Ex vivo study of molecular changes of stained teeth following hydrogen peroxide and peroxymonosulfate treatments.

White teeth can give confidence and tend to be associated with a healthier lifestyle in modern society. Therefore, tooth-bleaching strategies have been developed, including the use of hydrogen peroxide. Recently, peroxymonosulfate has been introduced as an alternative bleaching method to hydrogen peroxide. Although both chemicals are oxidizing agents, their effects on the molecular composition of the stained teeth are yet unknown. In this study, the molecular profiles of teeth bleached with hydrogen peroxide and peroxymonosulfate were compared using Liquid Chromatography-Tandem Mass Spectrometry. Statistical analyses were used to assess the samples. In addition, reference spectral libraries and in silico tools were used to perform metabolite annotation. Overall, principal component analysis showed a strong separation between control and hydrogen peroxide and peroxymonosulfate samples (p < 0.001). The analysis of molecular changes revealed amino acids and dipeptides in stained teeth samples after hydrogen peroxide and peroxymonosulfate treatments. Noteworthy, the two bleaching methods led to distinct molecular profiles. For example, diterpenoids were more prevalent after peroxymonosulfate treatment, while a greater abundance of alkaloids was detected after hydrogen peroxide treatment. Whereas non-bleached samples (controls) showed mainly lipids. Therefore, this study shows how two different tooth-whitening peroxides could affect the molecular profiles of human teeth.

Evaluation of oral and perioral irritation and sensitization potential of a whitening gel and a whitening toothpaste containing potassium monopersulfate.

PURPOSE: Two clinical trials were conducted to investigate the oral and perioral irritation and sensitization potential of a tooth whitening leave-on-gel alone and in combination with a whitening toothpaste, each containing 1.0% of the active ingredient potassium monopersulfate (MPS). METHODS: Both clinical trials were Institutional Review Board (IRB) approved, double-blind, randomized, and parallel group designed studies. For the MPS leave-on gel study, 200 qualifying and consented subjects were randomly assigned to two groups: (1) 0.1% hydrogen peroxide (H2O2) gel pen (34 subjects); and (2) 0.1% H2O2 + 1.0% MPS gel pen (166 subjects). Subjects used the assigned products according to instructions provided and returned on Days 22 and 36 for oral and perioral tissue examination (pre-challenge). At the Day 36 visit, the subject applied the assigned gel on site (challenge) and received oral and perioral tissue examinations 1 and 24 hours following the application to detect any post-challenge tissue reactions. For the MPS toothpaste/MPS gel pen study, 200 qualifying and consented subjects were randomly assigned to three groups: (1) Placebo toothpaste + placebo gel pen (66 subjects); (2) 1.0% MPS toothpaste + 1.0% MPS gel pen (67 subjects); and (3) 1.0% MPS toothpaste + placebo gel pen (67 subjects). The study design and procedures were the same as those for the MPS gel pen study described above. RESULTS: For the MPS gel pen study, 192 subjects completed the study. None of the eight dropouts was related to the product use. The demographic data were comparable between the two groups. No evidence of tissue irritation and sensitization was detected in any subjects at any visit, and the findings were comparable between the groups. The detected and self-reported tissue issues were minimal and minor, and they were comparable between the two groups. For the MPS toothpaste/MPS gel pen study, 200 subjects were enrolled with 12 dropped from the study, resulting in an overall dropout rate of 6%. Of the 12 that did not complete the study, none were due to product-related use. The demographic data were comparable among the three groups. The detected and self-reported tissue issues were minimal and minor, and they were comparable among the three groups. CLINICAL SIGNIFICANCE: Potassium monopersulfate (MPS) at the active concentration of 1.0% in the tooth whitening leave-on-gel and the toothpaste plus the gel did not cause oral/perioral irritation nor sensitization.

Electrochemical mineralization of iron-tannate stain on HAp and bovine enamel-A non-peroxide approach.

Prolonged treatments for the destaining of teeth using high concentrations of hydrogen peroxide may cause secondary unwanted effects such as tooth hypersensitivity and gingival irritation. Hence, it is aimed to develop a non-peroxide-based method to oxidize iron-tannate (Fe-TA) stained hydroxyapatite (HAp) and bovine enamel (BE) samples. Constant current electrolysis (CCE) experiments were carried out on Pt working electrode in aqueous NaCl, KCl and KI solutions at discrete concentrations under continuous experiment and a non-continuous experiment. CCE shows that in the presence of iron tannate (Fe-TA) stained HAP, approximately 30 ppm of iodine was generated using 0.1M KI and nearly 40 ppm was produced with 0.2 M KI. By using a non-continuous CCE process, the lowest amount of chlorine was generated from NaCl solution, which was well within the safety limits for oral applications. Depending on the experimental conditions used, between 13 ppm and 124 ppm of chlorine was generated. CCE of Fe-TA stained on HAp using KCl reveals that at the lowest current density of 10 mA/cm2, the amount of hypochlorite generated was 20 ppm on Pt electrode having a surface area of 6 cm2. Ion chromatographic (IC) analysis revealed that non-continuous CCE of Fe-TA-BE in NaCl generated a low concentration of sodium perchlorate (0.8 ppm), whereas the continuous process generated no perchlorate, but a considerable higher quantity of chlorate for Fe-TA-BE (37 ppm) and Fe-TA-HAp (140 ppm) samples.

