Oligogalactofuranosides are essential glycoconjugates of the mycobacterial cell wall. The search for the biosynthetic origin of galactofuranoside residues has led to the discovery of an isomerase (UDP-Galactopyranose Mutase) that catalyzes an unusual ring contraction between UDP-galactopyranose and UDP-galactofuranose. The mechanism of this unique interconversion has attracted attention because of the unexpected role of the FAD cofactor. FAD seems to play the role of catalytic nucleophile by an unforeseen addition on the anomeric position of galactose. Importantly, the discovery of UGM inhibitors may lead to the development of novel therapeutic strategies for the treatment of tuberculosis.