Synthesis, NMR conformational analysis and pharmacological evaluation of 7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-a′]diindole analogues as melatonin receptor ligands

Article abstract of DOI:10.1039/b705550a

A structure for the self-condensation product of 2-(1H-indol-2-yl)ethyl tosylate 2a, previously proposed as 6,7,14,15-tetrahydro-15aH-azocino[1,2-a:6,5- b]diindole 3a, was revised based on the ¹³C-2D-INADEQUATE experiment, and proved to be 7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4- a′]diindole 4a. A mechanism for the unexpected formation of this novel hexacyclic heterocycle was proposed and its NMR solution structure was elucidated. Five derivatives of the title ring skeleton 12-16 designed as melatonin receptor ligands were synthesized and their affinities for the human MT₁ and MT₂ receptors were determined. Both butyramides 13 and 15, as well as the non-methoxy acetamide 12 exhibited micromolar binding affinities for both receptors being slightly MT₂ selective. The methoxy acetamide 14 showed the best pharmacological profile exhibiting a five times higher affinity for MT₁ (K_i = 49 nM) than for MT₂ (K_i = 246 nM) receptor. This journal is The Royal Society of Chemistry.

Full text of DOI:10.1039/b705550a

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis, NMR conformational analysis and pharmacological evaluation
of 7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]diindole
analogues as melatonin receptor ligands†
Mohamed I. Attia,a Deniz Gu¨clu¨,a Barbara Hertlein,a Justin Julius,b Paula A. Witt-Enderbyb and
Darius P. Zlotos*a
Received 12th April 2007, Accepted 11th May 2007
First published as an Advance Article on the web 25th May 2007
DOI: 10.1039/b705550a
A structure for the self-condensation product of 2-(1H-indol-2-yl)ethyl tosylate 2a, previously proposed
as 6,7,14,15-tetrahydro-15aH-azocino[1,2-a:6,5-b]diindole 3a, was revised based on the
13C-2D-INADEQUATE experiment, and proved to be 7,7a,13,14-tetrahydro-6H-
cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]diindole 4a. A mechanism for the unexpected formation of this novel
hexacyclic heterocycle was proposed and its NMR solution structure was elucidated. Five derivatives of
the title ring skeleton 12–16 designed as melatonin receptor ligands were synthesized and their affinities
for the human MT1 and MT2 receptors were determined. Both butyramides 13 and 15, as well as the
non-methoxy acetamide 12 exhibited micromolar binding affinities for both receptors being slightly
MT2 selective. The methoxy acetamide 14 showed the best pharmacological profile exhibiting a
five times higher affinity for MT1 (Ki = 49 nM) than for MT2 (Ki = 246 nM) receptor.
In the course of our studies on allosteric ligands of mus-
Introduction
carinic M2 receptors, we reported the self-condensation of 2a
Melatonin 1 (Fig. 1) is a neurohormone exerting its diverse
to give the pentacyclic 6,7,14,15-tetrahydro-15aH-azocino[1,2-
a:6,5-b]diindole 3a using NaH in DMF.5 The unusual formation
pharmacological actions mostly through activation of two G-
protein-coupled receptors MT1 and MT2.
1
of compound 3a was explained by an ambident nucleophilic
character of the indolyl anion, which can be alkylated either
at N or at C-3. Based on this result, we became interested in
the synthesis of a potential melatonergic ligand by applying the
same procedure to the tosylate of 5-methoxyindol-2-yl ethanol
2b to obtain 3b and a subsequent introduction of the melatonin-
like side chain. The desired compound is formally derived from
melatonin by attaching the indole moiety to N-1 and C-2 via
ethylene spacers, and therefore, it could be useful for probing
the aforementioned pharmacophore for MT2 antagonists with
respect to location and size of the hydrophobic binding pocket.
In order to determine the 3D structure of the ring system
3a, we analysed the NOESY spectrum of 3a finding several
NOE interactions which were not consistent with our previously
proposed structure. To our great surprise, analysis of the 13C-2D-
INADEQATE spectrum revealed that the condensation product
of 2a was not the previously reported pentacyclic ring system 3a,
but the isomeric hexacyclic ring skeleton 4a (Scheme 1). In the
first part of this paper, we describe the structure elucidation and
NMR conformational analysis of this novel 7,7a,13,14-tetrahydro-
6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]diindole ring system. The
second part reports the synthesis of some analogues of the
novel ring scaffold designed as melatonergic ligands and their
pharmacological evaluation.
Fig. 1 Structure of melatonin 1.
Examination of the physiological roles of these receptors, which
are not as yet clearly defined, requires MT1 and MT2 selective lig-
ands. However, pronounced subtype selectivity is still a challenge,
and only recently a limited number of selective compounds have
been identified.2 The majority of subtype selective agents behave as
MT2 receptor antagonists. A common structural feature in most of
MT2 selective antagonists is the presence of a lipophilic substituent
located out of the plane of their core nucleus in a position
corresponding to positions 1 and 2 of the indole in melatonin.3
However, there are only limited studies concerning the steric
tolerance of the hydrophobic binding pocket accommodating this
lipophilic group.4
aPharmaceutical Institute, University of Wu¨rzburg, Am Hubland, 97074,
Wu¨rzburg, Germany. E-mail: zlotos@pzlc.uni-wuerzburg.de; Fax: +49 931
8885494; Tel: +49 931 8885489
Results and discussion
bDivision of Pharmaceutical Sciences, School of Pharmacy, Duquesne
University, 421 Mellon Hall, Pittsburgh, PA 15282, USA
Structure elucidation of compound 4a
† Electronic supplementary information (ESI) available: NOESY spectrum
of 4a and the illustration of the observed NOEs in the 3D structure of 4a.
See DOI: 10.1039/b705550a
The conclusions drawn from the NMR spectra which led to the
previously assigned structure 3a also apply to the novel ring 4a.
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the quaternary carbon C-5a. Its chemical shift (d 83.3) indicates
that C-5a is located between both nitrogen atoms. Further direct
coupling partners of C-5a are the methine carbon C-7a (d 48.1)
and the methylene carbon C-6 (d 34.2), which in turn are both
connected with the same methylene carbon C-7 (d 21.5) clearly
indicating the presence of the cyclobutane ring incorporating the
carbon atoms 5a, 6, 7, and 7a. The position of this four-membered
ring could be identified by the correlation between C-7a (d 48.1)
and the aromatic carbon C-7b (d 132.2). The assignment in both
indole substructures was accomplished by following the coupling
paths starting from the already assigned carbon atoms C-15a and
C-7b.
Scheme 1 Reagents and conditions: (i) NaH, DMF, 0 ◦C–rt.
Conformational analysis
Thus, analysis of the 1H–1H-COSY, and HMQC data established
the presence of four independent spin systems including two indole
moieties and two aliphatic chains identified as -CH-CH2-CH2- and
-CH2-CH2-. The complete carbon sequence was now obtained by
means of a 13C-2D-INADEQATE spectrum displayed in Fig. 2.
The most easily assignable resonance signal belonging to the
indolic carbon C-15 (d 98.4) was used as a starting point. This
signal exhibited correlations with signals resonating at d 128.9
(C-15a) and d 135.3 (C-14a). From the latter, we could obtain
the chemical shift of C-14 (d 21.7), which in turn was correlated
with C-13 (d 36.6). Since C-13 shows no further cross peaks, the
ethylene moiety 14-CH2-13-CH2- must be connected to a nitrogen
atom. The second substructure can be deduced starting from
The structure of the ring scaffold 4a was first submitted to a
conformational analysis using the Cartesian method of the steric
energy minimization program GLOBAL-MMX implemented in
PCModel 9.0 (Serena Software)6 yielding two minimum geome-
tries which were further optimized by means of semiempirical PM3
calculations of HyperChem 7.1 (Hypercube Inc.).7 The resulting
possible conformations A and B are depicted in Fig. 3. The central
six-membered rings of A and B adopt different conformations
leading to a slightly different relative position of the aromatic
rings.
