Functionalization of Quinazolin-4-Ones Part 2#: Reactivity of 2-Amino-3, 4, 5, or 6-Nitrobenzoic Acids with Triphenylphosphine Thiocyanate, Alkyl Isothiocyanates, and Further Derivatization Reactions

Article abstract of DOI:10.1002/jhet.2235

2-amino-3, 4, 5, or 6-nitrobenzoic acids were reacted with PPh₃(SCN)₂ and alkyl isothiocyanates to give 5, 6, 7, or 8-nitro-2-thioxo-3-substituted quinazolin-4-ones, respectively. The position of the nitro group was found to have sig

Full text of DOI:10.1002/jhet.2235

Month 2014 Functionalization of Quinazolin-4-Ones Part 2#: Reactivity of 2-Amino-3,
4, 5, or 6-Nitrobenzoic Acids with Triphenylphosphine Thiocyanate, Alkyl
Isothiocyanates, and Further Derivatization Reactions
*
Jacob T. Heppell and Jasim M. A. Al-Rawi
School of Pharmacy and Applied Science, La Trobe University Bendigo, P.O. Box 199, Bendigo 3550, Australia
*
E-mail: J.Heppell@latrobe.edu.au
Additional Supporting Information may be found in the online version of this article.
Received December 18, 2013
DOI 10.1002/jhet.2235
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
2-amino-3, 4, 5, or 6-nitrobenzoic acids were reacted with PPh3(SCN)2 and alkyl isothiocyanates to give
5, 6, 7, or 8-nitro-2-thioxo-3-substituted quinazolin-4-ones, respectively. The position of the nitro group was
found to have significant influence on the outcome of the reactions. Similarly, the nature of the substituent at
position 8 (NO2, NH2, NH(C═O)CH3) in 8-substituted-2-methylthio quinazolin-4-ones was also found to
significantly influence their reactivity towards morpholine. A selection of the products were also tested for
in vitro antibacterial activity but little activity was observed.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
2-(N-methylamino)benzoic acid to their corresponding
2-thioxo quinazolin-4-ones in good yields [22]. This
method is cheap and does not require harsh conditions
but must be performed under strictly anhydrous conditions.
In continuation of our previous work, we are reporting on
the reactivity of 2-amino-3, 5, or 6-nitrobenzoic acids with
triphenylphosphine thiocyanate (PPh3(SCN)2) and alkyl
isothiocyanates (RNCS), which are two reagents employed
in the synthesis of substituted 2-thioxo quinazolin-4-ones
from substituted 2-aminobenzoic acids. Additionally, the
synthesis of 8-(nitro and amino)-2-morpholine quinazolines
is presented and its reactivity compared with our previously
reported work regarding 7-nitro quinazolines [23].
Quinazolines form a large family of compounds that are
well recognized for their ability to show a broad range of
biological activities, which are influenced significantly by
the type of substituents and where they are placed around
the quinazoline structure [1]. Observed biological activities
include, but are not limited to, CNS depressant [1,2],
anti-inflammatory [1,3–5], diuretic [1], antihypertensive
[1], analgesic [4], anticancer [6–8], antihypoxic [9], hypo-
glycemic [10], and antimicrobial [11–15] activities. The
ability to synthesize and functionalize quinazolines is
therefore of great importance, and the methods employed
will reflect the structure of the desired quinazolines. Syn-
thesis of 7, or 8-substituted-2-morpholino quinazolines
from 7, or 8-substituted-2-thioxo quinazolin-4-ones forms
the continuum of this research for the development of po-
tential DNA-PK and PI3K inhibitors, and antiplatelet com-
pounds, which have been observed for the chromone and
benzoxazine analogues [16–18]. There are many reported
methods for 2-thioxo quinazolin-4-one synthesis in the lit-
erature; some of which can possess inherent limitations to
functionalization and requires harsh conditions [19–21].
Recently, triphenylphosphine thiocyanate (PPh3(SCN)2)
has been successful in cyclizing 2-aminobenzoic acid and
RESULTS AND DISCUSSION
Synthesis of 8, 7, 6, or 5-nitro-2-thioxo-3-substituted
quinazolin-4-one (4a-l). Previously, we reported that compound
3b (4-NO2) was isolated from the reaction of compound 2b
(4-NO2) with PPh3(SCN)2 [23]. In continuation of our
investigation, 2-amino-3, 5, or 6-nitrobenzoic acid (2a, 2c–d),
synthesized from 6, 5, 4, or 3-nitro-2-methylanilines (1a–d)
(see Supporting Information for details), were likewise reacted
under the same conditions to determine the stability of their
benzoyl isothiocyanate intermediates (3a, 3c–d) (Scheme 1).
© 2014 HeteroCorporation

J. T. Heppell and J. M. A. Al-Rawi
Vol 000
Scheme 1. Synthesis of 5, 6, 7 or 8-nitro-2-thioxo quinazolin-4-ones. (i) = PPh3(SCN)2, 0°C to RT, reflux 16–20 h. (ii) = K2CO3, acetonitrile, reflux 1.5 h.
(iii) = R1NCS, TEA, ethanol, reflux, 6 h or R1NCS, TEA, acetonitrile, mw, 140°C, 2 h, P = 60–100 W.
Each of the compound 2a–d behaved in a different
manner when reacted with PPh3(SCN)2. Compound 2a
(3-NO2) formed the corresponding 8-nitro-2-thioxo
quinazolin-4-one (4a). Compound 2b (4-NO2), as previously
reported [23], yielded benzoyl isothiocyanate 3b. Compound
2c (5-NO2) gave a crude product containing ~80% of the
intermediate benzoyl isothiocyanate 3c and ~20% product
4c as estimated by 1H-NMR. However, compound 2d
(6-NO2) did not give any identifiable product. The cycliza-
tion of the benzoyl isothiocyanate intermediates 3b and 3c
to 4b and 4c, respectively, was achieved by refluxing with
potassium carbonate (K2CO3) in acetonitrile followed by
acidification with HCl.
