No job name

J. Med. Chem. 2000, 43, 1011-1018
2-Substituted Tryptamines: Agents with Selectivity for 5-HT6 Serotonin
Receptors|
Richard A. Glennon,*,† Mase Lee,† Jagadeesh B. Rangisetty,† Malgorzata Dukat,† Bryan L. Roth,‡Jason E. Savage,‡ Ace McBride,‡ Laura Rauser,‡ Sandy Hufeisen,‡ and David K. H. Lee§ Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23298,Departments of Biochemistry, Psychiatry, and Neurosciences, School of Medicine, Case Western Reserve University,Cleveland, Ohio 44106, and Allelix Biopharmaceuticals, Mississauga, Ontario L4V 1V7, Canada Several 2-alkyl-5-methoxytryptamine analogues were designed and prepared as potential 5-HT6
serotonin agonists. It was found that 5-HT6 receptors accommodate small alkyl substituents
at the indole 2-position and that the resulting compounds can bind with affinities comparable
to that of serotonin. In particular, 2-ethyl-5-methoxy-N,N-dimethyltryptamine (8) binds with
high affinity at human 5-HT
full agonist, at least as potent (8: K
adenylate cyclase. Compound 8 displays modest affinity for several other populations of 5-HT
receptors, notably h5-HT
receptors, but is otherwise quite selective. Compound 8 represents the first and most selective
5-HT6 agonist reported to date. Replacing the 2-ethyl substituent with a phenyl group results
in a compound that retains 5-HT
6 receptor affinity (i.e., 10: Ki
character. 2-Substituted tryptamines, then, might allow entry to a novel class of 5-HT6 agonistsand antagonists.
Introduction
tion, mood-dependent behavior, and early growth pro-cesses involving serotonin.9-11 Serotonin (5-hydroxytryptamine, 5-HT; 1a) receptors
Ro 04-6790 (2a) and Ro 63-0563 (2b) represent the
are classified as belonging to one of several different 6-selective antagonists.12 Several related struc- tures have also been reported including SB-271046 (3,
identified are the 5-HT6 receptors.1 5-HT6 serotonin R ) H).13 Repeated intracerebroventricular administra- receptors are members of the G-protein superfamily, are tion of antisense oligonucleotides to rats to prevent positively coupled to an adenylate cyclase second- messenger system, and are found primarily in the syndrome that consists of yawning, stretching, and central nervous system.2 The exact clinical significance chewing;6,7 administration of Ro 04-6790 and Ro 63-0563 of 5-HT6 receptors is unknown at this time. Of interest, to naive animals produced a similar effect.12 [3H]Ro 63- however, is that a number of typical and atypical 0563 has been developed as a radioligand for binding antipsychotic agents and tricyclic antidepressants bind with high affinity at 5-HT6 receptors (i.e., with Ki valuesof <100 nM).3-5 In rats prevented from expressing5-HT6 receptors, the animals behave in a manner thatseems to involve an increase in cholinergic function; thishas led to speculation that one of the roles of 5-HT6receptors may be to control cholinergic neurotransmis-sion and that 5-HT6-selective antagonists could beuseful in the treatment of anxiety and memory defi-cits.6,7 It has been further suggested that GABA-containing neurons in the striatum and glutamate-containing neurons in the hippocampus could be targetsof 5-HT actions mediated by 5-HT6 receptors.8 5-HT6ligands might thus be of value in the treatment ofanxiety and related disorders. Other studies suggestthat 5-HT6 receptors might be involved in motor func- | Presented in part at the Virginia Academy of Science Meeting, * Correspondence to: Richard A. Glennon, Ph.D., Box 980540, Department of Medicinal Chemistry, Virginia Commonwealth Uni-versity, Richmond, VA 23298-0540. Phone: 804-828-8487. Fax: 804-828-7404. E-mail: [email protected].
† Virginia Commonwealth University.
‡ No 5-HT6 -selective agonists have yet been identified.
Various indolealkylamines, including the tryptamines Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 Scheme 1a
a (a) i. nBuLi, THF, -78 °C, ii. CO2, iii. tBuLi, THF, -78 °C, iv. MeI; (b) Me2N-CH2CH2-NO2, CF3COOH; (c) LiAlH4, THF, ∆; (d) 5-HT (1a) and 5-methoxytryptamine (1b), and ergolines,
tors and because 2-methyl 5-HT has been previously such as (+)lysergic acid diethylamide (LSD) and li- considered a 5-HT3-selective agent, this seemed to be a suride, bind with high affinity. In fact, [125I]iodo-LSD suitable starting point for the exploration of potentially and [3H]LSD have been used to label 5-HT6 receptors.
