12,13-Epoxy-3,23,2'-tri-O-acetyl-4''-O-isovaleryldemycinosyltylosin 122076-87-3 Sch 38646 Sch-38646 Tylosin, 23-O-acetyl-23-O-de(6-deoxy-2,3-di-O-methyl-beta-D-allopyranosyl)-12,13-epoxy-12,13-dihydro-, 2A,3-diacetate 4B-(3-methylbutanoate), (12S,13S)-