CY-PSEUDACONITINE AND CY-VERATROYLPSEUDACONINE
Dec., 1946
[CONTRIBUTION FROM THE
DIVISIONOF
CHEMISTRY NATIONAL
2565
RESEARCH COUNCIL]
a-Pseudaconitine, and a-Veratroylpseudaconinel BY LBO MARION AND 0. E. EDWARDS Of the previously reported aconite alkaloids two only, bikhaconi tine2 and pseudaconitine3 yield acetic and veratric acid when hydrolyzed, together with basic fragments designated as bikhaconine and pseudaconine, respectively. A third, indaconitine,4 yields on hydrolysis, acetic acid, benzoic acid and pseudaconine identical with the alkamine obtained from pseudaconitine. Two only of the four hydroxyl groups present in pseudaconine are involved in ester linkages in the parent alkaloid and, therefore, several isomers of pseudaconitine are theoretically possible. It is the object of this paper to report one such naturally occurring isomer and a veratroylpseudaconine isomeric with but different from the veratroylpseudaconine produced by the partial hydrolysis of pseudaconitine, Coinmercial “Nepaul Aconite Root’’is known to contain a varying quantity of Aconitum A’apellus which is the best source of aconitine. h recent shipment that came to this Laboratory was found to contain no aconitine whatsoever. It has, however, been possible to isolate from the material two new bases which were separated through the different solubilities of their hydrochlorides in chloroform. One of these is isomeric with pseudaconitine and like it on hydrolysis yields acetic acid, veratric acid and pseudaconine. It is proposed to dcsignate it as a-pseudaconitine. The sc~coiitlbase yields, when hydrolyzed, veratric acid and pscudaconine but no acetic acid. It is identical with the veratroylpseudaconine obtained as ;Iproduct of the partial hydrolysis of a-pseudaconitine but diff (:rent from the veratroylpseudacoriine obtained similarly from pseudaconitine.* I t is, therefore, proposed to designate it as a-veratroylpseudaconine. The formula of pseudaconitine as corrected by Dunstan and Andrewsj4 C3&6101&, is accepted with reserve because of the unusual difficulty experienced in analyzing the alkaloids and their derivatives for nitrogen. Pseudaconine obtained from both bases is identical with the pseudaconine produced when pseudaconitine is hydrolyzed and it has been identified by analysis, by its properties and by the prc‘paration of its known derivatives. Pseudaconinc forms a tctraacetyl derivative which, when licsated a11ox.e its nielting point in V U C Z L O ,loses acetic acid and i: converted to triacetylpyropseudaconine.6 Thi:;, in turn, can be saponified to pyropseudaconine. . It has now been found that the formation of triacetylpyropseudaconine is ac( 1 ) Published as N. I?. C. N o , 1396. ( 2 ) W I < . T)tlnstitn and A . E. Anrlrews. J . C h e m . Soc.. 87, 1636 (I!lO.‘,) ‘ : i > W R. Duiisl.atl aiid 1’. Ii Carl-. t b ~ d .71, , 350 (1807). ‘ 4 1 i\’, K. 1)iiiistiiil aiicl A . 12 Aiidrews. i b i d . , 87. 1620 (1Y05) i.i)
1’.M Shatrp, i b i d , . 3UY.l (1928)
companied by the production of a small quantity of a second pyrolytic substance which had not previously been observed. Moreover, when pseudaconine was boiled with 10 N sulfuric acid it lost one methyl group attached to oxygen plus the elements of methanol and gave rise to des-0methyldemethoxydehydropseudaconinewhich contains two methoxyl groups whereas pseudaconine has four. It is already known that one of the methyl groups attached to oxygen is relatively unstable since pyropseudaconitine, on acetylation, yields a compound which contains three acetyl groups but has only five methoxyl groups whereas pyropseudaconitine has six.5 However, the removal of a second methoxyl group as inethanol has not hitherto been observed in the aconitine series. Like pseudaconitine, a-pseudaconitine pyrolyses readily, but it has not been possible to crystallize pyro-a-pseudaconitine. Furthermore when tetraacetylpseudaconine is pyrolyzed one, and only one, mole of acetic acid is lost. It is, therefore, likely that the acetyl group occupies the same position in the two isomers. Since a-veratroylpseudaconine is not identical with vcratroylpseudaconine, it is also likely that a-psuedaconitine differs from pseudaconitine in that the veratroy1 group does not occupy the same position in the former as it does in the latter. It may be nientioncd, incidentally, that this case of isonierisni is one of the very few of that type noticed so far in the naturally-occurring aconite alkaloids.
