Rutaecarpine-inspired scaffold-hopping strategy and Ullmann cross-coupling based synthetic approach: Identification of pyridopyrimidinone-indole based novel anticancer chemotypes.

Natural products as starting templates have shown historically major contribution to development of drugs. Inspired by the structure-function of an anticancer natural alkaloid Rutaecarpine, the Scaffold-hopped Acyclic Analogues of Rutaecarpine (SAAR) with 'N'-atom switch (1°-hop) and ring-opening (2°-hop) were investigated. A new synthetic route was developed for an effective access to the analogues, i.e. 2-indolyl-pyrido[1,2-a]pyrimidinones, which involved preparation of N-Boc-N'-phthaloyltryptamine/mexamine-bromides and pyridopyrmidinon-2-yl triflate, a nickel/palladium-catalysed Ullmann cross-coupling of these bromides and triflate, deprotection of phthalimide followed by N-aroylation, and Boc-deprotection. Fourteen novel SAAR-compounds were prepared, and they showed characteristic antiproliferative activity against various cancer cells. Three most active compounds (11a, 11b, and 11c) exhibited good antiproliferative activity, IC50 7.7-15.8 µM against human breast adenocarcinoma cells (MCF-7), lung cancer cells (A549), and colon cancer cells (HCT-116). The antiproliferative property was also observed in the colony formation assay. The SAAR compound 11b was found to have superior potency than original natural product Rutaecarpine and an anticancer drug 5-FU in antiproliferative activities with relatively lower cytotoxicity towards normal breast epithelial cells (MCF10A) and significantly higher inhibitory effect on cancer cells' migration. The compound 11b was found to possess favourable in silico physicochemical characteristics (lipophilicity-MLOGP, TPSA, and water solubility-ESOL, and others), bioavailability score, and pharmacokinetic properties (GI absorption, BBB non-permeant, P-gp, and CYP2D6). Interestingly, the compound 11b did not show any medicinal chemistry structural alert of PAINS and Brenk filter. The study represents for the first time the successful discovery of new potent anticancer chemotypes using Rutaecarpine natural alkaloid as starting template and reaffirms the significance of natural product-inspired scaffold-hopping technique in drug discovery research.

Microtubule-targeting agents impair kinesin-2-dependent nuclear transport of ß-catenin: Evidence of inhibition of Wnt/ß-catenin signaling as an important antitumor mechanism of microtubule-targeting agents.

An aberrant accumulation of nuclear ß-catenin is closely associated with the augmentation of cancer malignancy. In this work, we report that several microtubule-targeting agents (MTAs) such as vinblastine, taxol, and C12 (combretastatin-2-aminoimidazole analog) inhibit Wnt/ß-catenin signaling in oral squamous cell carcinoma (OSCC). We showed that the inhibition of microtubule dynamics by MTAs decreased the level of ß-catenin by increasing Axin and adenomatous polyposis coli levels and reducing the level of dishevelled. Furthermore, MTAs strongly reduced the localization of ß-catenin in the nucleus. The reduction in the level of nuclear ß-catenin was neither due to the degradation of ß-catenin in the nucleus nor due to an increase in the export of nuclear ß-catenin from the nucleus. A motor protein kinesin-2 was found to assist the nuclear transportation of ß-catenin. Interestingly, Wnt/ß-catenin signaling antagonist treatment synergized with MTAs and the activators of Wnt/ß-catenin signaling antagonized with the MTAs. C12 potently suppressed the growth of 4-Nitroquinoline 1-oxide-induced OSCC in the tongue of C57 black 6 mice and also abrogated Wnt/ß-catenin signaling pathway in the tumor. Our results provide evidence that the decrease in Wnt/ß-catenin signaling is an important antitumor effect of MTAs and the combined use of MTAs with Wnt/ß-catenin signaling antagonists could be a promising strategy for cancer chemotherapy.

Organocatalyzed umpolung addition for synthesis of heterocyclic-fused arylidene-imidazolones as anticancer agents.

