Mannich reaction of 5-hydroxy-β-carboline. Application to the synthesis of novel oxazinopyrimidocarboline derivatives

Article abstract of DOI:10.3987/COM-08-11447

5-Hydroxy-β-carboline 4 was synthesized and submitted to the Mannich reaction towards formaldehyde and some primary amines. It undergoes an original reaction of bis-aminomethylation-cyclisation giving the oxazinopyrimidocarboline derivatives 5a-d. The structure of these compounds was confirmed by their high-resolution mass, IR, ¹H NMR and ¹³C NMR spectral data. The Japan Institute of Heterocyclic Chemistry.

Full text of DOI:10.3987/COM-08-11447

HETEROCYCLES, Vol. 75, No. 11, 2008
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HETEROCYCLES, Vol. 75, No. 11, 2008, pp. 2761 - 2767. © The Japan Institute of Heterocyclic Chemistry
Received, 20th May, 2008, Accepted, 13th June, 2008, Published online, 16th June, 2008. COM-08-11447
MANNICH
REACTION
TO
OF
5-HYDROXY-β-CARBOLINE.
SYNTHESIS OF NOVEL
APPLICATION
THE
OXAZINOPYRIMIDOCARBOLINE DERIVATIVES
Samar Issa,a Nadia Walchshofer,a Issam Kassab,b Jacques Gentili,a
Aziz Geahchan,b and Zouhair Bouaziza*
aUniversity of Lyon, Lyon, F-69003, France. University Lyon 1, ISPB, Lyon,
b
F-69003, France. Inserm, U863, Lyon, F-69003, France. Faculty of Pharmacy,
Lebanon University of Beyrouth, Lebanon
E-mail: bouaziz@univ-lyon1.fr
Abstract – 5-Hydroxy-β-carboline 4 was synthesized and submitted to the
Mannich reaction towards formaldehyde and some primary amines. It undergoes
an original reaction of bis-aminomethylation-cyclisation giving the
oxazinopyrimidocarboline derivatives 5a-d. The structure of these compounds
was confirmed by their high-resolution mass, IR, 1H NMR and 13C NMR spectral
data.
INTRODUCTION
Recently, carbolines have received much interest due to their biological and pharmaceutical importance.
For example, in the case of β-carbolines, many investigations have been reported on their antitumor
activity1-5 and their variety of actions on the central nervous system.6-8 Moreover, many natural products
contain this heterocyclic system as harmine,9 a β-carboline alkaloid isolated from Peganum harmala L.
which has shown a strong cytotoxicity to tumor cell lines in vitro, 1-methoxycanthin-6-one10 isolated
from the medicinal plant Ailanthus altissima swingle described for its proapoptotic activity and its
synergism with agents that induce tumor cell death (Figure 1). On the other hand, N-substituted
dihydro-1,3-oxazines condensed with aromatic rings have various pharmacological properties. For
example, a number of oxazinoindoles 1 have been reported to possess diuretic, antihypertensive,
anti-inflammatory, antiulcerous, sedative and analgesic activities in rats and mice.11 Also; the
oxazinocarbazoledione derivative 2 has been reported to possess a strong cytotoxic activity against colon
cells and pulmonary carcinoma cells.12

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HETEROCYCLES, Vol. 75, No. 11, 2008
R1
N
OMe
R2O2C
Me
N
O
N
N
Me
N
OMe
N
H
H
O
harmine
1
1-methoxycanthin-6-one
Et
N
R2
O
O
N
O
N
N
R1
N
Me
O
3
2
Figure 1
RESULTS AND DISCUSSION
As part of our investigation13 on the biological properties of fused carbazole and carboline derivatives, we
planned to synthesize a series of oxazinocarbolines 3 through a normal Mannich reaction employing three
components: 5-hydroxy-β-carboline 4, primary amine and formaldehyde. According to literature,
aminomethylation of phenols always occurs at the position ortho to the hydroxyl group, even if the para
position is unoccupied.14 On the other hand, primary amines can react to give various products, like
secondary amines, dihydrooxazines or bis-hydroxyaryl-amines, depending upon the reaction conditions.
Additionally, it is known that polyfunctional substrates may produce a variety of cyclic compounds. In
this paper, we report the results of our preliminary work starting from hydroxycarboline 4. This latter was
prepared starting from meta-anisidine as previously reported by Quéguiner et al.15
The reaction of 4 with formaldehyde (2 equiv.) and primary amine (1 equiv.) in methanol at rt yielded a
small amount of the oxazinopyrimidocarboline 5 via a Mannich-type bis-aminomethylation followed by
intramolecular cyclization by formaldehyde. The expected oxazinocarbolines 3 were not observed.
Optimization of reaction conditions was made by using 4 equivalents of formaldehyde and 2 equivalents
of primary amine. However, the yields of compounds 5 remain moderate but a substantial amount of the
starting compound 4 was recovered (Scheme 1).

