Auto-SummaryThe post describes methods for synthesizing L-tryptophan, a naturally occurring amino acid. The first method involves decarboxylation of tryptophan using a high-boiling solvent, heating, and evaporation. The second method describes obtaining tryptophan from milk by separating casein, treating it with sodium hydroxide, and recrystallization. The third method details a more complex process involving casein precipitation, tyrosine separation, sulfuric acid treatment, mercury sulfate reduction, hydrogen sulfide precipitation, barium hydroxide treatment, and distillation to yield pure tryptophan.
searched a bit in my little archive :)
Posting found at Rhodium.
Decarboxylation, as described by Drone #342
Decarboxylation is accomplished by mixing about 80 g tryptophan in 250 mL of
high-boiling solvent (xylol, DMSO, cyclohexanol, etc.), adding a dash of a
ketone (I like 5 g of cyclohexanone, but a couple grams of MEK works reasonably
well), heat it to around 150 deg, and when evolution of CO2 ceases/solution is
clear, the reaction is complete. This takes anywhere from 1.5 to 4 hours. After
this is over, the solvent is boiled off (or at least greatly reduced in volume),
and the residue is dissolved in DCM. This is washed with a 5% baking soda soln,
then a distilled water solution, then the DCM layer is separated off, dried
with MgSO4, and the DCM is boiled off. You now have reasonably pure tryptamine.
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Since I'm a fan of natural products I thought that I would throw this out in
case it is of interest. It's from The Alkaloids Vol. II
The condensation of gramine methiodide with sodioacetaminomalonic ester gives
rise to a 63% yeild of ethyl-alpha-acetamino-alpha-carbethoxy-beta-(3-indolyl)-
propionate (IV), which by saponification and subsequent carboxylation and
hydrolysis can be converted into dl -tryptophan in 81% yeild (38,39).
This last systhesis has been improved by the discovery that gramine itself,
when heated in toluene with acetaminomalonic ester in the presence of a small
amount of powdered sodium hydroxide, produces a 90% yield of IV (40).
Tryptophan can also be obtained more directly by heating gramine with ethyl
nitroacetate in xylene solution. The resulting ethly alpha-nitro-beta-
(3-indolyl)-propionate is reduced catalytically to the corresponding amino
compound which on saponification yields dl -tryptophan (40). Gramine can
also be converted to alpha-ethyltryptamine by condensation with nitropropane
and catalytic hydrogenation of the product (42).
[38] J. Am. Chem. Soc. 66:200
[39] J. Am. Chem. Soc. 66:500
[40] J. Am. Chem. Soc. 67:38
[41] J. Am. Chem. Soc. 69:2118
7) L-Tryptophan From Milk
Casein [6]
To 1 liter of milk, from which the cream has been largely separated (by simple skimming), 0.05 M hydrochloric acid is slowly added, with stirring through a capillary tube extending to the bottom of the beaker. The addition is continued until the solution attains a pH of 4.6 (casein exists in milk in the form of a calcium derivative; pH 4.6 is the isoelectric point of free casein, which is soluble to the extent of only 0.11g/L water). Approximately 1 L of acid is required; the separation of the casein is practically complete at this point. Three liters of water is then added, stirring is discontinued, and the flocculent precipitate of casein is allowed to settle in the refrigerator for twelve to twenty-four hours. The clear supernatant liquid which contains soluble proteins and salts is removed as completely as possible by siphoning; the precipitate is collected on a suction funnel and washed with cold distilled water until the washings are free of calcium (test with ammonium oxalate)
The casein, which is contaminated with calcium phosphate and fats; is filtered to as small a volume as possible (about 500 cc.) and transferred to a 2000ml beaker. It is then treated with 0.1 M sodium hydroxide, the alkali being added slowly and with stirring through a capillary extending to the bottom of the beaker (it is important to avoid a local excess of alkali, which would tend to denaturate the casein). The addition of alkali is continued until the pH of the mixture reaches 6.3 (at this pH sodium caseinate is largely dissolved, whereas calcium caseinate is largely undissolved); 100-150 cc. of the alkali is required. At this pH the casein is completely in solution in the form of its sodium salt; fats, calcium phosphate, and any calcium caseinate remain undissolved. Care must be taken not to add more alkali than is necessary to bring the pH to the above point. The milky solution is filtered through a thick layer (10-15 mm.) of filter paper pulp tightly packed upon a suction funnel. The filtrate may be slightly opalescent; if it is less clear it is again filtered through a fresh layer of pulp.
The filtrate is brought to a pH of 4.6 with 0.05 M hydrochloric acid just as in the original precipitation, the necessary amount of acid being determined by titration of an aliquot portion, diluted fivefold, with 0.01 M hydrochloric acid, 220-250 cc. of 0.05 M acid is required. As the reprecipitation progresses, the rate at which the acid is added is decreased in order to prevent precipitation at the tip of the capillary tube; vigorous mechanical stirring is, of course, essential. When the acidification is complete, 5000ml of cold distilled water is added and the flocculent precipitate allowed to settle in the refrigerator. After siphoning off the clear supernatant liquid, the casein is collected on a suction funnel, using hardened paper, washed with cold distilled water until free of chloride, sucked as dry as possible, and dried over calcium chloride in a vacuum desiccator. The yield is 23-29 g. of a colorless coherent product which may readily be pulverized in a mortar.
