Synthesis and Antibacterial Activity of a Novel Class of 4‘-Substituted 16-Membered Ring Macrolides Derived from Tylosin

Dual Antibiotic Approach: Synthesis and Antibacterial Activity of Antibiotic-Antimicrobial Peptide Conjugates

In recent years, bacterial resistance to conventional antibiotics has become a major concern in the medical field. The global misuse of antibiotics in clinics, personal use, and agriculture has accelerated this resistance, making infections increasingly difficult to treat and rendering new antibiotics ineffective more quickly. Finding new antibiotics is challenging due to the complexity of bacterial mechanisms, high costs and low financial incentives for the development of new molecular scaffolds, and stringent regulatory requirements. Additionally, innovation has slowed, with many new antibiotics being modifications of existing drugs rather than entirely new classes. Antimicrobial peptides (AMPs) are a valid alternative to small-molecule antibiotics offering several advantages, including broad-spectrum activity and a lower likelihood of inducing resistance due to their multifaceted mechanisms of action. However, AMPs face challenges such as stability issues in physiological conditions, potential toxicity to human cells, high production costs, and difficulties in large-scale manufacturing. A reliable strategy to overcome the drawbacks associated with the use of small-molecule antibiotics and AMPs is combination therapy, namely the simultaneous co-administration of two or more antibiotics or the synthesis of covalently linked conjugates. This review aims to provide a comprehensive overview of the literature on the development of antibiotic-AMP conjugates, with a particular emphasis on critically analyzing the design and synthetic strategies employed in their creation. In addition to the synthesis, the review will also explore the reported antibacterial activity of these conjugates and, where available, examine any data concerning their cytotoxicity.

Conjugates of Desmycosin with Fragments of Antimicrobial Peptide Oncocin: Synthesis, Antibacterial Activity, Interaction with Ribosome

Design and synthesis of conjugates consisting of the macrolide antibiotic desmycosin and fragments of the antibacterial peptide oncocin were performed in attempt to develop new antimicrobial compounds. New compounds were shown to bind to the E. coli 70S ribosomes, to inhibit bacterial protein synthesis in vitro, as well as to suppress bacterial growth. The conjugates of N-terminal hexa- and tripeptide fragments of oncocin and 3,2',4''-triacetyldesmycosin were found to be active against some strains of macrolide-resistant bacteria. By simulating molecular dynamics of the complexes of these compounds with the wild-type bacterial ribosomes and with ribosomes, containing A2059G 23S RNA mutation, the specific structural features of their interactions were revealed.

Promising bioactive compounds from the marine environment and their potential effects on various diseases

Background

The marine environment hosts a wide variety of species that have evolved to live in harsh and challenging conditions. Marine organisms are the focus of interest due to their capacity to produce biotechnologically useful compounds. They are promising biocatalysts for new and sustainable industrial processes because of their resistance to temperature, pH, salt, and contaminants, representing an opportunity for several biotechnological applications. Encouraged by the extensive and richness of the marine environment, marine organisms’ role in developing new therapeutic benefits is heading as an arable field.

Main body of the abstract

There is currently much interest in biologically active compounds derived from natural resources, especially compounds that can efficiently act on molecular targets, which are involved in various diseases. Studies are focused on bacteria and fungi, isolated from sediments, seawater, fish, algae, and most marine invertebrates such as sponges, mollusks, tunicates, coelenterates, and crustaceans. In addition to marine macro-organisms, such as sponges, algae, or corals, marine bacteria and fungi have been shown to produce novel secondary metabolites (SMs) with specific and intricate chemical structures that may hold the key to the production of novel drugs or leads. The marine environment is known as a rich source of chemical structures with numerous beneficial health effects. Presently, several lines of studies have provided insight into biological activities and neuroprotective effects of marine algae, including antioxidant, anti-neuroinflammatory, cholinesterase inhibitory activity, and neuronal death inhibition.

Conclusion

The application of marine-derived bioactive compounds has gained importance because of their therapeutic uses in several diseases. Marine natural products (MNPs) display various pharmaceutically significant bioactivities, including antibiotic, antiviral, neurodegenerative, anticancer, or anti-inflammatory properties. The present review focuses on the importance of critical marine bioactive compounds and their role in different diseases and highlights their possible contribution to humanity.

Multicomponent synthesis of α-acylamino and α-acyloxy amide derivatives of desmycosin and their activity against gram-negative bacteria

Bacterial resistance to the existing drugs requires constant development of new antibiotics. Developing compounds active against gram-negative bacteria thereby is one of the more challenging tasks. Among the many approaches to develop successful antibacterials, medicinal chemistry driven evolution of existing successful antibiotics is considered to be the most effective one. Towards this end, the C-20 aldehyde moiety of desmycosin was modified into α-acylamino and α-acyloxy amide functionalities using isonitrile-based Ugi and Passerini reactions, aiming for enhanced antibacterial and physicochemical properties. The desired compounds were obtained in 45-93% yield under mild conditions. The antibacterial activity of the resulting conjugates was tested against gram-negative Aliivibrio fischeri. The antibiotic strength is mostly governed by the amine component introduced. Thus, methylamine derived desmycosin bis-amide 4 displayed an enhanced inhibition rate vs. desmycosin (99% vs. 83% at 1 µM). Derivatives with long acyclic or bulky amine and isocyanide Ugi components reduced potency, whereas carboxylic acid reagents with longer chain length afforded increased bioactivity. In Passerini 3-component products, the butyric ester amide 22 displayed a higher activity (90% at 1 µM) than the parent compound desmycosin (2).