A strategy of "Nature-to-new" with iterative scaffold-hopping was considered for investigation of privileged ring/functional motif-elaborated analogs of natural aurones. An organocatalyzed umpolung chemistry based method was established for molecular-diversity feasible synthesis of title class of chemotypes i.e. (Z)-2-Arylideneimidazo[1,2-a]pyridinones and (Z)-2-Arylidenebenzo[d]imidazo[2,1-b]thiazol-3-ones. Various biophysical experiments indicated their important biological properties. The analogs showed characteristic anticancer activities with efficiency more than an anticancer drug. The compounds induced apoptosis with arrest in the S phase of the cell cycle regulation. The compounds' significant effect in up/down-regulation of various apoptotic proteins, an apoptosis cascade, and the inhibition of topoisomerases-mediated DNA relaxation process was identified. The analysis of the structure-activity relationship, interference with biological events and the drug-likeness physicochemical properties of the compounds in the acceptable window indicated distinctive medicinal molecule-to-properties of the investigated chemotypes.

Annulation of Conjugated Azine-Imine with a Sulfoxonium Ylide in a Noncarbenoid Route to Synthesize Multisubstituted Imidazole-Fused Heterocycles.

A new [4+1]-annulation of in situ generated heterocyclic azine-aldimines with ß-keto sulfoxonium ylides has been developed. The reaction constructs N-fused imidazole rings. In the reaction, the ylides play a dual-functional role of a nucleophilic 1,1-dipolar one-carbon synthon and a source of an internal oxidant, dimethyl sulfoxide, that promotes in situ dehydrogenation to product scaffolds. The method enables access to imidazo-pyridine, pyrazine, and pyrimidine heteroaromatics.

Exploration of Benzo[b]carbazole-6,11-diones as anticancer agents: Synthesis and studies of hTopoIIα inhibition and apoptotic effects.

Two series of (hetero)arylamino-naphthoquinones and benzo-fused carbazolequinones were considered for study with the rationale that related structural motifs are present in numerous drugs, clinical trial agents, natural products and hTopoIIα inhibitors. Total 42 compounds were synthesized by reactions including dehydrogenative CN and Pd-catalyzed CC bond forming transformations. These compounds were screened against numerous cancer cells including highly metastatic one (MCF-7, MDA-MB-231, H-357 and HEK293T), and normal cells (MCF 10A). Some of the active compounds were evaluated for clonogenic cell survival and apoptotic effects in cancer cells (DAPI nuclear staining, Comet assay, Annexin-V-FITC/PI dual staining, flow cytometry, and western blot analysis with relevant proteins). All compounds were tested for hTopoIIα inhibitory activity. The investigated series compounds showed important properties like significant apoptotic antiproliferation in cancer cells with cell cycle arrest at S-phase and downregulation of NF- κß signaling cascade, relatively less cytotoxicity to normal cells, and hTopoIIα inhibition with more efficiency compared to an anticancer drug etoposide.

Synthesis of Polyfunctionalized Pyrroles via a Tandem Reaction of Michael Addition and Intramolecular Cyanide-Mediated Nitrile-to-Nitrile Condensation.

A new approach for the synthesis of tetrasubstituted/functionalized NH-pyrroles from gem-diactivated acrylonitriles and TMSCN has been developed. The strategy utilizes the generation of vic-dinitrile via Michael addition and cyanide-mediated nitrile-to-nitrile cyclocondensation, which proceed in tandem guided by manifold roles of "CN". An extended application to the production of fused pyrrole has also been realized.

Synthesis of Polysubstituted 2-Aminoimidazoles via Alkene-Diamination of Guanidine with Conjugated α-Bromoalkenones.

A step-economical access to polysubstituted aminoimidazoles has been accomplished via alkene vicinal C-N bonds formation of 2-bromo-2-alkenones with guanidine avoiding its NH-protection/derivatization prerequisite for electronic modulation. The approach has excellent substrate scope, is amenable to diverse guanidine-containing substrates, and introduces distinctive substitutions/functionalities into aminoimidazole core. It is also applicable to preparation of fused-imidazoles. The reaction involves a tandem pathway of aza-Michael addition, SN2, and a unique redox-neutral process, as evident by spectroscopic study and control experiments.

