Neu5Ac or NANA, described as purple diamond (Neelamegham et al. 2019); 5‑N‑neuraminic acid is the most common sialic acid in humans. It is a strong acid (pKa 2.6) through the carboxylate group at C‑1 carbon (Varki et al. 2015). Its presence in a human milk oligosaccharide defines the group of sialylated acidic human milk oligosaccharides.