3(R)-[1(S)-Acetamido-2-ethylbutyl]-4(R)-guanidino-2(S)-hydroxycyclopentane-1(S)-carboxylic acid; (1S,2S,3R,4R)-3-[1(S)-(Acetylamino)-2-ethylbutyl]-4-[[amino(imino)methyl]amino]-2-hydroxycyclopentanecarboxylic acid