5-Hydroxytryptophan occurrence

Very little is known about the occurrence of 1-hydroxytryptamine and/or 1-hydroxytryptophan derivatives in living organisms. Many 1-methoxyindole derivatives have been isolated as natural products (87MI629, 88BCJ285, 92H1877, 93MI22) for the simple reason that they are stable under isolating processes. 

Ribeiro, P. and Webb, R.A. (1 984) The occurrence, synthesis and metabolism of 5-hydroxytryptamine and 5-hydroxytryptophan in the cestode Hymenolepis diminuta. Comparative Biochemistry and Physiology C 79, 159-164. 

---