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  • Title: The synthesis and characterization of 8-methoxy-5'-deoxyadenosylcobalamin: a coenzyme B(12) analog which, following Co-C bond homolysis, avoids cyclization of the 8-methoxy-5'-deoxyadenosyl radical.
    Author: Doll KM, Fleming PE, Finke RG.
    Journal: J Inorg Biochem; 2002 Aug 15; 91(2):388-97. PubMed ID: 12161308.
    Abstract:
    The compound 8-methoxy-5'-deoxyadenosylcobalamin (8-MeOAdoCbl), has been synthesized in 37% yield and > or = 95% purity by HPLC, monitored at both 254 and 525 nm, or 90+/-2% purity as judged by the (1)H NMR spectrum of the aromatic cobalamin region. This is the first synthesis of this complex in which sufficient details are reported, where a yield and purity are reported, and where key problems in the synthesis and purification are overcome, so that 8-MeOAdoCbl can actually be obtained for use in other studies. Also demonstrated is the clean Co-C bond homolysis of 8-MeOAdoCbl to give initially 8-MeOAdoCbl and Co(II)Cbl in a UV-visible thermolysis experiment at 110 degrees C, results which show that the 8-MeO moiety suppresses the cyclization to the 8,5'-anhydro-adenosine otherwise seen for the adenosyl radical (Ado)*. Suppression of this cyclization pathway makes 8-MeOAdoCbl invaluable for studying the kinetic isotope effect (KIE) of the Ado* plus substrate H* abstraction reaction, a component of the first definitive test of Klinman's hypothesis that the optimization of enzyme catalysis may entail strategies that increase the probability of tunneling and thereby accelerate H* atom abstraction reaction rates.
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