Codeinone, biotransformation

Biotransformations of morphinan alkaloids have been reported for plant, fungal, and mammalian enzymatic systems with emphasis on rather specific reactions such as the reduction of ketones, N- and O-demethylation, and perox-idative transformations. Furuya et al. used immobilized tissue culture cells of Papaver somniferum to accomplish the selective reduction of codeinone (135) to codeine (136) (207) (Scheme 30). Suspension cultures of a well-established cell line of P. somniferum were grown for one week as a source of cell mass for immobilization in calcium alginate. The cells continued to live in the alginate matrix for 6 months maintaining their biological activity. The reduction of co-... 

Scheme 30. Biotransformation of codeinone and morphine by immobilized P. somniferum cells and peroxidases.

Production can be increased by addition of precursors to the culture media, in which cases the precursors are not metabolized in the medium and, after uptake, appear in the right compartment of the plant cell. For C. roseus cultures, for example, it was found that increased indole alkaloid production was obtained after feeding with L-tryptophan, tryptamine, secologanin, loganin, loganic acid, or shikimic acid (20). Cell cultures have also been used for biotransformations, for example, the conversion of (-)-codeinone to (-)-codeine in Papaver somniferum cultures (100). For the tropane alkaloids a large number of precursor feeding and biotransformation studies with cultures of various solanaceous plants have been performed (see below). 

The first reported biotransformation by means of cell cultures of P. somniferum was the conversion of thebaine to codeine (453). As P. som-nifemm cell cultures only produced alkaloids derived from (5)-reticuline (e.g., sanguinarine. Fig. 9) but none of the alkaloids derived from (/ )-reticuline, Furuya et al. 461) administered (R,S)-reticuline to the cell suspension cultures. After 3 days the alkaloids were isolated. Two alkaloids derived from (5)-reticuline were identified cheilathifoline and scoulerine. A third alkaloid isolated was identified as pure (/ )-reticuline. Thebaine, morphine, and codeine were not metabolized by these cell cultures. However, the cells were capable of stereospecifically reducing codeinone to codeine. Tam et al. 462) also found the same bioconversion. Furthermore, the conversion of thebaine to neopine was reported. Codeine, neopine, papaverine, and D,L-laudanosoline were not metabolized. Enzymatic reduction of codeinone to codeine was also achieved with cell-free preparations of whole plants of both P. somniferum and P. bracteatum 464). Yeoman and co-workers 108,465) reported the use of in reticulate polyurethane immobilized P. somniferum cells for this bioconversion. 

Furuya et al. (468) reported the immobilization of P. somniferum cells in calcium alginate. CeUs remained viable for 6 months after immobilization. The cells were used in shake flasks and column bioreactors for the biotransformation of codeinone to codeine. The immobilized cells had a higher biotransformation ratio (70%) than suspended cells (61%). Most of the codeine formed was excreted into the medium (88%). The column bioreactor had a lower biotransformation ratio (42%). The cells in the bioreactor operated at 20°C and an aeration rate of 3.75 vvm (volume gas/volume broth/min) remained catalytically active for 30 days. In a more detailed study on the influence of substrate transport in immobilized cells, it was concluded that limitation of oxygen inside the beads caused deactivation of the cells. However, the reaction rate of the system was not affected by the limitation of oxygen transfer (469). Immobilization of P. 

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