Phenyl dialkynylcarbinols, a Bioinspired Series of Synthetic Antitumor Acetylenic Lipids.

A series of 25 chiral anti-cancer lipidic alkynylcarbinols (LACs) were devised by introducing an (hetero)aromatic ring between the aliphatic chain and the dialkynylcarbinol warhead. The resulting phenyl-dialkynylcarbinols (PACs) exhibit enhanced stability, while retaining cytotoxicity against HCT116 and U2OS cell lines with IC50 down to 40 nM for resolved eutomers. A clickable probe was used to confirm the PAC prodrug behavior: upon enantiospecific bio-oxidation of the carbinol by the HSD17B11 short-chain dehydrogenase/reductase (SDR), the resulting ynones covalently modify cellular proteins, leading to endoplasmic reticulum stress, ubiquitin-proteasome system inhibition, and apoptosis. Insights into the design of LAC prodrugs specifically bioactivated by HSD17B11 vs its paralogue HSD17B13 were obtained. The HSD17B11/HSD17B13-dependent cytotoxicity of PACs was exploited to develop a cellular assay to identify specific inhibitors of these enzymes. A docking study was performed with the HSD17B11 AlphaFold model, providing a molecular basis of the SDR substrates mimicry by PACs. The safety profile of a representative PAC was established in mice.

SDR enzymes oxidize specific lipidic alkynylcarbinols into cytotoxic protein-reactive species.

Hundreds of cytotoxic natural or synthetic lipidic compounds contain chiral alkynylcarbinol motifs, but the mechanism of action of those potential therapeutic agents remains unknown. Using a genetic screen in haploid human cells, we discovered that the enantiospecific cytotoxicity of numerous terminal alkynylcarbinols, including the highly cytotoxic dialkynylcarbinols, involves a bioactivation by HSD17B11, a short-chain dehydrogenase/reductase (SDR) known to oxidize the C-17 carbinol center of androstan-3-alpha,17-beta-diol to the corresponding ketone. A similar oxidation of dialkynylcarbinols generates dialkynylketones, that we characterize as highly protein-reactive electrophiles. We established that, once bioactivated in cells, the dialkynylcarbinols covalently modify several proteins involved in protein-quality control mechanisms, resulting in their lipoxidation on cysteines and lysines through Michael addition. For some proteins, this triggers their association to cellular membranes and results in endoplasmic reticulum stress, unfolded protein response activation, ubiquitin-proteasome system inhibition and cell death by apoptosis. Finally, as a proof-of-concept, we show that generic lipidic alkynylcarbinols can be devised to be bioactivated by other SDRs, including human RDH11 and HPGD/15-PGDH. Given that the SDR superfamily is one of the largest and most ubiquitous, this unique cytotoxic mechanism-of-action could be widely exploited to treat diseases, in particular cancer, through the design of tailored prodrugs.

Total Synthesis of Proteasome Inhibitor (-)-Omuralide through Asymmetric Ketene [2 + 2]-Cycloaddition.

The total synthesis of (-)-omuralide, a potent specific proteasome inhibitor, has been achieved through an unprecedented route. The C3 and C4 chiral centers of the natural product have been selectively installed by an asymmetric [2 + 2]-cycloaddition between an unusual oxadisilinane ketene and a chiral enol ether, while the γ-lactam core was prepared by a single-pot two-step Beckmann transposition. The C5 quaternary center was eventually defined by an original selective oxidative desymmetrization of a spiro cyclic oxadisilinane thanks to the anchimeric assistance of a proximal hydroxyl group.

Skeletal Optimization of Cytotoxic Lipidic Dialkynylcarbinols.

In line with a recent study of the pharmacological potential of bioinspired synthetic acetylenic lipids, after identification of the terminal dialkynylcarbinol (DAC) and butadiynyl alkynylcarbinol (BAC) moieties as functional antitumor pharmacophoric units, this work specifically addresses the issue of carbon backbone length. A systematic variation of the aliphatic chain length was thus carried out in both the DAC and BAC series. The critical impact of the length of the lipidic skeleton was first confirmed in the racemic series, with the highest cytotoxic activity observed for C17 to C18 backbones. Enantiomerically enriched samples were prepared by asymmetric synthesis of the optimal C18 DAC and C17 BAC derivatives. Samples with upgraded enantiomeric purity were alternatively produced by enzymatic kinetic resolution. Eutomers possessing the S configuration displayed cytotoxicity IC50 values as low as 15 nm against HCT116 cancer cells, the highest level of activity reached to date in this series.

Safe and Facile Access to Nonstabilized Diazoalkanes Using Continuous Flow Technology.

Despite the high synthetic potential of nonstabilized diazo compounds, their utilization has always been hampered by stability, toxicity, and safety issues. The present method opens up access to the most reactive nonstabilized diazoalkanes. Among diazo compounds, nonstabilized alkyl diazo compounds are the least represented because of their propensity to degrade during preparation. The continuous flow oxidation process of hydrazones on a silver oxide column afforded an output stream of base- and metal-free pure diazo solution in dichloromethane. Starting from innocuous ketones and aldehydes, this methodology allows the production of a broad range of unprecedented diazoalkanes compounds in excellent yields, while highlighting their synthetic potential and the possibility of safe large-scale diazo production.

Thermal [2 + 2]-Cycloaddition of Ketenes with Chiral Enol Ethers: Route to Densely Substituted Cyclobutanones.

Access to chiral polysubstituted cyclobutanones by [2 + 2]-cycloaddition of ketenes with chiral acyclic enol ethers is reported. A wide variety of easily accessible di- and monosubstituted ketenes were found to react with a very high degree of stereoselectivity with chiral, Stericol derived, acyclic enol ethers. This combination of simple reagents provides straightforward entry to highly substituted enantioenriched cyclobutanones.

Difluorocarbene Addition to Alkenes and Alkynes in Continuous Flow.

The first in-flow difluorocarbene generation and addition to alkenes and alkynes is reported. The application of continuous flow technology allowed for the controlled generation of difluorocarbene from TMSCF3 and a catalytic quantity of NaI. The in situ generated electrophilic carbene reacts smoothly with a broad range of alkenes and alkynes, allowing the synthesis of the corresponding difluorocyclopropanes and difluorocyclopropenes. The reaction is complete within a 10 min residence time at high reaction concentrations. With a production flow rate of 1 mmol/min, continuous flow chemistry enables scale up of this process in a green, atom-economic, and safe manner.

Kinetic resolution in the [2+2] cycloaddition of ketenes: an experimental and theoretical study.

The kinetic resolution of Z and E olefins by [2+2] cycloaddition with ketenes allows the isolation of pure E olefin, as well as the synthesis of pure cis-cyclobutanones, starting from Z/E mixtures. A computational rationale for this kinetic difference is reported. The obtained difference of energy of activation matches with the experimental results.

Total synthesis of norcembrenolide B and scabrolide D.

An efficient stereoselective synthesis of norcembrenolide B (8) and scabrolide D (9) is reported. The strategy is inspired by biogenetic relationships of related cembrenoids. Central to this approach is the construction of norbipinnatin J which upon selective C2 deoxygenation and C8 oxygenation produces norrubifolide and norcoralloidolide A. A sequence of site-selective oxidations and skeletal reorganizations then yields, in a divergent manner, compounds 8 and 9. The studies allow revision of the proposed structure of scabrolide D (9), which is identical to norcembrenolide C.