Natural Abundance ²H Nuclear Magnetic Resonance Study of the Origin of Raspberry Ketone

Abstract

The site-specific natural abundance deuterium distribution of raspberry ketone 3 obtained through a variety of methods has been determined through (2)H NMR spectroscopy. This technique provided a means of distinguishing between "natural" raspberry ketones biogenerated from 4-hydroxybenzalacetone (2), obtained from 4-hydroxybenzaldehyde of extractive botanical origin and acetone produced by sugar fermentation by reduction using baker's yeast and other microorganisms, and other raspberry ketone samples obtained in different "non-natural" ways. Of natural origin is also a commercial sample obtained in an unspecified manner. A mechanistic interpretation has been proposed to explain the difference of site-specific deuterium content between the examined samples.

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

“…Accordingly, carbinol 2 was converted by biological and chemical oxidation to raspberry ketone 1 and the isotopic composition of extractive raspberry ketone and of the two samples obtained from the natural precursor 2 by the two above-mentioned procedures was determined. The comparison of the present results with those previously acquired (Fronza et al, 1998) allowed a precise distinction of the origin, i.e., natural extractive, natural biogenerated from 3, and synthetic, of different raspberry ketone samples, as indicated in Figure 3.…”

“…The residue obtained upon evaporation of the organic phase was chromatographed on SiO 2 to provide, from increasing amounts of ethyl acetate in hexane, 4-butylphenol (10), purified by bulb-to-bulb vacuum distillation, 0.75 g (50%): 1 H NMR (250 MHz, CDCl3), δ 0.91 (3H, t, J ) 7.4 Hz), 1.33 (2H, m), 1.55 (2H, m), 2.53 (2H, t, J ) 7.7 Hz), 4.75 (1H, s br), 6.74(2H, d, J ) 8.5 Hz), 7.03 (2H, d, J ) 8.5 Hz). The following samples were examined: one sample of raspberry ketone 1 extracted from T. baccata (sample 1); one sample of raspberry ketone 1 obtained by Candida boidinii oxidation of the extractive carbinol 2 (sample 2); one sample of raspberry ketone 1 obtained by CrO3 oxidation of the extractive carbinol 2 (sample 3); one sample of raspberry ketone 1 obtained by Candida boidinii oxidation of synthetic carbinol 2 (sample 4); one sample of raspberry ketone 1 obtained by CrO3 oxidation of the synthetic carbinol 2 (sample 5); one sample of extractive carbinol 2, used for the bio-and chemical oxidation to raspberry ketone 1 (sample 6); one sample of synthetic carbinol 2 used for the bio-and chemical oxidation to raspberry ketone 1 (sample 7); one sample of benzoic acid 6 obtained by chemical oxidation of extractive raspberry ketone 1 (sample 8); one sample of 4-phenylbutan-2-ol obtained by deoxygenation of extractive 2 (sample 9); two samples of synthetic raspberry ketone 1 from an unspecified producer and from Aldrich (samples 10 and 11); two samples of raspberry ketone obtained from sample 10 by base and acid treatment, respectively, as reported (Fronza et al, 1998) (samples 12 and 13); one sample of synthetic raspberry ketone 1 obtained from sample 11 by NaBH 4 reduction, followed by CrO3 oxidation (sample 14); two samples of 4-butylphenol (10) obtained from synthetic raspberry ketone analyzed as samples 10 and 11 (samples 15 and 16).…”

“…The deuterium NMR spectra of raspberry ketone 1 were recorded on a Bruker ARX 400 instrument following exactly the experimental procedure described previously (Fronza et al, 1998). The spectra were run in two different solvents: (a) dioxane producing a good separation for the signals of the aromatic hydrogens and (b) the mixture dioxane/benzene in the volume ratio 0.6/3.0 in which the signals of the methylene groups are well separated.…”

“…In this context, two biological approaches to the natural modification of 4-(4-hydroxyphenyl)butan-2-one (raspberry ketone, 1), impact flavor of raspberry fruit (Schinz and Seidel, 1957), based on the oxidation of extractive 4-(4-hydroxyphenyl)butan-2-ol (2) and on the reduction of the natural unsaturated ketone 3, respectively, were recently proposed (Dumont et al, 1995;Fronza et al, 1996a) (Scheme 1). In connection with these findings, in a study designed to the determination of the origin of raspberry ketone the 2 H natural abundance NMR data of commercial materials sold as natural were compared with those of the samples produced by synthesis or biogenerated from 3 (Fronza et al, 1998). The significance of the latter findings was limited by the lack of a sample of extractive raspberry ketone 1 as standard.…”

Potentials of Raspberry Ketone as a Natural Antioxidant

“…RK is the key compound responsible for the fruity aroma of raspberries and is widely used as a fragrance and flavoring agent for cosmetics, perfumes, soft drinks, and foods [33]. Although RK content is highest in red raspberries at 0.001-4.20 mg/kg [34][35][36][37][38], it has also been found in small amounts (0.00081-0.7 mg/kg) in a variety of other sources such as yew (Taxus baccata L.) [39,40], the lips (labellum) of orchid flowers (Bulbophyllum apertum Schltr.) [41], brewed coffee (Coffea arabica L.) [42,43], and kiwi berry (Actinidia arguta Planch.…”