmol) and ammonium acetate (0.539 g, 7.00 mmol)
were dissolved in nitromethane (12 mL) and heated to
90 °C for 2.5 h. Volatiles were removed in vacuo to give
an orange solid that was dissolved in CH2Cl2 and
washed with 3 M HCl, H2O, and once with brine. The
organic phase was dried using MgSO4 and the solvent
was removed in vacuo, leaving 1.61 g (97.3%) of a dark
orange solid that was recrystallized from MeOH to af-
ford 1.36 g (82.6%) of 15a as an orange crystalline solid:
mp 130–131 °C. 1H NMR (CDCl3) d 2.04 (p, 2, Ar-
OCH2CH2CH2), 2.87 (t, 2, ArOCH2CH2CH2,
J = 6.9 Hz), 3.18 (t, 2, ArOCH2CH2, J = 8.4 Hz), 4.09
(t, 2, ArOCH2CH2CH2, J = 5.1 Hz), 4.67 (t, 2, Ar-
OCH2CH2, J = 8.7 Hz), 6.80 (s, 1, ArH), 8.11 (s, 2,
ArCH@CH). Low-resolution EIMS, m/z (rel intensity)
247 (M+, 100). Anal. Calcd for C13H13NO4: C, 63.15;
H, 5.30; N, 5.66. Found: C, 62.88; H, 5.40; N, 5.57.
1
crystals: mp 75–76 °C. H NMR (CDCl3) d 1.96 (p, 2,
ArOCH2CH2CH2, J = 5.2, 6.3 Hz), 2.72 (t, 2, Ar-
OCH2CH2CH2, J = 6.3 Hz), 3.12 (t, 2, ArOCH2CH2,
J = 8.5 Hz), 4.12 (t, 2, ArOCH2CH2CH2, J = 5.2 Hz),
4.56 (t, 2, ArOCH2CH2, J = 8.5 Hz), 6.46 (s, 1, ArH),
and 6.65 (s, 1, ArH). Low-resolution ESIMS, m/z (rel
intensity) 176/178 (M+, 94/100). Anal. Calcd for
C11H12O2: C, 74.98; H, 6.86. Found: C, 74.65; H, 6.96.
4.2.6.
carbaldehyde (13) and 3,6,7,8-tetrahydro-2H-furo[2,3-
g]chromene-4-carbaldehyde (14). solution of 12
3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromene-9-
4.3.2.
4-[(E)-2-Nitroethenyl]-3,6,7,8-tetrahydro-2H-
A
furo[2,3-g]chromene (16a). Similar to the preparation
of 15a, aldehyde 14 (0.127 g, 1.65 mmol) was condensed
to give 0.301 g (73.8%) of 16a as fluffy bright orange col-
ored crystals: mp 139–140 °C. H NMR (CDCl3) d 2.01
(p, 2, ArOCH2CH2CH2), 2.77 (t, 2, ArOCH2CH2CH2),
3.31 (t, 2, ArOCH2CH2), 4.26 (t, 2, ArOCH2CH2CH2),
4.58 (t, 2, ArOCH2CH2), 6.61 (s, 1, ArH), 7.94 (d, 1,
ArCH@CH), 8.01 (d, 1, ArCH@CH). Low-resolution
EIMS, m/z (rel intensity) 247 (M+, 100). Anal. Calcd
for C13H13NO4: C, 63.15; H, 5.30; N, 5.66. Found: C,
63.08; H, 5.22; N, 5.51.
