Pyrrolidines ring systems

These alkaloids contain pyrrole or modified pyrrole, e.g. pyrrolidine, ring system. The simplest example of this class is nicotine. A pyrrolidine ring is the central structure of the amino acids proline and hydroxyproline. These alkaloids are also found in many drug preparations, e.g. procyclidine hydrochloride, which is an antichohnergic drug mainly used for the treatment of drug-induced Parkinsonism, akathisia and acute dystonia. 

The tobacco alkaloids, especially nicotine, are derived from nicotinic acid (see page 311) but also contain a pyrrolidine ring system derived from ornithine as a portion of their structure. 

Polycyclic Pyrrolidine Ring Systems from PTOC Precursors... 

There are many abundant naturally occurring compounds containing a pyrrolidine ring system. Remarkably, however, syntheses of kainoids from such materials have received relatively little attention. An important... 

As early as 1967, Huisgen and coworkers [37] had shown that, upon photolysis, certain aziridines of type 96 undergo C—C bond fragmentation stereospecifkally to produce octet-stabilized azomethine ylides which, on cycloaddition with electron-deficient dipolarophiles, produce pyrrolidine ring systems (Scheme 8.29). 

Pandey, G., Banerjee, P., and Gadre, S.R. (2006) Construction of enantiopure pyrrolidine ring system via asymmetric [3 + 2] cycloaddition of azomethineylides. Chemical Reviews, 106, 4484—4517. 

The efficient desilylation from amine radical cation in media favouring SSIP formation has also been used [104] for the sequential double desilylation reaction of amine 110 to generate azomethine ylide 111 which upon cycloaddition with a different dipolarophile gives a stereoselective pyrrolidine ring system 112 as depicted in Scheme 20. 

Thebaine, the methoxy derivative of morphine, is also a habit-forming substance, but its primary toxic effects are similar to those of strychnine, a convulsant poison, rather than narcosis. Also, there are alkaloids having different structures but similar toxic actions. Lobeline, a lobelia alkaloid, which has a piperidine nucleus, shows pharmacologic action similar (but less potent) to that of nicotine, a tobacco alkaloid that has a pyridine-pyrrolidine ring system. The structure, occurrence, physical properties, and toxicity of some important alkaloids are presented in the following sections. 

Construction of enantiopure pyrrolidine ring system via asymmetric [3 + 2] cycloaddition of azomethine ylides 06CRV4484. 

In Peganum harmala, [2- " C]-ornithine (119) and labeled proline, putrescine, and related compounds are more or less specifically incorporated into the pyrrolidine ring system of vasicine 127, 128). This result suggests that ornithine is decarboxylated affording putrescine, a symmetrical molecule, which is then incorporated, a process which results in equal labeling at C-1 and C-3 a. The results can be rationalized by postulating that a symmetrical intermediate such as putrescine is involved... 

A tandem aza-Payne/hydroamination reaction of aziridinols 65, mediated by dimethyl-sulfoxonium methylide afforded highly functionalized pyrrolidine ring systems in one pot at room temperature. ... 

Class 3 alkaloids are the pyrrolizidines as represented by australine [7] (Figure lA). In a formal sense, these alkaloids can be considered to be the result of a fusion of two pyrrolidine ring systems with the common nitrogen atom at the... 

---