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Author: Subject: Solvant-free Decarboxylation of Amino-acid
Mush
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[*] posted on 30-11-2010 at 03:14


Somebody somewhere translated that paper. Thanks for that!!

M. Wada - Biochem. Z. 260, 47, 1933

"Here's a translation of the interesting parts for non-German speaking chemists:


"It is known that, when amino acids are heated with urea, urethane (ethyl carbamate), potassium cyanate or phenylisocyanate, either in neutral or in basic solution, like a Ba(OH)2 solution, uramino acids are formed (1), which by the action of diluted acids easily form their anhydrides (hydantoins).

The author has now observed that these hydantoins by the action of concentrated acidic or alkaline solutions are converted to the corresponding amines.

Using this reaction the author has obtained phenethylamine, tyramine, methylamine, isoamylamine, histamine, putrescine, cadaverine, tryptamine, aminoethyldisulfide, pyrrolidine, beta-alanine and GABA from their corresponding amino acids. In every case the reaction was performed smoothly, and very good yields are obtained. Especially recommendable is this reaction for diamino acids, tryptophan, cystine etc."

Experimental part

Phenylethylamine from phenylalanine
10 g phenylalanine and 5 g urea (molar excess) were dissolved in 150 ml water and refluxed for 35 minutes. To convert the uramino acid to the hydantoin the solution was acidified with HCl, evaporated partly, and extracted with ether. After evaporation of the ether the hydantoin of phenylalanine was obtained as thin, long plates.

4.9 g of this hydantoin was refluxed with 70 ml water and 20 ml conc. H2SO4 for 10 hours, after cooling basified with KOH and extracted with ether. After evaporation of the ether phenethylamine was obtained as shiny plates, yield 2.5 g (80%), mp 189°C.


Methylamine from glycine
10 g glycine and 15 g urethane (molar excess) were dissolved in 50 ml 0.25M Ba(OH)2 and heated for 2 hours. After precipitating the baryta as the carbonate by passing CO2 through the solution, the filtrate was acidified with a couple of drops of HCl and the solution was evaporated. The hydantoin was not isolated, yet 50 ml conc HCl was added and this was refluxed for 10 hours, after which the major part of the solution was evaporated.

This caused the hydantoin to completely transform into methylamine, so that by addition of ethanol no hydantoin was precipitated, and the characteristic reaction (2) of amines with sodium nitroprusside and acetone was obtained.

The solution was decolorised with animal charcoal and picric acid was added. After evaporation the picrate was obtained as brightly yellow plates with mp 215°C. Yield: 29 g picrate (84%)


Tryptamine from tryptophan
1.3 g tryptophan, 0.5 g urea and 0.1 g Ba(OH)2 is heated in 10 ml water for 3 hours. A bit of HCl was added and the solution was evaporated in vacuo. The residue was again heated with 1.4 g Ba(OH)2 and 10 ml water for 1 hour. After precipitating the baryta as the carbonate by passing CO2 through the solution, the obtained tryptamine can be isolated as the picrate salt as dark red needles, mp 239-242°C. Yield: 1 g picrate (40%)


Beta-alanine from aspartic acid
2.2 g aspartic acid, 1.5 g urea and 2.2 g Ba(OH)2 were dissolved in 50 ml water and refluxed for 3 hours. It was then acidified with HCl and heated for 2 hours on the waterbath. To the solution was added 7 g Ba(OH)2 and this was heated for 1 hour, the baryta was precipitated as the sulfate, the filtrate was acidified with HCl and evaporated. Beta-alanine hydrochloride precipitates as small plates, mp 122°C, yield: 1.6 g (77%)


GABA from glutamic acid
10 g glutamic acid, 5 g urea and 10 g Ba(OH)2 were heated in 50 ml water for 2 hours. The baryta was precipitated with sulfuric acid, the filtrate acidified with HCl, evaporated and the residue was heated with 80 ml 30% H2SO4 for 8 hours. After removing the excess sulfuric acid with Ba(OH)2 the obtained GABA was isolated as the HCl salt. Feather-like crystals were obtained, which are slightly soluble in water. Yield: 7.8 g (82%), mp 135°C.
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[*] posted on 30-11-2010 at 04:46


Quote: Originally posted by Mush  
Somebody somewhere translated that paper. Thanks for that!!

M. Wada - Biochem. Z. 260, 47, 1933

"Here's a translation of the interesting parts for non-German speaking chemists:


"It is known that, when amino acids are heated with urea, urethane (ethyl carbamate), potassium cyanate or phenylisocyanate, either in neutral or in basic solution, like a Ba(OH)2 solution, uramino acids are formed (1), which by the action of diluted acids easily form their anhydrides (hydantoins).

The author has now observed that these hydantoins by the action of concentrated acidic or alkaline solutions are converted to the corresponding amines.

...

Experimental part

...

