The product was synthesized following general coupling procedure C, using 20 as the amine. The crude product was purified by silica gel (eluent 60:40 EtOAc-hexanes) to give the product as a white solid (48% The product was synthesized following general coupling procedure C, using Boc-D-Ser as the amino acid and 20 as the amine. The crude product was purified by silica gel (eluent 60:40 EtOAchexanes) to give the product as a white solid (57%