(8.29 g, 47.1 mmol) dissolved in CH2Cl2 (200 mL) was
stirred and cooled to 0 °C. The solution was charged
with SnCl4 (6.07 mL, 51.8 mmol) and the reaction was
held at 0 °C for 15 min before the slow addition of
dichloromethyl methyl ether (5.9 mL, 52 mmol). The
reaction was halted after 4 h by the addition of H2O
(50 mL). The reaction mixture was partitioned and the
organic phase was set aside. The aqueous layer was ex-
tracted with CH2Cl2, and the organic fractions were
combined and washed with 3 M HCl and once with
brine. The organic phase was dried over MgSO4 and
the solvent was removed under reduced pressure to give
a dark red oil (10.29 g) that contained the two regioi-
somers 13 and 14. The oil was recrystallized from
1
4.3.3. 2-(3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromen-9-
yl)ethanamine (17a). A dry reaction flask was purged
with N2, charged with anhydrous THF (100 mL), and

6248
D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
cooled to 0 °C before the dropwise introduction of 1 M
LiAlH4 (in THF) (25.0 mL, 25.0 mmol). Once the addi-
tion was complete, 15a (2.41 g, 9.76 mmol) was dis-
solved in anhydrous THF (25 mL) and added to the
suspension over a 30 min period. The flask was held at
reflux for 4 h before the reaction was quenched with
the addition of 2.5 M NaOH (15 mL). Celite was added
to the flask and the mixture was filtered, washing thor-
oughly with CH2Cl2. The yellow colored filtrate was
concentrated under vacuum, dissolved in CH2Cl2 and
washed with 3 M HCl. The aqueous extracts were com-
bined and cooled to 0 °C and made basic with the addi-
tion of 5 M NaOH. The basic solution was extracted
with CH2Cl2, and the organic fractions were washed
with brine. The organic phase was dried over MgSO4
and the volatiles were removed in vacuo to yield 17a
as a yellow oil. This free amine was converted to its
hydrochloride salt by dissolving the oil in Et2O and add-
ing 1.1 equivalents of 1 M HCl in anhydrous EtOH to
the flask. The salt was recrystallized from EtOH/Et2O
to afford 0.934 g (37.4%) of 17aÆHCl as a white crystal-
line solid: mp 279–280 °C. 1H NMR (free base in
CDCl3) d 1.11 (br s, 2, NH2), 1.96 (p, 2, Ar-
OCH2CH2CH2), 2.69 (t, 2, ArCH2CH2, J = 6.6 Hz),
superimposed onto 2.69 (t, 2, ArOCH2CH2CH2,
J = 7.2 Hz), 2.85 (t, 2, ArCH2CH2, J = 6.6 Hz), 3.12 (t,
2, ArOCH2CH2, J = 8.4 Hz), 4.06 (t, 2, Ar-
OCH2CH2CH2, J = 5.1 Hz), 4.45 (t, 2, ArOCH2CH2,
J = 8.4 Hz), 6.56 (s, 1, ArH). Low-resolution ESIMS,
m/z (rel intensity) 220 (M+H, 67), 203 ((M+H)ꢀNH3,
100). Anal. Calcd for C13H17NO2ÆHCl: C, 61.06; H,
7.09; N, 5.47. Found: C, 60.91; H, 7.05; N, 5.44.
the addition of 1.1 equivalents of 1 M HCl in anhydrous
EtOH, and recrystallization from EtOH/Et2O afforded
4aÆHCl as a white, crystalline solid: mp >300 °C. 1H
NMR (free base in CDCl3) d 1.09 (br s, 2, NH2), 1.98
(p, 2, ArOCH2CH2CH2), 2.63 (t, 2, ArCH2CH2,
J = 7.2 Hz), 2.73 (t, 2, ArOCH2CH2CH2, J = 6.3 Hz),
2.83 (q, 2, ArCH2CH2), 3.18 (t, 2, ArOCH2CH2,
J = 8.1 Hz), 4.17 (t, 2, ArOCH2CH2CH2, J = 5.1 Hz),
4.51 (t, 2, ArOCH2CH2, J = 8.4 Hz). Low-resolution
ESIMS, m/z (rel intensity) 298/300 (M+H, 71/66), 281/
283 ((M+H)ꢀNH3, 100/96). Anal. Calcd for
C13H16BrNO2ÆHCl: C, 46.66; H, 5.12; N, 4.18. Found:
C, 46.48; H, 4.96; N, 4.07.
