Morpholino oligonucleotide manufacturing method

A method of producing an n+p-mer morpholino oligonucleotide, comprising:

• (a) condensing:
• (i) a p-mer morpholino oligonucleotide, wherein p is any integer of one or more,
• wherein:
• a 5′-hydroxy group is activated phosphoramidated, and
• a morpholine ring nitrogen atom is protected by a temporary protecting group removable under acidic conditions, with
• (ii) an n-mer morpholino oligonucleotide, wherein n is any integer of one or more,
• wherein 5′-terminus and/or a nucleic acid base are/is each independently protected by a protecting group having an alkyl group having not less than 10 and not more than 300 carbon atoms and/or an alkenyl group having not less than 10 and not more than 300 carbon atoms or a protecting group removable under conditions different from those for the aforementioned temporary protecting group of the morpholine ring nitrogen atom, and the morpholine ring nitrogen atom is not protected,
• by a phosphoramidate bond or phosphorodiamidate bond via the morpholine ring nitrogen atom,
• to obtain a reaction mixture comprising said n+p-mer morpholino oligonucleotide;
• and
• (b) subjecting said reaction mixture to an extraction operation to separate said n+p-mer morpholino oligonucleotide as a resultant product into an organic phase,
• wherein at least one of said 5′-terminus and said nucleic acid base of said n-mer morpholino oligonucleotide, and said nucleic acid base of said p-mer morpholino oligonucleotide is protected by a protecting group having a branched chain alkyl group having not less than 10 and not more than 300 carbon atoms and/or a branched chain alkenyl group having not less than 10 and not more than 300 carbon atoms.