first total synthesis is described of the α- d -glucosidase inhibitor acarbose (1a). 1,6-Anhydro-4′-O-(3,4-anhydro-6-deoxy-α- d -galactopyranosyl)-β-maltose (21), prepared from 1,6-β-maltotriose (3a), and (+)-4,7:5,6-di-O-isopropylidenevalienamine (28) gave two pseudo-tetrasaccharide derivatives separable as the per-O-acetyl derivatives (29 and 31) by chromatography, and their structures were established