Total Synthesis of Euonymine and Euonyminol Octaacetate

Bioinspired Total Synthesis of Cephalotaxus Diterpenoids and Their Structural Analogues

Herein, we present a unified chemical synthesis of three subgroups of cephalotaxus diterpenoids. Key to the success lies in adopting a synthetic strategy that is inspired by biosynthesis but is opposite in nature. By employing selective one-carbon introduction and ring expansion operations, we have successfully converted cephalotane-type C18 dinorditerpenoids (using cephanolide B as a starting material) into troponoid-type C19 norditerpenoids and intact cephalotane-type C20 diterpenoids. This synthetic approach has enabled us to synthesize cephinoid H, 13-oxo-cephinoid H, 7-oxo-cephinoid H, fortalpinoid C, 7-epi-fortalpinoid C, cephanolide E, and 13-epi-cephanolide E. Furthermore, through the development of an intermolecular asymmetric Michael reaction between β-oxo esters and β-substituted enones, we have achieved the enantioselective synthesis of advanced intermediates within our synthetic sequence, thus formally realizing the asymmetric total synthesis of the cephalotaxus diterpenoids family.

Macrolide sesquiterpene pyridine alkaloids from Celastrus monospermus and evaluation of their immunosuppressive and anti-osteoclastogenesis activities

Phytochemical investigation of the stems of Celastrus monospermus Roxb enabled isolation and identification of fifteen new macrolide sesquiterpene pyridine alkaloids (1-15) along with five known analogues. Their structures were elucidated by comprehensive spectroscopic analysis (NMR, HRESIMS, IR, UV), chemical hydrolysis, and single crystal X-ray diffraction analysis. Bioassay of the abundant isolates revealed that seven compounds inhibited the proliferation of B lymphocytes with IC50 values ranging between 1.4 and 19.9 μM. Among them, celasmondine C (3) could significantly promote the apoptosis of activated B lymphocyte, especially late-stage apoptosis. Besides, compounds 3, 16, and 20 exhibited potent suppression of osteoclast formation at a concentration of 1.0 μM. This investigation enriched the chemical diversity of macrolide sesquiterpene pyridine alkaloids, and supported evidence for the development of new immunosuppressive and anti-osteoclastogenesis agents.

Total syntheses of Tetrodotoxin and 9-epiTetrodotoxin

Tetrodotoxin and congeners are specific voltage-gated sodium channel blockers that exhibit remarkable anesthetic and analgesic effects. Here, we present a scalable asymmetric syntheses of Tetrodotoxin and 9-epiTetrodotoxin from the abundant chemical feedstock furfuryl alcohol. The optically pure cyclohexane skeleton is assembled via a stereoselective Diels-Alder reaction. The dense heteroatom substituents are established sequentially by a series of functional group interconversions on highly oxygenated cyclohexane frameworks, including a chemoselective cyclic anhydride opening, and a decarboxylative hydroxylation. An innovative SmI2-mediated concurrent fragmentation, an oxo-bridge ring opening and ester reduction followed by an Upjohn dihydroxylation deliver the highly oxidized skeleton. Ruthenium-catalyzed oxidative alkyne cleavage and formation of the hemiaminal and orthoester under acidic conditions enable the rapid assembly of Tetrodotoxin, anhydro-Tetrodotoxin, 9-epiTetrodotoxin, and 9-epi lactone-Tetrodotoxin.

Convergent Total Synthesis of (-)-Cyclopamine

A concise and enantioselective total synthesis of the Veratrum alkaloid cyclopamine is disclosed. This highly convergent synthesis with a 16-step longest linear sequence (LLS) was enabled by a de novo synthesis of the trans-6,5-heterobicycle via a strain-inducing halocyclization process, a key Tsuji-Trost cyclization to construct the fully substituted, spirocyclic THF motif with exquisite diastereocontrol, and a late-stage ring-closing metathesis (RCM) reaction to forge the central tetrasubstituted olefin.

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N-Heterocyclic Carbene Ligand: Improved Stability and Activity

Formation of sterically hindered C-C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N-heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small-size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C-8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans-Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis-arrangement (cis-Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

Catalytic Enantioselective Construction of Decalin Derivatives by Dynamic Kinetic Desymmetrization of C2-Symmetric Derivatives through Aldol-Aldol Annulation

We have developed and investigated a catalytic desymmetrization reaction strategy that affords functionalized decalin derivatives with high enantioselectivities from C2-symmetric derivatives through aldol-aldol annulation. We identified the structural moieties of the catalyst necessary for the formation of the decalin derivative with high enantioselectivity. We elucidated the mechanisms of the catalyzed reactions: the first aldol reaction step was reversible, and the second aldol step was rate-limiting and stereochemistry-determining and was enantioselective. Using theoretical calculations guided by the experimental results, we identified the interactions between the catalyst and the transition state that led to the major enantiomer. The information obtained in this study will be useful for the development of catalysts and chemical transformations.

Highly (E)-Selective Trisubstituted Alkene Synthesis by Low-Valent Titanium-Mediated Homolytic Cleavage of Alcohol C-O Bond

Ti-mediated homolytic C-O bond cleavage was useful for cascade radical-ionic reactions. Benzyl alcohols treated with TiCl₄(col) (col = 2,4,6-collidine) and Mn powder generated the corresponding benzyl radicals; in addition, their reaction with 2-carboxyallyl acetates and the subsequent elimination of the acetoxy group yielded α,β-unsaturated carbonyl compounds with exclusive (E)-stereoselectivity. The simplicity of the procedure and its wide substrate scope represent a solution to the drawbacks associated with the reactions.

Testing enabling techniques for olefin metathesis reactions of lipophilic substrates in water as a diluent

Olefin metathesis reactions of diverse polyfunctional substrates were conducted in water emulsions using two hydrophobic ruthenium catalysts in the presence of air. Instead of using surfactants to increase the efficiency of the metathesis reaction in water, ultrasound and microwave techniques were tested on a small-scale reaction, whereas conventional heating and mechanical stirring were effective enough to provide high conversion and selectivity on a larger scale. The developed conditions extend known protocols for the aqueous metathesis methodology, utilizing relatively low catalyst loadings and allowing for simple product isolation and purification. The established synthetic protocol was successfully adopted in the large-scale synthesis of a pharmaceutically related product – sildenafil (Viagra) derivative.

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Sustainable approach for metathesis reaction in water emulsion system on air.

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Utilization of enabling techniques for boosting metathesis under aqueous conditions.

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RCM of medically important sildenafil derivative.