Synthesis of thioketal connecting unit and application thereof in DNA sequencing

The invention discloses synthesis of a thioketal connecting unit and application thereof in DNA sequencing. The connecting unit has a structural formula shown as the specification, wherein R=OH or COOH; R1=R2=methyl, or R1=phenyl, p-methoxyphenyl, 2, 4, 6-trimethoxyphenyl, naphthyl or p-methoxynaphthyl, R2=H, or R1 and R2 compose cyclohexyl and cyclopentyl together. A fluorescein labeled nucleotide obtained by connection of the connecting unit and fluorescein can be used for DNA sequencing. Compared with the prior art, when a reversible terminator based on the thioketal structure connecting unit synthesized by the invention is used for DNA sequencing, the extension efficiency is close to 100%, and when the template is multiple continuous identical bases, only one reversible terminator is extended at a time. At the same time, the synthesis required raw materials are simple and easily available, the synthesis processes are conventional chemical reactions, therefore the thioketal connecting unit can be used for large-scale promotion and use.