Catharanthus alkaloids Subject

The relatively high yield of vinblastine from Catharanthus extracts and the remarkable biological activity of this alkaloid render this compound a natural choice for structural modification. Vinblastine is subject to attack by electrophilic reagents at a number of sites (Fig. 6), but by careful selection of reagents and conditions it is possible to operate in this structurally complex theater with considerable selectivity. Potentially electrophilic sites are, in some cases, immune from electrophilic attack. 

Vinblastine has been found in the roots of Catharanthus trichophyllus (Bak.) Pichon, apparently for the first time.63rf Catharanthamine (322), a new alkaloid138 related to vinblastine, and with anti-tumour activity, is the first alkaloid of the group to contain oxygen at C-17 its structure was deduced from a comparison of its 13C n.m.r. spectrum with that of vinblastine. Proton n.m.r. data for vinblastine and leurosine are the subject of two further communications,139a,fc and 13C n.m.r. data form the subject of the third.,39c. 

The synonyms for the genus Vinca are Lochnera, Pervinca, Catharanthus and Ammocallis since the botany of the plants does not concern us here, the term Vinca is preferred (i), although this matter has been the subject of a recent discussion (2). The results now available show considerable differences between the alkaloids isolated from different species and this information ought to be of considerable value to the systematic botanist. The most marked contrast is between the bases of V. major and V. pubescens, and other Vinca species (see tables in this chapter). 

Biosynthesis The biosynthesis of these alkaloids begins with the key reaction, the condensation of tryptamine with secologanin to give strictosidine catalyzed by the enzyme strictosidine synthase. The biosynthesis was elucidated mainly by the use of plant cell suspension cultures. Cell cultures of Catharanthus and Rauvolfia species have been the subject of intense phytochemical studies. 

Formation of Alkaloids in Cell-Suspension Cultures.- This subject has been an active area of research in the last few years, and it is potentially a way to obtain economically useful natural products in a controlled environment, rather than by extracting whole plants, which are often difficult to cultivate in hospitable regions of our planet. Several books on this topic have appeared. The species Catharanthus roaeus has attracted much attention since it is a source of the clinically useful antitumor agents vinblastine and vincristine. Extensive work with this species has been carried out by Zenk ,Kutney ,Scott ,and their... 

---