Pelletierine, biosynthesis

Alkaloids with the piperidine nucleus, such as pelletierine (Punica grana-tum), lobelanine Lobelia inflata) and piperine Piper nigrum), have a typical biosynthesis pathway. It starts with L-lysine and continues via cadaverine (biogenic amine), A -piperideine and A -piperidinium cations and lobelanine, to be synthesized as lobeline. Piperine is synthesized from A -piperideine via piperidine (Figure 49). For the transformation from A -piperideine to A -piperideine cation, the residue from acetyl-CoA is needed, together with SAM activity in the transformation to lobelanine. Piperine is synthesized from piperidine through the formation of amide. 

A key stage in the biosynthesis of piperidine alkaloids is reached with the formation of A -piperideine. For the elaboration of diverse alkaloids, this intermediate undergoes condensation with a variety of nucleophiles, commonly a /3-keto-acid. (A similar situation is found for pyrrolidine alkaloid biosynthesis see, e.g., Scheme l).1,2 Existing evidence on Lythraceae alkaloid biosynthesis, taken up again below, indicated that condensation occurred in this case between A piperideine (17) and acetoacetic acid to give pelletierine (26), further elaboration yielding alkaloids like (22). In the event, however, labelled pelletierine was found not to be a precursor for (22) or (23).8 Negative evidence is always difficult to interpret, but is here made persuasive by the fact that other precursors that were fed concurrently were incorporated. Conclusive support for these results depended on others outlined below. 

Most of the work on the biosynthesis of Lythraceae alkaloids has been done by Spenser et al. (10, 84-87). First, the validity of the pelletierine hypothesis (c) of Ferris et al. (62) has been tested. The pelletierine (126) nucleus is generated from L-lysine (181) via cadaverine (182), and presumably A -piperideine (132) and its side chain originate from the acetate. Incorporation of radioactivity from 14C-labeled samples of these precursors to decodine (6) and decinine (2) in Decodon verticilatus has been investigated (85, 87). 

The piperidine alkaloid pelletierine was mentioned in the chapter but full details of its biosynthesis were not given. There follows an outline of the intermediates and reagents used. Fill in the details. Pyridoxal chemistry is discussed in Chapter 50. 

Lycopodine.—Lycopodine (4) is formed in Lycopodium tristachyum from lysine [via A -piperideine (2)] and acetic acid, " The labelling pattern observed with these precursors suggests that lycopodine (4) could be formed simply from two molecules of pelletierine (5) but in this case Occam s Razor does not apply since radioactive pelletierine (5) labels only one of these pelletierine units in lycopodine (4). - The hypothetical pathway proposed to take account of these results has been tested in further experiments.Piperidine-2-acetic acid (6), as its CoA ester, is one of the hypothetical intermediates but the evidence obtained most strongly points to it not being involved in lycopodine biosynthesis, [carftoxy- C]Piperidine-2-acetic acid fed in admixture with DL-[4- H]lysine [as (1)] gave lycopodine with a C ratio... 

Only routes (a) and (b) are consistent with these results. It is interesting to note that if pelletierine is implicated in the biosynthesis of these alkaloids [route (a)] it should be derived from a symmetrical intermediate as is apparently true for pelletierine in the biosynthesis of lycopodine alkaloids (see above). On the other hand, A -piperideine [route (b)] is derived in an unsymmetrical way from lysine in the biosynthesis of anabasine and iV-methylpelletierine (see above). Route (a) would, therefore, seem more likely. ... 

The biosynthetic derivation of the side chain of N-methylpelletierine (170) was established [443]. Feeding [ 1,2,3,4-13C4]-acetoacetate to Sedum sarmentosum and isolation of 170 showed that the side chain of 170 was derived from the labelled precursor as an intact unit. Feeding [l,2-13C2]-acetate showed that the -COCH3, but not the -CH2CO portion of the side chain was derived from the intact labelled acetate. A pathway for biosynthesis of the pelletierine skeleton consistent with these results is outlined in Scheme 4. 

It will be interesting to see if the hydrogen at C(2) of lysine is retained in the biosynthesis of the other alkaloids of this family, such as anabasine (86) and pelletierine (89), where the nitrogen atom is not methylated. It is significant that the pipecolic acid (88) produced along with the sedamine in this experiment, was devoid of tritium. Therefore, the pathway a could be in operation for this natural product and it may be the normal route for some of the alkaloids also. 

