The Intramolecular Povarov Tool in the Construction of Fused Nitrogen-Containing Heterocycles

In vitro and in vivo antibacterial activity, resistance analysis and molecular docking study of pleuromutilin derivatives against Streptococcus suis

OBJECTIVES

To evaluate the in vitro and in vivo antimicrobial activity of pleuromutilin derivatives modified with C14 side-chain against Streptococcus suis.

METHODS

To determine the minimum inhibitory concentrations (MICs) of 268 pleuromutilin derivatives with C14 side-chain modifications against S. suis ATCC 43 765 using the broth dilution method. Derivative B43, B49, B52, B53 and B54, which exhibited better antimicrobial activity, were selected for further investigation of their in vitro antibacterial effect, cytotoxicity, and in vivo antibacterial effect.

RESULTS

Determination activity of five derivatives against clinical strains (n = 37), as well as growth and time-killing curves. Those experiments showed that all the five derivatives had good activity against S. suis in vitro. Resistance-inducing assays demonstrated that, except for B43, the derivatives had similar abilities to induce resistance to tiamulin. In addition, the five derivatives did not have erythrocyte haemolytic toxicity (0.25-16 mg/L) and cytotoxicity (1.25-80 mg/L). In the mouse thigh infection model, the derivative of B49 exhibited superior antibacterial efficacy. About 40 mg/kg B49 had good activity and improved the survival rate of mice by 33.3% in the S. suis mouse peritonitis model. Molecular docking study and scanning electron microscopy revealed that B49 can effectively bind to the active site of the 50S ribosome and disrupt cell membranes.

CONCLUSIONS

A total of 68.66% of the 268 C14 side-chain modified pleuromutilin derivatives showed potent activity against S. suis. Among them, B49 showed good in vitro and in vivo antimicrobial effects against S. suis, indicating that B49 can be intensively studied as an antimicrobial candidate compound.

Visible-Light-Induced Cascade Cyclization of 1-(2-(Arylethynyl)benzoyl)indoles into Sulfonated Benazepino[1,2-a]indolones

1-(2-(Arylethynyl)benzoyl)indoles were developed as an innovative scaffold for radical cascade cyclization under visible-light and mild conditions, enabling efficient synthesis of sulfonated benazepino[1,2-a]indolones. This method operates at room temperature and demonstrates broad substrate compatibility and scalability, with promising potential for sunlight-driven reactions.

Phosphine Oxide Indenoquinoline Derivatives: Synthesis and Biological Evaluation as Topoisomerase I Inhibitors and Antiproliferative Agents

The synthesis of phosphorous indenoquinolines and their biological evaluation as topoisomerase 1 (TOP1) inhibitors and antiproliferative agents were performed. First, the preparation of new hybrid 5H-indeno[2,1-c]quinolines with a phosphine oxide group was performed by a two-step Povarov-type [4+2]-cycloaddition reaction between the corresponding phosphorated aldimines with indene in the presence of BF3·Et2O. Subsequent oxidation of the methylene present in the structure resulted in the corresponding indeno[2,1-c]quinolin-7-one phosphine oxides 10. The synthesized derivatives were evaluated as TOP1 inhibitors showing higher inhibition values than CPT at prolonged incubation times (5 min). Inhibition of TOP1 was even observed after 30 min of incubation. The cytotoxic activities of these compounds were also studied against different cancer cell lines and a non-cancerous cell line. While some compounds showed cytotoxicity against some cancerous cells, none of the compounds showed any cytotoxicity against the non-cancerous cell line, MRC-5, in contrast to CPT, which exhibits high toxicity against this cell line. These results represent a very interesting advance since the heterocyclic phosphine oxide derivatives have important properties as TOP1 inhibitors and show an interesting cytotoxicity against different cell lines.

Palladium-catalyzed cascade of aza-Wacker and Povarov reactions of aryl amines and 1,6-dienes for hexahydro-cyclopenta[b]quinoline framework

Palladium catalyzed tandem reaction represents a one-pot synthetic approach to efficiently synthesize complex functionalized molecules while reducing synthetic steps, aligning with the principles of green chemistry. However, achieving a direct cascade of the aza-Wacker and Povarov reactions in one-pot synthesis presents a challenge due to substrate compatibility issues between the two reactions. In this work, we describe an aza-Wacker/Povarov reaction employing a highly electrophilic palladium catalyst, which effectively converts anilines and 1,6-dienes into hexahydro-cyclopenta[b]quinolines. The optimized conditions yield up to 79%, with a diastereoselectivity > 20:1. Substrate range testing reveals compatibility with various sensitive functional groups, and successful late-stage modifications are performed on several natural products and drug molecules, demonstrating the versatility and practicality of the method. Additionally, a preliminary investigation into the reaction mechanism suggests an aza-Wacker process followed by a Povarov process.

Aza-Povarov Reaction. A Method for the Synthesis of Fused Tetracyclic Chromeno[4,3-d]pyrido[1,2-a]pyrimidines

A cornerstone in drug discovery is the development of strategies to provide privileged small molecules with specific structural and stereochemical complexity, allowing access to new potential therapeutic entities. In this work, a new strategy based on the [4 + 2] Povarov reaction involving 1,3-diazadiene was developed. This approach is applied for a straightforward procedure in the preparation of chromeno[4,3-d]pyrido[1,2-a]pyrimidine derivatives, with accessible substrates, 2-aminopyridine and unsaturated aldehydes, and excellent atom economy to obtain four fused ring heterocycles, in a regio- and diastereoselective way.

Antileishmanial Effect of 1,5- and 1,8-Substituted Fused Naphthyridines

In the absence of a vaccine, there is a need to find new drugs for the treatment of neglected tropical diseases, such as leishmaniasis, that can overcome the many drawbacks of those currently used. These disadvantages include cost, the need to maintain a cold chain, the route of administration, the associated adverse effects and the generation of resistance. In this work we have evaluated the antileishmanial effect of 1,5- and 1,8-substituted fused naphthyridines through in vitro and ex vivo assays, using genetically modified axenic and intramacrophagic Leishmania infantum amastigotes. The toxicity of these compounds has been tested in the mammalian host cell using murine splenic macrophages, as well as in murine intestinal organoids (miniguts) in order to assess their potential for oral administration. The 1,8- derivatives showed greater leishmanicidal activity and the presence of a nitrogen atom in the fused ring to the naphthyridine was important to increase the activity of both types of molecules. The aromatization of the pyridine ring also had marked differences in the activity of the compounds.