Synthesis of homologated amino acid derivatives containing three vicinal fluorine atoms placed stereospecifically along the backbone

When fluorine is incorporated into organic molecules, the C-F bond participates in a variety of stereoelectronic interactions with adjacent functional groups. These interactions can have a profound influence on the conformation of the molecule. Thus, controlled introduction of fluorine can be exploited as a tool for creating shape-controlled bioactive molecules, with the potential to tailor their activity and selectivity towards biomolecular targets. In this project, novel synthetic methodologies for the preparation of fluorinated amino acids have been developed. A series of backbone homologated alpha,beta,gamma-trifluoro-delata-amino acids were synthesised via an approach involving three successive deoxyfluorinations. This synthetic strategy allowed for the stereospecific introduction of three fluorine atoms along the carbon chain, generating a number of novel isomers of alpha,beta,gamma-trifluoro-delta-amino acids. Notable features of this synthetic approach include the successful stereochemical control throughout, and an expedient method for converting a nitroaryl moiety into a carboxylic acid group. Solid-state and solution-state analysis of the target molecules revealed that varying the stereochemistry of the fluorine atoms confers strikingly different conformations. The favoured conformation of the different isomers was rationalised by the known stereoelectronic effects of C-F bond incorporation.Finally, in an attempt to develop a new synthetic methodology, electrophilic fluorination methods were investigated towards the synthesis of alpha,beta,gamma-trifluoro-delta-amino acids. The electrophilic fluorination of protected piperidine-2,4-diones via asymmetric organocatalysis was not successful, since the desired monofluorinated product was formed in only a low yield alongside undesired difluorinated and aldol products. To overcome these limitations, another new synthetic strategy was proposed based on the concept of fluorocyclisation. A model fluorocyclisation reaction was attempted, but this method met with limited success.Overall, this project has completed the synthesis and conformational analysis of different stereoisomers of alpha,beta,gamma -trifluoro-delta-amino acids, the first time that these novel molecules have been studied. These fluorinated amino acids have the potential to be used as building blocks for the synthesis of shape-controlled bioactive peptides in the future

Cationic glycosylated block co-β-peptide acts on the cell wall of Gram-positive bacteria as anti-biofilm agents

Antimicrobial resistance is a global threat. In addition to the emergence of resistance to last resort drugs, bacteria escape antibiotics killing by forming complex biofilms. Strategies to tackle antibiotic resistance as well as biofilms are urgently needed. Wall teichoic acid (WTA), a generic anionic glycopolymer present on the cell surface of many Gram-positive bacteria, has been proposed as a possible therapeutic target, but its druggability remains to be demonstrated. Here we report a cationic glycosylated block co-β-peptide that binds to WTA. By doing so, the co-β-peptide not only inhibits biofilm formation, it also disperses preformed biofilms in several Gram-positive bacteria and resensitizes methicillin-resistant Staphylococcus aureus to oxacillin. The cationic block of the co-β-peptide physically interacts with the anionic WTA within the cell envelope, whereas the glycosylated block forms a nonfouling corona around the bacteria. This reduces physical interaction between bacteria-substrate and bacteria-biofilm matrix, leading to biofilm inhibition and dispersal. The WTA-targeting co-β-peptide is a promising lead for the future development of broad-spectrum anti-biofilm strategies against Gram-positive bacteria.Ministry of Education (MOE)Nanyang Technological UniversityAccepted versionThis research is supported by the Singapore Ministry of Education under its Singapore Ministry of Education Academic Research Fund Tier 3 (Grants MOE2013-T3-1-002 and MOE2018-T3-1-003) and Nanyang Technological Universit

Nontoxic antimicrobial cationic peptide nanoconstructs with bacteria-displaceable polymeric counteranions

Antimicrobial peptides that target the integrity of bacterial envelopes can eradicate pathogens with little development of resistance, but they often inflict nonselective toxicity toward mammalian cells. The prevailing approach to optimize the selectivity of cationic peptides has been to modify their composition. Instead, we invent a new generation of broad-spectrum antibacterial nanoconstructs with negligible mammalian cell toxicity through a competitive displacement of counter polyanions from the complementary polycations. The nanoconstruct, which has a highly cationic Au nanoparticles (NPs) core shielded by polymeric counterions, is inert in nonbacterial environments. When exposed to negatively charged bacterial envelopes, this construct sheds its polyanions, triggering a cationic Au NP/bacterial membrane interaction that rapidly kills Gram-positive and Gram-negative bacteria. The anionic charge and hydrophilicity of the polyanion provides charge neutralization for the peptide-decorated Au NP core, but it is also bacteria-displaceable. These results provide a foundation for the development of other cationic particles and polymeric counterion combinations with potent antimicrobial activity without toxicity.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityAccepted versionThis work was funded and supported by the Singapore Ministry of Education Tier 3 Grants (MOE2013-T3-1-002 and MOE2018-T3-1-003), ASTAR RIE2020 Advanced Manufacturing and Engineering (AME) IAP-PP Specialty Chemicals Programme Grant (No. A1786a0032), and NTU NAFTEC Funding

