Design syntheses and mitochondrial complex I inhibitory activity of novel acetogenin mimics

Some natural acetogenins are the most potent inhibitors of mitochondrial co mplex I. These compounds are characterized by two functional units [i.e. hy droxylated tetrahydrofuran (THF) and alpha,beta-unsaturated gamma-lactone r ing moieties] separated by a long alkyl spacer. To elucidate which structur al factors of acetogenins, including their active conformation, are crucial for the potent inhibitory activity we synthesized a novel bis-acetogenin a nd its analogues possessing two gamma-lactone rings connected to bis-THF ri ngs by flexible alkyl spacers. The inhibitory potency of the bis-acetogenin with bovine heart mitochondrial complex I was identical to that of bullata cin, one of the most potent natural acetogenins. This result indicated that one molecule of the bis-acetogenin does not work as two reactive inhibitor s, suggesting that a gamma-lactone and the THF ring moieties act in a coope rative manner on the enzyme. In support of this, either of the two ring moi eties synthesized individually showed no or very weak inhibitory effects. M oreover, combined use of the two ring moieties at various molar ratios exhi bited no synergistic enhancement of the inhibitory potency. These observati ons indicate that both functional units work efficiently only when they are directly linked by a flexible alkyl spacer. Therefore, some specific confo rmation of the spacer must be important for optimal positioning of the two units in the enzyme. Furthermore, the alpha,beta-unsaturated gamma-lactone, the 4-OH group in the spacer region, the long alkyl tail attached to the T HF unit and the stereochemistry surrounding the hydroxylated bis-THF rings were not crucial for the activity, although these are the most common struc tural features of natural acetogenins. The present study provided useful gu iding principles not only for simplification of complicated acetogenin stru cture, but also for further wide structural modifications of these molecule s.