Prodrugs of reverse fosmidomycin analogues

Inhibition of DXR in the MEP pathway with lipophilic N-alkoxyaryl FR900098 analogs

In Mycobacterium tuberculosis (Mtb) and Plasmodium falciparum (Pf), the methylerythritol phosphate (MEP) pathway is responsible for isoprene synthesis. This pathway and its products are vital to bacterial/parasitic metabolism and survival, and represent an attractive set of drug targets due to their essentiality in these pathogens but absence in humans. The second step in the MEP pathway is the conversion of 1-deoxy-d-xylulose-5-phosphate (DXP) to MEP and is catalyzed by 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR). Natural products fosmidomycin and FR900098 inhibit DXR, but are too polar to reach the desired target inside some cells, such as Mtb. Synthesized FR900098 analogs with lipophilic substitution in the position α to the phosphorous atom showed promise, resulting in increased activity against Mtb and Pf. Here, an α substitution, consisting of a 3,4-dichlorophenyl substituent, in combination with various O-linked alkylaryl substituents on the hydroxamate moiety is utilized in the synthesis of a novel series of FR900098 analogs. The purpose of the O-linked alkylaryl substituents is to further enhance DXR inhibition by extending the structure into the adjacent NADPH binding pocket, blocking the binding of both DXP and NADPH. Of the initial O-linked alkylaryl substituted analogs, compound 6e showed most potent activity against Pf parasites at 3.60 μM. Additional compounds varying the phenyl ring of 6e were synthesized. The most potent phosphonic acids, 6l and 6n, display nM activity against PfDXR and low μM activity against Pf parasites. Prodrugs of these compounds were less effective against Pf parasites but showed modest activity against Mtb cells. Data from this series of compounds suggests that this combination of substituents can be advantageous in designing a new generation of antimicrobials.

Design and synthesis of fosmidomycin analogs containing aza-linkers and their biological activity evaluation

BACKGROUND

The enzymes involved in the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway are attractive targets of a new mode of action for developing anti-infective drugs and herbicides, and inhibitors against 1-deoxy-d-xylulose 5-phosphate reductoisomerase (IspC), the second key enzyme in the pathway, have been intensively investigated; however, few works are reported regarding IspC inhibitors designed for new herbicide discovery.

RESULTS

A series of fosmidomycin (FOS) analogs were designed with nitrogen-containing linkers replacing the trimethylene linker between the two active substructures of FOS, phosphonic acid and hydroxamic acid. Synthesis followed a facile three-step route of sequential aza-Michael addition of α-amino acids to dibenzyl vinylphosphonate, amidation of the amino acid carboxyl with O-benzyl hydroxylamine, and simultaneous removal of the benzyl protective groups. Biological activity evaluation of IspC and model plants revealed that some compounds had moderate enzyme and model plant growth inhibition effects. In particular, compound 10g, which has a N-(4-fluorophenylethyl) nitrogen-containing linker, exhibited the best plant inhibition activities, superior to the control FOS against the model plants Arabidopsis thaliana, Brassica napus L., Amaranthus retroflexus and Echinochloa crus-galli. A dimethylallyl pyrophosphate rescue assay on A. thaliana confirmed that both 10g and FOS exert their herbicidal activity by blocking the MEP pathway. This result consistent with molecular docking, which confirmed 10g and FOS binding to the IspC active site in a similar way.

CONCLUSION

Compound 10g has excellent herbicidal activity and represents the first herbicide lead structure of a new mode of action that targets IspC enzyme in the MEP pathway. © 2023 Society of Chemical Industry.

3D-printed wound dressings containing a fosmidomycin-derivative prevent Acinetobacter baumannii biofilm formation

Acinetobacter baumannii causes a wide range of infections, including wound infections. Multidrug-resistant A. baumannii is a major healthcare concern and the development of novel treatments against these infections is needed. Fosmidomycin is a repurposed antimalarial drug targeting the non-mevalonate pathway, and several derivatives show activity toward A. baumannii. We evaluated the antimicrobial activity of CC366, a fosmidomycin prodrug, against a collection of A. baumannii strains, using various in vitro and in vivo models; emphasis was placed on the evaluation of its anti-biofilm activity. We also developed a 3D-printed wound dressing containing CC366, using melt electrowriting technology. Minimal inhibitory concentrations of CC366 ranged from 1 to 64 μg/mL, and CC366 showed good biofilm inhibitory and moderate biofilm eradicating activity in vitro. CC366 successfully eluted from a 3D-printed dressing, the dressings prevented the formation of A. baumannnii wound biofilms in vitro and reduced A. baumannii infection in an in vivo mouse model.

