Enantioselective Total Synthesis of the Morphogen (-)-Thallusin and Mediated Uptake of Fe(III) into the Green Seaweed Ulva.

A fully enantioselective, catalytic synthesis of the algal morphogen (-)-thallusin using polyene cyclization chemistry is reported. The synthesis features dedicated precursor design, introduction of a TMS-substituted arene as a regioselective terminator, very high enantiomer excess (ee) on gram scale, and productive scaffold functionalization. Furthermore, an ee determination methodology of thallusin samples was developed, and the ee of biosynthesized thallusin was determined. Fe(III)-uptake studies demonstrated that the cellular uptake of iron facilitated by thallusin derivatives was independent of their morphogenic activity, suggesting their active import via siderophore transporters as a shuttle system.

Thallusin Quantification in Marine Bacteria and Algae Cultures.

Thallusin, a highly biologically active, phytohormone-like and bacterial compound-inducing morphogenesis of the green tide-forming macroalga Ulva (Chlorophyta), was determined in bacteria and algae cultures. A sensitive and selective method was developed for quantification based on ultra-high-performance liquid chromatography coupled with electrospray ionization and a high-resolution mass spectrometer. Upon C18 solid phase extraction of the water samples, thallusin was derivatized with iodomethane to inhibit the formation of Fe−thallusin complexes interfering with the chromatographic separation. The concentration of thallusin was quantified during the relevant phases of the bacterial growth of Maribacter spp., ranging from 0.16 ± 0.01 amol cell−1 (at the peak of the exponential growth phase) to 0.86 ± 0.13 amol cell−1 (late stationary phase), indicating its accumulation in the growth medium. Finally, we directly determined the concentration of thallusin in algal culture to validate our approach for monitoring applications. Detection and quantification limits of 2.5 and 7.4 pmol L−1, respectively, were reached, which allow for quantifying ecologically relevant thallusin concentrations. Our approach will enable the surveying of thallusin in culture and in nature and will thus contribute to the chemical monitoring of aquaculture.

Stereoselective Total Synthesis of (-)-Thallusin for Bioactivity Profiling.

Chemical mediators are key compounds for controlling symbiotic interactions in the environment. Here, we disclose a fully stereoselective total synthesis of the algae differentiation factor (-)-thallusin that utilizes sophisticated 6-endo-cyclization chemistry and effective late-stage sp2 -sp2 -couplings using non-toxic reagents. An EC50 of 4.8 pM was determined by quantitative phenotype profiling in the green seaweed Ulva mutabilis (Chlorophyte), underscoring this potent mediator's enormous, pan-species bioactivity produced by symbiotic bacteria. SAR investigations indicate that (-)-thallusin triggers at least two different pathways in Ulva that may be separated by chemical editing of the mediator compound structure.

One-pot relay catalysis: divergent synthesis of furo[3,4-b]indoles and cyclopenta[b]indoles from 3-(2-aminophenyl)-1,4-enynols.

Described herein is an efficient divergent strategy for the synthesis of furo[3,4-b]indoles via a sequential Ag(i)/Bi(iii)/Pd(ii) catalysis and cyclopenta[b]indoles via a one-pot Ag(i)/Brønsted acid relay catalysis from 3-(2-aminophenyl)-4-pentenyn-3-ols, accessible in three simple steps from 2-aminobenzaldehydes.

One-Pot Trimetallic Relay Catalysis: A Unified Approach for the Synthesis of ß-Carbolines and Other [c]-Fused Pyridines.

A divergent strategy is presented for the synthesis of 1,3-di- and 1,3,4-trisubstituted ß-carbolines through an unprecedented one-pot triple-orthogonal-metal relay catalysis, and 1,3-disubstituted 4-hydroxy-ß-carbolines through a one-pot bimetallic relay catalysis from readily accessible 3-(2-aminophenyl)-5-hexenyn-3-ols. These strategies were elaborated to enable the synthesis of benzofuro[2,3-c]pyridines, benzothieno[2,3-c]pyridines, and isoquinolines, which otherwise require multistep synthesis.

