Scott T A
Biochem J. 1967 Jan;102(1):87-93. doi: 10.1042/bj1020087.
A chemical degradation scheme is reported, which permits the measurement of the radioactivity of each carbon atom of nicotinic acid. Nicotinic acid is decarboxylated by heating with copper chromite to give carbon dioxide (C-7) and pyridine. The pyridine is converted into 4-nitropyridine 1-oxide, which is heated with aqueous calcium hypobromite to give tribromonitromethane. Combustion of the latter gives carbon dioxide derived from C-4 of the nicotinic acid. Nicotinic acid is also reduced to nipecotic acid, which is oxidized to succinic acid by acidic potassium permanganate. Stepwise degradation of the succinic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-3, C-6 and C-4, C-5 of the nicotinic acid. Benzoylation of the nipecotic acid, followed by oxidation with permanganate at pH7, gives 5-amino-4-carboxyvaleric acid; this is converted into 2-methyleneglutaric acid by the action of nitrous acid. Hydrogenation of the 2-methyleneglutaric acid over rhodium in methanol gives 2-methylglutaric acid, which is oxidized with dilute chromic acid to acetic acid. Stepwise degradation of the acetic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-2 and C-3 of the nicotinic acid. Thus the radioactivities of C-2, C-3, C-4 and C-7 are determined directly and those of C-5 and C-6 by difference. The method was shown to be isotopically valid for [2,3,7-(14)C]-, [4,6-(14)C(2)]- and [5-(14)C]-nicotinic acid.
报道了一种化学降解方案，该方案可用于测定烟酸中每个碳原子的放射性。烟酸与亚铬酸铜加热进行脱羧反应，生成二氧化碳（C-7）和吡啶。吡啶转化为4-硝基吡啶1-氧化物，后者与次溴酸钙水溶液加热生成三溴硝基甲烷。三溴硝基甲烷燃烧生成源自烟酸C-4的二氧化碳。烟酸还可还原为哌啶酸，哌啶酸被酸性高锰酸钾氧化为琥珀酸。通过标准程序对琥珀酸进行逐步降解，得到两个二氧化碳样品，分别对应烟酸的C-3、C-6和C-4、C-5。哌啶酸进行苯甲酰化，然后在pH7条件下用高锰酸钾氧化，得到5-氨基-4-羧基戊酸；亚硝酸作用下将其转化为2-亚甲基戊二酸。2-亚甲基戊二酸在甲醇中用铑催化氢化得到2-甲基戊二酸，用稀铬酸将其氧化为乙酸。通过标准程序对乙酸进行逐步降解，得到两个二氧化碳样品，分别对应烟酸的C-2和C-3。因此，直接测定了C-2、C-3、C-4和C-7的放射性，C-5和C-6的放射性通过差值确定。该方法对[2,3,7-(14)C]-、[4,6-(14)C(2)]-和[5-(14)C]-烟酸在同位素方面是有效的。
