Gurudutt, K N

Nagarajan, S

Rao, L Jagan Mohan

NOPR

I:odian Journal of ChernistJyVol. 318, February 1998, pp. 132 - 134A convenient preparative method for the glucosides of fattyalcohols and sterolsS Nagarajan, L Japn Moban IUo ct. K N Gurudutt·Plaotatioo Products, Spices ct. Flavour TcclmoIOI)' Departmcot,Central Food Technological R.e3earch Institute, Myaoce 570 013, IndiaReceived 5 May 1997; accepted 23 October 1997The glucosidesof simplefatty alcoholslike n-octanol,n-triacootanoiand bc:azylalcoholas well asof cholesterolhavebeensynthesisedin verygood yields(70-85%) by reacting acetobromoglucosewithzinc salts of the substrates,prepared in situ, and then deacetylatingthe glucosideperacetate. It ispossible to obtain either of the anomers ( a or p) selectively,by choosing appropriate reactionconditions.Glucosides are also considered to beintermediates and precursors in the biosynthesis ofsecondary plant metabolites. For example,glucovanillin, present in the green fruit of vanilla,releases vanillin during curing of the beansI.Synthetic glucosides are reported to be useful inmasking the sidestream smoke of cigarette"Further, a- and J3-n-<>ety1glucosides find use asnonionic, dialysable detergents in the isolation andpurification of membrane proteins, and as drugcarrier'. Z-Hex-3-enyl glucoside present in fresh tealeaf, releases 'leaf alcohol' during black teamanufacture which gives fresh notes in teainfusion".The procedures available for O-glucosidesynthesis' can be categorised into the following fourmajor groups: (i) the Fischer-Helferich method, (ii)the Koenigs-Knorr method and its variants, (iii) thetrichloroacetimidate method and other anomericoxygen activations, and (iv) the anomeric 0-alkylation method. Of these, the Koenigs-Knorrmethod is most versatile and generally applicable.In this classical method as well as its variants,activation of the anomeric position is achievedthrough substitution of the hydroxyl with a halogenatom. In the second step of glycosyl transfer, 1-halosugar is condensed with the substrate in thepresence of salts of heavy metals like silver andmercury. However, this method has some severe,partly inherent, disadvantages such as low thermalstability and sensmvity to hydrolysis of manyglucosyl halides and the need for stoichiometricquantities of heavy metal salts which are eitherexpensive or hazardous in nature. This becomes aserious limitation, especially in large scalepreparation of glycosides. These disadvantageshave been overcome to a large extent in the presentmethod which involves the use of zinc salts. Itssalient features are, (i) one-pot synthesis, (ii) easywork-up procedure, (iii) improved yields and (iv)amenability to scale-up.The application of zinc-salt mediated substitutionreaction to the synthesis of O-glucosides wasstudied systematically using n-octanol as theaglycone moiety and acetobromoglucose as theglucosyl donor in different solvents. The glucosidesso obtained contained both a- and J3-anomers indifferent ratios ( Table I ). Structure andstereochemistry of the pure anomers weredetermined by their physical properties and IHTable I-Reaction of acetobromoglucose (50 mmoles) withZrAJ and n-octanol in different solvents under refluxconditionsEatry Solvent Temp. Reaction Glucoside a:pNo "C period (yield %)(hr)653123CH~bCHChC~20:8025:7586:14415480855184NAGARAJAN et al. : SYNTHESIS OF GLUCOSIDES OF FATIY ALCOHOLS & STEROLS 133NMR spectral analysis.When dichloromethane was used as solvent, theglucoside yield was excellent and ~-anomer waspredominantly formed. In chloroform medium, theglucoside yield was moderate, but the anomericratio was same. On the other hand, in benzenemedium, the a- anomer was obtained as the majorproduct.Under solvolytic conditions (i.e. when the solventis a low-molecular weight alcohol) as well as undernon-solvolytic conditions and at low temperature,~-D-glucosides are formed