Biomimetic total synthesis of (+)-gelsemine

Challenging: (+)-gelsemine was synthesized from (R,R)-aziridine 1 in 25 steps with approximately 1 % overall yield. A multistep, one-pot enol-oxonium cyclization cascade was used to construct, simultaneously, the E ring, F ring, C3 stereocenter, and C7 quaternary stereocenter. This synthesis using the enol-oxonium cyclization reaction as a key step to make the cage structure has demonstrated the proposed biosynthetic pathway of the gelsemine family.     

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.     

Enantiospecific formal total synthesis of (+)-dihydrokawain-5-ol

Abstract

Formal total synthesis of dihydrokawain-5-ol is accomplished starting from tartaric acid. Key reactions include Horner–Wadsworth–Emmons olefination, sodium borohydride mediated stereoselective reduction, orthogonal protection and deprotection of alcohols and ring closing metathesis.