'Second-generation' 1,2,3-triazole-based inhibitors of Porphyromonas gingivalis adherence to oral streptococci and biofilm formation

1,2,3-Triazole Hybrids Containing Isatins and Phenolic Moieties: Regioselective Synthesis and Molecular Docking Studies

The synthesis of hybrid molecules is one of the current strategies of drug discovery for the development of new lead compounds. The 1,2,3-triazole moiety represents an important building block in Medicinal Chemistry, extensively present in recent years. In this paper, we presented the design and the synthesis of new 1,2,3-triazole hybrids, containing both an isatine and a phenolic core. Firstly, the non-commercial azide and the alkyne synthons were prepared by different isatines and phenolic acids, respectively. Then, the highly regioselective synthesis of 1,4-disubstituted triazoles was obtained in excellent yields by a click chemistry approach, catalyzed by Cu(I). Finally, a molecular docking study was performed on the hybrid library, finding four different therapeutic targets. Among them, the most promising results were obtained on 5-lipoxygenase, an enzyme involved in the inflammatory processes.

Synthesis, Characterization, Cytotoxicity Analysis and Evaluation of Novel Heterocyclic Derivatives of Benzamidine against Periodontal Disease Triggering Bacteria

Periodontal disease (PD) is multifactorial oral disease that damages tooth-supporting tissue. PD treatment includes proper oral hygiene, deep cleaning, antibiotics therapy, and surgery. Despite the availability of basic treatments, some of these are rendered undesirable in PD treatment due to side effects and expense. Therefore, the aim of the present study is to develop novel molecules to combat the PD triggering pathogens. The study involved the synthesis of 4-((5-(substituted-phenyl)-1,3,4-oxadiazol-2-yl)methoxy)benzamidine (5a-e), by condensation of 2-(4-carbamimidoylphenoxy)acetohydrazide (3) with different aromatic acids; and synthesis of 4-((4-(substituted benzylideneamino)-4H-1,2,4-triazol-3-yl)methoxy)benzamidine (6a-b) by treatment of compound 3 with CS₂ followed by hydrazination and a Schiff reaction with different aromatic aldehydes. Synthesized compounds were characterized based on the NMR, FTIR, and mass spectrometric data. To assess the effectiveness of the newly synthesized compound in PD, new compounds were subjected to antimicrobial evaluation against P. gingivalis and E. coli using the micro-broth dilution method. Synthesized compounds were also subjected to cytotoxicity evaluation against HEK-293 cells using an MTT assay. The present study revealed the successful synthesis of heterocyclic derivatives of benzamidine with significant inhibitory potential against P. gingivalis and E. coli. Synthesized compounds exhibited minimal to the absence of cytotoxicity. Significant antimicrobial potential and least/no cytotoxicity of new heterocyclic analogs of benzamidine against PD-triggering bacteria supports their potential application in PD treatment.

The Application of Small Molecules to the Control of Typical Species Associated With Oral Infectious Diseases

Oral microbial dysbiosis is the major causative factor for common oral infectious diseases including dental caries and periodontal diseases. Interventions that can lessen the microbial virulence and reconstitute microbial ecology have drawn increasing attention in the development of novel therapeutics for oral diseases. Antimicrobial small molecules are a series of natural or synthetic bioactive compounds that have shown inhibitory effect on oral microbiota associated with oral infectious diseases. Novel small molecules, which can either selectively inhibit keystone microbes that drive dysbiosis of oral microbiota or inhibit the key virulence of the microbial community without necessarily killing the microbes, are promising for the ecological management of oral diseases. Here we discussed the research progress in the development of antimicrobial small molecules and delivery systems, with a particular focus on their antimicrobial activity against typical species associated with oral infectious diseases and the underlying mechanisms.

Chemoenzymatic route to stereodefined 2-(azidophenyl)oxazolines for click chemistry

Aryl-substituted esters of a racemic diprotected 2-azido-1-alkanol were submitted to the Staudinger/aza-Wittig reaction in order to assess scope and establish conditions for their cyclization to the corresponding 2,4,5-trisubstituted oxazolines. Following the cyclization study, the (2R,3R)-antipode of the azidoalkanol was obtained in high ee by incubation of the corresponding racemic azidoacetate with pig liver esterase (PLE). The p-nitrobenzoate of the enantioenriched 2-azido-1-alcohol was cyclized by the Staudinger/aza-Wittig to give the corresponding (4R,5R)-disubstituted-2-(4-nitrophenyl) oxazoline. Selective reduction of the nitrophenyloxazoline to the corresponding aminophenyloxazoline using aluminum amalgam followed by direct azidation of the 2-(4-aminophenyl) moiety provided the corresponding (4R,5R)-2-(4-azidophenyl) oxazoline derivative. The azidophenyl oxazoline was reacted with a proven click partner 4-ethynylfluorobenzene under copper/sodium ascorbate mediation to provide the click triazole product in high yield.

Applicability of aluminum amalgam to the reduction of arylnitro groups

An array of arylnitro compounds with various functionality were treated with freshly-prepared aluminum amalgam in THF/water solution and resulted in the corresponding arylamines. The Al(Hg)-mediated reductions are relatively rapid with consumption of the amalgam and disappearance of starting material occurring over 20-30 minutes. The workup of the reductions involves only removal of the insoluble by-products by filtration followed by concentration. Only in some cases is chromatography required to secure the pure product. The desired arylamines are furnished in quantities of 25-100 mg, which in some cases, could be taken on to the next reaction without further purification. Reductions of 4-nitrobenzyl derivatives of carbohydrates or nucleosides were selective in affording the corresponding 4-aminobenzyl products. To show applicability in click chemistry, selected aminobenzyl products are directly azidated to yield products that were then used in click reactions to afford the corresponding 1,2,3-triazoles.