predominantly". Thepresent study showed that the polarity of solventhad a marked effect on the anomeric composition ofthe products. Thus, by altering the reactionconditions, .it was possible to obtain either of theanomers as the major product. The glycosidicproduct was easily purified by isolating theindividual anomers as tetraacetate derivatives andthen hydrolysing them. This constitutes a simpleand convenient preparative method for 1-O-aJ~-glucosides. The glucosides prepared are not onlyillustrative of the general usefulness of this method,but they also find application in food, agricultureand pharmacy.Experimental SectionGeneral. 1H NMR spectra were recorded inCDCh on 2001270 MHz instruments using TMS asinternal standard. Optical rotations were recorded at22 "C and 589 nm. GC was performed under thefollowing conditions: 6'xlls"(0.d.) SS column, OV-17 (10 %) on Chromosorb-W, N2 30 mUmin; H2FID; injection and oven temperatures 250°C;detector temperature 300 "C. TLC (5x20 em)plates coated with silica gel-G, type 60 (E. Merck)were used.Acetobromoglucose (tetra-O-acetyl-a-D-gluco-pyranosyl bromide) was prepared' from n-glucose.The ZnO and ZnC03 used in the reaction weredried over P20s in a vacuum oven at 60°C beforeuse. CHCh, CH2Ch and CJ-16 were dried anddistilled.n-Octyl &Iucoside. n-Octanol (9.75 g, 75mmoles) was stirred with ZnC03 (4.7 g, 37.5mmoles) in refluxing CJ-16(150 mL) for 8 hr inSoxhlet apparatus containing anhydr. Na2S04 (40g). The solvent was then removed in a flashevaporator and the residual zinc salt dried overP20S in a vacuum desiccator.Acetobromoglucose (20.55 g, 50 mmoles) wasadded in parts to a suspension of the zinc salt of n-octanol suspended in CH2Ch (150 mL) understirring and the mixture set to total reflux.Refluxing was continued till the spot due toacetobromoglucose disappeared on TLC plate(spray with 1 % acetone solution of o-tolidinereagent and exposure to sunlight gave a bluishgreen spot). The reaction mixture was filtered at thepump and residue washed with the solvent.Combined filtrate and the washings were washedrepeatedly with distilled water, dried over anhydr.Na2S04and the solvent distilled off. To the residue,AC20 (10.5 mL) and pyridine (4 mL) were addedand the mixture was kept aside at room temperaturefor 24 hr and then poured onto crushed ice. Theseparated solid filtered at the pump, washed withcold water and dried in a desiccator'. The crudeproduct (19.7 g, 85 %) was chromatographed overSi02 (100 to 200 mesh, 150g) using hexane-EtOAcmixtures as eluents. Coloumn fractions werechecked by TLC (solvent: hexane-EtOAc (60:40),sprayed with 10 % H2S04 in MeOH and heated at110 °C1l5 min. n-Octyl O-a- and ~-glucosidetetraacetates were progressively eluted with 20 to30 % EtOAc in hexane mixtures. While the a-anomer was a viscous liquid (3.9g, [a ]0+102.4°),the ~-anomer crystal-lised from MeOH (15.7 g,m.p. 54°, [a]o -23.8°; lit.8 , m. p. 54°, [a]0-22°).n-Octyl O-(a or ~)-glucoside tetraacetate (3.7 g)was stirred with 20 mL of MeOH containing 1%NaOMe at room temperature for 2 hr and thenneutralised with Amberlyst 15' o-r form) resin.The resin was filtered off and MeOH removed in aflash evaporator. The residue crystallised fromanhydr. EtOAc in pellets (2.35 g, 99 %). a.:m.p.123°, [a.]0+117.5°;~: m.p. 68-69°, [0.]0-27.5°(lit.s a.: m.p.124°, [0.]0 +117.9°; ~: m.p. 69°,[0.]0 - 28°).Benzyl glucoside. The. zinc salt of benzylalcohol (3.24 g, 30 mmoles) was prepared usingzinc oxide (1.2 g, 15 mmoles) as in the previous134 INDIAN J CHEM, SEC. B, FEBRUARY 1998case. Acetobromoglucose (8.22 g, 20 mmoles)was added to a suspension of zinc salt of benzylalcohol in CH2Ch (50 mL) and the mixture set tototal reflux. On completion of the reaction (8 hr),the reaction mixture was worked-up and the crudeproduct acetylated as before to get benzyl 0-(0. and~)-glucoside tetraacetate (7.18 g, 82 %). Its a- and~- anomers were separated by Si02 