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Issue 4, 2015
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Tunneling in tocopherol-mediated peroxidation of 7-dehydrocholesterol

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The peroxidation of 7-dehydrocholesterol (7-DHC), a biosynthetic precursor to vitamin D3 and cholesterol, has been linked to the pathophysiology of Smith–Lemli–Optiz syndrome (SLOS), a devastating human disorder. In SLOS, 7-DHC plasma and tissue levels are elevated because of defects in the enzyme that convert it to cholesterol. α-Tocopherol can mediate the peroxidation of 7-DHC under certain circumstances and this prompted us to investigate the kinetic isotope effect (KIE) during this process. Thus, 9,14-d2-7-DHC was synthesized using a photochemical cyclization of deuterium-reinforced previtamin D3 (retro to its biosynthesis). Subsequently, we carried out co-oxidation of 9,14-h2-25,26,26,26,27,27,27-d7- and 9,14-d2-7-DHC in the presence of α-tocopherol under conditions that favor TMP. By monitoring the products formed from each precursor using mass spectrometry, the KIE for the hydrogen (deuterium) atom removal at C9 was found to be 21 ± 1. This large KIE value indicates that tunneling plays a role in the hydrogen atom transfer step in the tocopherol-mediated peroxidation of 7-DHC.

Graphical abstract: Tunneling in tocopherol-mediated peroxidation of 7-dehydrocholesterol

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The article was received on 10 Nov 2014, accepted on 14 Nov 2014 and first published on 14 Nov 2014

Article type: Paper
DOI: 10.1039/C4OB02377C
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Citation: Org. Biomol. Chem., 2015,13, 1249-1253
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    Tunneling in tocopherol-mediated peroxidation of 7-dehydrocholesterol

    H. Muchalski, L. Xu and N. A. Porter, Org. Biomol. Chem., 2015, 13, 1249
    DOI: 10.1039/C4OB02377C

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