General Synthetic Approach for the Laurencia Family of Natural Products Empowered by a Potentially Biomimetic Ring Expansion.

The Laurencia family of C15-acetogenins is Nature's largest collection of halogenated natural products, with many of its members possessing a brominated 8-membered cyclic ether among other distinct structural elements. Herein, we demonstrate that a bromonium-induced ring expansion, starting from a common tetrahydrofuran-containing bicyclic intermediate and using the highly reactive bromenium source BDSB (Et2SBr·SbCl5Br), can lead to concise asymmetric total syntheses of microcladallenes A and B, desepilaurallene, laurallene, and prelaureatin. Key advances in this work include (1) the first demonstration that the core bromonium-induced cyclization/ring-expansion can be initiated using an enyne with an internal ether oxygen nucleophile, (2) that reasonable levels of stereocontrol in such processes can be achieved both with and without appended ring systems and stereogenic centers, (3) that several other unique chemoselective transformations essential to building their polyfunctional cores can be achieved, and (4) that a single, common intermediate can lead to five different members of the class encompassing two distinct 8-membered cyclic ether ring collections. Considering this work along with past efforts leading to two other natural products in the collection, we believe the breadth of structures prepared to date affords strong evidence for Nature's potential use of similar processes in fashioning these unique molecules.

Uranyl uptake into metal-organic frameworks: a detailed X-ray structural analysis.

Metal-organic frameworks (MOF) are a subclass of porous framework materials that have been used for a wide variety of applications in sensing, catalysis, and remediation. Among these myriad applications is their remarkable ability to capture substances in a variety of environments ranging from benign to extreme. Among the most common and problematic substances found throughout the world's oceans and water supplies is [UO2]2+, a common mobile ion of uranium, which is found both naturally and as a result of anthropogenic activities, leading to problematic environmental contamination. While some MOFs possess high capability for the uptake of [UO2]2+, many more of the thousands of MOFs and their modifications that have been produced over the years have yet to be studied for their ability to uptake [UO2]2+. However, studying the thousands of MOFs and their modifications presents an incredibly difficult task. As such, a way to narrow down the numbers seems imperative. Herein, we evaluate the binding behaviors as well as identify the specific binding sites of [UO2]2+ incorporated into six different Zr MOFs to elucidate specific features that improve [UO2]2+ uptake. In doing so, we also present a method for the determination and verification of these binding sites by Anomalous wide-angle X-ray scattering, X-ray fluorescence, and X-ray absorption spectroscopy. This research not only presents a way for future research into the uptake of [UO2]2+ into MOFs to be conducted but also a means to evaluate MOFs more generally for the uptake of other compounds to be applied for environmental remediation and improvement of ecosystems globally.