Further studies on oxygenated tryptamines with LSD-like activity incorporating a chiral pyrrolidine moiety into the side chain

Article abstract of DOI:10.1021/jm990325u

The enantiomers of 3-(N-methylpyrrolidin-2-ylmethyl)-5-methoxyindole, 1, and 3-(N-methylpyrrolidin-2-ylmethyl)-4-hydoxyindole, 3, were prepared using an asymmetric synthesis that employed (+)- or (-)-proline. A new approach was developed that had certain

Full text of DOI:10.1021/jm990325u

J . Med. Chem. 1999, 42, 4257-4263
4257
F u r th er Stu d ies on Oxygen a ted Tr yp ta m in es w ith LSD-lik e Activity
In cor p or a tin g a Ch ir a l P yr r olid in e Moiety in to th e Sid e Ch a in
Madina Gerasimov,† Danuta Marona-Lewicka, Deborah M. Kurrasch-Orbaugh, Amjad M. Qandil, and
David E. Nichols*
Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences,
Purdue University, West Lafayette, Indiana 47907
Received J une 24, 1999
The enantiomers of 3-(N-methylpyrrolidin-2-ylmethyl)-5-methoxyindole, 1, and 3-(N-meth-
ylpyrrolidin-2-ylmethyl)-4-hydoxyindole, 3, were prepared using an asymmetric synthesis that
employed (+)- or (-)-proline. A new approach was developed that had certain advantages over
the synthesis originally reported for the isomers of 1. (()-3-(N-Methylpyrrolidin-3-yl)-4-
hydroxyindole, 5, was also prepared as a rigid analogue of psilocin and compared with its
5-methoxy counterpart 4. Radioligand competition assays were used to assess the affinity of
compounds for the 5-HT2A receptor labeled with the agonist ligand [125I]DOI and the antagonist
ligand [3H]MDL100907. Two-lever drug discrimination assays in rats trained to discriminate
either LSD or DOI from saline were employed to assess the hallucinogen-like behavioral
properties of these rigid tryptamine analogues. The receptor binding assay results clearly
demonstrated a stereochemical preference for the R enantiomers that did not discriminate the
position of the oxygen function. The receptor is 10-20-fold more selective for the R isomers.
The affinities of the R enantiomers were virtually identical for both 1 and 3 at the agonist-
labeled receptor, while racemic 4 and 5 had about one-tenth the affinity. The drug discrimination
data in both LSD- and DOI-trained rats paralleled the binding data using [125I]DOI displace-
ment. Both (R)-1 and (R)-3 are about equipotent, comparable to DOI in activity but about 10-
fold less potent than LSD. Compound 4 produced only partial substitution, even at a dose
nearly 5-fold higher than for (R)-1. Based on conformational energies, it seems doubtful that
these compounds bind to the 5-HT2A receptor in an ergoline-like conformation. The results
also suggest that both 1 and 3 would possess LSD-like psychopharmacology in humans.
In tr od u ction
A number of studies have examined conformational
restriction of the 3-(2-aminoethyl) side chain of serotonin
as an approach to 5-HT analogues with receptor subtype
selectivity.1-5 Introduction of a stereocenter R to the
amine nitrogen of serotonin, while also conformationally
restricting the C-N bond of the aminoethyl side chain
by incorporating it into a pyrrolidine ring, affords
compounds that serve as useful chiral probes of 5-HT
oxygen substituent from the 5 to the 4 position in the
tryptamines would have an effect on stereoselectivity
at the 5-HT2A receptor. We had previously found that
the S isomer of 5-methoxy-R-methyltryptamine, 2, had
higher affinity than the R isomer at both the serotonin
5-HT1B and 5-HT2 sites.6 This selectivity was reversed,
however, for 4-oxygenated R-methyltryptamines at the
5-HT1B site.
The present series of compounds was designed to
elucidate further how constraining the side chain ster-
eochemistry in 4-hydroxytryptamines affects activity at
the serotonin 5-HT2A receptor, compared with 5-meth-
oxy-substituted analogues. Although the synthesis of the
enantiomers of 1 is reported in the literature,1 we
describe here a new procedure for the preparation of
this compound and its 4-hydroxy analogue 3. The
synthesis of 5 employed a Michael reaction between the
appropriate indole and N-methylmaleimide, as de-
scribed previously for 4.6 These compounds were evalu-
ated for affinity at the 5-HT2A receptor in rat prefrontal
receptors. Macor et al.1 first reported that (R)-(+)-3-(N-
methylpyrrolidin-2-ylmethyl)-5-methoxyindole, 1, had
approximately 30-fold higher affinity than the S enan-
tiomer at 5-HT2A receptors and was as efficacious as
serotonin in stimulating phosphatidylinositol (PI) turn-
over in rat cortical slices.
For many years we have been exploring the structure-
activity relationships of hallucinogens and other cen-
trally active substances that interact with serotonin
receptors. Because the 5-HT2A receptor is believed to be
the primary target for hallucinogenic agents, the report
by Macor et al.1 prompted us to study the analogous
conformationally constrained 4-hydroxy compounds re-
lated to the naturally occurring hallucinogen psilocin.
We were also curious as to whether transposing the
* Author for correspondence: Dr. David E. Nichols. Phone: (765)-
494-1461. Fax: (765)-494-1414. E-mail: drdave@pharmacy.purdue.edu.
† Present address: Chemistry Department, Brookhaven National
Laboratory, Upton, NY 11973.
