The galactosyl derivatives Gal beta-Ser(N-Boc) and Gal beta-Thr(N-Boc) of N-Boc-protected serine and threonine were prepared with galactose or lactose as the glycosyl donor employing beta-galactosidase as the catalyst. Similarly, the mannosyl derivatives Man alpha-Ser(N-Boc) and Man alpha-Thr(N-Boc) were prepared with mannose as the glycosyl donor (equilibrium reaction) employing alpha-mannosidase as the catalyst.