Synthesis and properties of novel artificial nucleic acid analogs having chiral backbones

肽核酸(PNA)是一种寡核苷酸模拟物，具有非手性聚酰胺骨架，核苷酸碱基连接在该骨架上。由于PNA可与单链DNA和RNA结合，也可与双链DNA结合，因此被认为是一种潜在的反义策略分子。众所周知，PNA-DNA和PNA-RNA双链比相应的DNA-DNA和DNA-RNA双链更稳定。然而，最近对PNA-DNA和PNA-RNA双链的核磁共振结构研究表明，由于PNA的螺旋螺距远大于DNA和RNA的螺旋间距，PNA在这类复合体中的构象并不是最佳的RNA。在这项研究中，我试图合成一种从L衍生的新型脱氧核糖核酸类似物-含酯键的丝氨酸，即基于丝氨酸的核苷酸连接聚酯(SNE)。与PNA相比，目前以聚酯为骨架的DNA类似物有望具有更短的螺旋间距，这与与互补核酸杂交是相同的。我开发了一种新的策略来合成由N-(胸腺素-1-基)乙酰丝氨酸组成的聚酯型核酸类似物L-丝氨酸。以L-丝氨酸乙酯为原料，经三步反应合成了含胸腺嘧啶的单体单元，产率较高，且不需要外消旋。3-Nitro-1，2，4-triazol-1-yl-tris(pyrrolidin-1-yl)phosphonium六氟磷酸盐(PYNTP)在不消旋的情况下能快速形成酯键，具有很高的效率。采用2-苯基-2-(三甲基硅基)乙基作为羧基保护基固相合成。利用一种新型的连接剂和可在温和中性条件下去除的氨基保护基团，实现了SNE的固相合成。

Peptide nucleic acid(PNA), an oligonucleotide mimic, has an achiral polyamide backbone, to which nucleobases are attached. Since PNA binds to single stranded DNA and RNA as well as to double stranded DNA, it is regarded as a potentially useful molecule for antisense strategy. It is well known that the PNA-DNA and PNA-RNA duplexes are more stable than the corresponding DNA-DNA and DNA-RNA duplexes. However, the recent structural studies on PNA-DNA and PNA-RNA duplexes by NMR indicated that the conformation of PNA in such complexes was not optimal RNA because the helical pitch of PNA is much larger than that of DNA and RNA. In this study, I tried to synthesize a new type of DNA analog derived from L-serine with ester linkages, serine-based nucleobase-linked polyester (SNE). The present DNA analog bearing a polyester backbone is expected to have a shorter helical pitch compared with that of PNA, which is identical for the hybridization with complementary nucleic acids. I developed a new strategy for the synthesis of a polyester-type nucleic acid analog consist of N-(thymin-1-yl)acetyl L-serine. The monomer unit bearing thymine base was synthesized from L-serine ethyl ester by a three-step reaction in good yield without racemization. 3-Nitro-1,2,4-triazol-1-yl-tris(pyrrolidin-1-yl)phosphonium hexafluorophosphate (PyNTP) was found to be highly effective for the rapid ester bond formation without racemization. 2-Phenyl-2-(trimethylsilyl)ethyl group was successfully employed as a carboxyl protecting group in solution-phase synthesis. Solid-phase synthesis of SNE was achieved by using a novel type of linker and amino-protecting groups that can be removed under mild neutral conditions.