The reaction of 2-aminobenzoic acids with alkyl
isothiocyanates is a well-established method for the synthesis
of 2-thioxo-3-substituted quinazolin-4-ones (Scheme 2) [24].
The outcome of the reaction of 2-aminobenzoic acids 2a–d
with methyl and benzyl isothiocyanate was found to be
dependent on the position of the nitro group, the alkyl
isothiocyanate employed, and the reaction conditions. When
the nitro group was meta to the amino group, as seen in com-
pounds 2b (4-NO2) and 2d (6-NO2), the reaction with methyl
and benzyl isothiocyanate proceeded easily under thermal re-
flux to give compounds 4f (7-NO2, R1 = CH3), 4j (7-NO2,
R1 = CH2Ph), 4h (5-NO2, R1 = CH3), and 4l (5-NO2,
R1 = CH2Ph) in high yields. However, if the nitro group
was positioned ortho/para as seen in compounds 2a
(3-NO2) and 2c (5-NO2), little to no reaction was observed.
Compound 2a (3-NO2) reacted only with benzyl
isothiocyanate under microwave conditions to give com-
pound 4i (8-NO2, R1 = CH2Ph); thermal reflux with methyl
or benzyl isothiocyanate yielded no product. Compound 2c
(5-NO2) successfully reacted with methyl and benzyl isothio-
cyanate under thermal reflux to give 4g (6-NO2, R1 = CH3)
and 4k (6-NO2, R1 = CH2Ph), respectively, in low yields
(10% and 16%, respectively), which was improved upon
under microwave conditions (56% and 67%, respectively)
(Schemes 3 and 4).
Synthesis of 8-substituted-2-morpholino quinazolines (6a–e,
7a–c). It is known that 2-amino quinazolin-4-ones can be
Scheme 2. Synthesis of 8-substituted-2-methylthio quinazolin-4-ones.
(i) = KHCO3, CH3I, Acetone, reflux, 1.5 h. (ii) = K2CO3, CH3I, acetone,
reflux, 1.5 h. (iii) = Fe, AcOH, ethanol, reflux 1.5 h or SnCl2.2H2O,
ethylacetate, reflux, 8 h. (iv) = Ac2O, AcOH, reflux, 30 min.
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Month 2014
Reactivity of 2-Amino-3, 4, 5, or 6-Nitrobenzoic Acids with Triphenylphosphine
Thiocyanate, Alkylisothiocyanates, and Further Derivatization Reactions
Scheme 3. Synthesis of 8-amino-2-morpholino quinazolines. (i) = morpholine, reflux, 3–72 h. (ii) = K2CO3, CH3I or benzyl bromide, acetone, reflux,
1.5 h. (iii) = SnCl2.2H2O, ethylacetate, reflux, 8 h. (iv) = Fe, HCl, ethanol, reflux 1.5 h.
synthesized by treating 2-alkylthio quinazolin-4-ones with
amines [2]. From our previous investigations, it was shown
that substituents on the 7 position (NO2, NH2, NH(C = O)
CH3) did not affect the susceptibility of the methylthio group
toward morpholine [23]. The 8 position, however, is likely to
The nitro group can then be converted to other func-
tional groups such as an amino, which can then undergo
many reactions typical of the primary aromatic amines.
Further alkylation of 6a (R1 = NO2, R2 = H), according to
the previously reported procedure [23], with K2CO3 and
methyl iodide or benzyl bromide gave 4-O-alkylated prod-
ucts 7a–b. Compound 6d (R2 = H) was prepared in good
yields (60%) by reduction of compound 6a (R1 = NO2,
R2 = H) using SnCl2.2H2O. In contrast, reduction by iron
and hydrochloric acid in ethanol was preferred for the pro-
duction of compounds 6e (R2 = CH3) and 7c from 6b
(R1 = NO2, R2 = CH3) and 7a (R2 = CH3), respectively, as
they were both stable to strong acids, the method was
faster, and generally gave higher yields and purer products.
Structures of all the newly synthesized compounds were
confirmed by analysis of 1H and 13C-NMR spectroscopy in
addition to Fourier transform infrared and microanalysis
exert
a different electronic effect. The 2-methylthio
compounds 5a (R1 =H) and 5b (R1 =CH3) were readily
synthesized by refluxing in acetone with KHCO3 and K2CO3,
respectively, and CH3I. Reduction of compound 5a (R1 =H)
with SnCl2.2H2O gave 5c, which was subsequently
acetylated to give compound 5d (Scheme 2).
Substituents on the 8 position were found to signifi-
cantly affect the reactivity of the 2-methylthio compounds
5a–d with morpholine (Scheme 3). Compound 5a
(R1 = 8-NO2, R2 = H) reacted readily when refluxed in
neat morpholine and was complete after 3 h compared
with the 8 h required for the previously reported 7-nitro
analogue [23]. Compound 5c (R1 = 8-NH2, R2 = H) did
not yield any substantial amount of product even after
3 days of refluxing in neat morpholine. Compound 5d
(R1 = 8-NH(C = O)CH3, R2 = H) reacted to completion
only after 3 days of refluxing in neat morpholine as
was determined by thin layer chromatography; micro-
wave reflux did not improve the outcome. Additionally,
the 2-methylthio group of the N3 methyl compound 5b
(8-NO2, R2 = CH3) was easily replaced by morpholine
to yield compound 6b (8-NO2, R2 = CH3) without the
need to convert it to a sulfoxide as was required for
the previously reported 7-NO2 analogue of 5b [23].
The 8-nitro group can thus prove useful as it facili-
tates the synthesis of 2-amino quinazolines by increasing
the susceptibility of the 2-methylthio group toward
secondary amines.
1
(see Supporting Information for all H and 13C spectra).
Synthesis of 2-amino-N-(substituted(carbono or carbamo)
thioyl)-4-nitrobenzamides (8a–b).
