6-deoxy-6-iodo-, preparation

In view of the efficient inhibition of a particular crystalline glycan hydrolase by the epoxylbutyl -cellobioside 7 (n = 2), we decided to prepare the deoxy iodo derivative 21 to aid in the X-ray crystallographic analysis. We soon found that, although the alkene 22 was easily available as a direct precursor to our target, the epoxide functionality had to be introduced indirectly using bromo-hydrin 23 technology any direct oxidation of 22 invariably led to some loss of the iodine atom [23]. 

F rom 5-deoxy-5-iodo-1,2-0-isopropylidene-/ -l-arabinofura-nose (37). Anhydrous silver fluoride (600 mg.) was added to a solution of 300 mg. of 37 in pyridine (4.0 ml.), and the mixture was shaken at room temperature for 24 hours. Ether (4 ml.) was added, and the mixture was passed through a column of silica gel (1.5 X 12 cm.). The column was washed with ether/pyridine, 1 1 v/v. (10 ml.), and the effluent, which contained 5-deoxy-l,2-0-isopropylidene-/ -L-threo-pent-4-enofuranose (33), was concentrated to 4 ml. Acetic anhydride (0.2 ml.) was added, and the reaction mixture was kept at room temperature for 16 hours. Concentration afforded a sirup from which the last traces of solvent were removed by storage in high vacuum at 20°C. The sirup was distilled at 90°C. (bath) at 2.5 X HHmm. The distillate (110 mg., 51%), which crystallized on standing, had physical constants which were identical to material prepared as above. 

From 5-deoxy-5-iodo-1,2-0-isopropylidene- -d-xylofuranose (30). A solution of 1.14 grams of 30 in pyridine (8.0 ml.) was shaken at room temperature with silver fluoride (2.0 grams). The reaction was slower than with the corresponding 5-tosylate (22) and was complete after 72 hours. The reaction mixture was processed as described above to give a pale yellow sirup which contained, in addition to 28, three minor components. Distillation afforded pure material (0.4 grams, 75%) identical with material prepared as above. 

Many 5-alkyl-, 5-alkenyl-, and 5-alkynyl-l-(2-deoxy-2-fluoro- 5-D-arabin-ofuranosyl)pyrimidines (750 - 752 and 765 - 767) were prepared - " by condensation of 742 (or the equivalent, such as 743) with C-5-substituted pyrimidine derivatives, or by attachment of a C-fragment to C-5 of the existing nucleosides through their 5-iodo or 5-chloromercuri derivatives, or by further conversion of the attached C-5 substituent into another one. ... 

Unusually-substituted deoxy sugars are found in a number of biologically important natural products, and an application of iodoglycosylation for the preparation of these compounds is shown in Scheme 5.51 [142]. Protected glucals 1 or 14 were selectively converted into 2-deoxy-2-iodo-a-mannopyranosyl glycosides 56 or 57. The... 

Scheme 5.52 Preparation of 2-deoxy-2-iodo-(i-glycosy acetates and their use in formation of 2-deoxy-p-glycosides.

A number of enantiomerically pure chiral building-blocks, such as 292-294, have been prepared (270,271) by zinc-copper cleavage of 5-bromo-5-deoxy-2,3-0-isopropylidene-D-ribono-1,4-lactone, followed by reduction. Similarly, from the 5-iodo lactone analogue the enoic acid 295 was obtained by reaction with zinc/silver-graphite (272). 

Carbohydrate oxetanes have been prepared from deoxyiodo sugars without die use of strongly alkaline reagents. Thus, treatment of 5-deoxy-5-iodo-l,2-0-isopropylidene-a-D-xylofuranose with silver fluoride in cold pyridine afforded 3,5-anhydro-l,2-0-isopropylidene-... 

---