PROBLEM TO BE SOLVED: To provide a pharmaceutical composition having an amyloid β production inhibitory action, particularly a BACE1 inhibitory action, which is useful as a therapeutic or prophylactic agent, for diseases caused by the production, secretion, and/or deposition of amyloid β-protein.SOLUTION: The present invention provides a pharmaceutical composition comprising a compound of formula (I) or a pharmaceutically acceptable salt thereof. (X is -S- or -O- R3a is an allyl, haloalkyl, and the like R2a is H, halogen, alkyloxy, haloalkyloxy, etc . R2b is H R3b is H or alkyl ring A and ring B each independently represent a substituted/unsubstituted aromatic carbocyclic ring, substituted/unsubstituted aromatic heterocyclic ring, etc. and R1 is a substituted or unsubstituted alkyl)SELECTED DRAWING: NoneCOPYRIGHT: (C)2017,JPO&INPIT【課題】アミロイドβ産生抑制作用、特にBACE1阻害作用を有し、アミロイドβタンパク質の産生、分泌および/または沈着により誘発される疾患の治療または予防剤として有用な医薬組成物の提供。【解決手段】式(I)で示される化合物またはその製薬上許容される塩を含有する医薬組成物。(Xは-S-又は-O-;R3aはアルキル、ハロアルキル等;R2aはH、ハロゲン、アルキルオキシ、ハロアルキルオキシ等;R2bはH;R3bはH又はアルキル;環A及び環Bは各々独立して置換/非置換の芳香族炭素環、置換/非置換の芳香族複素環等;R1は置換/非置換のアルキル等)【選択図】なし
