The biosynthesis of NeuNAc begins with the formation of N-acetylmannosamine (ManNAc) from GlcNAc or UDP-N-acetylglucosamine (UDP-GlcNAc). In mammals, ManNAc is then phosphorylated to give ManNAc-6phosphate (ManNAc-6P). The second step involves the condensation of either ManNAc (in bacteria) or Mac-NAc-6P (in mammals) with phosphoenolpyruvate (PEP) to give NeuNAc or NeuNAc-9P, respectively. In mammals, NeuNAc-9P is then dephosphorylated to generate NeuNAc (see Figure 1 ). Hypocrea naturally degrades chitin almost exclusively to GlcNAc [22] . Therefore, the challenge was to engineer a pathway to convert GlcNAc to NeuNAc via ManNAc, which would enable the use of Hypocrea as a whole-cell catalyst.