Sodium-Hydroxide-Mediated Synthesis of Highly Functionalized [1,6]-Naphthyridines in a One-Pot Pseudo Five-Component Reaction

Synthesis and Anticancer Properties of Functionalized 1,6-Naphthyridines

The burgeoning interest in synthesis and biological applications of 1,6-naphthyridines reflects the importance of 1,6-naphthyridines in the synthetic as well as medicinal chemistry fields. Specially, 1,6-naphthyridines are pharmacologically active, with variety of applications such as anticancer, anti-human immunodeficiency virus (HIV), anti-microbial, analgesic, anti-inflammatory and anti-oxidant activities. Although collective recent synthetic developments have paved a path to a wide range of functionalized 1,6-naphthyridines, a complete correlation of synthesis with biological activity remains elusive. The current review focuses on recent synthetic developments from the last decade and a thorough study of the anticancer activity of 1,6-naphthyridines on different cancer cell lines. Anticancer activity has been correlated to 1,6-naphthyridines using the literature on the structure-activity relationship (SAR) along with molecular modeling studies. Exceptionally, at the end of this review, the utility of 1,6-naphthyridines displaying activities other than anticancer has also been included as a glimmering extension.

Pd-Catalyzed One-Pot Stepwise Synthesis of Benzo[b][1,6]naphthyridines from 2-Chloroquinoline-3-carbonitriles Using Sulfur and Amines As Nucleophiles

A palladium-catalyzed one-pot stepwise coupling-annulation reaction of 2-chloroqunoline-3-carbonitriles enabled the direct synthesis of sulfur-substituted benzo[b][1,6]naphthyridines via multiple bond formation. The reaction provided an unusual mode for cyclization as sodium sulfide, a soft nucleophile, preferred to attack on the carbon of the nitrile group rather than on the C-C triple bond. The developed chemistry was extended with the secondary amines as nucleophiles to afford nitrogen-substituted benzo[b][1,6]naphythyridines while primary amines afforded hydroamination products . The hydromination products were transformed to benzo[b][1,6]naphthyridones via a base-mediated cyclization reaction. The  developed protocol features inexpensive and easily synthesizable starting materials, easy operations, and a high efficiency and tolerance to a broad range of substrates.

Synthesis of Unsymmetrical Sulfides and Their Oxidation to Sulfones to Discover Potent Antileishmanial Agents

Unsymmetrical sulfides were first synthesized using combinations of a 1,3-dicarbonyl, an aromatic aldehyde and a thiol in the presence of 10 mol % ethanolic piperidine. These sulfides derivatives were subsequently converted into corresponding sulfones via oxidation in the presence of m-chloroperoxybenzoic acid (m-CPBA) at ice-bath to room temperature. The former reaction was achieved at room temperature through one-pot three-component. The later was obtained in good yields using mild reaction conditions with flexibility in choice from a range of substrates. The antimicrobial properties of the newly synthesized sulfone derivatives were investigated against the protozoan parasite, Leishmania donovani, a causative agent of visceral leishmaniasis (VL). Nine sulfone derivatives were found to be efficacious and exhibited significant antimicrobial activity. Further, these compounds were nontoxic on murine peritoneal macrophages thus eliminating potential cytoxicity in the host cells. These compounds may be indicated as potential leads in the treatment of visceral leishmaniasis.

Cubic Perovskite ZnTiO3 Nanopowder as a Recyclable Heterogeneous Catalyst for the Synthesis of 1,6-Naphthyridines in Water

Cubic perovskite ZnTiO₃ nanopowder has been prepared by means of a sustainable sol-gel method. The nanopowder (12-20 nm) has been thoroughly characterized by N₂ sorption analysis, high-resolution (HR) TEM, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), SEM, and FTIR analyses. The environmentally benign synthesis of highly substituted 1,6-naphthyridines catalyzed by ZnTiO₃ nanopowder in aqueous media has been demonstrated. It requires two different catalytic functions, that is, an acid one, which is provided by Ti^IV ions, and a basic one, which is provided by the oxide ion incorporated within the ZnTiO₃ metal oxide framework. 1,6-Naphthyridines are of tremendous biological importance, and this method is simple and environmentally friendly. The greenness of the process was satisfactorily established as water was exploited as the reaction medium and there was very high atom economy.

Beyond conventional routes, an unprecedented metal-free chemoselective synthesis of anthranilate esters via a multicomponent reaction (MCR) strategy

A hitherto unreported route for the synthesis of anthranilate esters is demonstrated using 2-nitrobenzaldehyde, malonitrile and an alcohol or amine via a metal and oxidant free multicomponent reaction (MCR) strategy.

Pseudo-five-component domino strategy for the combinatorial library synthesis of [1,6] naphthyridines-an on-water approach

This work features the base-promoted on-water synthesis of [1,6]-naphthyridines from methyl ketones, malononitrile and phenols or thiols. The reaction conditions were carefully tuned to drive the product selectivity from 3H-pyrroles to [1,6]-naphthyridines. The advantages of this method lie in its simplicity, cost effectiveness, and environmental friendliness, representing a new effort toward the on-water synthesis of [1,6]-naphthyridines without starting from a nitrogen-containing heterocycle and highlighting the versatility of the nitrile functional group.