The Hydrolytic Cleavage Products of Boron Trifluoride Complexes of β-Carotene, Some Dehydrogenated Carotenes and Anhydrovitamin A<sub>1</sub>

The reaction between beta,beta-carotene and BF3-etherates has been investigated, leading to structural elucidation of the blue product, formed in appropriate organic solvents, as a symmetrical charge delocalised dication (lambda(max) 985 nm at room temperature in CHCl3) with considerable stability. The reaction, monitored by EPR studies at -25 degrees C, occurred via free radical intermediates. A C40H56BF3 intermediate was captured by EIMS. The detailed structure of the dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -20 degrees C) leading to complete assignments of 1H and 13C chemical shifts and 3J(H,H) coupling constants. The effects of the two delocalised charges on chemical shift (charge distribution) and bond distance (3J(H,H)) were considered. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5'-C-9' regions and with bond inversion to retro shifted double bonds in the central C-13-C-13' region. A convention for denoting the charge delocalisation and bond types is presented. The experimental results are discussed relative to previous theoretical calculations of the beta,beta-carotene dication structure. (All-E) and (15-Z)-beta,beta-carotene provided the same dication. The NIR spectra and stability of dications prepared in the same manner from the related carotenes 20,20'-dinor-beta,beta-carotene, heptapreno-beta,beta-carotene and nonapreno-beta,beta-carotene were examined for comparison. Reactions of the beta,beta-carotene dication with selected nucleophiles provided products including isocryptoxanthin, isocarotene and mutatochrome with H2O as nucleophile, and isocryptoxanthin methyl ether, 8-methoxy-7,8-dihydro-beta,beta-carotene and isocarotene with CH3ONa as nucleophile. The formation of these products is rationalised from the structure assigned to the dication.

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“…Procedure adapted from ref. 47. β,β-Carotene (1, 3.2 mg) was dissolved in CHCl 3 (3 ml) and BF 3 -dee (1 ml) was added at room temperature.…”

Section: Reactions Of -Carotene Dication (5) With Nucleophilesmentioning

confidence: 99%

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

et al. 2003

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“…Recent results from a combined gas chromatographic-mass spectral examination of dicarboxylic acids obtained by ozonolysis show that the products from the Mucor sporopollenin are very similar to those from the oxidative polymers of /?-carotene and of iso-zeaxanthin ( Table 2). Iso-zeaxanthin is one of the earliest oxidation products during treatment of /?-carotene with oxygen and boron trifluoride (Petracek & Zechmeister, 1956) and so could also be an intermediate in the biosynthesis of sporopollenin from /?-carotene. Recent capillary-column pyrolysis gas chromatograms have confirmed the earlier evidence that the pyrolysis products from the Mucor sporopollenin and the /?-carotene polymer are very similar.…”

Section: G W G O O D a Y P Fawcett D G R E E N And G S H A Wmentioning

confidence: 99%

The Formation of Fungal Sporopollenin in the Zygospore Wall of Mucor mucedo: a Role for the Sexual Carotenogenesis in the Mucorales

Gooday

Fawcett

Green

et al. 1973

Journal of General Microbiology

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“…Wallcave and Zechmeister (1953) prepared isocryptoxanthin from 3,4-dehydro-/3-carotene via a boron trifluorideetherate complex at a yield of 34%. By changing the solvent system to chloroform, Petracek and Zechmeister (1956) were able to prepare the isocryptoxanthin (32% yield) directly from /3-carotene. They did, however, propose that the BF3 first acted to form dehydro-/3-carotene and that the BF3-etherate complex did not actually form with /3-carotene but rather with dehydro-/3-carotene, as described earlier by Wallcave and Zechmeister (1953).…”

Section: Resultsmentioning

confidence: 99%

A proposed mechanism for the hydroxylation of carotenoids on Micro-Cel C

Ritacco¹,

Britton²,

Simpson³

1984

J. Agric. Food Chem.

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The Hydrolytic Cleavage Products of Boron Trifluoride Complexes of β-Carotene, Some Dehydrogenated Carotenes and Anhydrovitamin A₁

Cited by 23 publications

References 0 publications

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

The Formation of Fungal Sporopollenin in the Zygospore Wall of Mucor mucedo: a Role for the Sexual Carotenogenesis in the Mucorales

A proposed mechanism for the hydroxylation of carotenoids on Micro-Cel C

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The Hydrolytic Cleavage Products of Boron Trifluoride Complexes of β-Carotene, Some Dehydrogenated Carotenes and Anhydrovitamin A1

Cited by 23 publications

References 0 publications

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

The Formation of Fungal Sporopollenin in the Zygospore Wall of Mucor mucedo: a Role for the Sexual Carotenogenesis in the Mucorales

A proposed mechanism for the hydroxylation of carotenoids on Micro-Cel C

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The Hydrolytic Cleavage Products of Boron Trifluoride Complexes of β-Carotene, Some Dehydrogenated Carotenes and Anhydrovitamin A₁