The 3D solution structure of the novel ring system was
examined by means of a 600 MHz NOESY spectrum shown
in the supplementary information†. Unfortunately, due to the
Fig. 2 13C NMR 2D-INADEQUATE (150.9 MHz) contour plot of 4a (70 mg in 0.7 mL CDCl3, 13C optimized 5 mm DCH cryoprobe, total acquisition
time 66 h).
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Fig. 3 Low energy conformations of compound 4a (PM3 calculations of
HyperChem 7.1).
very similar geometries of A and B the majority of the NOEs
detected are consistent with both conformations. The only NOE
signal clearly suggesting the presence of conformation B was
the strong interaction between the aromatic proton H-4 and the
methylene proton Hb-6 being in agreement with the H-4–Hb-6
˚
distance of 2.27 A (the corresponding distance in the conformer A
˚
is 3.34 A). Furthermore, the equally strong H-7a–H-4 and H-7a–
H-8 cross signals also indicate the presence of conformer B being
˚
˚
consistent with the respective distances of 2.76 A and 2.90 A (the
corresponding H-7a–H-4 and H-7a–H-8 distances in conformer
˚
˚
A are 1.81 A and 2.94 A, respectively). The essential NOEs of
compound 4a are shown in the supplementary information. The
preferred conformer B has, in fact, a slightly lower total energy
than conformer A (DE = 0.47 kcal mol−1).
Chemistry
Scheme 2 Reagents and conditions: (i) 1. CDI, MeCN, rt, 2. potassium
ethyl malonate, NEt3, MgCl2, MeCN, rt–reflux, 3. 13% HCl aq., rt;
(ii) HCO2NH4, Pd/C 10%, EtOH, rt; (iii) LiALH4, THF, 0 ◦C–rt; (iv) TsCl,
The synthetic route applied for the preparation of the desired
melatonergic ligands derived from the novel ring system is shown
in Scheme 2. Starting materials for the nine step synthesis were
the commercially available 2-nitrophenyl acetic acid 5a and the
known 5-methoxy-2-nitrophenyl acetic acid 5b.8 The b-ketoesters
6a and 6b were prepared under conditions reported by Mai et al.9
involving the reaction of potassium ethyl malonate with 5a and
5b-imidazolides in the presence of the magnesium dichloride–
triethylamine system in 94% and 90% yield, respectively. Transfer
hydrogenation of 6a and 6b using ammonium formate and a
catalytic amount of 10% Pd/C in absolute ethanol and the sub-
sequent spontaneous ring closure afforded the indole-2-acetates
7a (90%) and 7b (89%). Reduction of the ester groups using
LiAlH4 in THF provided the alcohols 8a (79%) and 8b (85%)
which could be converted to the corresponding tosylates 2a and
2b in 70% and 64% yield, respectively. In the next crucial double-
alkylation step, 2a and 2b were treated with an excess of NaH
in DMF affording the hexacyclic heterocycles 4a and 4b as
exclusive dimerisation products in 46% and 45% yield, respectively.
From both reactions, small quantities of impure elimination by-
products, 2-vinylindole and 5-methoxy-2-vinylindole could be
◦
+
−
=
NEt3, CH2Cl2, rt; (v) NaH, DMF, 0 C–rt; (vi) (CH2 NMe2) Cl ,
CH2Cl2, reflux; (vii) 1. MeI, CH2Cl2, rt, 2. KCN, dicyclohexyl-[18]-
crown-[6], MeCN, reflux; (viii) LiALH4, Et2O, toluene, 40 ◦C; (ix) res-
pective acylation agent, Et3N, CH2Cl2, rt.
isolated. The unprecedented formation of the title ring system can
be explained by the proposed mechanism displayed in Scheme 3.
The ambident indolyl anion, built by N-deprotonation of 2a with
NaH, can be alkylated either at N or at C-3. In the first step, the
four-membered ring was built in the intramolecular nucleophilic
substitution with C-3 acting as a nucleophilic center. The so
obtained imine was subsequently attacked by another indolyl
anion yielding 4a as a result of a double N-alkylation.
In order to obtain ligands binding at melatonin receptors, we
first introduced the ethylamine side chain into 4a and 4b at the
position corresponding to C-3 of melatonin using the procedure
we previously applied for another ring system.10 Our approach
involved a sequence of a Mannich reaction, quaternization of
the Mannich base, substitution of the trimethylamine moiety
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trend could be confirmed only in the acetamide series. Thus, while
the methoxy butyramide 15 exhibited nearly unchanged binding
constants at both receptor subtypes when compared to the non-
methoxy butyramide 13, the methoxy acetamide 14 displayed
22-fold higher affinity for the MT1 subtype and 3-fold higher
affinity for the MT2 subtype than the non-methoxy analogue 12.
Comparison of the binding constants at MT1 (Ki = 49 nM) and
MT2 (Ki = 246 nM) receptors indicates that 14 is five times more
selective for MT1 than for MT2 receptors. The MT1-selectivity of
14 is rather surprising, taking into account that most compounds
of this series seem to be slightly MT2-selective. In a series of
benzoxazole derivatives, the MT1-selectivity could be improved
by replacing the N-acetyl substituent with a cyclopropylcarbonyl
moiety.13 However, this did not occur in our series. In fact, the
selectivity of the cyclopropanecarboxamide 16 for the melatonin
receptors worsened from being five times more selective for MT1
to only 1.4 times more selective for MT1 (Ki = 385 nM) than MT2
(Ki = 547 nM).
Scheme 3 Proposed mechanism for the formation of compound 4a.
by a cyanide, and a final reduction of the cyanomethyl group
to the ethylamine moiety. Thus, aminomethylation of 4a and 4b
using dimethylmethyleneammonium chloride in dichloromethane
afforded the Mannich bases 9a and 9b in 78% and 95% yield,
respectively. Treatment of 9a and 9b with methyl iodide in
dichloromethane and heating of the resulting trimethylammonium
iodides with potassium cyanide and dicyclohexyl-[18]-crown-[6]
in acetonitrile provided the nitriles 10a (92%) and 10b (90%),
respectively. Reduction of 10a and 10b using LiAlH4 in diethyl
ether and toluene afforded the ethylamines 11a and 11b, re-
spectively, in a quantitative yield. Finally, both amines could be
easily converted to the desired melatonergic ligands 12–16 by N-
acylations using acetic anhydride (12, 14), butyric anhydride (13,
15), and cyclopropane carboxylic acid chloride (16) in good yields.
Conclusions
In summary, in search for subtype selective ligands of
melatonin receptors, we synthesized five derivatives of the
novel 7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-
aꢀ]diindole ring system. The non-methoxy and methoxy analogues
12, 13 and 14–16, respectively, were prepared in nine steps starting
from the corresponding 2-nitrophenyl acetic acids. A mechanism
for the unprecedented formation of the title ring system was
proposed and its NMR solution structure was elucidated. Both
butyramides 13 and 15, as well as the non-methoxy acetamide 12
exhibited rather poor micromolar binding affinities for the human
MT1 and MT2 receptors being slightly MT2 selective. The findings
indicate that the bulkiness and/or the spatial orientation of the
cyclobutanoindole moiety is unfavourable for receptor binding at
both subtypes. With respect to the MT2 receptor, its hydrophobic
pocket usually accommodating lipophilic substituents in positions
corresponding to N-1 or C-2 of melatonin seems to be sterically
restricted. The methoxy acetamide 14 showed the best pharma-
cological profile exhibiting surprisingly a five times higher affinity
for MT1 (Ki = 49 nM) than for MT2 (Ki = 246 nM) receptors.
