Synthesis, Structure, and Biological Activity of Products of Reactions of 3,4-Dioxohexane-1,6-dioic Acid Esters with 2-Aminophenol

Article abstract of DOI:10.1134/S1070363218070022

Bioactive derivatives of 1,4-benzoxazine have been prepared via reactions of 3,4-dioxohexane-1,6- dioic (ketipic) acid esters with 2-aminophenol. (2'Z)-2,2'-(2-Hydroxy-2H-1,4-benzoxazin-2-yl-3-ilidene)diacetic acid esters or (2Z)-[2-oxo-2H-1,4-benzoxazin-

Full text of DOI:10.1134/S1070363218070022

ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 7, pp. 1363–1368. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © P.P. Mukovoz, P.A. Slepukhin, E.A. Danilova, O.P. Aysuvakova, A.P. Glinushkin, 2018, published in Zhurnal Obshchei Khimii,
2018, Vol. 88, No. 7, pp. 1070–1075.
Synthesis, Structure, and Biological Activity of Products
of Reactions of 3,4-Dioxohexane-1,6-dioic Acid Esters
with 2-Aminophenol
P. P. Mukovoza*, P. A. Slepukhinb,c, E. A. Danilovad,
O. P. Aysuvakovaa, and A. P. Glinushkina
aAll-Russian Research Institute of Phytopathology, ul. Institut 5, Bolshie Vyazemy, 143050 Russia
*e-mail: mpp27@mail.ru
b Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
c Ural Federal University, Yekaterinburg, Russia
d Ivanovo State University of Chemistry and Technology, Ivanovo, Russia
Received February 8, 2018
Abstract―Bioactive derivatives of 1,4-benzoxazine have been prepared via reactions of 3,4-dioxohexane-1,6-
dioic (ketipic) acid esters with 2-aminophenol. (2'Z)-2,2'-(2-Hydroxy-2H-1,4-benzoxazin-2-yl-3-ilidene)diacetic
acid esters or (2Z)-[2-oxo-2H-1,4-benzoxazin-3(4H)-ylidene]acetic acid esters can be formed depending on the
conditions. The structures of the products of dialkyl ketipate esters reactions with 2-aminophenol were
determined by means of X-ray diffraction. It has been demonstrated that the prepared compounds exhibit
antimycotic activity against test cultures of plant pathogenic fungi (Fusauium sp., Alternarium sp., and
Bipolaris soraciniana).
Keywords: esters of 3,4-dioxohexane-1,6-dioic acid, dialkyl ketipates, 2-aminophenols, benzoxazines, antimycotic
activity
DOI: 10.1134/S1070363218070022
Reactions of 3,4-dioxohexane-1,6-dioic (ketipic)
acid esters 1a–1d [1, 2] with 2-aminophenols in
ethanol result the formation of (2'Z)-2,2'-(2-hydroxy-
2H-1,4-benzoxazin-2-yl-3-ilidene)diacetic acid esters
2a–2h; structure of these compounds has been
discussed in [3, 4]. The obtained compounds exhibit
antibacterial activity [5]. It should be noted that the
structure of esters 2 has not been determined so far, the
processes taking place in other solvents have not been
studied, and antimycotic activity of these compounds
has not been explored.
The obtained crystals of compounds 2b and 3a
were studied by means of X-ray diffraction. According
to the obtained data, compound 2b crystalized in chiral
space group, forming conglomerate. In the crystal,
molecules of compound 2b existed in the form of
stable cyclic O,O(C2)-hemiacetal 2A (Fig. 1). Unfor-
tunately, the absence of heavy atoms in the structure
did not allow determination of the absolute con-
figuration of the molecules in the crystal using
anomalous scattering effect. The benzoxazole unit in
the molecule of compound 2b was not planar and
existed in the pseudo sofa conformation. The С2 atom
deviated from the mean-square C3O1N4C4C9 plane by
0.567 Å; other atoms of the oxazine cycle were in the
same plane, the deviation not exceeding 0.1 Å. A hyd-
roxyl group of the hemiacetal was in the axial position
and formed a non-planar six-membered H···О=C-
chelate unit involving the carbonyl group of ethoxy-
carbonylmethyl fragment due to intramolecular hyd-
rogen bonding.
We investigated the reactions of dialkyl ketipates
1a–1d with 2-aminophenol in an acetic acid medium.
As a result, unexpected derivatives of compounds 2,
(2Z)-[2-oxo-2H-1,4-benzoxazine-3(4H)-ylidene]acetic
acid 3a–3d, were isolated. The formation of these
products has been observed in the reaction of
oxaloacetic acid esters with 2-aminophenol (Scheme 1)
[3]. The structure of compounds 3 has been discussed
in [3, 6].
1363

