Poranthera

Over seven-hundred references are concerned with the isolation and chemistry of alkaloids, and approximately one-third of these are devoted to synthesis and biosynthesis. It is perhaps in these areas that the most notable research is to be found. Although it is probably invidious to attempt the exercise, a personal selection of highlights would include new results on the biosynthesis of quinoliz-idine alkaloids (p. 4), the first synthesis of an eleven-membered macrocyclic pyrrolizidine diester (p. 49), the synthesis of Poranthera alkaloids (p. 68), and, in the indole field, the synthesis of tryptoquivalines G and L (p. 152), of a chiral intermediate in the construction of heteroyohimbine alkaloids (p. 167), and of a catharanthine intermediate, using palladium catalysts (p. 186). 

The structure (77) for lepistine has been established by AT-ray analysis. Lepistine has structural similarities with pyrrolizidine and Poranthera alkaloids. 

Porantherilidine (415), the only bicyclic member of a group of quinolizidine alkaloids from the Australian shrub Poranthera corymbosa, was described in the previous chapter on simple indolizidine and quinolizidine alkaloids in Volume 28 of this series (/). The related tricyclic alkaloid porantheiidine (416) is included here as an obvious carbinolamine derivative of the simple bicyclic system. 

In previous Reports the perhydro-9b-azaphenalene alkaloids derived from species of Coccinellidae (ladybird beetles) were discussed in the quinolizidine chapters while those isolated from the Australian shrub Poranthera corymbosa were included in the section devoted to miscellaneous alkaloids. In this Report the two groups of closely related alkaloids are considered together. 

The structures of the azaphenalene alkaloids of Poranthera corymbosa, poran-therine, porantheridine, poranthericine (51), and O-acetylporanthericine (52) and a related quinolizidine were determined by X-ray analysis (Vol. 5 of these Reports). The isolation and characterization of these alkaloids has now been described in full, and the structure of a new base, porantheriline (53), has been established. ... 

Porantherin (1) is an alkaloid from the Australian plant Poranthera corymbosa and possesses an interesting tetracyclic skeleton of the 9b-azaphenalene type [167]. In an instructive biomimetic synthesis of 1 developed by Corey [168] the key intermediate (X) was subjected to the following reactions (a) and (b) leading via A to B, which was further transformed to the target molecule 1 ... 

Certain other groups of alkaloids that coincidentally have a quinolizidine ring system are discussed in other chapters. For example, the alkaloids of the Lythraceae are discussed in Chapter 37 and those of the genus Nuphar are discussed in Chapter 36. Yet other quinolizidine alkaloids (18 and 19) are known from the Ericaceae (Vaccinium myrtillus) and the Euphorbiaceae (Poranthera corymbosa) (see Piperidine... 

Porantherine is a Euphorbaceae alkaloid isolated from the woody shrub Poranthera corymbosa Brogn. It is known to poison cattle wherever it grows. It came to light for poisoning cattle in New South Wales and Queensland, Australia. Some other members o( this iamily oi alkaloids are shown below. 

Porantheridine (1188) is included among the simple quinoHzidine alkaloids in this review as it can be viewed as the internal aminal of a hydroxy-quinohzidinium system. It is one of a handful of rare natural products obtained from the AustraHan shmb Poranthera corymbosa (Euphorbiaceae), most of which are 9b-azaphenalenes. Three enantioselective syntheses... 

The Kouklovsky/Vincent and co-workers formal synthesis of ( )-porantheridine 197 (discovered from the Australian bush Poranthera corymbosa) is complementary to the work of Kibayashi (Scheme 41.41). ° The treatment of hydroxamic acid 192 with sodium periodate in the presence of cyclopentadiene 33 in methanol and water at 0°C delivered the bicyclic 3,6-dihydro-oxazine 193 in 61% yield. Ring-rearrangement metathesis (ring opening/ring... 

Porantherine, characterized by a bridged 9b-aza-phenalene network, is the major alkaloid of the low, woody shrub, Poranthera corymbose growing in northern New South Wales. 

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