1 Major peaks in the mass spectra of the 1,g-diene group of Erythrima alkaloids Intensity of peak as % of base peak (VI) 83 84 68 83 44 40 M+ 72 M+ -Me 45 50 50 46 44 49 33 32
By using cell-free preparations of rat liver it was shown that the removal of the 14alpha-methyl group (C-32) of steroids containing either a delta7(8) or a delta8(9) double bond is attended exclusively by the formation of the corresponding 7,14- and 8,14-dienes respectively (structures of types III and VIII). Cumulative evidence from a variety of experimental approaches had led to the deduction that delta8(14)-steroids are not involved as intermediates on the major pathway of cholesterol biosynthesis. The metabolism of [32-3H]lanost-7-ene-3beta,32-diol (structure of type I) results in the formation of radioactive formic acid, no labelled formaldehyde being formed. By using appropriately labelled species of the compound (I) it was found that the release of formic acid and the formation of 4,4-dimethylcholesta-7,14-dien-3beta-ol (strurcture of type III) were closely linked processes, and that in the conversion of compound (I) into compound (III), 3-beta-hydroxylanost-7-en-32-al (II) is an obligatory intermediate. Both the conversion of lanost-7-ene-3beta,32-diol (I) into 3beta-hydroxylanost-7-en-32-al (II) and the further metabolism of the latter (II) to 4,4-dimethylcholesta-7,14-dien-3beta-ol (III) exhibited a requirement for NADPH and O2. This suggests that the oxidation of the 32-hydroxy group of compound (I) to the aldehyde group of compound (II) does not occur by the conventional alcohol dehydrogenase type of reaction, but may proceed by a novel mechanism involving the intermediacy of a gem-diol. A detailed overall pathway for the 14alpha-demethylation in cholesterol biosynthesis is considered, and proposals about the mechanism of individual steps in the pathway are made.
The incorporation of (+)-and (-)-N-norprotosinomenine into erythraline and erythratine in Eryfbrina crista gall; has been investigated and the specific utilisation of the (+)-isomer has been demonstrated. Double-labelling experiments have shown that in the same system 5,6,8,9-tetrahydro-2,12-dimethoxy-7H-dibenz[d,f]azonine-3,11 -diol and erysodienone are also genuine precursors. The nature of the symmetrical intermediate shown to be involved in the conversion of (+> 4-norprotosinomenine into (5s) -erysodienone, is discussed. Later stages in the biosynthesis of erythraline have been investigated and shown t o follow the lines previously postulated. The point of formation of the methylenedioxy-group i s apparently not critical.THE incorporation of N-norprotosinomenine (I; R1 = R2 = H) into the aromatic Erythriivca alkaloids indicated that these latter compounds should be added to the already diverse range of alkaloids known to be derived from 1-benzyltetrahydroisoquinoline precursors. We have now rigorously established the role of N-norprotosinomenine as a precursor of the aromatic Erythriaa alkaloids.A characterjstic of genuinely enzyme-controlled re-? Part XX, preceding paper.
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