Biosynthesis of Galactofuranose in Kinetoplastids: Novel Therapeutic Targets for Treating Leishmaniasis and Chagas' Disease

Figure 5

Proposed chemical mechanism for UGMs. Nucleophilic attack by the reduced flavin (1) leads to a flavin-galactose adduct (2). This step can either occur via an Sn1 or Sn2 reaction. Alternatively, the flavin can transfer one electron to a galactose oxocarbenium ion, forming a sugar and flavin radical that can also form the flavin-galactose adduct. Formation of a flavin iminium ion leads to sugar ring opening (4). Sugar ring contraction occurs by attack of the C4 hydroxyl to the C1-carbon (5). The final step is the bond formation to UDP (6).