[CONTRIBUTION NO.47 FROM THE
RESEARCH LABORATORIES OF HOFFMANN-LAROCHE,INC.]
ARYLAMINE - r\' - GLYCOSIDES. PART 11. ARYLAMINE - N - PENTOSIDES AND COMPLEX SALT FORMATION STUDIES LEO BERGER
AND
JOHN LEE
Received October &B, 1944
3,4-Xylidine-X-~-ribofuranoside is an intermediate in the manufacture of riboflavin (vitamin Bz)(l). During the course of the technical development of its preparation, U. V. Solmssen of these laboratories observed that the addition of 3 ,4-xylidine in alcohol to a technical solution of D-ribose containing scdium sulfate resulted in the formation of an insoluble "complex salt". This salt could be hydrogenated directly to yield ribitylxylidine (2). The present authors undertook the investigation of the reaction in the absence of sodium sulfate and found that a new class of N-ribosides, which in all probability are cu-arylamineX-D-ribopyranosides, are fornied when the sugar and the arylamine are condensed in alcohol or aqueous alcohol at low temperatures. The pyranosides are converted quantitatively to the corresponding furanosides merely by heating in alcoholic or aqueous alcoholic solution or can be prepared by direct condensation in hot alcoholic solution (3). Kuhn and co-workers (1, 4) obtained good yields of arylamine-N-glyco. furanosides by mixing the amine and the sugar in alcohol and boiling. Acid catalysts such as HC1 or ammonium chloride were found desirable in most condensations and absolutely necessary in some. Aniline, toluidine, phenetidine, etc. condensed readily with pentoses and hexoses in hot alcoholic solution in good yield ; however, o-nitroaniline did not react with pentoses and hexoses under these conditions. Two to five per cent of ammonium chloride catalyzed this reaction so that yields over 80% were obtained. The yield of this condensation was influenced greatly by the presence of small amounts of water in the alcohol. Thus, when D-ribose was condensed with 2-nitr0-4~5-dimethylanilinein 98% alcohol, a 30% yield of condensation product was obtained. If absolute alcohol vas used the yield was increased to 60% or more. As reported in the first paper in this series (3), aniline condensed with D-ribose in alcohol or aqueous alcohol solution a t room temperature to form cu-anilineX-D-ribopyranoside in excellent yield (90-96%). The reaction was accelerated with a trace of acid (pH 4.0) without any change in actual yield. o-Nitroaniline was condensed with D-ribose under these conditions to yield o-nitroaniline-ND-ribopyranoside in excellent yield (94.4%). Various other arylamines as orthochloroaniline, p-carboxyanilint:, p-methylaniline, p-methoxyaniline, m-hydroxyp-methoxyaniline, a-naphthylamine, and P-naphthylamine reacted with ribose under the same conditions to give the corresponding X-ribopyranoside in good yield. Arabinose condensed with aniline under these conditions to give aaniline-S-D-arabinopyranoside in 50% yield. The product obtained occurred as colorless large prisms melting a t 130"; [a]:' +8.9" -+ -13.2"; (c = 1.9% in methanol; 48 hrs.; [a]:' +68" + -4.3"; (c = 3% in pyridine; 48 hrs.). 84
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ARYLAMINE-N-GLYCOSIDES. I1
This material differed from the aniline arabinoside prepared by Hanaoka (5) whose compound had the following characteristics: m.p. 130”; colorless plates; CY]^^ +34.0” + f2.5”; (c = 1.0% in methanol). A preparation of aniline arabinoside, according to the method described by Hanaoka, had the following characteristiw :m.p. 130”;colorless plates; [CY]+27.4” --+ -8.0”;(c = 1.6% in methanol; 24 hrs.); [CY]:’ +82‘ + +1.48”; (c = 2.0% in pyridine; 24 hrs.). Following the observation of Solmssen, we have found that arylamine-N-Dribopyranosides are characterized generally by the ability to form “complex salts” with the soluble salts of rtlkali metals (preferably a t pH 4), which separate from aqueous alcohol,‘ and which contain the organic matter in a loose combination with the salt used. Sodium sulfate, lithium sulfate, sodium acid phosphate, sodium nitrate, potassium sulfate, sodium acetate, sodium citrate, etc. were among the salts that were used to form the “complex salt”. The pyranoside was extracted quantitatively from the “complex salt” by extraction with dioxane (acetone or pyridine), filtering and adding carbon tetrachloride to precipitate the N-ribopyranoside with varying amounts of solvent of crystallization. The pyranoside was also isolated from the “complex salt” by trituration and digestion with cold water, but this was a tedious process accompanied with losses. Extractions of the “complex salt” with hot alcohol (which converted the pyranoside to the furanoside) gave the S-ribofuranoside in excellent yield. Crystalline D-ribose was isolated in pure form from aqueous solutions containing crude D-ribose and salts in varying