Quinazolinone is the building unit of approximately 150 naturally occurring alkaloids isolated from microorganisms, plants and animals [1]. It is a very important heterocycle exhibiting excellent pharmacological activities such as antimicrobial [2], antifungal [3], antitumor [4], anticancer [5], antiinflammatory [6], antidepressant [7], and anticonvulsant [8] activities. 3-Aryl-2-thioxo-2,3-dihydroquinazolin-4(1H)-one are derivatives of quinazolinones have a wide range of pharmacological and biological activities such as anticonvulsant and antitumor [9]. Altanserin (3-(2-(4-(4-fluorobenzoyl)-l-piperidinyl)-ethyl)-2,3-dihydro-2-thioxo-1H-quinazolin-4-one) and nitro altanserin are used as drugs for 5-HT2A receptor antagonists [10].

The title compound was synthesized by slight modification of a reported method [11] according to the route depicted in Figure 1. 4-Methoxyaniline in DMSO was treated with carbon disulfide and aqueous sodium hydroxide to afford sodium 4-methoxyphenylcarbamodithioate (1) followed by reaction with dimethyl sulfate to furnish the methyl 4-methoxyphenylcarbamodithioate (2). A solution of (2) in ethanol (20 mL) was treated with methyl anthranilate in presence of anhydrous potassium carbonate to provide the methyl 2-(3-(4-methoxyphenyl)thioureido)benzoate as intermediate (3), which on basic hydrolysis yielded the title compound (4) which was recrystallized from ethanol as colorless crystals.

Formation of (4) was confirmed by IR which showed peaks at 3187.6 cm⁻¹ for NH, 1706.6 cm⁻¹ for C=O and 1224.9 cm⁻¹ for C=S, respectively. In the ¹H-NMR spectrum a singlet at δ 3.88 ppm due to OCH₃ group, a multiplet at δ 7–8.1 ppm for aromatic (8H) protons and a singlet at d 10.36 ppm indicated the presence of NH.

The molecular structure of (4) is shown in Figure 2. The dihydroquinazoline N1/C1/N2/C2-C8 ring system essentially planar with an r.m.s. deviation of 0.052(1) Å. The molecule is twisted around the C9-N2 bond with a dihedral angle of 79.84(4)° between the dihydroquinazoline ring system and the substituted phenyl C9-C14 ring. The C1=S1 and C2=O1 bond lengths are 1.6799(10) and 1. 2119(14) Å, respectively, which are comparable with the reported double bond lengths [12]. Packing diagrams of (4) are shown in Figures 3 and 4. The molecules are linked by an N-H… S hydrogen bond (N1-H1…S1ⁱ N1-H1 = 0.796(17) Å, H1…S1 = 2.656(18) Å, N1…S1 = 3.4181(10) Å, <H1-N1…S1 = 160.9(16)°; symmetry code: (i) 1−x, −1/2+y, −z) forming a zig-zag chain structure along the b axis (Figure 3). The molecular chains are further connected by a C-H… O hydrogen bond (C11-H11…O1ⁱⁱ C11-H11 = 0.95 Å, H11…O1 = 2.36 Å, C11…O1 = 3.2543(15) Å, C11-H11…O1 = 157°; symmetry code: (ii) 1−x, −1/2+y, 1−z), forming a layer parallel to the bc plane (Figure 4).

Melting points were recorded using a digital Gallenkamp (SANYO) model MPD BM 3.5 apparatus and are uncorrected. The FTIR spectra were recorded on FTS 3000 MX, Bio-Rad Merlin (Excalibur Model) spectrophotometer. ¹H NMR spectra were determined as CDCl₃ solutions at 300 MHz using a Bruker Mass Spectra (EI, 70 eV) on a GC-MS instrument. All compounds were purified by thick layer chromatography using silica gel from Merck.

Synthesis and molecular structure of a medicinally important compound is described. The dihydroquniazoline ring system is essentially planar; the molecule is twisted around the C9-N2 bond between the dihydroquinazoline ring system and the substituted phenyl C9-C14 ring. The molecules are linked by an N-H…S hydrogen bond forming a zig-zag chain structure along the b axis.