Incorporation of Intracellular NanoSIMS Tracers to Oligonucleotide Conjugates via Strain Promoted Sydnone-Alkyne Cycloaddition.

Extensive efforts have been dedicated to developing cell-specific targeting ligands that can be conjugated to therapeutic cargo, offering a promising yet still challenging strategy to deliver oligonucleotide therapeutics beyond the liver. Indeed, while the cargo and the ligand are crucial, the third component, the linker, is integral but is often overlooked. Here, we present strain-promoted sydnone-alkyne cycloaddition as a versatile linker chemistry for oligonucleotide synthesis, expanding the choices for bioconjugation of therapeutics while enabling subcellular detection of the linker and payload using nanoscale secondary ion mass spectrometry (NanoSIMS) imaging. This strategy was successfully applied to peptide and lipid ligands and profiled using the well characterized N-acetylgalactosamine (GalNAc) targeting ligand. The linker did not affect the expected activity of the conjugate and was detectable and distinguishable from the labeled cargo. Finally, this work not only offers a practical bioconjugation method but also enables the assessment of the linker's subcellular behavior, facilitating NanoSIMS imaging to monitor the three key components of therapeutic conjugates.

Total Synthesis of the Diterpene Waihoensene.

A racemic and scalable enantioselective total synthesis of (+)-waihoensene was accomplished. (+)-Waihoensene belongs to the diterpene natural product family, and it features an angular triquinane substructure motif. Its tetracyclic [6.5.5.5]backbone is all-cis-fused, containing six contiguous stereocenters, four of which are quaternary. These structural features were efficiently installed by means of a diastereoselective radical cyclization, followed by an intramolecular Pauson-Khand reaction, a diastereoselective α-alkylation, and a diastereoselective 1,4-addition reaction. Enantioselectivity was introduced at an early stage, by an asymmetric palladium catalyzed decarboxylative allylation reaction on gram scale.

Synthesis of Highly Selective Submicromolar Microcystin-Based Inhibitors of Protein Phosphatase (PP)2A over PP1.

Research and therapeutic targeting of the phosphoserine/threonine phosphatases PP1 and PP2A is hindered by the lack of selective inhibitors. The microcystin (MC) natural toxins target both phosphatases with equal potency, and their complex synthesis has complicated structure-activity relationship studies in the past. We report herein the synthesis and biochemical evaluation of 11 MC analogues, which was accomplished through an efficient strategy combining solid- and solution-phase approaches. Our approach led to the first MC analogue with submicromolar inhibitory potency that is strongly selective for PP2A over PP1 and does not require the complex lipophilic Adda group. Through mutational and structural analyses, we identified a new key element for binding, as well as reasons for the selectivity. This work gives unprecedented insight into how selectivity between these phosphatases can be achieved with MC analogues.

Enantioselective Synthesis of Cyclohepta[b]indoles via Pd-Catalyzed Cyclopropane C(sp3)-H Activation as a Key Step.

An enantioselective synthesis of functionalized cyclohepta[b]indoles via Pd-catalyzed cyclopropane C-H activation followed by olefination and indole-vinylcyclopropane rearrangement is reported. The design of the chiral cyclopropane precursor was such that both enantiomeric cyclohepta[b]indoles were accessed from a single compound exhibiting a "hidden" symmetry plane. The scope of the method was demonstrated by varying the substituents on the cyclopropane as well as on the heterocycle itself.