A number of synthetic approaches are assessed to prepare allantoin labelled with 14C given certain requirements and technical limitations. A method that fulfils these criteria is described to achieve the synthesis of highly pure 14C-labelled allantoin with the label introduced to the ureido carbonyl group in the final step by reaction of 5-chlorohydantoin with [14C]urea. The chosen method favours high purity at the expense of radiochemical yield, which is achieved at a level of 8%. The integrity of the label is then investigated by performing an NMR analysis of 13C-labelled allantoin synthesized by the same method. The 13C NMR spectrum confirms partial scrambling of the label to the C-2 position by equilibration of the product via a putative bicyclic intermediate, which had been suggested by other workers. The 14C-labelled allantoin synthesized by this method is therefore assigned as DL-[H2N14CO/14C-2]allantoin. This study also includes the first full characterization of a side product, 5-hydroxy-5-methoxyhydantoin, obtained by the reaction of a 5-hydroxyhydantoin intermediate with the methanol solvent. Copyright © 2009 John Wiley & Sons, Ltd.
鉴于某些要求和技术限制,对制备 14C 标记
尿囊素的一些合成方法进行了评估。本文介绍了一种符合这些标准的方法,通过 5-
氯海因与[14C]
脲的反应,在最后一步将标记引入
脲基羰基,从而合成高纯度的 14C 标记
尿囊素。所选方法有利于提高纯度,但牺牲了放射
化学产率,使产率达到 8%。然后,通过对以相同方法合成的 13C 标记
尿囊素进行核磁共振分析,研究标记的完整性。13C NMR 光谱证实,标签部分扰乱了 C-2 位置,通过一个假定的双环中间体对产物进行平衡,其他研究人员也曾提出过这一观点。因此,用这种方法合成的 14C 标记
尿囊素被命名为 DL-[H2N14CO/14C-2]
尿囊素。本研究还首次全面鉴定了一种副产品--5-羟基-5-甲氧基
尿囊素,它是由 5-羟基
尿囊素中间体与
甲醇溶剂反应得到的。Copyright © 2009 John Wiley & Sons, Ltd. All Rights Reserved.