Synthesis and Inhibition Mechanism of Δlac-Acetogenins, a Novel Type of Inhibitor of Bovine Heart Mitochondrial Complex I

Abstract

We have synthesized ∆lac-acetogenins that are new acetogenin mimics possessing two n-alkyl tails without an R, -unsaturated γ-lactone ring and suggested that their inhibition mechanism may be different from that of common acetogenins [Hamada et al. (2004) Biochemistry 43, 3651-3658]. To elucidate the inhibition mechanism of ∆lac-acetogenins in more detail, we carried out wide structural modifications of original ∆lac-acetogenins and characterized the inhibitory action with bovine heart mitochondrial complex I. In contrast to common acetogenins, both the presence of adjacent bis-THF rings and the stereochemistry around the hydroxylated bis-THF rings are important structural factors required for potent inhibition. The inhibitory potency of a derivative possessing an n-butylphenyl ether structure (compound 7) appeared to be superior to that of the original ∆lac-acetogenins and equivalent to that of bullatacin, one of the most potent natural acetogenins. Double-inhibitor titration of steady-state complex I activity showed that the extent of inhibition of compound 7 and bullatacin is not additive, suggesting that the binding sites of the two inhibitors are not identical. Competition tests using a fluorescent ligand indicated that the binding site of compound 7 does not overlap with that of other complex I inhibitors. The effects of compound 7 on superoxide production from complex I are also different from those of other complex I inhibitors. Our results clearly demonstrate that ∆lac-acetogenins are a novel type of inhibitor acting at the terminal electron-transfer step of bovine complex I.

Synthesis of photolabile .DELTA.lac-acetogenin for photoaffinity labeling of mitochondrial complex I

“…The inhibition of complex I activity was determined by NADH oxidase assay using bovine heart submitochondrial particles. 4) Previous study indicated that the inhibitory potency of compound 1 is comparable to that of bullatacin, 3) one of the most potent natural acetogenins. 14,15) The potency of 1 in terms of the IC 50 , i.e.…”

“…1). 3,4) Some Dlac-acetogenins elicited very potent inhibition with bovine heart mitochondrial complex I at the nanomolar level despite the lack of a g-lactone ring which is a structural feature common to a large number of natural acetogenins. 5,6) Interestingly, several lines of evidence, e.g.…”

Synthesis of Annonaceous Acetogenins from Muricatacin

“…In addition, the structural modification undertaken in order to discover their mechanism has afforded acetogenin analog with potent bioactivity, such as Á-lac acetogenin, reported by Miyoshi and co-workers. 52,53) These achievements not only exhibit the power of advanced organic chemistry, but also provide further opportunities for a variety of biological studies. Our research will continue in its use of organic synthesis as a tool to investigate the biology of annonaceous acetogenins.…”

Function of the alkyl side chains of Δlac-acetogenins in the inhibitory effect on mitochondrial complex I (NADH-ubiquinone oxidoreductase)

“…8 Previous study indicated that the inhibitory effect of 3 (C 11 -C 11 ) is comparable to that of bullatacin, 7 one of the most potent natural acetogenins. 15,16 The IC 50 , that is, the molar concentration needed to halve the control NADH oxidase activity, of 3 was 1.7 (±0.08) nM with the present submitochondrial particles preparation.…”

“…7,8 Some Dlac-acetogenins had strong inhibitory effect on bovine heart mitochondrial complex I at the nanomolar level despite lacking a c-lactone ring which is a structural feature common to a large number of natural acetogenins. [1][2][3] Interestingly, several lines of evidence, for example, competition tests using a fluorescent ligand and the effect on superoxide production from complex I, revealed that the binding site of Dlac-acetogenins is different from that of natural acetogenins as well as ordinary complex I inhibitors such as rotenone and piericidin A.…”