This series of experiments, therefore, settled beyond doubt the question of the orientation of the iodine atoms in thyroxine, since it is certain that the last two iodine atoms, introduced into the acid (IV) in alkaline solution, must have entered the ortho positions to the free phenolic group.The solution of the difficulty was finally obtained in a different manner. As is well known, the presence of a nitro-group exerts a powerful mobilising effect on a halogen in the para position, a somewhat less marked effect on one in the ortho position, and no effect at all on one in the meta position.
It was obvious, however, that formidable diffi- Mild Quinol monomethyl ether, to give 3: 5- This nitrile, on boiling with a 171 Page 4 C. R. HARINGTON AND G. BARGER culties were to be expected, since the reduction which would be involved in the synthesis, from this aldehyde, of the corresponding a-aminopropionic acid would be.Although no pure substances could be isolated as the result of these experiments, the products of alkali fusion did, never- theless, exhibit pyrogallol reactions, from which it appeared probable that one or both of the benzene rings of the thyroxine molecule had been converted into 3: 4: 5-trihydroxy-derivatives.
These experiments in the first place reinforce the suggestion of the presence of two benzene rings, one at least of which has a phenolic or phenol ether group in the para-position to a side chain from which a two carbon fragment is split off as oxalic acid; it is unsafe to draw rigid conclusions as.302 Page 4 CONSTITUTION OF DESIODO -THYROXINE CH3OOBrHO CH KOHCHO 303 C1l30O 0- XCH3 "HO, O- CH3 CH30Kj0 - CH CH300 COOH CH30 Q37- 7HOH 3 CH3
Selected References These references are in PubMed. This may not be the complete list of references from this article. Harington CR. Chemistry of Thyroxine: Constitution and Synthesis of Desiodo-Thyroxine. Biochem J.P-Bromoanisol was then condensed similarly with potassium phenate, giving (4'-methoxyphenoxy) benzene (IV from this, by Gattermann's hydro- cyanic acid method, was prepared an aldehyde. This aldehyde was identical with the aldehydeC14H.O3obtained in the degradation, and was further proved to be 4-(4'-methoxyphenoxy) benzaldehyde (V) by the fact that, on oxidation, it gave an acid identical with.
On fusion at 2500 in an open vessel, the products werep-hydroxy- benzoic acid, a substanceCJ. H.,02,and a minute amount of quinol, together with ammonia and oxalic acid; on fusion at 3100 in an atmosphere of hydrogen there were obtained p-hydroxybenzoic acid and quinol in good yield, and again ammonia and oxalic acid; the substanceCJZH.02possessed apparently.On hearing from Prof. Barger that I had communicated a paper on the subject to this. Joeurnal, Dr Dakin withdrew his paper, which was at that time in the hands of the Editor of the.
Reviewing the results up to the present point then, we have in the first place by the potash fusion demonstrated the probable presence in desiodo-thyroxine of two benzene rings. The behaviour of the compound on exhaustive methyla- tion proves almost with certainty that it is an amino-acid; moreover, the presence of one methoxyl group in.(2) Kendall and Osterberg 1919 have described a colour reaction with nitrous acid and ammonia as being characteristic of thyroxine; we have found that this colour reaction is given in general by benzene derivatives which contain two iodine atoms in the ortho positions to a hydroxyl (or amino-) 1I have since learned that Dr H.
The iodine is readily removed from thyroxine by the usual reducing agents, e.g. sodium amalgam or aluminium-mercury couple, but in these cases the reaction products are not easy to obtain pure.The experimental and theoretical considerations leading to the above- mentioned supposition regarding the position of the iodine atoms were as follows. (1) Thyroxine was fused with potash at a high temperature in the absence of oxygen, in the hope of obtaining identifiable degradation products in which iodinewasreplaced by hydroxyl.
On oxidation with potassium permanganate (30) this acid gave a neutral substance, C04H,.03,together with oxalic acid. The substance C04H1203 gave a semicarbazone and a phenylhydrazone; since its formation in the above oxidation occurred in good yield and was accompanied by the formation of practically no acidic products, it was at first thought to be a.A certain simplification could indeed be effected by the methylation and subsequent oxidation of thyroxine, by a series of steps precisely similar to that described in the case of desiodothyroxine Harington, 1926 leading to a tetraiodo-derivative of the acid CH3O.C6H4.
