Compounds of formula (II):
 wherein n is 0, 1 or 2, R₁, R₂, R₃ and R₄ are each separately selected from hydrogen, unsubstituted acyclic aliphatic hydrocarbon groups having a maximum of six carbon atoms and C₁₋₆ alkyl groups substituted by a hydroxy group or by a C₁₋₆ alkoxy group, or one of R₁ and R₂ and one of R₃ and R₄ is hydrogen and the others together are a trimethylene, tetramethylene or pentamethylene bridging group, and R₅ is a group such that under physiological conditions R₅OH undergoes elimination with the formation of a 3,5-dioxopiperazinyl ring, but with the provisos that (a) when n = 0 the combinations R₁ = R₂ = R₃ = R₄ = H and R₁ = R₂ = R₃ = H, R₄ = methyl are excluded and (b) when n is 0, R₁ and R₃ are each hydrogen, and each of R₂ and R₄ is other than hydrogen the compound is in other than the meso or erythro configuration, and salts thereof formed with a physiologically acceptable inorganic or organic acid, are of use in therapy, particularly as cardioprotective agents.  
                            式 (II) 的化合物:
 其中 n 为 0、1 或 2,R₁、R₂、R₃ 和 R₄ 分别选自氢、最多具有六个碳原子的未取代无环脂肪族烃基和被羟基或 C₁₋₆ 烷氧基取代的 C₁₋₆ 烷基、或 R₁、R₂和 R₃、R₄中的一个是氢,而其他两个一起是三亚甲基、四亚甲基或五亚甲基桥基,且 R₅ 是这样一个基团:在生理条件下,R₅OH 发生消去反应,形成 3、5-二氧代
哌嗪基环,但有以下限制条件:(a) 当 n = 0 时,排除 R₁ = R₂ = R₃ = R₄ = H 和 R₁ = R₂ = R₃ = H、R₄ = 甲基的组合;(b) 当 n 为 0 时,R₁ 和 R₃ 均为氢、且 R₂ 和 R₄ 中的每一个都不是氢时,该化合物的构型不是中位构型或赤位构型,其与生理上可接受的
无机酸或有机酸形成的盐可用于治疗,特别是作为心脏保护剂。