Glycosyl isothiocyanates

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). 

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

Scheme 65 Synthesis of an Octaantennary Mannoside Cluster by Reaction of a Glycosyl Isothiocyanate with a Dendritic Polyamine15001...

As has already been pointed out, the Finkelstein reaction can be conducted in situ in the absence of solvents. For example, alkylations of purine and pyrimidine bases with alkyl halides and dimethyl sulfate have been carried out by solid/liquid phase-transfer catalysis in the absence of any additional solvent [48], as have cyanation of haloalkanes [49] and / -eliminations [50]. Noteworthy is the synthesis of glycosyl isothiocyanates by the reaction of potassium thiocyanate with molten glycosyl bromide at 190 °C [51]. 

Thus, the synthesis of trehazolin and its analogues required two precursors, the glycosyl isothiocyanate or amine analogues thereof, and trehazolamine or isothicya-nate analogues, respectively. 

SCHEME 15.21 Preparation of p-linked aspargine glycoside 178 from glycosyl isothiocyanate 173. 

For the purpose of this chapter, three types of isothiocyanate derivatives of sugars are considered, depending on the location of the NCS group in the molecule glycosyl isothiocyanates, deoxyisothiocyanato sugars, and isothiocyanate conjugates. For a complete list of structures reported, see Tables I-III. 

The trimethylsilyl isothiocyanatc-tin tetrachloride system has been proposed55 as an alternative to the use of inorganic thiocyanate salts for the synthesis of glycosyl isothiocyanates. By applying this reagent, 1,2.3.4,6-penta-O-acctyl-a-D-glucopyranose was directly transformed into the corresponding (3-isothiocyanate in 80% yield. 

Although the transformation of glycosylamines (such as 15) into fully unprotected glycosyl isothiocyanates by reaction with thiophosgene was already reported in the 1970s,58 61 these compounds were later shown to be unstable,62 and no further chemistry has been reported. Hie synthesis of stable, fully protected hexopyranosyl isothiocyanates by the thiophosgene reaction was first reported by Fuentes Mota and coworkers.63 65 Hie reaction sequence involves a glycosyl enamine (for example, 16) as key intermediate which., after O-prolection (->17), is hydrolyzed under mild condi-... 

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