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

• A pentasaccharide analog has been synthesized for the first time.
• The plant growth regulation activity of this analog was studied.
• The activity data shows the analog can stimulate the growth of wheat coleoptile.

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 20 mg/L.

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