As isothiocyanates
(R-NCS) undergo addition reactions with amines, the
benzoyl isothiocyanate intermediate, 3b, was treated with
benzylamine and morpholine to give compounds 8a and 8b,
respectively (Schemes 4). Further reactions, discussions, and
experimental details are recorded in the Supporting Information.
Antibacterial properties. The antibacterial properties of
quinazolin-4-ones have been widely reported in the scientific
literature [14,25–28]. To assess the antibacterial properties of
the newly synthesized quinazolines, disk diffusion assays
were performed against the bacterial strains Escherichia coli,
Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus
aureus, and Enterococcus faecalis with Ciprofloxacin and
Penicillin G potassium salt as positive controls (Table 1).
Journal of Heterocyclic Chemistry
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J. T. Heppell and J. M. A. Al-Rawi
Vol 000
Scheme 4. Reaction of 2-amino-4-nitrobenzoyl isothiocyanate 3b with
aliphatic amines. (i) = aliphatic amine, dioxane, 50°C, 20 min.
EXPERIMENTAL
Chemistry. Infrared spectra were obtained using a Perkin
Elmer FT-IR 1720× spectrometer (Perkin Elmer Ltd.,
Buckinghamshire, Seer Green, UK). 1H-NMR and 13C-NMR
spectra were obtained using
a Bruker AC 200 NMR
spectrometer (Bruker, Banner Lane, Coventry, UK) at 200 and
50 MHz, respectively. All 1H-NMR and 13C-NMR spectral
results are recorded as chemical shifts (δ) relative to the internal
TMS for proton and 77.0 ppm in CDCl3 solvent and 39.5 ppm
in DMSO-d6 solvent for 13C-NMR. 1H-NMR multiplicities are
expressed as singlet (s), broad singlet (bs), doublet (d), double
doublet (dd), triple doublet (td), triplet (t), double triplet (dt),
quartet (q), multiplet (m), and broad multiplet (bm). Microanalysis
was performed by Chemical and Microanalytical Services,
Australia. Melting point determinations were carried out using a
Stuart Scientific melting point apparatus and all melting points are
uncorrected. All microwave reactions were carried out in a
Milestone Microwave Lab Station. All starting materials were
purchased from major chemical companies (Sigma Aldrich, Alfa
Aesar, Merck) and used without any further purification. All
solvents were purchased as laboratory grade and were used
without further purification unless otherwise stated.
Dichloromethane was dried over and distilled from calcium
hydride and stored over 0.4nm molecular sieves.
Table 1
Antibacterial data of the newly synthesized compounds.
Disk diffusion assay diameter of inhibition zone (mm)
No.
B. subtilis
S. aureus
4a
4b
4c, g-i, l
4f
4j
4 k
6a–e, 7a–c
8a
10
8
À
À
8
À
À
13
14
37
33
10
À
À
11
9
13
À
8
Synthesis of 2-amino-3, 4, 5, or 6-nitrobenzoic acids (2a–d)
8b
9
28
23
General procedure A: synthesis of 2a–d.
Synthesis of
Ciprofloxacin
Penicillin G (K salt)
2-amino-3, 4, 5, or 6-nitrobenzoic acids (2a–d) from 6, 5, 4, or
3-nitro-2-methylanilines, respectively, was performed according
to a previously reported procedure [23] except for 6-nitro-2-
aminobenzoic acid (2d) whereby the hydrolysis of the
acetylamino group was performed using 70 mL of 50% (v/v)
H2SO4 at 50°C for 16 h followed by neutralization with NaOH
then filtration of the precipitated product 2d (see Supporting
Information for experimental details).
Synthesis of 8, 7, 6, or 5-nitro-2-thioxo-3-substituted
quinazolin-4-one (4a–d)
General procedure B: synthesis of triphenylphosphine
thiocyanogen (PPh3(SCN)2). PPh3(SCN)2 (6.0 mmol) was freshly
Minus sign (À) = no zone of inhibition was observed around the 6 mm
blank susceptibility disks.
Compared with the positive controls, the tested com-
pounds showed very limited antibacterial activity. All the
7-nitro-2-thioxo quinazolin-4-ones 4b, f, and j showed
slight antibacterial activity against one of or both the
gram-positive bacteria B. subtilis and S. aureus. Activity
was also shown with compound 4a (8-NO2) but dimin-
ished with addition of the benzyl group at position 3 (4i)
unlike compound 4k (6-NO2), which showed improved
activity upon addition of a benzyl group. None of the 2-
morpholino compounds (6a–e, 7a–c) showed antibacterial
activity, and none of the tested compounds were active
against E. coli, P. aeruginosa, and E. faecalis.
prepared in situ according to a previously reported procedure [23].
General procedure C: reaction of 2-amino-3, 4, or
5-nitrobenzoic acids (2a-c) with PPh3(SCN)2 and cyclization of
stable benzoyl isothiocyanate intermediates 3b and 3c. Products
2a and 2b (4.8mmol) were reacted with freshly prepared PPh3
(SCN)2 according to the previously reported procedure [23] to
give 4a and 3b. Product 2c was reacted according to a modified
version of the same procedure in which the reaction mixture was
allowed to stir at 0°C for 8h, warm up to room temperature
overnight then refluxed for 24h to give a mixture of 3c(80%) and
4c(20%). Product 3b and the crude mixture of 3c(80%)/4c(20%)
were then reacted with K2CO3 in acetonitrile according to the
previously reported procedure to give 4b and 4c, respectively [23].
CONCLUSION
PPh3(SCN)2 has shown to be a useful reagent for
2-amino-3, 4, or 5-nitrobenzoic acids but failed to react
with 6-nitro-2-aminobenzoic acid. Additionally, benzyl
isothiocyanate successfully reacted with 2-amino-3, 4, 5,
or 6-nitrobenzoic acids under thermal and/or microwave condi-
tions. However, methyl isothiocyanate only reacted with 2-
amino-4, 5, or 6-nitrobenzoic acids. The reactivity of 8-
substituted-2-methylthio quinazolin-4-ones toward morpholine
was also found to be influenced significantly by the nature of
the substituent at the 8 position; this was not the case with their
previously reported 7-substituted analogues [23].
