Sugar thiocyanates

Sugar thiocyanates rearrange more or less readily into the corresponding isothiocyanates.8,20 23 According to the first comprehensive article24 concerned with the isomerization of organic thiocyanates into isothiocyanates, halides may react either by an SnI or an Sn2 mechanism. The SnI mechanism gives rise to the thiocyanate, which may isomerize to an isothiocyanate. 

Z. Pakulski, D. Pierozynski, and A. Zamojski, Reaction of sugar thiocyanates with Grignard reagents. New synthesis of thio glycosides, Tetrahedron, 50 (1994) 2975-2992. 

Grignard reagents are thiophilic towards sugar thiocyanates, forming thiogly- osides with retention of configuration. 

Benedict s quantitative reagent (sugar in urine) This solution contains 18 g copper sulfate, 100 g of anhydrous sodium carbonate, 200 g of potassium citrate, 125 g of potassium thiocyanate, and 0.25 g of potassium ferrocyanide per liter 1 mL of this solution = 0.002 g sugar. 

The reactivity at the C-4 position of hexose and hexoside sulfonates has been demonstrated in the gluco and galacto series and could undoubtedly be extended to other sugars as well. In another example (25), methyl 2,3-di-0-benzoyl-4-0-p-tolysulfonyl-a-D-glucopyranoside (18a) was treated with potassium thiocyanate in N,N-dimethylformamide at 140°C. for 9 hours to give the C-4 epimeric thiocyanato derivative 19 in 34% yield. The corresponding 4-p-bromobenzenesulfonate (18b) however, afforded a 55% yield of 19 in only 2% hours of reaction time. 

Another main subject of research of Garcia Gonzalez, with the collaboration of J. Femandez-Bolanos, was the reaction of amino sugars with isothiocyanic acid derivatives. 2-Amino-2-deoxy-D-glucose hydrochloride and potassium thiocyanate were shown to give rise to 4-(D-arabino-tetritol-l-... 

Kochetkov and coworkers have reported [154—156] an efficient approach for the synthesis of 1,2-cis pyranosides employing 1,2-trcms-glycosyl thiocyanates as glycosyl donors and tritylated sugar derivatives as glycosyl acceptors (Scheme 4.5). This... 

The second- and oldest-method for the preparation of thionocarbamates on carbohydrate scaffolds consists of the condensation of thiocyanic acid, generated in situ from potassium thiocyanate and a protic acid, with an anomeric-free sugar to form the thermodynamically more stable five-membered ring OZT as the major compound (Scheme 2).27,28... 

OZTs from keto sugars. An original approach for the synthesis of OZTs from carbohydrate-based a-hydroxyketones was recently published by Silva et al.4Sa who investigated the reactivity of carbohydrate-based a-hydroxyketone in the presence of thiocyanic acid. 

C-3 in the unsubstituted compound.176,177 However, at the time of these experiments, only C-3 substitution had been observed with 2,3-anhydropentofuranosides, and the results of investigation of this reaction suggest that the amino sugar substituted at C-2 is the major product.184 With thiocyanate ion, substitution also occurs at C-3, leading to the thietane derivative, namely, methyl 3,5-anhydro-3-thio-a-D-xylofuranoside (59) but, as this compound was obtained in only 25% yield, the major pathway may involve 2-substitution, leading to products not characterized.178... 

Another type of heterocycle accessible from sugars by a one-step reaction was investigated by Zemplen after a German patent reported that D-glucose reacts with thiocyanate to give a compound thought to be D-gluconothiolactone.136 He soon established that the product... 

Iron. Excess iron in wines causes cloudiness, interferes with the color, and can impair flavor. The mechanism of ferric phosphate precipitation has been intensively studied, and numerous colorimetric methods have been developed. For routine purposes the color developed with thiocyanate is adequate (6,9), but many enologists prefer the orthophenanthro-line procedures (3, 4, 6, 22). Meredith et al. (Ill) obtained essentially the same results for iron using 2,4,6-tripyridyl-s-triazine (TPTZ) to develop the color. Atomic absorption spectrophotometry can be used but, as with copper, corrections for reducing sugar and ethanol are necessary (51). 

Investigations by Hough and coworkers134 have shown that 4-sulfonyloxy groups of aldopyranose derivatives can be displaced rather readily with thiocyanate and iodide ions this constitutes a potential route to 4-deoxy sugars. 

This article collates information on the reactivity of sugar isothiocyanates and isomeric thiocyanates, and illustrates some of the chemical properties that have contributed to the synthesis of nucleoside analogs,1719 and thio and deoxy sugars. 

The classical, Fischer7 synthesis of sugar isothiocyanates involves treatment of an acylated glycosyl halide with an inorganic thiocyanate in a polar solvent. Depending on the reactivity of the halide and the reaction conditions, either a thiocyanate or an isothiocyanate is formed directly. 

Isomerization of organic thiocyanates to isothiocyanates is also discussed in other articles.25 29 The first sugar isothiocyanate reported, namely, 2,3,4,6-tetra-O-acetyl-/3- D-glucopyranosyl isothiocyanate (2) was synthesized by Emil Fischer7 in 1914 by treatment of 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide (1) with silver thiocyanate in anhydrous xylene. It was also prepared by Muller and Wilhelms8 by thermal isomerization of the corresponding thiocyanate 3, obtained by treatment of 1 with potassium... 

The Fischer method7 for preparation of sugar isothiocyanates is general however, many modifications have been introduced, using, for example, nonpolar solvents and silver thiocyanate,29 33 lead thiocyanate,33 or ammonium thiocyanate,34 and potassium thiocyanate in acetonitrile in the presence of tetrabutylammonium hydrogensulfate.34 ... 

Another route to sugar isothiocyanates involves thermal isomerization of the corresponding thiocyanates. Ferrier and Vethaviyasar20,21 and, later, Guthrie and Williams22-23 reported the allylic rearrangement of unsaturated thiocyanates to isothiocyanates see formulas 9-14. 

In an article that collates information not extensively treated before, Z. J. Witczak (West Lafayette) describes the synthesis, chemistry, and preparative applications of monosaccharide thiocyanates and isothiocyanates the thiocyanate anion is an ambident nucleophile of great synthetic versatility in approaches to nucleoside analogs and to thio and deoxy sugars. 

NS 5%(suitable for ignition rather than for detonation) and b)K chlorate 55 Pb thiocyanate 45% E)Colored smokes K chlorate 22-33, dye 30-50, Na or K bicarbonate 3-10, confectioner s sugar or lactose 20-35, kerosene or paraffin oil 2-4, kieselguhr 0-4 red iron oxide 0-3% F) Plastic Bonded colored smoke K chlorate 23, dye 51, sugar 18 K bicarbonate 8% combined with 2.2 parts of polyvinyl acetate plasticized by dichloro-methane and dried by evapn G) Cap mixtures a)K chlorate 67, red P 27, S 3 pptd Ca carbonate 3%, bound with unspecified amt of gum water and b)K chlorate 61, red P 4, black Sb sulfide 21,pptd Ca carbonate 2 animal glue 12% H)Railroad torpedo K chlorate 40, S 16, sand(60 mesh) 37, binder 5 8r neutralizer 2% I)Whistling compns K chlorate 73-77, gallic acid 24-19 red gum 3-4%(Ref 26,pp 270-80)... 

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