The synthesis of homothymine PNA-oligomers can be plagued by the occurrence of a significant amount of truncation products, probably because on-resin aggregation hinders access during the coupling reactions. The use of low resin loading and the addition of the chaotropic salt KSCN in DMF allowed a partial remedy by conferring enhancements to the coupling yields. However, protection of the imide group by using O-allyl-protected thymine Fmoc-tAll provided the most significant improvements to the yields, even in cases where the use of non-protected thymine building blocks resulted in 70% truncation products. Deallylation occurs during the TFA cleavage step. Thus, O-allyl-protection can be applied in combination with standard protocols used in automated PNA synthesis.
同胸腺
嘧啶 PNA-高分子的合成过程中会出现大量截短产物,这可能是因为
树脂上的聚集阻碍了偶联反应的进行。使用低
树脂负载量和在
DMF 中加入混沌盐 KSCN 可以提高偶联产率,从而部分解决这一问题。不过,通过使用 O-烯丙基保护的胸腺
嘧啶 Fmoc-tAll 来保护
酰亚胺基团,可以最显著地提高产量,即使在使用未受保护的胸腺
嘧啶结构单元会产生 70% 截短产物的情况下也是如此。脱烯丙基作用发生在反式
脂肪酸裂解步骤中。因此,O-烯丙基保护可与自动
PNA 合成中使用的标准方案结合使用。