Experimental A dricd 1)ctizcnc cxtract of coininercial ‘‘Nepaul Aconite Root” (4.55 kg.) obtained from the Fine Chemical Company, Toronto, was used as starting. material. The dry material was broken up, stirred into aqueous oxalic acid, the mixture filtered, basified with ammonia and exhaustively extracted with chloroform in continuous liquidliquid extractors. The combined chloroform extract was distilled t o dryness and the residue dissolved in aqueous oxalic acid. The filtered solution was extracted repeatedly with ether, basified with ammonia and again exhausted with chloroform in continuous extractors. The combined chloroform extract was concentrated t o about one liter and extracted with three portions of 3 N hydrochloric acid, each about one-third the volume cf the chloroform solution. There were thus ohtairicd a chloroform solution A of thc soluble base hydrochlorides and a n aqueous solution 13 containing the base hydrochlorides insolublc in chlorofortn. Isolation of a-Veratroy1pseudaconine.-The aqueous solution B was basified with ammonia and the solution thoroughly extracted k s t with ether and then witn chloroform. The chloroform extract was distilled to dryness and the residual bases dissolved in 3 N hydrochloric acid, the solution basified again with ammonia and extracted again first with ether and then with chlorcform (extract C ) . Thv combined ether cxtract was di.;tilled to drynfss and the rcsidual gum dissolved in a little wariii inethanol. Aftcr long standing this solutiori depo5ilecl a fcw crystals arid cautious additioii of absolute ethcr then brought
2566
Lko MARION AND 0.E.EDWARDS
down a copious precipitate of the crystalline base. After four recrystallizations from methanol-ether, from which it separated as colorless flat needles, a-veratroylpseudaconine melted a t 209-211 O6 when immersed in the bath a t 180"; wt. 0.5 g., [ a ] n+55" (c = 1.137 in chloroform in micro-tube) . A n d . Calcd. for C34H4gO11N: C, 63.06; H, 7.57; N, 2.16; 6 OCH,, 28.75. Found: C, 63.35, 63.14; H , 7.81, 7.66; 'RJ, 2.28, 2.20; OCH,, 28.15,26.15. A methanolic solution of a-veratroylpseudaconine was cautiously neutralized with 65% perchloric acid. Crystallization of the perchlorate was induced by the addition of a little absolute ether. After recrystallization from methanol, (2-veratroylpseudaconine perchlorate consisted of clusters of colorless rectangular plates sintering a t 231 and melting a t 232-233" (dec.) when immersed in the bathat210". A n d . Calcd. for C3dH4~OliN.HC104: C, 54.59; H , 6.69; N, 1.87; C1, 4.75. Found: C, 54.57, 54.65; H, 6.70, (i.84; X, 1.79; C1, 4.79, 4.66. A solution of a-veratroylpseuaaconine in a r y methanol was acidified to congo red by the dropwise addition of 40% hydrobromic acid. The addition of absolute ether combined nfith cooling in a Dry Ice-acetone-bath brought about the crystallization of the hydrobromide which, after 5everal recrystallizations from methanol-ether, was obtained as colorless flat needles melting a t 246247" (dec.) when immersed in the bath a t 235". And. Calcd. for C34H4POI~K.HBr: Br, 10.98. Found: Br, 10.64. A small quantity of a-veratroylpseudaconine in dry methanol was converted to the hydriodide by the procedure folloFved for the hydrobromide. The recrystallized hydriodide which separated as small faintly yellow buttons, melted a t 246" (dec.) when immersed in the bath a t 210". Isolation of a-Pseudaconitine .-The chloroform solution A containing the soluble base hydrochlorides was distilled to dryness, the residue dissolved in 3 -V' hydrochloric acid, the solution washed several times with ether and basified with ammonia. This caused the precipitation of an amorphous base which was filtered. The filtrate was extracted first with ether (extract D) and then with chloroform (extract E). The amorphous Precipitate was dried (13 g . ) , di iti methanol aiid the solution neutralized rsith 65 chloric acid. A crystalline salt was precipitated ~rhich after recrystallization from methanol began to sinter a t 233"andnielted at245' (dec.), wt.2.5g. Tht: ether extract of the basic filtrate (extract D) was conce;itrated on the steam-bath and dried over anhydrous sodiuin sulfate. a-Pseudaconitine crystallized from the ether solution and after repeated recrystallization from methanol n as obtained as colorless diamond-shaped prisms, i n . p. 205-2013" (dec.) when immersed a t lSO", wt. 1.2 g. [ ~ z ] .t2&.7" ~ ~ D (c = 2.40 in chloroform). I n admis.ture with ru-vc~ratroylpseudacn~iine it melted a t 193.195". A n a / . Calcd. for C&61012N: C, 62.70; 11, 7.40; N , 2.03; 6 OMe, 27.0. Found: C, 63.03, 63.12; 13, i . 7 3 , 7.92; .9,2.44,2.47; OMe,26.57,28.67. a-Psrudaronitinc dissolved i l l dry methanol \vas neutralized with 65% perchloric acid. A perchloratc crystallized ,out which after three recrystallizations from dry inethanol and one from acetone, was obtained as colorless diamond-shaped plates which began to sinter a t 233" and melted a t 246" (dec.) when immersed in the bath a t 210' either alone or in admixture with the perchlorate obtained from the above-described amorphous precipitate. A n d . Calcd. for C36Hj1012N.HC10*: C, 54.72; H , 6.58; S , 1.77; C1, 4.50. Found: C, 54.25, 54.27; €1, 6.96, 7.08; N, 1.27; C1,4.61,4.42.
