Protoberberine alkaloids 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... 

Samanani, N., Park, S.-U., Facchini, P.J. (2005) Cell type-specific localisation of transcripts encoding nine consecutive enzymes involved in protoberberine alkaloid biosynthesis. Plant Cell, 17, 915-26. 

Berberine bridge enzyme catalyses are specialized step in protoberberine alkaloid biosynthesis similar genes and proteins are, however, widely present in higher plants, indicating common ancestry (Fig. 7.17c). BBE or similar proteins, which share a number of common conserved sites (Table 7.8), could also be found in fungi and bacteria. A similar pattern can be seen in the distribution of CR (Fig. 7.17d, Table 7.9). 

Beecher, C. W. W. and W. J. Kelleher, Enzymatic study of the late stages of protoberberine alkaloid biosynthesis. Tetrahedron Lett., 25, 4595-4598 (1984). 

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. 

Lee MK, Kim HS. Inhibitory effects of protoberberine alkaloids from the roots of Coptis japonica on catecholamine biosynthesis in PC12 cells. Planta Med 1996 62 31-34. 

This observation was explained by the assumption that a portion of the protoberberine was formed via norreticuline (96) present in the same incubation mixture and derived from enzymic demethylation of reticuline. Reaction of 96 with an unlabeled one-carbon fragment and subsequent ring closure would then lead to C-8 unlabeled protoberberines. The authors suggest that this one-carbon fragment may be derived from S-adenosyl-methionine, and that the product of its combination with 96 may be converted directly to 91 or 94 without the intermediacy of free reticuline (99). If their assumption is correct, the conversion of norreticuline to the protoberberine alkaloids may not involve the formation of reticuline itself, a suggestion that is at variance with the known intermediacy of reticuline in the biosynthesis of alkaloids of this group. 

Protoberberine Alkaloids.—In the course of the bioconversion of the proto-berberine scoulerine (65) into chelidonine (62) and phthalide-isoquinolines, e.g. narcotine (63), C-13 becomes oxidized.61 Ophiocarpine (68), with a hydroxy-group at C-13, represents an intermediate stage in the modification of the protoberberine skeleton, and results62 of tracer experiments have shown that scoulerine (65) is also to be included in the biosynthesis of this alkaloid. Tetrahydro-protoberberine (67) is also a precursor, its incorporation indicating that C-13 hydroxylation is a terminal step. As for other protoberberine derivatives,63 nandinine (64) was not assimilated,62 and it follows then that (65) is probably converted into (67) by way of isocorypalmine (66). 

Speculations on the biosynthesis of berberine date back to the beginning of the century (121). Most of the early proposals recognized the structural relationship of the protoberberine alkaloids with the simpler benzylisoquinoline bases, from which it was supposed that they are derived. The additional carbon atom necessary for the formal conversion... 

Berberine chloride was evaluated for antimalarial activity against Plasmodium falciparum in vitro (two clones of human malaria Plasmodium falciparum D-6 [Sierra Leone clone] and W-2 (Indochina clone) and Plasmodium berghei in vivo (mice). The alkaloid exhibited an antimalarial potency equivalent to that of quinine in vitro, but was inactive in vivo. The results were consistent with those of others who have found berberine to be a potent inhibitor in vitro of both nucleic acid and protein biosynthesis in P. falciparum, and have demonstrated a strong interaction of berberine with DNA. In addition, the lack of in vivo antimalarial activity in mice observed with berberine and other protoberberine alkaloids agrees with clinical reports that have claimed berberine to be inactive as an antimalarial drug [228]. 

The biosynthesis of protoberberine alkaloids, including berberine, has been extensively studied, and all the enzymes of the biosynthetic pathway have been characterized (11,121,391,508). Interestingly the pathway leading to berberine in Berberis was found to be different from that in Coptis and Thalictrum (509). In the former species berberine is formed from columbamine, in the latter plant species from tetrahydroberberine (121). The production of isoquinoline alkaloids, including the protoberberine alkaloids, by plant cell cultures have been reviewed by Riiffer (390) and Ikuta (510). Table XXVI summarizes patents concerning the production of berberine by means of plant cell cultures. In Table XXVII a summary is given of the occurrence of berberine in some plant cell cultures. 

Protoberberine and Related Alkaloids.—Recent extensive work has allowed detailed description of the biosynthesis of protoberberine alkaloids, e.g. tetra-hydrocoptisine (67), and bases derived from them. ° Results of a study on the interrelationships of Corydalis incisa alkaloids provide supplementary information, particularly in regard to the intermediacy of compounds of type (69). ... 

Fig. 2. Alkaloid biosynthetic pathways are associated with a diverse variety of cell types. The tissue-specific localization (shaded) of enzymes and/or gene transcripts are depicted for the biosynthesis of tropane alkaloids in Atropa belladonna and Hyoscyamus niger roots (A), monoterpenoid indole alkaloids in Catharanthus roseus leaves (B), pyrrolizidine alkaloids in Senecio vernalis roots (C), pyrrolizidine alkaloids in Eupatorium cannabinum roots (D), benzyl-isoquinoline alkaloids in Papaver somniferum vascular bundles (E), and protoberberine alkaloids in Thalictrwn flamtm roots (F).

These vesicles could be detected in Berberis as well as in Coptis (ref. 27) and seem to be the general principle for the biosynthesis and the transport of protoberberines. Once reticuline has entered this vesicle its fate to be metabolized to protoberberine alkaloids is determined. Since the quaternary end products are not able to pass membranes these vesicles also seem to be the transport vehicles to the final storage compartment, the vacuole. Electron microscopic pictures show that they seem to fuse with the vacuole and release their contents into it (ref. 29) which strongly supports this assumption. 

Biosynthesis of the spirobenzylisoquinoline alkaloid ochotensimine (282) via the quinomethide intermediate (Scheme 49) was proposed by Shamma and Jones (7J0). On the basis of this hypothesis, several biomimetic transformations of phenolic protoberberines to spirobenzylisoquinolines have been realized by the base-induced rearrangement via the quinomethide. 

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