10.1021/jm990325u CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/16/1999

4258 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Gerasimov et al.
Sch em e 1a
Sch em e 2a
a
(a) i. n-BuLi, THF, -78 °C, ii. t-BuMe2SiCl, THF, 0 °C, iii.
a
(a) i. NaH, THF, ii. t-BuMe2SiCl, THF, 0 °C, iii. NBS, THF,
-78 °C; (b) i. n-BuLi, THF, -78 °C, ii. N-methylproline methyl
ester,10,11 THF, -78 °C; (c) LiAlH4, dioxane, reflux.
NBS, -78 °C; (b) i. n-BuLi, THF, -78 °C, ii. N-methylproline
methyl ester,10,11 THF, -78 °C; (c) LiAlH4, THF, reflux.
cortex homogenate. Compounds (R)-1, (R)-3, and (()-4
were evaluated in the drug discrimination assay in rats
trained to discriminate saline from either DOI or LSD.
obtained as anhydrous material after purification by
vacuum distillation. The total route leading to
3-(N-methylpyrrolidin-2-ylcarbonyl)-5-methoxyindole, 7
(Scheme 1), does have several advantages over the
literature procedure.1 Only 1 equiv of the indole starting
material is required. The use of the bulky tert-butyldim-
ethylsilyl group as the indole N-protecting group, be-
cause of the steric demands of this substituent, provided
lateral protection of the 2 position and prevented
rearrangement to the undesired 2-lithio isomer. More-
over, this protecting group was lost during the reaction/
workup, which further simplified the synthetic scheme.
To be certain that no racemization was occurring in the
acylation step, deuterium quench experiments were
performed. That is, the acylation reaction was worked
up using D2O and the resulting product was character-
ized by 1H NMR; no deuterium incorporation was
detected. Complete reduction of the ketone functionality
in 7 was accomplished smoothly and quantitatively with
lithium aluminum hydride in THF at reflux to afford
the desired enantiomers.
Synthesis of 8 was accomplished using the same
sequence as for compound 7, but starting from 4-benz-
yloxyindole (Scheme 2). The starting indole was pre-
pared from o-benzyloxybenzaldehyde using the Hemets-
berger azide pyrrolysis method.8,9 Initial attempts to
apply the N-protection protocol used for 5-methoxyin-
dole resulted in partial O-debenzylation, effected by
n-butyllithium due to the relatively high temperature
used in the reaction. The literature procedure for the
N-protection was modified, and the required deproto-
nation was carried out using the nonnucleophilic base
sodium hydride. O-Debenzylation was not expected to
be a problem in the bromine-exchange reaction because
the reaction temperature was maintained at -78 °C.
Indeed lithium-bromine exchange was favored over
O-debenzylation, and the desired acylated compound
was obtained in identical yield to the 5-methoxy com-
pound.
Ch em istr y
In the synthesis of (R)-1 Macor et al.1 reportedly
utilized the condensation of N-carbobenzoxy-D-proline
acid chloride and 2 equiv of the magnesium salt of
5-methoxyindole to append the conformationally re-
stricted C-3 substituent with retention of stereochemical
integrity. In our hands, this approach provided mixtures
of products and unacceptably low yields. Unsuccessful
attempts were made to affect the outcome of the
condensation by replacing magnesium with a less elec-
tropositive metal (e.g. transmetalation with ZnCl2), in
order to lower the degree of dissociation of the nitrogen-
metal bond, or by use of the Lewis acid catalyst SnCl4.
We next turned our attention to the chemistry of
N-protected 3-lithioindoles, anticipating an enhanced
reactivity of the 3 position in 5-methoxy- and 4-benzyl-
oxyindoles. Amat et al.7 reported preparation of 1-(tert-
butyldimethylsilyl)-3-lithioindole by metalation of the
corresponding 3-bromo derivative. This literature pro-
cedure was successfully employed with several modifi-
cations to prepare 3-bromo-1-(tert-butyldimethylsilyl)-
5-methoxyindole, 6, in 85% yield, in a one-pot reaction,
from 5-methoxyindole, by silylation, followed by regio-
selective bromination with N-bromosuccinimide at -78
°C (Scheme 1).
In our search for a suitable electrophilic acylating
reagent, we then considered simple esters. To avoid
working with a labile acyl chloride, the simple methyl
ester of N-methylproline seemed to be an excellent
choice. The ester was prepared in good yield starting
from proline following literature precedents10,11 and was
The reduction of 9 was initially problematic. The
ketone functionality was readily reduced to an alcohol,
but even after 7 days at reflux with LiAlH4 in THF, only
a trace of the fully reduced compound was detected.
Steric hindrance by the bulky O-benzyl protecting group
was hypothesized to be the problem. Use of a THF/

Oxygenated Tryptamines with LSD-like Activity
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20 4259
Sch em e 3a
Ta ble 1. Radioreceptor Data for New Compounds in
Competing for [3H]MDL100907 (K0.5 ( SEM, nM) and
[
125I]-2,5-Dimethoxy-4-iodoamphetamine (DOI) (KI ( SEM, nM)
at Serotonin 5-HT2A Sites in Rat Cortical Homogenate
compd
[
125I]DOI
[3H]MDL100907
5-MeO-DMT
4-OH-DMT (psilocin)
(S)-1
21 ( 3
1600 ( 250
390 ( 38b
9400 ( 2300
(>8400)d
6 ( 0.5a
64 ( 14
(680 ( 70)c
9.5 ( 1.6
(17 ( 2)c
290 ( 33
13 ( 2
(R)-1
400 ( 22
(730 ( 110)d
4700 ( 600
210 ( 22
1300 ( 150
440 ( 54
(S)-3
(R)-3
4e
150 ( 20
82 ( 33
5
a
Value from McKenna et al.15 for [125I]DOI displacement.