HETEROCYCLES, Vol. 75, No. 11, 2008
2763
R
O
N
OH
8
N
HCHO (4 equiv.)
RNH2 (2 equiv.)
N
N
MeOH/rt
N
H
N
R
4
5
O
N
O
N
N
N
N
N
N
N
5a (28%)
5b (34%)
N
O
N
Me
O
N
N
N
N
N
N
N
Me
5c (13%)
N
5d (34%)
Scheme 1
Concerning the regiochemistry, bis-aminomethylation may occur on the positions ortho and para to the
hydroxyl group or on the ortho position to the hydroxyl group and at the heterocyclic NH group. In either
case, the bis-aminomethylated compound reacts with two equivalents of formaldehyde. The resulting
intermediate may react intramolecularly with the phenolic oxygen to form the oxazine ring and with the
indolic N atom or the C-8 atom to form the tetrahydropyrimidine ring.
This unexpected transformation constitutes a novel example of Mannich reaction of phenolic substrate,
affording at the same time the oxazine and the diazine rings. Consequently it constitutes a convenient and
simple strategy to synthesize in one-pot, these new pentacyclic carboline derivatives. Similar pentacyclic
ring systems reported in the literature have shown potent biological activity. Among them,

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HETEROCYCLES, Vol. 75, No. 11, 2008
pyrimidocarbazole ER-3732816 exhibits a strong tumoricidal activity both in vitro and in vivo against
solid tumor cells, and substituted pentacyclic carbazolones 617 have been described as allosteric
modulators at muscarinic acetylcholine receptors (Figure 2).
O
Me
H
N
N
N
N
O
O
O
ER 37328
NMe2
6
Figure 2
In summary, some novel oxazinopyrimidocarboline derivatives have been synthesized by a one-pot
Mannich reaction of 5-hydroxy-β-carboline with primary amines and formaldehyde. Further studies to
extend this transformation to other primary amines and other heterocyclic phenols as
5-hydroxy-α-carboline and 5-hydroxycarbazole, are in progress.
EXPERIMENTAL
1. General: Melting points were measured with a Büchi apparatus (capillary tube). The IR spectra were
recorded with a Perkin-Elmer 1310 spectrophotometer. The NMR spectra were recorded with a Bruker
AM 300 spectrometer (1H-NMR: 300 MHz, 13C-NMR: 75 MHz). Chemical shifts (δ) are reported in ppm
using tetramethylsilane (TMS) as an internal reference. Coupling constant (J) values are given in Hz.
High-resolution mass spectra (HRMS) were recorded on a ThermoFinnigan MAT 95 XL spectrometer.
2. General procedure for the Mannich reaction: A 37% aqueous solution of formaldehyde (560 μL,
6.52 mmol) in MeOH (10 mL) was cooled in an ice bath. The corresponding primary amine (3.26 mmol)
was added and the resulting mixture was stirred at 0 °C for 30 min. Compound 4 (300 mg, 1.63 mmol) in
MeOH (10 mL) was then slowly added. After complete addition, stirring was continued at rt for a variable
amount of time, the evolution of the reaction being followed by TLC. After evaporation of the solvent,
the residue was purified by column chromatography on silica gel.
3,7-Diallyl-3,4,7,8-tetrahydro-2H,6H-1,3-oxazino[6,5-g]pyrimido[5,6,1-jk]-β-carboline
(5a):
Purification by column chromatography on silica gel with CH2Cl2/MeOH (95:5) yielded 5a in 28% yield.

