Nature-Derived Epoxy Resin Monomers with Reduced Sensitizing Capacity─Isosorbide-Based Bis-Epoxides.

Epoxy resin systems (ERSs) are a class of thermosetting resins that become thermostable and insoluble polymers upon curing. They are widely used as components of protective surfaces, adhesives, and paints and in the manufacturing of composites in the plastics industry. The diglycidyl ether of bisphenol A (DGEBA) is used in 75-90% of ERSs and is thus by far the most used epoxy resin monomer (ERM). Unfortunately, DGEBA is a strong skin sensitizer and it is one of the most common causes of occupational contact dermatitis. Furthermore, DGEBA is synthesized from bisphenol A (BPA), which is a petroleum-derived chemical with endocrine-disruptive properties. In this work, we have used isosorbide, a renewable and nontoxic sugar-based material, as an alternative to BPA in the design of ERMs. Three different bis-epoxide isosorbide derivatives were synthesized: the diglycidyl ether of isosorbide (1) and two novel isosorbide-based bis-epoxides containing either a benzoic ester (2) or a benzyl ether linkage (3). Assessment of the in vivo sensitizing potency of the isosorbide bis-epoxides in the murine local lymph node assay (LLNA) showed that all three compounds were significantly less sensitizing than DGEBA, especially 2 which was nonsensitizing up to 25% w/v. The peptide reactivity showed the same order of reactivity as the LLNA, i.e., 2 being the least reactive, followed by 3 and then 1, which displayed similar peptide reactivity as DGEBA. Skin permeation of 2 and 3 was compared to DGEBA using ex vivo pig skin and static Franz cells. The preliminary investigations of the technical properties of the polymers formed from 1-3 were promising. Although further investigations of the technical properties are needed, all isosorbide bis-epoxides have the potential to be less sensitizing renewable replacements of DGEBA, especially 2 that had the lowest sensitizing potency in vivo as well as the lowest peptide reactivity.

Nature-derived epoxy resins: Synthesis, allergenicity, and thermosetting properties of pinoresinol diglycidyl ether.

We describe a novel nature-derived epoxy resin monomer (ERM) derived from the plant lignan pinoresinol. Epoxy resins are thermosetting materials in global usage owing to their excellent technical properties such as flexibility and durability. However, their adverse health effects are often not considered and affect users of epoxy resins worldwide. Components of epoxy resin systems are strong skin sensitizers and cause allergic contact dermatitis. The reported prevalence attributable to epoxy chemicals is between 11.7 and 12.5% of all cases of occupational allergic contact dermatitis. We are committed to developing epoxy resins with reduced allergenic effect, while maintaining their excellent properties. The novel ERM, pinoresinol diglycidyl ether (PinoDGE), was synthesized in one step from pinoresinol and epichlorohydrin in 88% yield. It was not classified as a skin sensitizer in the in vivo local lymph node assay, at concentrations up to 0.17 m, as it did not cause a stimulation index >3 compared to control. Pinoresinol diglycidyl ether reacted with the model peptide AcPHCKRM in a reactivity assay and was predicted to be a skin sensitizer in the KeratinoSens assay. Preliminary cross-linking studies indicate that it has promising properties compared to commercially used ERMs. Pinoresinol diglycidyl ether could be seen as a lead compound for further development of alternative ERMs with a better safety profile based on natural and renewable sources for construction of epoxy resin polymers.

A scaffold replacement approach towards new sirtuin 2 inhibitors.

Sirtuins (SIRT1-SIRT7) are an evolutionary conserved family of NAD+-dependent protein deacylases regulating the acylation state of ε-N-lysine residues of proteins thereby controlling key biological processes. Numerous studies have found association of the aberrant enzymatic activity of SIRTs with various diseases like diabetes, cancer and neurodegenerative disorders. Previously, we have shown that substituted 2-alkyl-chroman-4-one/chromone derivatives can serve as selective inhibitors of SIRT2 possessing an antiproliferative effect in two human cancer cell lines. In this study, we have explored the bioisosteric replacement of the chroman-4-one/chromone core structure with different less lipophilic bicyclic scaffolds to overcome problems associated to poor physiochemical properties due to a highly lipophilic substitution pattern required for achieve a good inhibitory effect. Various new derivatives based on the quinolin-4(1H)-one scaffold, bicyclic secondary sulfonamides or saccharins were synthesized and evaluated for their SIRT inhibitory effect. Among the evaluated scaffolds, the benzothiadiazine-1,1-dioxide-based compounds showed the highest SIRT2 inhibitory activity. Molecular modeling studies gave insight into the binding mode of the new scaffold-replacement analogues.