1364
MUKOVOZ et al.
Scheme 1.
O
OAlk
H
N
(EtOH)
O
_H2O
H
O
X
O
H2N
HO
X = H, NO2
O
O
OAlk
OAlk
AlkO
X
2a_2h (2A)
OAlk
O
H
O
O
1a_1d
N
(AcOH)
_H2O
_MeCOOAlk
O
O
3a_3d
Х = Н; Alk = Me (a), Et (b), Pr (c), Bu (d), X = NO2; Alk = Me (2e), Et (2f), Pr (2g), Bu (2h).
The conformation of ethoxycarbonylmethylidene
unit (a six-membered chelate unit, planar within 0.01 Å)
was determined by the intramolecular NH···О=С-type
hydrogen bonding with NH-group of benzoxazine.
That chelate fragment was in general in the same plane
with the heterocycle, evidencing the conjugation of
NH-chelate with heterocycle into a common π-system.
Another evidence of that fact was the averaging of
lengths of “single” N4–C3 1.346(5), N4–C4 1.375(6),
and C14–C15 1.426(6) Å bonds and “double” C3–C14
1.343(6) Å bond; such behavior is typical of con-
jugated systems (Table 1). There were no inter-
molecular bonds in a crystal of compound 2b, yet a
developed system of short contacts, mainly of the
Сsp3–H···O-type, was observed. The contacts between
the O2 oxygen atom of the hemiacetal hydroxyl group
and the H12A proton of the ethoxyl methylene group
and between the H10A proton of the CH2COOEt
methylene group and the O3 carbonyl oxygen atom of
the same fragment of an adjacent molecule were the
most important. The X-ray diffraction data con-
tradicted the existence of linear enamine forms 2B and
2C in the crystal of compounds 2, which could not be
ruled out a priori (Scheme 2). It should be noted that
compounds 2 exists in form 2A in solutions as well [3, 4].
According to the X-ray diffraction data, the mole-
cules of compound 3a in crystal were planar within
0.07 Å (except for protons of methyl group) and
existed in the form of 1,4-benzoxazine-2-one, the
proton of the secondary amino group forming a six-
membered H···О=N-chelate fragment with the car-
bonyl group of the methoxycarbonylmethylidene unit
(Fig. 2). The benzoxazine fragment formed a common
π-system with the NH-chelate. The conjugation of the
NH-chelate with the heterocycle was indicated, for
instance, by the averaging of length of the “single”
N4–C3 1.367(3), N4–C5 1.388(3), and C12–C13 1.453(3) Å
and “double” C3–C12 1.342(3) Å bonds as well as
“single” O1–C2 1.355(3) and C2–C3 1.492(3) Å bonds
(Table 1).
Molecules of compound 3a formed a parquet-
stacking packing in the crystal and contained a system
of short СН···О-type contacts (Fig. 3). The contacts
between the O11 oxygen atom of the benzoxazine oxo
Fig. 1. General view of a molecule of compound 2b in the
crystal.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 7 2018

SYNTHESIS, STRUCTURE, AND BIOLOGICAL ACTIVITY OF PRODUCTS
Table 1. Selected bond lengths in compounds 2b and 3a
1365
2b
3а
Bond
d, Å
Bond
d, Å
Bond
d, Å
1.355
С2–О1
С9–О1
С2–С3
С2–O2
O2–H2
1.418
1.360
1.481
1.390
0.940
N4–C3
N4–C4
N4–H4
С4–С9
С10–С11
1.346
1.375
0.88
С2–О1
С10–О1
С2–С3
С2–O11
С3–С12
1.395
1.492
1.207
1.342
1.355
1.466
С2–С10
С2–С3
С3–C14
С14–С15
С15–O6
1.474
1.481
1.343
1.426
1.205
С11–O3
С11–O4
С12–O4
С15–O5
С16–O5
1.199
1.311
1.433
1.335
1.406
С12–С13
С13–O14
N1–C3
N4–C5
N4–H4
1.357
1.218
1.367
1.388
0.86
Scheme 2.
H
O
O
O
O
AlkO
AlkO
OAlk
X
OAlk
X
O
N
O
N
H
H
HO
HO
2B
2C
X = H, NO2.
group and the H16A proton of the methoxy unit and
between the O1 oxygen atom of oxazoline heterocycle
and the H9 proton of the aromatic ring of an adjacent
molecule were the most important. There were no
significant π–π-contacts and intermolecular hydrogen
bonds in the crystal.
Reaction of compounds 1a–d with 2-aminophenol
likely started with nucleophilic addition of the reactant
amino group to the carboxylic group C3 of the
substrate, to form the linear enamine 2B (Scheme 3).
Further reaction might occur via two paths. The first
one consists in heterocyclization of the enamine
Fig. 2. General view of a molecule of compound 3a in the
crystal.
Fig. 3. Molecular packing of compound 3a in a crystal.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 7 2018

