(2S)-2-[(2R)-2-[(4S)-4-[(2R)-2-[(4S)-4-[(2R)-2-[(4S)-4-amino-4-carboxybutanamido]-3-sulfanylpropanamido]-4-carboxybutanamido]-3-sulfanylpropanamido]-4-carboxybutanamido]-3-sulfanylpropanamido]-4-{[(1R)-1-[(carboxymethyl)carbamoyl]-2-sulfanylethyl]carbamoyl}butanoic acid