Value for [3H]ketanserin displacement; this laboratory. Values
b
c
from Macor et al.1 for [125I]DOI displacement. Values from Macor
et al.1 for [3H]ketanserin displacement. e Prepared according to
Macor et al.6
d
a
(a) AcOH, reflux; (b) LiAlH4, THF, reflux; (c) H2 (1 atm), Pd/
C, EtOH.
selective for the R isomer. The affinities of the individual
enantiomers are very similar for both 1 and 3. As would
be expected for agonists, the affinities of all the com-
pounds are correspondingly lower for the antagonist-
labeled receptor, although the relative affinity ratios for
enantiomeric pairs remain approximately the same.
Compounds 4 and 5 have lower affinities than the more
active enantiomers (R)-1 and (R)-3, respectively, but still
have 2-3-fold higher affinities than the less active S
enantiomers of 1 and 3.
Nonbonded interactions between the pyrrolidine ring
and the substituent at the 4 position (-H or -OH)
hinder the “ethylamine side chain” fragment in both 1
and 3 from adopting an ergoline-like conformation. This
interaction is more severe in (R)-3, however, due to the
larger size of the OH, compared with H. “LSD-like”
conformations for (R)-1 and (R)-3 are about 3 and 7 kcal/
mol (semiempirical, AM1) above their global minima,
respectively. Lowest-energy conformations for both com-
pounds exist where the ethylamine fragment of the
molecule is disposed in a plane nearly perpendicular to
the plane of the indole ring. Even though it is tempting
to envision these rigid tryptamines binding in an
ergoline-like conformation, these results suggest that
this is probably an incorrect view. One explanation for
decreased affinity of compounds 4 and 5 could be the
added bulk at the 1 position of the ethylamine side
chain.
dioxane mixture for the reduction improved the yield
only slightly. Key to the success of this reduction was
the choice of a single higher-boiling solvent, dioxane,
and the manner of addition of reagents (see Experimen-
tal Section for details). Surprisingly, these conditions
also effected an unprecedented O-debenzylation.
It seems possible that coordination of the aluminum
with the 3-benzylic oxygen atom of the intermediate
reduction product creates a transition state that is
ideally disposed to deliver hydride to the 4-benzylic
carbon. Cleavage of the carbon-oxygen bond is thereby
effected, with phenoxide serving as the leaving group
in a nucleophilic substitution reaction. Molecular mod-
eling using semiempirical methods and the AM1 Hamil-
tonian, as employed in the Spartan software (v 5.0,
Wavefunction, Inc.), confirmed that ideal geometries
could be obtained for such a reaction sequence.
Compound 5 was prepared using a modification of the
method of Macor et al.6 via Michael addition between
4-benzyloxyindole and 3 equiv of N-methylmaleimide in
acetic acid at reflux. Reduction of the resulting succin-
imide with LiAlH4 followed by removal of the O-benzyl
protecting group by catalytic hydrogenation afforded
target compound 5 (Scheme 3).
P h a r m a cology
The target compounds synthesized in this work were
evaluated for affinity at the rat brain 5-HT2A receptor,
labeled with the highly selective 5-HT2A receptor an-
tagonist [3H]MDL100907.13 In addition, competition
studies were also carried out using [125I]-2,5-dimethoxy-
4-iodoamphetamine (DOI) as an agonist to label this
site. The enantiomers with highest affinity for the
5-HT2A receptor were then assessed in the drug dis-
crimination paradigm (DD) in rats trained to discrimi-
nate either LSD tartrate from saline or DOI hydro-
chloride from saline.
The behavioral data from the drug discrimination
assay in both LSD (Table 2) and DOI (Table 3) trained
rats parallels the binding data using [125I]DOI displace-
ment. We have only obtained full substitution in this
assay when compounds were agonists. Macor1 has
previously shown that (R)-1 is an agonist, and these
data suggest, not surprisingly, that (R)-3 is also an
agonist. Both (R)-1 and (R)-3 are about 10-fold less
potent than LSD but have activity comparable to that
of DOI. Although it is possible that (R)-3 is slightly more
potent than (R)-1 in the LSD-trained rats, the overlap
of the ED50 confidence intervals prevents a firm conclu-
sion on this point.
Resu lts a n d Discu ssion
The receptor binding assay results (Table 1) clearly
demonstrate a stereochemical requirement at the 5-HT2A
receptor, but one that does not discriminate the position
of the oxygen function. As reported by Macor et al.1 for
the enantiomers of 1, the receptor is 20-30-fold more
Compound 4 produced only partial substitution, even
at a dose nearly 5-fold higher than for (R)-1. Because
of the similar loss in receptor affinity, and in view of
these results, compound 5 was not tested in the behav-
ioral assay.

4260 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Gerasimov et al.
