Vincadifformine-type alkaloids

The Aspidosperma alkaloid vincadifformine 1 is reasonably available, and can be readily transformed into the carbinolamine ether 2. Oxidation of 2 with MCPBA followed by methanolysis gives the hemiketal 3, and brief treatment of 3 with a 99 1 v/v mixture of CH2CI2/TFA at room temperature gives a mixture of 4 (42%) and 5 (11%). The yield of 4 is increased to 52%, while almost none of 5 is formed, if the treatment of 3 with acid is allowed to proceed at room temperature for 15 hours. Products 4 and 5 contain the gross skeleton of goniomitine 6, an indole alkaloid of an unusual structural type. 

A double bond in position 2,3 in alkaloids of the aspidospermidine type, as in vincadifformine, prevents the production of the characteristic fragment of mass 124 [249], but an easy correlation is possible after the hydrogenation of the double bond, as was shown for vincadifformine,132 minovincinine,133 minovincine,133 tabersonine,134 loch-nericine,135 and lochnerinine.135... 

Goniomitine (135), an alkaloid of a new structural type from the root bark of Gonioma malagasy E. May, is apparently the result of a much more far-reaching transformation of a vincadifformine precursor (146). Its structure was deduced on the basis of an analysis of its NMR spectra, including a comparison of its C chemical shift data with those of tryptophol and guettardine (136). It is included in this group on the basis of its presumed derivation from vincadifformine (77) by a series of plausible, unexceptional... 

Almost all the alkaloids isolated from V. minor are derived from the type III moiety 41) belonging to the vincamine, Aspidosperma, and quebrachamine subclasses. In this sense there is more uniformity among the alkaloids of V. minor than the other Vinca species. The alkaloids are also unusual in that amongst the three subclasses are found racemic alkaloids, namely, d(-eburnamine (vincanorine), dZ-A-methylquebrach-amine d -vincadifformine and its dZ-l-methyl derivative (minovine) (see Table II). 

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