Finally, the selectivity for the MT1 receptor could not be improved
by replacing the N-acetyl substituent with a cyclopropylcarbonyl
moiety as occurred previously.13
Pharmacology
The affinity of compounds 12–16 for human MT1 or MT2
melatonin receptors was measured by competition binding anal-
ysis using the radioligand 2-[125I]-iodomelatonin as described.11
Melatonin competition assays were run in parallel and the affinity
of melatonin for the MT1 (Ki = 457 pM) or MT2 (Ki = 955 pM)
melatonin receptors was in the range of the reported literature.11
As shown in Table 1, the non-methoxy acetamide 12 exhibits
rather poor micromolar binding affinity for both melatonin
receptors. Substitution of the N-acetyl group by a butyryl sub-
stituent yielding the butyramide 13 had no significant effect on
binding affinity and selectivity. Melatonergic ligands bearing a
methoxy substituent in a position equivalent to C-5 of melatonin
display generally considerably higher binding affinities than the
corresponding non-methoxy analogues.2 However, this affinity
Experimental
Table 1 Binding affinitya of compounds 12–16 for the human MT1 and
MT2 receptors expressed in CHO cells obtained in competition radioligand
binding assays using 2-[125I]-iodomelatonin
Melting points were determined using a capillary melting point
apparatus (Gallenkamp, Sanyo) and are uncorrected. Column
chromatography was carried out on silica gel 60 (0.063–0.200 mm)
obtained from Merck. Bruker AV-400 and AV-600 spectrometers
were used to obtain 1H NMR and 13C NMR spectra, respectively.
Proton chemical shifts are referenced to CHCl3 (7.24 ppm). J
values are given in Hz. Carbon chemical shifts are referenced to
CDCl3 (77.00 ppm). The NMR resonances were assigned by means
of HH-COSY, HMQC, and HMBC experiments. EI mass spectra
were determined on Finnigan MAT 8200, Finnigan MAT 90, and
on ESI-microTOF spectrometers. IR spectra, recorded as ATR,
were obtained using a Biorad PharmalyzIR FT-IR instrument.
Elemental analyses were performed by the microanalytical section
pKi MT1 SEM
pKi MT2 SEM
Melatonin
9.34 0.10
5.96 0.14
5.92 0.03
7.31 0.07
5.89 0.12
6.41 0.10
9.02 0.09
6.15 0.25
6.36 0.07
6.61 0.09
6.20 0.03
6.26 0.07
12
13
14
15
16
a pKi values were calculated from IC50 values obtained from competitive
curves according to the method of Cheng and Prusoff12 and are the mean
of at least three determinations.
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of the Institute of Inorganic Chemistry, University of Wu¨rzburg.
All reactions were carried out under an argon atmosphere.
step. Analytical samples were obtained by recrystallization from
isopropanol.
Ethyl 1H-indol-2-ylacetate (7a). 7a (2.30 g, 90%) was obtained
from 6a (3.14 g) as a light brown solid. The spectral data of 7a
were identical to those previously reported.14
General procedure for the synthesis of 6a,b
Triethylamine (8.7 ml, 62.4 mmol) was added to a stirred
suspension of potassium ethyl malonate (6.97 g, 40.95 mmol)
and anhydrous magnesium chloride (4.64 g, 48.73 mmol) in
dry acetonitrile (50 ml) and the reaction mixture was stirred
for 2 h at room temperature. A solution of the appropriate
imidazolide, prepared by stirring the respective phenylacetic acid
5a,b (19.49 mmol) and N,N-carbonyldiimidazole (CDI; 3.47 g,
21.40 mmol) in dry acetonitrile (20 ml) for 15 min at room
temperature, was added dropwise to the resulting reaction mixture.
The reaction was allowed to stir for 18 h at room temperature and
then heated at reflux for 2 h. 13% Hydrochloric acid (50 ml) was
added dropwise while keeping the temperature below 25 ◦C. The
resulting clear mixture was stirred at room temperature for 15 min
and then the organic phase was separated and evaporated under
reduced pressure. The residue was dissolved in ethyl acetate
(50 ml). The aqueous phase was extracted with ethyl acetate (2 ×
50 ml). The combined organic layers were washed with saturated
NaHCO3 solution (3 × 30 ml), saturated sodium chloride solution
(2 × 30 ml), dried (Na2SO4) and evaporated under vacuum to
afford 6a,b as viscous oils that were solidified by cooling at
Ethyl (5-methoxy-1H-indol-2-yl)acetate (7b). 7b (2.60 g, 89%)
was obtained from 6b (3.52 g) as colourless crystals (Found: C,
66.76; H, 6.54; N, 5.92. C13H15NO3 requires C, 66.94; H, 6.48; N,
6.00%); mp 57–59 ◦C; mmax/cm−1: 3404, 2990, 2911, 1722, 1624,
1591, 1487, 1319, 1026, 840, 800, 731; dH (400 MHz, CDCl3) 1.29
(3H, t, J 7.1, CH2-CH3), 3.79 (2H, s, CH2), 3.84 (3H, s, OCH3),
4.20 (2H, q, J 7.1, CH2-CH3), 6.25 (1H, s, 3-H), 6.81 (1H, dd, J
2.6, 8.8, 6-H), 7.02 (1H, d, J 2.5, 4-H), 7.21 (1H, d, J 8.8, 7-H),
8.59 (1H, s, NH); dC (100 MHz, CDCl3) 14.10 (CH2-CH3), 33.95
(CH2), 55.81 (OCH3), 61.31 (CH2-CH3), 101.58 (C-3), 102.05 (C-
4), 111.43 (C-7), 111.70 (C-6), 128.62, 131.27, 131.45 (C-2, C-2a,
C-7a), 154.14 (C-5), 170.57 (ester); m/z (EI): 233.1 (56%, M+),
160.1 (100), 145.1 (13), 117.1 (14), 89.1 (5).
General procedure for the synthesis of 8a,b
A solution of the respective indolyl acetate 7a,b (10 mmol) in dry
THF (50 mL) was added dropwise to an ice-cooled and stirred
suspension of LiALH4 (2 g) in dry THF (50 mL). The reaction
mixture was stirred at room temperature for 4 h and water (10 mL)
was carefully added under ice-cooling. After vigorous stirring for
1 h at room temperature the precipitated solid was removed by
filtration and washed with THF (2 × 30 mL). The combined
THF solutions were dried (Na2SO4), evaporated under vacuum
and the residual oil was purified by silica gel chromatography
(ethyl acetate–n-hexane 1 : 1).
◦
−30 C. Crude products were sufficiently pure to be used in the
next step without further purification. Analytical samples were
obtained by recrystallization from ethanol.
