Anabasine biosynthesis

In a notable piece of research it was shown that the L-isomer of lysine was much preferred for anabasine biosynthesis whereas the D-isomer was preferentially utilized for L-pipecolic acid biosynthesis in N. glauca. In a more rigorous study this was confirmed for sedamine (20), JV-methylpelletierine (22), N-methyl-allosedridine (25) (in two Sedm species), and anabasine (in N. glauca) and also for... 

Lysine.—Lysine is a common precursor of piperidine alkaloids. Of the two enantiomers of this amino-acid, the L-isomer is the more direct precursor, in plants, for piperidine alkaloids, e.g. anabasine, whereas D-lysine is more directly implicated in the biosynthesis of pipecolic acid (24)1,2,23 (cf Vol. 7, p. 7). It has now been shown that a pathway exists in the plant Nicotiana glauca,24 and also in the micro-organism Neurospora crassa2S which transforms D-lysine into L-lysine by way of L-pipecolic acid (24). 

The production of toxins is only one aspect of plant defense strategy. As a result of the persistent battle of plants and herbivores, many optimized phenotypes have evolved, such as the preferential accumulation of alkaloids in tissues with a pattern that is consistent with predictions of optimal defense theory,65 i.e., the defense metabolites are allocated preferentially to tissues with a high probability of attack.66 The inducibility of pathways leading to plant secondary compounds as a strategy to minimize the costs of plant defense is a result of permanent optimization. One of a few examples of inducible alkaloid biosynthesis is the different Nicotiana species that exhibit dramatic wound-induced increases of nicotine, nomicotine, or anabasine.67... 

The rather similar alkaloids anabasine and anatabine come from different biosynthetic pathways. Labelling experiments outlined below show the origin of one carbon atom from lysine and others from nicotinic acid. Suggest detailed pathways. (Hint. Nicotinic acid and the intermediate yoi have been using in Problem 3 in the biosynthesis of the piperidine alkaloid are both electrophilic at position 2. You also need an intermediate derived from nicotinic acid which is nucleophilic at position 3. The biosynthesis involves reduction.)... 

Figure 2.2 Biosynthesis of nicotine and anabasine. ODC, ornithine decarboxylase ADC, arginine decraboxylase PMT, putrescine N-methyltransferase DAO, diamine oxidase MPO, N-methylputresdne oxidase.

Anatabine and anabasine are both alkaloids of Nicotiana (tobacco) species. Their biosynthesis was elucidated by E. Leete, J. Chem. Soc., Chem. Commun., 1975, 9. 

The labelling and the hints given in the problem suggest an outline biosynthesis in which two molecules of nicotinic acid, one made nucleophilic by reduction, combine to give anatabine whilst the iminium salt we made in the last problem is attacked by the same nucleophilic derivative of nicotinic acid to give anabasine. 

The overexpression of both trl and h6h from H. niger in N. tabacum plants have been reported [160]. Here, transgenic and control tobacco plants were fed with the tropane intermediate tropinone. Thus, tropine, the TRI-reaction product, was detected only in leaves of transgenic plants, with no correlation with trl transcript level and tropine amounts. Surprisingly, transgenic tobacco plants contained 3 to 13-fold more nicotine than wild type plants. Also, the presence of considerable amounts of nornicotine, myosmine, anabasine and anatabine contrasted with low levels in wild-type plants, indicating that the overexpression of trl and h6h perturb the normal nicotine biosynthesis when these new genes taken from a different metabolic pathway are introduced in tobacco [160]. 

For studies on the interrelationsship among nicotine, nornicotine, anabasine and anatabine during the biosynthesis in Nicotiana glutinosa, Alworth and Rapoport used almost the same gas chromatographic conditions as reported above. On a polybutylene glycol column the alkaloids mentioned were satisfactorily resolved. 

As both lysine and ACpiperideine lead to unequal labelling of C-2 and C-6 in anabasine, and the biosynthetic sequence must be lysine— A -piperideine (11)— anabasine (14), any other precursors for (14) after lysine must be un-symmetrical in nature. Thus cadaverine, although incorporated into anabasine, cannot be a true precursor for the alkaloid. Two other groups of workers have also cast doubt on the role of cadaverine in alkaloid biosynthesis, and it is worth remembering in general that even if a proposed precursor is specifically incorporated it may not lie on the normal pathway to a particular alkaloid. Rather, it may merely test the adaptability of the plant in the face of an unusual substrate. 

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. ... 

Some earlier results for sedamine and anabasine are illustrated in Scheme 15. Activity was incorporated from cadaverine (84) into the piperidine ring of anabasine.51 However, the incorporation from lysine was specific for both sedamine52 and anabasine53 as indicated in Scheme 15, so that the two ends of the lysine chain must retain their separate identities throughout the biosynthesis. 

