5′-Thymidylic acid, 3′-O-[[(2,6-dichloro-3-hydroxy-4-methoxyphenyl)methylene]amino]-α-[[(3,8-dihydroxy-2-naphthalenyl)carbonyl]amino]-, mono[[(3R)-tetrahydro-2,5-dihydroxy-3-furanyl]methyl] ester