Ethyl 3-oxo-4-(2-nitrophenyl)butanoate (6a). 6a (4.60 g, 94%)
was obtained from 5a (3.53 g) as a pale yellow solid. The analytical
data of 6a were identical to those previously reported.14
Ethyl 4-(5-methoxy-2-nitrophenyl)-3-oxobutanoate (6b). 6b
(4.9 g, 90%) was obtained from 5b (4.12 g) as a pale yellow solid
(Found: C, 55.14; H, 5.41; N, 4.98. C13H15NO6 requires C, 55.51;
H, 5.38; N, 4.98%); mp 67–68 ◦C; mmax/cm−1: 2990, 2910, 1740,
1720, 1607, 1588, 1505, 1329, 1261, 1211, 1132, 1211, 1072, 1020,
860, 841, 752; dH (400 MHz, CDCl3) 1.27 (3H, t, J 7.1, CH2-CH3),
3.60 (2H, s, CH2), 3.86 (3H, s, OCH3), 4.19 (2H, q, J 7.1, CH2-
CH3), 4.20 (2H, s, C6H3-CH2), 6.72 (1H, d, J 2.8, 6-H), 6.88 (1H,
dd, J 2.8, 9.2, 4-H), 8.16 (1H, d, J 9.2, 3-H); dC (100 MHz, CDCl3)
14.07 (CH2-CH3), 48.41 (C6H3-CH2), 49.36 (CH2), 55.90 (OCH3),
61.49 (CH2-CH3), 113.21 (C-4), 118.81 (C-6), 128.08 (C-3), 132.75
(C-1), 141.25 (C-5), 163.52 (C-2), 167.06 (ester), 198.19 (ketone);
m/z (EI): 281.1 (2%, M+), 194.1 (10), 167.2 (9), 150.2 (100), 122.2
(15), 87.1 (13).
2-(1H-Indol-2-yl)ethanol (8a). 8a (1.28 g, 79%) was obtained
from 7a (2.03 g) as a colourless oil showing the same analytical
data as reported in the literature.5
2-(5-Methoxy-1H-indol-2-yl)ethanol (8b). 8b (1.63 g, 85%)
+
was obtained from 7b (2.33 g) as a slightly yellow oil (C11H13NO2
required 191.0941, found 191.0916); mmax/cm−1: 3395 br, 2941,
2831, 1624, 1588, 1483, 1451, 1222, 1199, 1166, 1026, 780; dH
(400 MHz, CDCl3) 2.90 (2H, t, J 5.8, CH2-CH2-OH), 3.82 (3H, s,
-OCH3), 3.86 (2H, t, J 5.8, CH2-CH2-OH), 6.18 (1H, br s, 3-H),
6.77 (1H, dd, J 8.8, 2.5, 6-H), 7.00 (1H, d, J 2.5, 4-H), 7.15 (1H,
d, J 8.8, H-7), 8.40 (1H, br s, NH); dC (100 MHz, CDCl3) 31.25
(CH2-CH2-OH), 55.89 (OCH3), 62.13 (CH2-CH2-OH), 99.98 (C-
3), 101.99 (C-4), 111.07 (C-6), 111.20 (C-7), 128.91 (C-3a), 131.23
(C-2), 137.82 (C-7a), 154.01 (C-5); m/z (EI) 191.1 (51%, M+),
160.1 (100), 117.1 (29).
General procedure for the synthesis of 7a,b
Ammonium formate (9.51 g, 142.2 mmol) was added to a stirred
suspension of the appropriate b-ketoester 6a,b (12.5 mmol) and
10% Pd/C (0.35 g) in absolute ethanol (80 ml). The resulting
reaction mixture was stirred for 1 h at room temperature. The
precipitates were removed by filtration and the solvent was evap-
orated under vacuum. The residue was dissolved in diethyl ether
(40 ml) and washed with water (2 × 20 ml). The ether layer was
dried (Na2SO4) and evaporated under reduced pressure to afford
7a,b as viscous oils that were solidified by cooling at −30 ◦C. The
crude products were used without further purification in the next
General procedure for the synthesis of 2a,b
A solution of p-toluensulfonyl chloride (1.8 g, 9.4 mmol) in dry
dichloromethane (20 mL) was added dropwise to a solution of
the respective alcohol 8a,b (7.5 mmol) and triethylamine (2.5 mL)
in dry dichloromethane (100 mL) under ice-cooling. The reaction
mixture was stirred overnight at room temperature. The solvent
was evaporated under reduced pressure and the residual oil was
purified by silica gel chromatography (ethyl acetate–n-hexane
1 : 2).
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2-(1H-Indol-2-yl)ethyl 4-methylbenzenesulfonate (2a). 2a
(1.66 g, 70%) was obtained from 8a (1.21 g) as a white solid
showing the same analytical data as reported in the literature.5
2.53–2.65 (2H, m, 6-Ha, 7-Hb), 2.80 (1H, br d, J 15.9, 14-Ha),
3.01–3.11 (1H, m, 14-Hb), 3.31–3.39 (1H, m, 6-Hb), 3.45 (1H,
ddd, J 14.4, 13.0, 3.3, 13-Ha), 3.69 (3H, s, C-9-OCH3), 3.83 (1H,
ddd, J 14.4, 5.3, 1.0, 13-Hb), 3.83 (3H, s, C-2-OCH3), 4.59 (1H,
t, J 8.2, 7a-H), 6.06 (1H, br s, H-15), 6.50 (1H, d, J 9.1, H-11),
6.62–6.65 (2H, m, H-8, H-10), 6.83 (1H, dd, J 8.8, 2.5 H-3),
6.99 (1H, d, J 2.5, H-1), 7.51 (1H, d, J 8.8, H-4); dC (100 MHz,
CDCl3) 21.31 (C-7), 21.43 (C-14), 34.19 (C-6), 37.03 (C-13), 48.43
(C-7a), 55.84 (C-9-OCH3), 56.04 (C-2-OCH3), 83.62 (C-5a), 98.12
(C-15), 102.41 (C-1), 105.82 (C-11), 110.26 (C-3), 111.49 (C-4),
111.94, 111.97 (C-8, C-10), 129.43 (C-4a), 129.57 (C-15a), 133.45
(C-7b), 136.12 (C-14a), 145.49 (C-11a), 153.02 (C-9), 154.20
(C-2); m/z (EI): 346.2 (2%, M+), 319.2 (24), 318.2 (100), 303.2 (9),
275.2 (19)
2-(5-Methoxy-1H-indol-2-yl)ethyl 4-methylbenzenesulfonate (2b).
2b (1.65 g, 64%) was obtained from 8b (1.43 g) as a grey solid
(Found: C, 62.75; H, 5.56; N, 4.13; S, 9.35. C18H19NO4S requires
C, 62.59; H, 5.54; N, 4.05; S, 9.28%); mp 106 ◦C; mmax/cm−1: 3430,
2992, 2955, 1622, 1591, 1485, 1449, 1352, 1196, 1170, 970, 899,
774, 660; dH (400 MHz, CDCl3) 2.38 (3H, s, CH3), 3.07 (2H,
t, J 6.3, CH2-CH2-O), 3.82 (3H, s, OCH3), 4.26 (2H, t, J 6.3,
CH2-CH2-OH), 6.10 (1H, br s, 3-H), 6.79 (1H, dd, J 8.8, 2.5,
6-H), 6.95 (1H, d, J 2.5, 4-H), 7.14 (1H, d, J 8.8, H-7), 7.20
(2H, d, J 8.3), 7.67 (2H, d, J 8.3), 7.94 (1H, br s, NH); dC
(100 MHz, CDCl3) 21.59 (CH3), 28.31 (CH2-CH2-OH), 55.85
(OCH3), 69.60 (CH2-CH2-OH), 100.90 (C-3), 102.03 (C-4), 111.29
(C-7), 111.64 (C-6), 127.76 (2 × Caromatic), 128.81 (C-3a), 129.82 (2 ×
Caromatic), 132.59 (C-2), 134.64 (C-7a), 144.93 (-OSO2C), 154.21 (C-
5); m/z (EI): 345.1 (1%, M+), 173.1 (100), 158.1 (56), 155.0 (26),
130.1 (38).
General procedure for the synthesis of 9a,b
N,N-Dimethylmethyleneiminium chloride (187 mg, 2 mmol) was
added to a solution of the respective hexacyclic compound 4a,b
(0.6 mmol) in dry CH2Cl2 (100 mL). After heating for 1 h at
reflux, the reaction mixture was made basic with 25% ammonia.