concentration (up to saturation) by utilization of this unique “complex salt” formation. Aniline was dissolved in sufficient alcohol to make a 30% aqueous alcohol solution when mixed with the aqueous crude sugar solution containing salts, and added to the solution (whose ,pH was brought to 4.0 with dilute HzS04) with stirring. The reaction was kept a t 25” for one hour and set in the refrigerator a t +5” overnight. The “complex salt” obtained contained the ribose in the form of a-aniline-N-Dribopyranoside loosely joined with varying amounts of salt. The yield of pyranoside (based on Fehling titration and/or extraction) ranged from 85% to 95%. The pyranoside, either in pure crystalline form or in the form of the “complex salt”, was then hydrolyzed to regenerate D-ribose and aniline. A more detailed discussion of this reaction will be reported in another paper in this series. The pyranoside in the “complex salt” form can be hydrogenated directly, and the reduction products then separated from the accompanying salts. Thus a solution of D-ribose, prepared by the electrolytic reduction of D-ribonolactone
:’
1 When acetone or dioxane was substituted for alcohol in the preparation of the “complex salt,” there was a considerable drop in yield. However, aqueous alcoholic solutions containing as little as 5% alcohol were used successfully with little change in the resultant yield. It was found that enough alcohol t o keep the amine in solution and still not precipitate much of the salts present was the most satisfactory mixed solvent and gave the maximum yields. An aqueous alcohol solution containing 30% water by volume was generally used.
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in an electrolytic solution of sodium sulfate, was condensed with an alcoholic solution of aniline (also 3,4-xylidine) in the usual manner. The "complex salt" precipitate obtained was separated and hydrogenated in alcohol with Raney nickel to give N-ribitylaniline (or N-ribityl-3 4-xylidine) in excellent yields. D-Glucose, D-arabinose, D-galactose, L-sorbose, D-xylose, and fructose did not form "complex salts" which separate when condensed with aniline in aqueous alcohol in the presence of sodium sulfate, whereas D-mannose and D-lyxose did form "complex salts" under these conditions. Indications are that sugars with hydroxyls in the 2- and 3-position in cis-configuration favor the formation of N-glycopyranoside "complex salts". The ability to form these "complex salts" was used to separate a prepared mixture of ribose and arabinose in fair yield. Equal parts of ribose and arabinose were condensed with one mole of aniline in the presence of sodium sulfate in the usual manner. The complex obtained yielded a-aniline-N-D-ribopyranoside in 67% yield on extraction. The utilization of this unique property of N-ribopyranosides (also N-mannoand N-lyxo-pyranosides) would perhaps facilitate the separation of these sugars from crude reaction liquors containing salts or other impurities. )
EXPERIMENTAL
Preparation of substituted aniline-N-D-ribopyranosidev. General procedure. Two grams of crystalline D-ribose was dissolved in 25 cc. of 95% ethyl alcohol. One drop of 3 N sulfuric acid was added. Two grams (slight excess) of the required amine (substituted aniline) was added with stirring. The reaction was kept at room temperature for two hours and then set in the refrigerator a t 5" overnight. The product that crystallized out was filtered off, washed with cold alcohol, and finally with dry ether. The product was dried at room temperature and submitted far analysis as such. The yields were excellent; in some instances quantitative. Table I lists the physical constants and the analysis of the compounds prepared. a-Aniline-N-D-arabinopyranoside. Five grams of D-arabinose was dissolved in 35 cc. of water and 4 cc. of aniline dissolved in 15 cc. of alcohol was added with stirring. The mixture was set aside a t 5" for two days after standing a t room temperature for ten minutes. The reaction mixture was then concentrated to dryness in vacuo a t 35'. The residual syrup was crystallized froni alcohol and ether t o yield 3.5 g. of large colorless prisms melting at 130". The mother liquor grtve another crop (1.0 g.) on concentration (total yield: 54%); [e]$+8.9" -+ -13.2'; (e = 1.9% in methanol; 48 hrs.); /CY]: +68.0" -+ -4.3"; ( c = 3.0% in pyridine; 24 hrs.). a-Aniline-N-~-arabinofuranoside. Prepared according to the directions of Hanaoka (5) a n aniline arabinoside was obtained which occurred as colorless plates (from alcohol) melting at 130'; [elb'+27.4" --+ -8.0'; (e = 1.6% in methanol; 24 hrs.); [a]: $82" --+ +1.48'; (c = 2.0% in pyridine; 24 hrs.). Hanaoka (5) reported the melting point 130' (colorless plates); [e]: $34.0' -+ +2.5"; ( c = 1.0% in methanol). A mixed melting point of the two aniline arabinosides gave no appreciable depression (129-130"). Aniline-N-D-ribopyranosides and -furanosides as a rule do not give depressions in mixed melting points. a-Aniline-N-D-ribopyranoszde-Na2SOa complex. Crude D-ribose (1.39 g.) was dissolved in 25 cc. of 9% sodium sulfate solution and 7 cc. of alcohol was added. The p H was adjusted t o 4.0 with 3 N sulfuric acid, and 1 cc. of aniline dissolved in 5.5 cc. of alcohol was added
