CHEMISTRY OF COBALAMINS AND RELATED COMPOUNDS .48. STERICALLY INDUCED, SPONTANEOUS DEALKYLATION OF SECONDARY ALKYLCOBALAMINS DUE TO AXIAL BASE COORDINATION AND CONFORMATIONAL-CHANGES OF THE CORRIN LIGAND
CHEMISTRY OF COBALAMINS AND RELATED COMPOUNDS .48. STERICALLY INDUCED, SPONTANEOUS DEALKYLATION OF SECONDARY ALKYLCOBALAMINS DUE TO AXIAL BASE COORDINATION AND CONFORMATIONAL-CHANGES OF THE CORRIN LIGAND
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DOI：
10.1021/ja00510a027
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发表时间：
1979-01-01
影响因子：
15
通讯作者：
SCHRAUZER, GN
中科院分区：
文献类型：
--
作者：
GRATE, JH;SCHRAUZER, GN
本文叙述了由烯烃、烷基碘和溴与维生素B12反应合成各种以前不能得到的仲烷基和环烷基钴醇。烷基钴的轴向5，6-二甲基苯并咪唑配体的配位依赖于烷基部分的空间体积，并且大多数仲烷基钴在中性溶液中主要以碱脱形式存在。仲烷基钴和高级伯烷基钴通过顺式β-环烷基化进行空间诱导的自发脱烷基化。消除，维生素B12与非活化烯烃的反应的逆。它们通常在酸性介质中更稳定，其中轴向碱被质子化，而在中性或碱性溶液中，该碱的轴向配位引起咕啉配体的构象变化，其加速Co-C键裂解几个数量级。
The synthesis of various, previously inaccessible, secondary alkyl- and cycloalkylcobalamins by the reactions of olefins, alkyl iodides and bromides with hydridocobalamin is described. The coordination of the axial 5,6-dimethylbenzimidazole ligand of alkylcobalamins is dependent on the steric bulk of the alkyl moiety, and most secondary alkylcobalamins exist predominantly in the base-off form in neutral solution. Secondary and higher primary alkylcobalamins undergo sterically induced spontaneous dealkylation by way of syn .beta.-elimination, the reverse of the reaction of hydridocobalamin with nonactivated olefins. They are generally more stable in acidic media, in which the axial base is protonated, while in neutral or alkaline solution, axial coordination of this base causes a conformational change of the corrin ligand which accelerates the Co-C bond cleavage by orders of magnitude.