PROBLEM TO BE SOLVED: To provide an mRNA maturation inhibitor which is derived from a natural product and is also suitable as an active ingredient of an antitumor agent. An mRNA maturation inhibitor, which comprises a compound represented by any of the following formulas (1) to (6) as an active ingredient. [Chemical 1] [Selection diagram] None【課題】天然物由来であって、抗腫瘍剤の有効成分としても好適なmRNA成熟阻害剤の提供。【解決手段】下記式(1)~(6)のいずれかで表される化合物を有効成分とすることを特徴とする、mRNA成熟阻害剤。[化1]【選択図】なし