8-Nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one (4a). Yellow
solid. Yield: 3.9 mmol (82%). Solvent: acetonitrile. Mp 246–247°
C. IR (KBr): 3319.7 (NH), 1693.5 (C═O), 1509.8 (s, NO2),
1
1313.0 (s, NO2) cmÀ1. H-NMR (DMSO-d6, T = 340 K): δ = 7.49
(t, J6–5 = J6–7 = 7.8Hz, 1H, H-6), 8.34 (dd, J5–6 = 8.0Hz,
J5–7 = 1.2 Hz, 1H, H-5), 8.54 (dd, J7–6 = 8.0 Hz, J7–5 = 1.2 Hz, 1H,
H-7), 11.34 (bs, 1H, NH), 12.93 (bs, 1H, NH) ppm. 13C-NMR
(DMSO-d6, T = 340 K): δ = 118.4, 123.4, 131.2, 133.3, 134.0,
134.2, 157.7, 174.5ppm. Anal. Calcd for C8H5N3O3S (223.21):
C, 43.05; H, 2.26; N, 18.83. Found: C, 43.11; H, 2.31; N, 19.01.
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Thiocyanate, Alkylisothiocyanates, and Further Derivatization Reactions
2-Amino-4-nitrobenzoyl isothiocyanate (3b). Yellow solid
with identical physical and spectroscopic data to those previously
reported [23]. Yield= 82%.
175.4 ppm. Anal. Calcd for C9H7N3O3S (237.24): C, 45.57; H,
2.97; N, 17.71. Found: C, 45.51; H, 3.04; N, 17.69.
3-Benzyl-8-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
7-Nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one (4b). Yellow
solid with identical physical and spectroscopic data to those
previously reported [23]. Yield = 93% from 3b and 76% from 2b.
6-Nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one (4c). Light
yellow solid. Yield: 2.3 mmol (48%). Solvent: ethanol. Mp
309–310°C (lit. mp = 267–268°C) [29]. IR (KBr): 3324.0
(m, NH), 3221.0 (m, NH), 1671.7 (s, C═O), 1341.0 (m, NO2)
(4i).
Pale yellow solid. Yield: 1.75 mmol (35%). Solvent:
diethyl carbonate. Mp 188–189°C. IR (KBr): 3334.9 (m, NH),
1685.1 (s, C═O), 1625.2 (m, NH bd), 1499.5 (s, NO2), 1313.3
(s, NO2) cmÀ1 1H-NMR (DMSO-d6, T = 340 K): δ = 5.68
.
(s, 2H, H-9), 7.25–7.40 (m, 5H, benzylic hydrogens), 7.53
(t, J6–5 = J6–7 = 8.0Hz, 1H, H-6), 8.41 (dd, J5–6 = 8.0 Hz,
J5–7 = 1.4 Hz, 1H, H-5), 8.59 (dd, J7–6 = 8.0 Hz, J7–5 = 1.4 Hz,
1H, H-7), 11.69 (bs, 1H, NH) ppm. 13C-NMR (DMSO-d6,
T = 340 K): δ = 49.1, 117.7, 123.6, 126.9, 127.0, 127.9, 131.5,
132.9, 133.2, 134.9, 135.4, 157.6, 175.4 ppm. Anal. Calcd for
C15H11N3O3S (313.33): C, 57.50; H, 3.54; N, 13.41. Found:
1
cmÀ1. H-NMR (DMSO-d6, T = 340 K): δ = 7.50 (d, J8–7 = 9.0Hz,
1H, H-8), 8.47 (dd, J7–8 =9.0 Hz, J7–5 = 2.6 Hz, 1H, H-7), 8.58
(d, J5–7 = 2.6Hz, 1H, H-5), 12.8 (bs, 2H, NH) ppm. 13C-NMR
(DMSO-d6, T = 340K): δ = 116.2, 117.0, 122.5, 129.5, 142.7,
144.2, 158.2, 175.4 ppm. Anal. Calcd for C8H5N3O3S (223.21):
C, 43.05; H, 2.26; N, 18.83. Found: C, 43.30; H, 2.49; N 18.80.
Synthesis of 3-substituted-8, 7, 6, or 5-nitro-2-thioxo-2,3-
dihydroquinazolin-4(1H)-one (4f-l)
C, 57.47; H, 3.62; N, 13.38.
3-Benzyl-7-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
(4j). Yellow solid with identical physical and spectroscopic
data to those previously reported [23]. Yield = 87%.
3-Benzyl-6-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
(4k). Light yellow solid. Yield: 0.8mmol (16%) and 3.35 mmol
(67%) from general procedures D and E, respectively. Solvent:
nitromethane. Mp 267–268°C. IR (KBr): 3280.9 (m, NH), 1670.1
General procedure D: reaction of 2-amino-3, 4, 5, or
6-nitrobenzoic acids (2a–d) with alkylisothiocyanates under
thermal conditions.
Products 2b–d (5.0 mmol) was reacted
with methyl and benzyl isothiocyanate (6.0 mmol) according to
previously reported procedure [24] to give 4f–h and 4j–l,
respectively. The products were used without any further
purification but can be purified by an appropriate technique.
Product 2d required a modified version in which the reaction
was allowed to proceed at 50°C for 24 h to give 4h and 4l.
General procedure E: reaction of 2-amino-3, 4, 5 or
6-nitrobenzoic acids with alkylisothiocyanates under microwave
(s, C═O), 1344.4 (s, NO2) cmÀ1
.
1H-NMR (DMSO-d6,
T = 340K): δ = 5.67 (s, 2H, H-9), 7.23–7.38 (m, 5H, benzylic
hydrogens), 7.57 (d, J8–7 = 9.0Hz, 1H, H-8), 8.51 (dd,
J7–8 = 9.0Hz, J7–5 =2.4 Hz, 1H, H-7), 8.64 (d, J5–7 = 2.4Hz, 1H,
H-5), 13.31 (bs, 1H, NH) ppm. 13C-NMR (DMSO-d6, T = 340 K):
δ = 48.7, 115.3, 117.0, 123.3, 126.7, 127.0, 127.9, 129.6, 142.8,
142.9, 158.2, 176.3 ppm. Anal. Calcd for C15H11N3O3S (313.33):
conditions.