columnchromatography and crystallised from MeOH(yield: a-anomer 0.77 g and ~-anomer 6.23 g); a:m.p. 110-12°, [0.]0 +143.8°; j3: m.p. 97- 98°. [0.]0-43.4° (lit.9 a: m.p. 111°, [a]o +143°; j3:m.p. 98°,[0.]0-44°).Benzyl 0- (a / p)-glucoside tetraacetate (4.38 g)was stirred with 20 mL of MeOH containing I %NaOMe at room temperature for 2hr and thenneutralised with cation (W form) resin. The resinwas filtered off and MeOH removed in a flashevaporator. The residue was crystallised fromanhydr. diethyl ether in needles (2.69 g, 99 %). a:m.p.l Zl", [a]o +132°; 13:m.p. 123°(Iit.IO a: m.p.121-22° [a]o +133°; 13:m.p.123-35°).Cholesterol glucoside. The zinc salt ofcholosterol was prepared by reacting ZnO (1.2 g,15 mmoles) and cholosterol (11.5 g, 30 mmoles) inCH2Ch. Acetobromoglucose (8.22 g) was addedand the mixture set to total reflux. On completion ofthe reaction (16 hr), the reaction mixture wasworked-up and acetylated. The yield of cholesterol-O-(alp)-D-glucoside tetraacetate was 10.5 g (73%). The 0.- and j3-anomerswere separated by Si02gel column chromatography and crystalliscd fromMeOH (yield: a-anomer 1.26 g and p-anomer 9.24g). a: m.p.191-92°, [a]o +90.2°; 13:m.p. 155-56°[a]o -27.4° (1it.11 a: m.p. 193°, [0.]0+92°; 13:m.p.15r, [a]0-26°).Cholesterol-O-(alj3)-glucoside tetraacetate (7.16g) was stirred with 20 mL of MeOH containing 1%NaOMe at room temperature for 2 hr and thenneutralised with cation (W form) resin. The resinwas filtered off and MeOH removed in a flashevaporator. The residue was crystallised fromanhydr. EtOAc in pellets (5.46 g, 99 %). a: m.p.208° [a]o +24°; p:m.p. 262°, [a]o -49° (1it.12 a:m.p. 205-11°, [a]o +23°; 13:m.p. 262-64°, [a]o+50°).n-Triacontanol-a and j3-glucoside. To the zincsalt prepared from 6.15 g of n-triacontanol and 1.0g of ZnC03 and suspended in CH2Ch (100 ml.),acetobromoglucose (4. II g) was added and themixture set to total reflux. On disappearance ofacetobromoglucose (12 hr), the reaction mixturewas worked-up and acetylated as before to get n-triacontanol -ex and j3-D-glucoside tetraacetates(5.18 g, 70 %). The product mixture was stirredwith 20 mL of MeOH containing I % NaOMe atroom temperature for 2 hr, and then neutralisedwith cation (If form) resin. The resin was filteredoff and the methanolic solution concentrated in aflash evaporator. The residue was crystallised frommethanol, yield 3.99 g (99%).ReferencesFuria T E & Bellanca N (Eds), Fenaroli's hand book offlavour ingredients ; Vol. I, 2nd Edn (CRC Press,Cleveland, Ohio) 1975,484.2 Herron J N, U.S Patent, 4,804,002 (1989); Chem Abstr,111,1989,112377v.3 Gould R J, Ginsberg G H & Spector A A, Biochemistry.20,1981,6776.4 Kobayashi A, Kubota K, Joki Y, Wada E & WakabayashiM, Biosci Biotech Biochem, 58, 1994, 592.5 (a) Schmidt R R, Allgew Chem. [lit Ed(Engl), 25, 1986,212.(b)Schmidt R R, in: Comprehensive organic synthesis,Vol. Edited by B M Trost, I Fleming and E Winterfrldt(Pergamon Press, Oxford) 1991, 33.6 Gwudutt K N, Jagan Mohan Rao L, Sanjay Rao &Srinivas S, Carbohydr Res. 285, 1996, 159.7 Lemieux R V, in: Methods ill carbohvdrate chemistry,Vol. 2, edited bv R L Whistler and J N Bemitter(Academic Press, New York) 1963,221.8 Weber N & Benning H, Chem Phvs Lipids, 31, 1982,325.9 (a) HeIferich B & Gootz R, Ber Dtsch Chem Ges. 62B,1929,2788.(b) Hickinbottom W J,JChemSoc. 1928,3140.10 Dictionary of organic compounds, 5th Edn, Vol. I,(Chapman & lIall) 1982,609.II Uvarova N I, Atopkina L N & Elvakov G. Carbohvdr Res.83, 198Q, 33.12 Khorlin A Ya, Bochkov A F, Bakinovskii L V &Kochetkov N K, Dokl Akad Nallk. SSSR, 143, 1962,1119; Chem Abstr, 57, 1962, 7354h.

A convenient preparative method for the glucosides of fatty alcohols and sterols

http://nopr.niscair.res.in/bitstream/123456789/56716/1/IJCB%2037B%282%29%20132-134.pdf

A convenient preparative method for the glucosides of fatty alcohols and sterols

Abstract

Similar works

Full text

Available Versions

NOPR