Well, I heard that Hjalmar P., a Hungarian architect, performed this reaction a while ago
:
To a stirring solution of L-tryptophan (2 g, 10 mmol) and NaOH (0.42 g, 10.5 mmol) in 25 mL MeOH was added a 30% formaline solution (3 g, ~30 mmol). After 15 min of stirring at RT (~25°C), the mixture was cooled in an ice/salt bath and NaBH
4 (600 mg, 15 mmol) was added bit by bit, care was taken that the temperature did not rise above 5°C. After an hour, all ice was melted, and the solution was stirred overnight.
It was then carefully acidified with HCl, to the iso-electric point of tryptophan (pH 5.89), where a small amount of solid, unreacted L-tryptophan, precipitated. This was filtered off, and the MeOH was evaporated in vacuo. An attempt was done to wash the remaining solid with acetone, but after the acetone was evaporated it left nothing.
The precipitate was extracted with a small amount of hot ethanol, (what was presumed to be) NaCl remained undissolved and was filtered off, and the warm EtOH was allowed to come to RT. After sitting overnight in the freezer, a offwhite precipitate formed.
This was filtered and the precipitate was air-dried, it weighed 0.5 g. Evaporation of the alcohol left 0.7 g of yellow substance which was gummy at first, but quickly became a hard solid.
The
Harvey, Miller and Robson test was employed according to
J. Chem. Soc. (1940) p. 154-155:
A small amount of the substance was dropped in a test-tube containing sulphuric acid and a trace of oxidizing agent. The paper suggests to use FeCl
3 among others, but in this case 50% H2O2 was used. Tryptophan, its methyl ester and N-methyltryptophan gave a colour reaction within a couple of minutes from
pale pink -> weak purple -> yellow with strong fluorescence, so does tryptamine.HCl but with a less marked fluorescence. Most
beta-carboline-4-carboxylic acids give a blue colour
Both obtained substances were tested this way, together with pure L-tryptophan. All three gave the same colour reactions, ascribed to tryptophan.
The melting point still has to be obtained. These melting points were found in the literature:
by Chimimanie, thanks L-tryptophan : 289°C
N-Methyltryptophan : mp ranges over 100° (!)
N,N-dimethyltryptophan : 239-243°C
2,3,4,5-tetrahydro-
beta-carboline-4-carboxylic acid : 306°C
3-methyl-2,3,4,5-tetrahydro-
beta-carboline-4-carboxylic acid : 208°C, after softening at 194°C
Also, most
beta-carboline-4-carboxylic acids have a tendency to separate after recrystallisation as typical rod-like crystals, which makes identification easier.
Now after reading the above ref
(digged up by Chimimanie, thanks again ), I propose a somewhat different approach :
I.
p. 157
alpha-hydroxymethylamino-beta-3-indolylpropionic acidl-Tryptophan (0.6 g) was dissolved in water (12 mL), formalin (2 mL) added and the mixture was incubated at 38°C for not more than 3-4 hours. The colourless, crystalline, but rather granular solid which had then separated was collected, washed with cold water, and dried in a vacuum.
Yield 60%. mp 226-240°C
If the above mixture is incubated at 38°
for 15 hours in presence of 10 mL 0.1 N NaOH, the
beta-carboline is obtained in 80% yield. The
beta-carboline is also formed when l-tryptophan is boiled in aqueous solution for 2 hours.
Also, the
beta-carboline crystallises from an equimolar aqueous solution of tryptophan and acetaldehyde when kept overnight at RT, according to Harvey and Robson,
J. Chem. Soc. (1938) 97.
II.
Reduction of this with NaBH
4 as described in the above post yields N-methyltryptophan.
III.
p.158
3-methyl-2,3,4,5-tetrahydro-beta-carboline-4-carboxylic acidTo a cool solution of r-
alpha-methylamino-
beta-3-indolylpropionic acid (0.5 g) in water (75 mL), a slight excess (0.4 mL; 2.3 mols.) of commercial formalin was added, the whole incubated
at 38° for 15 hours. The "solid" which separated was collected (0.11 g), and the filtrate concentrated to a small volume on a boiling water bath. The bundles of stout rods which settled on cooling were collected, washed with absolute alcohol, and dried in a dessicator. Concentration of the mother-liquor gave another crop of the carboline-4-carboxylic acid.
Yield, 0.40 g (76%)
Now, there is a good chance that, if N-methyltryptophan and formaline are incubated for only 2-3 hours at 38° N-hydroxymethyl-N-methyltryptophan will be the main product.
If so, then this can be isolated and again reduced as described before.