Amino acid phenylalanine is the precursor of all the following, except:
Tyrosine
Epinephrine
Thyroxine
Melatonin
Phenylalanine hydroxylase conves phenylalanine to tyrosine. The amino acid tyrosine is the staing point in the synthesis of the catecholamines and of the thyroid hormones tetra iodothyronine (thyroxine; T4) and triiodothyronine (T3). Tyrosine is also conveed into DOPA, dopamine, norepinephrine and finally epinephrine. Ref: Harper's Illustrated Biochemistry, 26th Edition, Pages 239, 255, 266-267; Textbook of Biochemistry By D M Vasudevan, 3rd Edition, Pages 185, 187