Chemical synthesis using enzymatically generated building units for construction of the human milk pentasaccharides sialyllacto-N-tetraose and sialyllacto-N-neotetraose epimer

• Dirk Schmidt and
• Joachim Thiem

Beilstein J. Org. Chem. 2010, 6, No. 18, doi:10.3762/bjoc.6.18

• by 6 catalyzed by N-iodosuccinimide and trifluoromethane sulfonic acid (as introduced by van Boom et al. [11]) gave the β,1-3-linked pentasaccharide 7 in 61% yield. About 5% of the corresponding α,1-3-linked compound and ca. 7% of the bis (β,1-3- and β,1-4-) linked octasaccharide were observed as

• give the β,1-4-linked pentasaccharide derivative 13 in 53% yield. In addition, the corresponding α,1-4-linked pentasaccharide was obtained in 8% yield. Finally, the azido group was reduced by the nickel boride method with sodium borohydride, nickel chloride and boric acid [12][13]. During this step

• partial cleavage of the tert-butyldiphenylsilyl groups was also observed. Complete removal was achieved with trifluoroacetic acid in dichloromethane. For characterization purposes, peracetylation was carried out to give the completely protected pentasaccharide 14 in 67% yield (Scheme 2). As evident from a