Late-Stage Formal Double C-H Oxidation of Prenylated Molecules to Alkylidene Oxetanes and Azetidines by Strain-Enabled Cross-Metathesis

Prenylation is a ubiquitous late-stage modification in nature that often confers significantly improved bioactivity for secondary metabolites. While this lipophilic modification renders enhanced potency, the lipophilic tag(s) can diminish bioavailability and adversely alter drug transportation and metabolism. Thus, a functional-group-tolerant, mild, and selective late-stage C-H functionalization of prenyl tags would present a great potential in drug discovery programs but could also impact other fields, such as agrochemistry and chemical biology. Herein we report an exocyclic-strain-driven cross-metathesis reaction of prenyl tags, a formal double C-H oxidation protocol, that can be used for the selective late-stage derivatization of prenylated compounds and natural products. This methodology avoids the need for prefunctionalization of target molecules and affords ready access to an unprecedented library of oxo- and aza-prenylated complex molecules. Thus, in a broader context, this methodology extends late-stage functionalization beyond that available to nature.

New derivatives from dehydrodieugenol B and its methyl ether displayed high anti-Trypanosoma cruzi activity and cause depolarization of the plasma membrane and collapse the mitochondrial membrane potential

In the present work, dehydrodieugenol B (1) and its methyl ether (2), isolated from Nectandra leucantha twigs, were used as starting material for the preparation of two new derivatives (1a and 2a) containing an additional methoxycarbonyl unit on allyl side chains. Compounds 1a and 2a demonstrated activity against trypomastigotes (EC₅₀ values of 13.5 and 23.0 μM, respectively) and against intracellular amastigotes (EC₅₀ values of 10.2 and 6.1 μM, respectively). Additionally, compound 2a demonstrated no mammalian cytotoxicity up to 200 μM whereas compound 1a exhibited a CC₅₀ value of 139.8 μM. The mechanism of action studies of compounds 1a and 2a demonstrated a significant depolarization of the plasma membrane potential in trypomastigotes, followed by a mitochondrial membrane potential collapse. Neither calcium level nor reactive oxygen species alterations were observed after a short-time incubation. Considering the potential of compound 2a against T. cruzi and its simple preparation from the natural product 2, isolated from N. leucantha, this compound could be considered a new hit for future drug design studies in Chagas disease.

Acetalization of Glycerol with Citral over Heteropolyacids Immobilized on KIT-6

Glycerol acetalization with citral was studied using a heteropolyacid (tungstophosphoric acid) supported on KIT-6, as a catalyst, at 100 °C. Different catalysts were synthesized. Catalysts were characterized by scanning electron microscopy (SEM), inductively coupled plasma (ICP), X-ray diffraction (XRD), attenuated total refletion-Fourier transform infrared spectroscopy (ATR-FTIR), and potentiometric titrations. At a fixed time, the glycerol conversion increased with the H3PW12O40 (PW) on KIT-6. PW4-KIT-6 material had a higher conversion than other catalysts. The optimization of glycerol’s acetalization with citral was studied under the PW4-KIT-6 catalyst. After 5 h, it was found that, at T = 100 °C, with m = 0.3 g of solid, molar glycerol:citral = 1:2.25, the conversion of glycerol was 89%. Moreover, the PW4-KTI-6 catalyst showed good catalytic stability.

Relay Cross Metathesis for the Iterative Construction of Terpenoids and Synthesis of a Diterpene-Benzoate Macrolide of Biogenetic Relevance to the Bromophycolides

We report a relay cross metathesis (ReXM) reaction for the construction of terpenoids in an iterative protocol. The protocol features the cross metathesis of a relay-actuated Δ^6,7-functionalized C₁₀-monoterpenoid alcohol with C₁₀-monoterpenoid citral to form a C₁₅-sesquiterpene. Subsequent functional group manipulation allows for the method to be repeated in an iterative fashion. The method is used for the synthesis of a diterpene-benzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.

A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids for Cross-Metathesis with Trisubstituted Alkenes

A retrosynthetic disconnection-reconnection analysis of epoxypolyenes-substrates that can undergo cyclization to podocarpane-type tricycles-reveals relay-actuated Δ^6,7-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross-metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (E/Z, ca. 2-3:1). The method is further generalized for the cross-metathesis of pre-existing trisubstituted olefins in other relay-actuated Δ^6,7-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the E-geometrical isomer).

Vortex Fluidic Ethenolysis, Integrating a Rapid Quench of Ruthenium Olefin Metathesis Catalysts

Ruthenium-catalysed ethenolysis occurs in a vortex fluidic device (VFD) – a scalable, thin-film microfluidic continuous flow process. This process takes advantage of the efficient mass transfer of gaseous reagents into the dynamic thin film of liquid. Also reported is the rapid quenching of the ruthenium-based olefin metathesis catalyst by the addition of a saturated solution of N-acetyl-l-cysteine in MeCN, as a convenient alternative to previously reported quenching methods.

Bimolecular Cross-Metathesis of a Tetrasubstituted Alkene with Allylic Sulfones

Exquisite control of catalytic metathesis reactivity is possible through ligand‐based variation of ruthenium carbene complexes. Sterically hindered alkenes, however, remain a generally recalcitrant class of substrates for intermolecular cross‐metathesis. Allylic chalcogenides (sulfides and selenides) have emerged as “privileged” substrates that exhibit enhanced turnover rates with the commercially available second‐generation ruthenium catalyst. Increased turnover rates are advantageous when competing catalyst degradation is limiting, although specific mechanisms have not been defined. Herein, we describe facile cross‐metathesis of allylic sulfone reagents with sterically hindered isoprenoid alkene substrates. Furthermore, we demonstrate the first example of intermolecular cross‐metathesis of ruthenium carbenes with a tetrasubstituted alkene. Computational analysis by combined coupled cluster/DFT calculations exposes a favorable energetic profile for metallacyclobutane formation from chelating ruthenium β‐chalcogenide carbene intermediates. These results establish allylic sulfones as privileged reagents for a substrate‐based strategy of cross‐metathesis derivatization.

Solvent-Free Method for the Copolymerization of Labile Sugar-Derived Building Blocks into Polyamides

This research focuses on the preparation of biobased copolyamides containing biacetalized galactaric acid (GalX), namely, 2,3:4,5-di-O-isopropylidene-galactaric acid (GalXMe) and 2,3:4,5-di-O-methylene-galactaric acid (GalXH), in bulk by melt polycondensation of salt monomers. In order to allow the incorporation of temperature-sensitive sugar-derived building blocks into copolyamides at temperatures below the degradation temperature of the monomers and below their melting temperatures, a clever selection of salt monomers is required, such that the sugar-derived salt monomer dissolves in the other salt monomers. The polymerization was investigated by temperature dependent FT-IR and optical microscopy. The structure of the obtained copolyamides was elucidated by NMR and matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) techniques. The positive outcome of this modified polycondensation method depends on the solubility of sugar-derived polyamide salts in polyamide salts of comonomers and the difference between their melting temperatures, however does not depend on the melting temperature of the used sugar-derived monomer. A variety of comonomers was screened in order to establish the underlying mechanisms of the process.