Pd-Catalyzed Ag(I)-Promoted C3-Arylation of Pyrido[1,2-a]pyrimidin-4-ones with Bromo/Iodo-Arenes.

A regioselective Ag(I)-promoted Pd-catalyzed C3-H activation-arylation of pyrido[1,2-a]pyrimidin-4-ones with bromo/iodo-(hetero)arenes under aqueous conditions has been developed. It affords an efficient access to pharmaceutically important versatile 3-aryl-pyrido[1,2-a]pyrimidin-4-ones. Interestingly, the arylation undergoes via a pathway with an unusual feature involving the formation of cationic arylpalladium species promoted by halo-sequestering Ag salts enabling concerted C3-palladation-deprotonation, as explored by relevant experiments and spectroscopic studies. The present approach is step economical, good yielding, and compatible with various functionalities and applicable to a wide range of starting materials.

Synthesis of 2-Arylpyridopyrimidinones, 6-Aryluracils, and Tri- and Tetrasubstituted Conjugated Alkenes via Pd-Catalyzed Enolic C-O Bond Activation-Arylation.

A new and efficient approach for the synthesis of biologically important 2-aryl-4H-pyrido[1,2-a]pyrimidin-4-ones and 6-aryluracils via previously unknown Pd-catalyzed enolic C-OH activation-arylation of pyridopyrimidin-2,4-diones and barbituric acids, respectively, with boronic acids is reported. The starting materials are readily available, and products are obtained in high yields. An efficient and chemo- and stereoselective access to various tri- and tetrasubstituted conjugated alkenones and alkenoates is also obtained in this arylation approach. Interestingly, the procedure for the construction of such diverse molecular frameworks is general and featured with excellent substrates scope, tolerance of a broad range of functionalities, the unusual viability of performing the reaction under open air and in aqueous cosolvent, and the amenability to a scale-up synthesis, which have been found to be common limitations in the conventional/classical routes. The application of the protocol in a simple one-step high-yield route to pharmaceutically important polyarylated pyridopyrimidinone demonstrates its further synthetic utility.

Desilylative activation of TMSCN in chemoselective Strecker-Ugi type reaction: functional fused imidazoles as building blocks as an entry route to annulated purines.

A pathway of desilylative activation of TMSCN as a functional isonitrile equivalent, and DABCO-THF as an appropriate system for activation in a chemoselective Strecker-Ugi type reaction, has rendered ethyl glyoxalate and various heterocyclic-2-amidines as feasible substrates, and afforded the successful synthesis of 3-amino-2-carboxyethyl substituted fused imidazoles as useful building blocks. This class of functional scaffold has provided, via construction of the fused pyrimidinone motif, the synthesis of biologically important C8-N9 annulated purines, adenines and their oxo/thio analogs. This new approach is convenient and flexible for the preparation of versatile purine-condensed heterocycles.

Natural-Product-Inspired Discovery of Trimethoxyphenyl-1,2,4-triazolosulfonamides as Potent Tubulin Polymerization Inhibitors.

An approach of natural product-inspired strategy and incorporation of an NP-privileged motif has been investigated for the discovery of new tubulin polymerization inhibitors. Two series, N-Arylsulfonyl-3-arylamino-5-amino-1,2,4-triazole derivatives, and their isomers were considered. The compounds were synthesized by construction of the N-aryl-1,2,4-triazole-3,5-diamine motif and sulfonylation. Although the chemo- and regioselectivity in sulfonylation were challenging due to multiple ring-tautomerizable-NH and exocyclic NH2 functionalities present in the molecular motifs, the developed synthetic method enabled the preparation of designed molecular skeletons with biologically important motifs. The approach also led to explore interesting molecular regio- and stereochemical aspects valuable for activity. The X-ray crystallography study indicated that the hydrogen bonding between the arylamine-NH and the arylsulfonyl-"O" unit and appropriate molecular-functionality topology allowed the cis-locking of two aryls, which is important for tubulin-binding and antiproliferative properties. All synthesized compounds majorly showed characteristic antiproliferative effects in breast cancer cells (MCF-7), and four compounds exhibited potent antiproliferative activity. One compound potently bound to tubulin at the colchicine site and inhibited tubulin polymerization in vitro. The compound significantly depolymerized microtubules in MCF-7 cells, arrested the cells at the G2/M phase, and induced cell death. This study represents the importance of the design strategy in medicinal chemistry and the molecular structural features relevant to anticancer anti-tubulin properties. The explored molecules have the potential for further development.

