New heterocycles from the reaction between some natural α-amino acid hydrazides and formaldehyde

Article abstract of DOI:10.1002/(sici)1099-0690(199911)1999:11<2943::aid-ejoc2943>3.0.co;2-x

The ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L- tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8- diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3- phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2- phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality.

Full text of DOI:10.1002/(sici)1099-0690(199911)1999:11<2943::aid-ejoc2943>3.0.co;2-x

FULL PAPER
New Heterocycles from the Reaction between Some Natural
␣-Amino Acid Hydrazides and Formaldehyde
Giancarlo Verardo,*[a] Nicoletta Toniutti,[a] Andrea Gorassini,[a] and Angelo G. Giumanini[a]
Keywords: Amino acids / α-Amino acid phenylhydrazides / Heterocycles / Cyclization reactions
The ring forming condensation between some natural α-
amino acid phenylhydrazides (1) and aqueous formaldehyde
(2) has opened a novel synthetic route to hexahydro-1,2,4-
triazin-6-one derivatives (3). Polycyclic systems were
gave perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d]-
[1,2,4]triazepine (5) perhydro-1-oxo-3-phenylimidazo[5,4-
d][1,2,4]triazino[4,5-a]pyridine
(7)
and
1,2,3-H-3-(2-
phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1
obtained from the same reaction carried out with
acid 1,4-bis(2-phenylhydrazide) (1d), -histidine phenyl-
hydrazide (1e) and -tryptophan phenylhydrazide (1f) which original chirality.
L-aspartic
were conveniently obtained by direct reaction of
L
phenylhydrazine with L-α-amino acid esters retaining the
L
Combining our recent interest in some aspects of the spectra for double bonded methylene group confirmed that
chemistry of hydrazides[1] and our long standing research the monomeric imine structure did not form.
in the reactions of formaldehyde with amines,[2] we investi-
gated the reaction of a few hydrazides of natural amino
acids with aqueous formaldehyde, a study which does not
appear to have precedent in the chemical literature.
The oligomeric structures of 1 were excluded by consider-
ing the 1H-NMR features of the NHNH(Ar) skeleton: these
two protons usually showed up in the range δ ϭ 6Ϫ10, as
two singlets.[1] In our products one of the proton reson-
ances for the hydrazine function was missing in the range
δ ϭ 6Ϫ10, whereas an amino proton showed up at δ ϭ 2Ϫ3
as a broad singlet. Both facts are good evidence for the
cyclic structure 3 or 4.
Results and Discussion
When phenylhydrazides of -amino acids such as alanine,
leucine and phenylalanine (1aϪc) were allowed to react
with formaldehyde, the expected hexahydro-1,2,4-triazin-6-
ones (3aϪc) were isolated in good to moderate yields
(Scheme 1).
Absence of both the parent ions for oligomeric products
of the imines (which are usually very weak) and any deolig-
omerization ions were partial evidence for the absence of
such products. Moreover, hydrazides previously investi-
gated,[1] and those prepared during this work, showed a
very intense ion at m/z ϭ 108, corresponding to the compo-
sition C6H8N2, which was poorly represented in 1-phenyl-
1-alkyl hydrazides[1] and in two of the products prepared
(3a and 3c). Compound 3b actually showed such a peak,
but most likely it originated from the involvement of the
side chain during fragmentation. On the other hand, a com-
mon feature in the MS spectra of 3aϪc was the presence of
an intense peak at m/z ϭ 120 which likely corresponds to
the composition C7H7N.
We were then left with the isomeric structures 3 and 4
(Scheme 1) for the definitive identification of the separated
products. The well-known reductive cleavage of NϪN
bonds by Raney nickel[3] proved to be effective on phenyl-
hydrazide 1a, yielding aniline and 2-aminopropanamide as
confirmed by GC-MS; moreover, the same reaction carried
Scheme 1
Since monomeric and oligomeric N-methylene derivatives out on 3a was ineffective even for prolonged reaction per-
of 1 have the same elemental composition as 3, the presence iods. Furthermore, silylation of 3a yielded a monotrimethyl-
of a ring containing three nitrogen atoms had to be care- silyl derivative, an important indication of the presence of
fully deduced. The absence of resonance in the 13C-NMR a single amino nitrogen as in 3. Analogously, the reaction
of this compound with acetyl chloride gave a monoacetyl
[a]
Dipartimento di Scienze e Tecnologie Chimiche,
derivative, while phenylhydrazine undergoes double acety-
`
Universita di Udine,
lation under the same conditions.[4] All these results were
via del Cotonificio 108, I-33100 Udine, Italy
E-mail: gverardo@tin.dstc.uniud.it
consistent with a structure like 3 but not 4.
