Transition metals and carbohydrates: the methyl-4,6-O-benzylidene-2,3-diazo-2,3-dideoxy-alpha-D-mannopyranoside skeleton as building block for new chiral nitrogen chelates

This paper describes a straightforward strategy for the synthesis of new nitrogen chelates by employing the chirality of readily available sugars. Thus, diimino and diamino ligands can be attained easily by using the methyl-4,6-O-benzylidene-2,3-diazo-2,3-dideoxy-alpha-D-mannopyranoside skeleton. The coordinating ability of one ligand has also been assessed by preparing a square-planar palladium complex [PdCl2(N,N-chelate)].

Preparation of 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride and its N-trifluoroacetyl derivative

Methyl 3-acetamido-4,6-O-benzylidene-2,3-dideoxy-alpha-D-arabino-hexopyranoside (5) was converted by treatment with N-bromosuccinimide into the 4-O-benzoyl-6-bromo derivative 6. Reduction with Raney nickel followed by catalytic transesterification of the resultant 4-benzoate 7 afforded methyl 3-acetamido-2,3,6-trideoxy-alpha-D-arabino-hexopyranoside (8), which could readily be converted into the 4-acetate 11. N-Decetylation of 7 and subsequent acid hydrolysis furnished 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride (9), the D enantiomorph of acosamine. The 3-benzamido analog (12) of 8 was prepared from 8 by N-deacetylation and subsequent benzoylation. Hydrolysis of 8 and 12 gave the 3-acetamido (10) and 3-benzamido (13) analogs of 9, which crystallized in the alpha anomeric form. 2,3,6-Trideoxy-3-trifluoro-acetamido-alpha-D-arabino-hexopyranose (15), a key intermediate for the synthesis of glycosidically coupled derivatives of 9, was obtained from 7 by saponification with barium hydroxide followed by N-trifluoracetylation of the resultant glycoside 14 and subsequent selective hydrolysis.