Molecular medicinal insights into scaffold hopping-based drug discovery success.

In both academia and the pharmaceutical industry, innovative hypotheses, methodologies and technologies that can shorten the drug research and development, leading to higher success rates, are vital. In this review, we demonstrate how innovative variations of the scaffold-hopping strategy have been used to create new druggable molecular spaces, drugs, clinical candidates, preclinical candidates, and bioactive agents. We also analyze molecular modulations that enabled improvements of the pharmacodynamic (PD), physiochemical, and pharmacokinetic (PK) properties (P3 properties) of the drugs resulting from these scaffold-hopping strategies.

Molecular editing of NSC-666719 enabling discovery of benzodithiazinedioxide-guanidines as anticancer agents.

DNA polymerase ß (Polß) is crucial for the base excision repair (BER) pathway of DNA damage repair and is an attractive target for suppressing tumorigenesis as well as chemotherapeutic intervention of cancer. In this study, a unique strategy of scaffold-hopping-based molecular editing of a bioactive agent NSC-666719 was investigated, which led to the development of new molecular motifs with Polß inhibitory activity. NSC compound and its analogs (two series) were prepared, focusing on pharmacophore-based molecular diversity. Most compounds showed higher activities than the parent NSC-666719 and exhibited effects on apoptosis. The inhibitory activity of Polß was evaluated in both in vitro reconstituted and in vivo intact cell systems. Compound 10e demonstrated significant Polß interaction and inhibition characteristics, including direct, non-covalent, reversible, and comparable binding affinity. The investigated approach is useful, and the discovered novel analogs have a high potential for developing as anticancer therapeutics.

Indenoindolone derivatives as topoisomerase II-inhibiting anticancer agents.

Based on known heterocyclic topoisomerase II inhibitors and anticancer agents, various indenoindolone derivatives were predicted as potential topoisomerase II-inhibiting anticancer agents. They are hydrazones, (thio)semicarbazones, and oximes of indenoindolones, and indenoindolols. These derivatives with suitable substitutions exhibited potent specific inhibition of human DNA TopoIIα while not showing inhibition of topoisomerase I and DNA intercalation, despite the fact that parent indenoindolones are known poor/moderate inhibitors of topoisomerase II. The potent topoisomerase II inhibitor indenoindolone derivatives exhibited good anticancer activities compared to etoposide and 5-fluorouracil, and relatively low toxicity to normal cells. These derivatizations of indenoindolones were found to result in enhancement of anticancer activities.

CuSO4-glucose for in situ generation of controlled Cu(I)-Cu(II) bicatalysts: multicomponent reaction of heterocyclic azine and aldehyde with alkyne, and cycloisomerization toward synthesis of N-fused imidazoles.

The catalytic efficiency of mixed Cu(I)-Cu(II) system in situ generated by partial reduction of CuSO(4) with glucose in ethanol (nonanhydrous) under open air has been explored. With this catalysis, the multicomponent cascade reaction of A(3)-coupling of heterocyclic amidine with aldehyde and alkyne, 5-exo-dig cycloisomerization, and prototropic shift has afforded an efficient and eco-friendly synthesis of therapeutically important versatile N-fused imidazoles. Diverse heterocyclic amidines, several of which are known to be poorly reactive, and aldehydes are compatible in this catalytic process.

C-H bond functionalization under metalation-deprotonation process: regioselective direct arylation of 3-aminoimidazo[1,2-a]pyrazine.

Concerted metalation deprotonation (CMD) approach with appropriate proton shuttle precursor, base, and solvent (PivOH-K(2)CO(3)-toluene) has rendered a regioselective Pd-catalyzed C6-arylation of 3-aminoimidazo[1,2-a]pyrazine, a therapeutically relevant scaffold accessible by multicomponent reaction. The arylation of this heteroarene suffers from competing C5 and C2'-arylation reactions, while the developed process has virtually eliminated these competing arylations. Density functional calculations for CMD C-H activation at C6, C5, C8, and C2' sites imply that the energy barrier with distortion energy penalty as major contributing component influences the regioselectivity.