Eur. J. Org. Chem. 1999, 2943Ϫ2948
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ193X/99/1111Ϫ2943 $ 17.50ϩ.50/0
2943

G. Verardo, N. Toniutti, A. Gorassini, A. G. Giumanini
FULL PAPER
Scheme 2
Some further spectroscopic features of 3 are noteworthy. hydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]-
A notable feature in NMR spectra of 3a؊c is the non- triazepine (5) or their analogues. A route similar to our
equivalence of NϪCH2ϪN protons, likely due to the dia- [6ϩ1] atom combination has been employed in the prep-
stereotopic effect of the α-chiral centre: a doublet of dou- aration of 1,3,4-benzotriazepine system.[10]
blets was thus detected instead of a singlet. In the case of
1b and 3b, the diastereotopic effect was observed also for amino acid phenylhydrazides such as -histidine and -tryp-
the geminal methyl groups. tophan phenylhydrazide (1e and 1f), whose reactivity was
A different behaviour was observed for heteroaromatic
Hexahydro-1,2,4-triazin-6-ones represent interesting ex- strongly conditioned by the presence of an imidazole and
amples[5] of derivatives of 1,2,4-triazines, for which an an indole group, respectively. The hydrochlorides of 1e and
extensive research concerning both synthetic methods and 1f gave complex mixtures under the same experimental con-
biological activity is documented. Although the most fre- ditions employed for 1a؊c: in both cases a single product
quently reported methods of their preparation involve a [4 was obtained by heating the reaction mixture in DMSO.
ϩ 2] cyclization, where hydrazines play the role of the two The presence of both HCl and DMSO turned out to be
centre component,[6] a recent work reported the [5 ϩ 1] necessary for a good outcome to the reactions, providing a
cyclization performed by the reaction of amino acid hydra- catalytic environment for the complete conversion of the
zides and orthocarboxylates.[7] No straightforward method intermediates. -Histidine phenylhydrazine hydrochloride
is yet available for the preparation of hexahydro-1,2,4-tria- (1e) yielded a triazine ring fused with a six-membered heter-
zin-6-ones, and very few examples of simple derivatives can ocycle,
be found in the literature.[8][9]
d][1,2,4]triazino[4,5-a]pyridine (7), isolated as a hydrochlo-
Under similar experimental conditions, -aspartic acid ride (Scheme 3).
namely
perhydro-1-oxo-3-phenylimidazo[5,4-
1,4-bis(2-phenylhydrazide) (1d) reacted with two molecules
The structure of 7 was determined by NMR: the 13C-
of formaldehyde affording an interesting triazine ring fused NMR spectrum, if compared with that of the starting hy-
with a seven-membered heterocycle, namely perhydro-4,6- drazide 1e, showed a quaternary carbon, instead of a pri-
1
dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) mary one, in the region of aromatic signals, and the H
(Scheme 2).
NMR revealed the absence of a singlet at δ ϭ 7.0 in DMSO,
The isomeric structure 6, a 5/6 rings combination instead due to an imidazole CH. This is a good indication that for-
of 6/7, was excluded because the treatment with Raney maldehyde was responsible for an electrophilic attack on
nickel left the compound unchanged even after long reac- the imidazole ring.
tion times.
Cyclization reactions like this one were reported for his-
The spectroscopic data are in agreement with the struc- tamine and histidine under acidic conditions.[11] As already
ture proposed for 5. An interesting feature observed in the observed for 5, all the six methylene protons were non-
1H-NMR spectra is the non-equivalence of all six methyl- equivalent, each showing up with a geminal coupling con-
ene protons, each appearing with a geminal coupling con- stant.
stant, likely due to a diastereotopic effect. Two singlets were
In the case of -tryptophan phenylhydrazide hydrochlo-
present at δ ϭ 9.9 and 10.2 for the two hydrazide protons ride, the electrophilic substitution on the reactive 2-position
in DMSO. Some examples of compounds in the class of of the indole ring upon treatment with formaldehyde was
fused rings involving 1,2,4-triazepines have been re- preferred to the ring closure to 1,2,4-triazine system. No
ported,[10] nevertheless there are no reports either on per- triazine was formed, but 1,2,3-H-3-(2-phenylcarbazoyl)-β-
2944
Eur. J. Org. Chem. 1999, 2943Ϫ2948

New Heterocycles
FULL PAPER
Scheme 3
Scheme 4
carboline (8) was isolated as the hydrochloride (Scheme 4). The sole exceptions were 1f and 8, whose spectra in DMSO
This behaviour suggested that the initial reaction of formal- at 40°C revealed the presence of two isomers: their signals
dehyde with 1 occurred at the amino group.
merged at 100°C, thus confirming the existence of a confor-
Compounds containing the heterocyclic skeleton of mational equilibrium
perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]triazino[4,5-
a]pyridine (7) have not been reported so far. Conversely,
Experimental Section
General: All reagents were of commercial quality (Aldrich, Fluka)
and were used without further purification. Ϫ GC-MS analyses
many derivatives containing the β-carboline moiety present
in 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline (8), have been
extensively described in the literature. This subunit was
found in many naturally occurring compounds, subjected
to intensive chemical and biochemical research[12] due to
their pharmacological importance. The β-carboline system
containing the pyridine ring in a reduced state has received
special attention because it is the starting point for several
alkaloids.[13]
In the cases 1a, 3a, 1b, 3b, 1c, and 3c where the stereo-
chemistry of the products was established, the enantiomeric
purity of the original -α-amino acids was retained. These
compounds with rigid frameworks containing a natural am-
ino acid moiety could be attractive targets in the design of
new peptidomimetic structures with biological activity.
