Synthesis of a Cyclic Dinucleotide Analogue with Ambiguous Bases, 5-Aminoimidazole-4-carboxamide.

Cyclic dinucleotides (CDNs) are second messengers composed of two purine nucleotides. In recent years, the structural diversity of CDNs and their functionality in biological processes are being intensely studied. Herein we report the chemical synthesis of cyclic di-5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranosyl monophosphate (c-di-ZMP) (1), which consists of two 5-amino-4-imidazolecarboxamide ribonucleotides (Z-ribonucleotides) linked via two phosphodiester linkages. Construction of the CDN skeleton with an N1-dinitrophenylhypoxanthine base (HxaDNP-base) by phosphoramidite chemistry and the subsequent ring-opening reaction of HxaDNP-base successfully yielded the desired 1.

Gene Expression of 4'-Thioguanine DNA via 4'-Thiocytosine RNA.

DNA and RNA nucleotides are ubiquitous molecules that store and transmit genetic information. The emergence of synthetic elements that fulfill the function of DNA and RNA provides an alternative gene expression system. Herein, we demonstrate the gene expression of 4'-thioguanine DNA (dSG DNA) via 4'-thiocytosine RNA (dSC RNA) to give green fluorescent protein (GFPuv) in a single test tube. In replication, transcription, and translation, DNA/RNA polymerases and Escherichia coli (E. coli) ribosome can tolerate the replacement of O4' with S4' in the nucleotide, despite the fact that sulfur has a larger atomic radius than oxygen. Additionally, dSG DNA and dSC RNA acted as alternative genetic polymers to natural DNA and RNA for protein synthesis in artificial cells comprising a reconstituted E. coli gene expression machinery. This work involved simple experiments that are widely used in molecular biology, but which underscore the feasibility of life control by substances other than DNA/RNA nucleotides.