Eburnane alkaloids

Eburnane Alkaloids. A short and highly efficient synthesis of a key intermediate Wenkert Enamine (223) for the synthesis of Eburnane alkaloids such as vincamine has been reported (126,127). 

Szepesi and Gazdag studied the separation of 22 eburnane alkaloids on an octyl and octadecyl type of column. Optimal results were obtained on both columns with the mobile phase acetonitrile - 0.01 M aqueous ammonium carbonate (3 2). The octadecyl stationary phase gave better resolution than the octyl packing (Table 8.3, Fig. 8.3). The reversed-phase system was capable of separating the three different groups of eburnane alkaloids as well as separating... 

CAPACITY RATIOS, k, FOR EBURNANE ALKALOIDS ON OCTADECYL AND OCTYL SILICA PACKINGS WITH DIFFERENT ELUENTS54... 

Szepesi et al. reported an ion-pair separation of eburnane alkaloids on a chemically bonded cyanopropyl stationary phase. As counter-ion, di-(2-ethyl hexyl)phosphoric acid or (+)-10-camphorsulfonic acid were used in a mobile phase consisting of hexane - chloroform -acetonitrile mixtures (Table 8.8, 8.9). Because of the poor solubility of the latter pairing ion, diethylamine (Table 8.9) was added to the mobile phase. Addition of diethylamine considerably reduced the k1 of the alkaloids, due to suppression of the ionization of the alkaloids. However, due to the strong acidic character of the pairing ion, ion-pairs were still formed under these conditions. The camphorsulfonic acid containing mobile phases were found to be very useful for the separation of optical isomers (Table 8.10, 8.11, Fig.8.8) 6. It was also found that the selectivity of the system could be altered by choosing different medium-polarity solvents (moderator solvents) as dioxane, chloroform or tetrahydrofuran. The polar component of the solvent system affected peak shape. Based on these observations, a method was developed to analyze the optical purity of vincamine and vinpocetine. For the ana-... 

DEPENDENCE OF THE CAPACITY RATIOS (k1) MEASURED FOR EBURNANE ALKALOIDS ON THE DI-(2-ETHYL-HEXYL)PHOSPHORIC ACID (DHP) CONCENTRATION 3... 

SEPARATION OPTICAL ISOMERIC EBURNANE ALKALOIDS DEPENDENCE OF CAPACITY FACTORS (k ) AND SEPARATION FACTORS (r,.) ON THE CONCENTRATION OF CHLOROFORM AND ALCOHOLS IN THE ELUENT 8 J... 

Separation eburnane alkaloids (Table 8.14, 8.15) Micropak Si 10 or Lichrosorb Si60 5 un vBondapak CN 250x2 250x4.6 300x3.9 Hexane-CHCl.-ACN-MeOH(55 25 20 3) and various3other ratios Hexane-CHClACN(65 20 15),(7 2 1) (75 20 5) 3 55... 

Separation eburnane alkaloids vBondapak CN (Table 8.8, 8.9) 300x3.9 Hexane-CHCl,-ACN-di-(2-ethyl hexyl)-phosphoric acid in various ratios Hexane-i soprOH-DEA-camphorsulfonic acid in various ratios 73... 

It is of interest to compare the occurrence of the eburnane alkaloids in Malaysian Kopsia with that of the Chinese species (118]. From such a comparison, it would appear that the Malaysian Kopsia (and Leuconotis) species elaborate exclusively eburnane alkaloids of one enantiomeric group (20R, 21R or 20P, 2ip configuration) [18-20,58,110-112,115-119], while the Chinese species appear to elaborate eburnane alkaloids of the opposite enantiomeric group (205, 215 or 20a, 21a configuration) [118,120-122]. Notable exceptions are the dimeric alkaloids kopsoffinol and kopsoffine isolated from the Malaysian Borneo species Kopsia pauciflora [124] which were reported to be constituted from union of kopsinine and dihydroebumamenine units with the 20a, 21a configuration [vide infl-a). 

Farkas, M., Szombathelyi, Z., Karpati, E., Sohar, P., Kessel, M., Kreidl, J., Syntheses and cardiovascular activity of stereoisomers and derivatives of eburnane alkaloids, Liebigs Ann. Chem. 1993, 221-229. 

Eburnane alkaloid synthesis, 54 Elaeokanine A, 63-64 Ellipticine, 303 Enamine, 257... 

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