N-acetylglucosamine is an acyl-amino sugar molecule. It is composed of a saccharide unit (glucosamine) linked with an acetic acid. In humans, GlcNAc is ubiquitously synthesised and involved in various metabolic pathways (PubChem). 

GlcNAc is one of the five building blocks of human milk oligosaccharides (HMO) (Bode, 2012). In the context of HMO synthesis, GlcNAc is referred to as monosaccharide and visualised as blue square (Neelamegham et al., 2019).