Ta ble 2. Data from Substitution Tests in LSD-Trained Ratsa
°C over 10 min. After 15 min of stirring at this temperature,
the reaction mixture was cooled back to -50 °C, and a solution
of tert-butyldimethylsilyl chloride (844 mg, 5.76 mmol) in 5
mL of anhydrous THF was added. After stirring at 0 °C for 3
h the temperature was lowered to -78 °C and freshly crystal-
lized N-bromosuccinimide (900 mg, 5.28 mmol) was added to
the reaction mixture. After stirring for 3 h the temperature
was raised to 25 °C and hexane (25 mL) followed by pyridine
(0.25 mL) was added. The resulting suspension was filtered
through a Celite pad, and the filtrate was concentrated under
reduced pressure. The crude product was purified by column
chromatography over silica gel with 5% ethyl acetate/hexane
as the eluent to afford the title compound as a yellow solid
(1.38 g, 85% yield). An analytical sample was recrystallized
from hexane to give white crystals: mp 75 °C; 1H NMR δ 7.36
(d, 1H, ArH, J ) 6.0 Hz), 7.12 (s, 1H, ArH), 6.97 (d, 1H, ArH,
J ) 2.2 Hz), 6.83 (dd, 1H, ArH, J ) 6.0 and 2.2 Hz), 3.88 (s,
3H, OCH3), 0.92 (s, 9H, tert-butyl), 0.58 (s, 6H, dimethylsilyl);
CIMS 341 (MH+). Anal. (C15H22BrNOSi) C, H, N.
dose
ED50 (95% CI)
mg/ µmol/
drug kg
kg
N
%D %SDL
µmol/kg
mg/kg
LSD 0.01 0.023 13
0.02 0.046 14
0
0
0
46
78 0.026
81 (0.014-0.045) (0.006-0.02)
100
0.012
0.04 0.093 16
0.08 0.186 15
0
(R)-1 0.08 0.25
6
9
17
11
8
17
0
20
0.16 0.50
0.33 1.00 12
0.65 2.00
63 0.44
82 (0.25-0.74)
100
0.14
(0.08-0.24)
8
(R)-3 0.03 0.125 10
0.06 0.25 10
30
0
8
40 0.26
64 (0.15-0.45)
100
0.06
(0.04-0.1)
0.12 0.50 12
0.23 1.00 10 10
4
0.68 2.0
1.36 4.0
2.72 8.0
12
10
12
0
0
0
33
50 PS
75
PS
(S)-(-)-3-(N-Met h ylp yr r olid in -2-ylca r b on yl)-5-m et h -
oxyin d ole, (S)-7. A solution of n-butyllithium (0.56 mL of a
2.5 M solution in hexane, 1.53 mmol) was added dropwise at
-78 °C to a solution of 3-bromo-1-(tert-butyldimethylsilyl)-5-
methoxyindole (435 mg, 1.28 mmol) in 10 mL of anhydrous
THF. The mixture was stirred at this temperature for 30 min
and transferred via cannula into a flask containing a -78 °C
solution of N-methyl-L-proline methyl ester (276 mg, 192
mmol) in anhydrous THF (3 mL). After stirring at -78 °C for
9 h the reaction mixture was warmed to -10 °C over a period
of 1 h and quenched by addition of ice-water. The resulting
reaction mixture was concentrated under reduced pressure.
Trituration of the resulting residue with ether produced an
off-white solid, which was collected by filtration, washed on
the filter with ether, and dried under vacuum to provide the
title compound (115 mg, 35% yield). An analytical sample was
crystallized from acetonitrile to afford shiny white needles: mp
a
Slopes of dose-response curves for (R)-1 and (R)-3 are not
significantly different and are not different from the slope of the
LSD dose-response curve (p > 0.05).
Ta ble 3. Data from Substitution Tests in DOI-Trained Ratsa
dose
ED50 (95% CI)
mg/ µmol/
drug kg
kg
N
%D %SDL
µmol/kg
mg/kg
DOI 0.1
0.2
0.28
0.56 10 10
9
0
56
89
0.28
0.12
0.4
1.12 10
0
12.5
11
11
0
100
43
63
88
14
(0.19-0.43) (0.08-0.16)
(R)-1 0.08 0.25
0.16 0.50
8
9
9
7
7
8
7
6
8
0.32
0.11
0.33 1.00
(0.14-0.7) (0.04-0.23)
(R)-3 0.06 0.25
0.12 0.50
0
43
0.47 0.11
1
0.23 1.00
12.5 100
(0.26-0.84) (0.06-0.2)
PS PS
180 °C dec; H NMR (DMSO-d6) δ 11.80 (br s, 1H, NH), 8.48
4
0.68 2.0
1.36 4.0
2.72 8.0
0
0
0
14
50
62.5
(s, 1H, ArH), 7.75 (d, 1H, ArH, J ) 2.1 Hz), 7.33 (d, 1H, ArH,
J ) 8.5 Hz), 6.82 (dd, 1H, ArH, J ) 8.5 and 2.1 Hz), 3.78 (s, 3,
OCH3), 3.51 (m, 1H, -CH-N), 3.12 (m, 1H, NCH2CH2), 2.30
(m, 1H, NCH2CH2), 2.25 (s, 3H, NCH3), 2.13 (m, 1H, NCH2CH2),
1.80 (m, 3H, NCH2CH2CH2 and NCH2CH2CH2); [R]D25 ) -125°
[c ) 0.01, DMF]; CIMS 259 (MH+). Anal. (C15H18N2O2) C, H,
N.
a
None of the slopes of the dose-response curves deviated
significantly from parallelism.
