Initial rates of epimerization. Initial rates were measured using the following coupling conditions: AAs/HATU/TMP=1:1:12. The initial rates were as follows: Fmoc-Ser(Ac3GlcNAcβ)-OH (13), k = 0.37±0.01%/min; Fmoc-Ser(Ac3GlcNAcα)-OH (11), k = 0.27±0.01%/min; Fmoc-Ser(Ac3GalNAcα)-OH (7), k = 0.241±0.002%/min; Fmoc-Ser(Ac4Galβ1-3Ac2GalNAcα)-OH (9), k = 0.197±0.005%/min; Fmoc-Ser(Trt)-OH, k = 0.066±0.003%/min.