Preparation of functionalized tertiary thiols and nitrosothiols

Enhanced antibacterial efficacy against antibiotic-resistant bacteria via nitric oxide-releasing ampicillin polymer substrates

The emergence of antibiotic-resistant bacteria poses a pressing threat to global health and is a leading cause of healthcare-related morbidity and mortality. Herein, we report the fabrication of medical-grade polymers incorporated with a dual-action S-nitroso-N-acetylpenicillamine-functionalized ampicillin (SNAPicillin) conjugated molecule through a solvent evaporation process. The resulting SNAPicillin-incorporated polymer materials act as broad-spectrum antibacterial surfaces that improve the administration efficacy of conventional antibiotics through the targeted release of both nitric oxide and ampicillin. The polymer surfaces were characterized by scanning electron microscopy and static contact angle measurements. The nitric oxide (NO) release profile and diffusion of SNAPicillin from polymers were quantified using a chemiluminescence-based nitric oxide analyzer (NOA) and ultraviolet-visible (UV-vis) spectroscopy. As a result, the films had up to 2.96 × 10-7 mol cm-2 of total NO released within 24 hr. In addition, >79 % of the SNAPicillin reservoir was preserved in the polymers after 24 hr of incubation in the physiological environment, indicating their longer-term NO release ability and therapeutic window for antibacterial effects. The SNAPicillin-incorporated polymers reduced the viability of adhered bacteria in culture, with >95 % reduction found against clinically relevant strains of Staphylococcus aureus (S. aureus). Furthermore, SNAPicillin-modified surfaces did not elicit a cytotoxic effect toward 3T3 mouse fibroblast cells, supporting the material's biocompatibility in vitro. These results indicate that the complementary effects of NO-release and ampicillin in SNAPicillin-eluting polymers can enhance the properties of commonly infected medical device surfaces for antibacterial purposes.

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin-Anh and Chelation-Control Models

This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents. In many cases, allylmagnesium reagents either react with low stereoselectivity when other Grignard reagents react with high selectivity, or allylmagnesium reagents react with the opposite stereoselectivity. This review collects hundreds of examples, discusses the origins of stereoselectivities or the lack of stereoselectivity, and evaluates why selectivity may not occur and when it will likely occur.

New 4-aryl-1,3,2-oxathiazolylium-5-olates: Chemical synthesis and photochemical stability of a novel series of S-nitrosothiols

S-nitrosothiols (RSNOs) remain one of the most popular classes of NO-donating compounds due to their ability to release nitric oxide (NO) under non-enzymatic means whilst producing an inert disulphide by-product. However, alligning these compounds to the different biological fields of NO research has proved to be problematic due to the inherent instability of such compounds under a variety of conditions including heat, light and the presence of copper ions. 1,3,2-Oxathiazolylium-5-olates (OZOs) represent an interesting subclass of S-nitrosothiols that lock the -SNO moiety into a five membered heterocyclic ring in an attempt to improve the compound's overall stability. The synthesis of a novel series of halogen-containing OZOs was comprehensively studied resulting in a seven-step route and overall yields ranging between 21 and 37%. The photochemical stability of these compounds was assessed to determine if S-nitrosothiols locked within these mesoionic ring systems can offer greater stability and thereby release NO in a more controllable fashion than their non-cyclic counterparts.

Inhibition of bacterial adhesion and biofilm formation by dual functional textured and nitric oxide releasing surfaces