HETEROCYCLES, Vol. 75, No. 11, 2008
2765
1
mp 116 °C. IR (KBr): 2923, 1626, 1499 cm-1. H NMR (300 MHz, CDCl3): δ ppm 8.74 (d, 1H, J = 0.9
Hz, H-10), 8.42 (d, 1H, J = 5.3 Hz, H-13), 8.07 (dd, 1H, J = 0.9 and 5.3 Hz, H-12), 8.07 (s, 1H, H-5),
5.90 (m, 2H, CH2CH=CH2), 5.28-5.00 (m, 4H, CH2CH=CH2), 5.19 (s, 2H, H-2), 5.10 (s, 2H, H-8), 4.15
(s, 2H, H-6), 4.11 (s, 2H, H-4), 3.48 (d, 2H, J = 6.4 Hz, CH2CH=CH2), 3.12 (d, 2H, J = 6.4 Hz,
CH2CH=CH2). 13C NMR (75 MHz, CDCl3): δ ppm 49.7, 50.4, 54.7, 55.9, 62.3, 82.8, 118.3, 119.0, 117.4,
124.1, 131.1, 134.9, 135.3, 139.1, 108.0, 109.7, 110.9, 127.3, 137.4, 135.5, 149.7. HRMS (CI): calcd for
C21H23N4O (M+H+) 347.1872, found 347.1879.
3,7-Dibenzyl-3,4,7,8-tetrahydro-2H,6H-1,3-oxazino[6,5-g]pyrimido[5,6,1-jk]-β-carboline
(5b):
Purification by column chromatography on silica gel with AcOEt/MeOH (90:10) yielded 5b in 34% yield.
1
mp 190 °C. IR (KBr): 2924, 1633, 1591 cm-1. H NMR (300 MHz, CDCl3): δ ppm 8.69 (s, 1H, H-10),
8.46 (d, 1H, J = 5.3 Hz, H-13), 8.15 (d, 1H, J = 5.3 Hz, H-12), 7.41-7.23 (m, 10H, H aromat.), 6.81 (s,
1H, H-5), 5.17 (s, 2H, H-2), 5.15 (s, 2H, H-8), 4.19 (s, 2H, H-6), 4.12 (s, 2H, H-4), 4.05 (s, 2H, CH2Ph),
3.65 (s, 2H, CH2Ph). 13C NMR (75 MHz, CDCl3): δ ppm 49.3, 50.4, 55.7, 56.9, 62.2, 83.0, 117.4, 124.3,
127.7, 127.5, 128.5 (2C), 128.6 (2C), 129.0 (2C), 129.3 (2C), 131.1, 139.1, 108.0, 109.7, 111.0, 127.3,
135.1, 137.4, 137.8, 138.3, 149.7. HRMS (CI): calcd for C29H27N4O (M+H+) 447.2185, found 447.2186.
3,7-Bis(alpha-Methylbenzyl)-3,4,7,8-tetrahydro-2H,6H-1,3-oxazino[6,5-g]pyrimido[5,6,1-jk]-β-
carboline (5c): Purification by column chromatography on silica gel with AcOEt/MeOH (90:10) yielded
1
5c in 13% yield. mp 125 °C. IR (KBr): 2972, 1631, 1531 cm-1. H NMR (300 MHz, CDCl3): δ 8.58 (s,
1H, H-10), 8.42 (d, 1H, J = 5.3 Hz, H-13), 8.09 (d, 1H, J = 5.3 Hz, H-12), 7.36-7.14 (m, 10H, H aromat.),
5.68 (s, 1H, H-5), 5.22 (d, 1H, J = 12.2 Hz, H-2), 5.02 (d, 1H, J = 12.2 Hz, H-2), 4.20 (s, 2H, H-8), 4.02
(s, 2H, H-6), 3.98 (s, 2H, H-4), 3.39 (s, 2H, CH(Me)Ph), 1.3 (s, 3H, J = 6.52 Hz, CH(Me)Ph), 1.5 (s, 3H,
13
J = 6.52 Hz, CH(Me)Ph). C NMR (75 MHz, CDCl3): δ ppm 21.86, 22.07, 48.7, 49.3, 61.4, 81.1, 58.1,
58.5, 117.8, 124.5, 127.7 (2C), 127.8 (2C), 128.0, 128.9 (2C), 129.0 (2C), 129.5, 131.1, 139.1, 108.2,
110.5, 111.3, 112.6, 128.9, 129.9, 138.5, 140.8, 144.4. HRMS (CI): calcd for C31H31N4O (M+H+)
475.2498, found 475.2500.
3,7-Bis(pyridin-2-ylmethyl)-3,4,7,8-tetrahydro-2H,6H-1,3-oxazino[6,5-g]pyrimido[5,6,1-jk]-β-
carboline (5d): Purification by column chromatography on silica gel with CH2Cl2/MeOH (90:10) yielded
5d in 34% yield. mp 122 °C. IR (KBr): 2923, 1633, 1592 cm-1. 1H NMR (300 MHz, CDCl3): δ ppm 8.70
(s, 1H, H-10), 8.61 (dd, 2H, J = 4.3 Hz, H-6’), 8.42 (d, 1H, J = 5.3 Hz, H-12), 8.11 (d, 1H, J = 5.3 Hz,
H-13), 7.69-7.18 (m, 6H, H aromat.), 6.80 (s, 1H, H-5), 5.23 (s, 2H, H-2), 5.17 (s, 2H, H-4), 4.22 (s, 4H,
H-6 and H-8), 4.14 (s, 2H, CH2Py), 4.02 (s, 2H, CH2Py). 13C NMR (75 MHz, CDCl3): δ ppm 50.4, 51.1,

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57.9, 59.1, 63.5, 83.8, 117.8, 123.1, 123.3, 123.5, 123.7, 124.8, 131.4, 137.0, 137.1, 139.4, 150.0, 150.2,
108.5, 110.1, 111.3, 127.7, 135.1, 137.8, 158.2, 158.3, 158.8. HRMS (CI): calcd for C27H25N6O (M+H+)
449.2090, found 449.2094.
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