Modification of simmondsin and its demethylated
analogues
Rogers E. Harry-O’kuru *
New Crops Research,National Center for Agricultural Utilization Research,Agricultural Research Ser6ice,USDA, 1815N.Uni6ersity Street,Peoria,IL61604,USA
Accepted 12 May 2000
Abstract
Simmondsin and its analogues, demethyl-, didemethylsimmondsins (DMS/DDMS) and the 2%- and 3%-simmondsin ferulates are components isolable from jojoba (Simmondsia chinensis) seed meal. While the parent compound, simmondsin, is reported to exhibit anorexic properties, its demethylated analogues not only lack this behavior, they also have no identifiable market value. To create optimum utilization of these by-products, the goal of this research project was to chemically functionalize DMS and DDMS thereby transforming them to materials having economic potential. Thus using the intrinsic chemical properties of the olefin groups in DMS, simmondsin oxide analogues have been generated. It is expected these simmondsin oxiranes would provide platforms for expanding utilization of the otherwise waste materials of jojoba seed meal processing. Published by Elsevier Science B.V.
Keywords: Simmondsin; Demethyl simmondsin; Didemethyl simmondsin; Heptamethyl simmondsin; Heptaacetyl simmondsin; Hexaacetyl simmondsin; Lipase, 6,6-dihydroxy-1,1,4,4-tetramethyl-1,4-diazepin triflate; Oxone; 3-Chloroperoxybenzoic acid; Sim-mondsin epoxide
www.elsevier.com/locate/indcrop
1. Introduction
Simmondsin is a component of the seed meal of the jojoba plant (Simmondsia chinensis), a
semi-arid evergreen shrub that is native to the south-west of the United States and northsouth-western Mexico. Earlier work by Elliger et al. (1973), Booth et al. (1974), Van Boven et al. (1993), Van Boven et al. (1994) and more recently in this laboratory by Abbott et al. (1999) indicated that simmondsin is preliminarily co-extracted from the seed meal with its analogues demethyl-, didemethyl-, and its two ferulates before purifica-tion. And whereas pure simmondsin is reported to induce anorexic behavior when ingested in minute quantities (Cokelaere et al., 1992; Flo et al., 1998), the demethyl- and the didemethyl compounds
Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the stan-dard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.
* Corresponding author. Tel.: +1-309-6816341; fax: + 1-309-6816524.
E-mail address:[email protected] (R.E. Harry-O’kuru).
lack this biological activity and thus have no known market value (Scheme 1).
For the economic success of a new industrial crop, maximal utilization of its resources is cru-cial. Although these by-products do not constitute the bulk of the isolate, they do provide a track to new materials; thus the objective in this work was to maximize utilization of simmondsin isolates by modifying the demethyl- and didemethyl sim-mondsins (DMS/DDMS) either to the parent compound or to new derivatives by exploiting the intrinsic chemistries of the nitrile and olefinic functionalities in these molecules. To achieve a chemical modification of these functional groups, prior stabilization of the simmondsin nucleus is required because of the known sensitivity of sim-mondsin to both acid and alkaline environments (Elliger et al., 1973, 1974). Two processes concep-tually attractive for manipulating the carbon – car-bon double car-bond of protected simmondsin is a lipase-catalyzed epoxidation and the second pro-cess is oxirane formation mediated by dioxiranes as catalysts (Murray, 1989). The particular dioxi-rane triflate salt shown in Scheme 2 is claimed to be impervious to the Baeyer – Villiger reaction that often plagues dioxirane catalysts with the produc-tion undesired by-products.
In addition the dioxirane triflate was recently reported as an efficient catalytic route for trans-forming many organic functional groupings (Den-mark and Wu, 1997). The reaction conditions in the dioxirane method suggested neutral reaction conditions that could be suitable for manipulating simmondsin analogues to potentially useful com-pounds. In this paper, preliminary results of epox-idation of simmondsin and its demethylated analogues by means of both lipase and dioxirane catalysis are reported.