In conclusion, oxygenation at either the 4- or 5-indole
position has no consequences for receptor stereoselec-
tivity and affords rigid tryptamine analogues with
identical pharmacological properties, at least in the
assays employed here. Further, based on conformational
energy scans, it seems doubtful that these compounds
bind to the 5-HT2A receptor in an ergoline-like confor-
mation. These results also suggest that both 1 and 3
would possess LSD-like psychopharmacology in hu-
mans.
(R)-(+)-3-(N-Met h ylp yr r olid in -2-ylca r b on yl)-5-m et h -
oxyin d ole, (R)-7. The above-described procedure was used,
but employing N-methyl-D-proline methyl ester: mp 185 °C.
The spectral properties of this compound were identical to
those described above for (S)-7, except: [R]D ) +114° [c )
0.01, DMF]. Anal. (C15H18N2O2) C, H, N.
25
(S)-(-)-3-(N-Meth ylp yr r olid in -2-ylm eth yl)-5-m eth oxy-
in d ole, (S)-1.1 To a stirred mixture of lithium aluminum
hydride (570 mg, 15 mmol) in anhydrous THF (100 mL) at 0
°C was added (S)-7 (780 mg, 3 mmol) portionwise. The
resulting mixture was heated at reflux for 18 h. After cooling,
1 g of sodium sulfate decahydrate was added carefully, followed
by ethyl acetate (10 mL) and then water (0.2 mL). The
resulting slurry was stirred at room temperature for 6 h. The
mixture was filtered through Celite with copious washing with
ethyl acetate, and the combined filtrates were evaporated
under reduced pressure. The residual yellow oil was purified
by column chromatography over silica gel with methylene
chloride/methanol/ammonium hydroxide (9:1:0.1) as the eluent
to afford the title compound (700 mg, 95%) as a slightly tan
thick oil, which solidified upon standing in the freezer: mp
for the free base 52-54 °C (lit.1 mp 54-57 °C); 1H NMR
(fumarate salt; DMSO-d6) δ 10.7 (br s, 1H, NH), 7.22 (d, 1H,
ArH, J ) 8.8 Hz), 7.15 (s, 1H, ArH), 7.02 (d, 1H, ArH, J ) 2.4
Hz), 6.71 (dd, 1H, ArH, J ) 8.8, 2.4 Hz), 6.53 (s, 2H, fumarate
vinyl), 3.73 (s, 3H, OCH3), 3.34 (m, 1H, -CH-N), 3.16 (dd,
1H, ArCH2, J ) 15, 6 Hz), 3.02 (m, 1H, NCH2CH), 2.75-2.62
(m, 2H, ArCH2 and NCH2CH), 2.6 (s, 3H, NCH3), 1.9-1.55 (m,
Exp er im en ta l Section
Ch em istr y. Melting points were determined using a Thomas-
Hoover apparatus and are uncorrected. 1H NMR spectra were
recorded using either a 500 MHz Varian VXR-500S or 300
MHz Bruker ARX-300 NMR spectrometer. Chemical shifts are
reported in δ values ppm relative to an internal reference
(0.03%, v/v) of tetramethylsilane (TMS) in CDCl3, except where
noted. Chemical ionization mass spectra (CIMS) using meth-
ane as a carrier gas were obtained with a Finnigan 4000
spectrometer. Elemental analyses were performed by the
Purdue University Microanalysis Laboratory and are within
(0.4% of the calculated values unless otherwise noted. All
reactions were carried out under an inert atmosphere of argon.
3-B r om o-1-(t er t -b u t y ld im e t h y lsilyl)-5-m e t h o xyin -
d ole, 6. To a solution of 5-methoxyindole (705 mg, 4.80 mmol)
in 30 mL of anhydrous THF at -78 °C was added dropwise a
solution of n-butyllithium in hexane (3.5 mL of a 1.6 M
solution, 5.76 mmol) and the temperature was raised to -10
25
4H, NCH2CH2CH2, NCH2CH2CH2); [R]D ) -103° [c ) 1,
25
CHCl3] (lit. [R]D ) -98° [c ) 0.01, CHCl3]).

Oxygenated Tryptamines with LSD-like Activity
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20 4261
(R)-(+)-3-(N-Meth ylp yr r olid in -2-ylm eth yl)-5-m eth oxy-
in d ole, (R)-1.1 The above-described procedure was used, but
employing (R)-3-(N-methylpyrrolidin-2-ylcarbonyl)-5-methoxy-
indole. The physical and spectral properties of this compound
were identical to the physical and spectral properties of (S)-1,
except: [R]D ) +94° [c ) 0.01, CHCl3] (lit. [R]D ) +100° [c
) 0.01, CHCl3]).