Development of New Epoxy Resin Monomers - A Delicate Balance between Skin Allergy and Polymerization Properties.

Epoxy resin monomers (ERMs) are used as building blocks for thermosetting polymers in applications where strong, flexible, and lightweight materials are required. Most epoxy resins are polymers of diglycidyl ether of bisphenol A (DGEBA). It is highly allergenic and causes occupational allergic contact dermatitis and contact allergy in the general population. Thus, measures to prevent exposure by protective clothing and education are not enough. This work describes a continuation of our research aiming at reducing the skin-sensitizing potency of ERMs while maintaining the ability to form polymers. Alternative ERMs were designed and synthesized whereafter the sensitizing potency was determined using the murine local lymph node assay (LLNA). The reactivity of the diepoxides toward a nucleophilic peptide was investigated, and the differences in reactivity explained using computational studies. The diepoxides were reacted with triethylenetetramine, and the formed polymers were tested for technical applicability using thermogravimetric analysis. We had previously shown that the absence of an oxygen atom in the side chains or removal of aromaticity reduced the sensitizing potency compared to that of DGEBA. Thus, a cycloaliphatic analogue 1 of DGEBA without ether oxygen in the side chains was considered promising and was synthesized. As predicted, the sensitizing potency was considerably reduced (10 times) compared to that of DGEBA. However, the technical properties of the polymer of this compound were not considered sufficient. More polar aromatic analogues were investigated, but they could not compete with our previously described ERMs regarding polymerization properties and with 1 regarding low skin sensitization properties. Development of alternative epoxy materials is a delicate balance between allergenic activity and polymerization properties. Tuning of structural properties together with investigation of polymerization conditions combined with skin sensitization studies should be used in industrial research and development. ERM 1 could be used as a lead compound for further studies of aliphatic ERMs.

Can the epoxides of cinnamyl alcohol and cinnamal show new cases of contact allergy?

BACKGROUND: Cinnamyl alcohol is considered to be a prohapten and prehapten with cinnamal as the main metabolite. However, many individuals who are allergic to cinnamyl alcohol do not react to cinnamal. Sensitizing epoxides of cinnamyl alcohol and cinnamal have been identified as metabolites and autoxidation products of cinnamyl alcohol. OBJECTIVE: To investigate the clinical relevance of contact allergy to epoxycinnamyl alcohol and epoxycinnamal. METHODS: Irritative effects of the epoxides were investigated in 12 dermatitis patients. Epoxycinnamyl alcohol and epoxycinnamal were patch tested in 393 and 390 consecutive patients, respectively. In parallel, cinnamyl alcohol and cinnamal were patch tested in 607 and 616 patients, respectively. RESULTS: Both epoxides were irritants, but no more positive reactions were detected than when testing was performed with cinnamyl alcohol and cinnamal. Late allergic reactions to epoxycinnamyl alcohol were observed. In general, patients with late reactions showed doubtful or positive reactions to cinnamal and fragrance mix I at regular patch testing. CONCLUSION: The investigated epoxides are not important haptens in contact allergy to cinnamon fragrance. The high frequency of fragrance allergy among patients included in the irritancy study showed the difficulty of suspecting fragrance allergy on the basis of history; patch testing broadly with fragrance compounds is therefore important.

Identification of the Binding Site of Chroman-4-one-Based Sirtuin 2-Selective Inhibitors using Photoaffinity Labeling in Combination with Tandem Mass Spectrometry.

Photoaffinity labeling (PAL) was used to identify the binding site of chroman-4-one-based SIRT2-selective inhibitors. The photoactive diazirine 4, a potent SIRT2 inhibitor, was subjected to detailed photochemical characterization. In PAL experiments with SIRT2, a tryptic peptide originating from the covalent attachment of photoactivated 4 was identified. The peptide covers both the active site of SIRT2 and the proposed binding site of chroman-4-one-based inhibitors. A high-power LED was used as source for the monochromatic UV light enabling rapid photoactivation.

