Codeine biosynthesis

Morphine and codeine biosynthesis (Samuelsson, 1999 Herbert et al., 2000 Novak et al., 2000) Studies on the biosynthesis of morphine have been carried out mainly on cell cultures mainly of Coptis japonica and species of Thalictrum. Two enzymes (tyrosine decarboxylase and phenolase) catalyze the formation of dopamine from one molecule tyrosine. Dopamine is also the key intermediate in the biosynthesis of mescaline. 

In order to understand the continuation of the biosynthesis of codeine and morphine from reticuline, the structure for (S)-reticuline can be written as follows ... 

Or they may be grouped according to the genus of their plant source (morphine and codeine, Section 23-2, are examples of opium alkaloids), or by their physiological effects (antimicrobials, antibiotics, analgesics), or by similarities in the route by which they are synthesized by the organism (biosynthesis). The structural and biosynthetic classifications make the most sense to the chemist and is the organization chosen here. 

Biosynthetic research relating to the isoquinoline family was extremely successful, with such important members as morphine [3, 14], codeine [3, 15] or berberine [3, 14,16-18]. Extensive efforts have provided details pertaining to multiple sets of enzymes participating in the biosynthesis of the alkaloids above, in many cases with the help of plant cell suspension culture techniques. Since 1988, when the breakthrough in cloning of cDNA from alkaloid biosynthesis occurred [19, 20], a significant number of enzymes known from the indoles and isoquinolines biosynthesis have been isolated, their biochemical properties described and the majority of their corresponding cDNAs cloned and functionally over-expressed in non-plant hosts such as Escherichia coli, yeast or insect cells. 

Labelled reticuline was readily incorporated into thebaine 14, codeinone 15a, codeine 15b, and morphine 16 without scrambling of the labels. Salutaridine is not present in detectable quantities in Papaver somniferum. However, when appropriately labelled, it is well incorporated into morphine alkaloids. Salutaridine can be readily reduced to two stereo-isomeric allylic alcohols 17, both of which are converted by mild acid catalysis (17, see arrows) to give thebaine 14. The alkaloids 17, 14, 15a, and 15b were all shown to be precursors of morphine. This was of interest, because the earlier theory of Robinson suggested that unmethylated alkaloids were first assembled and methylation was a terminal stage of biosynthesis. 

S)-Reticuline is a branch-point intermediate in the biosynthesis of most BAs. Most work has focused on branch pathways leading to the benzophenanthridine (e.g., sanguinarine), protoberberine (e.g., berberine), and morphinan (e.g., morphine and codeine) alkaloids.19 Most enzymes involved have been isolated, many have been purified, and four corresponding cDNAs have been cloned.19 The first committed step in benzophenanthridine and protoberberine alkaloid biosynthesis involves the conversion of (S)-reticuline to (5)-scoulerine by the berberine bridge enzyme (BBE) (Fig.7.2). BBE was purified from Berberis beaniana,20 corresponding cDNAs were cloned from E. californica and B. stolonifera,21 22 and BBE genes have been isolated from P. somniferum and E. californica.23,24... 

S)-Reticuline is also the precursor for the biosynthesis of benzophenanthri-dine (e.g. sanguinarine, marcarpine), protoberberine, berberine, palmatine) and morphinan alkaloids (morphine, codeine) (see next few paragraphs). 

Keywords chemotaxonomy patchy distribution biosynthesis genes horizontal gene transfer endophytes evolution tryptophan decarboxylase tyrosine decarboxylase phenylalanine ammonia-lyase chalcone synthase strictosidine synthase berberine bridge enzyme codeine reductase... 

The isoquinoline alkaloids include the analgesics morphine and codeine as well as the antibiotic berberine (Fig. la). Morphine and codeine are two of the most important analgesics used in medicine, and plants remain the main commercial source of the alkaloids (8). Development of plant cell cultures of Eschscholzia califomica, Papaver somniferum, and Coptis japonica has aided in the isolation and cloning of many enzymes involved in the biosynthesis of isoquinoline alkaloids (9). 

Battersby AR, Binks R, Francis RJ, McCaldin DJ, Ramuz H. Alkaloid biosynthesis. IV. 1-Benzylisoquinolines as precursors of thebaine, codeine, and morphine. J. Chem. Soc. 1964 3600-3610. 

