Stable Isotope Characterization of Raspberry Ketone Extracted from Taxus baccata and Obtained by Oxidation of the Accompanying Alcohol (Betuligenol)

Abstract

The natural abundance (2)H NMR characterization of raspberry ketone 1 extracted from himalayan Taxus baccata and of the accompanying (R) carbinol 2 is performed and compared with that of samples of 1 obtained from 2 by oxidation with Candida boidinii and CrO(3), respectively. The determination of the delta((13)C) and/or delta((18)O) values of the above extractive products and of benzoic acid (6) and 4-butylphenol (10), obtained from natural of synthetic 1, and of 4-phenylbutan-2-ol (8), prepared from extractive 2, allows a description of the labeling pattern of this set of products. A graph of (D/H)(3)/(D/H)(2) vs (D/H)(5)/(D/H)(4) (Figure 3) of the presently examined samples and of those previously characterized in the laboratory, including three commercial samples sold as natural, defines three areas, containing (a) the material of botanical origin and that produced from extractive 2 by biooxidation, (b) those produced by bioreduction of the unsaturated ketone 3, and (c) the synthetic samples.

A Labeling Study To Elucidate the Biosynthesis of 4-(4-Hydroxyphenyl)-Butan-2-one (Raspberry Ketone) by Nidula niveo-tomentosa

“…The addition of 3 mmol of sterile-filtered L- [2-13 C]phenylalanine liter Ϫ1 resulted in an empty AED chromatogram for the 13 C trace (data not shown), just like the addition of the 1-13 C-isotopomer in the preceding study (12). This indicated correct subtraction of the natural 13 C background but also nonincorporation of 1-and 2-13 C of the phenylalanine side chain. Accordingly, no isotope labeling of phenylbutanoid compounds was found by GC-MS. 13 C-labeled target compounds occurred only upon feeding of L-[3-…”

“…A previous time course study of the incorporation of ring-perdeuterated phenylalanine over 16 days did not show a pronounced isotope effect or scrambling of the added isotope label (12). The addition of 3 mmol of sterile-filtered L- [2-13 C]phenylalanine liter Ϫ1 resulted in an empty AED chromatogram for the 13 C trace (data not shown), just like the addition of the 1-13 C-isotopomer in the preceding study (12). This indicated correct subtraction of the natural 13 C background but also nonincorporation of 1-and 2-13 C of the phenylalanine side chain.…”

“…Signals derived from concurrently occurring lighter or heavier isotopes have to be subtracted electronically or manually. This is particularly true for 13 C measurement, as the natural abundance (1.108% of total C) is much higher than that for deuterium (0.0145% of total H). Because of the selective detection of isotopes, chromatographic overlap of isotopomers is irrelevant, a significant advantage over GC-MS. Quantification is carried out as usual by electronic integration of peak areas (HP ChemStation software).…”

“…The GC-AED technique provides rapid and selective, in part also simultaneous, measurement of most elements of the periodic table and of some stable isotopes including 2 H, 13 C, and 15 N, even in the presence of a large excess of the lighter isotope (23). The eluting compounds are atomized in a microwave-induced plasma tube.…”

“…Free or glycosidically bound 4-(4-hydroxyphenyl)-butan-2-one (p-HPB) has been found in numerous plant genera, such as Artemisia, Capparis, Dendrobium, Hippophae, Larix, Limonium, Pinus, Prunus, Rheum, Rubus, Saxifraga, Taxus, Vaccinium, Vanilla, and Vitis, and in the glands of the melon fly, Dacus cucurbitae, and of the North American beaver, Castor canadensis (4,8,9,13,17,20,24). Surface cultures of the basidiomycete Nidula niveo-tomentosa were reported as another source as early as 1980 (2).…”