| Abstract
| - The absolute configuration of the two natural diastereoisomers of 6β-hydroxyhyoscyamine has been determined usingvibrational circular dichroism (VCD) spectroscopy. The predicted VCD and IR spectra of (3R,6R,2‘S)-6β-hydroxyhyoscyamine (1) and (3S,6S,2‘S)-6β-hydroxyhyoscyamine (2) were calculated using density functional theory (DFT)with the B3LYP functional and 6-31G(d) basis set and considering the eight lower energy conformations of eachdiastereoisomer. In both cases, the first four conformers showed the N-Me group in the syn orientation, permitting theformation of a hydrogen bond between the hydroxy group at the tropane ring and the tertiary nitrogen atom. In additionthe eight conformers showed an intramolecular hydrogen bond between the hydroxy and carbonyl groups of the tropicester moiety. The calculated IR spectra of both molecules showed good agreement with the experimental spectra, whilecomparison of the experimental and calculated VCD spectra showed that the absolute configuration of dextrorotatory6β-hydroxyhyoscyamine is (3R,6R,2‘S), while the levorotatory isomer is (3S,6S,2‘S).
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