US6649756B2 - Process Improvement in the Preparation of (4r, 5s, 6s)-3-[[(2r,3r)-2-[[[(s)-2-Amino-3-Methyl-1-Oxobutyl]amino]methyl]tetrahydro-3-Furanyl]thio]-6-[(r)-1-Hydroxyethyl]-4-Methyl-7-Oxo-1-Azabicyclo[3.2.0]hept-2-Ene-2-Carboxylic Acid