4.3.6. 2-(9-Bromo-3,6,7,8-tetrahydro-2H-furo[2,3-g]chro-
men-4-yl)ethanamine (5a). In a manner analogous to that
reported for the preparation of 4a, 18aÆHCl (0.051 g,
0.20 mmol) was brominated to yield 0.051 g (86%) of
5a as a pale yellow oil that was taken up in Et2O and
converted to its hydrochloride salt 5aÆHCl with the addi-
1
tion of 1 M HCl in anhydrous EtOH: mp >300 °C. H
NMR (free base in CDCl3) d 1.24 (br s, 2, NH2), 1.98
(p, 2, ArOCH2CH2CH2), 2.65 (t, 2, ArCH2CH2) super-
imposed onto 2.71 (t, 2, ArOCH2CH2CH2), 2.86 (t, 2,
ArCH2CH2), 3.24 (t, 2, ArOCH2CH2), 4.06 (t, 2, Ar-
OCH2CH2CH2), 4.60 (t, 2, ArOCH2CH2). Low-resolu-
tion ESIMS, m/z (rel intensity) 298/300 (M+H, 100/
96), 281/283 ((M+H)ꢀNH3, 69/67). Anal Calcd for
C13H16BrNO2ÆHCl: C, 46.66; H, 5.12; N, 4.18. Found:
C, 46.73; H, 5.07; N, 4.02.
4.4. Synthesis of 4b and 5b
4.3.4.
2-(3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromen-4-
4.4.1. 9-[(1E)-2-Nitroprop-1-en-1-yl]-3,6,7,8-tetrahydro-
2H-furo[2,3-g]chromene (15b). In a manner analogous
to that used in the preparation of 15a, aldehyde 13
(3.50 g, 17.1 mmol) was condensed with nitroethane to
give 2.90 g (64.7%) of 15b as orange needle-like crystals:
mp 88–89 °C. IR (NaCl, cmꢀ1) 3054, 2986, 1422, 1264.
1H NMR (CDCl3) d 1.96 (p, 2, ArOCH2CH2CH2),
2.16 (s, 3, CH3), 2.63 (t, 2, ArOCH2CH2CH2,
J = 6.4 Hz), 3.19 (t, 2, ArOCH2CH2, J = 8.4 Hz), 4.11
(t, 2, ArOCH2CH2CH2, J = 5.2 Hz), 4.55 (t, 2, Ar-
OCH2CH2, J = 8.5 Hz), 6.76 (s, 1, ArH), 7.84 (s, 1,
ArCH@C). Low-resolution EIMS, m/z 262 (M+), 244
(MꢀOH). Anal. Calcd for C14H15NO4: C, 64.35; H,
5.78; N, 5.36. Found: C, 64.07; H, 5.64; N, 5.29.
yl)ethanamine (18a). Similar to the preparation of 17a,
16a (0.572 g, 2.31 mmol) was reduced to give 0.408 g
(68.9%) of 18a as pale yellow oil which was converted
to its hydrochloride salt 18aÆHCl with the addition of
1
1 M HCl in anhydrous EtOH: mp 272 °C. H NMR
(free base in CDCl3) d 1.27 (br s, 2, NH2), 1.93 (p, 2, Ar-
OCH2CH2CH2), 2.65 (t, 2, ArCH2CH2) superimposed
onto 2.70 (t, 2, ArOCH2CH2CH2), 2.87 (t, 2,
ArCH2CH2), 3.11 (t, 2, ArOCH2CH2), 4.10 (t, 2, Ar-
OCH2CH2CH2), 4.49 (t, 2, ArOCH2CH2), 6.34 (s, 1,
ArH). Low-resolution ESIMS, m/z (rel intensity) 220
(M+H, 100), 203 ((M+H)ꢀNH3, 49), 175. High resolu-
tion MALDI-TOF m/z calculated for C13H18NO2
(M+H) 220.1346. Found 220.1332.