The purpose of our present study was to identifypotential agonists with enhanced selectivity for 5-HT Chemistry
receptors that might be useful for investigating this The 2-methyl derivative 7 was prepared via a litera-
population of receptors and receptor function.
ture procedure17 from 2-methylindole using the Speeter- 5-HT and 5-methoxytryptamine have been demon- Anthony method, and the 2-ethyl homologue 8 was
strated to act as 5-HT6 agonists and produce a potent prepared by treatment of the free base of 7 with tBuLi
dose-dependent increase in cAMP levels.14 Unfortu- followed by the addition of MeI (Scheme 1). The 2-phen- nately, these tryptamines are notoriously nonselective yl derivative 10 was prepared from 5-methoxy-2-phen-
and bind at multiple populations of 5-HT receptors.15 ylindole as shown in Scheme 1. Reaction of 5-methoxy- It has been demonstrated, however, that with appropri- 2-phenylindole with N,N-dimethylamino-2-nitroethyl- ate molecular modification tryptamine derivatives can ene afforded the nitrovinyl derivative 22; compound 22
be developed that display enhanced selectivity for was reduced to amine 23 using LiAlH4, and the amine
different populations of 5-HT receptors.15 was reductively methylated with formaldehyde and We began our investigation by exploring the structure- affinity relationships for the binding of tryptamines at Many of the 5-methoxy-substituted tryptamines were prepared from 5-methoxy-N,N-dimethyltryptamine (free 6 receptors.16 We found that O-methylation of 5-HT (1a: K )
base of 11) (Scheme 2). Direct alkylation of 11 (free base)
75 nM) to 5-methoxytryptamine (1b: Ki
nM) had little effect on affinity and that removal of the under basic conditions with the appropriate alkyl halide hydroxyl group to give tryptamine (1c: K )
1-substituted derivatives 12-15. The
only halved affinity.16 Most other changes led to sig- procedure is exemplified for compound 15. The 2-n-
nificant decreases in affinity. For example, lengthening propyl homologue 9 was also obtained from 11 (Scheme
the alkyl chain by one methylene unit, conformational 2). The N1-position of 11 (free base) was protected with
restriction of the side chain as a 1,2,3,4-tetrahydropy- a benzenesulfonyl group, and the resulting compound, rido[3,4-b]indole, replacement of the indolic nitrogen 18, was treated with nPrI to give 19; hydrolysis of the
atom with an sp3-hybridized carbon atom, and quater- protecting group provided compound 9. Reaction of the
nization of the terminal amine all resulted in a dramatic indolyl anion of 11 (free base) with anhydrous γ-buty-
reduction in affinity (i.e., K > rolactone afforded the N-butyrate 20. Attempts to
hand, N-monomethylation and N,N-dimethylation re- cyclize 20 using PPA at 100 °C were unsuccessful and
sulted in retention or a slight increase in affinity. More resulted in decomposition; however, substitution of importantly, we found that introduction of a 2-methyl PPE18 for PPA gave the desired 21, which was reduced
substituent was tolerated. That is, 2-methyl 5-HT (4:
with borane to give the desired 16 (Scheme 2). Com-
pound 17 was synthesized via debenzylation of its
46 nM) possessed an affinity at least comparable to that of 5-HT itself. This is particularly noteworthy because, with the exception of 5-HT3 receptors, 2-methylsubstitution is generally thought to reduce the affinity Results and Discussion
of tryptamines for most populations of 5-HT receptors.
2-Methyl 5-HT (4) is currently considered a 5-HT3-
Indeed, 2-methyl 5-HT (4) is currently considered a
selective ligand; on the other hand, it is known that 5-HT3-selective ligand. Interestingly, we have now 5-HT3 receptors do not readily accommodate a tryptamine demonstrated that 2-methyl 5-HT binds at 5-HT6 recep- 5-methoxy group. For example, 5-methoxytryptamine (1b), the O-methyl ether of 5-HT (1a), is completely
devoid of activity at 5-HT3 receptors.20 Hence, the first that 2-methylation of 5-HT is tolerated by 5-HT6 recep- compound that we examined was the simple 2-methyl Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 Scheme 2a
a (a) NaH, DMF, rt, and Me2SO4, EtBr, nPrCl or iPrCl; (b) NaH, DMF, PhSO2Cl, rt; (c) BuLi, DME, nPrI, -10 °C; (d) Mg, MeOH, rt; (e) γ-butyrolactone; (f) PPE, CHCl3, reflux; (g) B2H6/THF, rt.
