Vincatine

The stereochemistry of vincatine (340) was finally established by a partial synthesis from (-)-vincadifformine (76), which conclusively proved that its absolute stereochemistry is 1R,2QS,21R (Scheme 15) (236). Initially assigned the enantiomeric configuration (7S,20f ,21S) (237,238), (-)-vincatine was synthesized from (-)-vincadifformine A b-oxide by a process that did not affect the stereochemistry at C-20, although the lability of the stereochemistry at C-7 and C-21 resulted in the formation of all four... 

The structure (94) for vincatine from Vinca minor was arrived at by mass spectral examination of the alkaloid and its lithium aluminium hydride reduction product (95), which has since been synthesised (Scheme 14). It is the first oxindole alkaloid with an aspidospermine aliphatic skeleton. 

Dopke et al. (77) obtained an interesting seco ring C Aspidosperma alkaloid from Vinca minor L. to which they gave the name vincatine (163). 

Vincatine (mp 111-112°) gave a molecular ion at m/e 370, in agreement with a molecular formula of C22H30N2O3. The IR spectrum showed carbonyl absorptions at 1705 and 1735 cm-1 and the UV spectrum indicated the presence of a 2-oxindole. Four aromatic protons were observed in the PMR spectrum together with JV-methyl (3.20 ppm) and carbomethoxyl (3.62 ppm) groups. Lithium aluminum hydride reduction gave a diol 164 but acetylation of this compound gave only a monoacetyl derivative. The structure of vincatine (163) was deduced on the basis of a rationalization of the mass spectra of the parent compound and its various derivatives, particularly the ions at m/e 297, 211, 182, and 124 in the parent compound (Scheme 3) and the base peak at m/e 184 (165) in the mass spectrum of the diol. 

The structure elucidation of vincatine (163) was described in Section II,F,2. Harley-Mason and co-workers (202) have reported a synthesis of a... 

Utilizing a route similar to that used by Harley-Mason in the synthesis of the reduced product from vincatine, the French group has successfully extended this work to a more select group of alkaloids (235,236). 

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