Synthesis of 2-( p -Trifluoroacetamidophenyl)ethyl O -β-D-Mannopyranosyl-(l→2)- O -α-D-Mannopyranosyl-(l→2)- O -[α-D-Glucopyranosyl-(1→3)]- O -α-D-Mannopyranosyl-(1→2)- O -β-D-Manpopyranosyl-(1→3)-2-Acetamido-2-Deoxy-β-D-Gluco-Pyranoside, Corresponding to the Repeating Unit of the Salmonella Thompson , Serogroup C 1 O-Antigen Lipopolysaccharide, and of a Pentasaccharide Fragment Thereof