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 alkaloids Af-methylpelletierine (90) and pseudopelletierine (91) of Punica granatum and also anaferine (92) of Withania somnifera are probably related in biosynthesis to sedamine and anabasine. The proposed biosynthesis (Scheme 17) has received support from recent tracer studies.57... 

The Early Stages of Alkaloid Biosynthesis. — It is well established that L-lysine (13) is incorporated into some piperidine alkaloids by way of a symmetrical intermediate it is accepted that this symmetrical intermediate is cadaverine (17), which is also an alkaloid precursor. Lysine, however, is incorporated into other alkaloids, e.g. anabasine (12) (Section 1.5) and sedamine (18), without the intervention of any symmetrical intermediate. Cadaverine (17), although able to act as an alkaloid precursor. 

B32. Leete, E. Biosynthesis of anatabine and anabasine in 17B48. 

Solt, M.L., R.F. Dawson, and D.R. Christman Biosynthesis of anabasine and of nicotine by excised root cultures of Nicotiana glauca. Plant Physiol. 35 (1960) 887-894. 

Although amino-acids have been administered to plants on occasions legion in number, rarely has attention been paid to the question of whether there is any selectivity for the D- or L-amino-acid in alkaloid biosynthesis. An exception appears in work on the Amaryllidaceae alkaloids where it was shown that d- and L-tyrosine were equally well utilized in lycorine biosynthesis. The question has now been answered in Nicotiana glauca for the biosynthesis of anabasine (118) and pipecolic acid (113) from lysine. Pipecolic acid was found to be derived preferentially from the D-isomer ( 48 times better), in accord with a similar preference in intact rats and corn seedlings, whereas L-lysine was the more effective precursor ( 30 times) for anabasine. 

These results tie in neatly with others obtained for the biosynthesis of sedamine (117), anabasine (118), and N-methylpelletierine (119) where, it was shown, the pathway differs from that which leads to pipecolic acid. In essence the results show that (117), (118), and (119) derive from lysine without loss of the hydrogens from C-2 and C-6, whereas the genesis of pipecolic acid (113) is with retention of the hydrogens from C-6 and loss of the one from C-2. Further, all these piperidine derivatives arise from lysine without the intermediacy of a symmetrical intermediate. The results may be summarized in terms of the... 

The biosynthesis of nicotine and anabasine can reasonably proceed via (30), which will be electrophilic towards (31) and (3), which are intermediates for the other parts of the alkaloids, subsequent aromatization leading to loss of tritium. Coupling of two molecules of (30), decarboxylation, and aromatization would give anatabine, with 50% retention of tritium observed the stereochemistry of (30) follows from that determined in anatabine (34). [Direct coupling of two molecules of (30) makes use of the higher electrophilicity associated with this molecule cf. fatty acid biosynthesis), and so is preferred to the suggested coupling with two molecules of (35).]... 

Physiology biosynthesis Like the tropane alkaloids, T. a. are formed in the roots and transported to the aboveground parts for storage by the plant s phloem system. In some sorts of tobacco plants a part of the nicotine is demethylated to nomicotine during transport to the shoot. Nomicotine and anabasine are often the main alkaloids in the so-called nicotine-poor tobacco plant types. The T. a. are formed biogenetically from nicotinic acid, made available via the pyridine nucleotide cycle (see nicotinamide), and a pyrrolidine or piperidine building block (figure). In the case of nicotine, like for the tropane alkaloids, Al-methylpyr-roline is an intermediate, in the biosynthesis of anabasine the intermediate is a piperidine derived from the amino acid lysine (see piperidine alkaloids). 

It was already described in Section 3.1 that ornithine is incorporated into nicotine in the form of a symmetrical intermediate, putrescine. Although the last stages in the biosynthesis of (-)-anabasine are potentially quite similar to those of (-)-nicotine, during this biosynthetic pathway, it is considered that a symmetrical intermediate, such as cadaverine, is not involved.Thus, when [2- C]lysine was incorporated into (-)-anabasine, was introduced only into the C-2 position of the piperidine ring of... 

Anabasine a Nicotiana alkaloid, M, 162.2. It is isolated in the L-form, primarily from Nicotiana glau-ca and the asiatic Anabasis aphylla, being the most abundant alkaloid in both of these species. In other tobacco species it is only a secondary alkaloid. Its physiological effects are similar to those of nicotine, and like nicotine, it is used as an insecticide. For biosynthesis, see Nicotiana alkaloids. 

Lysine has also a role in the biosynthesis of Nicotiana alkaloids, e.g., anabasine, in which beside nicotinic acid, the precursor of pyridine ring, lysine formed the piperidine core. 

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