antibiotic PS 6

(5R,6R)-3-[2-(Acetylamino)ethylthio]-6-isopropyl-7-oxo-1-azabicyclo[3.2.0]hepta-2-ene-2-carboxylic acid

(5R,6R)-3-[2-(Acetylamino)ethylthio]-6-(1-methylethyl)-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid