Isoquinoline, biosynthesis

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. 

Later steps of biosynthesis follow as the joining together of (22) with a tyrosine-derived molecule to give the amino-acid (23), analogues of which are involved in isoquinoline biosynthesis.40 Appropriate oxidative phenol coupling41 and subsequent steps as indicated (Scheme 5) could afford tylophorine (17) and tylophorinine (24).39... 

Isoquinoline biosynthesis begins with the substrates dopamine and p-hydroxyphenylacetaldehyde (Fig. lb). Dopamine is made from tyrosine by hydroxylation and decarboxylation. Enzymes that catalyze the hydroxylation and decarboxylation steps in either order exist in the plant, and the predominant pathway... 

The localization of isoquinoline biosynthesis has been investigated at the cellular level in intact poppy plants by using in situ RNA hybridization and immunoflouresence microscopy. The localization of 4 -OMT (reticuline biosynthesis), berberine bridge enzyme (saguinarine biosynthesis), salutaridinol acetyltransferase (morphine biosynthesis), and codeinone reductase (morphine biosynthesis) has been probed. 4 -OMT and salutaridinol acetyltransferase are localized to parenchyma cells, whereas codeinone reductase is localized to laticifer cells in... 

Ironically, the answer to this problem has rested in the literature since Hahn published in 1935 his theory of isoquinoline biosynthesis.34 In his hypothesis (illustrated for anhalonidine in Scheme 5) the phenethylamine is condensed with the appropriate pyruvic acid to form an amino-acid (44) which is decarboxylated to provide the alkaloid (43). 

Further evidence implicating (68) as an intermediate in isoquinoline biosynthesis comes from the efficient incorporation of labelled (68) into (70) and with the specific incorporation, albeit with low efficiency, of labelled (68) into morphine (71). The amino-acid (72) was a very poor precursor for morphine, which indicates that both aromatic building blocks must be dihydroxylated before they are joined together. Simple chemical decarboxylation of (68) affords (69), which was found to act as a precursor for morphine [the triphenol (73) was incorporated too but at a lower level]. These observations taken with the labelling of (69) by dopa in P. orientale suggest that the imine (69) may also be an intermediate in isoquinoline biosynthesis. 

The unique substitution pattern of ancistrocladine (1), however, which was first isolated by Govindachari from the Indian liana Ancistrocladus heyneanus Wall. (Ancistrocladaceae) (4), can barely be brought into line with such a conventional isoquinoline biosynthesis. Its unprecedented structure, for which it was termed the most unusual of all the isoquinoline alkaloids (5), makes obvious that its biosynthesis must also differ from that of all other tetrahydroiso-quinoline alkaloids by starting not from aromatic amino acids, but from poly-ketide precursors, as first proposed by Govindachari (6). 

A stimulating review on unsolved problems in isoquinoline biosynthesis has been published. ... 

Fig. 15.4 Flowchart representing the branching points and links to different pathways in isoquinoline biosynthesis pathways...

The protoberberine alkaloids (5-75) play important roles as precursors in the biosynthesis of a variety of related isoquinoline alkaloids such as protopine, phthalideisoquinoline, spirobenzylisoquinoline, rhoeadine, inde-nobenzazepine, secoberbine, and benzo[c]phenanthridine alkaloids. Chemical transformations of protoberberines to these alkaloids are particularly interesting and exciting from the biogenetic viewpoint and further from ready availability of starting protoberberines in nature or synthesis. 

FACCHINI, D., DELUCA, V., Phloem-specific expression of tyrosine dopa decarboxylase genes and the biosynthesis of isoquinoline alkaloids in opium poppy, Plant Cell, 1995, 7, 1811-1821. 

Fig. 10.8 Selected cDNAs isolated in recent years that encode enzymes involved in the biosynthesis of various classes of isoquinoline alkaloids. 6-OMT, norcoclaurine 6-0-methyltransferase 23 CYP80A1, berbamunine synthase 19 CYP80B1, (S)-A-methylcoclaurine 3 -hydroxylase 20 CPR, cytochrome P-450 reductase 29 4 -OMT, (5)-3 -hydroxy-A-methylcoclaurine 4 -0-methyltransferase 30 BBE, berberine bridge enzyme 12 SalAT, salutaridinol 7-O-acetyltransferase 28 COR, codeinone reductase.25...

In summary, the de novo isolation of the cDNAs encoding enzymes of alkaloid biosynthesis is still achieved by using a variety of classical techniques, such as protein purification followed by partial amino acid sequence determination, and by newer techniques such as proteomics coupled to functional heterologous expression. The current status of cloned cDNAs specifically related to isoquinoline alkaloid biosynthesis is schematically presented in Figure 10.8. New additions to this list will certainly be made in the future as a result of a combination of approaches both new and old. 

FRICK, S., KUTCHAN, T.M., Molecular cloning and functional expression of O-methyltransferases common to isoquinoline alkaloid and phenylpropanoid biosynthesis, Plant J., 1999,17, 329-339. 

MORISHIGE, T TSUJITA, T YAMADA, Y SATO, F., Molecular characterization of the S-adenosyl-L-methionine 3 -hydroxy-A-methylcoclaurine 4 -0-methyltransferase involved in isoquinoline alkaloid biosynthesis in Coptis japonica, J. Biol. Chem., 2000, 275, 23398-23405. 

Berberine (Fig. 3), an isoquinoline alkaloid, is used for the treatment of leisimaniasis. Its biosynthesis was potentiated in cell cultures of Coptis japonica. ... 

Reticuline (38), one of the most important intermediates in the biosynthesis of opium alkaloids, has been synthesized in racemic form (Scheme 7) (78). 6-Methoxy-7-benzyloxyisoquinoline (39), prepared from O-benzylisovanillin via a modified Pomeranz-Fritsch isoquinoline synthesis, was treated with benzoyl chloride and potassium cyanide to obtain Reissert compound 40. Alkylation of the anion generated from 40 with 3-benzyloxy-4-methoxybenzyl chloride gave the corresponding 1-substituted Reissert compound 41 which was hydrolyzed in alkaline medium to 1-benzylisoquinoline derivative 42. Quatemarization of 42 with methyl iodide followed by sodium borohydride reduction and debenzylation led to ( )-reticuline (38) in about 25% overall yield from 39. 

Tetrahydroisoquinoline-l-carboxylic acids have been anodically decarboxylated in MeOH-NaOMe on a graphite felt anode, giving 3,4-di-hydroisoquinolines (50-90%)417 This may be an example of a pseudo-Kolbe reaction in support of Hahn s theory of the biosynthesis of isoquinoline alkaloids by providing a laboratory analogy for the crucial decarboxylation step. 

Poly(vinylpyrrolidones) polymerization, 1, 271 Polyviologens synthesis, 1, 286 Pomeranz-Fritsch synthesis isoquinolines, 2, 428 6, 218 Pongapin synthesis, 4, 710 Poranthericine, 4, 494 ( )-Porantherine synthesis, 2, 377 Porphin, 4, 386 structure, 4, 378 Porphin, maso-aryltri-p-tolyl-synthesis, 4, 230 Porphin, maso-tetraalkyl-synthesis, 4, 230 Porphin, meso-tetraaryl-synthesis, 4, 230 Porphin, meso-tetraferrocenyl-synthesis, 4, 230 Porphin, meso-tetraphenyl-synthesis, 7, 767 Porphobilinogen biosynthesis, 1, 100... 

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