Calystegines

The only carbohydrate derivatives used for the synthesis of calystegines are those of D-glucose. 

31 in 81 % yield. Catalytic hydrogenation of 31 and subsequent LiAlHq reduction produced 

32 in 95% yield. lodination of 32 and subsequent elimination of hydrogen iodide with potassium ferf-butoxide afforded 33 in 77% yield, which upon acetolysis and deacetylation furnished the 6-deoxy-6-vinyl-D-glucopyranose 34 in 48% overall yield from 30. Oximation of 34 afforded the oxime 35, which underwent intramolecular olefinic nitrile oxide cycloaddition to afford the isoxazolines 36 (50%) and 37 (3%). Substitution of the hydroxyl group at C-5 in 36 with azido group via zinc azide mediated Mitsunobu substitution led to the azido-isoxazoline 38 in 79% yield. Hydrogenolysis of 38 furnished the enantiomerically pure hydroxymethyl calystegine B2 (39) in 45% yield. 

41 with an excess of reagents afforded a diastereoisomeric mixture of the a-chloroketones 

42 (84%) and 43 (88%), respectively, via the corresponding a-formyl-a-chloroketone intermediate. Reductive dechlorination of the a-chloroketones 42 and 43 with zinc in ethanol gave the ketones 44 and 45, respectively. Diisobutylaluminum hydride reduction of 44 and 45 afforded the corresponding alcohol 46 and 47 the reduction occurred quantitatively with 

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Scheme 5 Carbohydrate carbocyclization in the total synthesis of calystegine B2 (28) [27,28]...

The Staudinger/aza-Withg procedure has recently also been used by Mellet and Fernandez for the synthesis of calystegine B2, B3, and B4 analogues, emphasizing the growing importance of this methodology [12]. 

The Hanna group developed a rapid route to (+)-calystegine B2 (7-79) [35], a natural product with strong glycosidase enzyme-inhibiting properties [36]. As the key step, a triple domino procedure first published by Madsen and coworkers was em-... 

Scheme 7.21. Zinc-mediated domino reaction in the total synthesis of (+)-calystegine B2 (7-79).

Preparation of polyhydroxylated 6-oxanortropane glycomimetics (e.g. 32), structurally related to the glycosidase inhibitor family of the calystegines, was reported. The synthetic strategy involves the furanose/piperidine... 

A syndrome in livestock occurs with respect to Ipomoea species, which have been found to poison sheep in Australia and goats in Africa (Molyneux et ah, 1995). The analysis of 7. calobra and 7. polpha from Queensland showed that these plants contain not only calystegines B2 and Cl, but also swainsonine. An... 

Examples of other fluorinated inhibitors, mainly of D-glucosidases, are the 2-deoxy-2-fluoro derivative 106 (Scheme 27) of miglitol (A-hydroxyethy I -1 -deoxynoj i i i my-cin, 107),229 4-deoxy-4,4-difluoroisofagomine (108),230 3-deoxy-3-fluoro-calystegin B2 (109),231 the 1-deoxyfluoro derivative (110) of 2,5-dideoxy-2,5-imino-D-mann-itol,232 as well as the 3-deoxyfluoro analogue (111) of nonnatural l-DMDP (2,5-dideoxy-2,5-imino-L-mannitol)233 and the 3-deoxy-3,3-difluoro derivative (112) of 2,5-dideoxy-2,5-imino-D-glucitol (113).234 All of these are weaker inhibitors than the parent compounds. l,4,6-Trideoxy-6-fluoro-l,4-imino-D-mannitol (114) was prepared by Winchester and coworkers.210... 

Many alkaloids can be produced by root cultures. The most known applications are with anabasine, nicotine, harmine, harmaline, hyoscyamine, calystegine, scopolamine, Enzymes such as... 

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. 

Table 6.2 Glycoalkaloid and calystegine content of potato flesh, potato peel, and whole potatoes of eight potato cultivars... 

We validated and improved a GC-MS method to measure the two major potato calystegines A3 and B2 in freeze-dried potato peel and potato flesh samples (Friedman et al., 2003c). We used this method to analyze the same potatoes that we previously analyzed for glycoalkaloids (Table 6.2). 

Figure 6.4 illustrates the separation on GC-MS total ion chromatograms of calystegines A3 and B2 extracted from potato powders. Results of the GC-MS analyses for calystegines A3 and B2 are shown in Table 6.2. For whole potatoes, there is a 12-fold variation from lowest... 

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