washed copiously with ether, and the combined filtrates were
evaporated under reduced pressure. The residual oil was
dissolved in ether, washed with brine, dried with MgSO4, and
placed under high vacuum to provide the title compound (160
mg, 92% yield) as a white solid. An analytical sample was
25
25
1
crystallized from ethyl acetate/hexane: mp 135 °C; H NMR
δ 13.8 (br s, 1H, OH), 7.92 (s, 1H, NH), 7.04 (t, 1H, ArH, J )
8 Hz), 6.84 (m, 2, ArH), 6.54 (d, 1, ArH, J ) 8 Hz), 3.12 (m,
2H, CH2), 2.89 (m, 2H, CH2), 2.43 (s, 3H, NCH3), 2.36 (dt, 1H,
N-CH), 1.94 (m, 1H, N-CH2), 1.68 (m, 2H, CH2), 1.47 (m, 1H,
3-Br om o-1-(t er t -b u t yld im e t h ylsilyl)-4-b e n zyloxyin -
d ole, 8. To a solution of 4-benzyloxyindole (2.50 g, 11.21 mmol)
in anhydrous THF (100 mL) at 0 °C was added portionwise
sodium hydride (60% suspension in mineral oil, 538 mg, 13.5
mmol). The resulting suspension was allowed to warm to room
temperature over a period of 1 h and then was cooled to 0 °C,
and a solution of tert-butyldimethylsilyl chloride (1.85 g, 12.31
mmol) in anhydrous THF (25 mL) was added. After stirring
at 0 °C for 2.5 h the resulting mixture was cooled to -78 °C
and freshly crystallized N-bromosuccinimide (2.19 g, 12.31
mmol) was added. After stirring at this temperature for 4 h
the resulting mixture was allowed to warm to 25 °C, and
hexane (100 mL) and pyridine (2 mL) were added. The
resulting suspension was filtered through Celite and the
filtrate was concentrated under reduced pressure. The crude
product was purified by column chromatography over silica
gel with 50% CH2Cl2/hexane as eluent to afford the title
compound (3.95 g, 85% yield) as an off-white solid. An
analytical sample was crystallized from hexane: mp 95 °C;
1H NMR δ 7.61 (d, 2H, ArH, J ) 7 Hz), 7.42 (t, 2H, ArH, J )
7 Hz), 7.32 (m, 2H, ArH, J ) 7 Hz), 7.15-7.04 (m, 2H, ArH),
6.62 (dd, 1H, J ) 7.5 and 0.89 Hz), 5.23 (s, 2H, CH2), 0.93 (s,
9, tert-butyl), 0.58 (s, 6, dimethyl); CIMS 417 (MH+). Anal.
(C21H26BrNOSi) C, H, N.
25
CH2); [R]D ) -18° [c ) 0.01, DMF]. Measured exact mass
(FAB, M + H+): 231.1495. Calcd: 231.1497.
(R)-3-(N-Met h ylp yr r olid in -2-ylm et h yl)-4-h yd r oxyin -
d ole, (R)-3. The above-described procedure was used, but
employing (R)-3-(2-N-methylpyrrolidin-2-ylcarbonyl)-4-benz-
yloxyindole. The physical and spectral properties of this
compound were identical to the physical and spectral proper-
ties of (S)-3, except: [R]D25 ) +15° [c ) 0.01, DMF]. Measured
exact mass (FAB, M + H+): 231.1496.
(R,S)-(()-3-(4-Ben zyloxyin d ol-3-yl)-N-m eth ylsu ccin im -
id e, 10. Following a modification of the method of Macor et
al.6 a solution of 4-benzyloxyindole (1 g, 4.48 mmol) and
N-methylmaleimide (1.49 g, 13.44 mmol) in AcOH (25 mL) was
heated at reflux for 6 days. Upon consumption of the starting
material as observed by TLC, the mixture was cooled, the
solution was evaporated under reduced pressure, and the
residue was purified by crystallization from ethyl acetate to
afford the desired compound as a tan solid in 75% yield. An
analytical sample was obtained following several recrystalli-
1
zations from EtOAc: mp 195 °C dec; H NMR (DMSO-d6) δ
11.02 (s, 1H, NH), 7.41-7.25 (m, 5, ArH), 7.2 (s, 1H, ArH),
6.98-6.82 (m, 2H, ArH), 6.36 (d, 1, ArH, J ) 7.8 Hz), 5.08 (s,
2H, ArCH2), 4.28-4.16 (dd, 1H, COCHCH2, J ) 9.1, 7.4 Hz),
3.08 (dd, 1H, COCHCH2, J ) 9.1 and 17.4 Hz), 2.72 (dd, 1H,
COCHCH2, J ) 7.4 and 17.4 Hz), 2.65 (s, 3, NCH3); CIMS 335
(MH+). Anal. (C20H18N2O3) C, H, N.
(S)-(-)-3-(N-Met h ylp yr r olid in -2-ylca r b on yl)-4-b en z-
yloxyin d ole, (S)-9. A three-neck flask containing a solution
of 3-bromo-1-(tert-butyldimethylsilyl)-4-benzyloxyindole (1.5 g,
3.6 mmol) in anhydrous THF (50 mL) was cooled to -78 °C. A
solution of n-butyllithium (1.65 mL of a 2.5 M solution in
hexane, 4.32 mmol) was then slowly added, allowing it to run
in along the inside walls of the flask in order to cool to -78
°C, and the mixture was stirred at this temperature for 1 h.
The resulting 3-lithioindole was transferred via cannula into
a precooled solution of N-methyl-L-proline methyl ester (776
mg, 5.4 mmol) in anhydrous THF (10 mL). After stirring at
-78 °C for 20 h, the reaction mixture was allowed to warm to
-30 °C over a period of 2 h and was then poured into ice. The
resulting mixture was concentrated under reduced pressure.
