Enzymatic/Chemical Synthesis and Biological Evaluation of Seven-Membered Iminocyclitols

Abstract

Several polyhydroxyperhydroazepines have been obtained either by chemoenzymatic or chemical synthesis. Condensation of (±)-3-azido-2-hydroxypropanaldehyde and dihydroxyacetone phosphate (DHAP) in the presence of a DHAP dependent aldolase followed by treatment with acid phosphatase and an isomerase gave a 6-azido-6-deoxyaldopyranose, which upon reductive amination afforded the title compound. The iminocyclitols can also be obtained by chemical manipulations of aldopyranoses, protected as benzyl glycosides or diisopropylidene ethers. Thus, d-galactose leads to a meso-3,4,5,6-tetrahydroxyperhydroazepine, d-mannose to a derivative with a C2 symmetry axis, and N-acetylglucosamine to a 6-acetamidoiminocyclitol. Asymmetrization of the meso azasugar was carried out by chemical means, to yield a 3-methoxy-4,5,6-trihydroxyazepane. An attempted enzymatic synthesis of the methoxy derivatives of these azasugars was unsuccessful, leading, however, to both enantiomers of 1-deoxy-2-O-methylmannojirimycin. Some of these c...