Evidence on the structure of coyolosa. Synthesis of 6,6′-ether linked hexoses

The structure previously reported for coyolosa, a hypoglycemic substance isolated from natural sources, as a 6,6′-ether linked pseudo-disaccharide derived from allose, is incorrect since 6-O-(6-deoxy-d-allos-6-yl)-d-allose 10, synthesised by an unequivocal route, and its derived peracetate 11, both have spectral properties, which differ from those reported for coyolosa and its peracetate. A versatile synthesis has been developed for this type of compound, containing two carbohydrate moieties joined through an ether linkage at their primary centres, which involves the displacement of a primary carbohydrate triflate with a carbohydrate alkoxide, and it allows the preparation of both symmetrical and unsymmetrical representatives of this class of compound.