Synthesis of Potential Cytotoxic Quaternary Ammoniums by Oxidation of Eburnane Alkaloids
摘要:
Oxidation of vincamine and substituted analogs on ring-A was carried out in two steps: benzylic oxidation by Jones reagent and aromatization of ring-C with Hg(OAc)(2) or TI(OCOCF3)(3) in trifluoroacetic acid. Final compounds are quaternary ammoniums which exhibited weak cytotoxicity or no cytotoxicity according to substituents on ring-A and nature of ring-E.
Synthesis of Vinca Alkaloids and Related Compounds, XXXIV Synthesis of (3S, 14S, 16S)-Bromovincamines and Bromoapovincamines by Regioselective Bromination
By bromination of the iminium salt 2a (X‐Cl), the 9‐bromo derivative 2c (X=ClO4) is obtained in isomerfree state. Bromination of the lactam 8d leads to a ca. 7.5:1 mixture of 11‐bromo (8c) and 9‐bromo (8a) lactams. These precursors have been used to synthesize 9‐, 10‐ and 11‐bromovincamines (11a‐c), and 9‐, 10‐ and 11‐bromoapovincamines (12a‐c).