Pyrrolizidine alkaloids structural types

A new type of pyrrolizidine alkaloid has been isolated from the leaves of Ehretia aspera Willd. by Suri et al.n The structure (39) for ehretinine was established by spectroscopic evidence and by hydrolysis to give retronecanol and p-methoxy-benzoic acid. Confirmation of the structure (39) was obtained by synthesis of ehretinine from retronecanol and pmethoxybenzoyl chloride. This is the first reported occurrence of a retronecanol ester, although it should be pointed out that retronecanol esters can be produced by hydrogenolysis of retronecine diesters. The authors do not appear to have considered the possibility that ehretinine could have been formed by hydrogenolysis of the common type of ester (40) on treatment with the zinc and sulphuric acid that are used in their extraction procedure. 

Apart from the chemistry of these pyrrolizidine alkaloids, their physiological effects, in particular their hepatotoxicity, have been investigated in depth by the CSIRO Division of Animal Health, as a result of which it has been possible to establish correlations between activity and structure liver damage is caused by alkaloids such as 90 or 91 because unsaturated amino alcohols of this type, which are esterified on one or both hydroxyl groups, undergo metabolism in the liver to form the toxin 93 this substance is immediately responsible for the mutagenic and carcinogenic effects observed [106, 107], which include... 

Otonedne C9H13NO3, Mr 185.22, oil as hydrochloride mp. 146-148 °C, [a]i)-18.5 (CjHjOH) is the N. base of about 30 known pyrrolizidine alkaloids, most of which are of the senecionine structural type (see also senkirkine) and a few of which ate of the monocrotaline structural type. For synthesis, see Lit. ... 

Figure Pyrrolizidine alkaloids, skeletons, and structural types.

Pyrrolizidine alkaloids (PAs) belong to a class of naturally occurring compounds characterized by a bridged dipyrrole structure. They encompass more than 400 different structures, which consist of a necine base of type 25 that may also be saturated between carbons 1 and 2 and esterified with one or more necic acids which exist as 5-11 carbon membered types (Figure 5.25). Thus, there are monosters such as supi-nine 27, indicine 28 obtained from retronecine 25a, and (-)-trachelanthic acid 26. Heliosupine 29 is an example of an open-chain diester, and retrorsine 30 is, instead, a macrocyclic diester. PAs are constitutively produced by the plant and are believed... 

Occurrence in the Convolvulaceae. In this family phenylacetic acid is integrated as an acyl moiety into the structure of certain ester-type pyrrolizidine alkaloids (Sect. 3.7 Fig. 3.30). 

Alkaloids can be divided into different t q3es according their pure chemical structures pointing first at the alkaloid base, a basic chemical nucleus. The following are basic types of alkaloids acridones, aromatics, carbo-lines, ephedras, ergots, imidazoles, indoles, bisindoles, indolizidines, manza-mines, oxindoles, quinolines, quinozolines. quinolizidines, phenylisoquinolines, phenylethylamines, piperidines, purines, pyrolidines, pyrrolizidines, pyrro-loindoles, pyrydines, sesquiterpenes, simple tetrahydroisoquinolines, stereoids, tropanes, terpenoids, diterpenes, and triterpenes. 

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