| abstract |
Disclosed is a nucleoside derivative of formulae (I-1) or a salt thereof: n nin which R 1 , R 2 , R 3 , R 5 , A 1 to A 3 , B, X, Y, and k are described herein. Also provided are a 5′-phosphate ester and a 3′-phosphoramidite derivative of the nucleoside derivative and substrate solutions thereof. A polynucleotide is produced using the 5′-phosphate ester or 3′-phosphoramidite derivative of the nucleoside derivative. A library of the produced polynucleotide is used in a method of selecting a nucleic acid aptamer. Further provided is a vesicular endothelial growth factor binding agent of formula (i). |