Over 40 Years of Fosmidomycin Drug Research: A Comprehensive Review and Future Opportunities

To address the continued rise of multi-drug-resistant microorganisms, the development of novel drugs with new modes of action is urgently required. While humans biosynthesize the essential isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the established mevalonate pathway, pathogenic protozoa and certain pathogenic eubacteria use the less well-known methylerythritol phosphate pathway for this purpose. Important pathogens using the MEP pathway are, for example, Plasmodium falciparum, Mycobacterium tuberculosis, Pseudomonas aeruginosa and Escherichia coli. The enzymes of that pathway are targets for antiinfective drugs that are exempt from target-related toxicity. 2C-Methyl-D-erythritol 4-phosphate (MEP), the second enzyme of the non-mevalonate pathway, has been established as the molecular target of fosmidomycin, an antibiotic that has so far failed to be approved as an anti-infective drug. This review describes the development and anti-infective properties of a wide range of fosmidomycin derivatives synthesized over the last four decades. Here we discuss the DXR inhibitor pharmacophore, which comprises a metal-binding group, a phosphate or phosphonate moiety and a connecting linker. Furthermore, non-fosmidomycin-based DXRi, bisubstrate inhibitors and several prodrug concepts are described. A comprehensive structure-activity relationship (SAR) of nearly all inhibitor types is presented and some novel opportunities for further drug development of DXR inhibitors are discussed.

Nickel-Catalyzed Defluorophosphonylation of Aryl Fluorides

A Ni-catalyzed cross-coupling reaction between aryl fluorides and dialkyl phosphonates [HP(O)(OR)₂] (R = secondary alkyl groups) in the presence of potassium tert-butoxide as a base is reported. The reaction converted various aryl fluorides into the corresponding aryl phosphonates even when electron-donating substituents were present on the aromatic ring. The combined experimental and computational studies suggested Ni-K⁺ cooperative action of a Ni(0) complex chelated with a strongly electron-donating ion-bridged dimeric phosphite ligand system [P(OR)₂O^-K⁺]₂ that facilitates turnover-limiting C-F bond oxidative addition of aryl fluorides.

Title: A Comprehensive Review on Classifying Fast-acting and Slow-acting Antimalarial Agents Based on Time of Action and Target Organelle of Plasmodium sp

The clinical resistance towards malarial parasites has rendered many antimalarials ineffective, likely due to a lack of understanding of time of action and stage specificity of all life stages. Therefore, to tackle this problem a more incisive comprehensive analysis of the fast and slow-acting profile of antimalarial agents relating to parasite time-kill kinetics and the target organelle on the progression of blood-stage parasites was carried out. It is evident from numerous findings that drugs targeting food vacuole, nuclear components, and endoplasmic reticulum mainly exhibit a fast-killing phenotype within 24h affecting first-cycle activity. Whereas drugs targeting mitochondria, apicoplast, microtubules, parasite invasion and egress exhibit a largely slow-killing phenotype within 96-120h, affecting second-cycle activity with few exemptions as moderately fast-killing. It is essential to understand the susceptibility of drugs on rings, trophozoites, schizonts, merozoites, and the appearance of organelle at each stage of 48h intraerythrocytic parasite cycle. Therefore, these parameters may facilitate the paradigm for understanding the timing of antimalarials action in deciphering its precise mechanism linked with time. Thus, classifying drugs based on the time of killing may promote designing new combination regimens against varied strains of P. falciparum and evaluating potential clinical resistance.

The Hydrolysis of Phosphinates and Phosphonates: A Review

Phosphinic and phosphonic acids are useful intermediates and biologically active compounds which may be prepared from their esters, phosphinates and phosphonates, respectively, by hydrolysis or dealkylation. The hydrolysis may take place both under acidic and basic conditions, but the C-O bond may also be cleaved by trimethylsilyl halides. The hydrolysis of P-esters is a challenging task because, in most cases, the optimized reaction conditions have not yet been explored. Despite the importance of the hydrolysis of P-esters, this field has not yet been fully surveyed. In order to fill this gap, examples of acidic and alkaline hydrolysis, as well as the dealkylation of phosphinates and phosphonates, are summarized in this review.

