Chemical modification of lactose. XIII. Synthesis of lacto-N-tetraose.

Abstract

The protected tetrasaccharide (7) was synthesized in 79% yield by condensation of 1, 6-anhydro-2, 2', 3, 4', 6'-penta-O-benzyl-β-lactose (4) with the acetylated oxazoline derivative of lacto-N-biose I (6). The protecting groups of 7 were removed by the following series of reactions to provide lacto-N-tetraose (13) : debenzylation, acetylation, acetolysis, and de-O-acetylation. The synthetic product (13) was crystallized from aqueous ethanol as hygroscopic fine needles, mp 225-228°, [α]21D+27° (4 min)→+21.3°(3 hr) (c=0.45, H2O). The homogeneity and the mobility of 13 were confirmed by gel permeation chromatography using a Bio-Gel P-4 column. The specific rotation and IR spectrum of 13 were in good agreement with those of the natural product reported by Kuhn, Gauhe, and Baer [Chem. Ber., 86, 827 (1953)]. 13C-NMR spectral data for 1, 6-anhydro-β-lacto-N-tetraose (9) are also presented.