Copolymer including uncharged hydrophilic block and cationic polyamino acid block having hydrophobic group in part of side chains, and use thereof

1. A block copolymer comprising:

an uncharged hydrophilic polymer chain block selected from a polyethylene glycol block and a polyoxyethylene block; and

a cationic polyamino acid chain block which is a polylysine block, wherein the hydrophilic polymer chain block is covalently bound to one end of the main chain if the polyamino acid chain block and

a hydrophobic group selected from a residue of a sterol derivative and a C 12-24 hydrocarbyl group, bound to the side chains of not less than 10% and not greater than 70% of the amino acid units in the polyamino acid side chain block via —NH—, —NHCOO—, OR—NHCO—.

2. The block copolymer according to claim 1 , represented by general formula I:

or II:

wherein,

A represents a hydrogen atom or a group represented by a formula R 1 (R 2 )CH(CH 2 ) q — wherein

R 1 and R 2 independently represent a hydrogen atom, a C 1-6 alkoxy group, an aryloxy group, a cyano group, a carboxyl group, an amino group, a C 1-6 alkoxycarbonyl group, a C 2-7 acylamide group, a tri-C 1-6 alkylsiloxy group, or a silylamino group, or

R 1 and R 2 together form an ethylenedioxy or propylenedioxy group, which is unsubstituted or substituted with a C 1-3 alkyl group, or

R 1 and R 2 , together with the CH group to which they are attached, form a formyl group,

q represents an integer of 0 to 10,

L represents —(CH 2 ) r NH—, —NHCH 2 CH 2 NH—, —NHCH 2 CH 2 CH 2 NH—, or —COCH 2 CH 2 —NH— provided that r represents an integer of 0 to 5,

L′ represents —CO—, —OCO—(CH 2 ) r′ —CO—, or —NHCO—(CH 2 ) r′ —CO— provided that r′ represents an integer of 1 to 5,

B represents a sterol derivative residue or a C 12-24 hydrocarbyl group bound via —NH—, —NHCOO—, or —NHCO—,

Q represents NH 2 , —NHC(═NH)NH 2 or a substituent represented by formula IV:

Z represents a hydrogen atom, a C 2-12 alkylcarbonyl group, a C 3-12 alkenylcarbonyl group, a C 3-12 alkenylcarbonyl group, an arylcarbonyl group, an aryloxycarbonyl group, or the same group as defined in B,

Z′ represents —NH—R 3 , provided that R 3 is an unsubstituted or substituted, linear or branched C 1-12 alkyl group,

m is an integer of 55 to 5,000,

n is an integer of 10 to 100,

p is 4,

x is an integer representing the number of units having a substituent Q contained in the polyamino acid chain block, and

y is an integer representing the number of units having a substituent B contained in the polyamino acid chain block, wherein x+y=n, and y accounts for not less than 10% and not greater than 70% of n.

3. The block copolymer according to claim 2 , wherein the sterol derivative residue is derived from a compound selected from the group consisting of cholesterol, cholestanol, dihydroxycholesterol, and cholic acid.

4. The block copolymer according to claim 2 , wherein the hydrocarbyl group is a C 12-20 alkyl group.

5. The block copolymer according to claim 2 , wherein the hydrocarbyl group is selected from the group consisting of a phenyl, naphthyl and an arylalkyl group comprising phenyl and C 1-5 alkyl.

6. A complex of a nucleic acid and the block copolymer according to claim 1 .

7. The complex according to claim 6 , wherein the nucleic acid is selected from the group consisting of oligo- or poly-double stranded RNA, oligo- or poly-double stranded DNA, oligo- or poly-single stranded DNA, and oligo- or poly-single stranded RNA.

8. The complex according to claim 7 , wherein the nucleic acid is selected from the group consisting of plasmid DNA, siRNA, micro RNA, antisense nucleic acid, decoy nucleic acid, aptamer, and ribozyme.

9. The complex according to claim 6 , which has a core-shell polymeric micelle structure, and encapsulates the nucleic acid in the core part.

10. The complex according to claim 6 , which has an N/P ratio of between 1 and 50, wherein the N/P ratio is defined by [the concentration of cation residues in the block copolymer]/[the concentration of the phosphate group in the nucleic acid].

11. The complex according to claim 6 , which is in the form of particles having an average particle diameter of from 10 to 300 nm.