Divergent regioselective synthesis of 2,5,6,7-tetrahydro-1H-1,4-diazepin-2-ones and 5H-1,4-benzodiazepines

Metal-free internal nucleophile-triggered domino route for synthesis of fused quinoxaline [1,4]-diazepine hybrids and the evaluation of their DNA binding properties

An unprecedented metal-free synthesis of fused quinoxaline 1,5-disubstituted-[1,4]-diazepine hybrids have been reported under mild conditions through a domino intermolecular SNAr followed by an internal nucleophile-triggered intramolecular SNAr pathway. Our strategy offers the flexibility for the introduction of a broad variety of functionalities at the N-1 position of fused diazepine moiety by using suitable diamine tails to design structurally diverse scaffolds. The DNA binding properties of representative quinoxaline diazepine hybrids were studied using UV-vis absorbance and EtBr displacement assay and were found to be governed by the functionalities at the N-1 position. Interestingly, compound 11f containing the N-1 benzyl substitution demonstrated significant DNA binding (KBH ∼ 2.15 ± 0.25 × 104 M-1 and Ksv ∼ 12.6 ± 1.41 × 103 M-1) accompanied by a bathochromic shift (Δλ ∼ 5 nm). In silico studies indicated possible binding of diazepine hybrid 11f at the GC-rich major groove in the ct-DNA hexamer duplex and showed comparable binding energies to that of ethidium bromide. The antiproliferative activity of compounds was observed in the given order in different cell lines: (HeLa > HT29 > SKOV 3 > HCT116 > HEK293). Lead compound 11f demonstrated maximum cytotoxicity (IC50 value of 13.30 μM) in HeLa cell lines and also caused early apoptosis-mediated cell death in cancer cell lines. We envision that our work will offer newer methodologies for the construction of fused quinoxaline 1,5-disubstituted-[1,4]-diazepine class of molecules.

Catalytic Asymmetric Formal [3+2] Cycloaddition of Azoalkenes with 3-Vinylindoles: Synthesis of 2,3-Dihydropyrroles

Chiral phosphoric acid-catalyzed highly enantioselective formal [3 + 2] cycloaddition reaction of azoalkenes with 3-vinylindoles has been established. Under mild conditions, the projected cycloaddition proceeded smoothly, affording a variety of 2,3-dihydropyrroles in high yields and excellent enantioselectivities, and also in a diastereospecific manner. As opposed to the common 4-atom synthons in the previous literature reports, azoalkenes served as 3-atom synthons. Besides, the observed selectivity was supported by primary theoretical calculation. The unique chemistry of azoalkenes disclosed herein will empower asymmetric synthesis of nitrogen-containing ring structural motifs in a broader context.

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Chiral phosphoric acid catalyzed formal [3 + 2] cycloaddition reaction

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2,3-Dihydropyrroles were enantioselectively synthesized

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Azoalkenes served as 3-atom synthons

Construction of bis-, tris- and tetrahydrazones by addition of azoalkenes to amines and ammonia

Exhaustive Michael-type alkylations of amines and ammonia with azoalkenes (generated from α-halohydrazones) were demonstrated as an efficient approach to poly(hydrazonomethyl)amines - a novel class of polynitrogen ligands. An intramolecular cyclotrimerization of C=N bonds in tris(hydrazonomethyl)amine to the respective 1,4,6,10-tetraazaadamantane derivative was demonstrated.