Methyl 4-O-[4-O-[4-O-[4-O-[2-O,3-O,4-O-trimethyl-6-O-sodiosulfo-α-D-glucopyranosyl]-β-D-glucopyranuronosyl]-3-O-methyl-2-sodiosulfo-α-D-glucopyranosyl]-2-O,3-O-dimethyl-α-L-idopyranuronosyl]-2-O,3-O,6-O-tris(sodiosulfo)-α-D-glucopyranoside・2sodium salt