Acridine–Isoxazole and Acridine–Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine–azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320–420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine–isoxazole hybrids linked at the C9–C3 or C2–C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine–azirine, acridine–isoxazole, and acridane–isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4)

(Z)-N-[1-(Aziridin-1-yl)-2,2,2-trifluoroethylidene]-4-bromoaniline

The title compound, C10H8BrF3N2, crystallizes with two independent molecules in the asymmetric unit, which can be considered as being related by a pseudo-inversion center, so their conformations are different; the corresponding N=C—N—C torsion angles are 54.6 (5) and −50.5 (5)°. In the crystal, molecules related by translation in [001] interact through short intermolecular Br...F contacts [3.276 (2) and 3.284 (2) Å], thus forming two types of crystallographically independent chains

(E)-1,5-Diphenylpent-2-en-4-yn-1-one

The title compound, C17H12O, has an E conformation about the C=C bond. The C—C[triple-bond]C—C torsion angle is 7.7 (2)°, and the mean planes of the phenylethylenone [r.m.s. deviation = 0.059 (1) Å] and phenylacetylene [r.m.s. deviation = 0.023 (1) Å] fragments form a dihedral angle of 14.16 (7)°. In the crystal, weak C—H...O interactions link the molecules into zigzag chains propagated in [010]

7-Nitro-2-phenylimidazo[2,1-b][1,3]benzothiazole

In the title molecule, C15H9N3O2S, the central imidazo[2,1-b][1,3]benzothiazole heterotricyclic unit is essentially planar (r.m.s. deviation = 0.021 Å). The terminal phenyl ring and nitro group are twisted by 9.06 (1) and 11.02 (4)°, respectively, from the mean plane of the heterotricycle. In the crystal, molecules are linked by π–π stacking interactions into columns along [100]; the interplanar distance between neighboring imidazo[2,1-b][1,3]benzothiazole planes within the columns is 3.370 (2) Å. Furthermore, the columns interact with each other by secondary S...O [2.9922 (10) and 3.1988 (11) Å] interactions, forming a three-dimensional framework

3-Bromo-2-[4-(methylsulfanyl)phenyl]-5,6,7,8-tetrahydro-1,3-benzothiazolo[3,2-a]imidazole

In the title molecule, C16H15BrN2S2, the central imidazo[2,1-b]thiazole fragment is almost planar (r.m.s. deviation = 0.012 Å), and the fused 5,6,7,8-tetrahydrobenzene ring adopts an unsymmetrical half-chair conformation. The dihedral angle between the imidazo[2,1-b]thiazole and benzene planes is 18.25 (4)°. The terminal methylsulfanyl substituent lies practically within the benzene plane [the dihedral angle between the corresponding planes is 7.20 (10)°] and is turned toward the C—Br bond. In the crystal, molecules form infinite chains along [100] via secondary Br...N interactions [3.1861 (16) Å]. The chains are arranged at van der Waals distances

2-Bromo-1-[1-(4-bromophenyl)-5-methyl-1H-1,2,3-triazol-4-yl]ethanone

The asymmetric unit of the title compound, C11H9Br2N3O, contains two crystallographically independent molecules with similar geometries; the Br—C—C=O torsion angles are 1.2 (4) and −2.8 (4)°, and the benzene and triazole rings are inclined o one another by 51.90 (16) and 51.88 (16)°. The two molecules are related by a pseudo-screw 21 axis directed along [100]. In the crystal, molecules are linked into a three-dimensional network by weak C—H...O and C—H...N hydrogen bonds and secondary Br...Br [3.5991 (8) and 3.6503 (9) Å] interactions

6-(4-Chlorophenyl)-3-methylimidazo[2,1-b]thiazole

In the title compound, C12H9ClN2S, the imidazo[2,1-b]thiazole fragment is planar (r.m.s. deviation = 0.003 Å), and the benzene ring is twisted slightly [by 5.65 (6)°] relative to this moiety. In the crystal, molecules are linked by π–π stacking interactions into columns along [010]. The molecules within the columns are arranged alternatively by their planar rotation of 180°. Thus, in the columns, there are the two types of π–π stacking interactions, namely, (i) between two imidazo[2,1-b]thiazole fragments [interplanar distance = 3.351 (2) Å] and (ii) between an imidazo[2,1-b]thiazole fragment and the phenyl ring [interplanar distance = 3.410 (5) Å]. There are no short contacts between the columns