A facile, metal-free based one-pot annulation reaction of several Morita-Baylis-Hillman acetates of MVK/acrylate with 4hydroxy-6H-pyrido[3,2,1-jk]carbazol-6-one as C/O-1,3-binucleophile promoted by DABCO as an organobase in 2-MeTHF at room temperature is reported. This environmentally benign method delivers a family of pyrano-fused pyridocarbazolones in high yields with medium to good diastereoselectivities under mild conditions. Antibacterial studies showed that attaching carboxylate group on pyran ring of pyrano-fused pyridocarbazolones has shown better activities (MIC up to � 6.25 μg/mL) as compared to acetyl one. Interestingly, incorporation of several substituents namely CF 3 , NO 2 , MeO, F, Cl and Br on the aryl rings of pyridocarbazolones carboxylates sharply enhanced the antibacterial activities which make them more potent or equipotent than commercial antibiotic ofloxacin. Furthermore, in silico docking studies indicated that MolDock scores of transisomers with E. coli protein are in general higher than cisisomers which are in good agreement with their observed in vitro antibacterial activities.
Results and DiscussionWe started our initial reaction by involving 4-hydroxy-6Hpyrido[3,2,1-jk]carbazol-6-one (1) and MBH acetate of methyl vinyl ketone (MVK) 2 a as model substrates in CH 2 Cl 2 in the [a] Dr.
The present paper discloses an interesting microwave‐assisted solvent‐free protocol for the synthesis of thermally stable, highly fluorescent pyrano[2′, 3′:4,5]pyrido[3, 2,1‐jk]carbazole‐5,8‐diones in good to high yields with good quantum yields (Ø ≥ 0.70) through a [3+3] annulation reaction of aryl‐substituted Morita‐Baylis‐Hillman acetates with a 4‐hydroxy‐6H‐pyrido[3, 2,1‐jk]carbazol‐6‐one in the presence of Hünig's base. The solvatochromic properties of synthesized compounds have been determined which showed blue shifts in absorption and emission spectra with increasing the polarity of solvents. Similarly, the higher quantum yields were also observed in case of non‐polar solvents as compared to polar ones. Interestingly, the experimental results of photophysical properties were in good agreement with theoretical data obtained using B3LYP/6‐311G++(d,p) level of theory. Furthermore, the synthesized chromophoric scaffolds exhibited good thermal stability (342‐387 °C) and average fluorescence lifetime in the range of 2.011‐2.139 ns for 408 nm, 2.268‐2.277 ns for 428 nm.
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