The organic layer was separated, washed with water and dried
over MgSO4. The solvent was removed in vacuo and the residue
was purified by silica gel chromatography (CHCl3–methanol–25%
ammonia, 100 : 10 : 1).
General procedure for the synthesis of 4a,b
NaH (300 mg of 60% suspension in mineral oil, 7.5 mmol) was
added in small portions to the stirred solution of the respective
tosylate 2a,b (3 mmol) in dry DMF (30 mL) under ice-cooling.
The ice bath was removed after 20 min and stirring was continued
for further 40 min. Water (20 mL) was added carefully and the
reaction mixture was extracted with diethyl ether (3 × 50 mL).
The combined ether extracts were washed with water (2 × 10 mL)
and dried (Na2SO4). The solvent was evaporated in vacuo and the
residues were purified by silica gel chromatography (CHCl3–n-
hexane 1 : 1).
1-(7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]-
diindol-15-yl)-N,N-dimethylmethanamine (9a). 9a (160 mg,
0.47 mmol, 78%) was obtained from 4a (172 mg) as a white solid
(C23H25N3H+ required 344.2127, found 344.2121); mp 89 ◦C;
mmax/cm−1: 2942, 2807, 2760, 1605, 1477, 1456, 1321, 1196, 1012,
733; dH (400 MHz, CDCl3) 1.98–2.04 (1H, m, 7-Ha), 2.20 (6H, s,
2 × CH3), 2.58–2.69 (2H, m, 6-Ha, 7-Hb), 2.92–3.05 (2H, m,
CH2-14), 3.37–3.54 (2H, m, H-6b, 13-Ha), 3.40 (1H, d, J 13.1,
HCH-NMe2), 3.49 (1H, d, J 13.1, HCH-NMe2), 3.94 (1H, ddd,
J 14.4, 4.9, 1.8, 13-Hb), 4.71 (1H, t, J 8.2, H-7a), 6.60–6.66
(2H, m, H-9, H-11), 6.98 (1H, d, J 7.0, H-8), 7.06–7.10 (2H, m,
H-2, H-10), 7.19 (1H, m, H-3), 7.62–7.66 (2H, m, H-1, H-8); dC
(100 MHz, CDCl3) 20.17 (C-14), 21.54 (C-7), 34.32 (C-6), 36.46
(C-13), 45.51 (2 × CH3), 48.20 (C-7a), 52.95 (CH2-NMe2), 83.29
(C-5a), 105.71 (C-11), 110.73 (C-4), 118.20 (C-9), 119.02 (C-1),
119.63 (C-2), 120.56 (C-3), 124.15 (C-8), 127.66 (C-10), 129.58
(C-15a), 132.22 (C-7b), 133.70 (C-4a), 133.97 (C-14a), 151.14
(C-11a).
7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]diin-
dole (4a). 4a (198 mg, 46%) was obtained from 2a (950 mg)
as a white solid (Found: C, 83.54; H, 6.27; N, 9.44. C20H18N2
requires C, 83.88; H, 6.34; N, 9.78%; C20H17N2 requires 285.1392,
found 285.1393; mp 150 ◦C; mmax/cm−1: 2992, 2967, 1607, 1480,
1454, 1387, 1351, 1320, 1199, 1018, 739; dH (600 MHz, CDCl3)
2.00–2.07 (1H, m, 7-Ha), 2.59–2.67 (2H, m, 6-Ha, 7-Hb), 2.87 (1H,
br d, J 15.8, 14-Ha), 3.11 (1H, dddd, J 15.8, 13.0, 5.4, 1.4, 14-Hb),
3.41 (1H, m, 6-Hb), 3.51 (1H, ddd, J 14.3, 13.0, 3.2, 13-Ha), 3.91
(1H, ddd, J 14.3, 5.4, 1.0, 13-Hb), 4.71 (1H, t, J 8.2, 7a-H), 6.14
(1H, br s, H-15), 6.60–6.65 (2H, m, H-9, H-11), 6.99 (1H, d, J 7.1,
H-8), 7.07–7.11 (2H, m, H-2, H-10), 7.18 (1H, m, H-3), 7.52 (1H,
d, J 7.8, H-1), 7.66, 1H, d, J 8.2, H-1); dC (150 MHz, CDCl3)
21.48 (C-7), 21.56 (C-14), 34.15 (C-6), 36.58 (C-13), 48.07 (C-7a),
83.30 (C-5a), 98.41 (C-15), 105.70 (C-11), 110.91 (C-4), 118.19
(C-9), 119.76 (C-2), 120.31 (C-1), 120.43 (C-3), 124.13 (C-8),
127.65 (C-10), 128.88 (C-15a), 132.15 (C-7b), 134.10 (C-4a),
135.29 (C-14a), 151.14 (C-11a); m/z (EI): 286 (3%, M+), 258
(100), 257 (26), 129 (15), 128 (16).
1-(2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyri-
mido[1,2-a:3,4-aꢀ]diindol-15-yl)-N,N-dimethylmethanamine (9b).
9b (230 mg, 0.51 mmol, 95%) was obtained from 4b (242 mg) as a
white solid (C25H29N3O2Na+ required 426.2157, found 426.2152);
mp 71 ◦C; mmax/cm−1: 2940, 2760, 1616, 1584, 1477, 1455, 1296,
1244, 1225, 1165, 1031, 794; dH (400 MHz, CDCl3) 1.99–2.09 (1H,
m, 7-Ha), 2.22 (6H, s, 2 × CH3), 2.54–2.64 (2H, m, 6-Ha, 7-Hb),
2.87–3.01 (2H, m, CH2-14), 3.30–3.51 (2H, m, H-6b,13-Ha), 3.39
(1H, d, J 13.0, HCH-NMe2), 3.49 (1H, d, J 13.0, HCH-NMe2),
3.69 (3H, s, C-9-OCH3), 3.82–3.89 (1H, m, J 13-Hb), 3.86 (3H, s,
C-2-OCH3), 4.59 (1H, t, J 8.1, H-7a), 6.51 (1H, d, J 9.3, H-11),
6.61–6.65 (2H, m, H-8, H-10), 6.84 (1H, dd, J 8.8, 2.5 H-3), 7.08
(1H, d, J 2.5, H-1), 7.51 (1H, d, J 8.8, H-4); dC (100 MHz, CDCl3)
19.74 (C-7), 21.40 (C-14), 34.28 (C-6), 36.80 (C-13), 45.51 (2 ×
CH3), 48.46 (C-7a), 52.89 (CH2-NMe2), 55.90 (C-9-OCH3), 55.98
2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido-
[1,2-a:3,4-aꢀ]diindole (4b). 4b (250 mg, 45%) was obtained from
2b (1.036 g) as a white solid (Found: C, 75.89; H, 6.19; N, 7.94.
C22H22N2O2 requires C, 76.26; H, 6.41; N, 8.09%); mp 73 ◦C;
mmax/cm−1: 2944, 2830, 1615, 1579, 1475, 1450, 1352, 1292, 1157,
1031, 794; dH (400 MHz, CDCl3) 1.99–2.09 (1H, m, 7-Ha),
2134 | Org. Biomol. Chem., 2007, 5, 2129–2137
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(C-2-OCH3), 83.52 (C-5a), 101.33 (C-1), 105.80 (C-11), 110.13
(C-3), 111.34 (C-4), 111.90, 111.92 (C-8, C-10), 129.22 (C-4a),
130.15 (C-15a), 133.41 (C-7b), 134.76 (C-14a), 145.41 (C-11a),
152.98 (C-9), 154.15 (C-2).