Assessment of cross-reactivity of new less sensitizing epoxy resin monomers in epoxy resin-allergic individuals.

BACKGROUND: Measures to prevent occupational exposure to epoxy resins, including education, medical examination, and voluntary agreements between employers and workers, have not been effective enough to protect against skin sensitization. Therefore, alternatives to the major epoxy resin haptens that have been found to be less sensitizing in the local lymph node assay have been developed. OBJECTIVES: To study the cross-reactivity of two newly designed epoxy resin monomers, with decreased skin-sensitizing potency and good technical properties as compared with diglycidyl ether of bisphenol A (DGEBA), in subjects with known contact allergy to epoxy resin of DGEBA type. PATIENTS AND METHODS: Eleven individuals with previous positive patch test reactions to epoxy resin of DGEBA participated in the study. The two alternative epoxy resin monomers were synthesized and patch tested in dilution series in parallel with epoxy resin of DGEBA from the baseline series (containing 92% DGEBA). RESULTS: All participants reacted to epoxy resin of DGEBA on retesting. Three participants reacted to monomer 1. No reactions were seen to monomer 2. CONCLUSIONS: The alternative monomers studied showed little or no cross-reactivity with epoxy resin of DGEBA. Decreasing the risk of sensitization by using less sensitizing compounds is important, as contact allergy to epoxy resins is common in spite of thorough preventive measures.

Chroman-4-one and chromone based somatostatin ß-turn mimetics.

A scaffold approach has been used to develop somatostatin ß-turn mimetics based on chroman-4-one and chromone ring systems. Such derivatives could adopt conformations resembling type II or type II' ß-turns. Side chain equivalents of the crucial Trp8 and Lys9 in somatostatin were introduced in the 2- and 8-positions of the scaffolds using efficient reactions. Interestingly, this proof-of-concept study shows that 4 and 9 have Ki-values in the low µM range when evaluated for their affinity for the sst2 and sst4 receptors.

Design, Synthesis and Evaluation of 2,5-Diketopiperazines as Inhibitors of the MDM2-p53 Interaction.

The transcription factor p53 is the main tumour suppressor in cells and many cancer types have p53 mutations resulting in a loss of its function. In tumours that retain wild-type p53 function, p53 activity is down-regulated by MDM2 (human murine double minute 2) via a direct protein-protein interaction. We have designed and synthesised two series of 2,5-diketopiperazines as inhibitors of the MDM2-p53 interaction. The first set was designed to directly mimic the α-helical region of the p53 peptide, containing key residues in the i, i+4 and i+7 positions of a natural α-helix. Conformational analysis indicated that 1,3,6-trisubstituted 2,5-diketopiperazines were able to place substituents in the same spatial orientation as an α-helix template. The key step of the synthesis involved the cyclisation of substituted dipeptides. The other set of tetrasubstituted 2,5-diketopiperazines were designed based on structure-based docking studies and the Ugi multicomponent reaction was used for the synthesis. This latter set comprised the most potent inhibitors which displayed micromolar IC50-values in a biochemical fluorescence polarisation assay.

Chroman-4-one- and chromone-based sirtuin 2 inhibitors with antiproliferative properties in cancer cells.

Sirtuins (SIRTs) catalyze the NAD(+)-dependent deacetylation of N(ε)-acetyl lysines on various protein substrates. SIRTs are interesting drug targets as they are considered to be related to important pathologies such as inflammation and aging-associated diseases. We have previously shown that chroman-4-ones act as potent and selective inhibitors of SIRT2. Herein we report novel chroman-4-one and chromone-based SIRT2 inhibitors containing various heterofunctionalities to improve pharmacokinetic properties. The compounds retained both high SIRT2 selectivity and potent inhibitory activity. Two compounds were tested for their antiproliferative effects in breast cancer (MCF-7) and lung carcinoma (A549) cell lines. Both compounds showed antiproliferative effects correlating with their SIRT2 inhibition potency. They also increased the acetylation level of α-tubulin, indicating that SIRT2 is likely to be the target in cancer cells. A binding mode of the inhibitors that is consistent with the SAR data was proposed based on a homology model of SIRT2.