Tryptamine from tryptophan
1.3 g tryptophan, 0.5 g urea and 0.1 g Ba(OH)2 is heated in 10 ml water for 3 hours. A bit of HCl was added and the solution was evaporated in vacuo. The residue was again heated with 1.4 g Ba(OH)2 and 10 ml water for 1 hour. After precipitating the baryta as the carbonate by passing CO2 through the solution, the obtained tryptamine can be isolated as the picrate salt as dark red needles, mp 239-242°C. Yield: 1 g picrate (40%)

i]


There is a mistake in the translation of preparation No. 8, Tryptamine from tryptophan (see above): Obviously the reaction of tryptophan, urea and baryte does not directly form the picrate. The original text states that: "... the thus formed indolethylamine was then transformed into its picrate (salt)..."

Following Sedit's request I have only read and translated preparation No. 8 (see below).
If there is an interest I can try to review the translation also for the rest of the paper.



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[*] posted on 30-11-2010 at 14:23


So, I guess all that remains is experimentation..
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[*] posted on 1-12-2010 at 00:13


Quote: Originally posted by Nicodem  
The hydrolysis of the alpha-amino acid derived hydantoins gives back the starting amino acid. Due to the weirdness of the claims, a group of researchers actually went so far as to repeat Wada's work and confirmed no decarboxylation occurs. I don't remember in which paper I read about this (and don't really have the time and will to again do a literature search), but it was when doing a literature search for the post here.

Quote: Originally posted by Bolt  
Here is Wada's publication (obviously in German).

I am quite interested in the work of the researchers who attempted to reproduce the decarboxylation. This would be an easy method of preparing valuable amines, if it works. Can anyone provide a reference for the more modern attempt?


Eine neue Methode zur Darstellung von Aminen aus Aminosäuren
Wada, M
Biochemische Zeitschrift 1933 pp. 47-51

I'm surprised there is so much interest in something that makes no sense mechanistically. Basic hydrolysis of hydantoins might not be as well known as their enzymatic hydrolysis, but it is well known to give back amino acids rather than primary amines. In fact Ba(OH)2 is quite often used for this purpose! Don't you think that if it would give primary amines as end products, this would be mentioned by those many who reported the use of Ba(OH)2 for the hydrolysis of hydantoins? Yet nobody here bothered to check the literature before wasting further time:

An investigation of Wada's method of converting α-aminoacids into 2-substituted ethylamines.
H. Burton and P. F. Hu
J. Chem. Soc., 1949, 181-182
DOI: 10.1039/JR9490000181

Checking the literature is the first thing any researcher does, but apparently some forum members still believe doing this is a waste of time and prefer to waste time otherwise and to others.




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[*] posted on 1-12-2010 at 04:09


Quote: Originally posted by Bolt  
In fact, I have looked up this reference in scifinder, and it shows no citing articles.


Actually, I did check for citing articles using scifinder, but it showed none. Also, you claim that the decarboxylation makes no sense mechanistically. Lemme read the paper to see if it sheds any light on your attack.

Edit: Having read the article, I believe that all we can currently say is that the method failed in the hands of those authors. They say that the method is bunk 1) because they couldn't get it to work and 2) because the Rimini rxn could give false positives for the success of the reaction. Wada actually used mass spectroscopy and the melting points of the compound in question and often its picrate derivative to characterize his products.

No, I don't think we can throw out this method without further experimentation.

[Edited on 1-12-2010 by Bolt]

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[*] posted on 1-12-2010 at 09:12


Quote: Originally posted by Bolt  
Quote: Originally posted by Bolt  
In fact, I have looked up this reference in scifinder, and it shows no citing articles.


Actually, I did check for citing articles using scifinder, but it showed none.

You can not rely on that. Those articles were abstracted way before citations were integrated into SciFinder (or WoS). Such a search would only give you recent articles citing the old one, but not also an old article citing an even older article. When you search the literature you really need to do it properly. Shortcuts like that are useless.
Quote:
Edit: Having read the article, I believe that all we can currently say is that the method failed in the hands of those authors. They say that the method is bunk 1) because they couldn't get it to work and 2) because the Rimini rxn could give false positives for the success of the reaction.

Well, the problem is that they are not the only ones who report that method does not work as described, though they are probably the only ones who directly evaluate it and say it explicitly. If you bother to search the literature for the hydrolysis methods from hydantoins into the corresponding amino acids, you will find plenty of more or less comparable reactions using all kind of hydroxides or carbonates as bases. Examples of acidic hydrolysis are harder to find though. The hydrolysis of hydantoins is simply too well known to give amino acids, while Wada was the only one ever reporting it giving primary amines. So either he was wrong or all later researchers (and even industrial processes) are wrong.
Quote:
Wada actually used mass spectroscopy and the melting points of the compound in question and often its picrate derivative to characterize his products.

Mass spectroscopy in the year 1933? There is no mass spectroscopy there. He only gives melting points and N elemental analysis. Besides, if you check, already the first experimental makes no sense. He claims the product was 2-phenylethylamine, yet what he obtained was a solid with the m.p. of 189 °C.




…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)

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[*] posted on 1-12-2010 at 15:23


^ Oops, you're right, he just gives the N elemental analysis. And that "melting point" is a little strange.. maybe it's the boiling point? or the melting point of a salt or derivative? :\
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