Jacobsen D W, Holland R J, Montejano Y, Huennekens F M
J Inorg Biochem. 1979 Feb;10(1):53-65. doi: 10.1016/s0162-0134(00)81005-3.
Upper-axial (beta-position) ligand analogs of the B12 coenzymes 5'-deoxy-5'-adenosylcob(III)alamin and methylcob(III)alamin have been synthesized by reaction of the 5'-chloro-5'-deoxy derivatives of fluorescent nucleosides (1,N6-ethenoadenosine, formycin, 2-amino-nebularine, and 2,6-diaminonebularine) and a fluorescent alkyl halide (dansylamidopropyl chloride) with cob(I)alamin. These analogs were nonfluorescent, but fluorescent products could be generated by photolysis or cyanolysis of the carbon-cobalt bonds. Under anaerobic and aerobic conditions, the major fluorescent photolysis products of 1,N6-ethenoadenosylcob(III)alamin were 1,N6-etheno-5',8-cyclic-5'-deoxyadenosine, and the 5'-aldehyde of 1,N6-ethenoadenosine, respectively. The cryptofluorescent property of these analogs was utilized to follow the kinetics of aerobic photolysis. First-order rate constants determined by this method were comparable to those obtained spectrophotometrically [via appearance of of aquacob(III)alamin]. Pseudo-first-order rate constants determined fluorometrically for the cyanolysis (at 25 degrees C) of 1,N6-ethenoadenosylcob(III)alamin, 2,6-diaminonebularinylcob(III)alamin, 2-aminonebularinylcob(III)alamin and formycinylcob(III)alamin were 5.8 X 10(-2), 2 X 10(-2), 1.8 X 10(-2), and 3 X 10(-5) min-1, respectively; values in good agreement were obtained spectrophotometrically (via appearance of dicyanocobalamin). Dansylamidopropylcob(III)alamin was stable in the presence of cyanide. The nucleoside alpha-ribazole is fluorescent in the free state but nonfluorescent when present as the lower axial (alpha-position) ligand in cobalamin coenzymes. Thus fluorescence of ligands in both the alpha- and beta-positions of cobalamins is quenched, probably as a result of intramolecular energy transfer between the ligands and the nonfluorescent corrinoid.
通过荧光核苷（1,N⁶-乙烯腺苷、间型霉素、2-氨基-珠碱和2,6-二氨基珠碱）的5'-氯-5'-脱氧衍生物以及荧光烷基卤（丹磺酰胺丙基氯）与钴胺素（I）反应，合成了维生素B₁₂辅酶5'-脱氧-5'-腺苷钴胺素（III）和甲基钴胺素（III）的上轴向（β-位）配体类似物。这些类似物本身无荧光，但碳-钴键经光解或氰解可产生荧光产物。在厌氧和好氧条件下，1,N⁶-乙烯腺苷钴胺素（III）的主要荧光光解产物分别为1,N⁶-乙烯基-5',8-环-5'-脱氧腺苷和1,N⁶-乙烯腺苷的5'-醛。利用这些类似物的隐荧光特性来跟踪好氧光解动力学。用该方法测定的一级速率常数与通过分光光度法[通过水合钴胺素（III）的出现]获得的速率常数相当。通过荧光法测定的1,N⁶-乙烯腺苷钴胺素（III）、2,6-二氨基珠碱基钴胺素（III）、2-氨基珠碱基钴胺素（III）和间型霉素基钴胺素（III）在25℃下氰解的伪一级速率常数分别为5.8×10⁻²、2×10⁻²、1.8×10⁻²和3×10⁻⁵ min⁻¹；通过分光光度法（通过二氰钴胺素的出现）获得了吻合度良好的值。丹磺酰胺丙基钴胺素（III）在氰化物存在下稳定。核苷α-核唑在游离状态下有荧光，但作为钴胺素辅酶中的下轴向（α-位）配体时无荧光。因此，钴胺素α-位和β-位配体的荧光均被淬灭，这可能是由于配体与无荧光类咕啉之间的分子内能量转移所致。
