Antibiotic produced by the mold Aspergillus flavus from a Czapek-Dox medium supplemented with corn steep liquor or by Penicillium chrysogenum Q176 or by P. notatum strains: McKee, MacPhillamy, Proc. Soc. Exp. Biol. Med. 53, 247 (1943); Bush, Goth, J. Pharmacol. Exp. Ther. 78, 164 (1943); McKee et al., J. Bacteriol. 47, 187 (1944); Bush et al., J. Pharmacol. Exp. Ther. 84, 264 (1945); Fried et al., J. Biol. Chem. 163, 341 (1946); see also Wintersteiner under “Flavacidin” in Chemistry of Penicillin (Princeton, 1949). Prepn by hydrogenation of 2-pentenylpenicillin: Catch et al., GB 584852; Cook, Heilbron in Chemistry of Penicillin (Princeton, 1949). Characterization and antibacterial activity: Leigh, Nature 163, 95 (1949).