A51493A is an anthracyclinone antibiotic with antimicrobial activities against Gram-positive bacteria[1].
References
[1] Paschal JW, et al. A51493A, a novel anthracyclinone antibiotic produced by a strain of Streptomyces humifer. J Antibiot (Tokyo). 1989 Apr;42(4):623-6. DOI:10.7164/antibiotics.42.623