A-Fucoside

SCHEME 15.10 a-Fucosylation of serine and threonine building blocks with thioglycoside 95, which is protected with non-participating methoxybenzyl groups (Mpm), or with peracetylated 98 which, via anomerisation, gives the thermodynamically more stable a-fucosides 97 and 99. 

For instance a-fucosides and a-sialosides, which are both difficult to produce by means of classical carbohydrate chemistry, have been synthesized using the corresponding nitrophenyl glycoside donors by applying pig liver a-fucosidase [59] and the sialidase from Vibrio cholerae [60], respectively. 

Corey et al. reported a successful total synthesis of pseudopterosin E (116) through a crucial coupling reaction of 2-0-benzyl-3,4-di-0-p-methoxybenzoyl-a-L-fucosyl bromide (115) and catechol 114 the fucosylation of 114 with 115 proceeded in the complete position-selective and a-stereoselective manner, providing exclusively a-fucoside 116 (Scheme 20), and the a-stereoselectivity of the reaction was ascribed to the internal 1,4-remote participation of the p-methox-ybenzoyl group (Fig. 9) [72],... 

The p anomer spontaneously reacts with nucleophiles to give the desired a-fucoside. On the other hand, so-called disarmed donors such as AcaFucBr carrying electron-withdrawing protecting groups do not react under these eonditions. 

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