Table 1. Physicochemical Properties and 5-HT6 Receptor Affinities of Tryptamine Analogues
a Recrystallization solvents: EtOH represents absolute ethanol; Et2O, anhydrous ether; A, acetone; B, ethyl acetate. b Ki values represent replicate determinations and SEM are (25%; for purpose of comparison, clozapine was determined to possess a K ) compounds analyzed correctly to within 0.4% of theory for C, H, and N except where noted. d Crystallized with 0.7 mol of H2O. e Crystallizedwith 1 mol of H2O. f Ki value previously reported;16 included for purpose of comparison.
analogue of 5-methoxytryptamine (1b: K )
be a useful 5-HT6 ligand; however, given that 5 pos-
namely, 5-methoxy-2-methyltryptamine (5). Compound
sesses a primary amine, its utility for future in vivo 5 (K )
98 nM; Table 1) was found to bind at 5-HT6 studies might be hampered by its reduced ability to receptors with an affinity comparable to that of 5-meth- penetrate the blood-brain barrier and/or due to its oxytryptamine. It was also found that 5 lacks affinity
potential for rapid metabolism by oxidative deamina- 10000 nM). Compound 5 might
tion. To address these problems, we sought to prepare Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 Table 2. Binding Profile of Compounds 7, 8, and 10a
a Compounds displayed Ki values of >10000 nM at the following populations of receptors: histamine, NMDA, PCP, acetylcholine, opiate, and vasopressin receptors; see Experimental Section for specific subpopulations examined. Ki values were >10000 nM for compounds
7 and 8 at hD1, rD2, rD3, rD4, and hD5 receptors and >10000 nM for 10 at hD1, rD2, and rD4 receptors; although 10 produced 70%
inhibition at 10000 nM at rD3 and hD5 receptors, it was not further evaluated. NET and SERT represent the norepinephrine and serotonin
transporters. Ki values for all three compounds at the dopamine transporter were >10000 nM.
several related derivatives that were somewhat more In a final attempt to enhance lipophilicity in the lipophilic and/or that might be less prone to metabolism.
2-substituted DMT series, the propyl group of 9 was
One approach to enhancing lipophilicity and hinder- tethered to the DMT side chain to afford 17; compound
ing metabolism was to add N,N-dimethyl substituents 17 (K )
168 nM) was found to bind at 5-HT6 receptors to the terminal amine; a second approach to enhancing with about 3-fold lower affinity than 8. Although
lipophilicity was to homologate the 2-position substitu- compound 17 possesses an asymmetric center and can
ent. 2-Methyl-N,N-dimethyltryptamine (2-methyl DMT, exist as a pair of optical isomers, no attempt was made 6: K )
300 nM), an N,N-dimethyl analogue of 5 lacking
to examine the individual isomers because structurally the 5-methoxy group, binds with severalfold lower related agents have been shown to bind at 5-HT1D affinity than 5 itself. Reintroduction of the 5-methoxy
receptors,21,22 and it was anticipated that the isomers group, affording 2-methyl-5-methoxy DMT (7: K )
of 17 might lack the desired selectivity.
nM), enhanced affinity. Homologation of the 2-methyl Binding Profile. Compounds 7, 8, and 10 were
substituent to an ethyl group (i.e., 8: K )
selected for examination of detailed binding profiles. All sulted in a slight increase in affinity and in a compound three agents were examined at more than 30 different with affinity at least comparable to that of 5-HT itself.
receptor populations and produced <50% inhibition of Further homologation of the ethyl substituent to a 2-n- binding at a concentration of 10000 nM at most of these propyl group (i.e., 9: K )
populations. Where >50% displacement was observed, To explore the possibility of bulk tolerance, we examined Ki values were determined (Table 2). For these studies, the 2-phenyl derivative 10 (K )
Ki values were redetermined for 7, 8, and 10. Com-
bind with an affinity comparable to that of 8.
