|Lycaeum > Leda > Documents > The Alkaloids of the Common Poppy and the opium alkaloid porphyroxine|
W. Awe, W. Winkler, 1958 'Papaver Rhoeas and Papaver somniferum contain a special substance of an alkaloid character...'
of the Institute of Applied Pharmacy of the Brunswick Technical University (Director, Professor Dr. W. Awe)
Papaver Rhoeas and Papaver somniferum contain a special substance of an alkaloid character, obtained primarily from the flower petals and capsules, as regards Papaver Rahoeas, and from opium by extraction in the case of Papaver somniferum. In both cases, and herein lies the similarity, the substance takes on a reddish colouring when heated in a mineral acid, as a result of some hitherto unidentified reaction.
The alkaloid from Papaver somniferum, which turns red in this way, was in the first place given the double-barrelled name of porphyroxine-meconidine for external reasons. The history of its discovery and isolation, and its characteristics are described in the same publication (1). Through the good offices of Charles G. Farmilo we have also become acquainted with the thesis written by D. L. Klayman (2), which also deals with the isolation and characteristics of this alkaloid, in this case just called porphyroxine.
An obviously similar red-colour reaction of a Papaver Rhoeas alkaloid, together with the isolation of rhoeadine, was first reported by O. Hesse (3), the reaction being attributed to rhoeadine. Hesse also described rhoeagenine, which has a different melting point from rhoeadine and which he was able to obtain by alkalizing a solution of the above-mentioned rhoeadine. He at first regarded both rhoeadine and rhoeagenine as isomeric substances, and considered that other alkaloids were probably present, more particularly in the petals.
As one of us (4) had already written a paper about the common poppy alkaloids, we have done some more work on the subject and arrived at the following results :
By means of column chromatography on basic aluminium oxide, we (5) succeeded in obtaining from the original solution, after the rhoeadine had been crystallized out, a basic substance of a particularly vivid red which, however, differed from rhoeadine in certain respects. For the purposes of this article we shall call it " the red-colouring principle" and compare it with isomeric rhoeadine on the one hand and porphyroxine on the other, this being done by means of a table (table 1) for the sake of clarity. The data on porphy-roxine have been taken from the paper of D. L. Klayman (2) and do not derive from our own research.
6th paper on Papaver Rhoeas alkaloids. 4th and 5th papers, Arch. Pharmaz. Ber. dtsch. pharmaz. Ges., in the press.
As regards porphyroxine, D. L. Klayman (2) has also established the presence of two methoxyl groups and con siders the absence of a N-methyl grouping as probable. His investigations go to show that porphyr (oxine) hydrochloride is not homogeneous, but consists of three distinct elements. The porphyr (oxine) hydrochloride formation process is not itself reversible.
Pure porphyroxine or porphyr (oxine) hydrochloride was not available to us. If the porphyroxine-containing alkaloid mixture - isolated by the Fulton (1) method - is subjected, after admixture to rhoeadine from which the "red-colouring principle" has not been removed, to separation by paper chromatography, according to the butanol-glacial acetic acid-water process, it turns red as a result of hydrochloric acid steaming at various R f.values (chromatogram 1).
This experiment should be repeated with pure porphyroxine and pure " red-colouring principle" before arriving at a final opinion. Our experience so far leads us to the conclusion that there is great structural similarity between the red-staining substances of the two types of papaver, but that they are identical only as far as their configuration leads to colour formation.
We had only a very limited supply of red-coloured crystalline substance deriving from a Papaver Rhoeas alkaloid, the I-R absorption of which as compared with rhoeadine and the "red-colouring principle" is shown in diagram 1. Paper chromatography was used almost exclusively for its investigation. Paper chromatographically speaking, the red crystalline substance and the also dark red-brown pentahy-droxy-flavylium chloride (Cyanidin), which also melts at over 350°, are not in any way identical.
The red crystalline substance does not separate [**] on buffered paper in the above-mentioned solvent (chromatogram 2/3). Both in the case of self-staining and detection by the Dragendorff reagent, as modified by Thies & Reuther (6), no more than one spot of substance is discoverable.
The method used in preparing the base corresponding to the red crystalline substance seemed to us to be of some importance. The red crystalline substance is dissolved in a little water and then alkalized; the resulting yellow-green base is then shaken out in ether and dried. The ether residue dissolved in alcohol is used for the purposes of paper chromatographical analysis (chromatogram 2). The base in question has not the R f value of the "red-colouring principle" (chromatogram 3); its R f value is lower and about the same as that of rhoeagenine.