Antiproliferative activity of new 2-glyco-3-nitro-1,2-dihydroquinolines and quinolines synthesized under solventless conditions promoted by neutral alumina

This paper describes the syntheses of new 2-glyco-3-nitro-1,2-dihydroquinolines and 2-glyco-3-nitroquinolines by one-pot aza-Michael–Henry-dehydration reactions using green procedures, as well as the evaluation of their antiproliferative activity.

An atom economical method for the direct synthesis of quinoline derivatives from substituted o-nitrotoluenes

A one-pot procedure for the preparation of substituted quinolines from substituted o-nitrotoluenes with electron-withdrawing groups and olefins (acrylic esters and acrylonitriles) using a cesium catalyst under mild reaction conditions is reported. The process involves a [2+4] cycloaddition mechanism.

ONO pincer type Pd(ii) complexes: synthesis, crystal structure and catalytic activity towards C-2 arylation of quinoline scaffolds

Four new palladium(ii) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. Utility of these complexes to catalyze C–C bond formation in quinoline scaffolds were assessed.

Synthesis and biological activity of some nucleoside analogs of hydroquinoline-3-carbonitrile

Hydroquinoline acyclonucleosides 2, 4, 6a,b, 8a,b, 9a,b, and their corresponding N-alkyl derivatives (10-12) were obtained by the reaction of 1a,b with acetoxybutylbromide, (2-acetoxyethoxy)methyl bromide, 3-chloropropanol, 1,3-dichloro-2-propanol, epichlorohydrin, propargyl/allyl bromides in the presence of K(2)CO(3) in dry dimethylformamide (DMF). In a similar manner, reaction of 1a,b with glycosyl/galactosyl and lactosyl bromide afforded the corresponding N-nucloside derivatives 13a,b, 15a,b, and 17, respectively. Deacetylation of the N-nucleosides derivatives in the presence of Et(3)N/MeOH and few drops of water gave the deprotected derivatives 3, 5, 7a,b, 14a,b, 16a,b, and 18 in good yields, respectively. All the newly synthesized compounds are elucidated by infrared, (1)H, (13)C NMR and elemental analyses. Some of these compounds were screened for antimicrobial activities.

Green chemical approach: microwave assisted, titanium dioxide nanoparticles catalyzed, convenient and efficient C–C bond formation in the synthesis of highly functionalized quinolines and quinolinones

TiO₂ nanoparticles was effectively applied in the microwave assisted synthesis of quinolines and quinolones.

A convenient and efficient C–OH bond activation, PdCl2(PPh3)2catalyzed, C–C bond formation of tautomerizable quinolinones with the aid of BOP reagent and boronic acids

C–C bond formation of tautomerizable quinolinones. C–OH bond activation using BOP reagent and boronic acids.

Effect of solvents on the spectroscopic properties of LD-489 & LD-473: estimation of ground and excited state dipole moments by solvatochromic shift method

The absorption and fluorescence spectra of 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoro methyl)-2H-pyrano[2,3-b][1,8]naphthyridin-2-one (LD-489) and 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyl-5-(trifluoromethyl)-7H-pyrrolo[3,2-g]quinolin-7-one (LD-473) have been recorded at room temperature in different solvents and 1,4-dioxane-acetonitrile solvent mixtures. The UV-Visible absorption spectra are less sensitive to solvent polarity than the corresponding fluorescence spectra in both the dyes which show pronounced solvatochromic effect. The effects of solvents upon the spectral properties are analyzed using Lippert-Mataga polarity function, Richardts microscopic solvent polarity parameter and Catalán's multiple linear regression approach. Both general solute-solvent interactions and specific interactions are operative in these systems. The solvatochromic correlations are used to estimate excited state dipole moments using experimentally determined ground state dipole moments. The excited state dipole moment for both the dyes are found to be larger than their corresponding ground state dipole moment and is interpreted based on their resonance structures.

Synthesis and antibacterial activity of novel modified 5-O-desosamine ketolides

A series of novel modified 5-O-desosamine-ketolides were synthesized. The 5-O-desosamine fragment was removed from ketolide by an efficient and mild manipulation. 4-O-substituted desosamine was introduced into the ketolide aglycon and various coupling methods were essayed for the glycosylation. Three novel ketolides were tested for in vitro antibacterial activity against a panel of susceptible and resistant pathogens. Compound 26 showed potent activity against all the methicillin-sensitivity and resistant pathogens.

Molecular mechanics (MM3(pi)) conformational analysis of molecules containing conjugated pi-electron fragments: Leucomycin-V

The conformations of the 16-membered macrolide antibiotic leucomycin-V (1) were studied with molecular mechanics. Leucomycin-V contains a conjugated pi-electron fragment and necessitates special treatment with the MM3(pi) modeling protocol. Comparison was made with results from the standard MM3 scheme. The CONFLEX conformational search procedure was used for finding low-energy conformations. The computed data are indicative for the existence of mainly one conformation of the macro-ring of 1 and minor participation of several others. Intramolecular hydrogen bonds play important roles for the preferred geometry of the macro-ring and the conformations of the side chains. The most probable macro-ring conformation of 1 is very similar to the preferred conformation of another 16-ring macrolide antibiotic, tylosin. The same order of conformational preference for 1 was estimated with the MM3 and the MM3(pi) methods. Surprisingly, when changing the chirality of the C(9) macro-ring atom of 1, the two methods produced different order of conformational preferences for the 9-epi form (2), as well as enhanced population of several clusters of conformations.