4-O-β-d-galactopyranosyl-3-O-methyl-d-glucose: A new synthesis and application to the evaluation of intestinal lactase

Abstract 4- O -β- d -Galactopyranosyl-3- O -methyl- d -glucose ( 1 , 3- O -methyl-lactose) has been prepared from benzyl 2,6-di- O -benzyl-4- O -(2,6-di- O -benzyl-3,4- O -isopropylidene-β- d -galactopyranosyl)-β- d -glucopyranoside ( 5 ) and from benzyl 2,6-di- O -benzyl-4- O -(2,3,4,6-tetra- O -benzyl-β- d -galactopyranosyl)-β- d -glucopyranoside ( 15 ). Partial benzylation of benzyl 3′,4′- O -isopropylidene-β-lactoside ( 4 ) gave 5 and partial benzylation of either benzyl β-lactoside ( 13 ) or benzyl hepta- O -acetyl-β-lactoside ( 24 ) gave 15 . All other products from the partial benzylation of 4, 13 , and 24 were also isolated and characterised. The hydrolysis of 1 in vitro by intestinal lactase was linear during 20 h; the V max was 5% of that with lactose and the K m was 120m m ( cf . 30m m for lactose). Oral administration of 1 to suckling rats led to urinary excretion of 3- O -methyl- d -glucose.