Investigation of Chemical Stability of Dihalogenated Organotelluranes in Organic–Aqueous Media: The Protagonism of Water

The biological activity of tellurium compounds is closely related to the tellurium oxidation state or some of their structural features. Hypervalent dihalogenated organotelluranes 1-[butyl­(dichloro)-λ⁴-tellanyl]-2-(methoxymethyl)­benzene (<b>1a</b>) and 1-[butyl­(dibromide)-λ⁴-tellanyl]-2-(methoxymethyl)­benzene (<b>1b</b>) have been described as inhibitors of proteases (cysteine and threonine) and tyrosine phosphatases. However, poor attention has been given to their physicochemical properties. Here, a detailed investigation of the stability in water of these organotelluranes is reported using ¹²⁵Te NMR analysis. Dihalogenated organotelluranes <b>1a</b> and <b>1b</b> were both stable in DMSO-<i>d</i>₆ (from 25 to 75 °C), demonstrating their thermal stability. However, the addition of a phosphate buffer solution (pH 2–8) to <b>1a</b> or <b>1b</b> resulted in an immediate conversion to a new Te species, assumed to be the corresponding telluroxide. Similar behavior was observed in pure water, demonstrating the low chemical stability of these dihalogenated species in the presence of water. These results allow concluding that previous biological activity reported for dihalogenated organotelluranes <b>1a</b> and <b>1b</b> could be attributed to the corresponding derivatives from the reaction with water. In the same way as for AS-101, we demonstrated that organotelluranes <b>1a</b> and <b>1b</b> are not stable in aqueous solution. It suggests a proactive role of these organotelluranes in previously reported biological activity

Chemical composition and antiparasitic activity of essential oils from leaves of <i>Guatteria friesiana</i> and <i>Guatteria pogonopus</i> (Annonaceae)

<p>Natural products represent a valuable source for discovery of antiparasitic agents. Here, we describe the antiparasitic activity from essential oils extracted from leaves of <i>Guatteria friesiana</i> (EOGF) and <i>Guatteria pogonopus</i> (EOGP) (Annonaceae). The essential oils were obtained by hydrodistillation and analyzed by GC/MS and GC-FID. The sesquiterpenes are more abundant in both essential oils. <i>G. friesiana</i> are dominated by β-eudesmol (51.9%), γ-eudesmol (18.9%) andα-eudesmol (12.6%). The major compounds identified for EOGP were spathulenol (24.8%), γ-amorphene (14.7%) and germacrene D (11.8%). The essential oils demonstrated potent trypanocidal and antimalarial activities with values of IC₅₀ lower than 41.3 μg/mL<i>.</i> EOGF also inhibits the proliferation of amastigotes. In addition, we identified significant ultrastructural alterations induced by the essential oils, especially in the cell membrane, Golgi complex, endoplasmatic reticulum and mitochondria. The results presented herein reinforce the potential of other members of this family for search of antiparasitic compounds.</p