Chemistry and Biological Activity of 11H-Indeno[1,2-b]quinoxalin-11-ones and Tryptanthrins, Their Oximes, and Related...

Nitrogen-containing fused tetracyclic systems, exemplified by the synthetic 11H-indeno[1,2-b]quinoxalin-11-one core and the natural alkaloid tryptanthrin (indolo[2,1-b]quinazolin-6,12-dione), constitute structural scaffolds whose rigid, planar architecture enables high-affinity interaction with nucleic acids and kinase active sites. Converting the exocyclic carbonyls at C-11 and C-6, respectively, into oximes has become a productive strategy in medicinal chemistry. This transformation modulates frontier orbital energies, installs N,O- and N,N-chelating pharmacophores, and enables nitric oxide (NO) release. Here, we summarize current knowledge of the synthesis, stereochemical characterization, and diverse biological activities of these tetracyclic ketoximes and related derivatives. Microwave, sonochemical, visible-light photocatalytic, and multicomponent methods now afford efficient, economical routes to the parent ketones and their oximes. X-ray crystallography, spectroscopy, and density functional theory have firmly established the thermodynamic preference for the E-oxime configuration and clarified how this geometry, along with potential target-induced isomerization, shapes binding. The oximes bind c-Jun N-terminal kinases (JNK1-3) with high affinity, a property that accounts for their neuroprotective effects in models of cerebral ischemia and Alzheimer-like pathology, their dual JNK inhibition and NO-mediated cardioprotection in hypertension and myocardial infarction, and their anti-inflammatory activity via suppression of NF-κB/AP-1 signaling. Broader studies also document anticancer, antimicrobial, antiviral, and antidiabetic activities arising from DNA intercalation, topoisomerase inhibition, metal-ion coordination, and kinase blockade. Compelling preclinical profiles notwithstanding, low oral bioavailability and rapid hepatic clearance remain major pharmacokinetic obstacles. Ongoing work on new formulations, prodrug strategies, and structure-activity optimization seeks to slow systemic elimination. Precise stereochemical definition combined with pleiotropic pharmacology positions tetracyclic ketoximes as attractive candidates for next-generation agents against complex multifactorial diseases.