A certain proportion of the base in question is always reconverted into red crystalline substance in the mobile acid phase. On the other hand, neither the "red-colouring principle" nor rhoeagenine (chromatogram 3/4) gives off a red crystalline substance in the acid solvent. It is therefore to be assumed that the "red-colouring principle" obtained from Papaver Rhoeas suffers a structural alteration when converted into red crystalline substance (heating with 2N hydrochloric acid) and then has a base of the same R f value as rhoeagenine; this base then probably forms a hydrochloride, the red crystalline substance, in fact, as a secondary process.
Red crystalline substance in aqueous solution when combined with zinc and hydrochloric acid (i.e., by means of catalytic hydrogenation) can very easily be reduced to a completely colourless solution, from which the resulting base can easily be shaken out in the graduated tube in the usual way, and then prepared for paper chromatographical separation. Calculation of the R f value of this basic hydrogenation product reveals rather surprisingly that it is the same as that of the "red-colouring principle" (see chromatogram 2). This R f value is also the same as that of rhoeadine since we have not been able to achieve the paper chromatographical separation of the two bases - rhoeadine and the "red-colouring principle " - with the solvents used so far.
Since it can be shown by experiment that an opium alkaloid mixture containing porphyr(oxine) hydrochloride in the form of a dark red solution can very easily be reduced by the addition of zinc and hydrochloric acid with a consequent loss in colour, it can confidently be assumed, first, that the structurally conditioned red-colour reaction of both types of papaver is reversible in whole or in part, and secondly, that, in view of the fact that it is decolourized by means of a reducing agent, this structural alteration is oxydative or dehydrogenating by nature and is not connected in any way with the possibly salt-like structure of the red crystalline substance or the porphyr(oxine) hydrochloride.
As demonstrated by Awe (4), nitrogen can be eliminated from rhoeadine by a double Hofmann degradation, and according to Späth, Schmid & Sternberg (7) the same applies as regards rhoeagenine. In neither case could the degradation product be obtained in crystalline form. We repeated the degradation process with rhoeadine (8) and obtained des-N-methyl-rhoeadine in crystalline form with crystallized N-methyl-rhoeadinium-iodide as an intermediate stage. The hydrogenation product of the des-base, des-N-methyl-dihy-dro-rhoeadine, can also be isolated in crystalline form. From des-N-methyl-rhoeadine, nitrogen-free des-des-rhoeadine (C 20H 16O 6) in crystalline form was obtained via the related methiodide. Double Hofmann degradation carried to the point of nitrogen elimination with the resulting crystalline intermediate and end products demonstrates the simple ring formation of n - nitrogen and the presence of an N-methyl con- figuration. The double bond of the des-base absorbs at 267 mµ, hence the double bond actually obtained very probably belongs to one of the styryl configurations; the further double bond expected as a result of the second Hofmann degradation absorbs at 320 mµ. The nitrogen-free degradation product may therefore have a stilbene structure.
Probably by oxydative hydrolysis in the manner of the fission of narcotine into cotarnine or hydrastine into hydra-stinine, one of us (9) succeeded, with the help of 2N nitric acid, in converting rhoeadine into hydrastinine with rhoeagenine as an intermediate stage. The resulting hydrastinine was isolated in the form of picrate.
The elementary analysis shows:
Among other methods, separation by paper chromatography was used for identification by comparison with hydrastinine chloride (as supplied by Merck). The isolated picrate was for this purpose converted into chloride by means of a suitably pre-treated anion exchanger (chromatogram 5).
The ultra-violet absorption of (Merck) hydrastinine chloride and of hydrastinine chloride obtained from rhoeadine by degradation is much the same (diagram 2).
From the point of view of the mechanism of the red-colour reaction, the fact that rhoeagenine can be obtained from rhoeadine by oxidation seems very interesting. Again, rhoeagenine has the same R f value as the red crystalline substance base rhoeagenine can also be hydrogenated.
A change in the R f value is apparent from chromatogram 6. According to this finding rhoeagenine is not reconverted into rhoeadine by means of lithium aluminium hydride. We see in the similarity of the degradatory reaction of two certainly only slightly differentiated bases, very good support for our assumption that the first stage in the red-colour reaction is represented by oxidation or dehydration. (The nitric acid end oxydation is transferable to the red crystalline substance and therefore very probably also to porphyr (oxine) hydro- chloride (see in this connexion chromatogram 4).) The difference seen after hydrogenation could result from a difference in the agents used for reduction (for the red crystalline substance, zinc and hydrochloric acid; for rhoeagenine, lithium aluminium hydride); it may, however, also represent a real difference in the degradation products of the two Papaver Rhoeas alkaloids, rhoeadine and the "red colouring principle".
Summing-up: We have delineated a very probable course for the red-colour reaction process in the case of a Papaver Rhoeas alkaloid, and have reason to believe that the same process holds good for porphyroxine obtained from Papaver somniferum.
