8-O-Debutanoylthapsigargin (II) was obtained by triethylamine-catalyzed methanolysis of thapsigargin (I). Coupling of (II) with N-Boc-4-aminocinnamic acid (III) in the presence of DCC and DMAP provided ester (IV). The Boc protecting group of (IV) was then cleaved by treatment with trifluoroacetic acid.