1366
MUKOVOZ et al.
Scheme 3.
δ−
O
H2N
HO
O
OAlk
O
H
N
AlkO
O
O
δ+
OAlk
δ+
AlkO
O
O
N
OAlk
H
O
H
O
O
O
δ_
HO
OAlk
_H2O
2B
2A
+H2O
_MeCOOAlk
(AcOH)
(OH)2 O
O
OAlk
OH
H
N
AlkO
O
OAlk
AlkO
OAlk
H
N
O
O
HN
HO
O
HN
_MeCOOAlk
O
O
O
O
HO
3
B
3
А
leading to the intermediate О,О-hemiacetal 2A [3, 4]
which eliminates the alkyl acetate in the presence of
acetic acid, thus affording compounds 3a–d. The
second way is less probable: the C4–C5 bond of
enamine 2B can be hydrolyzed in the acetic acid
medium with the formation of geminal diol A which
can further eliminate alkyl acetate to give intermediate
B is formed. Further heterocyclization of structure B
will lead to compounds 3a–3d.
Since biological activity of compounds 3a–3d
which are structural analogs of bioactive 3-ilidene
derivatives of 1,4-benzoxazine-2-one [7] has not been
studied so far, we investigated antimycotic activity of
compounds 3a, 3d, and 2a–2h (Table 2) against test
cultures of plant pathogenic fungi (Fusauium sp.,
Alternarium sp., Bipolaris soraciniana). It was shown
that compounds 2c, 2e, 2f, 2h were the most active
against Fusauium sp. test culture, the activity being
comparable to that of phytolavin reference sample.
Compounds 3a and 3d showed moderate activity
against Fusauium sp. teat culture, not exceeding that of
phytolavin and previkur reference samples. Com-
pounds 2a, 2e, 2g, and 3d demonstrated moderate
activity against Alternarium sp. test culture, not
exceeding that of phytolavin and previkur reference
samples. Compounds 2f and 2g demonstrated
moderate activity against Bipolaris soraciniana test
culture, not exceeding that of phytolavin and previkur
reference samples. Other studied compounds did not
reveal noticeable activity. It should be noted that
relatively high activity of hemiacetals 2f and 2h
against Fusauium sp. may be caused by the presence of
nitro group at position 7 of benzoxazine heterocycle in
molecules of these compounds.
Table 2. Antimycotic activity of compounds 2 and 3a
Lowest inhibiting concentration, µg/mL
Comp. no.
Fusauium
Alternarium
Bipolaris
sp.
sp.
soraciniana
2a
н/а
125
125
31
500
No active
500
No active
No active
No active
No active
500
2c
2e
2f
No active
500
2g
500
63
2h
No active
No active
500
500
3a
500
250
16
No active
No active
63
3d
Phytolavin
Previkur
63
8
8
31
a
The data are statistically significant with respect to the control
sample (p = 0.001).
In summary, the reaction of dialkyl ketipate 1a–1d
with 2-aminophenol in acetic acid medium does not
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 7 2018

