A PRECURSOR TO THE BETA-PYRANOSIDES OF 3-AMINO-3,6-DIDEOXY-D-MANNOSE (MYCOSAMINE)

S(N)2-type reaction of 3-O-(1-imidazyl)sulfonyl-1.2:5.6-di-O-isopropylidene-alpha-D-glucofuranose with benzoate gave the 3-O-benzoyl-alpha-D-allo derivative 2, which was hydrolysed to give the 5.6-dio 3. Compound 3 was converted into the 6-deoxy-6-iodo derivative 4 which was reduced with tributylstannane, and then position 5 was protected by benzyloxymethylation, to give 3-O-benzoyl-5-O-benzyloxymethyl-6-deoxy-1,2-O-isopropylidene-alpha-D-allofuranose (6). Debenzoylation of 6 gave 7, (1-imidazyl)sulfonylation gave 8, and azide displacement gave 3-azido-5-O-benzyloxymethyl-3,6-dideoxy-1,2-O-isopropylidene-alpha-D-glucofuranose (9. 85 %). Acetolysis of 9 gave 1,2,4-tri-O-acetyl-3-azido-3,6-dideoxy-alpha,beta-D-glucopyranose (10 and 11). Selective hydrolysis of AcO-1 in the mixture of 10 and 11 with hydrazine acetate (--> 12), followed by conversion into the pyranosyl chloride 13. treatment with N,N-dimethylformamide dimethyl acetal in the presence of tetrabutylammonium bromide. and benzylation gave 3-azido-4-O-benzyl-3.6-dideoxy-1,2-O-(1-methoxyethylidene)-alpha-D-glucopyranose (15). Treatment of 15 with dry acetic acid gave 1,2-di-O-acetyl-3-azido-4-O-benzyl-3,6-dideoxy-beta-D-glucopyranose (16, 86 %, yield) that was an excellent glycosyl donor in the presence of trimethylsilyl triflate. allowing the synthesis of cyclohexyl 2-O-acetyl-3-azido-4-O-benzyl-3,6-dideoxy-beta-D-glucopyranoside (17, 90 %). O-Deacetylation of 17, conversion of the product into the (1-imidazyl)sulfonic ester, and S(N)2 substitution with benzoate gave cyclohexyl 3-azido-2-O-benzoyl-4-O-benzyl-3,6-dideoxy-beta-D-mannopyranoside (18). which was reduced and N-acetylated to give cyclohexyl 3-acetamido-2-O-benzoyl-4-O-benzyl-3,6-dideoxy-beta-D-mannopyranoside (19).