As a closing remark we wish to point out the straightfor-
ward preparation of -amino acid phenylhydrazides (1) by
the simple condensation of the appropriate -amino acid
esters and an excess of neat phenylhydrazine at 60°C: ne-
ither a catalyst nor the protection of the amino group was
required.[14] This observation may find an application in the
chemistry of peptide synthesis where the phenylhydrazide
protecting group has received recent attention for its easy
removal.[15] It is quite interesting to notice that the NMR
spectra of phenylhydrazides 1aϪe did not show the (E/Z)
isomerism reported for other hydrazides:[1][16] in solution
were performed with
a Fisons TRIO 2000 gas-chromatog-
raphϪmass spectrometer, working in the positive ion 70 eV electron
impact mode. Spectra were recorded in the range 35Ϫ450 u. Injec-
tor temperature was kept at 250°C and the column (Supelco
SPBTM-5, 30 m long, 0.25 mm i.d.) temperature was programmed
from 60°C to 300°C with a gradient of 10°C/min. Ϫ The enantiom-
eric purity of 1a, 3a, 1b, 3b, 1c, and 3c was determined using chiral
GC analysis, upon comparison with the corresponding , mix-
tures (the column was a Chrompack 7495 WCOT, liquid phase Chi-
rasil-val-L, i.d. 0.22 mm, o.d. 0.35 mm). Ϫ Optical rotations were
determined at 21°C using a POLAX-D polarimeter purchased
from ATAGO (Japan). Ϫ IR spectra were obtained with a Nicolet
FT-IR Magna 550 spectrophotometer using KBr technique for
solids and recorded in the range 4000Ϫ400 cmϪ1. Ϫ H- and 13C-
1
NMR spectra were recorded in CDCl3 at room temperature on a
Bruker AC-F 200 spectrometer at 200 and 50 MHz, respectively.
NMR peak locations are reported as δ-values from TMS (1H
NMR) and the central peak of CDCl3 (13C NMR). Ϫ Elemental
analyses were performed with a Carlo Erba Mod. 1106 elemental
analyzer. Ϫ Melting points were determined with an automatic
Mettler (Mod. FP61) apparatus and are not corrected.
Preparation of the L-α-Amino Acid Phenylhydrazides 1a؊c: The ap-
propriate -α-amino acid methyl ester hydrochloride (9.3 mmol)
and freshly distilled phenylhydrazine (5.0 mL, 46.5 mmol) were
mixed in a flask fitted with a condenser and a magnetic stirring
these compounds were present in one conformation only. bar. The mixture was stirred at 60°C for 16 h under inert atmos-
Eur. J. Org. Chem. 1999, 2943Ϫ2948 2945

G. Verardo, N. Toniutti, A. Gorassini, A. G. Giumanini
FULL PAPER
phere. The reaction was allowed to cool down to room temperature ([D6]DMSO): δ ϭ 39.0, 50.9, 112.2, 118.3, 118.4, 128.5, 149.2,
and CH2Cl2 (100 mL), Na2CO3 · 10 H2O (11 g), and H2O (ca. 170.1, 173.8. Ϫ C16H19N5O2 (313.3): calcd. C 61.33, H 6.11, N
3 mL) were added. The mixture was vigorously stirred for 3 h. After
filtration of salts the solvent was reduced, and the unchanged phe-
nylhydrazine was removed under reduced pressure (60°C at ca.
0.5 mbar). After addition of Et2O (20 mL) and ca. 3 mL of hexane,
the mixture was stirred for 3 h and the solid product was filtered
and washed with Et2O. 1a was obtained in spectroscopically pure
form; 1b and 1c were recrystallised from iPrOH/hexane.
22.35; found C 61.57, H 6.28, N 22.51.
Preparation of -Amino Acid Phenylhydrazides Hydrochloride
L
(1e؊f): -Histidine methyl ester dihydrochloride or -tryptophan
methyl ester hydrochloride (16.3 mmol) and freshly distilled phenyl-
hydrazine (9.0 mL, 82.0 mmol) were mixed in a flask fitted with a
condenser and a magnetic stirring bar. The mixture was stirred at
90°C for 6 h under inert atmosphere. After the addition of 100 mL
of iPrOH, the solid was filtered. 1e was recrystallised from iPrOH/
MeOH under stirring (which prevented the precipitation of the
product in the form of a gel). Compound 1f was crystallised from
MeOH/iPrOH/Et2O. The product was hygroscopic. Potentiometric
titration of chloride with a silver nitrate solution[17] in the presence
of HNO3 confirmed that 1e and 1f were isolated as the monohyd-
rochlorides.
