Chemical modification of trehalose. Part VI. The synthesis of analogues containing 2,2′-dideoxy-functions

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Abstract
Reduction of 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranosyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside with lithium aluminium hydride afforded, by nucleophilic trans-diaxial ring-opening, the 2,2′-dideoxy-D-ribo-trehalose derivative in high yield. Selective acid-catalysed removal of the benzylidene groups in the latter derivative could not be achieved because of the sensitivity of the glycosidic bond to acid hydrolysis, but they could be removed from the corresponding 3,3′-dibenzoate by oxidation with N-bromosuccinimide, affording 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-α-D-ribo-hexopyranosyl 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-α-D-ribo-hexo-pyranoside.This dibromo-derivative was then converted into the disaccharides 2,6-dideoxy-α-D-ribo-hexo-pyranosyl 2,6-dideoxy-α-D-ribo-hexopyranoside and 6-acetamido-2,6-dideoxy-α-D-ribo-hexopyranosyl 6-acetamido-2,6-dideoxy-α-D-ribo-hexopyranoside by standard methods, except that reductive dehalogenation was effected by hydrazine–Raney nickel, which is a more effective than catalytic hydrogenation for this purpose. Furthermore, 6-azido-2,6-dideoxy-3,4-di-O-mesyl-α-D-ribo-hexopyranosyl 6-azido-2,6-dideoxy-3,4-di-O-mesyl-α-D-ribo-hexopyranoside, derived from the foregoing 6,6′-dibromo-derivative underwent azide displacement of all four sulphonate groups to give a hexa-azido-disaccharide, 3,4,6-triazido-2,3,4,6-tetradeoxy-α-D-lyxo-hexopyranosyl 3,4,6-triazido-2,3,4,6-tetradeoxy-α-D-lyxo-hexopyranoside, which was reduced to the hexa-amine. 4,6-O-Benzylidene-2-deoxy-3-O-mesyl-α-D-ribo-hexopyranosyl 4,6-O-benzylidene-2-deoxy-3-O-mesyl-α-Dribo-hexopyranoside reacted with sodium azide in hexamethylphosphoric triamide to give two products: one was the product of normal SN2 displacement of both of the sulphonate groups and the other was an unsaturated product formed by normal displacement in one of the pyranosyl units and elimination, probably of the E2C type, in the other. 1 H N.m.r. spectroscopy was used for structural elucidation of these products.

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