Vol. 68
from a-pseudaconitine but it formed a hydriodide which crystallized from methanol-ether as clusters of needles meltin! a t 220-220.5" (dec.) when immersed in the bath at210 Anal. Calcd. for C36Hj1Ol?N.HI: C, 52.88; H, 6.36. Found: C, 52.77, 52.69; H , 6.31, 6.53. Both the hydrobromide and hydriodide of pseudaconitinie contain water of crystallization and melt a t 199 and 230 , respectively .? Hydrolysis of a-Pseudaconitine.-a-Pseudaconitine (1.2 9.) was hydrolyzed by boiling with methaiiolic potassium hydroxide. Most of the methanal was evaporated, water added and the solution extracted repeatedly with chloroform. The combined chloroform extract when distilled to dryness left a basic residue which crystallized from acetone. After two recrystallizations from the same solvent the base was obtained as colorless prisms containing 1 mole of acetone; sintered a t 81" and melted a t 86" (dec.) [a]*+38.1" (G = 1.272 in water). Henry and Sharp? give for pseudaconine crystallized from acetone, 38.7" (in water), whereas I h n s t a n m. p. 93-94', [ C X ] ~ O D and Andrews4give m. p. 86-87', [a]*f 39.0" (in water). Anal. Calcd. for C Z ~ H ~ ~ O ~ N . CC, ~ H62.04; ~ O : II, 8.69; Ti, 2.59; 4 OCHI, 22.92; C ~ H B O10.72. , FOUII~: C, 62.18, 62.23; H , 8.62, 8.70; A-, 2.89, 3.00; OCHa, 22.76,22.82; CaHsO, 9.94,10.2. Pseudaconine can also be crystallized from ethanol from which it separated as colorless prisms containing 1 mole of ethanol which began to sinter a t 90 O and melted completely a t 97". Anal. Calcd. for C ~ S H ~ ~ O & . C P H C, ~ O 61.25; : H, 8.88. Found: C, 61.58, 61.60; H , 8.68, 9.00. For pseudaconine crystallized from ethanol, Dunstan and Andrews4 give m. p. 94-95'. The aqueous potassium hydroxide solution which had heen extracted with chloroform was acidified with sulfuric acid. This caused the precipitation of a crystalline acid which, after cooling, was filtered and washed with a little water. After two recrystallizations from aqueous methanol it consisted of colorless leaflets, m. p. 180-182" either alone or after admixture with ail authentic sample of veratric acid. The aqueous mother liquor from which veratric acid had first separated was tlistillcd with steam so long as the distillate showed ari acid rcactioii. The distillate wah neutralized with 0.1 N sodium hydroxide atid evaporated to dryiicss. The solid residue was dissolved in water (2 cc.) a i d p-hrornophenacyl bromide (0.2 g.) added together with suficient ethanol to producc a clear solution which \vas refluxed for two hours and allowed to cool. Some unchanged P-bromophenacyl bromide first separated anti then a crop of crystals which after thrcc recrystallizations from aqueous methanol melted a t 80-83" either alone or after admixture with an authentic samplt, of p-bromophenacyl acetate (m. p . 85-86'). Hydrolysis of a-Veratroylpseudaconine.-a-i'eratroylpseudaconine (93 mg.) mas hydrolyzed by refluxing with methanolic potassium hydroxide. The resulting solution when worked up exactly as above yielded pseudaconine which was crystallized from acetone. Either alone or i n admixture with the hydrolytic base obtained from apseudaconitine, i l bcgan to sinter a t 81' and melted at 84" (der.). Thc. hydrolysis liquor also yielded a small quantity of veratric acid but no acetic acid. Tetraacety1pseudaconine.-Pseudaconine 70 m g . obtained from a-pseudaconitine) was refluxed for two hours with acetyl chloride (2 cc.), the excess reagent distilled off and the residue dissolved in water. The solution was basified with sodium carbonate and extracted repeatedly. with ether. The combined and dried extract when distilled to dryness left a crystalline residue which !vas crystallized four times from methanol. Tetraacetylpseudaconine formed clusters of colorless neecllcs, m . p. 327-228' idee.) when immerscd in the bath at ? I ( 7 " ; wt 76 mg., l a ] ---8.2" ~ ( t - = 1.12in ethani,li.
