drug stability, solubility [challenge] was excellent and benz having a crystalline [d] to provide [1,3] oxazine derivatives. [MEANS FOR SOLVING PROBLEMS] 2- [2 - ((S) -3- dimethylamino-1-yl) pyridine-3-yl]-5-ethyl-7-methoxy--4H- benz [d] [1,3] maleate oxazine-4-one. None [Selection Figure]【課題】優れた原薬安定性、溶解性および結晶性を有するベンズ[d][1,3]オキサジン誘導体を提供する。【解決手段】2-[2-((S)-3-ジメチルアミノピロリジン-1-イル)ピリジン-3-イル]-5-エチル-7-メトキシ-4H-ベンズ[d][1,3]オキサジン-4-オンのマレイン酸塩。【選択図】なし