2. Materials and methods
2.1. Materials
Chromatographically purified simmomdsin and a mixture of the DMS/DDMS were from R&S Technologies (Wakefield, RI). Lipase SP435 was a gift from Novo Nordisk Bioindustries (Danbury,
CT). Dichloromethane (DCM), N,N -dimethylfor-mamide (DMF), chloroform and 1,3-dibromoace-tone were obtained from Fisher Scientific (Chicago, IL). Celite, N,N,N%,N% -te-tramethylethylenediamine (TMEDA), acetic an-hydride, triethylamine, silver (I) oxide, iodomethane, silver trifluoromethanesulfonate, 3-chloroperoxybenzoic acid and oxone, were from Aldrich (Milwaukee, WI). Fourier transform in-frared (FTIR) spectra were run on a Bomem MB-Series (Bomem, Quebec, Canada) spectrome-ter using Grams 32 software from Galactic Indus-tries (Salem, NH).1
H (400 MHz) and13
C (100.62 MHz) nuclear magnetic resonance (NMR) spectra were obtained on a Bruker ARX-400 (Bruker Spectrospin, Ballerica, MA) with a 5-mm dual proton/carbon probe. Melting points (m.p.) were determined on a Barnsted/Thermolyne Melt-Temp apparatus (Dubuque, IA) and are uncor-rected. Specific rotation [a]20
D measurements performed on a Perkin-Elmer Polarimeter model 341 (Perkin-Elmer, Norwalk, CT).
2.2. Heptamethylsimmondsin
Hz, 1H), 4.16 d (J=7.7 Hz, 1H), 3.68 m (1H), 3.55 s (1H), 3.53 s (3H), 3.52 s (3H), 3.49 dd (J=4.4, 3.18, 4.5 Hz, 2H), 3.45 t (J=2.6 Hz, 2H) 3.43 s (3H), 3.41 s (3H), 3.34 s (3H), 3.33 s (3H), 3.26 s (3H), 3.17 bm (2H), 3.05 m (3H), 2.25 m (1H), 1.60 m (1H). 13C NMR (CDCl3) d: 162.5, 161.9, 116.1, 103.1, 101.9, 99.4, 95.6, 95.2, 86.4, 83.4, 83.3, 83.2, 80.2, 79.1, 79.0, 75.6, 74.8, 74.7, 74.6, 71.2, 60.7, 60.5, 60.4, 60.3, 60.29, 59.03, 58.65, 58.30, 56.95, 36.40, 31.36, 31.22, 31.06, 30.84. Compare 13
C NMR (CD3OD of DMS/ DDMS unmodified) d: 166.73, 166.71, 117.6,
117.4, 104.4, 104.0, 94.93, 94.61, 79.46, 77.99, 77.95, 77.68, 76.87, 76.80, 74.70, 71.98, 71.31, 71.11, 71.08, 70.43, 62.61, 62.29, 58.28, 58.15, 35.13, 31.83.
2.3. 3:2%,3%,4%,6%-Penta-O-acetylsimmondsin
To 99% simmondsin (10.0 g, 26.6 mmol) in a dry 100 ml round-bottomed flask was added ace-tic anhydride (70.0 ml) and triethylamine (5.00 ml). The reaction was stirred at room temperature until thin layer chromatography (silica gel, ethyl acetate – methanol 4:1) indicated no starting mate-rial. The reaction mixture was diluted with ethyl ether, washed sequentially with saturated solution of NaHCO3(100 ml×3), saturated NaCl solution (100 ml×2), dried over anhydrous Na2SO4 and
concentrated to yield a light yellow syrup (13.8 g, 86.8%), [a]20
D=D−41.84° (c 1.14, CH2Cl2). FTIR (cm−1): 3066, 2941, 2832, 2223, 1754, 1641, 1432, 1374, 1225, 1170, 1121, 1065, 1042, 954, 909, 846, 823, 750, 735, 699.
