Trehalase inhibitor salbostatin has been completely synthesized by coupling of 1,5:2,3 dianhydro-D-mannitol and di-O-isopropylidene-α-valienamine followed by deprotection. Very recently, new trehalase inhibitor salbostatin (1) was discovered as a novel metabolite of Streptomyces albus, ATCC 21838, and the structure has been established mainly on the basis of ¹H NMR spectroscopic data. Salbostatin inhibits trehalase from porcine kidneys with an inhibition constant Ki = 1.8 × 10⁻⁷ M, and possesses a very unique pseudo-disaccharide structure composed of 2-amino-1,5-anhydro-2-deoxy-D-glucitol to which an unsaturated 5a-carba-sugar, α-valienamine (2) residue, is attached by way of an imino bridge. Similar pseudo-disaccharidic glycosidase inhibitors containing α-valienamine (2), validoxylamine A (3) and methyl α-acarviosin (4), a core component of acarbose, have been known so far. The former is a potent trehalase inhibitor and its dihydro derivative more likely mimicking substrate α,α-trehalose-structure exhibits also high inhibitory activity. We have been studying a structure-inhibitory activity relationship of this type of inhibitors and, especially, our interests now have been focused on trehalase inhibitors such as validoxylamine A (3) and trehazolin. In this paper, convenient total synthesis of salbostatin has been attempted in order both to confirm the structure proposed and to elaborate a general method for the preparation of salbostatin analogues. The method involves coupling of an anhydro sugar acceptor, 1,5:2,3-dianhydro-D-mannitol (6), with a versatile carba-sugar donor, 2,3:4,6-di-O-isopropylidene-α-valienamine (7). As anhydro sugar acceptor, we chose the unprotected 1,5:2,3-dianhydro-D-mannitol (6), which was readily derived (95%) by hydrogenolysis (10% Pd/C) of the known corresponding 4,6-O-benzylidene derivative (5). Removal of the benzylidene group of 5 seemed to enhance reactivity of the 2,3-epoxide and, hopefully, to improve desired regioselectivity of its cleavage by the bulky amine, owing to relief from the structural rigidity. Coupling of a slight excess of 6 (1.3 molar equivalent) and 7 was thus carried out conventionally in 2-propanol in a sealed tube for 4 days at 120°C. TLC showed as had been expected a formation of two coupling products. Chromatography of the mixture on a silica gel column with butanone-toluene (3:1, v/v) as an eluent afforded the diequatorial-opening product (8, 58%) and the diaxial-opening product (9, 25%), the structures of which were tentatively assigned on the basis of the ¹H NMR spectra. The spectrum (270 MHz, CDCl₃) of 8 was well resolved, being amenable to a first-order analysis. Thus, the coupled signals due to 1,1-H and 2-H appeared as a doublet of doublets (δ 4.08, J = 4.8 and 11.0 Hz), a triplet (δ 3.19, J = 11.0 and 11.0 Hz), and a doublet of doublets of doublets (δ 2.80, J = 4.8, 9.2, and 11.0 Hz), respectively, supporting an 1,5-anhydroglucitol structure of the sugar moiety. Preferential attack of the amine at C-2 may be due to the C-1 position being unsubstituted, and might be further rationalized by assuming that 6-hydroxyl group of 6 involves in stabilizing the favorable transition state that leads to diequatorial product. O-Deisopropylidenation of 8 was effected in aqueous 70% acetic acid for 1 h at 60°C to give, after purification by a column of Dowex 50W-X2 (H⁺) resin with aqueous ammonia, salbostatin (1) in 97% yield. The ¹³C and ¹H NMR spectra were in good accordance with those of an authentic sample. The synthetic 1 was further characterized as the hepta-O-acetyl derivative (1a), the ¹H NMR spectrum of which was shown to be superimposable on that reported. The present synthesis constitutes the first total synthesis of the inhibitor salbostatin (1), thereby confirming the structure proposed, and also provides one of the convenient methods for preparation of its analogues useful for elucidation of the structure-activity relationship.