Utilizing a degradation prediction pathway system to understand how a novel methacrylate derivative polymer with flipped external ester groups retains physico-mechanical properties following esterase exposure.

OBJECTIVE: The region of failure for current methacrylates (i.e. derivatives of acrylates) are ester bond linkages that hydrolyze in the presence of salivary and bacterial esterases that break the polymer network backbone. This effect decreases the mechanical properties of methacrylate-based materials. METHODS: The ethylene glycol dimethacrylate (EGDMA) or novel ethylene glycol ethyl methacrylate (EGEMA) discs were prepared using 40 µL of the curing mixture containing photo/co-initiators for 40 s in a PTFE mold at 1000 mW/cm2. The degree of conversion was used as a quality control measure for the prepared discs, followed by physical, mechanical, and chemical characterization of discs properties before and after cholesterol esterase treatment. RESULTS: After 9 weeks of standardized cholesterol esterase (CEase) exposure, EGDMA discs showed exponential loss of material (p = 0.0296), strength (p = 0.0014) and increased water sorption (p = 0.0002) compared to EGEMA discs. We integrated a degradation prediction pathway system to LC/MS and GC/MS analyses to elucidate the degradation by-products of both EGEMA and EGDMA polymers. GC/MS analysis demonstrated that the esterase catalysis was directed to central polymer backbone breakage, producing ethylene glycol, for EGDMA, and to side chain breakage, producing ethanol, for EGEMA. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to esterase biodegradation and changes in mechanical and physical properties than EGDMA. SIGNIFICANCE: EGEMA is a potential substitute for common macromer diluents, such as EGDMA, based on its resistance to biodegradation effects. This work inspires the flipped external group design to be applied to analogs of current larger, hydrophobic strength bearing macromers used in future dental material formulations.

A novel methacrylate derivative polymer that resists bacterial cell-mediated biodegradation.

This study tests biodegradation resistance of a custom synthesized novel ethylene glycol ethyl methacrylate (EGEMA) with ester bond linkages that are external to the central polymer backbone when polymerized. Ethylene glycol dimethacrylate (EGDMA) with internal ester bond linkages and EGEMA discs were prepared in a polytetrafluoroethylene (PTFE) mold using 40 µl macromer and photo/co-initiator mixture cured for 40 s at 1000 mW/cm2 . The discs were stored in the constant presence of Streptococcus mutans (S. mutans) in Todd Hewitt Yeast + Glucose (THYE+G) media up to 9 weeks (n = 8 for each macromer type) and physical/mechanical properties were assessed. Initial measurements EGEMA versus EGDMA polymer discs showed equivalent degree of conversion (45.69% ± 2.38 vs. 46.79% ± 4.64), diametral tensile stress (DTS; 8.12± 2.92 MPa vs. 6.02 ± 1.48 MPa), and low subsurface optical defects (0.41% ± 0.254% vs. 0.11% ± 0.074%). The initial surface wettability (contact angle) was slightly higher (p ≤ .012) for EGEMA (62.02° ± 3.56) than EGDMA (53.86° ± 5.61°). EGDMA showed higher initial Vicker's hardness than EGEMA (8.03 ± 0.88 HV vs. 5.93 ± 0.69 HV; p ≤ .001). After 9 weeks of S. mutans exposure, EGEMA (ΔDTS-1.30 MPa) showed higher resistance to biodegradation effects with a superior DTS than EGDMA (ΔDTS-6.39 MPa) (p = .0039). Visible and scanning electron microscopy images of EGEMA show less surface cracking and defects than EGDMA. EGDMA had higher loss of material (18.9% vs. 8.5%, p = .0009), relative changes to fracture toughness (92.5% vs. 49.2%, p = .0022) and increased water sorption (6.1% vs. 1.9%, p = .0022) compared to EGEMA discs. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to bacterial degradation effects than an internal ester group linkage design methacrylate.

Antibacterial activity of 2-amino-4-hydroxypyrimidine-5-carboxylates and binding to Burkholderia pseudomallei 2-C-methyl-d-erythritol-2,4-cyclodiphosphate synthase.

Enzymes in the methylerythritol phosphate pathway make attractive targets for antibacterial activity due to their importance in isoprenoid biosynthesis and the absence of the pathway in mammals. The fifth enzyme in the pathway, 2-C-methyl-d-erythritol-2,4-cyclodiphosphate synthase (IspF), contains a catalytically important zinc ion in the active site. A series of de novo designed compounds containing a zinc binding group was synthesized and evaluated for antibacterial activity and interaction with IspF from Burkholderia pseudomallei, the causative agent of Whitmore's disease. The series demonstrated antibacterial activity as well as protein stabilization in fluorescence-based thermal shift assays. Finally, the binding of one compound to Burkholderia pseudomallei IspF was evaluated through group epitope mapping by saturation transfer difference NMR.

Synthesis and biological evaluation of pyrazolopyrimidines as potential antibacterial agents.

The fragment FOL7185 (compound 17) was found to be a hit against IspD and IspE enzymes isolated from bacteria, and a series of analogs containing the pyrazolopyrimidine core were synthesized. The majority of these compounds inhibited the growth of Burkholderia thailandensis (Bt) and Pseudomonas aeruginosa (Pa) in the Kirby­Bauer disk diffusion susceptibility test. Compound 29 shows inhibitory activity at 0.1 mM (32.2 lg/mL), which is comparable to the control compound kanamycin (48.5 lg/mL). Compound 29 also shows inhibitory activity at 0.5 mM against kanamycin resistant P. aeruginosa. Saturation transfer difference NMR (STD-NMR) screening of these compounds against BtIspD and BtIspE indicated that most of these compounds significantly interact with BtIspE, suggesting that the compounds may inhibit the growth of Bt by disrupting isoprenoid biosynthesis. Ligand epitope mapping of compound 29 with BtIspE indicated that hydrogens on 2,4-dichlorophenyl group have higher proximity to the surface of the enzyme than hydrogens on the pyrazolopyrimidine ring.