Products 2c or 2a (5.0mmol), methyl, or benzyl
C, 57.50; H, 3.54; N, 13.41. Found: C, 57.43; H, 3.60; N, 13.57.
3-Benzyl-5-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
isothiocyanate (10.0 mmol), triethylamine (10.0mmol) were
suspended in 10mL acetonitrile in a 30 mL quartz tube and placed
in a 40 bar sealed housing. The reaction mixture was placed in a
Milestone Microwave Lab Station and heated to 140°C for 2 h
while sustaining a power level of 60–100 W. The acetonitrile was
then evaporated under reduced pressure, and the resulting solid
was triturated with minimal ether then collected by filtration with
suction to give 4g, 4k, and 4i, respectively. The product was used
without any further purification but can be purified by an
appropriate technique.
3-Methyl-7-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
(4f). Yellow solids with identical physical and spectroscopic
data to those previously reported [23]. Yield = 89%.
(4l). White solid. Yield: 4.5 mmol (90%). Solvent: methanol. Mp
242–243°C. IR (KBr): 3182.0 (m, NH), 1708.0 (C═O), 1621.0
(s, NH bd), 1541.9 (s, NO2) cmÀ1 1H-NMR (DMSO-d6,
.
T = 340K): δ = 5.62 (s, 2H, H-9), 7.23–7.36 (m, 5H, benzylic
hydrogens), 7.57 (dd, J8–7 =8.0 Hz, J8–6 = 1.0 Hz, 1H, H-8),
7.62 (dd, J6–7 = 8.0Hz, J6–8 = 1.0Hz, 1H, H-6), 7.89 (t, J7–6
=
J7–8 = 8.0Hz, 1H, H-7), 13.26 (bs, 1H, NH) ppm. 13C-NMR
(DMSO-d6, T = 340K): δ = 48.7, 106.1, 117.7, 118.2, 126.7,
127.0, 127.9, 135.7, 135.8, 139.9, 148.5, 155.8, 175.6 ppm. Anal.
Calcd for C15H11N3O3S (313.33): C, 57.50; H, 3.54; N, 13.41.
Found: C, 57.50; H, 3.64; N, 13.36.
Synthesis of 8-substituted-2-morpholino quinazolin-4-one
3-methyl-6-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
(6a–e)
General procedure F1: alkylation with KHCO3. Products
(4g). Light yellow solid. Yield: 0.5 mmol (10%) and 2.8mmol
(56%) from general procedures D and E, respectively. Solvent:
ethanol. Mp 306–307°C (decomp.) IR (KBr): 3243.0 (m, NH),
1668.4 (s, C = O), 1630.1 (s, NH bd), 1551.5 (s, NO2), 1340,1 (s,
4a (5.0mmol) was reacted with KHCO3 (10.0mmol) or K2CO3
(20.0 mmol) and methyl iodide (40.0mmol) according to
previously reported procedure [23] to give 5a and 5b, respectively.
General procedure F2: alkylation with K2CO3. Products 6a
(5.0mmol) was reacted with K2CO3 (10.0 mmol) and methyl
iodide (40.0 mmol) or benzyl bromide (40.0mmol) according to
previously reported procedure [23] to give 7a and 7b, respectively.
General procedure G: reduction of nitro to amino using tin
(II) chloride dihydrate. Products 5a and 6a (1.0 mmol) were
reduced to the amino with SnCl2.2H2O (6.0 mmol) according to
previously reported procedure [30] to give 5c and 6d.
NO2) cmÀ1 1H-NMR (DMSO-d6, T = 340 K): δ = 3.67 (s, 3H,
.
H-9), 7.52 (d, J8–7 = 9.0Hz, 1H, H-8), 8.48 (dd, J7–8 = 9.0Hz,
J7–5 = 2.4 Hz, 1H, H-7), 8.62 (d, J5–7 = 2.4Hz, 1H, H-5), 13.19 (bs,
1H, NH) ppm. 13C-NMR (DMSO-d6, T = 340K): δ = 33.1, 115.1,
116.8, 123.1, 129.4, 142.6, 142.7, 158.3, 176.2ppm. Anal. Calcd
for C9H7N3O3S (237.24): C, 45.57; H, 2.97; N, 17.71. Found: C,
45.63; H, 3.06; N, 17.76.
3-Methyl-5-nitro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one
(4h).
White solid. Yield: 4.5 mmol (90%). Solvent:
General procedure H: reduction of nitro to amino using iron/
acid in ethanol. Products 6b and 7a (2.0 mmol), iron powder
(10.0 mmol), 32% hydrochloric acid (3 ml), and ethanol (20 mL)
are placed in a 250 mL round bottom flask and refluxed with
stirring for 90 min. The ethanol/acid is then evaporated
completely under reduced pressure. 20% NaOH (50 mL) is then
added to the remaining solid followed by filtration of the
nitromethane. Mp 275–276°C. IR (KBr): 3168.5 (m, NH), 1690.5
(s, C═O), 1622.9 (m, NH bd), 1547.4 (s, NO2), 1386.1 (m, NO2)
cmÀ1 1H-NMR (DMSO-d6, T =340 K): δ = 3.61 (s, 3H, H-9),
.
7.52–7.60 (m, 2H, H-6, H-8), 7.86 (t, J7–6 = J7–8 = 7.8Hz, 1H,
H-7), 13.12 (bs, 1H, NH) ppm. 13C-NMR (DMSO-d6, T = 340K):
δ = 33.0, 105.9, 117.4, 118.0, 135.5, 139.7, 148.5, 155.9,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

J. T. Heppell and J. M. A. Al-Rawi
Vol 000
resulting precipitate, which is boiled in ~100 mL of acetone then
(m, NO2) cmÀ1
.
