Benzyl-O-(4-O-benzoyl-2-brom-2,6-didesoxy-3-O-formyl-β-D-glucopyranosyl)-(1->3)-O-(4-O-benzoyl-2-brom-2,6-didesoxy-β-D-glucopyranosyl)-(1->3)-4-O-benzoyl-2-brom-2,6-didesoxy-β-D-glucopyranosid