Pleiocarpa pycnantha

To conclude this Section, the structure of the Ci9-skeleton will be briefly discussed the isomeric mixture obtained from cleavage of 6, 7 -dihydropycnan-thine (194) shows a mass spectrum identical to that of (-l-)-tuboxenine, isolated from Pleiocarpa pycnantha. Isotuboxenine could be isolated from the same plant and has been shown to be identical by mass spectroscopy and thin-layer chromatography with the isotuboxenine obtained by reductive cleavage of 6, 7 -dihydropycnanthine (194). Under the conditions employed, tuboxenine is the thermodynamically more stable isomer. Concerning possible mechanisms of the tuboxenine-isotuboxenine interconversion see ref 113. 

Once known, the characteristic spectra of alkaloids of the second category are of great value in the classification of new alkaloids. For instance, pycnan-thinine (195), a trace alkaloid of Pleiocarpa pycnantha, exhibits a u.v. spectrum which is virtually identical to that of pycnanthine (193). The nature of its monomeric chromophores and the mode of linkage were thus immediately clear. Two fission reactions then yielded the complete structure. 

Aspidosperma peroba) Pleiocarpa tubicina (= Pleiocarpa pycnantha var. tubicina) Strychnos amazonica Strychnos decussata Strychnos ignatii Strychnos toxifera Strychnos usambarensis... 

Pleiocarpa pycnantha (K. Schum.) Stapf. var. tubicina (Stapf.) Pichon... 

The new alkaloids of this group, all from Pleiocarpa species, are tubo-flavine (I) from Pleiocarpa tubicina Stapf [P. pycnantha. (K. Schum.) Stapf var. tubicina (Stapf) Pichon], the same alkaloid, isotuboflavine (II) (mp 263°-265°) and norisotuboflavine (III) (mp 282°-284°) from Pleiocarpa mutica Benth. l-Methoxycarbonyl-(8-carboline was also isolated along with the latter alkaloids (3). 

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