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 C to C backbones. Enantiomerically enriched samples were prepared by asymmetric synthesis of the optimal C DAC and C BAC derivatives. Samples with upgraded enantiomeric purity were alternatively produced by enzymatic kinetic resolution. Eutomers possessing the S configuration displayed cytotoxicity IC values as low as 15 nm against HCT116 cancer cells, the highest level of activity reached to date in this series.

Among acetylenic natural products, chiral lipidic alkynylcarbinol (LAC) metabolites, mostly extracted from marine sponges, have revealed a broad spectrum of biological activities, in particular, remarkable antitumor cytotoxicity. With reference to one of the simplest natural representatives, [(S)-eicos-(4E)-en-1-yn-3-ol], and a given cancer cell line (HCT116), combined extensive efforts in chemical synthesis (relying on the use of a large chemical toolbox) and biological analysis (in vitro tests), have provided systematic structure–activity relationships (SARs) where the initially selected four structural parameters appear as independent principal components: (i) and (ii) the sp/sp2 content and extent of the terminal and internal unsaturations adjacent to the carbinol center, (iii) the absolute configuration of the latter, (iv) the length of the n-aliphatic backbone. Two key criteria have also been established regarding the functional alkynylcarbinol pharmacophore: the alkynylcarbinol unit must be both secondary and terminal (i.e., substituted by a short ethynyl or ethenyl C2 group). This review is intended to provide a further illustration of the value of a simple rational approach for drug design, and to act as a benchmark for future optimization of LACs as antitumor agents.1 Introduction2 2C2-Unsaturated Pharmacophore Candidates2.1 Alkenylalkynylcarbinols (AACs)2.2 Dialkynylcarbinols (DACs or DACys)2.3 Alkynylalkenylcarbinols (iso-AACs) and Dialkenylcarbinols (DACes)2.4 Oxidation-Protected Dialkynylcarbinols and Dialkynylketones2.5 Fluorophore-Labeled Lipidic Dialkynylcarbinols3 C2/C3-Unsaturated Pharmacophore Candidates3.1 Cyclopropylalkynylcarbinols (CACs)3.2 Allenylalkynylcarbinols (AllACs)4 C2/C4- and 3C2-Unsaturated Pharmacophore Candidates4.1 Butadiynylalkynylcarbinols (BACs)4.2 Trialkynylcarbinols (TACs)5 Double-AC-Headed Pharmacophore Candidates6 Screening on the Lipidic Chain Length7 Conclusion

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.