Regioselective Radical Cascade Cyclizations of Alkyne-Tethered Cyclohexadienones with Chalcogenides under Visible-Light Catalysis.

Herein, we demonstrated a silver/K2S2O8-mediated highly regio- and diastereoselective 6/5-exo trig radical cascade cyclization of alkyne-tethered cyclohexadienones with sulfonyl hydrazides or sodium sulfinates and subsequent selenation to access 6,6-dihydrochromenone and 6,5-fused tetrahydro benzofuranone derivatives. This reaction protocol features high functional group compatibility and has a wide substrate scope providing a variety of dihydrochromenones and tetrahydro benzofuranone derivatives in good to excellent yields. The reaction proceeds via the attack of a sulfonyl radical to alkyne over the activated Michael acceptor. The TEMPO quenching experiment implies the presence of a radical intermediate. Further synthetic versatility of 6,6- and 5,6-fused derivatives is also showcased.

Silver Ions Promoted Palladium-Catalyzed Inactive ß-C(sp3)-H Bond Arylation in Batch and Continuous-Flow Conditions.

A palladium(II)-catalyzed protocol for inactive ß-C(sp3)-H bond functionalization has been first accomplished. The reaction proceeds through five-membered carbocycles for the formation of C-C bonds via the Pd(II)/Pd(IV) cycle. This reaction was carried out with various aryl iodides and benzothiazoles/benzoxazoles/benzimidazoles, which were well-tolerated in this reaction and successfully generated ß-C(sp3)-H arylated products. Further implementation of this batch protocol to continuous flow by utilizing a PTFE (polytetrafluoroethylene) capillary reactor enhanced the reaction efficiency and decreased the reaction time (18.4 min) as compared to batch conditions (8 h). Even on the gram scale, the process produced excellent yield with negligible diarylations. Functional group tolerance, a continuous-flow approach, and easy-to-handle reaction conditions make this inactive ß-C(sp3)-H bond functionalization protocol very attractive.

Regioselective C-3-alkylation of quinoxalin-2(1H)-ones via C-N bond cleavage of amine derived Katritzky salts enabled by continuous-flow photoredox catalysis.

An efficient, transition metal-free visible-light-driven continuous-flow C-3-alkylation of quinoxalin-2(1H)-ones has been demonstrated by employing Katritzky salts as alkylating agents in the presence of eosin-y as a photoredox catalyst and DIPEA as a base at room temperature. The present protocol was accomplished by utilizing abundant and inexpensive alkyl amine (both primary and secondary alkyl) and as well as this a few amino acid feedstocks were converted into their corresponding redox-active pyridinium salts and subsequently into alkyl radicals. A wide variety of C-3-alkylated quinoxalin-2(1H)-ones were synthesized in moderate to high yields. Further this environmentally benign protocol is carried out in a PFA (Perfluoroalkoxy alkane) capillary based micro reactor under blue LED irradiation, enabling excellent yields (72% to 91%) and shorter reaction times (0.81 min) as compared to a batch system (16 h).

Visible-Light-Induced Deaminative Alkylation/Cyclization of Alkyl Amines with N-Methacryloyl-2-phenylbenzoimidazoles in Continuous-Flow Organo-Photocatalysis.

Herein, we present a metal-free visible-light-induced eosin-y-catalyzed deaminative strategy for the sequential alkylation/cyclization of N-methacryloyl-2-phenylbenzoimidazoles with alkyl amine-derived Katritzky salts, which provides an efficient avenue for the construction of various benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-one derivatives in moderate to excellent yields under mild reaction conditions. The key enabling feature of this novel reaction includes utilization of redox-active pyridinium salts from abundant and inexpensive primary amine feedstocks that were converted into alkyl radicals via C-N bond scission and subsequent alkylation/cyclization with N-methacryloyl-2-phenylbenzoimidazoles by the formation of two new C-C bonds. In addition, we implemented this protocol for a variety of amino acids, affording the products in moderate yields. Moreover, the novel, environmentally benign batch protocol was further carried out in a continuous-flow regime by utilizing a perfluoroalkoxy alkane tubing microreactor under optimized reaction conditions with a blue light-emitting diode light source, enabling excellent yields and a shorter reaction time (19 min) versus the long reaction time (16 h) of the batch reaction. The reaction displays excellent functional group tolerance, easy operation, scalability, mild reaction conditions, and broad synthetic utility.

