5'-phosphate modified nucleoside, and preparation method and use thereof

A modified nucleoside compound, wherein the modified nucleoside compound is a compound represented by formula (I), a pharmaceutically acceptable salt thereof, or a stereoisomer thereof:

• wherein
• R1 is H, and R2 is —OCH3;
• R3 is a protecting group or a phosphorus-containing active reactive group, wherein the phosphorus-containing active reactive group is any one of a phosphoramidite, an H-phosphonate, a phosphotriester, or a phosphorus-containing chiral auxiliary, and the phosphorus-containing chiral auxiliary is selected from
• R4 and R5 are each independently selected from H, C1-6 alkyl, —CH2CH2CN, and —CH2O(CO)C(CH3)3;
• X is O or S;
• L is —CH2— or —CH2CH2—;
• A is O;
• B is a modified or unmodified base or a salt thereof;
• D is O.