Enantiospecific syntheses of 3,4-dideoxy-oct-2-ulosonic acids

Ethyl 5,6,7,8-tetra-O-acetyl-3,4-dideoxy-d-arabino-oct-2-ulosonate and ethyl 3,4-dideoxy-5,6:7,8-di-O-isopropylidene-d-arabino-oct-2-ulosonate have been synthesised from peracetylated and bisacetonated aldehydo-d-arabinose respectively by a two stage procedure: Wittig reaction and catalytic hydrogenation. Deprotection of the blocked ethyl oct-2-ulosonate afforded the 3,4-dideoxy-d-arabino-oct-2-ulosonic acid (4-deoxy-KDO), isolated as its calcium salt in an overall yield of 37% from d-arabinose. Likewise reactions of d-xylose gave calcium 3,4-dideoxy-d-xylo-oct-2-ulosonate in an overall yield of 34%. Both calcium salts were derivatised as crystalline quinoxaline tetraacetates. Other routes attempted are also described.