Pore-Surface Engineering by Decorating Metal-Oxo Nodes with Phenylsilane to Give Versatile Super-Hydrophobic Metal-Organic Frameworks (MOFs).

Hydrophobization of metal-organic frameworks (MOFs) is important to push forward their practical use and thus has attracted increasing interest. In contrast to the previous reports, which mainly focused on the modification of organic ligands in MOFs, herein, we reported a novel strategy to decorate the metal-oxo nodes of MOFs with phenylsilane to afford super-hydrophobic NH2 -UiO-66(Zr), which shows highly improved base resistance and holds great promise in versatile applications, such as organic/water separation, self-cleaning, and liquid-marble fabrication. This work demonstrates the first attempt at metal-oxo node modification for super-hydrophobic MOFs, advancing a new concept in the design of MOFs with controlled wettability for practical applications.

Synthesis and biological evaluation of pyrazole linked benzothiazole-ß-naphthol derivatives as topoisomerase I inhibitors with DNA binding ability.

A series of new pyrazole linked benzothiazole-ß-naphthol derivatives were designed and synthesized using a simple, efficient and ecofriendly route under catalyst-free conditions in good to excellent yields. These derivatives were evaluated for their cytotoxicity on selected human cancer cell lines. Among those, the derivatives 4j, 4k and 4l exhibited considerable cytotoxicity with IC50 values ranging between 4.63 and 5.54 µM against human cervical cancer cells (HeLa). Structure activity relationship was elucidated by varying different substituents on benzothiazoles and pyrazoles. Further, flow cytometric analysis revealed that these derivatives induced cell cycle arrest in G2/M phase and spectroscopic studies such as UV-visible, fluorescence and circular dichroism studies showed that these derivatives exhibited good DNA binding affinity. Additionally, these derivatives can effectively inhibit the topoisomerase I activity. Viscosity studies and molecular docking studies demonstrated that the derivatives bind with the minor groove of the DNA.

Flow-Assisted Switchable Catalysis of Metal Ions in a Microenvelope System Embedded with Core-Shell Polymers.

Many efforts have been made on stimuli-responsive switchable catalysis to trigger catalytic activity over various chemical reactions. However, the reported light-, pH- or chemically responsive organocatalysts are mostly incomplete in the aspects of shielding efficiency and long-term performance. Here, we advance the flow-assisted switchable catalysis of metal ions in a microenvelope system that allows  the on-off catalysis mode on demand for long-lasting catalytic activity. Various metal-ion catalysts can be selectively embedded in a novel polymeric core-shell of the heteroarm star copolymer of poly(styrene) and poly(4-vinylpyridine) emanated from a polyhedral oligomeric silsesquioxane center. The immobilized core-shell polymer on the inner wall of a poly(dimethylsiloxane) envelope microreactor shows on-off switching catalysis between the expanded active mode and contracted protective mode under continuous flow of solvents or subsequent dry conditions. In particular, the preserved catalytic activity of toxic Hg2+ for oxymercuration was demonstrated even for 2 weeks without leaching, whereas the activity of moisture-sensitive Ru3+ ions for polymerization of methyl methacrylate was maintained even after 5 days from an open atmosphere. It is practical that the tight environment of the enveloped microfluidic system facilitates cyclic switching between the reaction-"on" and -"off" modes of such toxic, sensitive/expensive catalysts for long-term prevention and preservation.

Development of pyrrolo[2,1-c][1,4]benzodiazepine ß-glucoside prodrugs for selective therapy of cancer.