General procedure for the synthesis of 11a,b
A solution of the respective cyanide 10a,b (0.35 mmol) in dry
toluene (30 ml) was added to a stirred suspension of LiAlH4
(0.30 g) in dry diethyl ether (30 ml) at 0–5 ◦C. The reaction
mixture was heated at 40 ◦C for 2 h. Water (3 ml) was added
dropwise under ice-cooling and the reaction mixture was stirred
for 1 h at room temperature. The precipitate was filtered off and
washed with diethyl ether. The combined filtrates and washings
were dried (Na2SO4), filtered and evaporated under vacuum to
afford the respective ethylamine 11a,b that was used in the next
step without further purification.
General procedure for the synthesis of 10a,b
Methyl iodide (0.4 ml) was added to a solution of the respective
Mannich base 9a,b (0.45 mmol) in dry CH2Cl2 (50 ml). The
reaction mixture was stirred at room temperature for one hour. The
volatiles were removed under vacuum and the residual ammonium
salt was dissolved in dry acetonitrile (100 ml). Dicyclohexyl-[18]-
crown-[6] (200 mg) and potassium cyanide (400 mg) were added
and the resulting reaction mixture was heated at reflux for 2 h. The
solvent was evaporated under reduced pressure and the residue was
subjected to silica gel chromatography (CHCl3).
2-(7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]-
diindole-15-yl)ethanamine (11a). 11a (115 mg, 100%) was
obtained from 10a (114 mg) as a colourless oil. dH (400 MHz,
CDCl3) 2.00–2.10 (1H, m, 7-Ha), 2.59–2.69 (2H, m, 6-Ha, 7-Hb),
2.70–2.93 (5H, m, CH2-CH2-NH2, H-14a), 2.96–3.06 (1H, m,
H-14b), 3.37–3.46 (1H, m, H-6b), 3.50 (1H, ddd, J 14.4, 12.5,
3.5, 13-Ha), 3.96 (1H, ddd, J 14.4, 5.1, 1.2, 13-Hb), 4.72 (1H, t,
J 8.2, H-7a), 6.61–6.67 (2H, m, H-9, H-11), 7.00 (1H, d, J 7.1,
H-8), 7.08–7.29 (3H, m, H-2, H-10, H-3), 7.55 (1H, d, J 7.8, H-1),
7.67 (1H, d, J 8.3, H-4); dC (100 MHz, CDCl3) 20.09 (C-14),
21.41 (C-7), 27.76 (CH2-CH2-NH2), 34.25 (C-6), 36.51 (C-13),
42.49 (CH2-CH2-NH2), 48.19 (C-7a), 83.24 (C-5a), 105.67 (C-11),
107.72 (C-15), 110.82 (C-4), 118.19 (C-9), 118.52 (C-1), 119.33
(C-2), 120.57 (C-3), 124.13 (C-8), 125.26 (C-10), 127.65 (C-15a),
128.99 (C-7b), 132.20 (C-4a), 134.40 (C-14a), 151.11 (C-11a).
7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,4-aꢀ]diin-
dole-15-carbonitrile (10a). 10a (135 mg, 92%) was obtained
from 9a (155 mg) as a white solid (Found: C, 79.85; H, 5.81; N,
12.84. C22H19N3 requires C, 81.20; H, 5.89; N, 12.91%); mp 95 ◦C;
mmax/cm−1: 2948, 2120, 1605, 1479, 1457, 1353, 1323, 1197, 743;
dH (400 MHz, CDCl3) 2.01–2.11 (1H, m, 7-Ha), 2.60–2.70 (2H,
m, 6-Ha, 7-Hb), 2.89 (1H, dd, J 15.9, 3.5, 14-Ha), 3.05 (1H, ddd,
J 15.9, 12.8, 5.4, 14-Hb), 3.38 (1H, ddd, J 20.0, 11.3, 2.3, H-6b),
3.53 (1H, ddd, J 14.3, 12.6, 3.5, 13-Ha), 3.66 (2H, s, CH2-CN),
3.99 (1H, dd, J 14.5, 5.3, 13-Hb), 4.69 (1H, t, J 7.9, H-7a),
6.61–6.67 (2H, m, H-9, H-11), 6.99 (1H, d, J 7.0, H-8), 7.10 (1H,
m, H-2), 7.18 (1H, t, J 7.8, H-10), 7.25 (1H, m, H-3), 7.55 (1H,
d, J 7.8, H-1), 7.68 (1H, d, J 8.3, H-4); dC (100 MHz, CDCl3)
12.36 (CH2-CN), 19.79 (C-14), 21.50 (C-7), 34.25 (C-6), 36.00
(C-13), 48.19 (C-7a), 83.27 (C-5a), 98.41 (CN), 105.82 (C-11),
111.20 (C-4), 117.70 (C-15), 117.79 (C-9), 118.59 (C-1), 120.30
(C-2), 121.47 (C-3), 124.26 (C-8), 127.43 (C-10), 127.82 (C-15a),
131.91 (C-7b), 132.95 (C-4a), 133.93 (C-14a), 150.85 (C-11a);
m/z (EI): 325.2 (2%, M+), 324.2 (3), 298.2 (23), 297.2 (100),
257.2 (36).
2-(2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyri-
mido[1,2-a:3,4-aꢀ]diindole-15-yl)ethanamine (11b). 11b (135 mg,
100%) was obtained from 10b (135 mg) as a colourless oil. dH
(400 MHz, CDCl3) 1.98–2.09 (1H, m, 7-Ha), 2.53–2.63 (2H, m, 6-
Ha, 7-Hb), 2.66–3.00 (6H, m, CH2-CH2-NH2, 14-CH2), 3.29–3.38
(1H, m, H-6b), 3.44 (1H, ddd, J 14.4, 12.6, 3.5, 13-Ha), 3.69 (3H, s,
C-9-OCH3), 3.84 (3H, s, C-2-OCH3), 3.83–3.89 (1H, m, 13-Hb),
4.57 (1H, t, J 8.1, H-7a), 6.51 (1H, d, J 9.3, H-11), 6.61–6.65
(2H, m, H-8, H-10), 6.83 (1H, dd, J 8.9, 2.5 H-3), 6.98 (1H, d, J
2.5, H-1), 7.51 (1H, d, J 8.9, H-4); dC (100 MHz, CDCl3) 19.70 (C-
14), 21.40 (C-7), 27.75 (CH2-CH2-NH2), 34.27 (C-6), 36.92 (C-13),
42.34 (CH2-CH2-NH2), 48.52 (C-7a), 55.98 (C-9-OCH3), 56.02 (C-
2-OCH3), 83.54 (C-5a), 100.86 (C-1), 105.79 (C-11), 107.24 (C-15),
110.18 (C-3), 111.47 (C-4), 111.92, 111.97 (C-8, C-10), 129.35 (C-
4a), 129.60 (C-15a), 133.06 (C-7b), 133.48 (C-14a), 145.44 (C-11a),
153.01 (C-9), 154.00 (C-2).