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Dec., 1946
a-PSEUDACONITINE AND CY-VERATROYLPSEUDACONINE
2567
Henry and Sharp' describe tetraacetylpseudaconine as, as colorless six-sided plates, m. p. 154", [ a ] D +157.3" (c = 0.642 in abs. ethanol). Triacetylpyropseudacnine colorless stout needles, m. p. 228" (dec.), [ a ] " D -8.1 has been described6 as six-sided plates, m. p. 155-158', (c = 0.956 in alcohol). [ a ]+156.4'(c ~ = 1.2inethanol). Anal. Calcd. for C33&9Oi?N: C, 60.83; H, 7.53; Anal. Calcd. for C J ~ H ~ ~ OC, ~ ~62.94; N : H, 7.61; N, IT,2.15; 4 OCH3, 19.05; 4 CHjCO, 26.42. Found: C, 2.37. Found: C, 63.13; H , 7.48; N,2.71. 60.46, 60.70: H , 7.58, 7 . 5 5 ; S , 2.31, 2.35; OCH,, 19.69; 19.40; C€€,CO, 25.08, 25.58. Hydrolysis of Triacety1pyropseudaconine.---Triacetylpyrops.eudaconine when hydrolyzed with methanolic The tetraacetyl derivative was also prepared from a small quantity of .pseudaconine obtained from the hydroly- putasslum hydroxide yields pyropseudaconine which ' wheii crystallizes from ether as colorless needles, m . p. sis of a-veratroylpseudaconine and found by melting immersed in the bath at 155", :a]" '927' (c = 0.2736 i n point and mixed melting point to he identical with that ahs. ethanol). Sharp6 describes pyropseudaconine as described above. prismatic iieedles, m . p. 173-174', ! n ] o -230.1' ( c = The mot?ier-liquorsfrom the crystallization of a-pseuda1.12 in ethanol). conitine and a-veratroylpseudaconine were combined with Extracts C and E and evaporated to dryness. The resid.Am!. Calctl. for C2.111907S: C, & I . Z ; H, 8.30. ual gum was saponified with methanolic potassium Found: C, E4.30, 154.57; H , 8.01, '3.44. hydroxide and the basic product refluxed with acetyl chloI'yropsrudaconiric can a12.o IJC crystallizctl froin ivater ride. This yielded tetraacctylpseudaconinr, m. p. 227froin \vhich it separated as colorle,s, prismatic needle.. con228", wt. 6.4 g. taining f! moles cf watcr, ni. p . 92'. Partial Hydrolysis of a-Pseudaconitine.-a-Pseuda. 4 n , / l . Calcd. for C?jlTa'07S.2H20: C, ,j9.W; I i , conitine (92 mg.) was dissolved in dilute sulfuric acid, 8.58. Found: C, 59.38, 39.71; H, 8.42,8.67. the solution made just neutral by the addition of dilute Des-0-methyldemethoxydehydropseudaconine. - l k m l a sodium hydroxide and heated in a sealed pressure tube a t 135" for three hours. After cooling sulfuric acid was conine (0.33 g.) was rcfliixetl for ninety rnii1uti.s i v i t l i 10 -Y sulfuric acid (30 w.;, the ,olutioii zooid, bn-iadded and the solution repeatedly extracted with absolute ether. The combined extract on evaporation yielded no ficd with ,odium carboiiatc aiic! thoroughly r\tractcd \villi veratric acid but a. volatile acid which was distilled from a chloroform I 10 rimes). The combinctl extract o : ~evaporation yicltlcd a gumlily resitlut, which crystalliLed from small bulb heated in an air-bath (120-130"). The colorless acid which had a strong odor of acetic acid was con- watt-r froin lvhicti i t \vai u1,taiiic.d as color1t.Y- ~icc(llci verted t o the silver salt by shaking with water and silver coiitaiiiiiig 3 i i i o l c , of watc.r, which iiiitcrul a t 11,s' at!d oxide. The filtervd solution when evaporated to a small melted at 1 1 4 ' t1cr.i; w t . t ~ . I - L g . volume ica. 0.5 ce.) deposited needles of silver acetate, wt. duel. Calcd. for c..?lI..o-S.:3II.o: c. .Td.2O: 11. 2 mg. The previou: identification of acetic acid in the 8.35; 2 OCHJ, 1 2 5 3 ; 3 H 2 0 , 11.0.