We see in the convertibility of rhoeadine into hydrastinine via rhoeagenine substantial evidence of the benzylisoquinoline structure of rhoeadine or rhoeagenine. Primarily theoretical considerations lead to a similar deduction as regards the structurally related porphyroxine.
In conclusion, we propose Rhoearubine as the name of the "red-colouring principle" of Papaver Rhoeas.
Chromatogram 1 - Chromatogramme 1
Chromatogram 1 shows the following substances, from left to right:
(1-4) Rhoeadine, from which the "red-colouring principle" had not yet been extracted, mixed with porphyroxine-containing opium alkaloids:
The development (turning red) takes place as a result of hydrochloric acid steaming; hence the other opium alkaloids are not identifiable. The R 1 values vary, even if their mutual influence upon one another through mixing is discarded.
Chromatogramme 1. - De gauche à droite:
(1-4) Rhoéadine, dont le" principle donnant une coloration rouge " n'a pas encore été isolé, mélangée aux alcaloïdes de l'opium renfermant la porphyroxine;
(6) Rhoéadine contenant le " principe donuant une coloration rouge".
La révélation (virage au rouge) se fait par exposition aux vapeurs de CIH; cette méthode ne permet pas d’identifier les autres alcaloïdes de l' opium. Les valeurs de R fvarient, même si l' on tient compte de l' influence que ces substances exercent les unes sur les autres par suite du mélange.
Diagram 1 - Diagramme 1
Chromatogram 2 shows the following substances from left to right :
Chromatogramme 2. -- De gauche à droite :
1) Rhoéadine, obtenue par extraction au benzol; une trés faible quantité de rhoéagénine adhére à la base extraite (tache trés légère);
2) Substance cristalline rouge, traitée par hydrogénation catalytique (zinc-acide chlorhydrique);
3) Base correspondant à la substance cristalline rouge; dans un solvant acide, la substance cristalline rouge se reconstitue en partie;
4) Substance cristalline rouge. 1-4). Révélation au réactif de Dragendorff; en 4) le réactif de Dragendorff en donne qu'une seule tache;
5) Substance cristalline rouge, mise en éividence par sa conleur naturelle.
Chromatogram 3 shows the following substance from left to right:
(1 to 4) Detection by means of the Dragendorff reagent.
Chromatogramme 3. - De gauche à droite:
3) Substance cristalline rouge aprés réaction à 1NO 3H 2N (voir page 22 du texte) (par suite de la faible concentration, tache trés pâle);
4) Base correspondant à la substance cristalline rouge (se reporter au chromato-gramme 3 ci-dessus);
5) Comme en 4); la tache inférieure est duc à la couleur naturelle de la substance, la tache supérieure à la révélation au réactif de Dragendorff;
6) Substance cristalline rouge;
1-4) Révélation au réactif de Dragendorff.
Chromatogram 4 - Chromatogramme 4
Chromatogram 4 shows the following substances from left to right :
(1-4) Detection by means of the Draendroff reagent;
Chromatogramme 4. - De gauche à droite :
(1-4) Révélation au reactif de dragendroff;
Diagram 2 - Diagramme 2
WAVE NUMBER V
NOMBRE D'ONDE V
- - - hydrastinine chloride " Merck " chlorure d'hudrastinine " Merck "
- - - hydrastinine chloride obtained through HNO 3 - oxydation of rhoeadine chlorured'hydrastinine obtenupar oxydation de la rhoéadine à l'aide de NO 3H
WAVE LENGTH λ
LONGUEUR D'ONDE λ
Chromatogram 5 - Chromatogramme 5
Chromatogram 5 shows the following substances from left to right:
(1-5) Detection by means of the Dragendorff reagent.
Chromatogram 5. - De gauche a droite:
1) Chlorure d'hydrastinine " Merck";
2) Chlorure d'hydrastinine obtenu par oxydation de la rhoéagedine à l’aid de NO 3H2N;
3) Rhoéagénine obtenue par oxydation de la rhoéadine à Paide de NO 3H2N (s'obtient comme produit intermédiaire de la réaction à NO 3H 2N);
1-5) Révélation au réactif de Dragendorff.
Chromatogram 6 - Chromatogramme 6
Chromatogram 6 shows the following substances from left to right :
Chromatogramme 6. - De gauche à droite:
2) Base obtenue par hydrogénation de la rhoèagènine à Paide de LiA1H 4;
3) Rhoéagénine obtenue à partir de la rhoéadine à l’aide de NO 3H 2N.
Fluorescence of various colours occurs, but is of no importance as regards the alkaloid character of the primary substance.20