Synthesis and cholinesterase inhibitory activity study of Amaryllidaceae alkaloid analogues with N-methyl substitution.

Polycyclic compounds with N-methyl substitution, structurally related to Amaryllidaceae alkaloids, have been synthesised, together with their analogues bearing a quaternary nitrogen atom. To prevent the lone electron pair of the nitrogen from interfering with the reaction sequence, two approaches to the synthesis were investigated: N-oxidation and Boc protection of the nitrogen. The second method was more successful due to the limited stability of N-oxides in the halocyclisation step. An asymmetric version of the synthesis was also developed for this type of compounds. The prepared products were tested in vitro for their cholinesterase inhibitory activity and the results were rationalised by molecular docking studies with human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBuChE). In general, our products were more active against BuChE than against AChE, and it was noted that larger ligands should be prepared for future studies, since in some cases acetylcholine can still fit into the active site along with the bound ligand.

Synthesis of fused 1,2-naphthoquinones with cytotoxic activity using a one-pot three-step reaction.

A method for the synthesis of fused 1,2-naphthoquinones, as analogues of biologically active natural terpene quinones, is described. The intermediate polycyclic naphthalenes were prepared by a one-pot palladium-catalysed process from simple alkynes, one of which was made from an optically pure biomass-derived levoglucosenone. The prepared methoxy-substituted naphthalenes were subsequently transformed in one step to 1,2-naphthoquinones by a trivalent-iodine-mediated oxidation. The naphthoquinone products were found to have cytotoxic properties.

Enantioselective Synthesis of All-Carbon Quaternary Centers Structurally Related to Amaryllidaceae Alkaloids.

Enantioselective synthesis of all-carbon quaternary centers remains a considerable challenge for synthetic organic chemists. Here, we report a two-step protocol to synthesize such centers including tandem cyclization/Suzuki cross-coupling followed by halocarbocyclization. During this process, two rings, three new C-C bonds and a stereochemically defined all-carbon quaternary center are formed. The absolute configuration of this center is controlled by the stereochemistry of the adjacent stereocenter, which derives from an appropriate enantioenriched starting material. Using this method, we synthesized polycyclic compounds structurally similar to Amaryllidaceae alkaloids in high enantiomeric excesses. Because these products resemble naturally occurring compounds, our protocol can be used to synthesize various potentially bioactive compounds.

The Palladium-Catalyzed Intramolecular Alder-Ene Reactions of O- and N-Linked 1,6-Enynes Incorporating Triethylsilyl Capping Groups.

A series of O- and N-linked 1,6-enynes (e.g., 11) have been prepared with each subjected to a palladium-catalyzed intramolecular Alder-ene (IMAE) reaction, thus producing the isomeric and cyclic 1,4-diene (e.g., 12). These processes proceed most effectively when a triethylsilyl group is attached to the alkyne moiety and so generating alkenylsilanes that can be manipulated in various useful ways, including via iododesilylation (to give, for example, iodoalkene 62).

Synthesis and biological activity of desmethoxy analogues of coruscanone A.

A series of simple desmethoxy analogues of coruscanone A was prepared via a novel version of Ti(iPrO)(4)-mediated Knoevenagel condensation of cyclopentenedione with substituted benzaldehydes and cinnamic aldehydes, and the compounds were evaluated for antifungal activity and cytotoxicity. The most potent 2-benzylidenecyclopent-4-ene-1,3-dione possessed antifungal effect comparable to coruscanone A and a somewhat broader spectrum of activity against Candida species. The compound was also superior to fluconazole against several non-albicans Candida sp. Evaluation of the ability of the compound to influence cell proliferation using two different assays showed that 2-benzylidenecyclopent-4-ene-1,3-dione has lower cytotoxicity compared to the natural product.

Enantioselective Synthesis of the Unsaturated Fragment of Callyspongiolide.

A synthesis of the unsaturated side chain of callyspongiolide has been accomplished from two chiral building blocks prepared by catalytic asymmetric procedures applied on simple starting materials. The synthesis of the chiral benzylic alcohol was based on an enantioselective aldol reaction of a substituted benzaldehyde catalyzed by a chiral amine, whereas the chiral homoallyl alcohol was prepared by the enantioselective crotylboration of iodomethacryl aldehyde catalyzed by a chiral phosphoric acid. Both fragments were joined together by using standard Sonogashira coupling conditions.

A chemoenzymatic total synthesis of the protoilludane aryl ester (+)-armillarivin.

The title natural product, 1, has been synthesized in 20 steps from the enantiomerically pure cis-1,2-dihydrocatechol 2, itself obtained through the whole-cell biotransformation of toluene. The pivotal steps in the reaction sequence involve a Diels-Alder cycloaddition reaction between diene 2 and cyclopentenone (3) and the photochemically promoted 1,3-acyl rearrangement of the bicyclo[2.2.2]oct-4-en-1-one 20 derived from the cycloadduct 4.

TFP as a ligand in Au(I)-catalyzed dihydropyran synthesis. Unprecedented rearrangement of dihydropyrans into cyclopentenones.

Dihydropyrans have been prepared by the cyclisation of easily accessible propargyl vinyl ethers with (TFP)AuCl/AgBF(4) as a catalyst in high yields. These compounds undergo acid-catalysed rearrangement into cyclopentenone derivatives.