Georgette Hugel

Méthylène-indolines, indolénines et indoléniniums—XIII: L'hydroxy-16 déhydro-1 vincadifformine, intérmédiaire dans le réarrangement biomimétique de la vincadifformine en vincamine

Abstract The title compound is a crucial intermediate in the biomimetic conversion of vincadifformine 1 into vincamine 7 . Its configuration at C-16 is established by a combination of chemical and spectroscopic evidence. Iodine oxidation converts 14 into the bridged lactam 18 , thus proving a β configuration for the hydroxy group at C-16. The same reaction applied to vindoline 19 gives 21 identical with one of the compounds obtained by microbiological transformation of 19 . The 13 C NMR spectra of derivatives 3 and 8 (obtained by oxidation of vincadifformine) show that oxidation proceeds with introduction of the substituent at C-16, with a β-configuration. The alcohol 3 however, posesses a different conformation due to strong hydrogen bonding with N-4.

Methylene-indolines, indolenines et indoleniniums—XII : Hemisynthese de la dehydro-14,15 vincamine et de la criocerine

Resume (-)-Tabersonine 1 was oxidised and rearranged to (+)-14,15-dehydrovincamine 5, (+)-14,15-dehydro,16-epi vincamine 6, and the rhazinilam derivative 9. Iodine and potassium iodate oxidised 5 to 14-iodo criocerine 13, Which led to criocerine 14.

Synthesis of hexacyclic indole alkaloids related to vindolinine by sonochemical cyclization

Abstract Upon treatment with sodium in THF under sonication, 19-iodotabersonine underwent cyclization to the vindolinine ring system. The yields and ratio of the diastereomers thus obtained depended on the sonication parameters.

Thermal rearrangements of some indole alkaloid derivatives

Under both static and flow thermolysis conditions, several compounds with an “aspidosperma” framework rearranged to “vinca” derivatives. Thus (-)1,2-dehydroaspidospermidine (4) rearranged to (-) gave vincane 14. Compound 6 rearranged to vincamine (13a) and 16-epi vincamine (13b) under either condition ; increasing the temperature resulted in formation of apovincamine (19) (pyrolysis) or vincamone thermolysis).

Derives 14-hydroxyles de la vincadifformine et de la vincamine

Abstract Hydroboration-oxidation of tabersonine 1 yielded as major product 14 β-hydroxy vincadifformine 9b, which was correlated with 14 β-hydroxy N(1)-methyl 2β-H, 16β-H dihydro vincadifformine 6b (previously prepared and characterised), and 14α-hydroxy vincadifformine 9a as minor product. The regio- and stereoselectivity of hydroboration-oxidation were interpreted. 9a and 9b were respectively oxidised and rearranged to the corresponding 14-hydroxy vincamines 13a and 13b. The coupling constants of H(14) on the NMR of the acetyl derivatives of 9a, 9b, 13a and 13b are consistent with an inversion of N(4) during the rearrangement leading from the vincadifformine to the vincamine skeleton.

A biomimetic entry in the hexacyclic tuboxenin ring system methylene-indolines, indolenines and indoleniniums, XXII☆

indolenine 9 was reacted with Na in THF to yield tuboxenine 1a, 19-epi tuboxenine 1b, indoline 10 and the two indoles 13 and 14.