L-Alanine Phenylhydrazide (1a): Yield 85%, m.p. 116°C. Ϫ IR
(KBr): ν˜ ϭ 3284 cmϪ1, 3203, 1662, 1600, 1533, 1497. Ϫ MS
(70 eV); m/z (%): 179 [Mϩ] (41), 162 (47), 134 (35), 109 (10), 108
(100), 107 (14), 105 (6), 93 (17), 92 (17), 77 (17), 65 (7). Ϫ 1H NMR
(CDCl3): δ ϭ 1.40 (d, 3 H, J ϭ 6.5 Hz), 1.54 (broad s, 1 H), 3.61
(q, 1 H, J ϭ 6.5 Hz), 6.14 (broad s, 1 H), 6.75Ϫ6.95 (m, 3 H),
7.15Ϫ7.30 (m, 2 H). Ϫ 13C NMR (CDCl3): δ ϭ 21.7, 50.2, 113.5,
121.1, 129.1, 147.9, 175.1. Ϫ [α]D ϭ ϩ3.8 (c ϭ 0.17, MeOH). Ϫ
C9H13N3O (179.2): calcd. C 60.32, H 7.31, N 23.45; found C 60.55,
H 7.52, N 23.56. Registry no.: 97458Ϫ28Ϫ1.
L
-Histidine Phenylhydrazide Hydrochloride (1e): Yield 50%, m.p.
(dec.) ϭ 195°C. Ϫ IR (KBr): ν˜ ϭ 3484 cmϪ1, 3414, 3257, 3224,
1707, 1606, 1497. Ϫ MS (70 eV); m/z (%): 245 [Mϩ] (17), 228 (2),
164 (6), 138 (6), 123 (7), 121 (10), 110 (100), 108 (23), 93 (32), 92
L
-Leucine Phenylhydrazide (1b): Yield 70%, m.p. 148°C (ref.[14c]
1
122°C). Ϫ IR (KBr): ν˜ ϭ 3238 cmϪ1, 2958, 1650, 1603, 1500. Ϫ
MS (70 eV); m/z (%): 221 [Mϩ] (24), 204 (17), 134 (16), 109 (10),
108 (100), 107 (15), 93 (54), 92 (30), 86 (95), 77 (22), 65 (13). Ϫ 1H
NMR (CDCl3): δ ϭ 0.93 (d, 3 H, J ϭ 6.3 Hz), 0.97 (d, 3 H, J ϭ
6.1 Hz), 1.30Ϫ1.60 (m, 3 H), 1.70Ϫ1.90 (m, 2 H), 3.53 (dd, 1 H,
CH, J ϭ 9.8, 4.0 Hz), 6.10 (broad s, 1 H), 6.75Ϫ6.95 (m, 3 H),
7.20Ϫ7.30 (m, 2 H). Ϫ 13C NMR (CDCl3): δ ϭ 21.3, 23.3, 24.7,
44.0, 53.0, 113.6, 121.1, 129.1, 148.0, 175.0. Ϫ [α]D ϭ ϩ20.7 (c ϭ
0.20, MeOH). Ϫ C12H19N3O (221.3): calcd. C 65.13, H 8.65, N
18.99; found C 65.33, H 8.88, N 19.20. Registry no.: 6278Ϫ97Ϫ3.
(17), 82 (46). Ϫ H NMR ([D6]DMSO): δ ϭ 3.00Ϫ3.15 (m, 2 H),
4.10 (t, 1 H, J ϭ 5.8 Hz), 6.50Ϫ7.20 (m, 6 H), 7.70 (s, 1 H), 7.80
(s, 1 H). Ϫ 13C NMR ([D6]DMSO): δ ϭ 29.4, 51.8, 112.3, 116.0,
118.5, 128.5, 132.9, 135.0, 148.6, 168.9. Ϫ C12H16ClN5O (281.7):
calcd. C 51.16, H 5.72, N 24.86; found C 50.18, H 6.17, N 23.72.
L
-Tryptophan Phenylhydrazide Hydrochloride (1f): Yield 60%, m.p.
(dec.) ϭ 200°C. Ϫ IR (KBr): ν˜ ϭ 3305 cmϪ1, 3227, 1683, 1603,
1495, 1481. Ϫ MS (70 eV); m/z (%): 306 [Mϩ] (10), 294 (60), 277
(18), 170 (80), 164 (77), 163 (37), 159 (60), 158 (38), 143 (41), 132
(44), 130 (100), 117 (29), 115 (25), 108 (35), 93 (80), 92 (58), 77
1
(65). Ϫ H NMR ([D6]DMSO, 100°C): δ ϭ 3.30 (d, 2 H, J ϭ 7.2
L
-Phenylalanine Phenylhydrazide (1c): Yield 80%, m.p. 147°C
(ref.[14c] 134°C). Ϫ IR (KBr): ν˜ ϭ 3291 cmϪ1, 3223, 1684, 1656,
1604. Ϫ MS (70 eV); m/z (%): 255 [Mϩ] (30), 238 (10), 164 (53),
147 (11), 134 (26), 131 (32), 120 (100), 108 (43), 103 (21), 93 (25),
Hz), 4.17 (t, 1 H, J ϭ 7.3 Hz), 6.50Ϫ7.90 (m, 10 H), 11.10 (broad
s, 1 H). Ϫ 13C NMR ([D6]DMSO, 100°C): δ ϭ 26.6, 51.7, 106.8,
111.0, 112.4, 118.0, 118.5, 120.5, 124.2, 126.9, 128.0, 136.0, 147.9,
167.6. Ϫ 13C NMR ([D6]DMSO, 45°C; the two (E/Z) isomers, indi-
cated with A and B, were present in ca. 1:12 ratio): δ ϭ 26.3 (A),
27.1 (B), 50.1 (A), 51.7 (B), 107.0 (B), 111.3 (B), 112.4 (B), 112.6
(A), 118.2 (A), 118.4 (B), 118.6 (B), 119.7 (A), 121.0 (B), 124.6 (B),
125.0 (A), 126.9 (A), 127.0 (B), 127.9 (A), 128.4 (B), 128.9 (A),
136.2 (B), 136.4 (A), 168.1 (B), 172.9 (A). Ϫ C17H19ClN4O (330.8):
calcd. C 61.8, H 5.76, N 17.0; found C 61.27, H 5.82, N 16.70.
