Pradimicins FS and FB, new pradimicin analogs: directed production, structures and biological activities

Chemistry and biology of specialized metabolites produced by Actinomadura

Covering: up to the end of 2022In recent years rare Actinobacteria have become increasingly recognised as a rich source of novel bioactive metabolites. Actinomadura are Gram-positive bacteria that occupy a wide range of ecological niches. This review highlights about 230 secondary metabolites produced by Actinomadura spp., reported until the end of 2022, including their bioactivities and selected biosynthetic pathways. Notably, the bioactive compounds produced by Actinomadura spp. demonstrate a wide range of activities, including antimicrobial, antitumor and anticoccidial effects, highlighting their potential in various fields.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Antimicrobial aromatic polyketides: a review of their antimicrobial properties and potential use in plant disease control

Aromatic polyketides are secondary metabolites widely found in bacteria, fungi, and plants, which are well-known for their diverse chemical structures and biological functions. The structural diversity of aromatic polyketides arises from a series of enzymatic modifications of the linear poly-β-ketone intermediates during biosynthesis. Their versatile bioactivities are exemplified by reports of their use as antibacterials, antifungals, antivirals, and antiparasitics. Despite many reports on the antimicrobial nature of aromatic polyketides, their potential use as plant disease control agents has still not been systematically explored and discussed. This review highlights examples of the use of aromatic polyketides as plant disease control agents and discusses their function and merits as agrochemicals.

Carbohydrate-Binding Non-Peptidic Pradimicins for the Treatment of Acute Sleeping Sickness in Murine Models

Current treatments available for African sleeping sickness or human African trypanosomiasis (HAT) are limited, with poor efficacy and unacceptable safety profiles. Here, we report a new approach to address treatment of this disease based on the use of compounds that bind to parasite surface glycans leading to rapid killing of trypanosomes. Pradimicin and its derivatives are non-peptidic carbohydrate-binding agents that adhere to the carbohydrate moiety of the parasite surface glycoproteins inducing parasite lysis in vitro. Notably, pradimicin S has good pharmaceutical properties and enables cure of an acute form of the disease in mice. By inducing resistance in vitro we have established that the composition of the sugars attached to the variant surface glycoproteins are critical to the mode of action of pradimicins and play an important role in infectivity. The compounds identified represent a novel approach to develop drugs to treat HAT.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Molecular architecture and therapeutic potential of lectin mimics

Lectins are proteins of non-immune origin that bind specific carbohydrates without chemical modification. Coupled with the emerging biological and pathological significance of carbohydrates, lectins have become extensively used as research tools in glycobiology. However, lectin-based drug development has been impeded by high manufacturing costs, low chemical stability, and the potential risk of initiating an unfavorable immune response. As alternatives to lectins, non-protein small molecules having carbohydrate-binding properties (lectin mimics) are currently attracting a great deal of attention because of their ease of preparation and chemical modification. Lectin mimics of synthetic origin are divided roughly into two groups, boronic acid-dependent and boronic acid-independent lectin mimics. This article outlines their representative architectures and carbohydrate-binding properties, and discusses their therapeutic potential by reviewing recent attempts to develop antiviral and antimicrobial agents using their architectures. We also focus on the naturally occurring lectin mimics, pradimicins and benanomicins. They are the only class of non-protein natural products having a C-type lectin-like ability to recognize d-mannopyranosides in the presence of Ca^2 + ions. Their molecular basis of carbohydrate recognition and therapeutic potential are also discussed.

A key cytochrome P450 hydroxylase in pradimicin biosynthesis

Pradimicins A-C (1-3) are a group of antifungal and antiviral polyketides from Actinomadura hibisca. The sugar moieties in pradimicins are required for their biological activities. Consequently, the 5-OH that is used for glycosylation plays a critical role in pradimicin biosynthesis. A cytochrome P450 monooxygenase gene, pdmJ, was amplified from the genomic DNA of A. hibisca and expressed in Escherichia coli BL21(DE3). PdmJ introduced a hydroxyl group to G-2A (4), a key pradimicin biosynthetic intermediate, at C-5 to form JX134 (5). A d-Ala-containing pradimicin analog, JX137a (6) was tested as an alternative substrate, but no product was detected by LC-MS, indicating that PdmJ has strict substrate specificity. Kinetic studies revealed a typical substrate inhibition of PdmJ activity. The optimal substrate concentration for the highest velocity is 115μM under the test conditions. Moreover, the conversion rate of 4 to 5 was reduced by the presence of 6, likely due to competitive inhibition. Coexpression of PdmJ and a glucose 1-dehydrogenase in E. coli BL21(DE3) provides an efficient method to produce the important intermediate 5 from 4.