Another:
L-Tryptophan [7]
In an 8-l. (2-gal.) bottle is placed 600 g. of commercial casein (coarse powder), which is then covered with about 3200 ml of tap water at 37_C. The bottle is shaken until all the casein is moistened. A solution of 60 g. of anhydrous sodium carbonate and 6 g. of sodium fluoride (to inhibit oxidase enzymes present) in 1 1. of water at 37_ is added. A thin paste of 20 g. of commercial pancreatin in 100 cc. of water (37_) is poured in. The mixture is covered with a layer of toluene (80 cc.), diluted to 6 1., stoppered, shaken thoroughly, and placed in a warm room or bath at 37_. After four or five days, with daily shakings, most of the casein is in solution and chalky masses of tyrosine begin to separate. After five days, a second 20-g. portion of pancreatin in 100 cc. of water is added. After twelve days, the bottle is cooled in an icebox overnight and the undissolved material is filtered off (This filtration may be slow. B_chner funnels of 20-cm. diameter are best used; the material from a single filling is allowed to suck dry and the filter paper then changed).
The filtrate (6.9-7 1.) is measured into a 16-1. (4-gal.) stone jar, and for every liter there is added 163 cc. of dilute sulfuric acid (one volume of 95 per cent sulfuric acid and one volume of water, cooled to room temperature). The first part of the acid must be added cautiously on account of the liberation of carbon dioxide. The tryptophan is precipitated by adding a solution of 200 g. of mercuric sulfate (Note 5) in a mixture of 1860 cc. of water and 140 cc. of 95 per cent sulfuric acid. After standing for twenty-four to fortyeight hours, the clear liquid is siphoned out and the yellow precipitate is filtered and washed with a solution of 100 cc. of concentrated sulfuric acid in 1.9 1. of distilled water containing 20 g. of mercuric sulfate, until the filtrate is colorless and Millon's test is atypical; about 1.5 1. is necessary. The precipitate is washed with three successive 500-cc. portions of distilled water to remove most of the sulfuric acid.
The moist precipitate (120-130 g.) is suspended with mechanical stirring in 1.2-1.3 1. of distilled water, and a hot, 20 per cent aqueous solution of barium hydroxide is added until the mixture is permanently alkaline to phenolphthalein (about 120 cc. is required). A rapid stream of hydrogen sulfide is passed in with stirring until the mercury is completely precipitated. The precipitate is filtered and washed with water until a sample of the washings gives a negative test for tryptophan with bromine water. The barium is removed from the combined filtrate and washings by adding the exact amount of dilute sulfuric acid and filtering. The filtrate is concentrated under reduced pressure to about 80 cc.
The tryptophan is extracted from the aqueous solution by repeated shaking in a separatory funnel with 25-cc. quantities of n-butyl alcohol; water is added from time to time to keep the volume approximately constant. The butyl alcohol extract is distilled under reduced pressure. After the water present has distilled, the tryptophan precipitates in the distilling flask and may cause bumping. When all the water has been removed, as is indicated by non-formation of drops on the side of the condenser, the distillation is stopped and, after cooling, the tryptophan is filtered and washed with a little fresh butyl alcohol. Such extractions and distillations are continued until the quantities of tryptophan obtained are negligibly small.
The tryptophan so produced (7-8 g.) varies somewhat in quality in different runs. It is purified by recrystallization from 60 cc. of dilute alcohol (two volumes of 95 per cent alcohol to one volume of water), filtering from the hot solution an appreciable quantity of insoluble matter, and subjecting this to a second extraction with an additional 10 cc. of aqueous alcohol. The solution is decolorized by the addition of 1 g. of Norite and allowed to stand in the icebox; the silvery leaflets of tryptophan are filtered and washed successively with cold 70 per cent, 80 per cent, 95 per cent alcohol, and, finally, with a little ether. Less than half the tryptophan is obtained in each crystallization. The yield of pure tryptophan is 4.0-4.1 g., together with under 0.1 g. of less pure product.
7) References
[1] D. H. R. Barton, On the origin of the C-1 Fragment in Indole Alkaloids, J. Chem. Soc., 3990-3994 (1965)
[2] T. Kametani, , Synthesis 475 (1972)
[3] T. Kametani, , Synthesis 171 (1974)
[4] S. Takano, Efficient Synthesis of Tryptamine, Heterocycles 6(8), 1167-1171 (1977)
[5] M. Hashimoto, A Novel Decarboxylation of alpha-Amino Acids, Chem. Lett., 893-896 (1986)
[6] E. J. John, Casein, Org. Syn. Coll. Vol. 2, 120-122 (1943)
[7] G. J. Cox, L-Tryptophan, Org. Syn. Coll. Vol. 2, 612-616 (1943)
[8]
Hope that wasn?t too much,
try The Hive for questions about that.
Bye
Uriel
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