Synthesis of DTPA-conjugated (1,4)-linked 2-aminoglycosides varying in the anomeric configuration and their MRI contrast effect
作者:Hiroshi Tanaka、Yoshio Ando、Masatoshi Wada、Takashi Takahashi
DOI:10.1039/b507824e
日期:——
We describe the efficient synthesis of DTPA-conjugated oligosaccharides composed of α- and/or β-linked tri to monoglucosamines. Gd(III) complex with DTPA-conjugated chitotriitol 1 has been reported to be an effective MRI contrast agent. In order to elucidate the structure–property relationships, we planned to synthesize the DTPA-conjugated 2-amino-tri-, di-, and monosaccharides varying in configuration at the anomeric positions and the C2 position on the reducing end. Our strategy for the synthesis of the DTPA-conjugated oligosaccharides involves O-perbenzyl protected 2-amino-tri-, di-, and monosaccharides as key intermediates. The 2-aminoglycosides were prepared by non-selective glycosidation of 2-azido-2-deoxyglycosyl donors, followed by separation of two anomeric isomers. Although the synthesis involves separation of the stereoisomers, it circumvents not only the careful tuning of reaction conditions, but also the time-consuming preparation of glycosyl donors attached to different protecting groups. The protected 2-aminoglycosides were converted to the fully deprotected DTPA-conjugated tri- to monosaccharides by the same operation. MRI phantom study using the Gd(III) complexes of DTPA-conjugated oligosaccharides indicates that the number of the monosaccharide units was critical for enhancing the relative signal intensity of water protons per Gd, and various stereoisomers would be candidate scaffolds for MRI contrast agents.
我们描述了由α-和/或β-连接的三葡糖胺与单葡糖胺组成的 DTPA 共轭寡糖的高效合成。据报道,Gd(III)与 DTPA 共轭壳三醇 1 的复合物是一种有效的磁共振成像造影剂。为了阐明其结构-性质关系,我们计划合成 DTPA 键合的 2-氨基三糖、二糖和单糖,它们在异构体位置和还原端 C2 位置的构型各不相同。我们合成 DTPA 共轭寡糖的策略是以 O-perbenzyl 保护的 2-氨基三糖、二糖和单糖为关键中间体。2-aminoglycosides 是通过 2-azido-2-deoxyglycosyl 给体的非选择性糖苷化反应制备的,然后分离出两种异构体。虽然这种合成方法涉及立体异构体的分离,但它不仅避免了对反应条件的精心调整,还避免了制备连接不同保护基团的糖基供体的耗时过程。通过同样的操作,受保护的 2-氨基糖苷被转化为完全去保护的 DTPA 共轭三糖和单糖。使用 DTPA 共轭低聚糖的 Gd(III) 复合物进行的磁共振成像模型研究表明,单糖单元的数量对于增强每个 Gd 的水质子的相对信号强度至关重要,各种立体异构体将成为磁共振成像造影剂的候选支架。