Identification of Small-Molecule Inhibitors Targeting Porphyromonas gingivalis Interspecies Adherence and Determination of Their In Vitro and In Vivo Efficacies

Porphyromonas gingivalis is one of the primary causative agents of periodontal disease and initially colonizes the oral cavity by adhering to commensal streptococci. Adherence requires the interaction of a minor fimbrial protein (Mfa1) of P. gingivalis with streptococcal antigen I/II (AgI/II). Our previous work identified an AgI/II peptide that potently inhibited adherence and significantly reduced P. gingivalis virulence in vivo, suggesting that this interaction represents a potential target for drug discovery.

Porphyromonas gingivalis is one of the primary causative agents of periodontal disease and initially colonizes the oral cavity by adhering to commensal streptococci. Adherence requires the interaction of a minor fimbrial protein (Mfa1) of P. gingivalis with streptococcal antigen I/II (AgI/II). Our previous work identified an AgI/II peptide that potently inhibited adherence and significantly reduced P. gingivalis virulence in vivo, suggesting that this interaction represents a potential target for drug discovery. To develop targeted small-molecule inhibitors of this protein-protein interaction, we performed a virtual screen of the ZINC databases to identify compounds that exhibit structural similarity with the two functional motifs (NITVK and VQDLL) of the AgI/II peptide. Thirty three compounds were tested for in vitro inhibition of P. gingivalis adherence and the three most potent compounds, namely, N7, N17, and V8, were selected for further analysis. The in vivo efficacy of these compounds was evaluated in a murine model of periodontitis. Treatment of mice with each of the compounds significantly reduced maxillary alveolar bone resorption in infected animals. Finally, a series of cytotoxicity tests were performed against human and murine cell lines. Compounds N17 and V8 exhibited no significant cytotoxic activity toward any of the cell lines, whereas compound N7 was cytotoxic at the highest concentrations that were tested (20 and 40 μM). These results identify compounds N17 and V8 as potential lead compounds that will facilitate the design of more potent therapeutic agents that may function to limit or prevent P. gingivalis colonization of the oral cavity.

Identification of functional domains of the minor fimbrial antigen involved in the interaction of Porphyromonas gingivalis with oral streptococci

Porphyromonas gingivalis is associated with chronic periodontitis and may initially colonize the oral cavity by adhering to streptococci. Adhesion to streptococci is driven by interaction of the minor fimbrial antigen (Mfa1) with streptococcal antigen I/II. We identified the region of antigen I/II required for this interaction and developed small molecule mimetics that inhibited P. gingivalis adherence. However, the functional motifs of Mfa1 involved in the interaction with antigen I/II remain uncharacterized. A series of N- and C-terminal peptide fragments of Mfa1 were expressed and tested for inhibition of P. gingivalis adherence to S. gordonii. This approach identified residues 225-400 of Mfa1 as essential for P. gingivalis adherence. Using the three-dimensional structure of Mfa1, a putative binding cleft was identified using SiteMap and five small molecule mimetics could dock in this site. Site-specific mutation of residues in the predicted cleft, including R240A, W275A, D321A and A357P inhibited the interaction of Mfa1 with streptococci, whereas mutation of residues not in the predicted cleft (V238A, I252F and ΔK253) had no effect. Complementation of an Mfa1-deficient P. gingivalis strain with wild-type mfa1 restored adherence to streptococci, whereas complementation with full-length mfa1 containing the R240A or A357P mutations did not restore adherence. The mutations did not affect polymerization of Mfa1, suggesting that the complemented strains produced intact minor fimbriae. These results identified specific residues and structural motifs required for the Mfa1-antigen I/II interaction and will facilitate the design of small molecule therapeutics to prevent P. gingivalis colonization of the oral cavity.

Peptide and non-peptide mimetics as potential therapeutics targeting oral bacteria and oral biofilms

The development of the oral biofilm requires a complex series of interactions between host tissues and the colonizing bacteria as well as numerous interspecies interactions between the organisms themselves. Disruption of normal host-microbe homoeostasis in the oral cavity can lead to a dysbiotic microbial community that contributes to caries or periodontal disease. A variety of approaches have been pursued to develop novel potential therapeutics that are active against the oral biofilm and/or target specific oral bacteria. The structure and function of naturally occurring antimicrobial peptides from oral tissues and secretions as well as external sources such as frog skin secretions have been exploited to develop numerous peptide mimetics and small molecule peptidomimetics that show improved antimicrobial activity, increased stability and other desirable characteristics relative to the parent peptides. In addition, a rational and minimalist approach has been developed to design small artificial peptides with amphipathic α-helical properties that exhibit potent antibacterial activity. Furthermore, with an increased understanding of the molecular mechanisms of beneficial and/or antagonistic interspecies interactions that contribute to the formation of the oral biofilm, new potential targets for therapeutic intervention have been identified and both peptide-based and small molecule mimetics have been developed that target these key components. Many of these mimetics have shown promising results in in vitro and pre-clinical testing and the initial clinical evaluation of several novel compounds has demonstrated their utility in humans.