A nucleoside derivative represented by any of the following formulae (I-1) to (I-6) or a salt thereof:
in the formulae (I-1) to (I-6), R
1
to R
5
, A
1
to A
3
, B, X, Y, and k represent the meanings as described in claim
1.
由以下任一式(I-1)至(I-6)或其盐所表示的核苷衍
生物:在式(I-1)至(I-6)中,R1至R5、A1至A3、B、X、Y和k代表如权利要求书中所述的含义。