The alkaloid (93) which is produced by Haloxylon salicornicum shows a structural resemblance to pelletierine (89). A feeding experiment58 with [6-14C]-lysine in intact plants has supported the related biosynthesis in Scheme 18. Activity was incorporated at C(6) of the alkaloid as shown. Surprisingly, no activity was incorporated from [2-14C]acetate but this negative result could be due to the failure of acetate to reach the site of synthesis. 

In the next two sections studies are reported on the biosynthesis of lycopodine and cernuine which demonstrate that the polyacetate hypothesis does not account for the biosynthesis of these alkaloids and that the pathway to the alkaloids incorporates some but not all features of the pelletierine hypothesis outlined above. 

The experiments reviewed up to this point demonstrate that the labeled compounds are incorporated with equal efficiency into both halves of the lycopodine system. This is consistent with the premise that two monomeric precursors combine to a dimeric product that is an intermediate in the biosynthetic pathway. However, experiments with multiply labeled pelletierine demonstrated that an intact unit was incorporated only into that portion of the lycopodine molecule corresponding to carbons 9-16. Contrary to the predictions of Schemes 3 and 7, carbons 1-8 were not derived from pelletierine. A more thorough study of the role of pelletierine in the biosynthesis of lycopodine was therefore necessary. 

C-cadaverine and 2- C-A -piperideine is altered when the labeled compounds are administered in conjunction with large amounts of inactive pelletierine. The inactive pelletierine repressed the incorporation of the labeled precursors into that portion of the molecule comprising C-9 to C-16. In the piperideine experiment approximately 90% of the activity was located at C-5 compared to approximately 50% when inactive pelletierine was absent. The comparable figures in the cadaverine experiment were 44% and 25%. These results provide evidence that pelletierine is an intermediate in the biosynthesis of lycopodine. 

In order to account for the apparent anomaly that pelletierine is incorporated into only one half of the molecule while the other precursors are incorporated with equal efficiency into both halves of lycopodine the proposals outlined in Scheme 9 have been put forward 73). This hypothesis is tenable provided that the steady-state concentration of pelletierine is small compared to that of its immediate precursor and that the reaction leading to pelletierine is irreversible. This scheme also proposes that 2-piperidineacetic acid is implicated in the biosynthesis. At the present time experiments are in progress in this laboratory to test this hypothesis. 

In this area the biosynthesis of the Lycopodium alkaloids, e.g. lycopodine (14) and cernuine (15), is of further interest. Lycopodine and cernuine were considered to be modified dimers of pelletierine (16) because two intact molecules of precursors like lysine and A -piperideine were used for the construction of a single molecule of the alkaloids. Paradoxically, however, pelletierine (16) only gives rise... 

Work on the biosynthesis of lycopodine (126) in Lycopodium tristachyum and cernuine (127) ° in L. cernuum, previously published in preliminary form and reviewed,has appeared in full lycopodine and cernuine.It was established that the two alkaloids are derived from two molecules of lysine via a symmetrical intermediate which is in all probability cadaverine. The hypothesis that the Lycopodium alkaloids were modified dimers of pelletierine (125) (Scheme 12) required reappraisal, as pelletierine gave only one each (shown with heavy bonding) of the two CgN units of (126) and (127). 

The Piperidine Family. It was noted in section 3.2.1.2 that the piperidine ring is biosynthesized from the amino add lysine, and the example of coniine biosynthesis was given in that section. On the pathway to coniine (3.14), a highly toxic compound isolated from the hemlock tree is the ketone derivative 3.13 this happens to be the well-known alkaloid pelletierine, which is isolated from the pomegranate tree (Scheme 3.7). It has found use in the treatment of parasitic infections (called an anthelmintic agent). 

The full paper on the biosynthesis of the lycopodium alkaloids from lysine was published.29 xhe possibility that two identical pelletierine units (20). derived from lysine and acetate, would combine to form lycopodlne (21) was not corroborated by double labeling experiments with [4,5-%2 2" "P ll tierine.30 Only the portion of the molecule drawn in heavy line was derived from pelletierine. 

In the biosynthesis of pelletierine, lysine was incorporated without the involvement of a symmetrical intermediate such as cadaverine. On the other hand, it was established that in the biosynthesis of matrine, a symmetrical intermediate is incorporated, implying that cadaverine is involved. 

That is to say, in the biosynthesis of pelletierine, lysine was transformed into an asymmetric alkaloid -piperideine without forming a symmetrical inter-... 