1H-NMR (DMSO-d6, T = 360 K): δ = 3.67
filtered. The filtrate is then evaporated to yield oil, which is
triturated into a solid with ether or petroleum spirit and
collected by filtration with suction to give 6e and 7c,
respectively. The product was used without any further
purification but can be purified using an appropriate technique.
General procedure I: synthesis of 8-substituted-2-morpholino
(s, 8H, H-9, H-10), 7.20 (t, J6–5 = J6–7 = 7.8 Hz, 1H, H-6),
8.05 (dd, J5–6 = 7.8 Hz, J5–7 = 1.6 Hz, 1H, H-5), 8.14 (dd,
J7–6 = 7.8 Hz, J7–5 = 1.6 Hz, 1H, H-7), 11.38 (bs, 1H, NH) ppm.
13C-NMR (DMSO-d6, T = 360 K): δ = 44.7, 65.3, 118.7, 120.2,
128.3, 129.8, 142.6, 143.9, 151.5, 161.5 ppm. Anal. Calcd for
C12H12N4O4 (276.25): C, 52.17; H, 4.38; N, 20.28. Found: C,
quinazolin-4-one.
Products 5a, 5c, and 5d (3.0 mmol) were
52.03; H, 4.41; N, 20.31.
3-Methyl-2-morpholino-8-nitroquinazolin-4(3H)-one (6b).
reacted with morpholine for 3, 8, and 3 days, respectively,
according to previously reported procedure [23] to give 6a, 6b,
and 6c as orange, yellow, and off-white solids, respectively. The
product was used without any further purification but can be
purified using an appropriate technique.
Yellow solid. Yield: 2.31 mmol (77%). Solvent: isopropanol. Mp
309–310°C (decomp.). IR (KBr): 2926.6 (w, sp3 C–H st),
2860.1 (w, sp3 C–H st), 1683.3 (s, C═O), 1524.2 (m, NO2),
1360.3 (m, NO2) cmÀ1
.
1H-NMR (DMSO-d6, T = 340 K):
δ = 3.31 (t, J10–9 = 4.8 Hz, 4H, H-10), 3.48 (s, 3H, H-11), 3.74
(t, J9–10 = 4.8 Hz, 4H, H-9), 7.41 (t, J6–5 = J6–7 = 7.8 Hz, 1H,
H-6), 8.16 (dd, J7–6 = 7.8 Hz, J7–5 = 1.4 Hz, 1H, H-7), 8.25
(dd, J5–6 = 7.8 Hz, J5–7 = 1.4 Hz, 1H, H-5) ppm. 13C-NMR
(DMSO-d6, T = 340 K): δ = 33.1, 48.9, 65.1, 119.9, 122.7,
128.0, 130.0, 139.5, 144.6, 156.0, 161.8 ppm. Anal. Calcd for
C13H14N4O4 (290.27): C, 53.79; H, 4.86; N, 19.30. Found: C,
53.61; H, 4.83; N, 19.20.
2-(Methylthio)-8-nitroquinazolin-4(1H)-one (5a).
White
solid: Yield: 4.75 mmol (95%). Solvent: toluene. Mp 274–275°C.
IR (KBr): 3388.9 (m, NH), 1666.6 (m, C═O), 1614.0 (m, NH
bd), 1510.1 (m, NO2) cmÀ1 1H-NMR (DMSO-d6, T = 360K):
.
δ = 2.55 (s, 3H, H-9), 7.52 (t, J6–5 = J6–7 = 8.0 Hz, 1H, H-6), 8.19
(dd, J5–6 = 8.0Hz, J5–7 =1.4 Hz, 1H, H-5), 8.27 (dd, J7–6 = 8.0Hz,
J
7–5 = 1.4 Hz, 1H, H-7), 12.78 (bs, 1H, NH) ppm. 13C-NMR
(DMSO-d6, T = 360K): δ = 12.4, 121.3, 124.3, 127.8, 129.6,
139.7, 144.8, 159.2, 159.2, 159.8ppm. Anal. Calcd for
C9H7N3O3S (237.24): C, 45.57; H, 2.97; N, 17.71. Found: C,
45.60; H, 3.02; N, 17.90.
3-Methyl-2-(methylthio)-8-nitroquinazolin-4(1H)-one
N-(2-morpholino-4-oxo-1,4-dihydroquinazolin-8-yl)acetamide
(6c).
Off-white solid. Yield: 2.9 mmol (58%). Solvent:
nitromethane. Mp 320–340°C (decomp.) IR (KBr): 3367.2
(m, NH), 2956.5 (w, sp3 C–H st.), 1661.7 (s, C═O) cmÀ1
.
1H-NMR (DMSO-d6, T = 360K): δ = 2.19 (s, 3H, H-12), 3.70
(s, 8H, H-9, H-10), 7.09 (t, J6–5 = J6–7 = 7.8 Hz, 1H, H-6), 7.61
(dd, J5–6 = 8.0 Hz, J5–7 = 1.4 Hz, 1H, H-5), 8.43 (dd, J7–6 = 7.8 Hz,
J7–5 = 1.4 Hz, 1H, H-7), 9.10 (bs, 1H, NH), 11.33 (bs, 1H, NH)
ppm. 13C-NMR (DMSO-d6, T = 360 K): δ = 24.1, 44.9, 65.5,
116.4, 119.3, 121.5, 122.0, 131.7, 139.7, 150.2, 162.4,
167.9 ppm. Anal. Calcd for C14H16N4O3 (288.30): C, 58.32; H,
5.59; N, 19.43. Found: C, 58.38; H, 5.58; N, 19.52.
(5b).
