Figure 1.

Reaction scheme for the de novo synthesis of GDP-l-fucose from GDP-d-mannose, involving 4,6-dehydratase (step 1), which produces a 4-keto-6-deoxy intermediate, 3,5-epimerization (step 2), and the final NADPH-dependent reduction of the 4-keto group (step 3). Expected products from the chemical reduction and hydrolysis of the 4-keto-6-deoxy intermediate, are also included.