Epoxyalcohols: bioactivation and conjugation required for skin sensitization.

Allylic alcohols, such as geraniol 1, are easily oxidized by varying mechanisms, including the formation of both 2,3-epoxides and/or aldehydes. These epoxides, aldehydes, and epoxy-aldehydes can be interconverted to each other, and the reactivity of them all must be considered when considering the sensitization potential of the parent allylic alcohol. An in-depth study of the possible metabolites and autoxidation products of allylic alcohols is described, covering the formation, interconversion, reactivity, and sensitizing potential thereof, using a combination of in vivo, in vitro, in chemico, and in silico methods. This multimodal study, using the integration of diverse techniques to investigate the sensitization potential of a molecule, allows the identification of potential candidate(s) for the true culprit(s) in allergic responses to allylic alcohols. Overall, the sensitization potential of the investigated epoxyalcohols and unsaturated alcohols was found to derive from metabolic oxidation to the more potent aldehyde where possible. Where this is less likely, the compound remains weakly or nonsensitizing. Metabolic activation of a double bond to form a nonconjugated, nonterminal epoxide moiety is not enough to turn a nonsensitizing alcohol into a sensitizer, as such epoxides have low reactivity and low sensitizing potency. In addition, even an allylic 2,3-epoxide moiety is not necessarily a potent sensitizer, as shown for 2, where formation of the epoxide weakens the sensitization potential.

Epoxy resin monomers with reduced skin sensitizing potency.

Epoxy resin monomers (ERMs), especially diglycidyl ethers of bisphenol A and F (DGEBA and DGEBF), are extensively used as building blocks for thermosetting polymers. However, they are known to commonly cause skin allergy. This research describes a number of alternative ERMs, designed with the aim of reducing the skin sensitizing potency while maintaining the ability to form thermosetting polymers. The compounds were designed, synthesized, and assessed for sensitizing potency using the in vivo murine local lymph node assay (LLNA). All six epoxy resin monomers had decreased sensitizing potencies compared to those of DGEBA and DGEBF. With respect to the LLNA EC3 value, the best of the alternative monomers had a value approximately 2.5 times higher than those of DGEBA and DGEBF. The diepoxides were reacted with triethylenetetramine, and the polymers formed were tested for technical applicability using thermogravimetric analysis and differential scanning calorimetry. Four out of the six alternative ERMs gave polymers with a thermal stability comparable to that obtained with DGEBA and DGEBF. The use of improved epoxy resin monomers with less skin sensitizing effects is a direct way to tackle the problem of contact allergy to epoxy resin systems, particularly in occupational settings, resulting in a reduction in the incidence of allergic contact dermatitis.

Bioactivation of cinnamic alcohol forms several strong skin sensitizers.

Cinnamic alcohol is a frequent contact allergen, causing allergic contact dermatitis (ACD) in a substantial number of individuals sensitized from contacts with fragrances. Hence, cinnamic alcohol is one of the constituents in fragrance mix I (FM I) used for screening contact allergy in dermatitis patients. Cinnamic alcohol lacks structural alerts for protein reactivity and must therefore be activated by either air oxidation or bioactivation to be able to act as a sensitizer. In the present study, we explored the bioactivation of cinnamic alcohol using human liver microsomes (HLM), and the potential pathways for these reactions were modeled by in silico (DFT) techniques. Subsequently, the reactivity of cinnamic alcohol and its metabolites toward a model hexapeptide were investigated. In addition to cinnamic aldehyde and cinnamic acid, two highly sensitizing epoxides previously unobserved in studies of bioactivation were detected in the incubations with HLMs. Formation of epoxy cinnamic aldehyde was shown (both by the liver microsomal experiments, in which no depletion of epoxy cinnamic alcohol was observed after initial formation, and by the very high activation energy found for the oxidation thereof by calculations) to proceed via cinnamic aldehyde and not epoxy cinnamic alcohol.