Yield: 4.7mmol (94%). Solvent: isopropanol. Mp 170–
171°C. IR (KBr): 2931.7 (w, sp3 C–H st), 1698.7 (s, C═O),
1615.5 (m, C═N), 1524.9 (s, NO2), 1320.3 (m, NO2) cmÀ1. H-
1
NMR (DMSO-d6, T = 340K): δ = 2.59 (s, 3H, H-9), 3.52 (s, 3H,
H-10), 7.54 (t, J6–5 = J6–7 = 8.0Hz, 1H, H-6), 8.23-8.34 (m, 2H,
H-5, H-7) ppm. 13C-NMR (DMSO-d6, T =340 K): δ = 14.4, 30.0,
119.8, 124.5, 128.2, 130.4, 138.3, 144.4, 159.0, 161.3ppm. Anal.
Calcd for C10H9N3O3S (251.26): C, 47.80; H, 3.61; N, 16.72.
Found: C, 47.71; H, 3.66; N, 16.58.
8-Amino-2-morpholinoquinazolin-4(1H)-one (6d).
Light-
8-Amino-2-(methylthio)quinazolin-4(1H)-one (5c).
solid. Yield: 0.5 mmol (50%). Solvent: nitromethane. Mp
White
yellow solid. Yield: 3.0 mmol (60%). Rf = 0.62 (methanol–
ethylacetate, 5:95). Mp 229–230°C IR (KBr): 3440.7 (m, NH),
3342.2 (m, NH), 2959.8 (w, sp3 C–H st), 1673.6 (s, C═O),
259–260°C. IR (KBr): 3440.1 (m, NH), 3350.0 (m, NH),
1
1665.7 (s, C═O), 1609.6 (m, NH bd) cmÀ1. H-NMR (DMSO-
1614.0 (s, NH bd.) cmÀ1 1H-NMR (DMSO-d6, T = 340 K):
.
d6, T = 340 K): δ = 2.60 (s, 3H, H-9), 5.51 (bs, 2H, NH2),
δ = 3.59 (t, J9–10 = 4.6 Hz, 4H, H-9), 3.69 (t, J10–9 = 4.6 Hz, 4H,
H-10), 5.23 (bs, 2H, NH2), 6.81–6.93 (m, 2H, H-5, H-6), 7.14
(dd, 1H, H-7, J7–6 = 7.0 Hz, J7–5 = 2.2 Hz), 11.10 (bs, 1H, NH)
ppm. 13C-NMR (DMSO-d6, T = 340 K): δ = 45.2, 65.4, 111.9,
114.8, 116.8, 122.5, 137.4, 142.3, 149.3, 163.0 ppm. Anal.
Calcd for C12H14N4O2 (246.27): C, 58.53; H, 5.73; N, 22.75.
6.97 (dd, J5–6 = 7.6 Hz, J5–7 = 1.6 Hz, 1H, H-5), 7.09 (t, J6–5
=
J6–7 = 7.6 Hz, 1H, H-6), 7.20 (dd, J7–6 = 7.6 Hz, J7–5 = 1.6 Hz,
1H, H-7), 12.23 (bs, 1H, NH) ppm. 13C-NMR (DMSO-d6,
T = 340 K): δ = 12.5, 111.7, 115.8, 119.7, 125.5, 135.5, 143.2,
152.7, 161.2 ppm. Anal. Calcd for C9H9N3OS (207.25): C,
52.16; H, 4.38; N, 20.27. Found: C, 51.25; H, 4.31; N, 19.83.
N-(2-(methylthio)-4-oxo-1,4-dihydroquinazolin-8-yl)acetamide
Found: C, 58.32; H, 5.74; N, 22.80.
8-Amino-3-methyl-2-morpholinoquinazolin-4(3H)-one (6e).
Off-white solid. Yield: 1.42 mmol (71%). Rf = 0.57 (2-propanol-
chloroform, 5:95). Mp 126–127°C. IR (KBr): 3457.6 (m, NH),
3326.6 (m, NH), 2857.0 (w, sp3 C–H st), 1675.0 (m, C═O),
(5d).
Product 5c (2.0mmol) was refluxed in acetic anhydride
(8.0 mmol) in acetic acid (15mL) for 30min. The reaction mixture
was evaporated, triturated with petroleum spirits, and collected by
filtration with suction to give compound 5d as a white solid.
Yield: 1.8mmol (90%). Solvent: acetic acid. Mp 219–220°C. IR
1614.3 (s, NH bd) cmÀ1 1H-NMR (DMSO-d6, T = 340 K):
.
δ = 3.19 (t, J9–10 = 4.6Hz, 4H, H-9), 3.48 (s, 3H, H-11), 3.77
(t, J10–9 = 4.6 Hz, 4H, H-10), 5.40 (bs, 2H, NH), 6.92 (dd, 1H,
(KBr): 3376.2 (m, NH), 1695.3 (s, C═O), 1662.2 (s, C═O) cmÀ1
.
1H-NMR (DMSO-d6, T = 340K): δ = 2.20 (s, 3H, H-11), 2.68
(s, 3H, H-9), 7.34 (t, J6–5 = J6–7 = 8.0 Hz, 1H, H-6), 7.71
(dd, J5–6 = 8.0Hz, J5–7 =1.4 Hz, 1H, H-5), 8.49 (dd, J7–6 = 8.0Hz,
J7–5 = 1.4 Hz, 1H, H-7), 9.30 (bs, 1H, NH), 12.53 (bs, 1H, NH)
ppm. 13C-NMR (DMSO-d6, T = 340 K): δ = 12.6, 24.0, 119.5,
119.5, 122.9, 124.9, 132.6, 138.0, 156.0, 160.5, 168.1ppm. Anal.
Calcd for C11H11N3O2S (249.29): C, 53.00; H, 4.45; N, 16.86.
Found: C, 52.77; H, 4.48; N, 16.60.
H-7, J7–6 = 7.8Hz, J7–5 = 1.6 Hz), 7.05 (t, 1H, H-6, J6–5
=
J6–7 = 7.8Hz), 7.21 (dd, J5–6 = 7.8 Hz, J5–7 = 1.6 Hz, 1H, H-5) ppm.