Design and synthesis of small molecule-sulfotyrosine mimetics that inhibit HIV-1 entry.

In the absence of a cure or vaccine for HIV/AIDS, small molecule inhibitors remain an attractive choice for antiviral therapeutics. Recent structural and functional studies of the HIV-1 surface envelope glycoprotein gp120 have revealed sites of vulnerability that can be targeted by small molecule and peptide inhibitors, thereby inhibiting HIV-1 infection. Here we describe a series of small molecule entry inhibitors that were designed to mimic the sulfated N-terminal peptide of the HIV-1 coreceptor CCR5. From a panel of hydrazonothiazolyl pyrazolinones, we demonstrate that compounds containing naphthyl di- and tri-sulfonic acids inhibit HIV-1 infection in single round infectivity assays with the disulfonic acids being the most potent. Molecular docking supports the observed structure activity relationship, and SPR confirmed binding to gp120. In infectivity assays treatment with a representative naphthyl disulfonate and a disulfated CCR5 N-terminus peptide results in competitive inhibition, with combination indices >2. In total this work shows that gp120 and HIV-1 infection can be inhibited by small molecules that mimic the function of, and are competitive with the natural sulfated CCR5 N-terminus.

Characterization and carbohydrate specificity of pradimicin S.

The pradimicin family of antibiotics is attracting attention due to its anti-infective properties and as a model for understanding the requirements for carbohydrate recognition by small molecules. Members of the pradimicin family are unique among natural products in their ability to bind sugars in a Ca(2+)-dependent manner, but the oligomerization to insoluble aggregates that occurs upon Ca(2+) binding has prevented detailed characterization of their carbohydrate specificity and biologically relevant form. Here we take advantage of the water solubility of pradimicin S (PRM-S), a sulfated glucose-containing analogue of pradimicin A (PRM-A), to show by NMR spectroscopy and analytical ultracentrifugation that at biologically relevant concentrations, PRM-S binds Ca(2+) to form a tetrameric species that selectively binds and engulfs the trisaccharide Manα1-3(Manα1-6)Man over mannose or mannobiose. In functional HIV-1 entry assays, IC(50) values of 2-4 µM for PRM-S corrrelate with the concentrations at which oligomerization occurs as well as the affinities with which PRM-S binds the HIV surface envelope glycoprotein gp120. Together these data reveal the biologically active form of PRM-S, provide an explanation for previous speculations that PRM-A may contain a second mannose binding site, and expand our understanding of the characteristics that can engender a small molecule with the ability to function as a carbohydrate receptor.

Peptides from second extracellular loop of C-C chemokine receptor type 5 (CCR5) inhibit diverse strains of HIV-1.

To initiate HIV entry, the HIV envelope protein gp120 must engage its primary receptor CD4 and a coreceptor CCR5 or CXCR4. In the absence of a high resolution structure of a gp120-coreceptor complex, biochemical studies of CCR5 have revealed the importance of its N terminus and second extracellular loop (ECL2) in binding gp120 and mediating viral entry. Using a panel of synthetic CCR5 ECL2-derived peptides, we show that the C-terminal portion of ECL2 (2C, comprising amino acids Cys-178 to Lys-191) inhibit HIV-1 entry of both CCR5- and CXCR4-using isolates at low micromolar concentrations. In functional viral assays, these peptides inhibited HIV-1 entry in a CD4-independent manner. Neutralization assays designed to measure the effects of CCR5 ECL2 peptides when combined with either with the small molecule CD4 mimetic NBD-556, soluble CD4, or the CCR5 N terminus showed additive inhibition for each, indicating that ECL2 binds gp120 at a site distinct from that of N terminus and acts independently of CD4. Using saturation transfer difference NMR, we determined the region of CCR5 ECL2 used for binding gp120, showed that it can bind to gp120 from both R5 and X4 isolates, and demonstrated that the peptide interacts with a CD4-gp120 complex in a similar manner as to gp120 alone. As the CCR5 N terminus-gp120 interactions are dependent on CD4 activation, our data suggest that gp120 has separate binding sites for the CCR5 N terminus and ECL2, the ECL2 binding site is present prior to CD4 engagement, and it is conserved across CCR5- and CXCR4-using strains. These peptides may serve as a starting point for the design of inhibitors with broad spectrum anti-HIV activity.

Unliganded HIV-1 gp120 core structures assume the CD4-bound conformation with regulation by quaternary interactions and variable loops.