Sequential Deoxyfluorination Approach for the Synthesis of Protected α,β,γ-Trifluoro-δ-amino Acids

Backbone-homologated amino acids have been synthesized, containing three vicinal fluorine atoms placed stereospecifically along the carbon chain. Different trifluoro stereoisomers are found to have contrasting conformations, consistent with known stereoelectronic effects associated with C–F bonds

Mixed-charge pseudo-zwitterionic copolymer brush as broad spectrum antibiofilm coating

Zwitterionic polymers are classical antifouling polymers but they require specialized monomers that have cationic and anionic charges integrated into a single monomer. Herein, we show that pseudo-zwitterionic copolymers synthesized from a mixture of 2 monomers each having a single opposite polarity has excellent antibiofilm efficacy. We have discovered a new mixed-charge copolymer brush (#1-A) synthesized from 2 oppositely charged monomers, the anionic SPM (3-Sulfopropyl methacrylate) and the cationic AMPTMA ((3-Acrylamidopropyl) trimethylammonium chloride), that achieves broad spectrum in vitro antibiofilm effect of greater than 99% reductions against all six Gram-positive and Gram-negative bacteria tested. In the murine subcutaneous wound catheter infection models, the #1-A has good long-term anti-biofilm efficacy against MRSA and Pseudomonas aeruginosa of 3.41 and 3.19 orders respectively, outperforming previous mixed-charge copolymer coatings. We discovered a new method to choose the cationic/anionic pair combination to form the best antibiofilm copolymer brush coating by exploiting the solution polymerization kinetics disparity between the cationic and anionic monomers. We also showed that #1-A is softer and has higher hydration than the classical zwitterionic polymer. This study shows the possibility of achieving potent antibiofilm efficacy by combining readily available opposite singly charged monomers.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Ministry of Health (MOH)Nanyang Technological UniversityAccepted versionThis research is supported by the Singapore Ministry of Education under its Singapore Ministry of Education Academic Research Fund Tier 3 grants (MOE2013-T3-1-004 and MOE2018-T3-1-003). The authors also thank the funding support from a Singapore Ministry of Health Industry Alignment Fund (NMRC/MOHIAFCAT2/003/2014), an A*STAR Industry Alignment Fund (Wound Care Innovation for the Tropics IAF-PP (HBMS Domain), H17/01/a0/0M9), an A*STAR RIE2020 Advanced Manufacturing and Engineering (AME) IAP-PP Specialty Chemicals Program (Grant No. A1786a0032) and Nanyang Technological University (NTU)

Enantiomeric glycosylated cationic block co-beta-peptides eradicate Staphylococcus aureus biofilms and antibiotic-tolerant persisters

The treatment of bacterial infections is hindered by the presence of biofilms and metabolically inactive persisters. Here, we report the synthesis of an enantiomeric block co-beta-peptide, poly(amido-D-glucose)-block-poly(beta-L-lysine), with high yield and purity by one-shot one-pot anionic-ring opening (co)polymerization. The co-beta-peptide is bactericidal against methicillin-resistant Staphylococcus aureus (MRSA), including replicating, biofilm and persister bacterial cells, and also disperses biofilm biomass. It is active towards community-acquired and hospital-associated MRSA strains which are resistant to multiple drugs including vancomycin and daptomycin. Its antibacterial activity is superior to that of vancomycin in MRSA mouse and human ex vivo skin infection models, with no acute in vivo toxicity in repeated dosing in mice at above therapeutic levels. The copolymer displays bacteria-activated surfactant-like properties, resulting from contact with the bacterial envelope. Our results indicate that this class of non-toxic molecule, effective against different bacterial sub-populations, has promising potential for the treatment of S. aureus infections.MOE (Min. of Education, S’pore)NMRC (Natl Medical Research Council, S’pore)MOH (Min. of Health, S’pore)Accepted versio