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

Abstract

The protected tetrasaccharide (6) was synthesized in 77% yield by condensation of 1, 6-anhydro-2, 2', 3, 4', 6'-penta-O-benzyl-β-lactose (4) with the oxazoline derivative of lacto-N-biose I (5). The protecting groups of 6 were removed by the following series of reaction to provide lacto-N-tetraose (10) : debenzylation, acetylation, acetolysis, and de-O-acetylation. The synthetic product (10) was crystallized from aqueols ethanol as white needles, mp 225-228°, [α]21D+27° (4 min)→+21.3° (3 hr) (c=0.45, H2O). The homogeneity and the mobility of 10 were confirmed by the gel permeation chromatography using Bio-Gel P-4 column. The specific rotation and IR spectrum of 10 were similar to those of the natural material reported by Kuhn, Gauhe, and Baer [Chem. Ber., 86, 827 (1953)].