Diels–Alder reactions of activated furans to cyclopentenone derivatives: a regiodivergent Diels–Alder approach towards polyfunctionalised cis-hydrindanones

Enantioselective Total Synthesis of Otteliones A and B, Novel and Powerful Antitumor Agents from the Freshwater Plant Ottelia alismoides

Otteliones A and B isolated from the freshwater plant Ottelia alismoides have attracted significant attention because of their potential as novel anticancer agents. In this review four independent enantioselective total syntheses and one formal synthesis of these natural products are presented with particular focus on their methodology and strategy.

Enantioselective Total Synthesis of (+)-Ottelione A, (−)-Ottelione B, (+)-3-epi-Ottelione A and Preliminary Evaluation of Their Antitumor Activity

Enantioselective total synthesis of (+)-ottelione A (1) and (-)-ottelione B (2), novel and potent antitumor agents from a freshwater plant, and (+)-3-epi-ottelione A (3), the earlier proposed stereostructure of 1, was efficiently achieved starting from the known tricyclic compound 10. The synthesis involved the following key steps: i) coupling reactions of aldehydes 8 and 9 with the aromatic portion 7 (8+7-->15 and 9+7-->27), ii) base-induced hemiacetal-opening/epimerization reactions of the cyclic hemiacetals 6 and 27 (6-->17 and 27 a-->26 a), and iii) Corey-Winter's reductive olefination of the cyclic thiocarbonates 21 and 36 (21-->22 and 36-->37). The present total synthesis fully established the absolute configuration of these natural products. The cell growth inhibition profile, COMPARE analysis, and tubulin inhibitory assay of (+)-3-epi-ottelione A (3) and its O-acetyl derivative 24 demonstrated that these unnatural substances could be prominent lead compounds for the development of anticancer agents with a novel mode of action.

Total Synthesis and Absolute Configuration of Otteliones A and B, Novel and Potent Antitumor Agents from a Freshwater Plant

[reaction: see text] The first enantioselective total synthesis of otteliones A and B, biologically important and structurally novel natural products, has been successfully achieved. This total synthesis fully confirms the absolute configuration of these natural products.