Branched type hetero monodispersed polyethylene glycol, production method thereof, and conjugate thereof

A method of producing a compound represented by formula (40):

• in formula (40),
• n represents an integer of 6 to 12, and
• Y2 represents —NH2 or —O—(CH2)m4—NH2, and m4 represents an integer of 1 to 5,
• the method comprising:
• step (1′) of performing coupling of a monodispersed polyethylene glycol derivative represented by formula (41) shown below with a compound represented by formula (42) shown below using a base catalyst having a pKa in an aqueous solution of 15 to 20 to obtain a compound represented by formula (43) shown below,
• Z—CH2CH2—(OCH2CH2)n-1—B (41)
• in formula (41),
• Z represents —Z1 or —O—(CH2)m5—Z1, Z1 represents any of a protected form of an amino group, an azide group and a cyano group, and m5 represents an integer of 1 to 5,
• B represents a leaving group, and
• n represents an integer of 6 to 12,
• in formula (42),
• A represents a protective group for a hydroxyl group,
• in formula (43),
• A represents a protective group for a hydroxyl group,
• Z represents —Z1 or —O—(CH2)m5—Z1, Z1 represents any of a protected form of an amino group, an azide group and a cyano group, and m5 represents an integer of 1 to 5, and
• n represents an integer of 6 to 12;
• step (2′) of deprotecting the protective group A of the compound represented by the formula (43) to obtain a compound represented by formula (44) shown below,
• in formula (44),
• Z represents —Z1 or —O—(CH2)m5—Z1, Z1 represents any of a protected form of an amino group, an azide group and a cyano group, and m5 represents an integer of 1 to 5, and
• n represents an integer of 6 to 12;
• step (3′) of subjecting the compound represented by the formula (44) to deprotection treatment or reduction treatment to obtain the compound represented by formula (40);
• and
• step (4′) of subjecting the compound represented by the formula (40) to separatory purification, in an order described above.