B- and C-Rings components of phycobilin derivatives were efficiently prepared starting from the corresponding lactones. This synthetic method made it possible to prepare not only phycocyanobilin (PCB), but also PCB derivatives having butanoic acid side chain(s) instead of propanoic one(s), regioselectively monoesterified PCB derivatives at C8 or C12. and regioisomers of PCB with respect to methyl and propanoic acid substituents of B- and C-rings for the first time toward the structure/function analysis of phytochrome.