Glycosyl imidates, 47. Stereospecific synthesis of α‐ and β‐L‐fucopyranosyl phosphates and of gdp‐fucose via trichloroacetimidate

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Abstract
Reaction of the benzyl‐ and acetyl‐protected α‐trichloroacetimidates 1 and 6α with dialkyl and diaryl phosphates in the presence of traces of acid affords stereoelectively the thermodynamically more stable α‐L‐fucopyranosyl phosphates 2, 7 and 8, respectively, in high yields. The use of very pure, recrystallized dibenzyl phosphate results in the stereoeletive formation of the β‐L‐fucopyranosyl phosphates 3 and 9. In each case separation of the anomers is not required because of the very high stereoselectivity of the reactions. After deprotection the fucose 1‐phosphate 12 is coupled with GMP morpholidate 10 to yield GDP‐fucose 13. After the development of a new purification procedure for GDP‐fucose 13 we have obtained a very pure compound suitable for biochemical investigations. Analytical and preparative HPLC has been performed on reversed‐phase columns using a volatile buffer system (triethylammonium hydrogen carbonate) as the eluant.