Glucose, a monosaccharide (sugar). Glucosylation (O-glucosylation at Ser and Thr, N-glucosylation of Asn) is a common post-translational modification of proteins.

Ser/Thr(Glc/GlcNAc)-peptides are best obtained by Fmoc-SPPS, as the O-glycosyl bond is acid-labile.