A Kinase‐Independent One‐Pot Multienzyme Cascade for an Expedient Synthesis of Guanosine 5′‐Diphospho‐d‐mannose

Biomimetic synthesis routes towards the important natural d-mannosyl donor guanosine 5′-diphospho-d-mannose (GDP-Man) rely on kinase-catalyzed nucleotide triphosphate (NTP)-dependent phosphorylations of d-mannose (Man), to give d-mannose 6-phosphate or α-d-mannose 1-phosphate (αMan 1-P) as an intermediate product. A GDP-Man synthesis not requiring the kinase/NTP system would be practical and cost-effective. Here, we have developed a multienzyme cascade towards GDP-Man, characterized in that αMan 1-P was obtained by a diastereoselective phosphatase-catalyzed phosphorylation of Man. α-d-Glucose 1-phosphate (αGlc 1-P), prepared in situ through phosphorylase-catalyzed conversion of sucrose in the presence of inorganic phosphate, was used as an expedient phosphoryl donor. The incipient αMan 1-P and guanosine triphosphate (GTP) were converted into GDP-Man by a highly manno compared to gluco selective nucleotidyltransferase. Pyrophosphatase was additionally required to hydrolyze the pyrophosphate released from the GTP, thus driving the reaction towards GDP-Man. The enzymatic cascade was operated with the αMan 1-P and the GDP-Man formation decoupled from one another (sequential mode) or having all steps run concurrently (simultaneous mode). Detailed time course analysis revealed that kinetic pull due to the constant removal of the intermediate αMan 1-P in simultaneous-mode reactions was important to promote phosphorylation of Man from αGlc 1-P in high efficiency, avoiding loss of sugar 1-phosphates by hydrolysis. Under optimized conditions for the one-pot transformation involving four enzymes, 100 mM (67 g L−1) GDP-Man was prepared from 140 mM sucrose and phosphate, using 400 mM Man as the phosphoryl acceptor. The product was recovered by anion-exchange and size-exclusion chromatography in ≥95% purity in about 50% yield (100 mg). These results demonstrate for the first time the practical use of a phosphorylase-phosphatase combi-catalyst as an alternative to the canonical kinase for the anomeric phosphorylation of the sugar substrate in nucleoside diphospho-sugar synthesis. Phosphorylation from inorganic phosphate via the intermediate αGlc 1-P rather than from NTP, particularly GTP, appears advantageous specifically in cases where the sugar acceptor is a bulk commodity that can be applied in suitable excess to the phosphatase reaction.