General Synthesis Route to Benanomicin-Pradimicin Antibiotics

A general approach to the regio- and stereoselective total synthesis of the benanomicin-pradimicin antibiotics (BpAs) is described. Construction of the aglycon has been achieved by 1) the diastereoselective ring-opening of a biaryl lactone by using (R)-valinol as a chiral nucleophile and 2) the stereocontrolled semi-pinacol cyclization of the aldehyde acetal by using SmI(2) in the presence of BF(3)OEt(2) and a proton source to afford the ABCD tetracyclic monoprotected diol. This strategy enabled us to control the two stereogenic sites in the B ring (C-5 and C-6) and the regioselective introduction of the carbohydrate moiety. The ABCD tetracycle could serve as an ideal platform for the divergent access to various BpAs. The amino acid (D-alanine) was introduced onto the ABCD tetracycle. Glycosylation was promoted by the combination of Cp(2)HfCl(2) and AgOTf (1:2 ratio). Construction of the E ring followed by deprotection completed the first total synthesis of benanomicin A (2 a), benanomicin B (2 b), and pradimicin A (1 a). The route is flexible enough to allow the synthesis of other congeners differing in their amino acid and carbohydrate moieties.

Recent developments in pradimicin-benanomicin and triazole antibiotics

Fungal infections are on the rise as the number of patients with compromised immune systems continues to increase. The need for safer and more effective antifungals has resulted in the search for novel drug classes and for modifications to existing classes, with the aim of enhancing their antifungal spectra and potency. In this review, two classes of antifungals are discussed: the pradimicin-benanomicin antibiotics and the newer triazole derivatives. These have activity against Candida spp., Cryptococcus neoformans and Aspergillus spp., as well as variable activity against other less commonly encountered fungi including Pneumocystis carinii. Pradimicins-benanomicins are generally fungicidal, whereas the newer azoles appear to be selectively fungicidal to Cryptococcus neoformans and Aspergillus spp. Pradimicin-benanomicin acts by binding to mannan and alters membrane integrity. One water-soluble pradimicin candidate, BMS-181184, has been selected for clinical development. The triazoles act by inhibiting cytochrome P450 sterol 14a-demethylase. Four triazoles either currently in clinical development (voriconazole and D0870) or being considered as clinical candidates (ER-30346 and Sch 56592) will be discussed. The antifungal spectra, pharmacokinetic and toxicologic data in animals, and efficacy results in experimental infection models will be reviewed for BMS-181184 and the four newer triazoles. Results from the early clinical trials for voriconazole and D0870 will also be discussed.

Current and future approaches to antimycotic treatment in the era of resistant fungi and immunocompromised hosts

Due to the ever-increasing number of immunocompromised patients, both localised and life-threatening systemic fungal infections are on the increase. Conventional treatment is of limited help, not in the least due to a less optimum benefit-to-risk ratio. Moreover, emerging pathogens with reduced antimicrobial susceptibility and the development of resistance in Candida albicans form a new challenge. Fortunately, conventional antimycotics have been improved and entirely new ones are on the horizon as well as alternative approaches such as immunoreconstitution.

Interaction of three pradimicin derivatives with divalent cations in aqueous solution

This study focused on further analysis of the aggregation behavior of pradimicin derivatives and their interaction with cations in aqueous solution. BMY was compared with two other pradimicin antibiotics (T2 and FB) with the same aglycone moiety but consisting of different substitute groups. The surface tension measurement showed a clear critical micelle concentration at 1-2 mM of the BMY aqueous solution. The role of Zn2+ in replacing the Ca2+ was examined using 1H nuclear magnetic resonance (NMR) method. From changes in the NMR spectrum and precipitability, it was concluded that zinc ion has lower affinity and higher precipitating ability to BMY than the divalent cations of alkaline earth metal. The aggregation behavior of T2 and FB in aqueous solution was also studied using NMR method. The results suggest that the supramolecular behavior of T2 is similar to BMY whether or not Ca2+ ions are present in solution and that there are two binding sites for calcium ions in a T2 molecule. Unlike BMY and T2, the NMR spectrum of FB does not show distinct change upon Ca2+ addition. The interaction of pradimicin antibiotics with divalent metal ions was thought to be related to ionic electronegativity and to the amphoteric property of the antibiotics.

[Review article. Molecular basis of antimycotic therapy]

A review is presented on the hitherto clinically administered antimycotic drugs, their action mechanisms and limitations as well as on the presently newly developed antifungals and their molecular targets.