- Founh: C, 56.441 complete hydrolysis of a-pseudaconitine and the isolation 56.43; H , 8.22, 8.43; OCH3, 12.46, 11.88; H20, 10.0, of cu~veratroylpseudaconine described below show that 9.55 (in "JQCUOover boiling water). this salt must be silver acetate. The base left after heating for two hours a t 100" (0.5 The aqutious acid solution which had been extracted mm.) consisted of a white powder which readily absorbed with ether was basified with sodium carbonate and water from the air. Even after prolonged and repeated thoroughly extracted with chloroform. The base recovheating, analysis revealed a trace of water still present. crcd from t hc combined chloroform extract was dissolved Anal. Calcd. for C d & x : C, 63.16; H, 8.01. i n acetone, thc iolution concentrated to a thin sirup and allowed t o statid. A crystalline base separated which was Calcd. for C23H360'hT.0.5H20: C, 61.88; H, 8.07. rccrystallizcd twice from methanol-ether from which it Found: C, 61.84,62.03; H, 8.37, 7.86. Des-0-niethyldemethoxydehydropseudacoriincwhen In separated ;is colorless needles, ni. p. 207-211 admisture n i t h ~-.veratroylpseudaconine,the in. p. was crystallized from methanol separated as colorless iicedks which sintered at 127" and melted a t 133" (dec.), Thc 208-211 '; wt. ti2 mg. [ a I u +49" (c = 1.12 ill cliiorofortn crystals contain one mole of methanol which is gradually iri a Hilger iiiicrotube) .g Veratroylpseudacotlinc obtained lost on standing, [ a ] n 1.17.9' (c = 0.488 in dry methafrom pseudaconitine mclts a t 199" arid has [ a i l , -38.18" nol) . (c = 1.5 in ;rlcohol) . 3 Pyrolysis of Tetraacety1pseudaconine.--TetraacetylAnal. Calcd. for C P ~ H ~ ~ O ? N . C HC ~ ,O :til.41; I+, pseudaconine (0.323 9.) was heated for three minutes a t 8.32. Found: C, 61.49,61.34; H, 8.46, 8.17. 240°/1 mm. when a vigorous reaction took placc. After Pseudaconine was not altered by boiling with 285; cooling, the residue in the flask (wt. 0.30 g.) was dissolved phosphoric acid but hoiling with 65% phosphoric acid proin warm dry methainol. A small precipitate of fine, color- duced the same compound as 10 iV sulfuric acid. less needles separa.ted almost immediately. After three recrystallizatioris from riiethanol the product sintered a t Summary 281 and melted a t 284 '. Anal. Found: C , 62.36, 62.19; H, 8.05, 8.07; N, 1. Two new alkaloids have been isolated. 2.87; O M e , 21.87. One of these, a-pseudaconitine, is isomeric with 'l'hc foregoing stibstaiice which had not yet been reIwrtetl was ohtaiiietl iu too small a yield to pcrmit the pseudaconitine. The other is identical with the imparatiori of derivatives. Saponification yielcled a gum base obtained on removal of the acetyl group of which could not be crystallized. Because of the uncera-pseudaconitine by partial hydrolysis and it has tainty of thc nitrogen determinations in pseudaconine and been named a-veratroylpseudaconine. the product:; tierivd from it, no attempt is made a t sug2. On complete hydrolysis a-pseudaconitine, gesting an empirical formula for the product melting a t like pseudaconitine, gave rise to acetic acid, vera281O. The original methanolic mother-liquor from which the above compound had separated was concentrated on tric acid and pseudaconine whereas a-veratroylthe steam-bath. On cooling it deposited a second product pseudaconine yielded veratric acid and pseuda-
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