Thanks @elisafadda.bsky.social for all the suggestions. I can build the correct structure with glycam.org (which is actually correct compared to charmm-gui) but yes, conversion to CHARMM FF will be a pain. Lets see :D

Absolutly, we also see the 1C4 chair conformation as the equilibrium one, however independent from sulfation level. I think this comes naturally with L-fucose.

Thanks for the hint. I haven't because we would really like to stick to the CHARMM36 FF and Glycam is only giving glycam06, so the Amber FF version.

The picture shows a fucose monosaccharide that has an axial placed sulfated group at C2 (blue circle), although that should be equatorial.