Amidite compound and method for producing polynucleotide using said compound

A method for preparing an ether compound represented by formula (7):

• wherein
• Ra and Rb are the same as defined below,
• which comprises the steps of:
• (a):
• reacting a compound represented by formula (5):
• wherein Ra and Rb are identical to or different from each other and each represents a methyl group, an ethyl group, or a hydrogen atom, with the proviso that Ra and Rb do not represent a hydrogen atom at the same time,
• with a cyanide ion, and
• (b):
• reacting 3-hydroxyalkylnitrile represented by formula (6):
• wherein
• Ra and Rb are the same as defined above,
• resulting from step (a), with bis(methylthiomethyl)ether in a solvent in the presence of an oxidizing agent and an acid.

A method for preparing a compound represented by formula (10):

• wherein
• Ba, Ra, Rb, n and G4 are the same as defined below, which comprises reacting a compound represented by formula (9):
• wherein
• Ba represented a compound containing optionally-protected nucleobase structure, and G4 represents a protecting group for a hydroxy group,
• with a compound represented by formula (4):
• wherein
• Ra and Rb are identical to or different from each other and each represents a methyl group, an ethyl group, or a hydrogen atom, with the proviso that Ra and Rb do not represent a hydrogen atom at the same time,
• Rc represents a C1-C6 alkyl group or a phenyl group, and
• n is an integer of 1 to 4,
• in the presence of an oxidizing agent.

A compound represented by formula (10):

• wherein
• Ra and Rb are identical to or different from each other, and each represents a methyl group, an ethyl group, or a hydrogen atom, with the proviso that Ra and Rb do not represent a hydrogen atom at the same time,
• n is an integer of 1 to 5,
• Ba represents a group containing an optionally protected nucleobase structure, and
• G4 represents a protecting group.