(2S)-2-[[(2S)-2-[[(2S)-2-acetamido-4-methylpentanoyl]amino]-4-methylpentanoyl]amino]hexanoic acid
(2S)-2-[[(2S)-2-[[(2S)-2-acetamido-4-methyl-pentanoyl]amino]-4-methyl-pentanoyl]amino]hexanoic acid
(2S)-2-[[(2S)-2-[[(2S)-2-acetamido-4-methyl-1-oxopentyl]amino]-4-methyl-1-oxopentyl]amino]hexanoic acid