2.4. Hepta-O-acetyl-/hexa-O-acetylsimmondsins
In a flame-dried 250 ml round flask equipped with a magnetic stirrer was placed a dry mixture (3:5) of DMS/DDMS (10.0 g, 28.2 mmol). Reagent grade acetic anhydride (120 ml) and dry triethylamine (5.0 ml) were added and the reac-tion mixture was stirred at room temperature until complete acylation was attained, 15 h. The reaction mixture was then diluted with ethyl ether (150 ml), washed with saturated NaHCO3 solu-tion (100 ml×3), then with saturated. NaCl solu-tion and dried over anhydrous Na2SO4. The dried solution was concentrated in vacuo to yield 16.8 g, (91%), [a]20
D= −21.47°C (c 3.86, CH2Cl2). FTIR (cm−1): 3459vw, 2943vw, 2224w, 1756vs, 1644w, 1432vw, 1374m, 1233vs, 1173w, 1052m, 754vw, 698vw. 1
H NMR (CDCl3) d: 5.45 d (J=
2.2 Hz,1H), 5.44 d (J=2.0 Hz,1H), 5.25 m (1H), 5.09 m (3H), 4.82 m (2H), 4.66 t (J=7.5, 7.8 Hz, 1H), 4.28 m (1H), 3.95 m (1H), 3.65 m (1H), 3.29 s (3H), 2.45 m (1H), 2.05 s (21H), 1.83 m (1H), 1.62 m (1H). 13C NMR (CDCl
3) d: 170.9,170.4, 170.0, 169.7, 169.3, 169.2, 169.0, 168.8, 168.3, 168.1, 158.9, 158.7, 115.3, 115.2, 102.3, 101.3, 96.16, 76.82, 76.08, 74.79, 74.30, 72.85, 72.80, 72.71, 72.08, 70.92, 68.84, 68.19, 68.03, 67.96, 67.79, 61.14, 61.08, 56.67, 33.0, 30.82, 20.79, 20.74, 20.58, 20.50, 20.48, 20.46, 20.42, 20.38. 13C NMR (CD3OD of DMS/DDMS) d: 166.73,
166.71, 117.6, 117.4, 104.4, 104.0, 94.93, 94.61, 79.46, 77.99, 77.95, 77.68, 76.87, 76.80, 74.70, 71.98, 71.31, 71.11, 71.08, 70.43, 62.61, 62.29, 58.28, 58.15, 35.13.
2.5. Preparation of 6,6-dihydroxy-N,N,N%,N%
-tetramethyl-1,4-diazepin triflate
TMEDA (99%, 13.86 g, 119 mmol) dissolved in dry acetone (80.0 ml) was placed in a 500 ml flame-dried round flask containing 200 ml of ace-Scheme 1.
tone. To the stirred solution was added 70% 1,3-dibromoacetone (25.0 g, 81.0 mmol) in 80 ml acetone dropwise under N2and stirring continued until no more precipitate formation was observed. The precipitate was filtered and washed with ace-tone (100 ml×3) and the light brown solid was dried in vacuo to yield 34.8 g of needles of the crude dibromosalt, m.p. 160.9 – 161.5°C dec. From this intermediate 16.59 g was dissolved in deionized water (150.0 ml) with stirring and silver triflate (22.8 g, 2 equivs) added in one portion. Stirring was continued for 4 h after which the silver halide was filtered off through celite. The filter cake The filter cake was washed with water (20 ml×2) and the combined filtrate and wash-ings was freeze-dried to give a quantitative yield (23.0 g) of the 6,6-dihydroxytriflate salt. A recrys-talized sample from acetonitrile/ethyl acetate gave a m.p. 204.5 – 205.3°C. FTIR (dibromide) nKBr
cm−1: 3422m, 3092vs, 3013s, 2979m, 2632m, 2459w, 1730w, 1628m, 1475s,1170 m,1095 s, 997 m, 959 m,923 m. FTIR (triflate) cm−1: 3270m, 3052vw, 3006vw, 1727vw, 1630vw, 1478m, 1279vs, 1250vs, 1167m, 1033s, 961w, 927w, 827w, 762w, 641s.1
H NMR (triflate, DMSO-d6)d: 7.68s
(1H), 4.34 bd (J=14.4 Hz, 1H), 3.75 bd (J=14.3 Hz, 1H), 3.57 m (2H), 3.27 m (8H). 13
C NMR (triflate, DMSO-d6) d: 90.33, 69.35, 57.28, 57.12, 52.57. Anal. calcd. for C11H22F6N2O8S2: C 27.05,
Acetyl simmondsin mixture (0.719 g, 1.12 mmol) was placed in a dry 500 ml 3-necked jacketed round flask equipped with a mechanical stirrer. Dichloromethane (100 ml) was added and the contents stirred at 35°C, followed by addition of lipase SP 435 (0.15 g, 21% w/w) and slow dropwise addition of hydrogen peroxide (2.0 ml) over 3 h when TLC (ethyl acetate/methanol 7:3) indicated complete reaction. The lipase was filtered, rinsed with dichloromethane and stored in toluene for reuse. The combined organic phase was washed with water and dried over Na2SO4.