Cancer chemotherapy has several limitations such as often insufficient differentiation between malign tissue and benign tissue. The clinical utility of the pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are inadequate because of the lack of selectivity for tumor tissues, high reactivity of the pharmacophoric imine functionality, low water solubility, and stability. To address these limitations two new ß-glucoside prodrugs of PBDs have been synthesized and evaluated for their potential use in selective therapy of solid tumors by ADEPT. The preliminary studies reveal the prodrugs are much less toxic compared to the parent moieties. These prodrugs are activated by ß-glucosidase to produce the active cytotoxic moiety signifying their utility in ADEPT of cancer. The prodrugs 1a and 1b were evaluated for their cytotoxic activity in three human cancer cell lines, i.e., A375, MCF-7 and HT-29 by employing MTT assay. The results reveal that the prodrugs have shown significant cytotoxic activity in the presence of enzyme. Another important property of these molecules is their enhanced water solubility and stability, which are essential for a molecule to be an effective drug.

Synthesis and biological evaluation of spiro[cyclopropane-1,3'-indolin]-2'-ones as potential anticancer agents.

Libraries of spiro[cyclopropane-1,3'-indolin]-2'-ones were synthesized and evaluated for their biological activity against five different human cancer cell lines HT-29 (colon cancer), DU-145 (prostate cancer), Hela (cervical cancer), A-549 (Lung cancer), and MCF-7 (breast cancer). Many compounds of the series exhibited promising anticancer activity (IC50<20 µM) against the studied cell lines. Based on the screening results, a structure activity relationship (SAR) of the pharmacophore was proposed. Among the series compound 6b and 6u showed significant activity against human prostate cancer cell line, DU-145. Flow cytometric analysis showed that these two compounds arrested the cell cycle in the G0/G1 phase leading to caspase-3 dependent apoptotic cell death. Further, measurement of mitochondrial membrane potential and Annexin V-FITC assay also suggested that 6b and 6u induced cell death by apoptosis.

Access to Imidazo[1,2-a]pyridines via Annulation of α-Keto Vinyl Azides and 2-Aminopyridines.

A novel strategy for the synthesis of imidazo[1,2-a]pyridines via efficient catalyst/metal-free annulations of α-keto vinyl azides and 2-aminopyridines is described. Several imidazo[1,2-a]pyridines were synthesized from readily available vinyl azides and 2-aminopyridines and obtained in highly pure form by simply evaporating the reaction solvent. This remarkably high yielding and atom economical protocol allows the formation of three new C-N bonds through cascade reactions and rearrangements.

One-pot, three-component approach to the synthesis of 3,4,5-trisubstituted pyrazoles.

An operationally simple and high yielding protocol for the synthesis of polyfunctional pyrazoles has been developed through one-pot, three-component coupling of aldehydes, 1,3-dicarbonyls, and diazo compounds as well as tosyl hydrazones. The reaction proceeds through a tandem Knoevenagel condensation, 1,3-dipolar cycloaddition, and transition metal-free oxidative aromatization reaction sequence utilizing molecular oxygen as a green oxidant. The scope of the reaction was studied by varying the aldehyde, 1,3-dicarbonyl, and diazo component individually.

Synthesis of α-amino amidines through molecular iodine-catalyzed three-component coupling of isocyanides, aldehydes and amines.

A facile and efficient synthetic protocol for the synthesis of α-amino amidines has been developed using a molecular iodine-catalyzed three-component coupling reaction of isocyanides, amines, and aldehydes. The presented strategy offers the advantages of mild reaction conditions, low environmental impact, clean and simple methodology, high atom economy, wide substrate scope and high yields.

Rapid access to novel 1,2,3-triazolo-heterocyclic scaffolds via tandem Knoevenagel condensation/azide-alkyne 1,3-dipolar cycloaddition reaction in one pot.

An operationally simple, one-pot, two-step cascade method has been developed to afford biologically important fused 1,2,3-triazolo-heterocyclic scaffolds from 2-alkynyl aryl(heteroaryl) aldehydes and phenacyl azides. This unique atom economical transformation engages four reactive centers (aldehyde, alkyne, active methylene, and azide) under metal-free catalysis.