Morphine and related alkaloids are specific to the genus Papaver (Berberidaceae), although the antipodal series of alkaloids is distributed in the Menisperma-ceae. Early in the biosynthesis of morphine, an inversion at C-1 of (5)-reticuline occurs, followed by ortho-para benzylic coupling to afford salutaridine. Stereospecific reduction and cyclization-elimination affords the 4,5-Ether bridge and thebaine. The dominant pathway from this point involves neopinone, codeinone, codeine, and morphine. Again, most of the enzymes in this sequence were isolated and characterized by Zenk s group (Fig. 30). 

There are two possible biosynthetic pathways for the conversion of thebaine to morphine, Fig. (67) [148]. One is orthodoxically known in the litreatures [4, 130, 131], that is morphine biosynthesis from thebaine via codeinone and codeine. Another one i.e. the first ever demonstrated by Brochmann-Hanssen in 1984 [149], is the biosynthesis via oripavine and morphinone. The transformed clone could synthesize codeine but lacked morphine though the non-transformed clone obtained from the same plant material accumulated morphine at the latter developmental stage (Table 21). This suppressed morphine content was also observed in the opium derived from the transformed P. somniferum plants that had been... 

Figure 2 Semisynthetic bulk drugs Ampicillin (antibacterial) from penicillin G. Modifications of biosynthetic structures are often created to improve the in vivo attributes of the original compound, utilizing the biosynthesis product as the starting material containing most, if not all, of the structural complexity that provides the basic biological activity. Similarly, codeine (analgesic), although found in opium from Papaver plants, is most economically made by methylation of morphine, which is more efficiently isolated from opium.

Fig. 4. Biosynthesis of the morphinan alkaloids thebaine (192), codeine (198), and morphine (204).

An early key intermediate in benzylisoquinoline biosynthesis is (57), which by decarboxylation affords (59) this in turn leads to (61) and on to alkaloids (Scheme 2). Confirmation of this pathway has come from a study using cell-free preparations of P. somniferum stems and seed capsules. It was found that this preparation catalysed the formation of (57), (59), and (61) from dopamine (54) plus 3,4-dihydroxyphenylpyruvic acid (55) without the addition of 5-adenosyl-methionine, NADPH, and pyridoxal phosphate, the reaction stopped at (57). The formation of the alkaloids reticuline, thebaine, codeine, and morphine, produced by whole plants, could not be detected with this cell-free system. The results confirm not only the intermediacy of (57) and (59) in benzylisoquinoline biosynthesis, but also the involvement of (54) and (55). 

Morphinan Alkaloids.—Extensive research on the biosynthesis of morphine (51) and related alkaloids in Papaver somniferum has allowed a detailed description of the pathway from the amino-acid tyrosine through reticuline (44), thebaine (46), and codeine (50) to morphine (51) (Scheme The incorporation of (R)-... 

The conversion of reticuline (44) into morphinan alkaloids, which occurs with loss of tritium from C-1 in P. somniferum (see above)," has been observed also for the formation of thebaine (46) in P. bracteatum, a plant which produces this alkaloid but not codeine or morphine. Radioactive 1,2-dehydroreticuline (47) labelled both reticuline (44) and thebaine (46), whilst radioactive reticuline again labelled thebaine (46). ° Codeinone (48) and codeine (50) are biosynthetic intermediates between thebaine (46) and morphine (51) in P. somniferum, and it was shown that (48) was efficiently reduced to (50) in P. bracteatumf It is apparent that alkaloid biosynthesis in the two plants is similar, with the important difference that in P. bracteatum the enzymes which effect demethylation of (46) are missing, and so biosynthesis goes no further than thebaine (46). 

Routes similar to those for morphine, codeine, and thebaine are also being considered for the biosyntheses of sinoacutine and sinomenine. Sinoacutine is the enantiomer of salutaridine the biosynthesis proceeds accordingly from (5)-reticuline. While morphine and morphine derivatives as well as sinoacutine are formed by an ortho-para-coupling of (R)- or (5)-reticuline, the... 

Despite the detection of COR and other known morphinan branch pathway enzymes in opium poppy cell cultures (63-65,67), morphine and codeine are not produced. The inability of cultured cells to accumulate morphine might reflect the absence of other relevant enzymes or structural proteins that preclude the formation of a requisite metabolic channel. Nevertheless, the efficient operation of the sang-uinarine pathway indicates that cultured opium poppy cells possess the essential regulatory, eellular, and metabolic components to support the biosynthesis and... 

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