Alkaloids precursor bioconversion

None of the precursors in the biosynthesis of quinoline alkaloids is available at a price lower than the alkaloids thus, bioconversion is not of interest, except for one step. This step would be the stereospecific conversion of quinidinone (obtained by oxidation of quinine or quinidine) to quinidine (8/ ,95) or quinine (85,97 ). This reaction offers the possibility of converting an excess of one of the naturally occurring stereoisomers to the other. It is now performed chemically as the demand for quinidine is higher than production from plant extracts. 

Bioconversion of Cinchona alkaloids is relatively less explored as compared to other natural products. The reason for this is the fact that none of the Cinchona alkaloid precursors are available at lower prices than the final alkaloids. The only exception is tryptophan however, it has no straightforward influence on the increasing production of alkaloids in cell cultures [267, 268]. 

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). 

In Table XIV through XVIII the occurrence of alkaloids in various types of cell and tissue cultures of Atropa, Datura, Duboisia, Hyoscyamus, and various other species in the family Solanaceae is summarized. From these data it is clear that the production of tropane alkaloids in cell suspension cultures is rather low. Only in root cultures has production similar to, or even higher than, the original plant been obtained. For this reason an extensive discussion on efforts to improve production in cell suspension cultures is not useful instead, we briefly deal with the application of plant biotechnology for the improvement of the tropane alkaloid-producing plants. Finally, we discuss the bioconversion of added precursors. 

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