13C-NMR (DMSO-d6, T = 340 K): δ = 31.6, 49.5, 65.4, 112.0,
114.9, 118.4, 124.8, 134.1, 143.1, 152.9, 163.0ppm. Anal. Calcd
for C13H16N4O2 (260.29): C, 59.99; H, 6.20; N, 21.52. Found: C,
60.05; H, 6.28; N, 21.56.
4-(4-Methoxy-8-nitroquinazolin-2-yl)morpholine (7a). Orange
solid. Yield: 3.9 mmol (78%). Solvent: methanol. Mp 142–143°C
2-Morpholino-8-nitroquinazolin-4(1H)-one (6a).
solid. Yield: 2.31 mmol (77%). Solvent: nitromethane. Mp
Orange
IR (KBr): 2860.1 (w, sp3 C–H st), 1636.1 (m, C═N), 1531.5
(s, NO2) cmÀ1
.
1H-NMR (CDCl3, T = 300 K): δ = 3.77
309–310°C (decomp.). IR (KBr): 1674.1 (s, C═O), 1528.1
(t, J9–10 = 5.0 Hz, 4H, H-9), 3.95 (t, J10–9 = 5.0 Hz, 4H, H-10), 4.10
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Reactivity of 2-Amino-3, 4, 5, or 6-Nitrobenzoic Acids with Triphenylphosphine
Thiocyanate, Alkylisothiocyanates, and Further Derivatization Reactions
(s, 3H, H-11), 7.11 (t, J6–5 = J6–7 = 8.0 Hz, 1H, H-6), 8.03
(dd, J5–6 = 8.0Hz, J5–7 =1.6 Hz, 1H, H-5), 8.10 (dd, J7–6 = 8.0Hz,
J7–5 = 1.6 Hz, 1H, H-7) ppm. 13C-NMR (CDCl3, T = 300K):
δ = 44.4, 54.3, 66.9, 113.4, 119.4, 128.8, 128.9, 144.0, 145.9,
158.9, 167.2 ppm. Anal. Calcd for C13H14N4O4 (290.27): C,
53.79; H, 4.86; N, 19.30. Found: C, 53.84; H, 4.93; N, 19.34.
4-(4-(Benzyloxy)-8-nitroquinazolin-2-yl)morpholine (7b).
Orange solid. Yield: 3.6 mmol (72%). Solvent: methanol. Mp
142–143°C. IR (KBr): 2860.0 (w, sp3 C–H st), 1630.1
controls and a DMSO blank as a negative control. The
diameter of the zone of inhibition was measured in
millimeters (mm) after 24 h of incubation at 37°C.
REFERENCES AND NOTES
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(s, C═N), 1522.5 (s, NO2), 1356.0 (m, NO2) cmÀ1 1H-NMR
.
(CDCl3, T = 300 K): δ = 3.76 (t, J9–10 = 4.8 Hz, 4H, H-9), 3.94
(t, J10–9 = 4.8 Hz, 3H, H-10), 5.55 (s, 2H, H-11), 7.10
(t, J6–5 = J6–7 = 8.0 Hz, 1H, H-6), 7.35–7.49 (m, 5H, benzylic
hydrogens), 8.02 (dd, J5–6 =8.0 Hz, J5–7 = 1.4 Hz, 1H, H-5), 8.15
(dd, J7–6 = 8.0 Hz, J7–5 = 1.4Hz, 1H, H-7) ppm. 13C-NMR (CDCl3,
T = 300 K): δ = 44.5, 66.9, 68.8, 113.4, 119.5, 128.1, 128.5, 128.7,
128.9, 129.0, 135.8, 144.0, 146.1, 158.8, 166.5ppm. Anal. Calcd
for C19H18N4O4 (266.37): C, 62.29; H, 4.95; N, 15.29. Found: C,
61.68; H, 4.93; N, 14.81.
4-Methoxy-2-morpholinoquinazolin-8-amine (7c).
White
solid. Yield: 0.8 mmol (40%). Rf = 0.72 (ethylacetate-petroleum
spirit, 3:2). Mp 120–121°C. IR (KBr): 3410.8 (m, NH), 3303.9
(m, NH), 2860.9 (w, sp3 C–H st), 1623.2 (m, NH bd) cmÀ1
.
1H-NMR (DMSO-d6, T = 380 K): δ = 3.72 (t, J9–10 = 4.8 Hz, 4H,
H-9), 3.83 (t, J10–9 = 4.8 Hz, 4H, H-10), 4.07 (s, 3H, H-11), 5.27
(bs, 2H, NH2), 6.86 (dd, J7–6 = 7.4Hz, J7–5 = 1.4 Hz, 1H, H-7),
6.94 (t, J6–5 =J6–7 = 7.4Hz, 1H, H-6), 7.10 (dd, 1H, H-5,
J5–6 = 7.4 Hz, J5–7 = 1.4Hz) ppm. 13C-NMR (DMSO-d6,
T = 340 K): δ = 44.1, 53.3, 65.8, 109.0, 110.3, 112.4, 122.2, 141.7,
141.9, 156.2, 166.7ppm. Anal. Calcd for C13H16N4O2 (260.29):
C, 59.99; H, 6.20; N, 21.52. C, 60.25; H, 6.17; N, 21.78.
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ANTIBACTERIAL ASSAY
The disk diffusion method with Mueller–Hinton agar
was used to evaluate the antibacterial activity against
E. coli, P. aeruginosa, B. subtilis, S. aureus, and E. faecalis.
All bacteria were grown from frozen cultures in nutrient
broth by overnight incubation, diluted to give an OD600
of 0.95–1.05 then evenly applied to the appropriately la-
beled agar plates using a sterile swab. Blank antibacterial
susceptibility disks (three per plate) were then placed on
each agar plate. A total of 2.5 μL of each compound as a
20 mM solution in DMSO (50 nmol) was applied to the ap-
propriate blank antibacterial susceptibility disks for each
bacterial strain. Ciprofloxacin and Penicillin G potassium
salt, of the same concentration, were used as positive
[30] Kulkarni, S. S.; et al. Eur J Med Chem 2012, 50, 264.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet