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Tandem Staudinger–aza-Wittig reaction of primary azidodeoxy sugars with triphenylphosphine–carbon disulfide affords the corresponding primary deoxyisothiocyanato sugars in high yield. No products arising from O→N acyl migration or formation of dimeric carbodiimides were observed. Interestingly, a polymer-supported triarylphosphine can advantageously replace triphenylphosphine, thus limiting the purification step to a simple filtration process. The reaction also allows the preparation of 5-deoxy-5-isothiocyanato sugars, a hitherto unknown class of compounds, from the corresponding azide precursors. Secondary sugar azides bearing the azido group at an endocyclic carbon atom afforded much lower isothiocyanation yields under these reaction conditions.

The preparation of sugar ureas and thioureas by nucleophilic addition of water or hydrogen sulfide, respectively, to sugar-derived carbodiimides has been examined. Acetic acid efficiently catalysed the formation of ureas, whereas silica gel was found to be a more convenient catalyst in the case of the thioxo analogues. The procedures have been exploited in the development of an amine- and isocyanate-free synthesis of urea- and thiourea-tethered pseudooligosaccharides via the corresponding glycosylcarbodiimido sugars. The fully unprotected compounds adopted, preferentially, the (Z,Z) configuration at the pseudoamide bonds in water solution.

Methyl 6,7-dideoxy-7-isothiocyanato-α- d - gluco ( manno )( galacto )-heptopyranosides have been synthesized in four steps by homologation of the respective methyl hexopyranosides via the corresponding heptopyranosydurononitriles. Neither intra- nor intermolecular thiocarbamate formation was observed, even under rather strenuous acidic or basic conditions. The reducing derivative 6,7-dideoxy-7-isothiocyanato-α- d - gluco -heptopyranose was also a stable compound in aqueous solution in the absence of base. Formation of a six-membered intramolecular cyclic thiocarbamate was achieved in DMF solution in the presence of triethylamine. The title compounds are the first examples of stable fully unprotected monosaccharide isothiocyanates.

The synthesis of unsymmetrical sugar carbodiimides through aza-Wittig coupling of sugar derived iminophosphoranes and isothiocyanates is reported. The reaction is particularly fast and efficient in the case of phosphoranylide derivatives of 6-azido-6-deoxysugars and glycosyl isothiocyanates, and has been exploited in the one-pot preparation of (1 → 6)-linked pseudodi- and trisaccharides incorporating carbodiimide bridges as convenient precursors for the corresponding ureido, thioureido, and guanidino derivatives. Kinetic considerations suggest that sugar phosphazides, formed in the early stages of the Staudinger reaction of triphenylphosphine and sugar azides, are the reactive intermediates.

The branched, sulfur-linked tetrasaccharide S-(β- d - glucopyranosyl )-(1 → 3)-S-[(6-S-β- d - glucopyranosyl )-3,6- dithio -β- d - glucopyranosyl ]-(1 → 3)-S-3- thio - d - glucopyranose ( 9 ) has been conveniently prepared by S N 2 displacement of the triflate group in 1,2:5,6- di -O- isopropylidene -3-O- trifluoromethylsulfonyl -α- d - allofuranose with the sodium salt of 2,4- di -O- acetyl -3,6- di -S-(2,3,4,6- tetra -O- acetyl -β- d - glucopyranosyl )-1,3,6- trithio -β- d - glucopyranose ( 5 ). Conversely, reaction of the sodium salt of 5 with 1,2,3,4- tetra -O- acetyl -6- deoxy -6- iodo -β- d - glucopyranose afforded the positional isomer S-(β- d - glucopyranosyl )-(1 → 6)-S-[(3-S-β- d - glucopyranosyl )-3,6- dithio -β- d - glucopyranosyl ]-(1 → 6)-S-6- thin - d - glucopyranose ( 12 ).

Synthese des composes du titre a partir de tri-O-benzoyl-2,3,6 isothiocyanate de β-D galactopyranosyle et d'amino-2 acetophenone

The synthesis of 2,3,5-tri- O -benzoyl-β- d -ribofuranosylamine hydrobromide and 2,3,4,-tri- O -benzoyl-β- d -ribopyranosylamine from d -ribosylamine, via ribosylenamines, is reported. The reaction of 2,3,4-tri- O -benzoyl-β- d -ribopyranosylamine hydrobromide with thiophosgene in a basic medium yields, 2,3,4,-tri- O -benzoyl-α-( 7 ) and -β- d -robopyranosyl isothiocyanate ( 8 ). 5-Methyl-1-(2,3,4,-tri- O -benzoyl-β- d -ribopyranosyl)-4-imidazoline-2-thione was obtained by reaction of 8 with aminoacetone hydrochloride. Treatment of 7 and 8 with phenacylamine hydrochlorides gave the N -phenacyl- N ′ -(2,3,4,-tri- O -benzoyl-α- and -β- d -ribopyranosyl)thioureas. The 5-aryl-2-(2,3,4-tri- O -benzoyl-α- and -β- d -ribopyranosylamino)thiazoles were prepared by cyclodehydration with acetic anhydride and phosphoric acid of the corresponding phenacylribopyranosylthioureas.

Regioselective benzoylations of N -(2,2-diethoxycarbonylvinyl)-β- d -galactopyranosylamine ( 1 ) yielded 2,3,6-tri- O - ( 3 ) and 3,6-di- O -benzoyl- N -(2,2-diethoxycarbonylvinyl)-β- d -galactopyranosylamine ( 4 ), whereas, from the β- d - gluco analogue 5 , the 2,3,6-tri- ( 7 ), 3,6-di- ( 8 ), and 2,6-di- O -benzoyl ( 9 ) derivatives were obtained together with the fully esterified compounds ( 2 and 6 ). Treatment of 3 with bromine and of 7 with chlorine gave the 2,3,6-tri- O -benzoyl-β- d -glycopyranosylamine hydrohalides ( 10 and 11 , respectively), which reacted with thiophosgene to afford 2,3,6-tri- O -benzoyl-β- d -galactopyranosyl isothiocyanate ( 12 ) and the β- d - gluco analogue 14 , respectively. 3,6-Di- O -benzoyl-β- d -galactopyranosyl isothiocyanate ( 13 ) was prepared from 4 by successive treatments with bromine and thiophosgene.