pounds 8 and 10 bind at human 5-HT6 receptors with
Another attempt to enhance lipophilicity was to incorporate small alkyl substituents at the indole N1- and with an affinity similar to that of clozapine; position. The idea was to subsequently incorporate a compound 7 binds with severalfold lower affinity (K )
2-alkyl substituent into whatever N1-substituted ana- 60 nM). Although 7 and 8 appear relatively selective,
logue retained high 5-HT6 receptor affinity. N1-Methy- they also bind at h5-HT1A, h5-HT1D, h5-HT1E, and h5- lation of 5-methoxy DMT (11: K )
HT7 receptors, yet compound 8, in particular, still
5-HT6 receptor affinity of the resulting compound by >6- displays 10-fold selectivity over 5-HT1A receptors and fold (12: K )
510 nM). Homologation of the N1-methyl nearly 20-fold selectivity over h5-HT1D and h5-HT7 group to an ethyl group (i.e., 13: K )
receptors. Compound 10 is more selective and displays
n-propyl group (i.e., 14: K )
735-fold selectivity over h5-HT1A receptors and >300- but the compounds did not bind as well as 11. Branching
fold selectivity over h5-HT1D receptors.
of 13 to the isopropyl derivative 15 (K )
Functional Studies. Compounds 7, 8, and 10 were
resulted in a further slight enhancement of affinity.
examined for their ability to activate adenylate cyclase.
However, none of these compounds displayed signifi- Whereas compounds 7 and 8 behaved as full agonists
cantly enhanced affinity. Compound 16 (K )
7.9 ( 5.0 and 3.6 ( 1.3 nM, respectively) relative which may be viewed as a cyclic 1,2-disubstituted 5.0 ( 3.0 nM), compound 10 showed no
analogue of 11, was also prepared for evaluation and
agonist activity (see Figure 1). Compound 10 inhibited
was found to bind with reduced affinity.
5-HT-stimulated adenylate cyclase at 10000 nM sug-gesting that it is an antagonist.
Molecular manipulation of a tryptamine template revealed that 2-methyl substitution was tolerated by5-HT6 receptors.16 Because 2-methyl 5-HT was previ-ously considered to be a 5-HT3-selective ligand and bytaking advantage of the fact that 5-HT3 receptors do notreadily accommodate a 5-methoxy group, a series of Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 to give a transparent solid. The flask was flushed with N2 anddry THF (7 mL) was added. The reaction mixture was degassedat -150 °C under reduced pressure of 1 mmHg, then allowedto warm to -78 °C; 1.7 M tBuLi (2.8 mL, 4.8 mmol) was addedto give a bright yellow solution. The cooling bath was replacedby an ice-salt bath and the reaction was kept at -20 °C for 45min, then cooled to -78 °C, and MeI (0.3 mL, 4.81 mmol) wasadded in a dropwise manner. The solution was kept at -78°C for 3 h. The reaction mixture was acidified with a saturatedethereal solution of HCl. Anhydrous Et2O was added to theresulting suspension and the supernatant was decanted. Theresidue was heated at 100 °C under reduced pressure for 20min. The resulting residue was purified by flash chromatog-raphy on silica gel (CH2Cl2/MeOH; 12:1) to give 0.17 g of abright yellow oil (16%): 1H NMR (CDCl3) δ 8.06 (s, 1H),7.14 (d, 1H, J ) 8.67 Hz), 6.98 (s, 1H), 6.76 (dd, 1H, J ) 2.34,8.73 Hz), 3.84 (s, 3H), 2.91-2.87 (m, 2H), 2.71 (q, 2H, J ) 7.38Hz), 2.57-2.52 (m, 2H), 2.38 (s, 6H), 1.25 (t, 3H, J ) 7.38 Hz).
The maleate salt was prepared and recrystallized from anEtOAc/Et2O mixture: mp 123 °C. Anal. (C15H22N2O‚C4H4O4) Figure 1. Typical dose-response curves for the effects of
compounds 7, 8, and 10 as 5-HT6 agonists in an adenylate
5-Methoxy-2-n-propyl-N,N-dimethyltryptamine Ox-
cyclase assay; serotonin was used as control. Each compound alate (9). Magnesium turnings (840 mg) and NH4Cl (77 mg,
was examined at five concentrations.
1.44 mmol) were added to a solution of 19 (free base) (259 mg,
0.65 mmol) in MeOH (17 mL) and the mixture was allowed to
2-alkyl-5-methoxytryptamines was synthesized for evalu- stir at room temperature for 1 h. Saturated NH4Cl solution ation at 5-HT6 receptors. Several compounds were was added and the reaction mixture was extracted with CH2- identified with affinities at least comparable to that of Cl2. The organic portion was dried (MgSO4) and the solvent was removed under reduced pressure. The residue was purified by flash chromatography on silica gel (CH methoxy-N,N-dimethyltryptamine (EMDT; 8) possessed
give 75 mg (45%) of a bright yellow oil: 1H NMR (CDCl 7.71 (brs, 1H), 7.16 (d, 1H, J ) 8.67 Hz), 6.99 (d, 1H, J ) 2.43 selectivity for 5-HT6 versus other receptors examined.
