Aliphatic C-H to C-C conversion: synthesis of (-)-cameroonan-7α-ol

A Modular Approach to Angularly Fused Polyquinanes via Ring-Rearrangement Metathesis: Synthetic Access to Cameroonanol Analogues and the Basic Core of Subergorgic Acid and Crinipellin

We describe a modular approach to angularly fused polyquinanes that are core units of many natural products such as cameroonanol, subergorgic acid, and crinepellin, etc. in excellent yields by employing atom-economic ring-rearrangement metathesis as a key step. Our work highlights, the synthesis of cameroonanol analogues 1-6 and their ester derivatives by using the stereoselective reduction of the carbonyl group by using DIBAL-H- and DCC-mediated coupling as the key reactions. The subergorgic acid core 7 was produced by LDA-mediated kinetically controlled regio- and stereoselective ring-junction allylation as a critical step. Moreover, it is worth mentioning that the present strategy relies on a less explored exo-dicyclopentadiene-1-one (8) and produces highly congested polycyclic frameworks containing up to seven contiguous stereogenic centers including quaternary carbons up to two. All of the new molecules were characterized by NMR data. The structure and relative stereochemistry of some compounds were confirmed by chemical methods and further supported by single-crystal X-ray diffraction studies. The newly reported tri- and tetraquinane skeletons are present in many naturally occurring bioactive polyquinanes. Hence, this strategy is useful for designing various "druglike molecules" and expands the chemical space of cyclopentanoids that are useful in medicinal chemistry.

Allylation of β-amino phosphonic acid precursor via palladium-NHC catalyzed allylic C–H activation

A Pd(ii)/N-heterocyclic carbene (NHC) catalyzed allylic C–H alkylation of allylbenzene with α-cyano-phosphate ester has been achieved under mild reaction conditions with the highest regioselectivity and stereoselectivity.

Synthesis of the Tricyclic Picrotoxane Motif by an Oxidative Cascade Cyclization

An oxidative cascade cyclization of β-keto esters has been developed for the construction of the tricyclic picrotoxane motif in a single step, and DFT calculations suggested a possible cationic cyclization mechanism. This cascade cyclization can be operated on a 20 g scale to obtain a 77% total yield of the tricyclic products, which in turn can be converted to versatile intermediates for further elaboration to picrotoxanes and their structurally related compounds.

Catalytic allylic functionalization via π-allyl palladium chemistry

This review highlights the palladium-catalyzed allylic C–H functionalizations via π-allyl palladium reported from early 2014 to present date.

Trypanosoma brucei Inhibition by Essential Oils from Medicinal and Aromatic Plants Traditionally Used in Cameroon (Azadirachta indica, Aframomum melegueta, Aframomum daniellii, Clausena anisata, Dichrostachys cinerea and Echinops giganteus)

Essential oils are complex mixtures of volatile components produced by the plant secondary metabolism and consist mainly of monoterpenes and sesquiterpenes and, to a minor extent, of aromatic and aliphatic compounds. They are exploited in several fields such as perfumery, food, pharmaceutics, and cosmetics. Essential oils have long-standing uses in the treatment of infectious diseases and parasitosis in humans and animals. In this regard, their therapeutic potential against human African trypanosomiasis (HAT) has not been fully explored. In the present work, we have selected six medicinal and aromatic plants (Azadirachta indica, Aframomum melegueta, Aframomum daniellii, Clausena anisata, Dichrostachys cinerea, and Echinops giganteus) traditionally used in Cameroon to treat several disorders, including infections and parasitic diseases, and evaluated the activity of their essential oils against Trypanosma brucei TC221. Their selectivity was also determined with Balb/3T3 (mouse embryonic fibroblast cell line) cells as a reference. The results showed that the essential oils from A. indica, A. daniellii, and E. giganteus were the most active ones, with half maximal inhibitory concentration (IC₅₀) values of 15.21, 7.65, and 10.50 µg/mL, respectively. These essential oils were characterized by different chemical compounds such as sesquiterpene hydrocarbons, monoterpene hydrocarbons, and oxygenated sesquiterpenes. Some of their main components were assayed as well on T. brucei TC221, and their effects were linked to those of essential oils.

Systemic study on the biogenic pathways of yezo’otogirins: total synthesis and antitumor activities of (±)-yezo’otogirin C and its structural analogues

A systematic study of the biomimetic pathways to yezo’otogirin C under aerobic and anaerobic conditions has been investigated, and both are found to be feasible pathways to the natural product depending on the physiological conditions. Because of the lower activation energy, the aerobic process would be more favorable when the in vivo oxygen level is high. In the course of this study, a highly efficient synthetic route to (±)-yezo’otogirin C has been established in four steps (31% overall yield) from a readily available compound without using any protecting groups. The natural product and its structural analogues exhibited antitumor activities against several human cancer cell lines and appeared to arrest cell cycles in different phases.

Palladium-catalyzed aerobic oxidative double allylic C–H oxygenation of alkenes: a novel and straightforward route to α,β-unsaturated esters

We reported a strategically distinct approach to synthesize α,β-unsaturated esters through palladium-catalyzed aerobic oxidative double allylic C–H oxygenation of alkenes.

Palladium-catalyzed regioselective azidation of allylic C–H bonds under atmospheric pressure of dioxygen

A palladium-catalyzed allylic azidation of alkenes with sodium azide under atmospheric pressure of dioxygen was developed.