1-Azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid, 3-((2-(acetylamino)ethyl)thio)-6-(2-hydroxy-1-methylethylidene)-7-oxo-, (R-(E))- 6643 X 6643-X 82889-90-5 Antibiotic 6643-X