Pd-Catalyzed Sequential Electrophilic Cyclization/Selective C-H Annulation Cascade: Synthesis of Isoxazole-Phthalimide-Fused Poly-Heterocyclics

Harnessing the organo-palladium intermediates generated from electrophilic cyclizations for tandem C-C bond construction is a challenging task but constitutes an excellent tool for constructing complex motifs from simpler substrates. We realize herein such a cyclative annulation of alkynyl-oxime ethers with maleimides for the facile construction of isoxazole-phthalimide hybrid motifs through Pd(II) catalysis. This protocol features excellent regio-selectivity in C-H selection, a broad substrate scope, good functional group tolerance, and scalability. Necessary KIE & labeling studies give insight into the reaction mechanism.

Identification of a bacteria-produced benzisoxazole with antibiotic activity against multi-drug resistant Acinetobacter baumannii

The emergence of multi-drug resistant pathogenic bacteria represents a serious and growing threat to national healthcare systems. Most pressing is an immediate need for the development of novel antibacterial agents to treat Gram-negative multi-drug resistant infections, including the opportunistic, hospital-derived pathogen, Acinetobacter baumannii. Herein we report a naturally occurring 1,2-benzisoxazole with minimum inhibitory concentrations as low as 6.25 μg ml-1 against clinical strains of multi-drug resistant A. baumannii and investigate its possible mechanisms of action. This molecule represents a new chemotype for antibacterial agents against A. baumannii and is easily accessed in two steps via de novo synthesis. In vitro testing of structural analogs suggest that the natural compound may already be optimized for activity against this pathogen. Our results demonstrate that supplementation of 4-hydroxybenzoate in minimal media was able to reverse 1,2-benzisoxazole's antibacterial effects in A. baumannii. A search of metabolic pathways involving 4-hydroxybenzoate coupled with molecular modeling studies implicates two enzymes, chorismate pyruvate-lyase and 4-hydroxybenzoate octaprenyltransferase, as promising leads for the target of 3,6-dihydroxy-1,2-benzisoxazole.

Synthesis and Screening of Pro-apoptotic and Angio-inhibitory Activity of Novel Benzisoxazole Derivatives both In Vitro and In Vivo

BACKGROUND

Triple Negative Breast Cancer (TNBC) tends to be more aggressive than other types of breast cancer. Resistance to chemotherapy is a major obstacle hence there is a significant need for new antineoplastic drugs with multi-target potency. Numerous Benzoisoxazole moieties have been found to possess a broad spectrum of pharmacological activities. In the present study, we have synthesized 9 novel derivatives of Benzisoxazole 7(a-i) and screened them for their biological potential.

METHODS

Chemical synthesis, Mass spectrometry (HRMS), cell proliferation and cytotoxicity assay, wound healing assay, flow cytometry and nuclear staining. Angio-inhibitory activity assessed by corneal micropocket assay and in vivo peritoneal angiogenesis assay.

RESULTS

The Benzisoxazole derivatives 7(a-i) were synthesized and screened for their biological potency by both in vitro and in vivo experimental models. Among the series, compound 3-(1-((3-(3(Benzyloxy)-4-methoxyphenyl)- 4,5-dihydroisoxazole-5-yl)methyl)piperidine-4-yl)6-fluorobenzo[d] isoxazole (7e) was found to be most promising, with an average IC50 value of 50.36 ± 1.7 µM in MTT assay and showed 81.3% cell death. The compound 7e also showed 60-70% inhibition on a recombinant Metastasis-Associated protein (MTA1) induced proliferation and cell migration in MDAMB-231 cells, which is known to play a major role in angiogenesis. The anti-tumour studies inferred the regression of tumour activity. This was due to inhibition of neovascularization and evoking apoptosis process as assessed by corneal vascularization, peritoneal angiogenesis and apoptotic hallmarks in 7e treated cells.

CONCLUSION

These findings not only show the biological efficacy of compound 7e but it is also an effective beginning to explore the mechanism of metastasis and cancer therapy strategy targeting MTA1. The observed biological activity makes compound 7e an attractive drug candidate.

Benzisoxazole: a privileged scaffold for medicinal chemistry

The benzisoxazole analogs represent one of the privileged structures in medicinal chemistry and there has been an increasing number of studies on benzisoxazole-containing compounds. The unique benzisoxazole scaffold also exhibits an impressive potential as antimicrobial, anticancer, anti-inflammatory, anti-glycation agents and so on. This review examines the state of the art in medicinal chemistry as it relates to the comprehensive and general summary of the different benzisoxazole analogs, their use as starting building blocks of multifarious architectures on scales sufficient to drive human drug trials. The number of reports describing benzisoxazole-containing highly active compounds leads to the expectation that this scaffold will further emerge as a potential candidate in the field of drug discovery.