A unified approach to polyene macrolides: synthesis of candidin and nystatin polyols

Reviving the interest in the versatile drug nystatin: A multitude of strategies to increase its potential as an effective and safe antifungal agent

Nystatin is an antifungal molecule with a remarkable yet squandered versatility. In this review, its mechanism of action is explored, along with its extensive action spectrum and toxicity. A multitude of methodologies to tackle the drug's physical and chemical hurdles are outlined along with some proven-effective strategies to increase its activity and/or decrease its toxicity. A separate detailed section focused on micro and nanotechnology solutions addresses new drug delivery systems made of polymeric, metallic or lipid materials. Although the topical route depicts greater representativeness amongst these formulations, the intravenous, dental, oral, vaginal and inhalation routes are also mentioned. The unsuccessful previous attempts at developing parenteral formulations of nystatin or even the withdrawal of a nystatin-loaded multilamellar liposome should not divert research away from this drug. In fact, the interest in nystatin ought to be reawakened with the ongoing clinical trials on the promising nystatin-like genetically engineered derivate BSG005.

New Glycosylated Polyene Macrolides: Refining the Ore from Genome Mining

Glycosylated polyene macrolides include effective antifungal agents, such as pimaricin, nystatin, candicidin, and amphotericin B. For the treatment of systemic mycoses, amphotericin B has been described as a gold-standard antibiotic because of its potent activity against a broad spectrum of fungal pathogens, which do not readily become resistant. However, amphotericin B has severe toxic side effects, and the development of safer alternatives remains an important objective. One approach towards obtaining such compounds is to discover new related natural products. Advances in next-generation sequencing have delivered a wealth of microbial genome sequences containing polyene biosynthetic gene clusters. These typically encode a modular polyketide synthase that catalyzes the assembly of the aglycone core, a cytochrome P450 that oxidizes a methyl branch to a carboxyl group, and additional enzymes for synthesis and attachment of a single mycosamine sugar residue. In some cases, further P450s catalyze epoxide formation or hydroxylation within the macrolactone. Bioinformatic analyses have identified over 250 of these clusters. Some are predicted to encode potentially valuable new polyenes that have not been uncovered by traditional screening methods. Recent experimental studies have characterized polyenes with new polyketide backbones, previously unknown late oxygenations, and additional sugar residues that increase water-solubility and reduce hemolytic activity. Here we review these studies and assess how this new knowledge can help to prioritize silent polyene clusters for further investigation. This approach should improve the chances of discovering better antifungal antibiotics.

Production, Detection, Extraction, and Quantification of Polyene Antibiotics

Polyene antibiotics are macrolide antifungal compounds obtained by fermentation of producer Streptomyces strains. Here we describe commonly used methods for polyene production, detection, and their subsequent extraction and purification. While bioassays are used to detect these compounds based on their biological activity, quantification by spectrophotometry or high-performance liquid chromatography (HPLC ) relies on their physiochemical properties and is more reliable.

Consecutive reactions to construct tricarbonyl compounds and synthetic applications thereof

A cascade process to construct synthetically valuable β-keto-β′-acylcycloalkanecarboxylic acid esters and their transformation into bicyclic and tricyclic systems through intramolecular condensation reactions.

The Chemistry of Drugs to Treat Candida albicans

Background::

Candida species are in various parts of the human body as commensals. However, they can cause local mucosal infections and, sometimes, systemic infections in which Candida species can spread to all major organs and colonize them.

Objective::

For the effective treatment of the mucosal infections and systemic life-threatening fungal diseases, a considerably large number of antifungal drugs have been developed and used for clinical purposes that comprise agents from four main drug classes: the polyenes, azoles, echinocandins, and antimetabolites.

Method: :

The synthesis of some of these drugs is available, allowing synthetic modification of the molecules to improve the biological activity against Candida species. The synthetic methodology for each compound is reviewed.

Results: :

The use of these compounds has caused a high-level resistance against these drugs, and therefore, new antifungal substances have been described in the last years. The organic synthesis of the known and new compounds is reported.

Conclusion: :

This article summarizes the chemistry of the existing agents, both the old drugs and new drugs, in the treatment of infections due to C. albicans, including the synthesis of the existing drugs.

Studies toward the synthesis of strevertenes A and G: stereoselective construction of C1–C19segments of the molecules

Efficient route for the stereoselective synthesis of common C₁–C₁₉segment of strevertenes A and G has been developed.

Pushing the boundaries of vinylogous reactivity: catalytic enantioselective mukaiyama aldol reactions of highly unsaturated 2-silyloxyindoles

The first example of catalytic, enantioselective hypervinylogous Mukaiyama aldol reaction (HVMAR) involving multiply unsaturated 2-silyloxyindoles is reported. The reaction utilizes a chiral Lewis base-catalyzed Lewis acid-mediated technology to deliver homoallylic 3-polyenylidene 2-oxindoles with extraordinary levels of regio-, enantio-, and geometrical selectivity. This work highlights a subtle yet decisive influence of the indole N-substituents on the propagation of the vinylogous reactivity space of the donor substrates up to ten bonds away from the origin of the vinylogy effect. Analysis of the (13) C NMR chemical shifts of the C-ω remote site within homologous silyloxyindole donors enabled rationalization of the results and easy qualitative prediction of the HVMAR reactivity/inertia toward a given aldehyde acceptor.

Dissociation of nystatin and amphotericin analogues: characterisation of minor anti-fungal macrolides

Tandem mass spectrometry combined with Fourier transform ion cyclotron resonance (FT-ICR) has been the basis for rationalizing the fragmentation mechanisms of anti-fungal macrolides nystatin A(1), amphotericin B and pimaricin. The positive ion mass spectra were not informative, however, the dissociation of deprotonated molecules led to structurally significant ring-opened fragments. Using this approach of tandem FT-ICR mass spectrometry and electrospray ionisation coupled with high-performance liquid -chromatography (HPLC), 11 macrolide natural analogues or degradation products were characterised in the nystatin mixture.

Synthesis and biophysical studies on 35-deoxy amphotericin B methyl ester

The use of molecular editing in the elucidation of the mechanism of action of amphotericin B is presented. A modular strategy for the synthesis of amphotericin B and its designed analogues is developed, which relies on an efficient gram-scale synthesis of various subunits of amphotericin B. A novel method for the coupling of the mycosamine to the aglycone was identified. The implementation of the approach has enabled the preparation of 35-deoxy amphotericin B methyl ester. Investigation of the antifungal activity and efflux-inducing ability of this amphotericin B congener provided new clues to the role of the 35-hydroxy group and is consistent with the involvement of double barrel ion channels in causing electrolyte efflux.