Proton and Carbon‐13 NMR Studies of Some Tryptamines, Precursors, and Derivatives: Ab Initio Calculations for Optimized Structures.

Proton and carbon‐13 NMR data are presented for 5‐methoxytryptamine, 1; 6‐methoxytryptamine, 2; N,N ‐diisopropyl‐5‐methoxytryptamine, 3, (5‐MeO‐DIPT); and N,N ‐diisopropyl‐5‐methoxyindole‐3‐glyoxylamide, 4, at 300 MHz ( 1 H) and 75 MHz ( 13 C) in CDCl 3 at ambient temperature. Compound 3, considered a potential hallucinogen, had been placed into Schedule I of the Controlled Substances Act, effective April 4, 2003, by the U.S. Drug Enforcement Administration. Compound 4 can serve as a possible precursor to 3. We believe that these are the first proton NMR assignments obtained at medium field (7 tesla) using selective homodecoupling and two‐dimensional homonuclear chemical shift correlation spectra (using one or more of the COSY45, COSY90, and COSYLR experiments) for rigorous aryl proton assignments in this group of compounds. Significant observed differences in the proton and carbon‐13 NMR spectra should allow facile distinction of the 5‐methoxy series, 1 and 3, from the 6‐methoxy series, 2. Energy minimizations to obtain optimized structures for each compound were performed at the Hartree–Fock level with the 6‐31G* basis set, and the resulting geometries are discussed. The presented geometry calculations appear to be the most accurate reported to date for 1 based on the basis set employed, and the first HF/6‐31G* structures for compounds 2, 3, or 4. Appreciable geometry differences in 3 and 4 for the pendant sidechain containing the N[CH(CH 3 ) 2 ] 2 moiety are noteworthy. Proximity of the carbonyl oxygens in 4 to H2 and H4 is suggested as a possible contributing factor in the deshielding of these protons in the NMR spectrum. [ABSTRACT FROM AUTHOR]