Hz), 6.77 (dd, 1H, J ) 2.25, 8.73 Hz), 3.85 (s, 3H), 2.89-2.83 In functional studies, EMDT (8) was demonstrated to
(m, 2H), 2.69 (t, 2H, J ) 7.56 Hz), 2.53-2.47 (m, 2H), 2.36 (s, 6H), 1.68 (tq, 2 H, J ) 7.28, 7.56 Hz), 0.98 (t, 3H, J ) 7.28 at least equivalent to that of 5-HT (K Hz). The oxalate salt was prepared and recrystallized from acetone: mp 146-147 °C. Anal. (C16H24N2O‚C2H2O4 0.7H2O) date. Also of interest is the 2-phenyl derivative 10
5-Methoxy-2-phenyl-N,N-dimethyltryptamine Oxalate
(10). 5-Methoxy-2-phenylindole26 (3 g, 13.44 mmol) was added
different binding profile than 8; compound 10 lacks
to a stirred ice-cooled solution of 1-dimethylamino-2-nitro- agonist activity up to concentrations of 10000 nM and ethylene (1.56, 13.44 mmol) in trifluoroacetic acid (8 mL). The may represent a novel 5-HT6 antagonist. Indeed, when resulting mixture was allowed to stir under N2 at room examined at the single concentration of 10000 nM, 10
temperature for 30 min and was then poured into ice/water.
behaved an antagonist. Hence, with the appropriate The solution was extracted with EtOAc and the organic portion substituents, 2-substituted tryptamines may provide was washed consecutively with saturated NaHCO3 solution,H 2O, then brine. The organic portion was dried (MgSO4) and 6-selective agonists and antagonists.
solvent was removed under reduced pressure. The residue wasrecrystallized from CH Experimental Section
2Cl2/hexane to give 2.36 g (60%) of 22
as a red powder: 1H NMR (acetone-d6) δ 8.82 (brs, 1H), 8.32 Synthesis. Melting points, determined with a Thomas-
(d, 1H, J ) 13.44 Hz), 7.94 (d, 1H, J ) 13.35 Hz), 7.69-7.41 Hoover melting point apparatus, are uncorrected. Proton (m, 7H), 6.98-6.94 (m, 1H), 3.92 (s, 3H); IR (KBr) 1606, 1475, magnetic resonance spectra were obtained with a GE QE-300 1251 cm-1. A solution of 22 (2.00 g, 6.75 mmol) in dry THF
or Varian Gemini 300 spectrometer; and tetramethylsilane was (20 mL) was added in a dropwise manner to a cooled (0 °C) used as an internal standard. Infrared spectra were recorded suspension of LiAlH4 (1.54 g, 40.5 mmol) in dry THF (40 mL) on a Nicolet 5ZDX FT-IR. Elemental analysis was performed under N2. The reaction mixture was heated at reflux for 1 h by Atlantic Microlab Inc. and determined values are within and then allowed to stand at room-temperature overnight. The 0.4% of theory. Flash chromatography was performed on silica resulting mixture was quenched with H2O then 15% NaOH gel (Merck grade 60, 230-400 mesh 60 Å). Certain compounds solution. Celite was added and the solution was filtered. The were previously reported in the literature but due to difficulty solvent was removed under reduced pressure. The residue was in either preparing or purifying the reported salt, a different purified by flash chromatography on silica gel (CH2Cl2/MeOH; salt was prepared. Specifically, compounds 7,17 10,23 and 1224
9:1) to give 1.00 g (55%) of the primary amine 2323 as an oil:
are known as their HCl salts but were isolated as their 1H NMR (CDCl3) δ 8.19 (brs, 1H), 7.59-7.58 (m, 2H), 7.49- monooxalate salts in the present investigation. Compound 6,
7.44 (m, 2H), 7.39-7.34 (m, 1H), 7.28-7.25 (m, 1H), 7.09 (d, prepared earlier as a maleate salt,25 was isolated as its HCl 1H, J ) 2.37 Hz), 6.88 (dd, 1H, J ) 2.24, 8.75 Hz), 3.89 (s, salt. All four of these compounds analyzed correctly for C, H, 3H), 3.04 (brs, 4H); IR (KBr) 3397, 3347 cm-1. Sodium cyanoborohydride (510 mg, 8.12 mmol) was added to a solution 2-Ethyl-5-methoxy-N,N-dimethyltryptamine Maleate
of primary amine 23 (700 mg, 2.63 mmol) and 37% aqueous
(8). A 2.5 M solution of nBuLi (1.75 mL, 4.38 mmol) was added
CH2O in MeCN (10 mL) at room temperature. The resulting in a dropwise manner to a stirred solution of 717 (free base)
mixture was adjusted to pH 5 with HOAc and was allowed to (1.00 g, 4.33 mmol) in dry THF (7 mL) at -78 °C under N2.