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with stirring. The mixture was stirred at 25’ for one hour, and set in the refrigerator at 5” overnight. The “complex salt” mass was filtered off triturated with ten volumes of absolute alcohol, and filtered again. After drying in vacuo at 25’, the white precipitate (aniline ribopyranoside “complex salt” I weighed 3.9 g. Analysis indicated that i t contained 1.81 g. of riboside equivalent to an 87.5% yield.2 Other salts were used t o form a similar “complex salt” in varying yields employing the above conditions, e.g.: lithium sulfate (20% yield) sodium hydrogen phosphate (43%), sodium nitrate (85%), potassium sulfate (36%) sodium acetate (68%). D-Mannose and D-lyxose formed similar “complex salts” with aniline and sodium sulfate under the above conditions. D-Glucose, D-arabinose, D-galactose, n-xylose, as well as fructose, and L-sorbose did not react at all. Isolation of a-aniline-N-D-ribopyranosidef r o m “complex salt.” a-Aniline-N-D-ribopyranoside-sodium sulfate “complex salt” (containing 1.81 g. riboside) was extracted with 20 volumes of dry acetone on the shaking machine for two hours. The salts were filtered off through a Hyflo matte and the solution was concentrated t o dryness in Vacuo t o yield 1.78 g. of pure a-aniline-N-D-ribopyranoside, m.p. 124-126’; [a]: +61.6”; (c = 4% in pyridine, initial rotation). The pyranoside was also extracted quantitatively from the “complex salt” with anhydrous dioxane and recovered by precipitation with carbon tetrachloride t o yield a riboside with varying amounts of dioxane of crystallization. Pyridine was also used t o remove the organic matter from the“comp1ex salt” but isolation of the pure pyranoside from the pyridine was difficult. The product was obtained in pure form from pyridine only if the Bolvent was removed in high vacuum at 0’ to 5”. Higher temperatures caused excessive decomposition. The product obtained through pyridine decomposed more rapidly than the pyranoside isolated via acetone or dioxane. a-Aniline-If-D-ribofuranosidef r o m “complex salt.” a-Aniline-N-D-ribopyranoside “complex salt” (50 g., containing the equivalent of 24.75 g. of pyranoside as determined by titration) was extracted with 400 cc. of boiling alcohol for thirty minutes. The hot solution was filtered through a Hyflo matte. The alcohol solution on cooling deposited 18.0 g. of a-aniline-N-D-ribofuranoside, m.p. 138-140”; [a]: 1-176” -+ 156’. The alcoholic mother liquor was concentrated in vucuo to yield 6.3 g. of additional material melting a t 137-139’. The total yield was 24.3 g., equivalent to 98%. a-S,4-Xylidine-N-D-ribopyvanoside “complex salt.” a-3,4-Xylidine-N-~-ribopyranoside-sodium sulfate “complex salt” was prepared from an electrolyte solution containing D-ribose and sodium sulfate and 3,4-xylidine in alcohol, following the procedure for the corresponding aniline “complex salt.” Excellent yields (8595%) were obtained. The “complex salt” obtained was dried in vucuo at 25“ and analyzed as follows: i l n a l . Calc’d for 5 CluH19S04.3Ka2S04.4 H20: C, 44.25; H , 5.84; JS.3.97; Na, 7.83. Found:C,44.08;€1,6 00;K,4.07;Sa,7.96. Subsequent runs contained varying amounts of salt and water depending upon the amount of salt present initially, the concentration of alcohol used, the temperature of precipitation, and the amount of drying. Extraction of the “complex salt” with acetone (or dioxane) gave pure a-3,4-xylidine ribopyranoside, m.p. 110-112”; [a]: +94.5” -+ +53.0”; (c = 1.0% in pyridine), ingood yield. When extracted with hot alcohol, the corresponding furanoside, m.p. 128-129’; la]:: +172”; (c = 6% in pyridine), was obtrtined. Hydrogenation of a-aniline-N-D-ribopyranoside-sodium sulfate complex salt .I7 Twenty grams of a-aniline-K-D-ribopyranoside-sodium sulfate “complex salt” (70.05% riboside by weight) was suspended in 120 cc. of dry alcohol and 3 g. of Raney nickel added. The mixture was hydrogenated at 65” at 50 lbs. for eight hours. The catalyst and salts were filtered off and the solution was concentrated t o dryness. The residue was extracted with boiling
* The amount of riboside in the “complex salt” was determined quantitatively by titration with Fehling solution (reference t o preceding paper for method employed). Extrttction of the riboside from the “complex salt” gave yields in agreement with titratedvalue.
