(2S)-2-amino-5-[2-(4-hydroxyphenyl)ethylamino]-5-oxopentanoic acid (2S)-2-amino-5-[2-(4-hydroxyphenyl)ethylamino]-5-oxo-pentanoic acid (2S)-2-amino-5-[2-(4-hydroxyphenyl)ethylamino]-5-keto-valeric acid