stir at room-temperature overnight. A 15% solution of NaOH After stirring the reaction mixture for 5 min, the cooling bath was added to neutralize the mixture and the mixture was was removed and CO2 gas was passed into the solution for 10 extracted with CH2Cl2. The combined organic portion was min. The solvent was removed at 0 °C under reduced pressure washed with saturated NaHCO3 solution and brine. The Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 organic portion was dried (MgSO4) and solvent was removed 1H, ArH), 6.90 (d, 1H, ArH), 6.70 (dd, 1H, ArH), 3.80 (s, 3H, under reduced pressure. The residue was purified by flash OCH3), 3.40 (t, 1H, CH), 3.15 (d, 1H, CH), 3.00 (t, 1H, CH), chromatography on silica gel (CH2Cl2/MeOH; 9:1) to give 195 2.82 (s, 6H, 2× CH3), 2.63-2.73 (m, 2H, CH2), 2.33 (m, 1H, mg (25%) of 10 (free base) as a white powder: 1H NMR (CDCl3)
CH), 1.8-2.0 (m, 3H, CH2-CH). Anal. (C16H22N2O‚C2H2O4) C, δ 8.05 (brs, 1H), 7.56-7.53 (m, 2H), 7.49-7.44 (m, 2H), 7.39- 7.34 (m, 1H), 7.29-7.25 (m, 1H), 7.11 (d, 1H, J ) 2.25 Hz), 1-Benzenesulfonyl-5-methoxy-N,N-dimethyltrypta-
6.87 (dd, 1H, J ) 2.52, 8.73 Hz), 3.89 (s, 3H), 3.13-3.08 (m, mine Oxalate (18). A mixture of 5-methoxy-N,N-dimethyl-
2H), 2.72-2.66 (m, 2H), 2.39 (s, 6H). Although the HCl salt tryptamine (11; free base) (4.35 g, 19.93 mmol) and 60%
has been previously reported,23 difficulties in its purification NaH (0.87 g, 21.75 mmol) was heated at 100 °C under N2 led to isolation of the product as its oxalate salt: mp 187- until evolution of H2 gas ceased. The resultant mass was 188 °C after recrystallization from acetone. Anal. (C19H22N2O‚ dissolved in anhydrous DMF (21 mL) and benzenesulfonyl chloride (2.8 mL, 21.94 mmol) was added in a dropwise man- 5-Methoxy-1-(2-propyl)-N,N-dimethyltryptamine Male-
ner at 0 °C. The reaction mixture was allowed to stir at room- ate (15). A mixture of 5-methoxy-N,N-dimethyltryptamine (11;
temperature overnight. Saturated NaHCO3 solution was added free base) (500 mg, 2.29 mmol) and 60% NaH (100 mg, 2.52 and the mixture was extracted with CH2Cl2. The organic mmol) was heated at 100 °C under N2 until evolution of H2 portion was dried (MgSO4) and the solvent was removed under gas ceased. The resultant mass was dissolved in anhydrous reduced pressure. The residue was purified by flash chroma- DMF (3 mL) and 2-bromopropane (0.25 mL, 2.84 mmol) was tography on silica gel (CH2Cl2/MeOH; 9:1) to give 4.39 g of added to the solution at 0 °C. The reaction mixture was allowed an oil (61%): 1H NMR (CDCl3) δ 7.89-7.87 (m, 1H), 7.83 (d, to stir at room temperature for 3 h. Brine was added and the 2H, J ) 8.0 Hz), 7.51 (t, 1H, J ) 7.8 Hz), 7.34 (s, 1H), 6.93- reaction