2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]pyrimido-
[1,2-a:3,4-aꢀ]diindole-15-carbonitrile (10b). 10b (156 mg, 90%)
was obtained from 9b (180 mg) as a white solid (Found: C, 74.35;
H, 6.07; N, 10.57. C24H23N3O2 requires C, 74.78; H, 6.01; N,
10.90%); mp 77 ◦C; mmax/cm−1: 2945, 2830, 1616, 1590, 1480, 1457,
1245, 1227, 1159, 1031, 798; dH (400 MHz, CDCl3) 2.01–2.11 (1H,
m, 7-Ha), 2.56–2.66 (2H, m, 6-Ha, 7-Hb), 2.82 (1H, ddd, J 15.9,
3.3, 1.2, 14-Ha), 3.01 (1H, ddd, J 15.9, 12.8, 5.3, 14-Hb), 3.33
(1H, ddd, J 20.0, 11.3, 2.2, H-6b), 3.48 (1H, ddd, J 15.9, 12.6,
3.5, 13-Ha), 3.62 (2H, s, CH2-CN), 3.69 (3H, s, C-9-OCH3), 3.86
(3H, s, C-2-OCH3), 3.89 (1H, dd, J 14.4, 5.3, 13-Hb), 4.57 (1H, t,
J 8.1, H-7a), 6.52 (1H, d, J 9.3, H-11), 6.63–6.67 (2H, m, H-8,
H-10), 6.89 (1H, dd, J 9.0, 2.5 H-3), 6.98 (1H, d, J 2.5, H-1), 7.54
(1H, d, J 9.0, H-4); dC (100 MHz, CDCl3) 12.38 (CH2-CN), 19.34
(C-14), 21.61 (C-7), 34.22 (C-6), 36.36 (C-13), 48.47 (C-7a), 55.85
(C-9-OCH3), 56.01 (C-2-OCH3), 83.50 (C-5a), 97.96 (CN), 99.81
(C-1), 105.92 (C-11), 111.28 (C-3), 111.92 (C-4), 112.02, 112.05
(C-8, C-10), 117.76 (C-15), 128.05 (C-4a), 129.04 (C-15a), 133.16
(C-7b), 133.61 (C-14a), 145.08 (C-11a), 153.21 (C-9), 154.54
(C-2); m/z (EI): 385.2 (3%, M+), 384.2 (2), 358.2 (24), 357.2 (100),
317.2 (25), 314.2 (14), 274.2 (8).
General procedure for the synthesis of 12–16
A stirred solution of the respective ethylamine 11a,b (0.35 mmol)
in dry CH2Cl2 (10 ml) was treated with triethylamine (0.30 mL)
and the respective acylation agent (0.20 mL) at 0–5 ◦C. The
reaction mixture was stirred at ambient temperature for 2 h. The
solvent was evaporated and the residue was purified by silica gel
chromatography (CHCl3, MeOH, 25% NH3 100 : 10 : 1 for 12–15;
CHCl3 for 16).
N-[2-(7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,
4-aꢀ]diindole-15-yl)ethyl]acetamide (12). 12 (105 mg, 81%) was
obtained from 11a (115 mg) and acetic anhydride (0.2 mL) as
a white solid (Found: C, 77.64; H, 6.96; N, 10.98. C24H25N3O
requires C, 77.60; H, 6.78; N, 11.31%); mp 97 ◦C; mmax/cm−1: 3281,
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=
2940, 1649, 1606, 1549, 1479, 1458, 1321, 1196, 741; dH (400 MHz,
CDCl3) 1.82 (3H, s, CH3), 1.99–2.09 (1H, m, 7-Ha), 2.58–2.69
(2H, m, 6-Ha, 7-Hb), 2.75–3.02 (4H, m, CH2-CH2-NH2,CH2-14),
3.32–3.52 (4H, m, CH2-CH2-NH2, 6-Hb, 13-Ha), 3.95 (1H, ddd, J
14.3,5.1, 1.2, 13-Hb), 4.69 (1H, t, J 8.2, H-7a), 5.39 (1H, br, NH),
6.60–6.65 (2H, m, H-9, H-11), 6.98 (1H, d, J 7.1, H-8), 7.07–7.14
(2H, m, H-2, H-10), 7.20 (1H, m, H-3), 7.51 (1H, d, J 7.6, H-1),
7.65 (1H, d, J 8.1, H-4); dC (100 MHz, CDCl3) 19.95 (C-14), 21.49
(C-7), 23.35 (CH3), 23.56 (CH2-CH2-NH), 34.23 (C-6), 36.45 (C-
13), 39.85 (CH2-CH2-NH2), 48.21 (C-7a), 83.35 (C-5a), 105.77
(C-11), 107.08 (C-15), 110.97 (C-4), 118.27 (C-9), 118.31 (C-1),
119.63 (C-2), 120.79 (C-3), 124.17, (C-8), 127.76 (C-10), 128.90
145.37 (C-11a), 153.06 (C-9), 154.19 (C-2), 169.94 (C O); m/z
(EI): 431.3 (2%, M+), 404.2 (15), 403.2 (55), 344.2 (23), 332.2 (25),
331.2 (100).
N-[2-(2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]-
pyrimido[1,2-a:3,4-aꢀ]diindole-15-yl)ethyl]butanamide
(15). 15
(105 mg, 65%) was obtained from 11b (135 mg) and butyric
anhydride (0.2 mL) as a white solid (Found: C, 72.84; H, 7.15;
N, 9.00 C28H33N3O3 requires C, 73.18; H, 7.24; N, 9.14%); mp
87 ◦C; mmax/cm−1: 3295, 2957, 2926, 2854, 1643, 1589, 1539, 1477,
1434, 1256, 1244, 1225, 1160, 1604, 1028, 796; dH (400 MHz,
CDCl3) 0.85 (3H, t, J 7.3, CH2-CH2-CH3), 1.53 (2H, quint., J 7.3,
CH2-CH2-CH3), 1.98 (2H, t, J 7.3, CH2-CH2-CH3), 1.99–2.09
(1H, m, 7-Ha), 2.53–2.64 (2H, m, 6-Ha, 7-Hb), 2.72–2.98 (4H, m,
CH2-CH2-NH2, CH2-14), 3.28–3.48 (4H, m, CH2-CH2-NH2,6-
Hb, 13-Ha), 3.69 (3H, s, C-9-OCH3), 3.84 (3H, s, C-2-OCH3),
3.83–3.89 (1H, m, 13-Hb), 4.57 (1H, t, J 8.1, H-7a), 5.41 (1H, br,
NH), 6.51 (1H, d, J 9.1, H-11), 6.61–6.65 (2H, m, H-8, H-10), 6.84
(1H, dd, J 9.1, 2.5 H-3), 6.96 (1H, d, J 2.3, H-1), 7.51 (1H, d, J 8.8,
H-4); dC (100 MHz, CDCl3) 13.75 (CH3), 19.02 (CH2-CH2-CH3),
19.55 (C-14), 21.38 (C-7), 23.69 (CH2-CH2-NH), 34.21 (C-6),
36.81 (C-13), 38.76 (CH2-CH2-CH3), 39.51 (CH2-CH2-NH2),
48.50 (C-7a), 55.94 (C-9-OCH3), 56.01 (C-2-OCH3), 83.59 (C-5a),
100.51 (C-1), 105.84 (C-11), 106.68 (C-15), 110.42 (C-3), 111.59
(C-4), 111.91, 111.98 (C-8, C-10), 129.28 (C-4a), 129.45 (C-15a),
(C-7b), 132.14 (C-15a), 132.35 (C-4a), 134.05 (C-14a), 151.10 (C-
+
=
11a), 169.99 (C O); m/z (EI): 371.2 (2%, M ), 370.2 (3), 344.2
(13), 343.3 (54), 284.2 (30), 272.2 (21), 271.2 (100), 256.1 (8).
