Glycosyl thioureas

The preparation and reactions of V-thiocarbonyl carbohydrate derivatives, such as sugar isothiocyanates, thioamides, thioureas, thiocarbamates and their conjugates have been the subject of valuable comprehensive as well as specialized accounts, which should be consulted for details.198 

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Khorlin and coworkers92 95 reported that the reaction of isothiocyanates 2 and 53 with acetic acid, as well as benzoic acid, in the presence of triethyl-amine, leads to the formation of N-glycosylacetamides 175 or 176 in 35% yield, and, as coproducts, l,3-bis(glycosyl)ureas (177 and 179) and 1,3-bis(glycosyl)thioureas (178 and 180). This method has been employed in... 

Synthesis.—Diarylthioureas have been made from arylamines and either bis-(alkoxythiocarbonyl) disulphides or CSj and an alumina catalyst. The standard reaction of amines with isothiocyanates was used in the preparation of adamantyl- and glycosyl- thioureas. Benzoyl isothiocyanate, when treated with sterically hindered amines, e.g. Pr jNH or dicyclohexylamine, gives... 

Nucleotides, 1981, 5, 437) as having structure [31, R= -d-G1c(Ac)4]. Peracylated -D-glucopyranosyl, -D-galactopyranosyl, and a-L-rhamnopyranosyl isothiocyanates have been condensed with a variety of heterocyclic amines to yield Af-glycosyl-thiourea derivatives. ... 

Glycosidic thiol groups can be introduced into glycosyl bromides by successive reactions with thiourea and aqueous sodium disulfite (D. Horton, 1963 M. Cemy, 1961, 1963). Such thiols are excellent nucleophiles in weakly basic media and add to electrophilic double bonds, e.g., of maleic esters, to give Michael adducts in high yields. Several chiral amphiphiles have thus been prepared without any need for chromatography (J.-H. Fuhrhop, 1986 A). 

An acylated glycosyl halide, such as a 2,3,4,6-tetra-O-acetyl derivative, is treated with thiourea. The resulting pseudothiouronium salt is hydrolyzed with aqueous potassium carbonate to give the 2,3,4,6-tetra-0-acetyl-l-thio-(3-D-glucopyranose,48 which then is alkylated. 

Treating glycosyl isothiocyanates 415 with 5,6-diamino-1,3-dimethyl-uracil (416) gave thioureas 417, which on oxidative cyclization with N-bromosuccinimide afforded 5,7-dioxopyrimido[5,4- ][1,2,4]triazine nucleosides 418 (80MI1 82MI2). 

Glycosyl halides (7a-e) were stereoselectively transformed into l,2-tra s-thio-glycoses by i) (8a-d, 8j) a two-step procedure via the pseudothiourea derivatives [9,10a] the substitution of halide by thiourea is mostly a S l-type reaction since acetylated 1-thio-a-D-mannose (8b) was obtained from acetobromoman-nose (7b) [9cj ii) (8e-i) using thiolates in protic and aprotic solvents [10], or under phase transfer catalysis conditions [11]. Another approach involved the reaction of thioacetic acid with 1,2-trans-per-O-acetylated glycoses catalyzed with zirconium chloride [12]. The 1,2-trans-peracetylated 1-thioglycoses (8e-h) were obtained in high yield. No anomerized products could be detected in these reactions (Fig. 1). 

Synthesis of Thiourea-Bridged Glycosides from Glycosyl Isothiocyanates... 

Analogously, Bognar and coworkers45-46 prepared the same thiourea derivative 33, and synthesized some other N-glycosyl heterocyclic derivatives, such as thiazole 36, 1,3,4-thiadiazole 38, and 1,2,3,4-thiatriazole 39, using as the starting material isothiocyanate 2, or its ureido (34) or semicar-bazide (37) analogs. It is noteworthy that treatment of semicarbazide 37 with a nitroso acid at 0° afforded the 1,2,3,4-thiatriazole derivative 39 by addition and cyclization. The same 1,2,3,4-thiatriazole derivative 39 was obtained by treatment of isothiocyanate 2 with hydrazoic acid. 

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