Addition Reactions of Glycal Esters: Access to Glycosyl Donors of Kdo, d-<i>glycero</i>-d-<i>talo</i>- and d-<i>glycero</i>-d-<i>galacto</i>-2-Octulosonic Acid Residues
作者:Paul Kosma、Harold Sekljic、Gregor Balint
DOI:10.1080/07328309608005686
日期:1996.8
Addition reactions of O-acetylated glycal esters of Kdo mono-, alpha-(2-->8)- and alpha(2-->4)- linked Kdo disaccharide derivatives 1a-c with NIS in acetic acid afforded good yields of trans-diaxial as well as minor amounts of trans-diequatorial and cis-configured 2-O-acetyl-3-deoxy-3-iodo derivatives, which were efficiently reduced with Bu(3)SnH/AIBN to give the corresponding per-O-acetylated Kdo methyl ester derivatives. Similar reactions of 1a with NBS or NCS furnished the trans-diaxial 2-O-acetyl-3-bromo-3-deoxy- as well as 3-chloro-3-deoxy derivatives as the main products. Reaction of 1a with NBS in aqueous MeCN provided the 2,3-trans-bromohydrin derivative 11c, which upon treatment with DBU in MeCN gave the elimination product 11 and the alpha-2,3-anhydro derivative 12 as a suitable donor of glycosides with D-glycero-D-talo- or D-glycero-D-galacto configuration, respectively.