56448-20-5 A-26771-B A26771B Antibiotic A 26771B BRN 5309307 BUTANEDIOIC ACID, MONO(16-METHYL-2,5-DIOXOOXACYCLOHEXADEC-3-EN-6-YL) ESTER Butanedioic acid, mono(16-methyl-2,5-dioxooxacyclohexadec-3-en-6-yl) ester, (6S-(3E,6R*,16S*))-