Linagliptin Impurity J Catalogue L562375 CAS 2436762-89-7 M.W 349.18 M.F C14H13BrN4O2 Specifications FAQs 8-bromo-1,7-di(but-2-yn-1-yl)-3-methyl-1H-purine-2,6(3H,7H)-dione