Scaffold hybridization in generation of indenoindolones as anticancer agents that induce apoptosis with cell cycle arrest at G2/M phase.

Scaffold hybridization of several natural and synthetic anticancer leads led to the consideration of indenoindolones as potential novel anticancer agents. A series of these compounds were prepared by a diversity-feasible synthetic method. They were found to possess anticancer activities with higher potency compared to etoposide and 5-fluorouracil in kidney cancer cells (HEK 293) and low toxicity to corresponding normal cells (Vero). They exerted apoptotic effect with blocking of cell cycle at G2/M phase.

A Core-Linker-Polyamine (CLP) Strategy Enables Rapid Discovery of Antileishmanial Aminoalkylquinolinecarboxamides That Target Oxidative Stress Mechanism.

A Core-Linker-Polyamine (CLP) strategy has been exploited to develop new antileishmanial agents. It involves the linker-based assembly of alkyl-polyamine side chain as a potential pharmacophore motif with a privileged heterocyclic motif, 4-arylquinoline. A series of aminoalkyl 4-arylquinoline-2-carboxamides and their analogs were synthesized and tested against L. donovani promastigotes. Among all synthesized derivatives, 10 compounds showed significant antipromastigote activities with more efficacy (IC50 : 4.75-8 µM) than an antileishmanial oral drug Miltefosine (IC50 : 8.9±1.55 µM). Most active aminoalkyl-quinoline-carboxamides 9 a and 9 b, displayed negligible cytotoxicity towards human monocytic (THP-1) macrophages. The compounds show antileishmanial activity by generating mitochondrial superoxide radicals. However, they did not show interference with trypanothione reductase, a redox enzyme of Leishmania. Significant change in the morphology of the L. donovani promastigote by the compounds was observed. The Structure-activity relationship analysis suggest the pharmacophoric importance of alkylpolyamine and carboxamide motifs. In silico evaluation indicated that the investigated active molecules 9 a and 9 b possess important drug-likeness, physicochemical and pharmacokinetic-relevant properties.

Identification of 2-arylquinazolines with alkyl-polyamine motifs as potent antileishmanial agents: synthesis and biological evaluation studies.

2-Arylquinazolines with a range of alkyl polyamines as side chain/ring functional motifs at the 4th-position were considered for antileishmanial study with the rationale that related heterocyclic scaffolds and polyamine functionalities are present in drugs, clinical trial agents, natural products and anti-parasitic/leishmanial agents. Synthesis involves construction of the 2-arylquinazolin-4-one ring and deoxyamination via deoxychlorination followed by SNAr-based amination or a methodology of SNAr-deoxyamination driven by BOP-mediated hydroxyl-activation. Various alkyl-polyamines important for activities were incorporated. A total of 26 compounds were prepared and screened against Leishmania donovani (Ld) promastigote cells using the MTT assay. Most of the investigated series of compounds showed characteristic leishmanicidal properties. Several compounds showed pronounced leishmanicidal activities (IC50: 5-6.5 µM) with higher efficiency than the antileishmanial drug miltefosine (IC50: 10.5 µM), and relatively less cytotoxicity to macrophage host cells (SI: 9.27-13.5) compared to miltefosine (SI: 3.42). Important pharmacophoric skeletons were identified.

A cascade reaction of indolyl-migratory isocyanide insertion, scaffold rearrangement and redox-neutral event with isocyanide as a C(sp3)H-N synthon efficiently constructs indolylisoindolinones.

Herein, we report a Pd(0)-catalyzed cascade reaction of intramolecular indolyl isocyanide-insertion, isocyanide-initiated scaffold-rearrangement with indolyl migration and redox-neutral process, which affords an efficient access to indolylisoindolinones. Isocyanide as a C(sp3)H-N synthon and the alkyl motif of isocyanide as a hydride source have been explored for the first time.