1-Piperazinecarboxylic acid, 4-[2-[4-[[(1,1-dimethylethoxy)carbonyl]amino]-1,2,5-oxadiazol-3-yl]-1-eth yl-4-phenyl-1H-imidazo[4,5-c]pyridin-7-yl]-, 1,1-dimethylethyl ester