The HIV-1 envelope (Env) spike (gp120(3)/gp41(3)) undergoes considerable structural rearrangements to mediate virus entry into cells and to evade the host immune response. Engagement of CD4, the primary human receptor, fixes a particular conformation and primes Env for entry. The CD4-bound state, however, is prone to spontaneous inactivation and susceptible to antibody neutralization. How does unliganded HIV-1 maintain CD4-binding capacity and regulate transitions to the CD4-bound state? To define this mechanistically, we determined crystal structures of unliganded core gp120 from HIV-1 clades B, C, and E. Notably, all of these unliganded HIV-1 structures resembled the CD4-bound state. Conformational fixation with ligand selection and thermodynamic analysis of full-length and core gp120 interactions revealed that the tendency of HIV-1 gp120 to adopt the CD4-bound conformation was restrained by the V1/V2- and V3-variable loops. In parallel, we determined the structure of core gp120 in complex with the small molecule, NBD-556, which specifically recognizes the CD4-bound conformation of gp120. Neutralization by NBD-556 indicated that Env spikes on primary isolates rarely assume the CD4-bound conformation spontaneously, although they could do so when quaternary restraints were loosened. Together, the results suggest that the CD4-bound conformation represents a "ground state" for the gp120 core, with variable loop and quaternary interactions restraining unliganded gp120 from "snapping" into this conformation. A mechanism of control involving deformations in unliganded structure from a functionally critical state (e.g., the CD4-bound state) provides advantages in terms of HIV-1 Env structural diversity and resistance to antibodies and inhibitors, while maintaining elements essential for entry.

Structure-based identification and neutralization mechanism of tyrosine sulfate mimetics that inhibit HIV-1 entry.

Tyrosine sulfate-mediated interactions play an important role in HIV-1 entry. After engaging the CD4 receptor at the cell surface, the HIV-1 gp120 glycoprotein binds to the CCR5 co-receptor via an interaction that requires two tyrosine sulfates, at positions 10 and 14 in the CCR5-N terminus. Building on previous structure determinations of this interaction, here we report the targeting of these tyrosine sulfate binding sites for drug design through in silico screening of small molecule libraries, identification of lead compounds, and characterization of biological activity. A class of tyrosine sulfate-mimicking small molecules containing a "phenyl sulfonate-linker-aromatic" motif was identified that specifically inhibited binding of gp120 to the CCR5-N terminus as well as to sulfated antibodies that recognize the co-receptor binding region on gp120. The most potent of these compounds bound gp120 with low micromolar affinity and its CD4-induced conformation with K(D)'s as tight as ∼50 nM. Neutralization experiments suggested the targeted site to be conformationally inaccessible prior to CD4 engagement. Primary HIV-1 isolates were weakly neutralized, preincubation with soluble CD4 enhanced neutralization, and engineered isolates with increased dependence on the N terminus of CCR5 or with reduced conformational barriers were neutralized with IC(50) values as low as ∼1 µM. These results reveal the potential of targeting the tyrosine sulfate interactions of HIV-1 and provide insight into how mechanistic barriers, evolved by HIV-1 to evade antibody recognition, also restrict small-molecule-mediated neutralization.

Motualevic acids and analogs: synthesis and antimicrobial structure-activity relationships.

Synthesis of the marine natural products motualevic acids A, E, and analogs in which modifications have been made to the omega-brominated lipid (E)-14,14-dibromotetra-deca-2,13-dienoic acid or amino acid unit are reported, together with antimicrobial activities against Staphylococcus aureus, methicillin-resistant S. aureus, Enterococcus faecium, and vancomycin-resistant Enterococcus.

Diastereoselective Synthesis of trans-beta-Lactams Using a Simple Multifunctional Catalyst.

A catalytic, highly diastereoselective process for the synthesis of trans-beta-lactams is reported. This system is based on a phosphonium fluoride precatalyst that both activates the nucleophile and directs the reaction process for high yield and diastereoselectivity.

An Asymmetric, bifunctional catalytic approach to non-natural alpha-amino acid derivatives.

A catalytic, asymmetric process for the synthesis of 1,4-benzoxazinones from o-benzoquinone imides and ketene enolates is reported. Addition of Lewis acids (Zn(OTf)2, In(OTf)3, and in particular Sc(OTf)3) creates a bifunctional catalytic system that dramatically increases the reaction rate and the yield of these non-natural amino acid precursors while preserving the remarkable enantioselectivity inherent to the reaction. Cocatalyst Sc(OTf)3 increases the yield by up to 42% while producing products in >99% ee.

Scalable methodology for the catalytic, asymmetric alpha-bromination of acid chlorides.

The optimization of a practical, catalytic, asymmetric process for the alpha-bromination of acid chlorides to produce synthetically versatile, optically active alpha-bromoesters is reported. A range of products is produced in high enantioselectivity and moderate to good chemical yields with retention of both upon scale-up. The reactions herein are catalyzed by cinchona alkaloid derivatives, with the best performance achieved by the use of a proline cinchona alkaloid conjugate designed in a de novo fashion.