Upon addition of ether to the resulting residue, an off-white
precipitate was formed, which was collected by filtration,
washed on the filter with ether ,and dried under high vacuum
to afford the desired product (450 mg, 35% yield). An analytical
sample was crystallized from acetonitrile: mp 175 °C dec; 1H
NMR (DMSO-d6) δ 8.08 (s, 1H, ArH), 7.6 (d, 2H, ArH, J ) 7.0
Hz), 7.3-7.4 (m, 3H, ArH), 7.14-7.03 (m, 2H, ArH), 6.75 (dd,
1H, ArH, J ) 8.1 and 1.1 Hz), 5.19 (s, 2H, ArCH2), 3.76 (m,
1H, N-CH), 2.94 (m, 1H, N-CH2), 2.14 (s, 3, NCH3), 2.14-
2.05 (m, 1H, N-CH2), 2.05-1.89 (m, 1H, CH), 1.78-1.56 (m,
(R,S)-(()-3-(N-Met h ylp yr r olid in -3-yl)-4-b en zyloxyin -
d ole, 11. To a stirred suspension of LiAlH4 (570 mg, 15 mmol)
in anhydrous THF (25 mL) at 0 °C was added 10 (1.0 g, 3.0
mmol) as a solid portionwise, and the resulting mixture was
heated at reflux for 3 h. The reaction mixture was cooled and
water (2 mL) was added slowly, followed by ether (70 mL).
The resulting slurry was filtered through Celite and the filtrate
was evaporated under reduced pressure. The residual oil was
dissolved in ether, washed with brine, dried with MgSO4, and
concentrated under reduced pressure. The resulting off-white
solid was purified by crystallization from chloroform/petroleum
ether to afford the title compound (780 mg, 84% yield): mp
1
130 °C; H NMR δ 8.0 (br s, 1H, NH), 7.46 (d, 2H, ArH, J )
7.5 Hz) 7.45-7.34 (m, 3H, ArH), 7.05 (t, 1H, ArH, J ) 8.1 Hz),
6.95-6.86 (m, 2H, ArH), 6.52 (d, 1H, ArH, J ) 7.6 Hz), 5.15
(s, 2H, ArCH2), 4.02-3.90 (p, 1H, CH2CHCH2, J ) 6.8 Hz),
2.95 (t, 1H, CH2N, J ) 6.8 Hz), 2.70-2.52 (m, 3H, CHCH2N
and CH2CH2N), 2.32-2.20 (m, 4H, CH2CH2N, NCH3), 1.95 (m,
1H, CH2CH2N); CIMS 307 (MH+). Anal. (C20H22N2O) C, H, N.
3H, CH); [R]D ) -102° [c ) 0.01, DMF]; CIMS 335 (MH+).
25
(R ,S )-(()-3-(N -Me t h ylp yr r olid in -3-yl)-4-h yd r oxyin -
d ole, 5. A solution of (R,S)-11 (570 mg, 1.86 mmol) in 95%
EtOH (20 mL) was stirred under 1 atm of hydrogen over 10%
Pd/C (60 mg) for 7 h. The catalyst was removed by filtration,
the filtrate was concentrated under reduced pressure, and the
residue was dried under vacuum to afford the title compound
as a white solid in 95% yield: mp 170 °C dec; 1H NMR δ 13.75
(br s, 1H, OH), 7.98 (s, 1H, NH), 7.08 (t, 1H, ArH, J ) 7.6
Hz), 6.84-6.81 (m, 2H, ArH), 6.55 (d, 1H, ArH, J ) 7.7 Hz),
3.71-3.59 (m, 1H, CH2CHCH2), 3.33 (t, 1H, CHCH2N, J ) 7.5
Hz), 3.12 (d, 1H, CHCH2N, J ) 7.5 Hz), 2.58 (t, 1H, CH2CH2N,
J ) 9 Hz), 2.50 (s, 3H, NCH3), 2.46-2.32 (m, 1H, CH2CH2N),
2.32-2.10 (m, 2H, CH2CH2N). Measured exact mass (FAB, M
+ H+): 217.1340. Calcd: 217.1341.
Anal. (C21H22N2O2) C, N, H.
(R)-(+)-3-(N-Met h ylp yr r olid in -2-ylca r b on yl)-4-b en z-
yloxyin d ole, (R)-9. The above-described procedure was used,
but employing N-methyl-D-proline methyl ester. The physical
and spectral properties of this compound were identical to the
physical and spectral properties of (S)-9, except: [R]D25 ) +91°
[c ) 0.01, DMF]. Anal. (C21H22N2O2) C, N, H.
(S)-(-)-3-(N-Meth ylp yr r olid in -2-ylm eth yl)-4-h yd r oxy-
in d ole, (S)-3. A suspension of LiAlH4 (142 mg, 3.72 mmol) in
anhydrous dioxane (6 mL) was brought to reflux, and a heated
solution of (S)-3-(2-N-methylpyrrolidin-2-ylcarbonyl)-4-benzyl-
oxyindole (250 mg, 0.75 mmol) in anhydrous dioxane (6 mL)
was added via syringe. The resulting mixture was held at
reflux until TLC indicated that the reaction was complete (72-
96 h). The reaction mixture was cooled to 25 °C, water (0.5
mL) was added carefully, followed by ether (12 mL), and the
resulting slurry was stirred at room temperature for 15 min.