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alcohol and set aside for crystallization. On cooling, 13.0 g. (92%) of D-ribitylaniline, m.p. 125-127’; [(Y]: -42.0’; (c = 2.7% in pyridine), was obtained. Separation of D-ribose f r o m D-arabinose b y means of aniline “complex salt” formation. One gram of D-ribose and one gram of D-arabinose were dissolved in 14 cc. of 9% sodium sulfate solution. The p H was adjusted to 4.0 and 1 cc. of aniline in 3.5 cc. of alcohol was added. The mixture was stirred at room temperature for two hours and set in the refrigerator overnight. The complex formed was filtered off, washed with alcohol, and dried. Titration indicated that 1.0 g. of pentoside was present in the “complex salt’’ (67%). Extraction of the “complex salt” with acetone, concentration of the acetone solution to dryness, and trituration with alcohol yielded a-aniline-N-D-ribopyranoside+1/2 HzO; m.p. 117-119”; [CY]: f55.7” -+ f47.3’; (c = 1.1% in pyridine). A n a l . Calc’d for CllH15hT04: C. 56.40; R,6.84. Found: C, 56.14; H , 6.79. Pure tr-aniline-N-D-ribopyranoside +1/2 H 2 0 , melts a t 125-127”; [CY]: +63.4” -+ f48.6’; (c = 1.0% in pyridine; 48 hrs.). Pure a-aniline-N-D-arabinopyranoside melts a t 130”; [a]: f68.0” + -4.25’; ( c = 3% in pyridine; 24 hrs.). The melting point and the optical rotation indicated that the product that was isolated contained more of the beta form than usually present. A mixture with an authentic samble of (Y-aniline-N-n-ribopyranoside (m.p. 125-127’) melted at 120-122”. A mixed melting point with an authentic sample of cu-ani1ine-K”D-arabinopyranoside(m.p. 130”) gave a depression (110-112”). ACKNOWLEDGMENT
We wish to acknowledge our indebtedness to Dr. U. V. Solmssen for the preliminary investigations he performed and passed on to us, and for his continued interest in the study of the nature of the “complex salt”. We also wish to thank Mr. Edward Wenis for technical assistance in the early phase of the investigation. The micro analyses were performed in the Microanalytical Division of these laboratories under the direction of Dr. A1 Steyermark. SUMMARY
1. Several substituted aniline bases (and naphthylamine) were condensed with D-ribose in aqueous alcohol solution a t low temperatures to give the corin excellent yield. responding arylamine-N-D-ribopyranosides 2. Aniline was condensed under these conditions with D-arabinose to yield a-aniline-K-D-arabinopyranoside. 3. Arylamine-N-D-ribopyranosidesare characterized by the ability to form “complex salts” with the soluble salts of the alkali metals, which contain the pyranoside in a loose combination with the inorganic salt. 4. The S-D-ribopyranoside was obtained in almost quantitative yield by extraction of the “complex salt” with suitable solvents. Extraction of the “complex salts” with hot alcohol yielded the N-D-ribofuranoside in excellent yield. 5 . The ribopyranoside “complex salt” was hydrogenated directly to the corresponding ribitylamine in excellent yield. 6. Sugars containing hydroxyls in the 2- and 3-position in cis-configuration as D-mannose and D-lyxose formed N-glycopyranoside “complex salts” while other sugars not possessing hydroxyls in that configuration did not form these “complex salts”.
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7. This unique property was used to separate a prepared mixture of D-ribose and D-arabinose. NUTLEY,N. J.
REFERENCES (1) (2) (3) (4) (5)
KUHNAND BIRKOFER, Ber., 71, 621 (1938). U. S. Patents, Nos. 2,384,102; 2,384,103; 2,384,105. BERGER AND LEE,J . Org. Chem., 11,75 (1946). KUHNAND S T R ~ B E LBer., E , 70, 773 (1937). HANAOKA, J. Biochem. (Japan), 31, 95 (1940).
