NMR‐based conformational analysis of perezone and analogues

Abstract

Complete assignment of the (1)H NMR chemical shift and coupling constant values of perezone (1), O-methylperezone (2) and 6-hydroxyperezone (3) was carried out by total-line-shape-fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers.

The Folded Conformation of Perezone Revisited. Long Range nOe Interaction in Small Molecules: Interpretable Small Signals or Useless Large Artifacts?

“…Although there was a distinct possibility that the observed nOes could be originated by the formation of dimers, the presence of association in large extent was discarded by dilution experiments and by using DOSY experiments. From the structural perspective, our results confirm the existence of folded conformers for perezone in contrast with previous reports using NMR data and vibrational circular dichroism [19,20].…”

Essential Parameters for Structural Analysis and Dereplication by 1H NMR Spectroscopy

“…Further perspectives for the importance of adequate precision in HNMR data reporting are provided by reported case studies of molecules that have been subjected previously to full spin analysis, recently referred to as HiFSA ( 1 H iterative full spin analysis): 9 the monoterpene β-pinene, 10 the sesquiterpenoid perezone and its analogues, 11 the diterpenoid ent-3β-hydroxytrachylobane, 12 a series of diterpenoid lactones (ginkgolides) and flavonoids from Ginkgo biloba L., 13,14 several alkaloids such as huperzine A, 15 indole derivatives, 16 anatabine 17 analogues from Nicotiana species, tropane derivatives, 18 flavonoids 19 and flavonolignans, and dimeric phenylpropanoids ([iso]silybins) from Silybum marianum (L.) Gaertn., 20 as well as mono- and oligosaccharides. 21 …”

Antidiabetic and Antihyperalgesic Effects of a Decoction and Compounds from Acourtia thurberi

“…5). The structures were elucidated using one-and two-dimensional NMR spectroscopic techniques and by comparison of their spectroscopic and spectrometric data (see Supporting Information) with those previously described in the literature [23][24][25]. This is the first report on the presence of compound 4 in this species.…”