The dried solution was concentrated to yield 0.8 g of a syrup, Rf 0.76 compared to the starting acetate ofRf0.69, [a]D20= −32.37 (c 8.9, CH2Cl2). FTIR (film on KBr) cm−1:3076w, 2963w, 2224w, 1755vs 1648w, 1432w, 1374m, 1232vs, 1051s, 804m. 1H NMR (CDCl3) d: 6.18 dd (J=2.1, 8.4 Hz, 1H), 6.12 dd (J=2.0, 8.4 Hz), 5.45 d (J=2.2 Hz), 5.44 d (J=2.0 Hz), 5.25 m(1H), 5.09 m (3H), 4.82 m (2H), 4.66 t (J=7.5, 7.8 Hz, 1H), 4.28 m (1H), 3.95 m (1H), 3.65 m (1H), 3.29 s (3H, OCH3 of hexaacetyl component), 2.45 m (1H), 2.05 s (21H), 1.83 m (1H), 1.62 m (1H). 13C NMR (CDCl3)d: 171.0, 170.5, 170.1, 169.8, 169.4, 169.3, 169.1, 168.3, 158.8(2), 115.29(2), 102.4, 101.4, 96.23, 76.98, 76.16, 74.84, 74.37, 72.92, 72.87, 72.77, 72.29, 72.14, 70.97, 68.90, 68.25, 68.09, 68.02, 67.86, 61.20, 61.14, 56.74, 33.13, 30.87, 20.87, 20.83, 20.67, 20.59, 20.57, 20.54, 20.50, 20.46.
2.7. Epoxidation of
3:2%,3%,4%,6%-penta-O-acetylsimmonsin
In a dry 500 ml jacketed reaction flask equipped with a mechanical stirrer was placed 3,2%,3%,4%,6%-penta-O-acetylsimmondsin (1.50 g, 2.51 mmol) dissolved in 120 ml dichloromethane. Lipase SP435 (0.50 g) was added and the temper-ature brought to 33.4°C; hydrgen peroxide (5.0 ml) was then added slowly and reaction stirred overnight. After 20 h the immobilized lipase was filtered off, rinsed with more dichloromethane and stored in toluene for further use. The reaction mixture was then washed with deionized water (80 ml×3), the organic phase was dried over Na2SO4 and concentrated to yield 1.60 g of crude epoxide of penta-O-acetylsimmondsin which was recrys-tallized in ethyl ether/dichloromethane to give a colorless solid, 1.485 g, 96%; m.p. 168.1 – 169°C, [a]D20
= −33.0° (c 0.52, CH2Cl2). FTIR nKBr
cm−1: 3477 overtone, 2943, 2833w, 2224, 1754vs, 1643, 1435, 1374m, 1227vs, 1044s, 805m. 1H (CDCl3) d: 6.02 dd (J=1.0, 7.5 Hz, 1H), 5.41 d
OCH3), 3.20 m (1H), 2.45 m (1H), 2.12 s (3H),
−270.1, tetraacetyl glucosyl oxonium ion, 24%), 229.1 (m/z 331.1 – 102, 5%), 169.1 (m/z
229.1 – 60, base peak).
2.8. Epoxidation of acetyl simmondsins using oxone-diazepinium triflate reaction
In a 500 ml 3-necked flask equipped with a mechanical stirrer was placed the acylated DMS/ DDMS mixture (1.76 g, 3.0 mmol), 6,6-dihy-droxy-1,1,4,4-tetramethyl-1,4-diazepinium triflate (1.465 g, 3.0 mmol), acetonitrile (36.0 ml), phos-phate buffer (pH 7.0, 18.0 ml). A solution of oxone (18.44 g) in water was placed in an addition funnel attached to the reaction flask. The third neck was fitted with a second addition funnel containing 2.0 M NaHCO3solution. The reaction mixture was stirred at 0°C and the oxone and bicarbonate slowly added simultaneously to maintain the mixture at pH 7.0. After 15 h, when TLC of the reaction mixture indicated the pres-ence of a single product (Rf 0.76), the cold aqueous solution was extracted with ethyl ether and the organic layer dried over Na2SO4 and concentrated at reduced pressure to yield 2.0 g of crude product. FTIR nneat cm−1: 2960vw, 2832vw, 2225m, 1754vs, 1646vw, 1436w, 1374m, 1224vs, 1044s, 805m.1H (CDCl
3) o: 6.12 dd (J= 2.0, 8.4 Hz, 1H), 5.45 d (J=2.2 Hz), 5.44 d (J=2.0 Hz), 5.25 m (1H), 5.09 m (3H), 4.82 m (2H), 4.66 t (J=7.5, 7.8 Hz, 1H), 4.28 m (1H), 3.95 m (1H), 3.65 m (1H), 3.29 s (3H, OCH3 of hexaacetyl component), 2.45 m (1H), 2.05 s (21H), 1.83 m (1H), 1.62 m (1H). 13C NMR (CDCl3)d: 171.0, 170.5, 170.1, 169.8, 169.4, 169.3,
169.1, 168.3, 158.8(2), 115.29(2), 102.4, 101.4, 96.23, 76.98, 76.16, 74.84, 74.37, 72.92, 72.87, 72.77, 72.29, 72.14, 70.97, 68.90, 68.25, 68.09, 68.02, 67.86, 61.20, 61.14, 56.74, 33.13, 30.87, 20.87, 20.83, 20.67, 20.59, 20.57, 20.54, 20.50, 20.46. 6.18 dd (J=2.13, 8.42, 2.14 Hz, 1H), 5.44d (J=2.15Hz, 1H).