Development of 7TM receptor-ligand complex models using ligand-biased, semi-empirical helix-bundle repacking in torsion space: application to the agonist interaction of the human dopamine D2 receptor.

Prediction of 3D structures of membrane proteins, and of G-protein coupled receptors (GPCRs) in particular, is motivated by their importance in biological systems and the difficulties associated with experimental structure determination. In the present study, a novel method for the prediction of 3D structures of the membrane-embedded region of helical membrane proteins is presented. A large pool of candidate models are produced by repacking of the helices of a homology model using Monte Carlo sampling in torsion space, followed by ranking based on their geometric and ligand-binding properties. The trajectory is directed by weak initial restraints to orient helices towards the original model to improve computation efficiency, and by a ligand to guide the receptor towards a chosen conformational state. The method was validated by construction of the ß1 adrenergic receptor model in complex with (S)-cyanopindolol using bovine rhodopsin as template. In addition, models of the dopamine D2 receptor were produced with the selective and rigid agonist (R)-N-propylapomorphine ((R)-NPA) present. A second quality assessment was implemented by evaluating the results from docking of a library of 29 ligands with known activity, which further discriminated between receptor models. Agonist binding and recognition by the dopamine D2 receptor is interpreted using the 3D structure model resulting from the approach. This method has a potential for modeling of all types of helical transmembrane proteins for which a structural template with sequence homology sufficient for homology modeling is not available or is in an incorrect conformational state, but for which sufficient empirical information is accessible.

Skin sensitization of epoxyaldehydes: importance of conjugation.

Structure-activity relationship (SAR) models are important tools for predicting the skin sensitization potential of new compounds without animal testing. In compounds possessing a structural alert (aldehyde) and an activation alert (double bond), it is important to consider bioactivation/autoxidation (e.g., epoxidation). In the present study, we have explored a series of aldehydes with regard to contact allergy. The chemical reactivity of these 6 aldehydes toward a model hexapeptide was investigated, and their skin sensitization potencies were evaluated using the local lymph node assay (LLNA). Overall, we observed a similar trend for the in vitro reactivity and the in vivo sensitization potency for the structural analogues in this study. The highly reactive conjugated aldehydes (α,ß-unsaturated aldehydes and 2,3-epoxyaldehydes) are sensitizing moieties, while nonconjugated aldehydes and nonterminal aliphatic epoxides show low reactivity and low sensitization potency. Our data show the importance of not only double bond conjugation to aldehyde but also epoxide-aldehyde conjugation. The observations indicate that the formation of nonconjugated epoxides by bioactivation or autoxidation is not sufficient to significantly increase the sensitization potency of weakly sensitizing parent compounds.

Cinnamyl alcohol oxidizes rapidly upon air exposure.

BACKGROUND: Cinnamyl alcohol and cinnamal are frequent fragrance contact allergens. Both are included in the European baseline fragrance mix I, which is used for screening of contact allergy in dermatitis patients. OBJECTIVES: The aim of this study was to investigate the autoxidation of cinnamyl alcohol and to identify the oxidation products formed on air exposure. We also wanted to evaluate the effect of autoxidation on the sensitization potency of cinnamyl alcohol. METHODS: Samples of commercially available cinnamyl alcohol with and without purification were exposed to air, and the autoxidation was followed by chemical analysis. The analysis was performed with mass spectrometry (LC/MS/MS). Sensitization potencies of compounds were determined with the murine local lymph node assay (LLNA) in mice. RESULTS: Chemical analysis showed that the concentration of cinnamyl alcohol in the air-exposed samples decreased rapidly over time, and that autoxidation products were formed. Cinnamal, epoxy cinnamyl alcohol and cinnamic acid were identified as oxidation products. According to our study, cinnamal and epoxy cinnamyl alcohol were the first autoxidation products formed. The epoxy cinnamyl alcohol was shown to be the oxidation product with the highest sensitization potency. The analysis of our samples of commercially available cinnamyl alcohol showed that there was already a content of 1.5% cinnamal at the start of the autoxidation experiments. CONCLUSION: Cinnamyl alcohol readily autoxidizes upon air exposure, and forms strong sensitizers as determined by the LLNA. Cinnamal was formed in the largest amounts, showing that cinnamal is not only formed via bioactivation, as has previously been shown. A highly sensitizing epoxide was also identified and quantified in the oxidation mixture.

