Abstract
Using X-ray single crystal diffraction, the crystal structures of biologically active benzoxazole derivatives were determined. DFT calculation was performed with standard 6-31G*(d), 6-31G** and 6-31+G* basis set to analyze the molecular geometry and compare with experimentally obtained X-ray crystal data of compounds. The calculated HOMO-LUMO energy gap in compound 2 (2-(2-hydroxynaphtalen-1-yl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol) is 3.80 eV and this small gap value indicates that compound 2 is chemically more reactive compared to compounds 1 (4-methyl-2-phenyl-7-isopropyl-1,3-benzoxazol-5-ol) and 3 (2-(4-chlorophenyl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol). The crystal structures are stabilized by both intra- and intermolecular hydrogen bonds in which an intermolecular O-H⋅⋅⋅N hydrogen bond generates N3 and O7 chain motif in compounds 1, 2, and 3, respectively. The calculated bond lengths and bond angles of all three compounds are remarkably close to the experimental values obtained by X-ray single crystal diffraction.
Highlights
Benzoxazoles are compounds with a wide range of biological activities and represent a very important structural motif in medicinal chemistry
The calculated HOMO-LUMO energy gap in compound 2 (2-(2-hydroxynaphtalen-1-yl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol) is 3.80 eV and this small gap value indicates that compound 2 is chemically more reactive compared to compounds 1 (4-methyl-2-phenyl-7-isopropyl-1,3-benzoxazol-5-ol) and 3 (2-(4-chlorophenyl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol)
The calculated bond lengths and bond angles of 1, 2 and 3 are remarkably close to the experimental values obtained by X-ray crystal diffraction
Summary
Benzoxazoles are compounds with a wide range of biological activities and represent a very important structural motif in medicinal chemistry. Benzoxazole ring can be found in natural and synthetic compounds used as pharmaceuticals.[1] Caboxamycin (Figure 1a) is a new antibiotic of the benzoxazole family produced by the deep-sea strain Streptomyces sp. NTK 937.2 Figure 1b presents the synthetic compound with a two times better Pseudomonas aeruginosa inhibitory activity than ampicillin and streptomycin.[3] Benzoxazoles have anti-inflammatory,[4] antimicrobial,[5,6,7] and antitumor[6,7,8,9,10] activities. Benzoxazoles have a certain structural similarity with nucleic bases such as adenine and guanine, and they interact with biopolymers in living organisms.[2] The mole-
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