4.4.2. 4-[(1E)-2-Nitroprop-1-en-1-yl]-3,6,7,8-tetrahydro-
2H-furo[2,3-g]chromene (16b). Aldehyde 14 (0.623 g,
3.05 mmol) and benzylamine (0.399 mL, 3.66 mmol)
were dissolved in benzene (50 mL) and refluxed for 2 h
with a Dean-Stark trap attached. After cooling to room
temperature, the solvent was removed in vacuo to give a
yellow oil that was combined with nitroethane (40 mL)
and AcOH (0.55 mL, 9.2 mmol) and stirred for 48 h.
The volatiles were removed in vacuo, leaving behind a
yellow oil that was taken up in Et2O and washed with
1 M HCl, H2O, and once with brine. The organic phase
was dried over MgSO4 and the solvent was removed un-
der reduced pressure to give a bright yellow oil that was
recrystallized from MeOH to afford 16b as an orange
4.3.5. 2-(4-Bromo-3,6,7,8-tetrahydro-2H-furo[2,3-g]chro-
men-9-yl)ethanamine (4a). A 0.776 M Br2 solution in
HOAc (0.75 mL, 0.58 mmol) was added dropwise to a
solution of 17aÆHCl (0.333 g, 0.520 mmol) dissolved in
glacial AcOH (10 mL). The reaction continued for
3.5 h before the volatiles were removed in vacuo. The
white solid that remained was taken up in 3 M HCl
and washed with Et2O. The aqueous phase was made
basic with the addition of 5 M NaOH and the basic
solution was extracted with CH2Cl2. The organic ex-
tracts were combined, washed once with brine, dried
over MgSO4, and the volatiles were removed in vacuo
to give 0.144 g (93.0%) of 4a as a pale yellow oil. The
free amine was converted to its hydrochloride salt with
crystalline solid: mp 103–104 °C. IR (NaCl, cmꢀ1
)

D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
6249
1
3054, 2986, 1422, 1264. H NMR (CDCl3) d 1.98 (p, 2,
C14H18BrNO2ÆHCl: C, 48.23; H, 5.49; N, 4.02. Found:
C, 47.85; H, 5.21; N, 4.10.
ArOCH2CH2CH2), 2.16 (s, 3, CH3), 2.77 (t, 2, Ar-
OCH2CH2CH2, J = 6.6 Hz), 3.01 (t, 2, ArOCH2CH2,
J = 8.7 Hz), 4.15 (t, 2, ArOCH2CH2CH2, J = 5.1 Hz),
4.53 (t, 2, ArOCH2CH2, J = 8.4 Hz), 6.55 (s, 1, ArH),
7.92 (s, 1, ArCH@C). Low-resolution EIMS, m/z 261
(M+), 244 (MꢀOH). Anal. Calcd for C14H15NO4: C,
64.35; H, 5.78; N, 5.36. Found: C, 64.23; H, 6.03; N,
5.25.
4.4.6. 1-(9-Bromo-3,6,7,8-tetrahydro-2H-furo[2,3-g]chro-
men-4-yl)propan-2-amine (5b). In a manner analogous to
that used for the preparation of 4a, 4b, and 5a, amine
18b (0.183 g, 7.84 mmol) was brominated to give
0.156 g (63.8%) of 5b that was converted to its hydro-
chloride salt by the addition of 1 M HCl in anhydrous
1
EtOH: mp 277–278 °C. H NMR (free base in CDCl3)
4.4.3.
