PROBLEM TO BE SOLVED: To provide neprilysin inhibitors.SOLUTION: The present invention provides a compound of the formula or a pharmacologically acceptable salt thereof (where Ris -ORor -NRR; Ris H or the like; X is (substituted) C1-9 heteroaryl for both Rand R; and R-Rare H, C1-8 alkyl or the like).SELECTED DRAWING: None【課題】ネプリライシン阻害剤の提供。【解決手段】式の化合物または薬学的に許容されるその塩。(式中、R1は、-OR7又は-NR8R9;R2は、H等;Xは、R3及びR4とともに、(置換)C1~9ヘテロアリール;R7~R9は、H、C1~8アルキル等。)【選択図】なし