Acid catalyzed ring transformation of benzofurans to tri- and tetrasubstituted furans.

An unusual Brønsted acid catalyzed benzofuran ring opening and furan ring closure sequence for the formation of tri- and tetrasubstituted furans is presented. Benzofuranyl carbinols and 1,3-dicarbonyls in the presence of a catalytic amount of an acid generated functionalized, polysubstituted furans in good to excellent yields via an unusual benzofuran ring opening and furan recyclization process. This reaction is found to be general even on furyl carbinols; however, it generates the rearranged polysubstituted furans in moderate yields.

Taming furfuryl cations for the synthesis of privileged structures and novel scaffolds.

Furfuryl cations are generated via a highly efficient bismuth-catalyzed reaction of furfuryl alcohols. This systematic study provides insight on the reactivity profile of furfuryl cations towards nucleophilic substitution reactions. Novel C-C, C-N, C-O and C-S bond forming reactions of furfuryl cations have been developed, thus providing access to a diverse array of building blocks for further manipulations.

Di- and triheteroarylalkanes via self-condensation and intramolecular Friedel-Crafts type reaction of heteroaryl alcohols.

An efficient synthetic approach to diheteroarylmethanes and 1,3-diheteroarylpropenes has been developed via Yb(III)-catalyzed sequential self-condensation of 2-furfuryl (or 2-thienyl or 3-indolyl) alcohols followed by intramolecular Friedel-Crafts type reaction and elimination of an aldehyde. This method offers a powerful entry and a potential alternative to the traditional synthesis of diheteroarylalkanes, which are precursors to the synthesis of several intriguing heteroaryls and more significantly, to the synthesis of biofuels.

Isolation, (bio)synthetic studies and evaluation of antimicrobial properties of drimenol-type sesquiterpenes of Termitomyces fungi.

Macrotermitinae termites have farmed fungi in the genus Termitomyces as a food source for millions of years. However, the biochemical mechanisms orchestrating this mutualistic relationship are largely unknown. To deduce fungal signals and ecological patterns that relate to the stability of this symbiosis, we explored the volatile organic compound (VOC) repertoire of Termitomyces from Macrotermes natalensis colonies. Results show that mushrooms emit a VOC pattern that differs from mycelium grown in fungal gardens and laboratory cultures. The abundance of sesquiterpenoids from mushrooms allowed targeted isolation of five drimane sesquiterpenes from plate cultivations. The total synthesis of one of these, drimenol, and related drimanes assisted in structural and comparative analysis of volatile organic compounds (VOCs) and antimicrobial activity testing. Enzyme candidates putatively involved in terpene biosynthesis were heterologously expressed and while these were not involved in the biosynthesis of the complete drimane skeleton, they catalyzed the formation of two structurally related monocyclic sesquiterpenes named nectrianolins.

One-Pot Relay Gold(I) and Brønsted Acid Catalysis: Cyclopenta[b]annulation of Indoles via Hydroamination/Nazarov-Type Cyclization Cascade of Enynols.

An expedient relay gold(I) and Brønsted acid catalyzed hydroamination/Nazarov cyclization of 1-(2-aminophenyl)pent-4-en-2-ynols for the synthesis of various polyfunctionalized cyclopenta[b]indoles is described. The synthetic utility of this method has been demonstrated by the synthesis of a few unprecedented pentacyclic indoles and indole-steroidal hybrids. Further, the new methodology has been successfully applied to the enantioselective synthesis of core carbon structure of the polyveoline family of natural products.

Synthesis of polysubstituted cyclopenta[b]indoles via relay gold(I)/Brønsted acid catalysis.

An efficient relay catalytic process involving Au(i)/Brønsted acid to access various polysubstituted cyclopentannulated indoles from easily accessible 1-(2-aminophenyl)prop-2-ynols and readily available 1,3-dicarbonyls has been developed. In an unprecedented event, the intermediate 2-indolylmethyl cations undergo the cation-Ene reaction with various 1,3-dicarbonyls followed by an intramolecular Friedel-Crafts-type reaction generating functionalized cyclopenta[b]indoles.