Armed and disarmed saccharides

This change in configuration is a high-energy transformation when cyclic protecting groups are present, and leads to the sugar being “disarmed”.

Further work has shown that the effect of 1,3-dioxanes and 1,3-dioxolanes on disarming sugars can be attributed to the electronics of the systems as well as torsional strain.

The loss of electron density at O-5 results in a destabilization of the oxocarbenium ion, slowing its formation, and “disarming” the sugar.

This increase in bond length decreases the inductive electron withdrawing ability of O-6, causing a higher rate of hydrolysis than the other two conformations.

This process can be repeated as many times as necessary to achieve an efficient synthesis of a desired oligosaccharide with minimal loss of material to undesired coupling.

This reacts with a donor that was disarmed, forming the oxocarbenium ion at a slower rate, producing the desired trisaccharide.