Analogues of the epoxy resin monomer diglycidyl ether of bisphenol F: effects on contact allergenic potency and cytotoxicity.

Diglycidyl ethers of bisphenol A (DGEBA) and bisphenol F (DGEBF) are widely used as components in epoxy resin thermosetting products. They are known to cause occupational and nonoccupational allergic contact dermatitis. The aim of this study is to investigate analogues of DGEBF with regard to contact allergy and cytotoxicity. A comprehensive knowledge of the structural features that contribute to the allergenic and cytotoxic effects of DGEBF will guide the development of future novel epoxy resin systems with reduced health hazards for those coming into contact with them. It was found that the allergenic effects of DGEBF were dependent on its terminal epoxide groups. In contrast, it was found that the cytotoxicity in monolayer cell culture was dependent not only on the presence of epoxide groups but also on other structural features.

Synthesis and evaluation of substituted chroman-4-one and chromone derivatives as sirtuin 2-selective inhibitors.

A series of substituted chromone/chroman-4-one derivatives has been synthesized and evaluated as novel inhibitors of SIRT2, an enzyme involved in aging-related diseases, e.g., neurodegenerative disorders. The analogues were efficiently synthesized in a one-step procedure including a base-mediated aldol condensation using microwave irradiation. The most potent compounds, with inhibitory concentrations in the low micromolar range, were substituted in the 2-, 6-, and 8-positions. Larger, electron-withdrawing substituents in the 6- and 8-positions were favorable. The most potent inhibitor of SIRT2 was 6,8-dibromo-2-pentylchroman-4-one with an IC(50) of 1.5 µM. The synthesized compounds show high selectivity toward SIRT2 over SIRT1 and SIRT3 and represent an important starting point for the development of novel SIRT2 inhibitors.

3-aminopiperidine-based peptide analogues as the first selective noncovalent inhibitors of the bacterial cysteine protease IdeS.

A series of eight peptides corresponding to the amino acid sequence of the hinge region of IgG and 17 newly synthesized peptide analogues containing a piperidine moiety as a replacement of a glycine residue were tested as potential inhibitors of the bacterial IgG degrading enzyme of Streptococcus pyogenes , IdeS. None of the peptides showed any inhibitory activity of IdeS, but several piperidine-based analogues were identified as inhibitors. Two different analysis methods were used: an SDS-PAGE based assay to detect IgG cleavage products and a surface plasmon resonance spectroscopy based assay to quantify the degree of inhibition. To investigate the selectivity of the inhibitors for IdeS, all compounds were screened against two other related cysteine proteases (SpeB and papain). The selectivity results show that larger analogues that are active inhibitors of IdeS are even more potent as inhibitors of papain, whereas smaller analogues that are active inhibitors of IdeS inhibit neither SpeB nor papain. Two compounds were identified that exhibit high selectivity against IdeS and will be used for further studies.

Investigation of D2 receptor-agonist interactions using a combination of pharmacophore and receptor homology modeling.

A combined modeling approach was used to identify structural factors that underlie the structure-activity relationships (SARs) of full dopamine D2 receptor agonists and structurally similar inactive compounds. A 3D structural model of the dopamine D2 receptor was constructed, with the agonist (-)-(R)-2-OH-NPA present in the binding site during the modeling procedure. The 3D model was evaluated and compared with our previously published D2 agonist pharmacophore model. The comparison revealed an inconsistency between the projected hydrogen bonding feature (Ser-TM5) in the pharmacophore model and the TM5 region in the structure model. A new refined pharmacophore model was developed, guided by the shape of the binding site in the receptor model and with less emphasis on TM5 interactions. The combination of receptor and pharmacophore modeling also identified the importance of His3936·55 for agonist binding. This convergent 3D pharmacophore and protein structure modeling strategy is considered to be general and can be highly useful in less well-characterized systems to explore ligand-receptor interactions. The strategy has the potential to identify weaknesses in the individual models and thereby provides an opportunity to improve the discriminating predictivity of both pharmacophore searches and structure-based virtual screens.