1
92 (26), 91 (27), 77 (23), 65 (20). Ϫ H NMR (CDCl3): δ ϭ 2.75
(dd, 1 H, J ϭ 13.5, 7.0 Hz), 2.95 (dd, 1 H, J ϭ 13.5, 6.5 Hz), 3.55
(t, 1 H, J ϭ 6.5 Hz), 6.55 (d, 2 H, J ϭ 8.2 Hz), 6.67 (t, 1 H, J ϭ
7.0 Hz), 7.07 (t, 2 H, J ϭ 7.6 Hz), 7.20Ϫ7.40 (m, 5 H), 7.62 (broad
s, 1 H). Ϫ 13C NMR (CDCl3): δ ϭ 41.5, 55.2, 112.1, 118.3, 126.1,
128.1, 128.5, 129.3, 138.5, 149.1, 174.1. Ϫ [α]D ϭ ϩ37.1 (c ϭ 0.27,
MeOH). Ϫ C15H17N3O (255.3): calcd. C 70.56, H 6.71, N 16.46;
found C 70.67, H 6.82, N 16.64. Registry no.: 14723Ϫ88Ϫ7.
Reaction of L-Alanine Phenylhydrazide (1a) with Raney Nickel: A
well stirred mixture of 1a (0.11 g, 0.6 mmol) and Raney nickel (ca.
0.08 g) in absolute EtOH (5 mL) was hydrogenated at 60°C at at-
mospheric pressure during 7 h. The reaction mixture was diluted
with MeOH (10 mL) and, after removal of the catalyst, the solvents
were distilled off under reduced pressure. The residue was washed
with Et2O. The ether extract contained aniline formed during the
reaction (0.05 g, 0.5 mmol, 89%); the solid residue consisted mainly
of 2-aminopropanamide (0.04 g, 0.48 mmol, 80%) identified by
comparison with an authentic specimen, prepared according to a
described procedure.[18]
Preparation of L-Aspartic Acid 1,4-Bis(2-phenylhydrazide) (1d): The
-aspartic acid methyl ester hydrochloride (3.9 g, 20.0 mmol) was
neutralised with an aqueous saturated solution of Na2CO3
(200 mL), pH 10Ϫ11, and extracted with AcOEt (2 ϫ 200 mL).
The free amino acid ester was obtained (2.6 g, 16.0 mmol) after
accurate solvent removal (at ca. 0.5 mbar, 50°C). Freshly distilled
phenylhydrazine (8.6 mL, 80.0 mmol) was added and the mixture
was stirred at 90°C for 24 h under inert atmosphere in a flask fitted
with a condenser. The unchanged phenylhydrazine was distilled un-
der reduced pressure (60°C at ca. 0.5 mbar) and the residue was
treated with 50 mL Et2O and ca. 3 mL of hexane. The solid was
filtered, washed with Et2O and recrystallised from MeOH/iPrOH/
Preparation of Hexahydro-1,2,4-triazin-6-ones (3a؊c): A solution
of the appropriate -amino acid phenylhydrazide (1aϪc)
(4.5 mmol) and aqueous formaldehyde (36%, 0.37 mL, 4.8 mmol)
in absolute EtOH (45 mL) was stirred at 40°C for 3 h. After solvent
removal under reduced pressure, the solid residue was purified: 3a
hexane (85%), m.p. (dec.) ϭ 178°C. Ϫ IR (KBr): ν˜ ϭ 3230 cmϪ1
,
1645, 1605, 1496. Ϫ MS (70 eV); m/z (%): 313 [Mϩ] (3), 296 (4),
205 (14), 177 (24), 161 (14), 134 (8), 108 (100), 107 (17), 106 (18),
105 (14), 93 (76), 92 (48), 91 (22), 78 (22), 77 (60), 70 (64), 65 (38). was recrystallised from AcOEt/hexane, 3c from iPrOH/hexane, and
1
Ϫ H NMR ([D6]DMSO): δ ϭ 2.37 (dd, 1 H, J ϭ 14.7, 8.8 Hz), 3b was purified by a treatment with charcoal in EtOH for 5 min at
2.52 (dd, 1 H, J ϭ 14.7, 4.7 Hz), 3.30 (broad s, 2 H), 3.69 (dd, 1
room temp. These products could not be purified by absorption
H, J ϭ 8.8, 4.7 Hz), 6.60Ϫ6.80 (m, 6 H), 7.00Ϫ7.20 (m, 4 H), 7.60 chromatography since they extensively decomposed upon contact
(s, 1 H), 7.63 (s, 1 H), 7.80 (s, 1 H), 9.00 (s, 1 H). Ϫ 13C NMR
on silica gel or alumina.
