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2,2’-Spirobis[chromene] Derivatives Chemistry and their Relation with the Multistate System of Anthocyanins. Artur J. Moro, A. Jorge Parola, Fernando Pina, Ana-Maria Pana, Valentin Badea, Iulia Pausescu, Sergiu Shova, and Liliana Cseh J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 25 Apr 2017 Downloaded from http://pubs.acs.org on April 27, 2017
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The Journal of Organic Chemistry
w2,2’-Spirobis[chromene] Derivatives Chemistry and their Relation with the Multistate System of Anthocyanins. Artur J. Moro a), A. Jorge Parola a), Fernando Pina,a),* Ana-Maria Pana b), Valentin Badea c), Iulia Pausescu b), Sergiu Shova d), Liliana Cseh b),*
a) LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal,
[email protected]. b) Institute of Chemistry Timisoara of Romanian Academy, 24 M. Viteazu Bvd, 300223 Timisoara, Romania,
[email protected] c) University Politehnica Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, 6 V. Parvan Bvd, 300223, Timisoara, Romania d) Petru Poni Institute of Macromolecular Chemistry, Inorganic Chemistry, 41A Aleea Gr. Ghica Voda, 700487, Iasi, Romania
ABSTRACT
The chemistry of 2,2’-spirobis[chromene] derivatives is intimately related to the one of anthocyanins and similar compounds. The 2,2’-spirobis[chromene] species plays a central role in the network of chemical reactions connecting two different flavyliumbased
multistate
systems.
In
the
present
work,
a
new
asymmetric
2,2’-spirobis[chromene] intermediate possessing a constrained propylenic bridge between carbons 3 and 3’ was isolated and its role as a pivot in the anthocyanins-type multistate of chemical reactions was investigated by the conjugation of absorption spectroscopy, stopped-flow, NMR and X-Ray crystallography. It was confirmed that the propylenic bridge is essential to stabilize the spirobis[chromene] species. Furthermore, under acidic conditions, two cis-trans styrylflavylium isomers were identified, which could be interconverted directly into one another with light. This is the first report of styrylflavylium cations with photoisomerization on the styryl moiety. KEY WORDS
Anthocyanins, spirochromene, stopped-flow, multistate systems, photochemistry
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Graphical Abstract
pH =1
2 >1 pH
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The Journal of Organic Chemistry
INTRODUCTION
Nature selected the multistate of species resulting from anthocyanins to confer color to most flowers and fruits.1 The multistate is constituted by a pH dependent sequence of chemical reactions that in moderately acidic medium involves five different chemical species, as exemplified for malvidin-3-O-glucoside (oenin), Scheme 1.2,3
Scheme 1. Multistate of chemical reactions of malvidin-3-O-glucoside (oenin) in water.
At sufficiently acidic medium the red flavylium cation, AH+, is the dominant species (Chatelier’s principle), and thus anthocyanins (and related compounds)4 are generally stored in vitro in their flavylium form at pH
