Benzo[h][1]benzopyrano[5,4,3-cde][1]benzopyran-5,12-dione, 6-hydroxy-1-methyl-10-[[2-O-(6-desoxy-3-O-methyl- .beta.-D-galactopyranosyl)-6-desoxy- 3,4-O-(phenylmethylene)-.beta.-D-galactopyranosyl]oxy]- NSC639831