Some aspidosperma bases

AspMospemiine. The first inkling that the structure of aspido spermine was different firom the yohimbine or strychnine types was the formation on zinc dust distillation of 3,5-diethyIpyridine and since this carbon nitrogen pattern turned out not to be present in the original alkaloid it could only lead to erroneous formulae, which it did. The nature of rings A and B became clear 

The first mass spectrometric investigation of desacetylaspido-spermine was brought about by the desire to confirm the structure guessed for quebrachamine and this was done by converting the former compound into the 12-methoxy derivative of the latter (Chart 11.3). It was argued that if the two compounds differed only in the substitution of an aromatic proton for a methoxyl they should have identical mass spectra except for those peaks containing the aromatic residues (i.e., they would differ by 30 mass units) and this was found to be true. This comparative method is known as the mass spectrometric shift technique and has since found widespread use. 

It is of value to point out here that the stereochemistry of the pentacyclic system must be the thermodvnamically stable one since reduction of the indolenine form (preferred in ether) with lithium aluminium hydride regenerated deacetylaspidospermine (cf. demethoxycarbonylakuammicine. Chart 6.7). 

A total synthesis of f/-aspidospermine and /-quebrachamine took advantage of these facts. The appropriate phenylhydrazone of the tricyclic ketone (Chart 11.3) cyclized in hot acetic acid to give the indolenine indole forms, reduction of which under the correct conditions gave the desired racemic penta- or tetracyclic alkaloid. The tricyclic ketone was prepared in nine steps from butyraldehyde. 

The Mass Spectrum of Aspidospennine. Upon electron impact an electron is probably kicked out of the non-bonding electrons of the alicyclic nitrogen. This ion seeks further stabilization through conversion to iminium ions either by loss of hydrogen (M-1 ion) or fission which would lead to a stabilized radical ion which in its turn may fragment. Thus aspidospennine yields species b (M-1), 

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Aspidosperma-type molecules whose structures were derived largely from a detailed physical examination of the bases and their derivatives (principally by mass spectra see Chart III), a technique discussed on a broader basis under Aspidosperma. Similarly, the structures of some of the strychnoid bases were obtained by physical methods. There is no way of knowing which of the alkaloids listed in the table could be identical with either the amorphous bases of Greshoff (10) or the base tartrates and sulfates reported by Australian workers (11). 

In 1980 Quaisuddin isolated from Aspidosperma peroba a quaternary alkaloid, which he designated alkaloid Q3 (198). Based on some chemical transformations, which were suggested to lead to the not yet naturally found 16-epipericyclivine (94), structure 95 was tentatively proposed for alkaloid Q3 (Scheme 3). If the structure proposed for alkaloid Q3 were correct, alkaloid Q3 would be identical with the synthetically prepared panarine methyl ester chloride (117). However, because the physical properties indicated for alkaloid Q3 and for its suggested derivative 94 (discussed... 

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