Synthesis and anti-parasitic activity of N-benzylated phosphoramidate Mg2+-chelating ligands

A series of N-benzylated phosphoramidate esters, containing a 3,4-dihydroxyphenyl Mg²⁺-chelating group, has been synthesised in five steps as analogues of fosmidomycin, a Plasmodium falciparum 1-deoxy-1-d-xylulose-5-phosphate reductoisomerase (PfDXR) inhibitor. The 3,4-dihydroxyphenyl group effectively replaces the Mg²⁺-chelating hydroxamic acid group in fosmidomycin. The compounds showed very encouraging anti-parasitic activity with IC₅₀ values of 5.6-16.4 µM against Plasmodium falciparum parasites and IC₅₀ values of 5.2 - 10.2 µM against Trypanosoma brucei brucei (T.b.brucei). Data obtained from in silico docking of the ligands in the PfDXR receptor cavity (3AU9)⁵ support their potential as PfDXR inhibitors.

Potent, specific MEPicides for treatment of zoonotic staphylococci

Coagulase-positive staphylococci, which frequently colonize the mucosal surfaces of animals, also cause a spectrum of opportunistic infections including skin and soft tissue infections, urinary tract infections, pneumonia, and bacteremia. However, recent advances in bacterial identification have revealed that these common veterinary pathogens are in fact zoonoses that cause serious infections in human patients. The global spread of multidrug-resistant zoonotic staphylococci, in particular the emergence of methicillin-resistant organisms, is now a serious threat to both animal and human welfare. Accordingly, new therapeutic targets that can be exploited to combat staphylococcal infections are urgently needed. Enzymes of the methylerythritol phosphate pathway (MEP) of isoprenoid biosynthesis represent potential targets for treating zoonotic staphylococci. Here we demonstrate that fosmidomycin (FSM) inhibits the first step of the isoprenoid biosynthetic pathway catalyzed by deoxyxylulose phosphate reductoisomerase (DXR) in staphylococci. In addition, we have both enzymatically and structurally determined the mechanism by which FSM elicits its effect. Using a forward genetic screen, the glycerol-3-phosphate transporter GlpT that facilitates FSM uptake was identified in two zoonotic staphylococci, Staphylococcus schleiferi and Staphylococcus pseudintermedius. A series of lipophilic ester prodrugs (termed MEPicides) structurally related to FSM were synthesized, and data indicate that the presence of the prodrug moiety not only substantially increased potency of the inhibitors against staphylococci but also bypassed the need for GlpT-mediated cellular transport. Collectively, our data indicate that the prodrug MEPicides selectively and robustly inhibit DXR in zoonotic staphylococci, and further, that DXR represents a promising, druggable target for future development.

Phosphonate prodrugs: an overview and recent advances

Phosphonates, often used as isosteric replacements for phosphates, can provide important interactions with an enzyme. Due to their high charge at physiological pH, however, permeation into cells can be a challenge. Protecting phosphonates as prodrugs has shown promise in drug delivery. Thus, a variety of structures and cleavage/activation mechanisms exist, enabling release of the active compound. This review describes the structural diversity of these pro-moieties, relevant cleavage mechanisms and recent advances in the design of phosphonate prodrugs.

Synthesis and biological evaluation of aryl phosphoramidate prodrugs of fosfoxacin and its derivatives

Aryl phosphoramidate prodrugs of fosfoxacin derivatives 15a-b and 8a-b were synthesized and investigated for their ability to target bacteria. No growth inhibition was observed neither for Mycobacterium smegmatis nor for Escherichia coli on solid medium, demonstrating the absence of release of the active compounds in the bacterial cells. Investigation of the stability of the prodrugs and their multienzymatic cleavage in abiotic and biotic conditions showed that the use of aryl phosphoramidate prodrug approach to deliver non-nucleotides compounds is not obvious and might not be appropriate for an antimicrobial drug.

