Stereochemistry of C-methylation in the biosynthesis of rhododendrin in Alnus and Betula

Using differently labelled precursors, it was established that rhododendrin (3-(4-hydroxyphenyl)-1-methylpropyl-β- -glucopyranoside) is formed through the phenylpropane pathway via p-coumaryl alcohol, dihydro-p-coumaryl alcohol and C-methylation of the γ-C-atom of the C6---C3 unit with methionine supplying the methyl group. It was demonstrated that the pro-(S)-hydrogen atom of dihydro-p-coumaryl alcohol is replaced stereospecifically by the methyl group

Canadine synthase from Thalictrum tuberosum cell cultures catalyses the formation of the methylenedioxy bridge in berberine synthesis

An enzyme system catalysing the formation of the methylenedioxy bridge at ring A of (S)-canadine [ = (S)-tetrahydroberberine] from (S)-tetrahydrocolumbamine has been detected in microsomal preparations from different Ranunculaceae and Berberidaceae cell cultures. The cytochrome P-450 enzyme complex has been partly characterized from a protoberberine alkaloid producing Thalictrum tuberosum L. cell line. The enzyme complex consisting of a microsomal associated oxidase with a cytochrome P-450 reductase has a pH optimum at pH 8.5 and a temperature optimum of 40°. The apparent Km values are 33 μM for NADPH and 11.5 μM for tetrahydrocolumbamine

Columbamine, the central intermediate in the late stages of protoberberine biosynthesis

A specific methyltransferase which in the presence of S-adenosylmethionine [SAM] converts columbamine to palmatine has been demonstrated to occur in cell cultures. The enzyme acts only on the quaternary alkaloid as substrate, not on its tetrahydro derivative, which fact is in sharp contrast to previous claims

Stereospecificity of cinnamyl alcohol dehydrogenase and synthesis of stereospecifically labelled coniferyl alcohol

Using horse liver alcohol dehydrogenase, stereospecifically tritiated (R)- and (S)-(γ-3H)-coniferyl alcohol was synthesized. Using both of these substrates it was demonstrated that cinnamyl alcohol dehydrogenase from lignifying Forsythia tissue specifically removes the pro-R-hydrogen atom of coniferyl alcohol in the oxidation to the aldehyde. This also means that in the reverse reaction the A-hydrogen of NADPH is transferred to the Re-site of coniferyl aldehyde

The formation of corydaline and related alkaloids in Corydalis cava in vivo and in vitro

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