This publication describes the straightforward and redox-neutral synthesis of 10-bromophenylethynylcobalamin and its facile conversion to 10-bromoaquacobalamin. In this approach, the phenylethynyl ligand acts as convenient light-stable protecting group that is removed in quantitative yield under acidic conditions. The proteolytic cleavage at pH 2.0 was studied under pseudo-first-order conditions and is 1.5 times slower than that of phenylethynylcobalamin with a hydrogen instead of a bromine at C(10). Preliminary electrochemical studies of organometallic ethynyl-Cbls (Cbl=cobalamin) are reported for the first time. A reduction potential of −0.94 V vs. Ag/AgCl was determined for the Co^III/Co^I reduction of 10-bromophenylethynylcobalamin. The positive potential shift of 180 mV compared to phenylethynylcobalamin is in agreement with earlier electrochemical studies of related cyanocobalamins.

中文翻译：

---

10-溴取代的光稳定抗维生素 B12 候选物的氧化还原中性合成和电化学研究

该出版物描述了 10-溴苯基乙炔基钴胺素的直接和氧化还原中性合成及其向 10-溴水钴胺素的轻松转化。在这种方法中，苯乙炔基配体充当方便的光稳定保护基团，在酸性条件下以定量产率去除。在拟一级条件下研究了 pH 2.0 下的蛋白水解裂解，并且比 C(10) 处的氢而不是溴的苯乙炔钴胺的裂解慢 1.5 倍。首次报道了有机金属乙炔基-Cbls（Cbl=钴胺素）的初步电化学研究。甲还原电位-0.94的V VS。确定了 Co ^III /Co ^{I 的}Ag/AgCl10-溴苯乙炔基钴胺素的还原。与苯乙炔钴胺素相比，180 mV 的正电位偏移与相关氰钴胺素的早期电化学研究一致。