Sulfonium salts as prenyl, geranyl, and isolavandulyl transfer agents towards benzoylphloroglucinol derivatives

Origin of product selectivity in a prenyl transfer reaction from the same intermediate: exploration of multiple FtmPT1-catalyzed prenyl transfer pathways

FtmPT1 is a fungal indole prenyltransferase that catalyzes the reaction of tryptophan derivatives with dimethylallyl pyrophosphate to form various biologically active compounds. Herein, we describe detailed studies of FtmPT1 catalysis involving dimethylallyl pyrophosphate and Brevianamide F following the native pathway (yielding Tryprostatin B) and an alternate pathway observed in the Gly115Thr mutant of FtmPT1 yielding a novel cyclized product. Importantly, these two products arise from the same intermediate state, meaning that a step other than the cleavage of the dimethylallyl pyrophosphate (DMAPP; C–O) bond is differentiating between the two product reaction channels. From detailed potential of mean force (PMF) and two-dimensional PMF analyses, we conclude that the rate-limiting step is the cleavage of the C–O bond in DMAPP, while the deprotonation/cyclization step determines the final product distribution. Hence, in the case of FtmPT1, the optimization of the necessary catalytic machinery guides the generation of the final product after formation of the intermediate carbocation.

The chemistry of the polycyclic polyprenylated acylphloroglucinols

With their fascinating biological profiles and stunningly complex molecular architectures, the polycyclic polyprenylated acylphloroglucinols (PPAPs) have long provided a fertile playing field for synthetic organic chemists. In particular, the recent advent of innovative synthetic methods and strategies together with C-C bond-forming reactions and asymmetric catalysis have revitalized this field tremendously. Consequently, PPAP targets which once seemed beyond reach have now been synthesized. This Review aims to highlight the recent achievements in the total synthesis of PPAPs, as well as notable methods developed for the construction of the bicyclo[3.3.1] core of these chemically and biologically intriguing molecules.

Antarafacial mediation of oxygen delivery by a phenylsulfinyl group in the epoxidation of proximal double bonds: intramolecular trapping of an early Pummerer intermediate with stereoelectronic control

Stereospecific intramolecular antarafacial epoxidation of a double bond via an early Pummerer reaction intermediate has been demonstrated. The intermediate is presumably generated via trifluoroacetylation of a sulfoxide precursor. Ionization of trifluoroacetate would formally generate a dipositive "sulfenium" equivalent. This species attacks an otherwise unactivated, proximal olefinic linkage in an antiperiplanar fashion, with trifluoroacetate serving as the nucleophile. Proposed mechanistic intermediates were characterized structurally (in several cases by crystallographic means) and shown to serve as precursors en route to the final antarafacial epoxides. The sense of the cyclization seems to be driven by principles inherent in Markovnikov's rule.