Nitro-fatty acids as activators of hSIRT6 deacetylase activity

Sirtuin 6, SIRT6, is critical for both glucose and lipid homeostasis and is involved in maintaining genomic stability under conditions of oxidative DNA damage such as those observed in age-related diseases. There is an intense search for modulators of SIRT6 activity, however, not many specific activators have been reported. Long acyl-chain fatty acids have been shown to increase the weak in vitro deacetylase activity of SIRT6 but this effect is modest at best. Herein we report that electrophilic nitro-fatty acids (nitro-oleic acid and nitro-conjugated linoleic acid) potently activate SIRT6. Binding of the nitro-fatty acid to the hydrophobic crevice of the SIRT6 active site exerted a moderate activation (2-fold at 20 μm), similar to that previously reported for non-nitrated fatty acids. However, covalent Michael adduct formation with Cys-18, a residue present at the N terminus of SIRT6 but absent from other isoforms, induced a conformational change that resulted in a much stronger activation (40-fold at 20 μm). Molecular modeling of the resulting Michael adduct suggested stabilization of the co-substrate and acyl-binding loops as a possible additional mechanism of SIRT6 activation by the nitro-fatty acid. Importantly, treatment of cells with nitro-oleic acid promoted H3K9 deacetylation, whereas oleic acid had no effect. Altogether, our results show that nitrated fatty acids can be considered a valuable tool for specific SIRT6 activation, and that SIRT6 should be considered as a molecular target for in vivo actions of these anti-inflammatory nitro-lipids.     

Influence of bulky substituents on the regioselective group-transfer reactions of diorganozinc compounds with N, N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene

Diorganozinc compounds R₂Zn (R=alkyl or aryl) react with N,N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene, (i-Pr₂Ph)N=CHCHp=N(i-Pr₂Ph) (i-Pr₂Ph-DAB) to give thermally unstable 1:1 coordination complexes R₂Zn(i-Pr2Ph-DAB), which subsequently undergo a slow regioselective alkyl or aryl group-transfer reaction from the zinc atom to an imine-nitrogen or a carbon atom of the NCCN system of the i-Pr₂Ph-DAB ligand. In the case of R=methyl, n-propyl, n-butyl, s-butyl, neopentyl and benzyl, C-alkylation occurs with a subsequent 1,2- hydrogen shift in the amino-imino skeleton affording RZn[(i-Pr₂Ph)N-CH₂-CR=N(i-Pr₂Ph)], whereas for R=t- butyl the C-alkylated product t-BuZn[(i-Pr₂Ph)N---CH(t-Bu)---CH=N(i-Pr₂Ph)] is stable. Surprisingly, diphenylzinc reacts with i-Pr₂Ph-DAB exclusively to give the N-arylated product PhZn[(i-Pr₂Ph)N=CHCH=N(Ph)(i-Pr₂Ph)].     

Novel selective biocatalytic deacetylation studies on dihydropyrimidinones

Five racemic ethyl 4-(3/4-acetoxyphenyl)-6-methyl-3,4-dihydropyrimidin-2-one-5-carboxylates have been synthesized by acetylation of corresponding hydroxy analogues, which in turn have been synthesized under microwave condition by multi-component Biginelli cyclocondensation of ethyl acetoacetate, urea and the corresponding hydroxybenzaldehydes in the presence of ferric chloride. These dihydropyrimidinones have been subjected to biocatalytic resolution using acetoxyl group on the phenyl ring as remote handle; Novozyme^®-435, an immobilized lipase from Candida antarctica in THF:DIPE has been found to catalyze the deacetylation reactions in an enantioselective fashion.     

Cytoplasmic SIRT6-mediated ACSL5 deacetylation impedes nonalcoholic fatty liver disease by facilitating hepatic fatty acid oxidation

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