Stable Isotope Characterization of the ortho-Oxygenated Phenylpropanoids: Coumarin and Melilotol

The natural abundance 2H NMR spectra of extractive coumarin 10 and of its dihydroderivative melilotol 11 produced by baker's yeast reduction has been compared with synthetic materials. Diagnostic for the differentiation of 10 are the (D/H)β values, which are in the 128.1−133.6 ppm interval for the natural compounds but 258.5 and 189.8 ppm for the synthetic materials. Such a dramatic difference is also found for methyl cinnamate 12, which shows (D/H)β values of 127.2 and 515.8 ppm, respectively. In extractive 10, the ratio (D/H)4(para)/(D/H)6(ortho) = 1.24 is similar to that observed in structurally related salicin and methyl salicylate. Coumarin 10 is transformed in salicyl alcohol 9, providing diacetate 14, showing in the natural series the trend (D/H)3(meta) > (D/H)4(para) > (D/H)5(meta) ∼ (D/H)6(ortho). A similar trend is shown also by the synthetic 10. A clear distinction between extractive and synthetic 10 is obtained through δ18O determinations on 10 and on chroman 13. The bulk δ18O values in the ex...