2946
Eur. J. Org. Chem. 1999, 2943Ϫ2948

New Heterocycles
FULL PAPER
Hexahydro-5-methyl-2-phenyl-1,2,4-triazin-6-one (3a): Yield 60%,
Preparation of Perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]tria-
m.p. 147°C. Ϫ IR (KBr): ν˜ ϭ 3272 cmϪ1, 3213, 1708, 1691, 1603, zino[4,5-a]pyridine Hydrochloride (7): A solution of 1e (2.0 g,
1498. Ϫ MS (70 eV); m/z (%): 191 [Mϩ] (100), 162 (13), 134 (63),
7.1 mmol) and aqueous formaldehyde (36%, 1.2 mL, 15.6 mmol) in
120 (81), 119 (33), 108 (13), 107 (20), 105 (22), 93 (21), 92 (60), 91 200 mL MeOH was stirred at 50°C for 3 h. After solvent removal
1
(15), 77 (28), 65 (21). Ϫ H NMR (CDCl3): δ ϭ 1.40 (d, 3 H, J ϭ under reduced pressure, 10 mL of DMSO were added and the solu-
6.7 Hz), 2.12 (broad s, 1 H), 3.56 (q, 1 H, J ϭ 6.7 Hz), 4.38 (d, 1
tion was heated at 40°C for 3 h. The solvent was distilled at ca.
H, J ϭ 7.3 Hz), 4.45 (d, 1 H, J ϭ 7.3 Hz), 6.44 (broad s, 1 H), 0.5 mbar, the residue dissolved in the minimum amount of MeOH
6.65Ϫ7.00 (m, 3 H), 7.15- 7.35 (m, 2 H). Ϫ 13C NMR (CDCl3):
δ ϭ 16.5, 53.8, 63.0, 113.0, 120.8, 129.0, 145.8, 175.4. Ϫ [α]D
ϩ59.2 (c ϭ 0.42, MeOH). Ϫ C10H13N3O (191.2): calcd. C 62.81,
and the solution was added dropwise to AcOEt under stirring in
order to let a white solid precipitate. It was filtered and obtained
in spectroscopically pure form (80%), m.p. (dec.) ϭ 220°C. Ϫ IR
(KBr): ν˜ ϭ 3420 cmϪ1, 3143, 1696, 1648, 1602, 1497. Ϫ MS
(70 eV); m/z (%): 269 [Mϩ] (75), 240 (6), 212 (10), 177 (7), 162 (6),
134 (100), 122 (48), 120 (41), 108 (17), 107 (43), 95 (30), 93 (25),
ϭ
H 6.85, N 21.97; found C 62.68, H 6.94, N 21.77.
Hexahydro-5-(2Ј-methylpropyl)-2-phenyl-1,2,4-triazin-6-one
(3b):
Yield 70%, m.p. 111°C. Ϫ IR (KBr): ν˜ ϭ 3247 cmϪ1, 2958, 1710,
1603, 1497. Ϫ MS (70 eV); m/z (%): 233 [Mϩ] (63), 204 (6), 177
(36), 176 (30), 162 (12), 161 (14), 149 (28), 146 (16), 134 (45), 120
(100), 119 (53), 108 (74), 107 (22), 105 (17), 98 (20), 93 (53), 92
1
92 (18), 77 (12), 36 (7). Ϫ H NMR ([D6]DMSO): δ ϭ 2.52 (t, 1
H, J ϭ 11.0 Hz), 3.08 (dd, 1 H, J ϭ 15.2, 4.0 Hz), 3.48 (dd, 2 H,
J ϭ 11.1, 4.1 Hz), 3.83 (d, 1 H, J ϭ 14.0 Hz), 4.22 (d, 1 H, J ϭ
11.7 Hz), 4.83 (d, 1 H, J ϭ 12.3 Hz), 6.80Ϫ7.50 (m, 5 H), 8.88 (s,
1 H), 10.30 (s, 1 H). Ϫ 13C NMR ([D6]DMSO): δ ϭ 23.8, 44.9,
59.6, 69.7, 117.4, 121.7, 124.9, 125.0, 128.7, 132.3, 150.0, 167.4. Ϫ
C14H16ClN5O (305.7): calcd C 54.99, H 5.27, N 22.90; found C
52.43, H 5.34, N 21.24.