The mixture was filtered through Celite, the filter cake was
P h a r m a cology Meth od s. Com p etition Assa ys in Ra t
Br a in Hom ogen a te. The procedure of J ohnson et al.12 was
employed with minor modifications. Briefly, 50 male Sprague-
Dawley whole rat brains (unstripped) were purchased from
Harlan Bioproducts for Science, Inc. and dissected over dry

4262 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Gerasimov et al.
ice. The frontal cortex tissue was homogenized (Kinetica
polytron, setting 4, 2 × 20 s) in 4 volumes (w/v) of ice-cold
0.32 M sucrose and centrifuged at 36000g for 10 min at 4 °C.
The pellet was again suspended in the same volume of sucrose,
homogenized (Kinematica polytron, setting 4, 20 s), and
separated into aliquots of 4.5 mL and stored at -70 °C.
two training sessions following a test session. 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 session was ended and scored as a disruption.
Treatments were randomized at the beginning of the study.
For each experiment one aliquot of frontal cortex tissue was
thawed and diluted with 25 volumes (w/v) of 50 mM tris-
(hydroxymethyl)aminomethane (Aldrich Chemicals) buffer,
adjusted to pH 7.4 by HCl. The tissues were homogenized
(Kinematica polytron, setting 4, 20 s) and incubated for 10 min
in a 37 °C shaking water bath. The homogenate was then
centrifuged twice at 36000g for 10 min at 4 °C, with the pellet
being resuspended in 25 volumes of Tris-HCl buffer between
centrifugations. The supernatant was discarded, and the pellet
was resuspended with 25 volumes of Te Pac buffer (0.5 mM
Na2EDTA, 10.0 µM pargyline, 5.7 mM CaCl2, 0.1% sodium
ascorbate), homogenized using the Kinematica polytron as
above, and incubated in a 37 °C shaking water bath for 10
min. The homogenate was then placed in an ice bath to cool.
Binding was initiated by adding 800 µL of homogenate tissue
(200-400 µg of protein) to assay tubes containing 100 µL of
[3H]MDL100907 (0.2 nM) and 100 µL of competing drug
solution. Nonspecific binding was determined in the presence
of cinanserin (10 µM). Binding assays were incubated for 15
min in a 37 °C shaking water bath. Incubation was stopped
by rapid vacuum filtration using a Brandel cell harvester
(Brandel Instruments, Gaithersburg, MD) through GF/C
filters. The filters were washed twice with 5-mL aliquots of
ice-cold Tris-HCl buffer, allowed to air-dry, and placed into
scintillation vials containing 10 mL of Ecolite scintillation
cocktail (ICN Biomedicals). Eight hours later the radioactivity
was measured using liquid scintillation spectroscopy (Packard
model 4430) at 37% efficiency for tritium. For experiments
with [125I]DOI, the dried filters were counted directly for 125I
at 79% efficiency in a gamma counter. EC50 (nM) values were
calculated from at least three experiments, each done in
triplicate, using GraphPad PRISM.
[3H]MDL100907 and [125I]DOI were purchased from Amer-
sham Life Sciences (Arlington Heights, IL) or New England
Nuclear (Boston, MA) at specific activities of 82 and 2000 Ci/
mmol, respectively. (+)-LSD tartrate was obtained from the
National Institute on Drug Abuse. Cinanserin was a gift from
the SQUIBB Institute for Medical Research, and 5-HT was
purchased from Sigma (St. Louis, MO).
Dr u g Discr im in a tion Stu d ies. The procedures for the
drug discrimination assays were essentially as described in
previous reports.14,15 Male Sprague-Dawley rats (Harlan
Laboratories, Indianapolis, IN), weighing 200-220 g at the
beginning of the study, were trained to discriminate LSD or
DOI from saline. None of the rats had previously received
drugs or behavioral training. Water was freely available in
the individual home cages, and a rationed amount of supple-
mental feed (Purina Lab Blox) was made available after
experimental sessions to maintain approximately 80% of free-
feeding weight. Lights were on from 0700 to 1900. The
laboratory and animal facility temperature was 22-24 °C, and
the relative humidity was 40-50%. Experiments were per-
formed between 0830 and 1700 each day, Monday-Friday.
The training drugs were (+)-lysergic acid diethylamide
tartrate (LSD, 0.08 mg/kg, 0.186 µmol/kg; NIDA) and (()-2,5-
dimethoxy-4-iodoamphetamine hydrochloride (DOI, 0.4 mg/kg,
1.12 µmol/kg; NIDA). All drugs were dissolved in 0.9% saline
and were injected intraperitoneally in a volume of 1 mL/kg,
30 min before the sessions. Data from the drug discrimination
study were scored in a quantal fashion, with the lever on which
the rat first emitted 50 presses in a test session scored as the
“selected” lever. The percentage of rats selecting the drug lever
(%SDL) for each dose of test compound was determined. The
degree of substitution was determined by the maximum %SDL
for all doses of the test drug. “No substitution” was defined as
59% SDL or less, and “partial” substitution is 60-79% SDL.
If the drug was one that completely substituted for the training
drug (at least one dose resulted in a %SDL ) 80% or higher),
the method of Litchfield and Wilcoxon16 was used to determine
the ED50 (log-probit analysis as the dose producing 50% drug-
lever responding) and 95% confidence interval (95% CI). This
method also allowed for tests of parallelism between dose-
response curves of the drug and the training drug. If 50% or
more of the animals tested were disrupted at a dose, even if
the nondisrupted rats gave 80% SDL, no ED50 was calculated.
Ack n ow led gm en t. This work was supported by
NIH Grant DA02189 from the National Institute on
Drug Abuse. M.G. wishes to thank Dr. M. Parker for
many helpful discussions and D. Miller for assistance
with some of the NMR spectra.
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