Chaconines

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. 

The structural features of the solanum alkaloids are based on two primary skeletal configurations solanidane, with or without glycoside functionalities, as featured by the toxic and teratogenic steroidal alkaloids a-chaconine and a-solanine with the indolizidine type E-F ring (Figure 2.7a) and the spirosolane... 

Figure 2.7 Two steroidal alkaloids from Solanum spp. (a) a-chaconine, with teratogenic activity, and (b) tomatidine, non-teratogenic alkaloid.

Weltring KM et al (1997) Metabohsm of potato saponins a-solanine and a-chaconine by Gibberella pulicaris. Phytochemistry 46 1005... 

The levels of antifeedants can be raised safely only in plants such as forest trees or fiber crops, not in food plants for humans or livestock. Such problems have arisen inadvertently. For instance, a new insect-resistant potato cultivarhad to be withdrawn from the market because it contained high levels of the carcinogens solanine and chaconine (Renwick etal, 1984). In another example, an insect-resistant celery had 10 times the usual concentration of the carcinogen 8-methoxypsoralen (and related psoralens), which caused dermatitis in produce handlers (Seligman etal, 1987). 

Alkaloids are active bioagents in animal tissues. There is clear scientific evidence of this. Crawford and Kocan" " have tested the toxicity of steroidal alkaloids from the potato Solanum tuberosum), such as a-chaconine, a-solanine, solanidine and solasodine, and Veratrum alkaloid, jervine on fish. The results of Crawford and Kocan s research proved that rainbow trout exhibited a toxic response to chaconine, solasidine and solanine, while medaka only did so to chaconine and solanine. Embryo mortality was observed as an effect of toxicity in both species. Many other alkaloids are known to disturb or cause disorder in animal reproductive systems. For example, gossypol from cotton-seed oil is known as a clear reducer of spermatogenesis and premature abortion of the embryo. 

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.

GL Science, Japan). The mobile phase was acetonitrile/20 mM KH2PO4 (80 20, v/v). For the aglycon solanidine, the mixture consisted of acetonitrile/2.5 mM KH2PO4 (93 7, v/v). The flow rate was 1 mL/min at a column temperature of 20° C. The concentrations of a-chaconine and a-solanine in the potato extracts were calculated by comparison with the integrated peak areas of known amounts of the standards by a Hitachi chromato-integrator. 

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). 

Bodart, P, Kabengera, C., Noirfalise, A., Hubert, P, Angenot, L. (2000). Determination of a-solanine and a-chaconine in potatoes by high-performance thin-layer chromatography/densitometry. J. AOAC Int., 83, 1468-1473. 

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. 

Friedman, M., Craig, C. F., Butchko, C. A., Blankemeyer, J. T. (1997). Folic acid protects against potato glycoal-kaloid a-chaconine-induced disruption of frog embryo cell membranes and developmental toxieity. J. Agric. Food Chem., 45, 3991-3994. 

Friedman, M., McDonald, G. M. (1995). Acid-catalyzed partial hydrolysis of carbohydrate groups of the potato glycoalkaloid a-chaconine in alcoholic solutions. J. Agric. Food Chem., 43, 1501-1506. 

Kozukue, N., Tsuchida, H., Friedman, M. (2001). Tracer studies on the incorporation of [2-14C]-DL-mevalonate into chlorophylls a and b, a-chaconine, and a-solanine of potato sprouts. J. Agric. Food Chem., 49, 92-91. 

Rayburn, J. R., Bantle, J. A., Qualls, C. W. Jr., Friedman, M. (1995a). Protective effects of glucose-6-phosphate and NADP against a-chaconine-induced developmental toxicity in Xenopus embryos. Food Chem. Toxicol, 33, 1021-1025. 

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. 

Potato GAs usually belong to one of two structural types, either solanidanes or spirosolanes (Figure 14.3). Solanine and chaconine, both solanidanes, often comprise upwards of 90% of the total GA complement of domesticated potatoes, with chaconine often more abundant than solanine (Griffiths et al., 1997 Sotelo and Serrano, 2000). 

Many in the potato industry may be familiar only with solanine and chaconine, but estimates have been made that the potato family, including wild species, may contain about 90 GAs (Friedman and McDonald, 1997). In the course of LCMS characterization of small molecule diversity in tubers from diverse potato germplasm, we observed that GAs constituted a major source of diversity. 

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