1-(3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromen-9-
d 1.21 (d, 3, ArCH2CHCH3), 1.95 (p, 2, Ar-
yl)propan-2-amine (17b). In a manner analogous to that
used in the preparation of 17a and 18a, 15b (2.01 g,
7.69 mmol) was reduced to afford 1.70 g (94.9%) of
17b as the free amine. The hydrochloride salt 17bÆHCl
was formed by the addition 1 M HCl in anhydrous
EtOH, and the solid was recrystallized from MeOH/
EtOAc: mp 255–256 °C. 1H NMR (free base in
CDCl3) d 1.15 (d, 3, ArCH2CHCH3, J = 6.3 Hz),
1.62 (br s, 2, NH2), 1.98 (p, 2, ArOCH2CH2CH2),
2.58 (d, 2, ArCH2CHCH3, J = 6.9 Hz), superimposed
upon 2.59 (t, 2, ArOCH2CH2CH2), 2.71 (m, 1,
ArCH2CHCH3, J = 6.6 Hz), 3.14 (t, 2, ArOCH2CH2),
4.08 (t, 2, ArOCH2CH2CH2, J = 5.1 Hz), 4.47 (t, 2,
ArOCH2CH2, J = 8.7 Hz), 6.58 (s, 1, ArH). Low-reso-
lution ESIMS, m/z (rel intensity) 234 (M+H, 64), 217
((M+H)ꢀNH3, 100). Anal. Calcd for C14H19NO2ÆHCl:
C, 62.33; H, 7.47; N, 5.19. Found: C, 62.10; H, 7.34;
N, 5.11.
OCH2CH2CH2), 2.55 (br s, 2, NH2), superimposed upon
2.65 (d, 2, ArCH2CHCH3), 2.73 (t, 2, Ar-
OCH2CH2CH2), 3.11 (m, 2, ArOCH2CH2), 3.40 (m, 1,
ArCH2CHCH3), 4.12 (t, 2, ArOCH2CH2CH2), 4.48
(m, 2, ArOCH2CH2). Low-resolution ESIMS, m/z (rel
intensity) 312/314 (M+H, 100/95). Anal. Calcd for
C14H18BrNO2ÆHCl: C, 48.23; H, 5.49; N, 4.02. Found:
C, 48.37; H, 5.47; N, 3.92.
4.5. Synthesis of 6
4.5.1. 2,2,2-Trifluoro-N-[1-methyl-2-(3,6,7,8-tetrahydro-
2H-furo[2,3-g]chromen-9-yl)ethyl]acetamide (19). Com-
pound 17b (1.52 g, 6.51 mmol) was dissolved in anhy-
drous THF (250 mL) and cooled to 0 °C before the
addition of ethyl trifluoroacetate (1.71 mL, 14.3 mmol)
and triethylamine (0.953 mL, 6.84 mmol). The reaction
continued at 0 °C for 30 min before being brought to re-
flux for 24 h. The volatiles were removed in vacuo, leav-
ing behind a light orange solid that was taken up in
CH2Cl2, washed with 3 M HCl, and once with brine.
The organic phase was dried over MgSO4 and the sol-
vent was removed in vacuo to afford 1.58 g (73.9%) of
a pale orange solid that was recrystallized from EtOAc
to give 1.27 g (59.3%) of 19 as fluffy white crystals: mp
4.4.4.
1-(3,6,7,8-Tetrahydro-2H-furo[2,3-g]chromen-4-
yl)propan-2-amine (18b). In a method analogous to that
used for the preparation of 17a, 17b, and 18a, 16b
(0.200 g, 0.765 mmol) was reduced to yield 0.142 g
(79.7%) of 18b as the free amine that was converted to
its hydrochloride salt by the addition 1 M HCl in anhy-
1
drous EtOH: mp 270–271 °C. H NMR (free base in
156–157 °C. 1H NMR (CDCl3)
d
1.32 (d, 3,
CDCl3) d 1.21 (d, 3, ArCH2CHCH3, J = 6.3 Hz), 1.95
(p, 2, ArOCH2CH2CH2, J = 5.1, 6.3 Hz), 2.55 (br s, 2,
NH2), superimposed upon 2.65 (d, 2, ArCH2CHCH3,
J = 6.9 Hz), 2.74 (t, 2, ArOCH2CH2CH2, J = 6.6 Hz),
3.11 (m, 2, ArOCH2CH2), 3.40 (m, 1, ArCH2CHCH3),
4.12 (t, 2, ArOCH2CH2CH2, J = 5.1 Hz), 4.49 (t, 2, Ar-
OCH2CH2, J = 8.4 Hz), 6.37 (s, 1, ArH). Low-resolu-
tion ESIMS, m/z (rel intensity) 234 (M+H, 100), 217
((M+H)ꢀNH3, 77). Anal. Calcd for C14H19NO2ÆHCl:
C, 62.33; H, 7.47; N, 5.19. Found: C, 61.98; H, 7.66;
N, 5.11.