In separate prior studies, physical topographic surface modification or nitric oxide (NO) release has been demonstrated to each be an effective approach to inhibit and control bacterial adhesion and biofilm formation on polymeric surfaces. Such approaches can prevent biomaterial-associated infection without causing the antibiotic resistance of the strain. In this work, both techniques were successfully integrated and applied to a polyurethane (PU) biomaterial surface that bears ordered pillar topographies (400/400nm and 500/500nm patterns) at the top surface and a S-nitroso-N-acetylpenicillamine (SNAP, NO donor) doped sub-layer in the middle, via a soft lithography two-stage replication process. Upon placing the SNAP textured PU films into PBS at 37°C, the decomposition of SNAP within polymer film initiates NO release with a lifetime of up to 10days at flux levels >0.5×10^-10molmin^-1cm^-2 for a textured polyurethane layer containing 15wt% SNAP. The textured surface reduces the accessible surface area and the opportunity of bacteria-surface interaction, while the NO release from the same surface further inhibits bacterial growth and biofilm formation. Such dual functionality surfaces are shown to provide a synergistic effect on inhibition of Staphylococcus epidermidis bacterial adhesion that is significantly greater than the inhibition of bacterial adhesion achieved by either single treatment approach alone. Longer term experiments to observe biofilm formation demonstrate that the SNAP doped-textured PU surface can inhibit the biofilm formation for >28d and provide a practical approach to improve the biocompatibility of current biomimetic biomaterials and thereby reduce the risk of pathogenic infection.

STATEMENT OF SIGNIFICANCE

Microbial infection remains a significant barrier to development and implementation of advanced blood-contacting medical devices. Clearly, determining how to design and control material properties that can reduce microbial infection is a central question to biomaterial researchers. In separate prior studies, physical topographic surface modification or nitric oxide (NO) release has been demonstrated to each be an effective approach to inhibit and control bacterial adhesion and biofilm formation on polymeric surfaces. Such approaches can prevent biomaterial-associated infection without causing antibiotic resistance of the bacterial strain. However, efficiency of antimicrobial properties of each approach is still limited and far from sufficient for widespread clinical use. This work successfully integrates both techniques and applies them to a polyurethane (PU) biomaterial surface that bears dual functions, surface topographic modification and NO release. The former reduces the surface contact area and changes surface wettability, resulting in reduction of bacterial adhesion, and NO release further inhibits bacteria growth. Such dual functionalized surfaces provide a synergistic effect on inhibition of Staphylococcus epidermidis bacterial adhesion that is significantly greater than the inhibition of bacterial adhesion achieved by either single treatment approach alone. Furthermore, longer-term experiments demonstrate that the dual functionalized surfaces can inhibit biofilm formation for >28days. The success of this work provides a practical approach to improve the biocompatibility of current biomaterials and thereby reduce the risk of pathogenic infection.

Origin of Long-Term Storage Stability and Nitric Oxide Release Behavior of CarboSil Polymer Doped with S-Nitroso-N-acetyl-D-penicillamine

The prolonged and localized delivery of nitric oxide (NO), a potent antithrombotic and antimicrobial agent, has many potential biomedical applications. In this work, the origin of the long-term storage stability and sustained NO release mechanism of S-nitroso-N-acetyl-D-penicillamine (SNAP)-doped CarboSil 20 80A polymer, a biomedical thermoplastic silicone-polycarbonate-urethane, is explored. Long-term (22 days) localized NO release is achieved by utilizing a cross-linked silicone rubber as topcoats, which can greatly reduce the amount of SNAP, NAP, and NAP disulfide leaching from the SNAP-doped CarboSil films, as measured by LC-MS. Raman spectroscopy and powder X-ray diffraction characterization of SNAP-doped CarboSil films demonstrate that a polymer-crystal composite is formed during the solvent evaporation process when SNAP exceeds its solubility in CarboSil (ca. 3.4-4.0 wt %). Further, when exceeding this solubility threshold, SNAP exists in an orthorhombic crystal form within the bulk of the polymer. The proposed mechanism of sustained NO release in SNAP-doped CarboSil is that the solubilized SNAP in the polymer matrix decomposes and releases NO, primarily in the water-rich regions near the polymer/solution interface, and the dissolved SNAP in the bulk polymeric phase becomes unsaturated, resulting in the dissolution of crystalline SNAP within the bulk of the polymer. This is a very slow process that ultimately leads to NO release at the physiological flux levels for >3 weeks. The increased stability of SNAP within CarboSil is attributed to the intermolecular hydrogen bonds between the SNAP molecules that crystallize. This crystallization also plays a key role in maintaining RSNO stability within the CarboSil polymer for >8 months at 37 °C (88.5% remains). Further, intravascular catheters fabricated with this new material are demonstrated to significantly decrease the formation of Staphylococcus aureus biofilm (a leading cause of nosocomial bloodstream infections) (in vitro) over a 7 day period, with 5 log units reduction of viable cell count on catheter surfaces. It is also shown that the NO release catheters can greatly reduce thrombus formation on the catheter surfaces during 7 h implantation in rabbit veins, when compared to the control catheters fabricated without SNAP. These results suggest that the SNAP-doped CarboSil system is a very attractive new composite material for creating long-term NO release medical devices with increased stability and biocompatibility.

