- Analysis of the kinetics of isomerization of spiro oxindole alkaloids
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The isomerization of the spiro oxindole alkaloids mitraphylline, isomitraphylline, pteropodine, isopteropodine, speciophylline and uncarine F in water has been studied at several temperatures and the rate coefficients have been determined. The effect of pH on the rate of reaction and the equilibrium composition has been investigated. The rate coefficients in water and in organic solvents correlate satisfactorily with the Dimroth-Reichardt solvent polarity parameter. The present results support the existence of a zwitterionic intermediate stabilized by polar solvents and show that protonation of the alkaloids inhibits the isomerization. The crystal structure of pteropodine has been determined.
- Laus, Gerhard,Broessner, Dagmar,Senn, Gilbert,Wurst, Klaus
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p. 1931 - 1936
(2007/10/03)
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- Alkaloids of Mitragyna parvifolia (Roxb) Korth. and their Transformations
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From the basic fractions of the leaves of Mitragyna parvifolia (Roxb) Korth, three oxindole alkaloids, mitraphylline, isomitraphylline and speciophylline Nb-oxide were isolated.A novel method has been developed for the transformation of mitraphylline, the major alkaloid of this species, to the corresponding heteroyohimbinoid base, ajmalicine without disturbing any chiral centre.Mitraphylline Nb-methoiodide, when treated with triethyloxonium fluoroborate, was converted to its corresponding imino-ether which on reduction with sodium borohydride in acetic acid furnished ajmalicine Nb-methoiodide.The latter could be transformed to ajmalicine by conventional procedure.
- Chatterjee, A.,Dhara, K. P.,Banerji, J.
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p. 1360 - 1363
(2007/10/02)
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