3,9-Diazabicyclo[3.3.1]non-6-ene-3,6-dicarboxylic acid, 7-[2-[3-[[(1,1-dimethylethyl)dimethylsilyl]oxy]propyl]-5-thiazolyl]-9-methyl- , 3-(1,1-dimethylethyl) 6-ethyl ester