Synthesis of a bis(sialic acid) 8,9-lactam

Methyl [2-(trimethylsilyl)ethyl 5-acetamido-9-azido-4-O-benzoyl-3,5,9-trideoxy-D-glycero-alpha-D-galacto- 2-nonulopyranosid]onate was sialylated with methyl (ethyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-thio-3-(phenylthio)- 2,3,5-trideoxy-D-erythro-alpha-L-gluco-2-nonulopyranosid)onate to give the corresponding bis(sialic acid) derivative in 23% yield. Removal of protecting groups, reduction of the azido group to an amino group, and removal of the auxiliary thiophenyl group gave the desired bis(sialic acid) 8,9-lactam. Comparison of the H-1 NMR spectra and energy-minimized (MM3) structures of the bis(sialic acid) lactam with those of the corresponding bis(sialic acid) lactone showed the conformations of the two compounds to be very similar (RMS = 0.027 Angstrom).