mixture was extracted with CH2Cl2. The organic 6.92 (m, 2H), 3.82 (s, 3H), 2.80 (t, 2H, J ) 7.8 Hz), 2.59 (t, 2H, portion was dried (MgSO4) and the solvent was removed under J ) 7.8 Hz), 2.33 (s, 6H); IR (CHCl3) 1357, 1115 cm-1. The reduced pressure. The residue was purified by flash chroma- oxalate salt was prepared and recrystallized from an acetone/ tography on silica gel (CH2Cl2/MeOH; 10:1) to give 294 mg of Et2O mixture: mp 224-226 °C. Anal. (C19H22N2O3S‚C2H2O4) a bright yellow oil (49%): 1H NMR (CDCl3) δ 7.23 (d, 1H, J ) 8.94 Hz), 7.04 (d, 1H, J ) 2.46 Hz), 7.01 (s, 1H), 6.86 (dd, 1H, 1-Benzenesulfonyl-5-methoxy-2-n-propyl-N,N-dimeth-
J ) 2.46, 8.88 Hz), 4.59-4.54 (m, 1H), 3.86 (s, 3H), 2.95-2.89 yltryptamine Oxalate (19). A 2.5 M solution of nBuLi (1.4
(m, 2H), 2.66-2.61 (m, 2H), 2.36 (s, 6H), 1.48 (d, 6H, J ) 6.72 mL, 3.5 mmol) was added in a dropwise manner to a stirred Hz). The maleate salt was prepared and recrystallized from solution of 18 (free base) (1.00 g, 2.79 mmol) in DME (4 mL)
an acetone/Et2O mixture: mp 101-102 °C. Anal. (C16H24N2O‚ at -10 °C under N2. The resulting solution was allowed to stir for an additional 10 min at -10 °C, and then nPrI (0.35 mL, 1H NMR data for compounds 13 and 14 are as follows: 13
3.59 mmol) was added. The reaction mixture was allowed to (CDCl3) δ 7.22 (d, 1H, J ) 9.0 Hz), 7.06 (d, 1H, J ) 2.5 Hz), stir for 1 h at -10 °C. Saturated NaHCO3 solution was added 6.95 (s, 1H), 6.88 (dd, 1H, J ) 2.5, 6.0 Hz), 4.10 (q, 2H, J ) and the reaction mixture was extracted with CH2Cl2. The 7.5 Hz), 3.88 (s, 3H), 3.01-2.97 (m, 2H), 2.76-2.73 (m, 2H), organic portion was washed with brine and dried (MgSO4); the 2.45 (s, 6H), 1.44 (t, 3H, J ) 7.5 Hz); 14 (CDCl3) δ 7.19 (d, 1H,
solvent was removed under reduced pressure and the residue J ) 8.85 Hz), 7.04 (d, 1H, J ) 2.37 Hz), 6.90 (s, 1H), 6.87- was purified by flash chromatography on silica gel (CH2Cl2/ 6.83 (m, 1H), 3.98 (t, 2 H, J ) 7.08 Hz), 3.86 (s, 3H), 2.93- MeOH; 30:1) to give 0.19 g (17%) of a bright yellow oil: 1H 2.87 (m, 2H), 2.64-2.59 (m, 2H), 2.35 (s, 6H), 1.82 (q, 3H, J ) NMR (CDCl3) δ 8.06 (d, 1H, J ) 8.79 Hz), 7.62 (d, 2H, J ) 7.2 Hz), 0.91 (t, 2H, J ) 7.4 Hz).
8.22 Hz), 7.51-7.46 (m, 1H), 7.38-7.33 (m, 2H), 6.95 (brs, 1H), 6,7,8,9-Tetrahydro-2-methoxy-10-(N,N-dimethylamino-
6.89-6.85 (m, 1H), 3.85 (s, 3H), 2.96-2.89 (m, 4H), 2.63-2.57 ethyl)pyrido[1,2-a]indole Oxalate (16). A solution of 1.0
(m, 2H), 2.48 (s, 6H), 1.73 (q, 2H, J ) 7.51 Hz), 1.00 (t, 3H, J M borane/THF (2 mL, 2 mmol) was added in a dropwise ) 7.51 Hz); IR (CHCl3) 1355 cm-1. The oxalate salt was manner to ice-bath cooled 21 (290 mg, 1.01 mmol) under N
prepared and recrystallized from acetone: mp 175-176 °C.
