The segment-A moiety of duocarmycin analogue (I) was formylated with dichloromethyl methyl ether in the presence of TiCl4 to produce aldehyde (II). Opening of the cyclopropane ring of (II) by means of HCl in EtOAc gave rise to chloromethyl compound (III), which was subsequently coupled with 4-methoxycinnamic acid (IV) by means of EDC to furnish the title amide.