Chemistry of the β-thiolactones: substituent and solvent effects on thermal decomposition and comparison with the β-lactones

The synthesis of a series of di-, tri-, and tetraalkyl β-thiolactones and β-lactones is described as well as their thermal decomposition with extrusion of carbon oxysulfide and carbon dioxide in two solvents of opposite polarities. The β-thiolactones are considerably more thermally stable than the β-lactones and require higher temperatures for efficient decomposition in both solvents, whatever the degree of substitution. The results are interpreted in terms of a zwitterionic mechanism for fragmentation with a change in the rate-determining step between the two series.

Long-term nitric oxide release and elevated temperature stability with S-nitroso-N-acetylpenicillamine (SNAP)-doped Elast-eon E2As polymer

Nitric oxide (NO) is known to be a potent inhibitor of platelet activation and adhesion. Healthy endothelial cells that line the inner walls of all blood vessels exhibit a NO flux of 0.5-4 × 10(-10) mol cm(-2) min(-1) that helps prevent thrombosis. Materials with a NO flux that is equivalent to this level are expected to exhibit similar anti-thrombotic properties. In this study, five biomedical grade polymers doped with S-nitroso-N-acetylpenicillamine (SNAP) were investigated for their potential to control the release of NO from the SNAP within the polymers, and further control the release of SNAP itself. SNAP in the Elast-eon E2As polymer creates an inexpensive, homogeneous coating that can locally deliver NO (via thermal and photochemical reactions) as well slowly release SNAP. Furthermore, SNAP is surprisingly stable in the E2As polymer, retaining 82% of the initial SNAP after 2 months storage at 37 °C. The E2As polymer containing SNAP was coated on the walls of extracorporeal circulation (ECC) circuits and exposed to 4 h blood flow in a rabbit model of extracorporeal circulation to examine the effects on platelet count, platelet function, clot area, and fibrinogen adsorption. After 4 h, platelet count was preserved at 100 ± 7% of baseline for the SNAP/E2As coated loops, compared to 60 ± 6% for E2As control circuits (n = 4). The SNAP/E2As coating also reduced the thrombus area when compared to the control (2.3 ± 0.6 and 3.4 ± 1.1 pixels/cm(2), respectively). The results suggest that the new SNAP/E2As coating has potential to improve the thromboresistance of intravascular catheters, grafts, and other blood-contacting medical devices, and exhibits excellent storage stability compared to previously reported NO release polymeric materials.

Photoinitiated nitric oxide-releasing tertiary S-nitrosothiol-modified xerogels

The synthesis of a tertiary thiol-bearing silane precursor (i.e., N-acetyl penicillamine propyltrimethoxysilane or NAPTMS) to enable enhanced NO storage stability at physiological temperature is described. The novel silane was co-condensed with alkoxy- or alkylalkoxysilanes under varied synthetic parameters (e.g., water to silane ratio, catalyst and solvent concentrations, and reaction time) to evaluate systematically the formation of stable xerogel films. The resulting xerogels were subsequently nitrosated to yield tertiary RSNO-modified coatings. Total NO storage ranged from 0.87 to 1.78 μmol cm(-2) depending on the NAPTMS concentration and xerogel coating thickness. Steric hindrance near the nitroso functionality necessitated the use of photolysis to liberate NO. The average NO flux for irradiated xerogels (20% NAPTMS balance TEOS xerogel film cast using 30 μL) in physiological buffer at 37 °C was ∼23 pmol cm(-2) s(-1). The biomedical utility of the photoinitiated NO-releasing films was illustrated by their ability to both reduce Pseudomonas aeruginosa adhesion by ∼90% relative to control interfaces and eradicate the adhered bacteria.