Double prodrugs of a fosmidomycin surrogate as antimalarial and antitubercular agents

A series of eleven double prodrug derivatives of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. A pivaloyloxymethyl (POM) phosphonate prodrug modification was combined with various prodrug derivatisations of the hydroxamate moiety. The majority of compounds showed activity comparable with or inferior to fosmidomycin against P. falciparum. N-benzyl substituted carbamate prodrug 6f was the most active antimalarial analog with an IC₅₀ value of 0.64 µM. Contrary to fosmidomycin and parent POM-prodrug 5, 2-nitrofuran and 2-nitrothiophene prodrugs 6i and 6j displayed promising antitubercular activities.

Acyloxybenzyl and Alkoxyalkyl Prodrugs of a Fosmidomycin Surrogate as Antimalarial and Antitubercular Agents

Two classes of prodrugs of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. To this end, a novel efficient synthesis route was developed involving a cross metathesis reaction as a key step. Alkoxyalkyl prodrugs show decent antimalarial activities, but acyloxybenzyl prodrugs proved to be the most interesting and show enhanced antimalarial and antitubercular activity. The most active antimalarial analogues show low nanomolar IC₅₀ values.

Phosphonic acid: preparation and applications

The phosphonic acid functional group, which is characterized by a phosphorus atom bonded to three oxygen atoms (two hydroxy groups and one P=O double bond) and one carbon atom, is employed for many applications due to its structural analogy with the phosphate moiety or to its coordination or supramolecular properties. Phosphonic acids were used for their bioactive properties (drug, pro-drug), for bone targeting, for the design of supramolecular or hybrid materials, for the functionalization of surfaces, for analytical purposes, for medical imaging or as phosphoantigen. These applications are covering a large panel of research fields including chemistry, biology and physics thus making the synthesis of phosphonic acids a determinant question for numerous research projects. This review gives, first, an overview of the different fields of application of phosphonic acids that are illustrated with studies mainly selected over the last 20 years. Further, this review reports the different methods that can be used for the synthesis of phosphonic acids from dialkyl or diaryl phosphonate, from dichlorophosphine or dichlorophosphine oxide, from phosphonodiamide, or by oxidation of phosphinic acid. Direct methods that make use of phosphorous acid (H3PO3) and that produce a phosphonic acid functional group simultaneously to the formation of the P-C bond, are also surveyed. Among all these methods, the dealkylation of dialkyl phosphonates under either acidic conditions (HCl) or using the McKenna procedure (a two-step reaction that makes use of bromotrimethylsilane followed by methanolysis) constitute the best methods to prepare phosphonic acids.

MEPicides: potent antimalarial prodrugs targeting isoprenoid biosynthesis

The emergence of Plasmodium falciparum resistant to frontline therapeutics has prompted efforts to identify and validate agents with novel mechanisms of action. MEPicides represent a new class of antimalarials that inhibit enzymes of the methylerythritol phosphate (MEP) pathway of isoprenoid biosynthesis, including the clinically validated target, deoxyxylulose phosphate reductoisomerase (Dxr). Here we describe RCB-185, a lipophilic prodrug with nanomolar activity against asexual parasites. Growth of P. falciparum treated with RCB-185 was rescued by isoprenoid precursor supplementation, and treatment substantially reduced metabolite levels downstream of the Dxr enzyme. In addition, parasites that produced higher levels of the Dxr substrate were resistant to RCB-185. Notably, environmental isolates resistant to current therapies remained sensitive to RCB-185, the compound effectively treated sexually-committed parasites, and was both safe and efficacious in malaria-infected mice. Collectively, our data demonstrate that RCB-185 potently and selectively inhibits Dxr in P. falciparum, and represents a promising lead compound for further drug development.

3-Hydroxy-N'-arylidenepropanehydrazonamides with Halo-Substituted Phenanthrene Scaffolds Cure P. berghei Infected Mice When Administered Perorally

Structural optimization of 3-hydroxy-N'-arylidenepropanehydrazonamides provided new analogs with nanomolar to subnanomolar antiplasmodial activity against asexual blood stages of Plasmodium falciparum, excellent parasite selectivity, and nanomolar activity against the earliest forms of gametocyte development. Particularly, derivatives with a 1,3-dihalo-6-trifluoromethylphenanthrene moiety showed outstanding in vivo properties and demonstrated in part curative activity in the Plasmodium berghei mouse model when administered perorally.

A structure guided drug-discovery approach towards identification of Plasmodium inhibitors

This article provides a comprehensive review of inhibitors from natural, semisynthetic or synthetic sources against key targets ofPlasmodium falciparum.