2.9. 2,7-Epoxy-3:2%,3%,4%,6%-penta-O
-acetylsimmondsin
In a dry 3-necked reaction flask equipped with a mechanical stirrer and a −1.0 – 0°C ice-bath was placed 3:2%,3%,4%,6%-penta-O-acetylsimmondsin (0.942 g, 1.579 mmol) dissolved in DCM (60.0 ml), NaHCO3 (0.3 M, 100 ml) and phosphate buffer (pH 7.0, 15 ml). The mixture was stirred and 58 – 85% 3-chloroperoxybenzoic acid (0.40 g, about 1.8 mmol) was added over 15 min. After 2 h the temperature was allowed to warm to 18°C and the reaction mixture was extracted with ethyl ether (80.0 ml×3). The extract was washed with saturated NaCl, dried over Na2SO4 and concen-trated under reduced pressure to a syrup which crystallized in ethyl ether/DCM to a colorless solid; 0.898 g (92.8%) yield, m.p. 168 – 169°C, [a]D20= −32.7° (c 0.41, CH2Cl2). FTIR n 23), m/z 331.1 (M+-270, i.e. tetraacetyl glucosyl oxonium ion), 229.1 (m/z 331.1 – 102), 169.1 (m/z
229.1 – 60, 100%).
3. Results and discussion
Scheme 3. Epoxidation of didemethyl/demethyl simmondsins (DDMS/DMS).
in satisfactory conversion of the substrate with very little side reaction (Scheme 3, step a). Occa-sionally, however, a minor amount of incomplete etherification product was observed and such a batch was usually treated with acetic anhydride to block the unreacted hydroxyl group. Peracetyla-tion was the second method of protecPeracetyla-tion used and generally gave the 3,4,5:2%,3%,4%,6%-hepta-O -acetylsimmondsin from the DDMS and 3,4:2%,3%,4%,6%-hexa-O-acetylsimmondsin from the DMS component, respectively, of the starting mixture, whereas for simmondsin the product was usually the expected 3:2%,3%,4%,6%-penta-O -acetyl-simmondsin (Scheme 3, step b). Since no effort was made to separate the two compounds result-ing from the DDMS – DMS mixture at this stage, the subsequent oxidation product from the acety-lated substrates (Scheme 3, step d) was also a mixture of the 2,7-epoxy-3,4,5:2%,3%,4%,6%-hepta-O -acetylsimmondsin and the 2,7-epoxy-3,4:2%,3%,4%,6% -hexa-O-acetylsimmondsin, respectively; whereas the subsequent epoxidation of 3:2%,3%,4%,6%
-penta-O-acetylsimmondsin (Scheme 3, step c) gave the expected 2,7-epoxy-3:2%,3%,4%,6%-penta-O -acetylsim-mondsin derivative. A distinctive 1H-NMR fea-ture of the products of epoxidation is the appearance of a doublet of doublets at 6.18 ppm corresponding to the methine proton at C7 com-pared to the doublets centered at 5.46 ppm in the starting material. For the mixed acetates from
DDMS/DMS, two sets of these doublets were observed in the product as would be expected and occurred in the same ratio as in the starting mixture. The infrared absorption for trisubsti-tuted oxiranes is expected at 770 – 750 cm−1 (C – O stretch), while the CH and CH2are expected at 3050 – 3029 and 3004 – 2990 cm−1 or both (Colthup et al., 1990). In the authors’ hands the intensity of the CH band is very weak. However, a weak to moderate band is observed for the products at 805 – 750 cm−1
. Because of the dearth of spectroscopic information on trisubstituted oxi-ranes in the literature, 3-chloroperoxybenzoic acid (MCPBA) has been used, the traditional epoxida-tion reagent, as oxidant for the carbon – carbon double bond in 3:2%,3%,4%,6%-penta-O -acetylsim-mondsin as a means of obtaining reference mate-rial for purposes of spectroscopic and other data comparison to the products (Scheme 4). The data (1
H and 13
diagnos-Scheme 4. Meta-chloroperoxybenzoic acid catalyzed oxidation of penta-O-acetylsimmondsin.