SYNTHESIS, STRUCTURE, AND BIOLOGICAL ACTIVITY OF PRODUCTS
1367
lead to compounds 2, rather giving esters of (2Z)-[2-
oxo-2H-1,4-benzoxazin-3(4H)-ylidene]acetic acid 3a–3d.
The studied compounds exhibit different anti-mycotic
activity against test cultures of plant pathogenic fungi:
Fusauium sp., Alternarium sp., and Bipola-ris
soraciniana. Benzoxazine derivatives bearing nitro
group in the heterocycle are the most active; their
activity is comparable to that of phytolavin.
General procedure for synthesis of (2Z)-[2-oxo-
2H-1,4-benzoxazin-3(4H)-ylidene]acetic acid esters
(3a–3d). 10 mmol of 2-aminophenol in 25 mL of
glacial acetic acid was added to 10 mmol of compound
1a–1d and refluxed for 5–10 min. The solvent was
evaporated; the residue was dried and crystallized from
ethanol or ethyl acetate.
Methyl ester of (2Z)-[2-oxo-2H-1,4-benzoxazine-
3(4H)-ylidene]acetic acid (3a). Yield 0.92 g (42%),
mp 122–124°С.
EXPERIMENTAL
The X-ray diffraction data were collected on with
an Xcalibur 3 automated 4-circle diffractometer
equipped with a CCD detector via a standard proce-
dure (ω-scanning with 1° step, monochromatic МоKα-
radiation) at 295(2) K. Empirical correction for
absorption was made. The structures were solved via
the direct statistical method and refined under aniso-
tropic approximation for the non-hydrogen atoms via
the full-matrix least squares method over F2. Hydrogen
atoms of the С–Н bonds were placed in the
geometrically calculated positions and refined under
isotropic approximation. Positions of the OH protons
were refined independently. The calculations were
performed using Olex software [8] implemented in the
software package [9].
Ethyl ester of (2Z)-[2-oxo-2H-1,4-benzoxazine-
3(4H)-ylidene]acetic acid (3b). Yield 1.14 g (49%),
mp 100–103°С.
Propyl ester of (2Z)-[2-oxo-2H-1,4-benzoxazine-
3(4H)-ylidene]acetic acid (3c). Yield 0.84 g (34%),
mp 87–89°С.
Butyl ester of (2Z)-[2-oxo-2H-1,4-benzoxazine-
3(4H)-ylidene]acetic acid (3d). Yield 0.68 g (26%),
mp 79–81°С.
The antimycotic activity of compounds 2a–2h against
the Fusauium sp., Alternarium sp., and Bipolaris
soraciniana fungi test cultures was determined via
serial dilution method in the Saburo solid nutrient
medium; the experiments were run in triplicate. The
compounds were dissolved in DMSO; the obtained
solution was diluted with sterile physiological solution
to concentrations from 1000 down to 8 µg/mL. The
investigated samples were placed into the test tubes
with the medium molten and cooled to 56°C, the
mixture was vigorously stirred. The medium was
inoculated with washing of the test culture in sterile
physiological solution. The corresponding test cultures
were obtained by growing the collection samples of
Fusauium sp., Alternarium sp., or Bipolaris
soraciniana in the sterile Saburo nutrient medium at
18–22°С for two weeks. The nutrient medium without
any additive was used as negative control, the data
were collected after 48 h of incubation. Phytolavin and
previkur were used as reference drugs. Statistical data
processing was performed using Excel 2012 software.
Major crystallographic parameters of compound
2b: monoclinic crystals, space group P21, unit cell
parameters: a 10.389(2), b 5.5083(11), c 14.009(3) Å,
α 90.00°, β 105.836(18)°, γ 90.00°, μ 0.106 mm–1.
3836 reflections were collected including 1995 inde-
pendent ones (Rint 0.0533) [864 with I > 2σ(I)] over
3.02° < θ < 28.34°. Final refinement parameters: R1
0.1311, wR2 0.0560 (all reflections), R1 0.0483, wR2
0.0505 [reflections with I > 2σ(I)].
Major crystallographic parameters of compound 3a:
monoclinic, space group P21/c, unit cell parameters: a
10.7651(13), b 5.1924(6), c 18.0267(16) Å, α 90.00°, β
92.350(9)°, γ 90.00°, μ 0.112 mm–1. 4605 reflections
were collected including 2486 independent ones (Rint
0.0330) [987 with I > 2σ(I)] over 2.63° < θ < 26.35°.
Final refinement parameters: R1 0.1521, wR2 0.1085
(all reflections), R1 0.0463, wR2 0.0747 [reflections
with I > 2σ(I)].
CONFLICT OF INTERESTS
The complete structural data on compounds 2b and
3a were deposited at the Cambridge Crystallographic
Data Center (CCDC 1581166 and 1405317, respectively).
No conflict of interest was declared by the authors.
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