New Palladium(II) Complexes Containing Methyl Gallate and Octyl Gallate: Effect against Mycobacterium tuberculosis and Campylobacter jejuni

This work describes the preparation, characterization and antimicrobial activity of four palladium(II) complexes, namely, [Pd(meg)(1,10-phen)] 1, [Pd(meg)(PPh₃)₂] 2, [Pd(og)(1,10-phen)] 3 and [Pd(og)(PPh₃)₂] 4, where meg = methyl gallate, og = octyl gallate, 1,10-phen = 1,10-phenanthroline and PPh₃ = triphenylphosphine. As to the chemical structures, spectral and physicochemical studies of 1-4 indicated that methyl or octyl gallate coordinates a palladium(II) ion through two oxygen atoms upon deprotonation. A chelating bidentate phenanthroline or two triphenylphosphine molecules complete the coordination sphere of palladium(II) ion, depending on the complex. The metal complexes were tested against the Mycobacterium tuberculosis H37Rv strain and 2 exhibited high activity (MIC = 3.28 μg/mL). As to the tests with Campylobacter jejuni, complex 1 showed a significant effect in reducing bacterial population (greater than 7 log CFU) in planktonic forms, as well as in the biomass intensity (IBF: 0.87) when compared to peracetic acid (IBF: 1.11) at a concentration of 400 μg/mL. The effect provided by these complexes has specificity according to the target microorganism and represent a promising alternative for the control of microorganisms of public health importance.

Asymmetric Total Synthesis of Ventilanones A and B, Two Naturally Occurring Pyranonaphthoquinones from Ventilago harmandiana

The asymmetric synthesis of the novel pyranonaphthoquinones ventilanone A and ventilanone B, isolated from the Thai endemic plant Ventilago harmandiana, is accomplished by employing l-rhamnose and gallic acid as the starting materials. The key reactions are the utilization of a newly introduced reagent, PhSCF2H/SnCl4, for the formyl­ation of sterically hindered aromatics containing an electron-withdrawing methyl ester, and the efficient Hauser annulation of phenyl­thiophthalides with optically active C-1 glycals derived from l-rhamnose. The developed synthetic methodologies solve the long-standing problem of the formylation of sterically hindered aromatics containing electron-withdrawing groups, and are applicable for the synthesis of other analogues with substituents on the aromatic and pyran rings.