Synthesis and plant growth regulation activity of α-d-ManpNAc-(1→2)-[α-L-Rhap-(1→3)-]α-L-Rhap-(1→4)-β-d-GlupNAc-(1→3)-α-L-Rhap, the repeating unit of O-antigen of Rhizobium trifolii 4s

The synthesis of a pentasaccharide 2 containing acetamido-2-deoxy-d-glucose and acetamido-2-deoxy-d-mannose related to the cell wall polysaccharide of Rhizobium trifolii 4s has been achieved by a [2+3] approach from commercially available l-rhamnose, d-glucose, and d-glucosamine as the starting materials. The target molecule was equipped with a p-methoxylphenyl handle at the reducing terminus to allow for further glycoconjugate formation via selective cleavage of this group. The bioassay suggested that the synthetic pentasaccharide 2 can stimulate the growth of wheat coleoptile similarly to indole-3-acetic acid (IAA), and promote the wheat seedling development before winter by seed treatment at a concentration of 20mg/L.