for the following products
1H-Purine-2,6-dione, 8-bromo-7-(2-butynyl)-3,7-dihydro-3-methyl- | 8-Bromo-7-(2-butynyl)-3,7-dihydro-3-methyl-1H-purine-2,6-dione | 8-Bromo-7-(but-2-ynyl)-3-methyl-1H-purine-2,6(3H,7H)-dione | 8-bromo-7-but-2-yn-1-yl-3-methyl-3,7-dihydro-1H-purine-2,6-dione and 3-Methyl-7-(2-butyn-1-yl)-8-bromoxanthine