Therefore, was condensed with 3: 4: 5-triiodonitrobenzene diiodo-4-(4'-methoxyphenoxy)nitro-benzene (I this compound was reduced to the corresponding aniline (II) and the latter converted, by means of Sandmeyer's reaction, into the nitrile (III).Thyroid hormones are derivatives of the the amino acid tyrosine bound covalently to iodine. The two principal thyroid hormones are: thyroxine (also known as T4 or L-3,5,3 5'-tetraiodothyronine) triiodothyronine (T3 or L-3,5,3'-triiodothyronine) As shown in the following diagram, the thyroid hormones are basically two tyrosines linked together with the critical addition of iodine at three.
In accordance with this fact it was found that, of the three iodine atoms in 3 :4 :5-triiodonitrobenzene, that in the 4-position is so far preferentially mobilised that this substance can be condensed with a phenol to give a good yield of the 3:5-diiodo-4-phenoxynitrobenzene.The desiodo-thyroxine so obtained proved to have the empirical formulaCOHu04N;it gave Millon's reaction and the ninhydrin reaction, and yielded the whole of its nitrogen with nitrous acid in Van Slyke's apparatus; it formed salts with acid and alkali; it was probably, therefore, an.
From this aldehyde it was then possible to synthesise 4-(4'-methoxy- phenoxy) cinnamic acid (VI) and also desiodo-thyroxine itself. By Perkin's reaction the unsaturated acid was obtained and identified with the degradation productC016H404.Journal of Biological Chemi8try, from publication. C. R. H. 2 The claim of Kendall and Osterberg 1919 to have synthesised thyroxine cannot be main- tained in view of the facts that no experimental evidence has been offered in support of this claim, and, further, that the views of these authors regarding the constitution of thyroxine.
Biochem J. 1934; 28(1 6872. The Department of Pathological Chemistry, University College Hospital Medical School, London. Full text Full text is available as a scanned copy of the original print version.Mixture of hydriodic and acetic acids, underwent simultaneous hydrolysis and demethylation, yielding 3:5-diiodo-4-(4'-hydroxyphenoxy)benzoic acid (IV on addition of iodine in potassium iodide to a solution of this acid in concentrated ammonia, iodine was rapidly taken up, the uptake ceasing abruptly at two molecules, and there was obtained a good yield of 3: 5- diiodo-4'-(3 5'-diiodo-4'-hydroxyphenoxy)benzoic.
In other words, iodine atoms (or other replaceable groups) had to be present in the ortho positions either to the halogen atom or to the phenolic group which was to take part in the phenyl ether condensation.The orientation of the iodine atoms in thyroxine remains to be finally determined, but experiments, which are as yet incomplete, indicate that the iodine atoms probably occupy the 3, 5, 3 5' positions.
(Received December 29th, 1926.) IN recently published work it has been shown by one of us Harington, 1926 that thyroxine is a tetraiodo-derivative of the p-hydroxyphenyl ether of tyrosinel; the orientation of the iodine atoms was left undetermined but it was suggested thatthey probably occupied the positions shown in the following formula: H H2.As regards the actual synthesis of thyroxine, the most favourable starting point appeared to be 3: 5-diiodo-4-(4'-methoxyphenoxy)benzaldehyde (VII) which could indeed be obtained in good yield from the nitrile (III) by the method of Stephen 1925.
The number and position of the iodines is important. Several other iodinated molecules are generated that have little or no biological activity; so called "reverse T3" (3,3 5'-T3) is such an example.Biochem J. 1930; 24 (2 456471. PMC free article PubMed Articles from Biochemical Journal are provided here courtesy of The Biochemical Society).
Thyroid hormones are poorly soluble in water, and more than 99 of the T3 and T4 circulating in blood is bound to carrier proteins. The principle carrier of thyroid hormones is thyroxine-binding globulin, a glycoprotein synthesized in the liver.This line of attack was therefore abandoned in favour of attempts to con- dense p-nitrohalogenbenzenes with 3: 5-diiodo-4-hydroxybenzene derivatives, e.g. to condense p-nitrobromobenzene with 3: 5-diiodo-4-hydroxybenzoic acid: 02N f 3Br i- HO i COOuch time was spent without success on experiments of this type.