ANALYSIS OF THE KINETICS OF ISOMERIZATION OF SPIRO OXINDOLE ALKALOIDS

The isomerization of the spiro oxindole alkaloids mitraphylline, isomi traphylline, pteropodine, isopteropodine, speciophylline and uncarine F in water has been studied at several temperatures and the rate coeff icients have been determined. The effect of pH on the rate of reaction and the equilibrium composition has been investigated, The rate coeff icients 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 po lar solvents and show that protonation of the alkaloids inhibits the i somerization, The crystal structure of pteropodine has been determined .