Potato alkaloids, analysis

Morris and Lee1 analyzed potato alkaloids on octyl and octadecyl-type stationary phases. Using a mobile phase consisting of acetonitrile - water that contained small amounts of etha-nolamine (less than 0.1%), detection at 200 nm was possible. The separation of a-chaconine and a-solanine could be achieved on an octadecyl column with acetonitrile - water - ethanol-amine (45 55 0.1)(Fig.10.9e) or on an octyl column with the same solvent in the ratio (55 45 0.l)(Fig,10.9f). The alkaloids could also be separated on silica gel with this mobile phase in the ratio (77.5 22.5 0.05)(Fig,10.9g). In the case when solanidine was present in the extracts, the silica gel column was preferred. Hydrolysates of the a-chaconine and a-solanine could also be analyzed with the octadecyl column (Fig.10.9a-d). The systems could also be used for the analysis of potato extracts (Fig,10.9e-g). For a total glycoalkaloid analysis, the normal-phase system gave the fastest results (Fig.10.9h). 

Potato alkaloids. The cultivated potato (Solanum tuberosum L.) contains two major glycoalkaloids, a-chaconine and a-solanine. The two components both contain the C i steroidal aglycone solanidine they differ only in the sugar moieties included in the trisaccharide part. a-Solanine and a-chaconine form up to 95% of the glycoalkaloids present in potatoes. Data on occurrence, chemistry, analysis, and toxicology of the steroidal glycoalkaloids present in potatoes have been comprehensively reviewed (77, 75). 

The synthesis of triterpenoid saponins from the skeletons shown in Fig. 2 involves a series of further modifications that may include a variety of different oxidation and substitution events [9]. Very little is known about the enzymes and genes involved in the elaboration of the triterpenoid skeleton, although genetic and biochemical analysis of saponin-deficient mutants of plants is likely to accelerate the dissection of these processes [16]. Progress has been made in the characterisation of saponin glucosyltransferases (primarily for steroidal and steroidal alkaloid saponins), and the first of these enzymes (StSGT from potato) has been cloned. Since glycosylation at the C-3 hydroxyl position confers am-... 

Analysis and Biological Activities of Potato Clycoalkaloids, Calystegine Alkaloids, Phenolic Compounds, and Anthocyanins... 

This limited overview on the analysis of four classes of the following secondary potato metabolites is, except for anthocyanins, largely limited to our own studies of glycoalkaloids, calystegine alkaloids, and phenolic compounds. Because interest in these potato constituents arises from potential health benefits and occasional toxicity, we also include in this overview a brief discussion of these aspects that relate to composition and a description of experimental methods. The interested reader should consult the cited references for an entry into the extensive worldwide literature on the diverse analytical and biological aspects for these metabolites. 

Chromatographic analysis of glycoalkaloids can be performed in a number of ways (321,322). The intact compounds can be analyzed by GC after derivatization (323). After hydrolysis the aglycone skeleton can be examined by GC without the need of derivatization (324). For routine determinations of the glycoalkaloids present in potato tubers, HPLC is probably the method of choice. Column acidity caused by active silanol sites on the packing surface strongly influences the chromatographic separation of Solanum alkaloids. In fact, basic compounds react with... 

The mass-spectral fragmentation of solasodine has been discussed.49 A g.I.c. method has been described for the analysis of potato glyco-alkaloids.50 A study has been reported on the separation of Solanum and Veratrum alkaloids by h.p.l.c.51... 

The amino-type stationary phase was also used in more recent studies by Bushway 9 10. For the separation of a-chaconine and a-solanine in potato extracts, the mobile phase tetrahydro-furan - acetonitrile - water - methanol (50 25 15.5 9.5) was used, resulting in a considerably reduced analysis time when compared to the previously reported methods. For analysis of the alkaloids and their metabolites, the mobile phase ratio was changed to (55 30 10 5)(Fig.10.7). For separation of the lower glycosides from a-chaconine and a-solanine, a carbohydrate analysis column was used in combination with the mobile phase tetrahydrofuran - water - acetonitrile (55 8 37)(Fig.l0.8)10. 

The coefficient "a" is a characteristic of each variety it determines the position of the graphs on the y-axis and reflects the glycolkaloid concentration in the potato. Coefficient "b" determines the slope of the curves. Analyses of a broad spectrum of different potato varieties revealed that b averages -0.5 for a-solanine and -0.42 for a-chaconine, respectively (25). This correlation offers the possibility to calculate the alkaloid content for a certain size tuber on the basis of the results obtained from the analysis of any other tuber size. Glycoalkaloid contents (GA, and GA2) of different tuber sizes (weights m, and mj) are determined by the following equations ... 

Fig. 5A-C. Gas chromatograms obtained simultaneously by FID (A) and PND (B) for a potato extract spiked with C27-steroidal alkaloids, 5a-cholestane, sterols, and steroidal sapogenins. Attenuation FID 2, PND 2 . Post-analysis reprocessing of the raw data from A and B (subtraction of the FID trace from the PND trace) is shown in C. 1 Octacosane 2 5a-cholestane 3 solanthrene 4 cholesterol 5 solanidine 6 demissidine 7 solasodiene 8 stigmasterol 9 diosgenin 10 tigogenin 11 solasodine 12 tomatidine 13 tetratriacontane 14 jervine. Column fused silica, 50m x 0.22 mm i.d., CP Sil 5cb, film thickness 0.12um. Carrier gas H2, linear velocity 49cms" oven temperature 270°C (Van Gelder et al. 1988)...

Some Solanum glycoalkaloids have been characterized by GC-MS analysis of their permethyl derivatives (60, 170 cf. 370) and determined in living plants and herbarium specimens by use of a radioimmunoassay (371). Like digitonin and a-tomatine, the steroidal gjycoalkaloid mixture from potato (a-solanine and a-chaconine) is able to complex with 3/ -hydroxysterols in vitro (370) which can be used for the quantitative analysis of these alkaloids (379). 

During a survey of actinobacteria known to suppress the growth of Streptomyces scabies, the causative agent of potato scab disease, a series of six new phenazine alkaloids were isolated and characterized by Salomon and coworkers [95]. NMR analysis of the ethyl acetate and butanol extracts of the culture supernatant and mycelium suggested a suite of aromatic compounds that were ultimately determined to be glycosylated 1,6-disubstituted phenazines (107—112). The structure of the phenazine and the various substituents that were substituted at the 1- and 6-positions are shown below. The structures of these phenazines, with the exception of 111, are the first examples of diglycosylated phenazine alkaloids. 

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