tic fragments that closely matched the assigned structures. It should also be pointed out that because of the preliminary nature of the data presented here, a detailed description of the pecu-liar stereochemistry of these oxiranes will be pre-sented elsewhere. In summary, this project is a continuing effort aimed at developing new co-products for simmondsin and jojoba from the plant’s non-useful seed meal isolates. It has been shown in this preliminary report that the olefinic functional groups of DMS/DDMS and indeed, of simmondsin itself can be converted to the epox-ides which are intermediates with several potential applications.
Acknowledgements
The author wishes to thank Dr Thomas Abbott for providing the simmondsin analogues and for his support of this project. Also the assistance of Dr D. Weisleder for running the NMR spec-troscopy of the products is greatly appreciated.
References
Abbott, T.P., Holser, R.A., Platner, B.J., Platner, R.D., Pur-cell, H.C., 1999. Pilot-scale isolation of simmondsin and related jojoba constituents. Ind. Crops Prod. 10, 65 – 72. Booth, A.N., Elliger, C.A., Waiss, A.C. Jr, 1974. Isolation of
a toxic factor from jojoba meal. Life Sci. 15, 1115 – 1120. Cokelaere, M.M., Dangrreau, H.D., Arnouts, S., Kuhn, E.R., Decuypere, E.M.-P., 1992. Influence of pure simmondsin on the food intake in rats. J. Agric. Food Chem. 40, 1839 – 1842.
Colthup, N.B., Daly, L.H., Wiberley, S.E., 1990. In: Introduc-tion to Infrared and Raman Spectroscopy, 3rd ediIntroduc-tion. Academic Press, New York, Ch. 10, pp. 331 – 332. Denmark, S.E., Wu, Z., 1997. Dioxiranes are the active agents
in ketone-catalyzed epoxidations with oxone. J. Org. Chem. 62, 8964 – 8965.
Elliger, C.A., Waiss, A.C. Jr, Lundin, R.E., 1973. Sim-mondsin, an unusual 2-cyanomethylenecyclohexyl glu-coside fromSimmondsia californica. J. Chem. Soc. Perkin I, 2209 – 2212.
Elliger, C.A., Waiss, A.C. Jr, Lundin, R.E., 1974. Structure and stereochemistry of simmondsin. J. Org. Chem. 29 (19), 2930 – 2931.
Flo, G., Van Boven, M., Vermaut, S., Decuypere, E., Dae-nens, P., Cokelaere, M., 1998. Effect of simmondsin derivatives on food intake: dose-response. J. Agric. Food Chem. 46, 1910 – 1913.
Kuhn, R., Trischmann, H., Low, I., 1955. Zur Perme-thylierung von Zuckern und Glykosiden. Angew. Chem. 67, 32.
Murray, R.W., 1989. Dioxiranes. Chem. Rev. 89, 1187 – 1201. Van Boven, M., Blanton, N., Cokelaere, M., Daenens, P., 1993. Isolation, purification and stereochemistry of sim-mondsin. J. Agric. Food Chem. 41, 1605 – 1607.
Van Boven, M., Toppet, S., Cokelaere, M.M., Daenens, P., 1994. Isolation and structural identification of a new Sim-mondsin Ferulate from Jojoba Meal. J. Agric. Food Chem. 42, 1118 – 1121.
Walker, H.G. Jr, Gee, M., McCready, M., 1962. Complete methylation of reducing carbohydrates. J. Org. Chem. 27, 2100 – 2102.
