Over the past decade, various specific modifications of the primary hydroxyl groups of sucrose have been accomplished, including the synthesis of disubstituted sucroses in which substituents to C-6 and C-6' have been modifiedlp6 and various monosubstitutions made','. The synthesis of cyclic acetals by Khan et a1.9 has made it possible to select just one of the primary hydroxyl groups* in later modifications. We now report the synthesis of 6-thiosucrose ( 7) and 6-deoxysucrose ( 9) via the 4,6_isopropylidene acetal of sucrose.
Selective iodination of 2,3,1',3',4',6'-hexa-0-benzoylsucrose'
(3) with triphenylphosphine, iodine, and imidazole" gave 2,3,1',3',4',6'-hexa-0-benzoyl-6deoxy-6-iodosucrose (4) in 75% yield. Nucleophilic displacement of the iodine by potassium thioacetate" gave 6-S-acetyl-2,3,1',3'4',6'-hexa-O-benzoyld-thiosucrose (5), which was de-esterified with sodium methoxide in methanol'*, and treated with 1,4-dithiothreitol13, to yield crystalline 6-thiosucrose (7) in 48% yield from the iodo derivative.
The synthesis of 6deoxysucrose (9) was accomplished by direct hydrogenation of 4 in tetrahydrofuran, in the presence of Pd-C catalysti4, to give 8 in a yield of 85%. De-esterification of 8 with sodium methoxide in methanol gave 6deoxysucrose (9) in 80% yield.
In none of the steps of the syntheses were chromatographic methods used, as had previously been done in the synthesis of many modified sucroses1-4,6,8. Instead, we employed selective crystallizations, which greatly increased the amounts of material that we could obtain.