Tropane alkaloids comprise a large group of bases occurring predominantly in the family of the Solanaceae. Structurally they are esters of carboxylic acids with tropine (3-hydroxy-8-aza-8-methyl-[3.2.1]-bicyclooctane) and are biosynthetically derived from amino acid and acetate precursors. Despite the relative structural simplicity of the alkaloids, their biosynthesis is not well understood from a mechanistic point of view. In this article the available information pertaining to this question is summarized and discussed in context with the information that is available from the analogous pelletierine class of alkaloids. A new proposal for the mechanism of assembly of the acetate derived C, fragment of these alkaloids is introduced. 

The present review will focus on progress made in the elucidation of the biosynthesis of tropane and related alkaloids from a more chemical perspective and will attempt to outline what in our current understanding is deficient and to identify the remaining problems. For this purpose, the discussion will be divided into two parts, dealing with the assembly of the amino acid derived C4N portion, C-l,C-5,C-6,C-7,N-8, of the five-membered ring and then with the assembly of the acetate derived C3 fragment, C-2,C-3,C-4, and the formation of the azabicy-clooctane system. A liberal definition of the term tropane wiU be used, so that the biosynthesis of cocaine and some biogenetically related pelletierine-type alkaloids may be included in the discussion. In the view of this author, results... 

The discussion of the observed labeling patterns in the alkaloids so far has focused on the interpretation of the data according to either only one or a combination of several of the paths outlined in Scheme 8. Our investigation of the biosynthesis of a seemingly related alkaloid, lycopodine (27), uncovered yet another mechanism for the assembly of the C3 fragments of the tropane- and the pelletierine-type alkaloids. These results will be discussed in the following section and the implications of this discovery for the biosynthesis of cocaine and tropane will be discussed subsequently. 

Scheme 13. Biosynthesis of lycopodine 27 pelletierine 28 is only incorporated into the left half...

Scheme 15. New proposal for the biosynthesis of pelletierine in Lyopodium tristachyum via acetonedicarboxylic acid...

Common characteristics in the biosynthesis of these alkaloids, that they are elaborated from the lysine derived A -piperideine, coupling either to an aliphatic- (from acetyl-CoA precursor, e.g., pelletierine and co-alkaloids), or an aromatic part (from cinnamoyl-CoA precursor, e.g., pipeline and other amides lobeline, lobelanine and related alkaloids). 

Biological activities biosynthesis of piperidine alkaloids HPLC and LC-MS/MS Lobelia inflata lobeline and their derivates pelletierine Piper nigrum piperine Punic a granatum... 

The biosynthesis of the structurally complex alkaloids of the primitive club moss Lycopodium species), e.g. lycopodine 6.43) and cernuine 6.44), has been analysed simply in terms of a pathway which involves the dimerization of two pelletierine units (Scheme 6.11). Substance is given to this hypothesis by the appropriate incorporations of acetate, lysine 6.17), and A -piperideine 6.18) into lycopodine 6.43) and cernuine 6.44). Significantly, these precursors were incorporated equally into both putative pelletierine (CgN) units [27]. 

Study lycopodine biosynthesis and is formed from lycopodine precursors. Unlabelled pelletierine, when fed with radioactive cadaverine or A -piperideine, very efficiently diluted activity in the one CgN unit (heavy bonding) of lycopodine 6.43) for which it is a precursor. It follows that pelletierine is a normal intermediate in the biosynthesis of lycopodine (and cernuine), but unlike the other precursors tested is involved in the biosynthesis of only one unit. The equal labelling of both CsN units by A -piperideine 6.18) (and lysine) requires that the second CgN unit must be closely related to pelletierine 6.42) significant differences in structure would be associated with differing pathways and hence unequal incorporation of label into the two CgN units. The results argue thus for the pelletierine-dimer hypothesis, but in modified form. It is not easy, however, to propose modifications to the pathway which will fit the results. Hypotheses surrounding 6.45) and 6.46) as intermediates have not been supported by subsequent experimentation. So the puzzle remains. One possibility not so far examined is 6.47), potentially an intermediate in the condensation of 6.18) with acetoacetate (cf Scheme 6.7). 

The biosynthesis of lycopodium, quinohzine, pyridine, or a-pyridone-type alkaloids isolated from Lycopodium species, shares some common steps with the biosynthesis of the previously mentioned piperidine alkaloids [28, 35, 36], The first general intermediate for all lycopodium alkaloids is the piperidine alkaloid pelletierine (45). Again, besides the... 

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