ArCH2CHCH3, J = 6.6 Hz), 2.01 (p, 2, Ar-
OCH2CH2CH2), 2.67 (m, 2, ArCH2CHCH3), superim-
posed upon 2.71 (m, 2, ArOCH2CH2CH2), 3.71 (t, 2,
ArOCH2CH2, J = 8.1 Hz), 4.02 (m, 1, ArCH2CHCH3),
superimposed upon 4.05 (m, 2, ArOCH2CH2CH2),
4.50 (t, 2, ArOCH2CH2, J = 8.7 Hz), 6.61 (s, 1, ArH),
7.64 (br s, 1, NH). Low-resolution ESIMS, m/z (rel
intensity) 328 (MꢀH, 100). High-resolution MALDI-
TOF m/z calculated for C16H19F3NO3 (M+H)
330.1323. Found 330.1312.
4.5.2.
N-[2-(4-Bromo-3,6,7,8-tetrahydro-2H-furo[2,3-
4.4.5. 1-(4-Bromo-3,6,7,8-tetrahydro-2H-furo[2,3-g]chro-
men-9-yl)propan-2-amine (4b). In a manner similar to the
preparation of 4a and 5a, amine 17b (0.818 g,
3.51 mmol) was brominated to give 0.441 g (63.9%) of
4b as a yellow oil that was converted to its hydrochloride
salt by the addition of 1 M HCl in anhydrous EtOH: mp
g]chromen-9-yl)-1-methylethyl]-2,2,2-trifluoroacetamide
(20). Amide 19 (0.538 g, 1.63 mmol) was dissolved (with
heating) in AcOH (15 mL) and dioxane (5 mL). The solu-
tion was cooled to 15 °C and covered with foil before the
dropwise addition of
a bromine-dioxane solution
(8.10 mL:0.10 mL bromine in 8.00 mL of dioxane) over
a 10 min period. The reaction continued at 25 °C for 6 h
before being quenched with H2O and a saturated sodium
bisulfite solution. The mixture was extracted with
CH2Cl2, and the organic fractions were combined and
washed once with brine, dried over MgSO4, and the vola-
tiles were removed in vacuo. The off-white solid that re-
mained in the flask was recrystallized from EtOAc/
hexanes to yield 0.425 g (63.9%) of 20 as white crystals:
1
269–270 °C. H NMR (free base in CDCl3) d 1.13 (d, 3,
ArCH2CHCH3), 1.48 (br s, 2, NH2), 1.99 (p, 2, Ar-
OCH2CH2CH2), 2.52 (t, 2, ArOCH2CH2CH2), superim-
posed upon 2.53 (d, 2, ArCH2CHCH3), 2.74 (m, 1,
ArCH2CHCH3), 3.18 (t, 2, ArOCH2CH2, J = 8.4 Hz),
4.18 (t, 2, ArOCH2CH2CH2, J = 5.1 Hz), 4.51 (t, 2, Ar-
OCH2CH2, J = 9.3 Hz). Low-resolution ESIMS, m/z
(rel intensity) 312/314 (M+H, 91/84). Anal. Calcd for

6250
D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
mp 156 °C. 1H NMR (CDCl3)
d
1.31 (d, 3,
Serotonin (5-HT) was obtained from Sigma–Aldrich
(St. Louis, MO).