1
(76), 86 (67), 77 (26). Ϫ H NMR (CDCl3): δ ϭ 1.00 (t, 6 H, J ϭ
6.4 Hz), 1.35Ϫ1.60 (m, 1 H), 1.70Ϫ1.95 (m, 2 H), 2.10 (broad s, 1
H), 3.50 (dd, 1 H, J ϭ 10.4, 3.8 Hz), 4.42 (d, 1 H, J ϭ 7.3 Hz),
4.50 (d, 1 H, J ϭ 7.3 Hz), 6.50 (s, 1 H), 6.65Ϫ6.90 (m, 3 H),
7.10Ϫ7.30 (m, 2 H). Ϫ 13C NMR (CDCl3) δ ϭ 21.4, 23.2, 25.0,
40.4, 56.5, 63.5, 113.4, 121.2, 129.2, 146.0, 175.6. Ϫ [α]D ϭ Ϫ6.8
(c ϭ 0.22, MeOH). Ϫ C13H19N3O (233.3): calcd C 66.92, H 8.21,
N 18.01; found C 66.72, H 8.33, N 17.77.
Preparation of Perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d]-
[1,2,4]triazepine (5): A solution of 1d (1.4 g, 4.5 mmol) and aqueous
formaldehyde (36%, 1.7 mL, 22.7 mmol) in EtOH (100 mL) was
stirred at 40°C for 2 h. The product precipitated and was filtered.
Compound 5 was obtained in spectroscopically pure form (70%),
m.p. 168°C. Ϫ IR (KBr): ν˜ ϭ 3229 cmϪ1, 3170, 1727, 1673, 1655,
1599, 1497. Ϫ MS (70 eV); m/z (%): 337 [Mϩ] (17), 308 (11), 230
(23), 217 (22), 201 (25), 188 (22), 174 (13), 161 (34), 147 (16), 121
(13), 120 (14), 108 (22), 106 (31), 105 (88), 104 (50), 93 (48), 92
(39), 91 (30), 77 (100), 65 (23). Ϫ 1H NMR ([D6]DMSO): δ ϭ 2.09
(t, 1 H, J ϭ 12.0 Hz), 2.67 (d, 1 H, J ϭ 13.5 Hz), 3.30Ϫ3.60 (m, 1
H), 3.90 (d, 1 H, J ϭ 13.5 Hz), 4.20 (d, 1 H, J ϭ 12.1 Hz), 4.80
(d, 1 H, J ϭ 12.1 Hz), 4.97 (d, 1 H, J ϭ 13.5 Hz), 6.50Ϫ6.75 (m,
3 H), 6.80Ϫ7.10 (m, 5 H), 7.20Ϫ7.35 (m, 2 H), 9.80 (s, 1 H), 10.20
(s, 1 H). Ϫ 13C NMR ([D6]DMSO): δ ϭ 60.4, 67.5, 69.2, 113.2,
117.6, 118.8, 121.9, 128.5, 128.6, 146.7, 150.2, 167.3, 175.5. Ϫ
C18H19N5O2 (337.3): calcd. C 64.08, H 5.68, N 20.76; found C
64.34, H 5.43, N 21.02.
Hexahydro-5-benzyl-2-phenyl-1,2,4-triazin-6-one (3c): Yield 85%,
m.p. 154°C. Ϫ IR (KBr): ν˜ ϭ 3288 cmϪ1, 1704, 1607, 1497, 1452.
Ϫ MS (70 eV); m/z (%): 267 [Mϩ] (58), 238 (3), 176 (91), 147 (15),
134 (35), 132 (48), 131 (28), 120 (100), 119 (35), 106 (23), 105 (37),
104 (20), 93 (33), 92 (80), 91 (65), 77 (30), 65 (24). Ϫ 1H NMR
(CDCl3): δ ϭ 3.12 (dd, 2 H, J ϭ 5.6, 2.0 Hz), 3.83 (t, 1 H, J ϭ 5.3
Hz), 4.21 (d, 1 H, J ϭ 7.0 Hz), 4.33 (d, 1 H, J ϭ 7.0 Hz), 6.00
(broad s, 1 H), 6.55 (d, 2 H, J ϭ 8.2 Hz), 6.90 (t, 1 H, J ϭ 7.0 Hz),
7.15 (t, 2 H, J ϭ 7.6 Hz), 7.20Ϫ7.35 (m, 5 H). Ϫ 13C NMR
(CDCl3): δ ϭ 36.6, 58.9, 63.8, 113.7, 121.6, 127.1, 128.7, 129.3,
129.8, 136.4, 145.9, 173.9. Ϫ [α]D ϭ ϩ43.2 (c ϭ 0.35, MeOH). Ϫ
C16H17N3O (267.3): calcd C 71.89, H 6.41, N 15.72; found C 71.65,
H 6.22, N 15.87.
Reaction of Hexahydro-5-methyl-2-phenyl-1,2,4-triazin-6-one (3a)
with Raney Nickel: A well stirred mixture of 3a (0.11 g, 0.57 mmol)
and Raney nickel (ca. 0.07 g) in absolute EtOH (5 mL) was hydro-
genated at 60°C at atmospheric pressure during 24 h. GC-MS and
TLC analysis of the reaction mixture showed the presence only of
the starting material 3a. This was confirmed by 1H- and 13C-NMR
analysis of the solid (0.10 g, 0.52 mmol, 91%) obtained after re-
moval of the catalyst and solvent.
