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Influence of the methyl group in isoprene epoxides on reactivity compared to butadiene epoxides: Biological significance

Lookup NU author(s): Emeritus Professor Bernard GoldingORCiD, Manuel Abelairas-Edesa, Daping Zhang, Dr Alistair Henderson, Dr Christine Bleasdale, Emeritus Professor Bill CleggORCiD

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved. Reactions of the epoxides of 1,3-butadiene and isoprene (2-methyl-1,3-butadiene) with oxygen, nitrogen and sulfur nucleophiles have been compared to enable a better molecular understanding of the relative human toxicities of these epoxides. Hydrolysis of rac.-ethenyloxirane in (18O)water gave 77% (2-18O)but-3-ene-1,2-diol and 23% (1-18O)but-3-ene-1,2-diol. The R:S ratio for but-3-ene-1,2-diol from hydrolysis of (S)-ethenyloxirane was 75:25. Hence, hydrolysis of ethenyloxirane occurs by competing SN2 attack at C-2 and C-3 in 3:1 ratio, with no SN1 component. Hydrolysis of rac.-2-ethenyl-2-methyloxirane gave 2-hydroxy-2-methylbut-3-en-1-ol (73%) and 27% of a 2:1 mixture of the E- and Z-isomers of 4-hydroxy-2-methylbut-2-en-1-ol. In (18O)water (2-18O)2-hydroxy-2-methylbut-3-en-1-ol was obtained. Formation of these products occurs via SN1 ionisation to resonance-stabilised allylic cations which are captured by water. Reaction of rac.-ethenyloxirane with l-valine methyl ester gave diastereoisomeric adducts from SN2 attack of the valine amino at both C-2 (substituted position) and C-3 of the oxirane. The corresponding reaction of rac.-2-methyl-2-ethenyloxirane gave diastereoisomeric adducts, (R, S)- and (S, S)-N-(2-hydroxy-2-methyl-3-buten-1-yl)-l-valine methyl ester, from SN2 attack of the valine amino solely at C-3. Reactions of rac.-2-ethenyl-2-methyloxirane with cysteine derivatives occurred at C-2 in neutral polar media (SN1 reaction) or at C-3 in basic media (SN2), whereas for ethenyloxirane products arose from attack at both C-2 and C-3. Reaction of meso-butadiene diepoxide (meso-2,2'-bioxirane) with l-valine methyl ester gave mainly 2:1 adducts, dimethyl 2,2'-(((2R,3S)-2,3-dihydroxybutane-1,4-diyl)bis(azanediyl))-(2S,2'S)-bis(3-methyl-butanoates), whereas 2-methyl-2,2'-bioxirane gave a mixture of 1:1 [methyl 2-(3,4-dihydroxy-3-methylpyrrolidin-1-yl)-3-methylbutanoates] and 2:1 adducts. Meso-2,2'-bioxirane reacted with N-acetylcysteine methyl ester in methanol to afford meso-thiolane-3,4-diol, by elimination of N-acetyldehydroalanine methyl ester from a precursor cyclic adduct. Similarly, 2-methyl-2,2'-bioxirane gave solely 3-methylthiolane-3,4-diols. Thus, the methyl group of isoprene has a subtle effect on the reactivity of its epoxides relative to those of butadiene and therefore, in the context of their toxicology, could abrogate crosslinking of nitrogen functions in biomolecules related to mutagenicity and carcinogenicity.


Publication metadata

Author(s): Golding BT, Abelairas-Edesa M, Tilbury RD, Wilson JP, Zhang D, Henderson AP, Bleasdale C, Clegg W, Watson WP

Publication type: Article

Publication status: Published

Journal: Chemico-Biological Interactions

Year: 2022

Volume: 361

Print publication date: 01/07/2022

Online publication date: 29/04/2022

Acceptance date: 11/04/2022

Date deposited: 01/07/2022

ISSN (print): 0009-2797

ISSN (electronic): 1872-7786

Publisher: Elsevier

URL: https://doi.org/10.1016/j.cbi.2022.109949

DOI: 10.1016/j.cbi.2022.109949

PubMed id: 35490797


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