Patent ID: 8653254

Claim:
A method of producing a purine nucleoside represented by the formula (I′) or a salt thereof, comprising reacting a pyrimidine nucleoside represented by the formula (I) or a salt thereof with a purine nucleobase represented by the formula B′H in a solvent, in the presence of a Lewis acid: wherein R 1 and R 1 ′ are each independently a hydrogen atom, a hydroxy-protecting group, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group optionally having substituent(s), an aralkyl group optionally having substituent(s), an acyl group, an aliphatic or aromatic sulfonyl group, or a silyl group, R 2 and R 2 ′ are each independently a hydrogen atom, a hydroxy-protecting group, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group optionally having substituent(s), an aralkyl group optionally having substituent(s), an acyl group, an aliphatic or aromatic sulfonyl group, or a silyl group, or R 1 and R 2 in combination or R 1 ′ and R 2 ′ in combination optionally form a group represented by the formula wherein R 4 in the number of p, R 5 in the number of p, R 6 , and R 7 are each independently an alkyl group or an aryl group, and p is an integer of 1 to 3, R 3 is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group optionally having substituent(s), an aralkyl group optionally having substituent(s), an acyl group, or an aliphatic or aromatic sulfonyl group, B is a residue derived from a pyrimidine nucleobase optionally having substituent(s), B′ is a residue derived from a purine nucleobase optionally having substituent(s), m is an integer of 0 to 2, and n is an integer of 1 to 3.