Tylophora alkaloids structures

Indollzidine alkaloids. A group of alkaloids from various classes based on the bicyclic ring system of in-dolizidine. They differ in structure, biogenesis, and occurrence thus, the indolizidine ring system has very little value as a characterizing structural. The I. a. include the pumiliotoxins (Dendrobates alkaloids), poly hydroxy alkaloids such as swainsonineand cas-tanospermine, Elaeocarpus alkaloids, Securinega alkaloids, Tylophora alkaloids, and the Ipom(o)ea alkaloids. 

Cynanchum vincetoxicum (L.) Pers. contains traces of an alkaloid vincetene, which shows an interesting relationship to the phenanthroindolizidines found in Tylophora and other genera of the Asclepiadaceae. Spectroscopic study has shown vincetene to be the benzopyrroloisoquinoline derivative (2), and this structure has been confirmed by synthesis of the racemic dihydro-desoxy-deriva-tive (3).2... 

The objective of this review article is to provide comprehensive information about isolation, total synthesis, antitumor activity, and structure-activity relationship (SAR) correlations of tylophorinc-related alkaloids in order to facilitate the anticipated drug discovery and development of the tylophora class. 

In addition to benzylisoquinolines, the family Lauraceae furnishes phenanthro-quinolizidine alkaloids such as the previously mentioned cryptopleurine (31) [77], a highly cytotoxic and vesicant substance first isolated from Cryptocarya pleurosperma [78]. These alkaloids are closely related structurally to the phenanthroindolizidines, a group of bases found in the families Asclepidaceae and Moraceae that are likewise vesicant. An example is tylocrebrine (56), which is elaborated by a Queensland plant from each family, Tylophora crebriflora [79] and Ficus septica [80], respectively. In the latter it occurs along with the seco analogue septicine (57), its presumed biosynthetic precursor. Apart from phenanthroindolizidines, certain Ficus spp. produce some simple pyrrolidine bases such as ficine (58) that are noteworthy because of their flavonoid substituents [81],... 

Phenanthroindoiizidine Alkaloids.—Previous results establish that the phenacyl-pyrrolidines (19), (20), and (21) are important precursors for phenanthroindoiizidine alkaloids, e.g. tylophorinine (28), in Tylophora asthmatica. These results and a consideration of the oxygenation pattern of the T. asthmatica bases in relation to possible biosynthesis by phenol oxidative coupling, as well as the structure (22) for the alkaloid septicine, pointed to (26) as a key intermediate. 

---