The reaction mixture was allowed to stir at room temperature Anal. (C22H28N2O3S‚C2H2O4) C, H, N.
for 2 h. Acetone (3 mL) was added, and the reaction mixture 6,7,8,9-Tetrahydro-2-methoxy-10-(N,N-dimethylamino-
was heated at reflux for 1 h to quench the unreacted borane ethyl)pyrido[1,2-a]indol-9-one Oxalate (21). A mixture of
reagent. The solvent was removed under reduced pressure. A 5-methoxy-N,N-dimethyltryptamine (11; free base) (2.00 g,
15% solution of NaOH was added and the mixture was 9.17 mmol) and 60% NaH (0.41 g, 10.1 mmol) was heated at extracted with CH2Cl2, and the CH2Cl2 portion was washed 100 °C under N2 until evolution of H2 gas ceased. The resultant with H2O, then brine. Solvent was removed under reduced mass was dissolved in anhydrous DMF (25 mL) and anhydrous pressure. The residue was purified by flash chromatography γ-butyrolactone (1.4 mL, 18.2 mmol) was added in a dropwise on silica gel (hexane/EtOAc; 4:1) to give 207 mg (75%) of a manner at room temperature. The reaction mixture was light yellow oil: 1H NMR (DMSO-d6) δ 7.34 (d, 1 H, J ) 8.85 heated at reflux for 20 h, cooled to 0 °C, and acidified by the Hz), 7.21 (s, 1H), 7.11 (s, 1H), 4.08 (t, 2H, J ) 6.65 Hz), 3.79 addition of a saturated ethereal solution of HCl. Additional (s, 3H), 3.40-3.35 (m, 2H), 3.30-3.25 (m, 2H), 3.06-3.01 (m, Et2O was added to the resulting suspension and the super- 2H), 2.83 (s, 6H), 1.76-1.69 (m, 2H), 1.40-1.31 (m, 2H). A natant was decanted. The residue was dissolved in PPE (52.5 small portion was converted to its oxalate salt: mp 114-115 mL) and CHCl3 (100 mL) and the reaction mixture was heated at reflux for 3 h under N2. The resulting mixture was 4-(Dimethylaminomethyl)-6-methoxy-1,2,3,4-tetrahy-
neutralized by the addition of 15% NaOH solution, at ice-bath drocarbazole Oxalate (17). Sodium metal (1.0 g) was added
temperature, and extracted with CH2Cl2. The organic portion portionwise over a 30-min period to a stirred solution of was dried (MgSO4) and solvent was removed under reduced 4-(dimethylaminomethyl)-9-benzyl-6-methoxy-1,2,3,4-tetrahy- pressure. The residue was purified by flash chromatography drocarbazole hydrochloride19 (4.0 g, 0.01 mol) in liquid NH 2Cl2/MeOH; 20:1) to give 0.52 g (20%) of 21
(free base) as a yellow oil: 1H NMR (DMSO-d 4Cl (3.0 g) was added until the blue color of the J ) 8.79 Hz), 7.18 (s, 1H), 6.88 (d, 1H, J ) 8.85 Hz), 4.06 (t, was added, and the mixture was extracted with CH 2H, J ) 6.60 Hz), 3.80 (s, 3H), 3.42-3.36 (m, 2H), 3.17-3.12 50 mL). The combined organic portion was washed with H (m, 2H), 2.85 (s, 6H), 2.66-2.62 (m, 2H); IR (CHCl A small sample was converted to the oxalate salt: mp 191- an oil. The oil was purified by column chromatography (CHCl MeOH; 9:1) and converted to an oxalate salt. The oxalate salt 5-HT6 Radioligand Binding Assay. The binding assay
was recrystallized from anhydrous Et2O/absolute EtOH to give employed human 5-HT6 receptors stably transfected to HEK 1.8 g (37%) of the desired target as a white powder: mp 224- 293 human embryonic kidney cells with [3H]lysergic acid 226 °C; 1H NMR (CDCl3, free base) δ 8.10 (s, 1H, NH), 7.20 (t, diethylamide (70 Ci/mmol; DuPont NEN) as radioligand. All Journal of Medicinal Chemistry, 2000, Vol. 43, No. 5 assays were conducted in triplicate using polypropylene 1 mL/ determinations. Data represent the mean of N ) 4 separate well plates (Anachemia). The radioligand was diluted in incubation buffer in borosilicate glass vials and protected fromlight. Competing agents (1 mM stock solutions) were dissolved Acknowledgment. Supported in part by MH57635
in DMSO or saline and stored at -20 °C in 1.2-mL polypro- and MH01366 (B.L.R.) and the NIMH Psychoactive pylene tubes (ElKay). Dilutions of compounds were made using incubation buffer in 96-well polypropylene plates and mixedby multichannel pipetting >25 times. Serial dilutions (1 in 4) References
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