Corynanthe-Strychnos alkaloids

Researches carried out to the early part of 1966 have been comprehensively reviewed and the present account will set out from that point. In brief, the situation reached at that time was as follows. Despite their bewildering variety, three main groups of alkaloids had been recognised (a) the Corynanthe-Strychnos type, e.g. ajmalicine (1) and akuammicine (2) which possess the non-tryptamine unit (3), (b) the Aspidosperma type, e.g. vindoline (4), in which the non-tryptamine unit appears as (5), and (c) the Iboga type, e.g. catharanthine (6), having still a different arrangement of the non-tryptamine unit (7). 

Constabel et al. (595) analyzed 76 cell clones derived from one leaf of a C. roseus plant. Although this work shows the variation in alkaloid spectra of cell lines derived from a single leaf, the variation was low when compared to that found previously with serially subcultured callus and cell suspensions derived from different plants. The majority of clones showed the occurrence of Corynanthe, Strychnos, and Aspidosperma alkaloids. Of the 76 clones analyzed, 41 produced ajmalicine. 

Proposed biogenetic pathways and mechanisms by which relatively simple indole alkaloids such as ajmalicine are converted into the subgroups of Corynanthe-Strychnos-iype alkaloids are reviewed by Atta-ur-Rahman and Basha (1983). 

These feeding experiments seem to suggest that As-pidosperma-Hunteria alkaloids (classes 3 and 5) arise by prior formation of Corynanthe and then Strychnos alkaloids (class I) (Atta-ur-Rahman and Basha, 1983). 

When seeds of Catharanthus roseus are germinated, iboga alkaloids do not appear for 100-160 h. Only class 1 (Corynanthe and Strychnos) alkaloids are found during that time. Vindoline (9) (a class 3 or Aspidosperma alkaloid) does not appear until 200 h after germination (Atta-ur-Rah-man and Basha, 1983). 

Most L-tryptophan-derived secondary products still possess the indole ring system of this amino acid. Some compounds, however, are quinoline, pyrrole or benzene derivatives. Additional rings may be present yielding complicated structures, like that of ergoline and / -carboline alkaloids (cf. the formulas of ergotamine, Corynanthe, Strychnos, Iboga and Aspidosperma-type alkaloids). 

B, Iridoid Indole Alkaloids. Most jS-carbolines are derived from tryptamine and the iridoid secologanin (D 6.1.2). In dependence on the structure of the iridoid part alkaloids of the Corynanthe-Strychnos type as well as of the Aspidosperma and Iboga types may be distinguished. The latter are formed by rearrangement of the iridoid part which is shown schematically in Fig. 259 and in detail in Fig. 261. 

One particular cell line of C. roseus. CSo. 943) was selected for detailed chemical investigation. Yields as high as 0.44% of alkaloids (based on the dry weight of cells) v ere obtained from this particular cell line. In addition to the known alkaloids of the Corynanthe, Strychnos, and Aspidosperma type, four new alkaloids (58-61), illustrated below,were isolated. None of the alkaloids... 

Alkaloids like preakuammicine (Figure 6.79) and akuammicine (Figure 6.75) contain the C10 and C9 Corynanthe type terpenoid units respectively. They are, however, representatives of a subgroup of Corynanthe alkaloids termed the Strychnos type because of their structural similarity to many of the alkaloids found in Strychnos... 

For (essentially) the first time recently, strains of C. roseus cultures have been obtained which will synthesize Strychnos, Iboga, and Aspidosperma alkaloids.34 This opens up the exciting possibility of studying the biosynthesis of those alkaloids lying beyond the Corynanthe type, such as (102), by using enzyme preparations from tissue cultures, which have proved so powerful for the early stages of biosynthesis (see above). 

Pawelka and Stockigt (5S5) identified eight different indole alkaloids from cell suspension cultures of O. elliptica. The pattern of the alkaloids found was quite different from the above-mentioned results reported by Kuoadio and co-workers (779). The alkaloids identified were tetrahydroal-stonine, cathenamine, pleiocarpamine and two other methoxy-substituted heteroyohimbine alkaloids Corynanthe/heteroyohimbine type), norfluo-rocurarine Strychnos type), and apparicine and epchrosine Aspi-dosperma type). The last mentioned alkaloid was a new compound (729) not known from intact plants. 

III. Tr5 tamine-Tryptamine Type with an Additional Monoterpene Unit and Related Alkaloids rV. Corynanthe-Tryptamine Type V. Corynanthe-Corynanthe Type VI. Coryn nthe-Strychnos Type... 

It is now considered [188 b, 188 c] that stemmadenine (XLIIA, Fig. 3) is likely to be a key intermediate between alkaloids of the Corynanthe type and the Ihoga and Aspidosperma types although whether it is a precursor [188b, 188 c] or further derivative [187a] of the Strychnos type skeleton is still unsettled. 

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