Oligosaccharide Synthesis on Controlled-Pore Glass as Solid Phase Material

Mercaptopropyl-functionalized controlled-pore glass (MP-CPG, 2) was employed as a solid phase material for the synthesis of α(1-2)-connected trimannoside 16. As a glycosyl donor O-(3,4,6-tri-O-benzyl-2-O-phenoxyacetyl-α-d-mannopyranosyl)trichloroacetimidate (6) was employed which was readily obtained from d-mannose. Glycosylation of 2 and of intermediates 9 and 13 was performed with excess 6 in CH2Cl2 at -40 °C in the presence of TMSOTf as the catalyst (→ 7, 11, 15). For the removal of the temporary phenoxyacetyl (PA) protective group guanidine in DMF was used (→ 9, 13). Cleavage of products 7, 9, 11, 13 and 15 from MP-CPG was carried out with N-bromosuccinimide (NBS) in THF/MeOH in the presence of 2,6-di-tert-butylpyridine (DTBP) affording 8, 10, 12, 14, and methyl trimannoside 16, respectively.