Nada Vukojević

A novel route to 2-deoxy-2-iodo-d-mannopyranose derivatives

1,5-Anhydro-2-deoxy-D-hex-1-enitols are versatile synthons’*2. Various functional groups, such as chloro3, fluoro4-7, bromo8, or iodo’-I’, may be introduced at position 2 by either direct or indirect addition of suitable agents across the double bond. Iodination of o-glucal triacetate, using iodine and silver benzoate in dry benzene9*10, iodine and silver acetate in methanol’, N-iodosuccinimide in dry methanol’*, or iodonium bis(2,4,6-trimethylpyridine)perchlorate12, have been described, corresponding to the formal addition of alkyl or acyl hypoiodite across the double bond. However, the formation of free 2-deoxy-2-iodo sugars has not been described hitherto. We now report a formal electrophilic addition of “hypoiodous acid” to 3,4,6-tri0-acetyl-o-glucal’3 (1) and 3,4-di-0-acetyl-6-0-tosyl-D-glucal’4 (2). Depending on the buffer system used and the pH, a mixture of the 2-deoxy-2-iodo esters 3 of 5 together with the corresponding 2-deoxy-2-iodo sugars 4 or 6, or only 4 or 6, were obtained. The compounds obtained could be used for the preparation of 2-deoxy sugars or Brigl’s anhydrides. Thus, treatment of 1 or 2 with iodine in tert-butyl alcohol in the presence of acetate buffer (pH 5, room temperature, 3 h) gave a mixture of the 2-deoxy-2iodo-manno-esters 3 or 5 together with the corresponding Zdeoxy-Ziodo-a-o-mannopyranose derivatives 4 or 6, in the ratio 3 : 1. However, when this reaction was carried out in the presence of a phosphate or carbonate buffer (pH 6-7, room temperature, 3 h), the 2-deoq&iodo-a-D-mannopyranose derivatives 4 or 6 were the only isolable products (50-60%). The structures of 3-6 were confirmed by the NMR data (Table I> and [cu], values. The above procedure for the preparation of the 2-deoxy-2-iodo-cu-D-manno-

Synthesis and structure assignment of the diastereoisomeric 1,2-O-cyclohexylidene-α-D-xylofuranose 3,5-O-methylphosphonates and the related thiono- and selenono-phosphonates

The diastereoisomeric 1,2-O-cyclohexylidene-α-D-xylofuranose 3,5-O-methylphosphonates have been synthesized as a mixture and separated by chromatography to give the pure (RP) and (SP) forms. The related thiono- and setenono-phosphonates have also been obtained. Their 13C, 1H, 31P, and 77Se NMR spectra are discussed and NOE experiments have been used to determine the chirality at phosphorus.

Synthesis and Chemical Behaviour of 4, 5-Dideoxy-4, 5-Epithio-2, 3-DI-0-Methanesulfonyl-L-Xylose Dimethyl Acetal

ABSTRACT Selective substitution of the primary sulfonate group in 2, 3, 4, 5-tetra-0-methanesulfonyl-D-arabinose dimethyl acetal (1) gives 5-S-acetyl-2, 3, 4-tri-0-methanesulfonyl--5-thio-D-arabinose dimethyl acetal (2) which is further converted into the title compound (3). Reductive desul-furization of 3 afforded deoxy dimethyl acetal derivatives 5 and 6 in a low yield. Unsaturated monosaccharide derivative 7 was obtained as the only reaction product from 3 with triphenylphosphine. Catalytic hydrogenation of 7 gave dideoxy-sugar 6 in a satisfactory yield. Finally, epi-sulfide 3 with acetyl chloride afforded 4-chloro-4-deoxy derivative 4, which can be recycled into the starting 3.

Synthesis and Stereochemistry of Some new Derivatives of 1,2-O-Cyclohexylidene-α-D-Xylofuranuronic Acid

Abstract 1,2-O-Cyclohexylidene-α-d-xylofuranuronic acid (2) has been converted into its 3-O-acetyl derivative and consecutively to the corresponding acid chloride and ethyl ester. Direct reaction of 2 with ethanol in the presence of p-to-luene sulphonic acid gave the ethyl ester. Reaction of 2 with phosphorus pentachloride in dry ether gave the acid chloride of 1,2-O-cyclohexylidene-3-O-dichlorophosphoryl–α-d-xylofuranuronic acid. Conformational data have been obtained from 1H and 13C NMR measurements.