C‐Linked Disaccharide Analogue of the Thomsen–Friedenreich (T)‐Epitope α‐O‐Conjugated to L ‐Serine

Condensation of a silylated β‐ D ‐galactopyranosylaldehyde ( 3 ) with isolevoglucosenone ( 4 ) in the presence of Et 2 AlI provided bicyclic enone 5 . Subsequent addition of BnNHOMe gave adduct 6 , which was converted into 4‐ O ‐acetyl‐1,6‐anhydro‐3‐ C ‐[(1  R )‐1,3,4,5,7‐penta‐ O ‐acetyl‐2,6‐anhydro‐ D ‐ glycer o‐ L ‐ manno ‐heptitol‐1‐ C ‐yl]‐2‐azido‐2,3‐dideoxy‐β‐ D ‐ galacto ‐hexopyranose after liberation of the 2‐amino group, its transformation into a 2‐azido moiety, desilylation, and peracetylation. Ring‐opening of the 1,6‐anhydro galactopyranosyl unit and O ‐glycosidation with Fmoc‐Ser‐O‐ t Bu afforded a 5:1 mixture of α‐ and β‐galactosides. Treatment with CH 3 COSH gave pure N ‐[(9 H ‐fluoren‐9‐ylmethoxy)carbonyl]‐{4,6‐di‐ O ‐acetyl‐3‐ C ‐[(1  R )‐2,6‐anhydro 1,3,4,5,7‐penta‐ O ‐acetyl‐ D ‐ glycero ‐ L ‐ manno ‐heptitol‐1‐ C ‐yl]‐2‐[( N‐ acetyl)amino]‐2,3‐dideoxy‐α‐ D ‐galactopyranosyl}‐ l‐ serine tert ‐butyl ester ( 2 ), a protected form of a C‐disaccharide analogue of the Thomsen–Friedenreich (or T) epitope (β‐ D ‐Gal p ‐(1→3)‐α‐ D ‐GalNAc p ) α‐O‐conjugated to L ‐serine.