ArCH2CHCH3, J = 6.6 Hz), 2.02 (p, 2, Ar-
OCH2CH2CH2), 2.68 (m, 2, ArCH2CHCH3), superim-
posed upon 2.72 (m, 2, ArOCH2CH2CH2), 3.22 (t, 2,
ArOCH2CH2, J = 8.7 Hz), 4.17 (m, 1, ArCH2CHCH3),
superimposed upon 4.21 (m, 2, ArOCH2CH2CH2), 4.55
(t, 2, ArOCH2CH2, J = 8.4 Hz), 7.41 (br s, 1, NH).
Low-resolution CIMS, m/z 408/410 (M+H), 329
((M+H)ꢀBr). Anal. Calcd for C16H17BrF3NO3: C,
47.08; H, 4.20; N, 3.43. Found: C, 47.36; H, 4.14; N, 3.40.
4.6.2. Cell culture methods. NIH-3T3 cells stably express-
ing the rat 5-HT2A receptor (GF-6; 5500 fmol/mg) were
the kind gift from Dr. David Julius (University of Califor-
nia, San Francisco, CA). Cells were maintained as de-
scribed previously by Braden et al.23 All DMEM media
contained 300 lg/mL G-418 (Sigma–Aldrich).
4.6.3. Radioligand binding assays. Membrane prepara-
tions and competition binding assays were performed
as previously described.7,24 Competition binding assays
were carried out using 0.5 nM [3H]ketanserin in the
presence of increasing concentrations of test compound
(ca. 10 pM–10 lM). Kd values and competition curves
were calculated using Prism (Graphpad Software, San
Diego, CA).
4.5.3. N-[2-(4-Bromo-7,8-dihydro-6H-furo[2,3-g]chro-
men-9-yl)-1-methylethyl]-2,2,2-trifluoroacetamide (21).
To a round bottom flask, 20 (0.408 g, 0.999 mmol) and
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ)
(0.590 g, 2.60 mmol) were added and dissolved in tolu-
ene (50 mL). The reaction refluxed for 3.5 h and was
cooled to room temperature. The volatiles were removed
in vacuo to afford a brown oil that was purified by silica
gel flash chromatography (eluting with CH2Cl2) to af-
ford a light yellow solid that was recrystallized from
EtOAc/hexanes to afford 0.152 g (37.4%) of 21 as white
4.6.4. Inositol phosphate accumulation assays. The ability
of test compounds to stimulate radiolabeled inositol
phosphate accumulation in NIH-3T3 cells stably express-
ing the rat 5-HT2A receptor was performed as previously
described.13 Each assay plate was normalized to wells
stimulated with water (0%) and 10 lM serotonin (100%).
1
crystals. H NMR (free base in CDCl3) d 1.31 (d, 3,
ArCH2CHCH3, J = 6.6 Hz), 2.08 (p, 2, Ar-
OCH2CH2CH2), 2.92 (qd, 2, ArOCH2CH2CH2), 3.07
(qd, 2, ArCH2CHCH3), 4.27 (m, 1, ArCH2CHCH3),
superimposed upon 4.28 (m, 2, ArOCH2CH2CH2),
6.57 (br s, 1, NH), 6.75 (d, 1, ArOCH@CH,
4.6.5. Behavioral pharmacology methods.
4.6.5.1. Animals. Four male Sprague–Dawley rats
(Harlan Laboratories, Indianapolis, IN) weighing 200–
220 g at the beginning of the drug discrimination study
were trained to discriminate LSD (186 nmol/kg;
0.08 mg/kg) from saline. The animal protocols used in
the present experiments were consistent with current
NIH principles of good laboratory animal care and were
approved by the Purdue University Animal Care and Use
Committee.
J = 2.1 Hz), 7.56 (d, 1, ArOCH@CH, J = 2.1 Hz).
