Stable Isotope Characterization of the <i>ortho</i>-Oxygenated Phenylpropanoids: Coumarin and Melilotol
作者:Elisabetta Brenna、Giovanni Fronza、Claudio Fuganti、Francesco G. Gatti、Valentina Grande、Stefano Serra、Claude Guillou、Fabiano Reniero、Francesca Serra
DOI:10.1021/jf0518507
日期:2005.11.1
The natural abundance H-2 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)(beta) 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)(beta) 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)) similar to (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 6180 determinations on 10 and on chroman 13. The bulk delta O-18 values in the extractive series of 10 are 20.3, 23.6, and 22.6 parts per thousand, while those of the aromatic oxygen are 2.3, 0.5, and -0.5 parts per thousand. In the synthetic sample, the values are 12.6 and 5.6%., respectively. As a final product, the reduction of 10 leads to the dihydroderivative 11. Both the baker's yeast reduction and the catalytic hydrogenation lead to a marked decrease of the deuterium content of 11, which is stronger for the beta-position than for the alpha-position.