Synthesis and structure of 4-hydroxy-N-isopropyltryptamine (4-HO-NiPT) and its precursors

Abstract

The title compound, 4-hydroxy-N-isopropyltryptamine (4) or 4-HO-NiPT (systematic name: 3-{2-[(propan-2-yl)amino]ethyl}-1H-indol-4-ol), C13H18N2O, was synthesized in three steps from 4-benzyloxyindole (1) (systematic name: 4-phenoxy-1H-indole), C15H13NO. (1) was treated with oxalyl chloride and isopropylamine to produce N-isopropyl-4-benzyloxy-3-indoleglyoxylamide (2) {systematic name: 2-[4-(benzyloxy)-1H-indol-3-yl]-2-oxo-N-(propan-2-yl)acetamide}, C20H20N2O3. (2) was reduced to generate 4-benzyloxy-N-isopropyltryptamine (3) or 4-HO-NiPT, which was characterized as its chloride salt 4-benzyloxy-N-isopropyltryptammonium chloride (3a) (systematic name: {2-[4-(benzyloxy)-1H-indol-3-yl]ethyl}(propan-2-yl)azanium chloride), C20H25N2O·Cl. Finally the benzyl group of (3) was removed via hydrogenation to generate 4-HO-NiPT. The crystal structures of the title compound and all three synthetic precursors are presented.