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Estimating Reactivity From Structure Using the OECD (Q)SAR Application Toolbox

Estimating Reactivity From Structure Using the OECD (Q)SAR Application Toolbox. T. W. Schultz Presented at the Logan Workshop March 23-24, 2010. Topics. Background & The Problem Michael Acceptors: An Example  Toolbox Applications Pathways Application Summary.

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Estimating Reactivity From Structure Using the OECD (Q)SAR Application Toolbox

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  1. Estimating Reactivity From Structure Using the OECD (Q)SAR Application Toolbox T. W. Schultz Presented at the Logan Workshop March 23-24, 2010

  2. Topics • Background & The Problem • Michael Acceptors: An Example •  Toolbox Applications • Pathways Application • Summary

  3. Coding Reactivity From Structure • Currently no universal QSAR model • Local models for simple congeneric groups • 2D structure • Qualitatively easy • Main drawback false positives • Quantitatively more difficult • Iso-reactive groups (lumping vs. splitting) • Sub-grouping and sub-sub-grouping

  4. 2D Coding Michael Acceptors Qualitatively Predicted as any Polarized a,b-Unsaturated Compound for example, C=CC(=O)

  5. 2D Coding Michael Acceptors Quantitative Predictions Impacted By Substitution at C1=C2(Pg)C3 Reactivity is extended fragment -based

  6. Structural Variation in Reactive Potency of Esters TYPE STRUCTURE RC50(mM) Acetylenedicarboxylates ROC(=O)C#CC(=O)OR 0.025 Propiolates C#CC(=O)OR 0.1 Vinylene dicarboxylates ROC(=O)C=CC(=O)OR 0.2 Acrylates C=CC(=O)OR 0.8 Alkyl 2-alkynoates RC#CC(=O)OR 1.5 Crotonates CC=CC(=O)OR 15.0 Methacrylates C=C(C)C(=O)COR >30.0

  7. Variations in RC50Values for Substituted Acrylates, C=CC(=O)OR Derivative RC50 (mM) _______________________________________ Ethyl 0.48, 0.55 Vinyl 0.11, 0.11 2-Hydroxyethyl 0.25, 0.29 n-Propyl 0.80, 0.92 Propargyl 0.19, 0.24 n-Hexyl 0.88, 0.76 Phenyl 0.016, 0.015

  8. To Quantitatively Predict Reactivity: Must Be Able to Separate C#CC(=O) C=CC(=O) CC=CC(=O) C=C(C)C(=O)

  9. To Quantitatively Predict Reactivity: Must Also be Able To Separate C=CNO2 C=CC#N C=CC(=O)C C=CC(O)OC C=CC(=O)NH2

  10. Toolbox Application • Use reactive to group chemicals into categories and to facilitate the selection of chemical analogues, which allows the integrates of the mechanism of reaction in defining the best category or sub-category • Then do read-across

  11. Read Across with GSH & LLNA Data EC3 = 0.01 RC50 = 0.03 RC50 = 0.05 RC50 = 0.05 RC50 = 0.09 RC50 = 0.02

  12. Protein Binding in Toxicity Mechanisms of Protein Binding In Vitro Measurements In Chemico Measurement Hazard Assessment Endpoints In vitro effects Reactive Potency Michael addition SN2 SNAr In vivo effects In silico modeling

  13. Application Reactivity to Catgorizing an Inventory • ≈ 1500 substances on the List of Flavor and Fragrance Related Substances • ≈1300 discrete substances of which: • 79 Fast- to moderate-reacting Michael-acceptors; • 19 Slow-reacting Michael-acceptors; • 57 Schiff-base aldehydes; • 29 Acetals; • 15 Disulfide formers; • 11 Cyclic addition diones; • 9 Disulfide exchangers; • 3 O-heterocyclic ring openers. >40 pro-electrophiles

  14. Pathway Applications • Screening Tool • Many be used in isolation • Risk Assessment • Must be used as part of an ITS • Represents the molecular initiating event of an adverse outcome pathway

  15. Pathway for Allergic Contact Dermatitis 1. Haptenation; 2. Epidermal inflammation & LC activation; 3. LC migration; 4. DC: T cell interaction; 5. T cell proliferation; 6. Increase in hapten-specific T cells; 7. Hapten re-exposure; 8. Acute inflammation; 9. T cell-mediated inflammation Karlberg et al.Chem. Res. Toxicol. 2008, 21, 53-69.

  16. LLNA-tested Michael Acceptor SUBSTRUCTURE MESSAGE C=CC=O Vinyl or vinylene with a carbonyl [CH2]=C(C)C=O -C-atom alkyl-substituted with a carbonyl O=CC=CC=O -C-atom substituted with a second carbonyl [CH]=C(C(=O))C=O -C-atom substituted with a second carbonyl C=[CH]c1ccncc1 Para-vinyl azaarene O=C1[CH]=CC(=O)C=C1 Para-quinone

  17. Michael Acceptor Not Tested in LLNA SUBSTRUCTURE MESSAGE C#CC=O Ethylnylene or acetylenic with a carbonyl C=CN(=O)=O Olefinic nitro C#CS(=O) Ethylnylene or acetylenic with a S=O C=CS=O Vinyl or vinylene with a S=O C=CC#N Olefinic cyano C#Cc1ncccc1 Ortho-ethylnylene azaarene C=[CH]c1ncccc1 Ortho-vinyl azaarene C#Cc1ccncc1 Para-ethylnylene azaarene C=[CH]C(=O)[OX1] Vinylene carboxylic acid O=C1C=C[CH]=CC1=O Ortho-quinone [CH2]=[CH][CH]=O Acrolein

  18. Subcategorization of Michael Acceptors by Reactivity • Extremely fast: quinones, propiolates , 1-alken-3-ones • Fast:acrylates, 2-alkenals, 3-alken-2-ones • Moderately Fast: alkyl 2-alkynoates • Slow: crotonates • Very Slow: methacryates, tiglates • Non-Reactive: non-,-unsaturated

  19. Summary • We have a 2D modeling strategy • Quantitative reactivity data is available for QSAR development • We have an application scheme

  20. Thank you

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