The X-ray crystal structure of 6,7-dihydro-5a,7a,13,14-tetraaza-pentaphene-5,8-dione, a potential antiproliferative agent against A2058 melanoma cells, was determined. The compound crystallizes in the monoclinic space group P21/c with cell parameters a = 24.879(3) Å, b = 6.868(2) Å, c = 26.068(4) Å, β = 110.49(2)°, and V = 4172.4(15) ų, with Z = 12. The crystal structure was refined to R1 = 0.1353 and wR2 = 0.1936. The compound features intermolecular C-Arom-H...O hydrogen bonds forming trimers. The molecule is a fused bis-quinazolin-4-one derivative synthesized via a modified Niementowski condensation. It showed high antiproliferative activity, with 40.2 ± 3.3% and 6.9 ± 3.5% growth inhibition at 10 and 1 μM, respectively. The compound was obtained by slow crystallization from a dichloromethane-methanol solution at 20°C. The molecular structure was determined using X-ray diffraction with a Cu Kα radiation source. The crystal structure was solved by direct methods and refined using SHELXS and SHELXL programs. The compound exhibits planar quinazolinone systems with maximum displacement of 0.067(3) Å from the mean plane. The interplanar dihedral angles between quinazolinone planes in each molecule were 18.15(8), 21.02(7), and 20.69(7)° for molecules A, B, and C, respectively. The torsion angles of the conjugated N1-C1-C18-N4 were observed at 19.9(6), 22.7(5), and 21.5(6)° for molecules A, B, and C. The C=O bonds were in the range of 1.222(5) to 1.231(5) Å. The crystal structure is stabilized by hydrogen bonds and π-stacking interactions. The crystallographic data have been deposited in the Cambridge Crystallographic Data Centre (CCDC 267198).The X-ray crystal structure of 6,7-dihydro-5a,7a,13,14-tetraaza-pentaphene-5,8-dione, a potential antiproliferative agent against A2058 melanoma cells, was determined. The compound crystallizes in the monoclinic space group P21/c with cell parameters a = 24.879(3) Å, b = 6.868(2) Å, c = 26.068(4) Å, β = 110.49(2)°, and V = 4172.4(15) ų, with Z = 12. The crystal structure was refined to R1 = 0.1353 and wR2 = 0.1936. The compound features intermolecular C-Arom-H...O hydrogen bonds forming trimers. The molecule is a fused bis-quinazolin-4-one derivative synthesized via a modified Niementowski condensation. It showed high antiproliferative activity, with 40.2 ± 3.3% and 6.9 ± 3.5% growth inhibition at 10 and 1 μM, respectively. The compound was obtained by slow crystallization from a dichloromethane-methanol solution at 20°C. The molecular structure was determined using X-ray diffraction with a Cu Kα radiation source. The crystal structure was solved by direct methods and refined using SHELXS and SHELXL programs. The compound exhibits planar quinazolinone systems with maximum displacement of 0.067(3) Å from the mean plane. The interplanar dihedral angles between quinazolinone planes in each molecule were 18.15(8), 21.02(7), and 20.69(7)° for molecules A, B, and C, respectively. The torsion angles of the conjugated N1-C1-C18-N4 were observed at 19.9(6), 22.7(5), and 21.5(6)° for molecules A, B, and C. The C=O bonds were in the range of 1.222(5) to 1.231(5) Å. The crystal structure is stabilized by hydrogen bonds and π-stacking interactions. The crystallographic data have been deposited in the Cambridge Crystallographic Data Centre (CCDC 267198).