Reaction of Perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d]-
[1,2,4]triazepine (5) with Raney Nickel: A well-stirred mixture of 5
(0.20 g, 0.59 mmol) and Raney nickel (ca. 0.07 g) in absolute EtOH
(7 mL) was hydrogenated at 60°C at atmospheric pressure during
24 h. TLC analysis of the reaction mixture showed the presence
only of the starting material 5. This was confirmed by 1H- and 13C-
NMR analysis of the solid (0.19 g, 0.56 mmol, 95%) obtained after
removal of the catalyst and solvent.
Silylation of Hexahydro-5-methyl-2-phenyl-1,2,4-triazin-6-one (3a):
A solution of 3a (0.04 g, 0.21 mmol) and a mixture of BSTFA and
TMCS (99:1; 0.3 mL) in pyridine (0.30 mL) was heated at 60°C
during 90 min in a sealed tube. GC-MS analysis of the reaction
mixture revealed the presence of two compounds: unchanged 3a
and its monosilyl derivative [MS (70 eV); m/z (%): 263 [Mϩ] (35),
234 (33), 219 (15), 191 (4), 178 (5), 150 (16), 129 (25), 73 (100),
56 (20)].
Preparation of 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline Hydro-
chloride (8): A solution of 1f (2.0 g, 6.1 mmol) and aqueous formal-
dehyde (36%, 1.0 mL, 13.4 mmol) in 170 mL MeOH was stirred at
room temp. for 17 h. After a treatment with charcoal at room temp.
(for at least 5 min) and solvent removal under reduced pressure,
10 mL of DMSO were added and the solution was heated at 50°C
for 3 h. The solvent was distilled at ca. 0.5 mbar, the residue dis-
solved in the minimum amount of iPrOH and the solution was
Acetylation of Hexahydro-5-methyl-2-phenyl-1,2,4-triazin-6-one
(3a): A solution of acetyl chloride (0.04 mL, 0.56 mmol) and 3a added dropwise to AcOEt under stirring in order to let a white
(0.025 g, 0.13 mmol) in pyridine (1.0 mL) was stirred at 40°C dur-
ing 40 min in a sealed tube. GC-MS analysis of the neutralised
reaction mixture showed the presence of the monoacetyl derivative
of 3a [MS (70 eV); m/z (%): 233 [Mϩ] (29), 192 (26), 191 (100), 162
solid precipitate. It was filtered and obtained in spectroscopically
pure form 8 (73%), m.p. (dec.) ϭ 215°C. Ϫ IR (KBr): ν˜ ϭ 3400
cmϪ1, 3215, 1690, 1603, 1499. Ϫ MS (70 eV); m/z (%): 318 [Mϩ]
(13), 215 (13), 211 (33), 183 (24), 171 (50), 170 (30), 169 (71), 168
(18), 134 (18) 120 (20) 93 (4), 92 (7), 65 (15), 57 (15), 56 (39), 44 (100), 167 (42), 144 (65), 143 (88), 140 (26), 130 (30), 93 (75), 77
1
(12), 43 (26)] as the sole product.
(18), 66 (32). Ϫ H NMR ([D6]DMSO, 100°C, the sample should
Eur. J. Org. Chem. 1999, 2943Ϫ2948
2947

G. Verardo, N. Toniutti, A. Gorassini, A. G. Giumanini
FULL PAPER
[5c]
Soc., (C) 1971, 1615Ϫ1618. Ϫ
S. G. Alexeev, V. N. Charu-
be very dilute): δ ϭ 3.00Ϫ3.52 (m, 2 H), 4.25Ϫ4.55 (m, 3 H),
6.70Ϫ7.55 (m, 9 H), 10.38 (s, 1 H), 11.01 (s, 1 H). Ϫ 13C NMR
([D6]DMSO, 100°C): δ ϭ 23.1, 40.4, 54.1, 104.4, 111.1, 112.5,
117.8, 118.7, 121.3, 125.7, 126.3, 128.3, 136.3, 148.6, 168.2. Ϫ 13C
NMR ([D6]DMSO, 45°C; the two (E/Z) isomers, indicated with A
and B, were present in ca. 1:12 ratio): δ ϭ 22.4 (A), 23.2 (B), 40.4
(B), 53.0 (A), 53.9 (B), 104.5 (B), 111.4 (B), 112.4 (B), 113.0 (A),
117.4 (A), 117.8 (B), 118.9 (B), 119.0 (B), 120.0 (A), 121.6 (B),
125.7 (B), 126.5 (B), 128.7 (B), 129.0 (A), 136.3 (B), 148.6 (B),
168.2 (B). Ϫ C18H19ClN4O (342.8): calcd. C 63.06, H 5.59, N 16.34;
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Acknowledgments
Financial support was obtained from the Italian National Research
Council (95.01044.CT03, 96.027420.CT03 to A.G.G.) and Italian
Ministry of University, Sciences and Technology (MURST 40%
and 60% 1993Ϫ95 to A.G.G., MURST 60% 1994Ϫ96 and
MURST 40% 1995 to G.V.). N.T. is the recipient of a scholarship
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