þ
Low-resolution EIMS, m/z 404/406 (MꢀH), 69 CF3
.
High-resolution MALDI-TOF m/z calculated for
C16H15BrF3NO3 (M+H) 406.0263. Found 406.0260.
4.5.4. 1-(4-Bromo-7,8-dihydro-6H-furo[2,3-g]chromen-9-
yl)propan-2-amine (6). To a solution of 21 (0.146 g,
0.359 mmol) dissolved in MeOH (20 mL) and cooled
to 0 °C, 5 M KOH (10 mL) was added, and the reaction
mixture was allowed to warm to room temperature over
a 5 h period. The mixture was diluted with Et2O and ex-
tracted with 3 M HCl. The aqueous fractions were com-
bined, cooled to 0 °C, and made basic with the addition
of 5 M KOH. The aqueous phase was extracted with
CH2Cl2, and the organic fractions were combined,
washed with brine, and dried over MgSO4. The solvent
was removed under reduced pressure to afford 0.109 g
(98.2%) of 6 as yellow oil. The hydrochloride salt was
formed by adding 1.1 equivalents of 1 M HCl in anhy-
4.6.5.2. Discrimination training and testing. A fixed ra-
tio (FR) 50 schedule of food reinforcement in a two-le-
ver paradigm was used. This method is described in
detail elsewhere.25 Briefly, training sessions lasted
15 min and were conducted at the same time each day.
Training continued until an accuracy of at least 85%
was attained for eight of 10 consecutive sessions. Once
criterion performance was attained, test sessions were
interspersed between training sessions, either one or
two times per week. At least one drug and one saline ses-
sion separated each test session. Rats were required to
maintain the 85% correct responding criterion on train-
ing days in order to be tested. In addition, test data were
discarded when the accuracy criterion of 85% was not
achieved on the two training sessions following a test
session. Test drugs were administered ip 30 min prior
to sessions; test sessions were run under conditions of
extinction, with rats removed from the operant chamber
when 50 presses were emitted on one lever. If 50 presses
on one lever were not completed within 5 min, the ses-
sion was ended and scored as a disruption. In combina-
tion tests, antagonists were administered 30 min before
the training drug. The percentage of rats selecting the
drug lever (% SDL) for each dose of test compound
was determined. Treatments were randomized at the
beginning of the study.
1
drous EtOH to the free amine dissolved in Et2O. H
NMR (free base in CDCl3) d 1.23 (d, 3, ArCH2CHCH3),
2.06 (p, 2, ArOCH2CH2CH2), superimposed upon 2.07
(m, 2, ArCH2CHCH3), 2.49 (br s, 2, NH2), 2.92 (m, 2,
ArOCH2CH2CH2), 3.02 (d, 2, ArCH2CHCH3), 4.27 (t,
2, ArOCH2CH2CH2), 6.78 (d, 1, ArOCH@CH,
J = 2.1 Hz), 7.58 (d, 1, ArOCH@CH, J = 2.1 Hz).
Low-resolution ESIMS, m/z (rel intensity) 310/312
(M+H, 72/79), 293/295 ((M+H)ꢀNH3, 92/100). High-
resolution
MALDI-TOF
m/z
calculated
for
C14H18BrNO2 (M+H) 310.0428. Found 310.0437.
4.6. Pharmacology
4.6.1. Materials. [3H]Ketanserin was obtained from Per-
kin-Elmer Life and Analytical Sciences (Boston, MA).

D. M. Schultz et al. / Bioorg. Med. Chem. 16 (2008) 6242–6251
6251
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Acknowledgment
This work was supported by NIH Grant DA02189 from
NIDA (DEN), the UW-La Crosse Undergraduate Re-
search Program, and a Purdue MCMP summer research
fellowship awarded to DMS. The authors thank Stewart
Frescas at Purdue for his technical assistance with the
syntheses, and Amy Harms at UW-Madison for her
assistance with the HRMS analyses.
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