N-[2-(7,7a,13,14-Tetrahydro-6H-cyclobuta[b]pyrimido[1,2-a:3,
4-aꢀ]diindole-15-yl)ethyl]butanamide (13). 13 (109 mg, 78%) was
obtained from 11a (115 mg) and butyric anhydride (0.2 mL) as
a white solid (Found: C, 77.85; H, 7.54; N, 10.40%. C26H29N3O
requires C, 78.16; H, 7.32; N, 10.52%); mp 96 ◦C; mmax/cm−1: 3280,
2930, 2940, 2872, 1642, 1606, 1543, 1479, 1456, 1321, 1196, 1163,
739; dH (400 MHz, CDCl3) 0.85 (3H, t, J 7.3, CH2-CH2-CH3),
1.53 (2H, quint., J 7.3, CH2-CH2-CH3), 1.97 (2H, t, J 7.3, CH2-
CH2-CH3), 1.99–2.09 (1H, m, 7-Ha), 2.58–2.68 (2H, m, 6-Ha, 7-
Hb), 2.73–3.02 (4H, m, CH2-CH2-NH2,CH2-14), 3.34–3.52 (4H,
m, CH2-CH2-NH2, 6-Hb, 13-Ha), 3.94 (1H, ddd, J 14.3,5.1, 1.2,
13-Hb), 4.69 (1H, t, J 8.2, H-7a), 5.38 (1H, br, NH), 6.59–6.65 (2H,
m, H-9, H-11), 6.98 (1H, d, J 7.3, H-8), 7.06–7.14 (2H, m, H-2,
H-10), 7.20 (1H, m, H-3), 7.51 (1H, d, J 7.8, H-1), 7.66 (1H, d,
J 8.1, H-4); dC (100 MHz, CDCl3) 13.74 (CH3), 18.98 (CH2-CH2-
CH3), 19.96 (C-14), 21.48 (C-7), 23.68 (CH2-CH2-NH), 34.22 (C-
6), 36.44 (C-13), 38.72 (CH2-CH2-CH3), 39.62 (CH2-CH2-NH2),
48.20 (C-7a), 83.34 (C-5a), 105.76 (C-11), 107.11 (C-15), 110.94
(C-4), 118.31 (C-9), 118.34 (C-1), 119.58 (C-2), 120.77 (C-3),
124.16 (C-8), 127.76 (C-10), 128.86 (C-7b), 132.13 (C-15a), 132.36
133.23 (C-7b), 133.40 (C-14a), 145.38 (C-11a), 153.06 (C-9),
154.16 (C-2), 172.85 (C O); m/z (EI): 459.2 (3%, M ), 458.2 (5),
+
=
432.2 (22), 431.2 (72), 344.2 (34), 331.1 (100).
N-[2-(2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]-
pyrimido[1,2-a:3,4-aꢀ]diindole-15-yl)ethyl]cyclopropanecarboxamide
(16). 16 (88 mg, 55%) was obtained from 11b (135 mg) and
cyclopropanecarboxylic acid chloride (0.2 mL) as a white solid
◦
(C28H31N3O3Na+ required 480.2263, found 480.2258); mp 94 C;
mmax/cm−1: 3298, 2936, 1643, 1589, 1534, 1478, 1434, 1245, 1227,
1157, 1064, 1030; 795; dH (400 MHz, CDCl3) 0.64 (2H, m, cPr-
CHH), 0.91 (2H, m, cPr-CHH), 1.10 (1H, m, cPr-CH), 1.99–2.09
(1H, m, 7-Ha), 2.53–2.64 (2H, m, 6-Ha, 7-Hb), 2.72–3.00 (4H,
m, CH2-CH2-NH2,CH2-14), 3.28–3.48 (4H, m, CH2-CH2-NH2,
6-Hb, 13-Ha), 3.69 (3H, s, C-9-OCH3), 3.85 (3H, s, C-2-OCH3),
3.81–3.89 (1H, m, 13-Hb), 4.57 (1H, t, J 8.1, H-7a), 5.60 (1H, br,
NH), 6.51 (1H, d, J 9.1, H-11), 6.61–6.64 (2H, m, H-8, H-10),
6.85 (1H, dd, J 8.8, 2.5 H-3), 6.97 (1H, d, J 2.3, H-1), 7.52 (1H,
d, J 8.8, H-4); dC (100 MHz, CDCl3) 6.89, 6.93 (2 × cPr-CH2),
14.73 (cPr-CH), 19.53 (C-14), 21.38 (C-7), 23.66 (CH2-CH2-NH),
34.23 (C-6), 36.84 (C-13), 39.88 (CH2-CH2-NH2), 48.50 (C-7a),
55.92 (C-9-OCH3), 56.01 (C-2-OCH3), 83.59 (C-5a), 100.48 (C-1),
105.84 (C-11), 106.76 (C-15), 110.43 (C-3), 111.57 (C-4), 111.89,
111.94 (C-8, C-10), 129.26 (C-4a), 129.48 (C-15a), 133.33 (C-7b),
133.39 (C-14a), 145.40 (C-11a), 153.03 (C-9), 154.16 (C-2), 172.35
=
(C-4a), 134.06 (C-14a), 151.10 (C-11a), 172.83 (C O); m/z (EI):
399.2 (2%, M+), 398.2 (4), 372.2 (15), 371.2 (56), 284.2 (55), 272.2
(23), 271.2 (100), 256.1 (8).
N-[2-(2,9-Dimethoxy-7,7a,13,14-tetrahydro-6H-cyclobuta[b]-
pyrimido[1,2-a:3,4-aꢀ]diindole-15-yl)ethyl]acetamide
(14). 14
(113 mg, 75%) was obtained from 11b (135 mg) and acetic
anhydride (0.2 mL) as a white solid (Found: C, 71.98; H, 6.89; N,
9.57. C26H29N3O3 requires C, 72.37; H, 6.77; N, 9.74%); mp 85 ◦C;
mmax/cm−1: 3320, 2937, 1649, 1586, 1543, 1477, 1294, 1244, 1225,
1030, 796; dH (400 MHz, CDCl3) 1.84 (3H, s, CH3), 1.99–2.09
(1H, m, 7-Ha), 2.54–2.64 (2H, m, 6-Ha, 7-Hb), 2.71–2.98 (4H,
m, CH2-CH2-NH2,CH2-14), 3.29–3.47 (4H, m, CH2-CH2-NH2,
6-Hb, 13-Ha), 3.69 (3H, s, C-9-OCH3), 3.84 (3H, s, C-2-OCH3),
3.83–3.89 (1H, m, 13-Hb), 4.57 (1H, t, J 8.1, H-7a), 5.41 (1H, br,
NH), 6.51 (1H, d, J 9.3, H-11), 6.62–6.65 (2H, m, H-8, H-10),
6.84 (1H, dd, J 8.8, 2.5 H-3), 6.96 (1H, d, J 2.3, H-1), 7.51 (1H,
d, J 8.8, H-4); dC (100 MHz, CDCl3) 19.53 (C-14), 21.39 (C-7),
23.40 (CH3), 23.59 (CH2-CH2-NH), 34.23 (C-6), 36.82 (C-13),
39.78 (CH2-CH2-NH2), 48.50 (C-7a), 55.93 (C-9-OCH3), 56.02
(C-2-OCH3), 83.59 (C-5a), 100.40 (C-1), 105.84 (C-11), 106.68
(C-15), 110.48 (C-3), 111.61 (C-4), 111.92, 111.98 (C-8, C-10),
129.26 (C-4a), 129.50 (C-15a), 133.19 (C-7b), 133.40 (C-14a),
=
(C O).
Acknowledgements
Thanks are due to Dr Matthias Gru¨ne and Elfriede Ruckde-
schel, Institute of Organic Chemistry, University of Wu¨rzburg
for recording the INADEQUATE and NOESY spectra and to
Anita Betz, Pharmaceutical Institute, University of Wu¨rzburg for
synthesizing some starting materials.
2136 | Org. Biomol. Chem., 2007, 5, 2129–2137
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