Glycoalkaloids a-solanine

Carman, A. S. Jr, Kuan, S. S, Ware, G. M.,Francis, O. J. Jr., Kirschenheuter, G. R. (1986). Rapid high-performance liquid chromatographic determination of the potato glycoalkaloids a-solanine and a-chaconine. J. Agric. Food Chem., 34, 279-282. 

Roddick, J. G., A. L. Rdnenberg, and S. F. Osman, Synergistic interaction between potato glycoalkaloids a-solanine and a-chaconine in relation to destabilization of cell membranes Ecological implications, J. Chem. Ecol., 14, 889-902 (1988). 

The fruit of a number of solanaceous plants, including tomato Lycopersicon esculentum), potato Solanum tuberosum) and eggplant Solarium melongena esculentum), have cholinesterase-inhibiting effects (Krasowski et al. 1997). They contain solanaceous glycoalkaloids o-solanine and o-chaconine, which are triglycosides of solanidine, a steroidal alkaloid derived from cholesterol. They are the only plant chemicals known to inhibit both acetlycholinesterase and butyrylcholinesterase, both in vitro and in vivo. 

In commercial potatoes (Solanum tuberosum) there are two major glycoalkaloids, a-chaconine and a-solanine, both trisaccharides of the common aglycone solanidine. These two compounds comprise about 95% of the glycoalkaloids in potato tubers. Their hydrolysis products, the p and 7 forms and solanidine, may also be present in relatively insignificant concentrations. The structures of these glycoalkaloids and their hydrolysis products are presented in Figure 6.1. 

Figure 6.1 Structures of potato glycoalkaloids a-chaconine and a-solanine, and hydrolysis products (metabolites).

Figure 6.2 A comparison of HPLC separation methods, (a) HPLC of a-chaconine and a-solanine in the flesh and the peel of one variety of potato. Conditions column, Inertsil NH2 (5 xm, 4.0 X 250 mm) mobile phase, acetonitile/20 mM KH2PO4 (80 20, v/v) flow rate, I.OmL/min column temperature, 20°C UV detector, 208 nm sample size, 20 (xL. (b) HPLC chromatogram of approximately 1 xg of each of potato glycoalkaloids and their hydrolysis products 1, solasonine (internal standard) 2, a-solanine 3, a-chaconine 4, P2-solanine 5, pi-chaconine 6, (32-chaconine 7, y-solanine 8, y-chaconine. Conditions column. Resolve Cl 8 (5 (xm, 3.9 x 300 mm) mobile phase, 35% acetonitrile/100 mM ammonium phosphate (monobasic) at pH 3 flowrate, I.OmL/min column temperature, ambient UV detector, 200 nm sample size, (c) HPLC chromatogram of the aglycones solanidine and solasodine. Conditions column Supelcosil C18-DB (3 (xm, 4.6x150 mm) mobile phase, 60% acetonitrile/10 mM ammonium phosphate pH 2.5 flowrate, 1.0 mL/min column temperature, ambient UV detector, 200 nm.

The two potato glycoalkaloids in the potato extract were identified as follows (a) comparison of thin-layer chromatography of standards a-chaconine and a-solanine and of samples of each peak collected from the HPLC column containing the individual glycoalkaloids and (b) HCl hydrolysis of the HPLC samples into sugars and the aglycon solanidine. These were identified by GLC-MS (Kozukue et al., 1999, 2008 Kozukue and Friedman, 2003). 

Friedman, M., McDonald, G. M., Haddon, W. F. (1993). Kinetics of acid-catalyzed hydrolysis of carbohydrate groups of potato glycoalkaloids a-chaconine and a-solanine. J. Agric. Food Chem., 41, 1397-1406. 

Smith, D. B., Roddick, J. G., Jones, J. L. (2001). Synergism between the potato glycoalkaloids a-chaconine and a-solanine in inhibition of snail feeding. Phytochemistry, 57,229-234. 

Figure 14.3 Potato glycoalkaloids. (a) is tomatine, a spirosolane and (b) solanine, a solanidane.

The function of these tomatinase in formae speciales that do not pathogenise tomato is unknown. One possible explanation could be the presence of tomatine or similar saponins in their host plant species. However, (i) tomatine has not yet been reported in these plants [2, 7, 9] and (ii) although some of these species contain small amount of tomatine and other saponins structurally related to tomatine (e.g. potato contains a- solanine and a-chaconine [2, 4, 9, 90]), these are inactive as inducers of tomatinase and, moreover, tomatinase cannot use any of these glycoalkaloids as substrate [89]. In addition, it is clear that tomatinase is not required for pathogenicity in these isolates, at least in the case of F. oxysporum f. sp. melonis, where some strains that are fully pathogens on muskmelon lack tomatinase activity [89]. 

An octadecyl stationary phase was used to separate the glycoalkaloids according to the number of glycosidic bonded hexoses in the molecule, and a stationary phase containing alkylamino groups was used to separate the glycoalkaloids a-chaconine, S-chaconine and a-solanine (Fig. 

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). 

Figure 11.3 Separation of potato tissue glycoalkaloids on an amino phase [reproduced with permission from K. Kobayashi, A.D. Powell, M. Toyoda and Y. Saito, J. Chromatogr, 331 (1989)]. Conditions sample, extract from young potato plantlets after solid-phase extraction pretreatment column, 30cm x 3.9mm i.d. stationary phase, [xBondapak NH2 mobile phase, ethanol-acetonitrile-potassium dihydrogenphosphate (3 2 1) UV detector, 205 nm. Peaks 1 = a-chaconine with Rq =/3-D-glucose, R2 — R3 —a-i-rhamnose 2 — a-solanine with Rl =/3-D-galactose, R2 = /3-D-glucose, R3 —a-L-rhamnose.

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 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 ... 

Solanidine see a-Solanine. o-Solanine, solanine a Solanum alkaloid, the chief toxic alkaloid of the potato (Solanum tuberosum), also present in other Solanum spp. It is a glycoalkaloid containing the aglycon solanidine (sola-nid-5-ene-3p-ol), M, 397.65, m.p. 218°C, [aJo -27° (CHCI3), and the trisaccharide p-solatriose (Fig.). Potato tubers contain no more than 0.01 % a-S., which is harmless in this quantity. Potato shoots contain 0.5 % c(. and therefore cannot be used as food. 

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