[CONTRIRUTIOK KO.48 FROM
THE
RESEARCH LABORATORIES OF HOFFMAXN-LAROCHE, INC.]
ARYLAMINE-N-GLYCOSIDES. PART 111. HYDROLYSIS OF ARYLAMINE-N-PENTOSIDES AND T H E PREPARATION OF CRYSTALLINE D-RIBOSE LEO BERGER, CLRICH V . SOLMSSEN, F R E D LEONARD, E D WENIS, JOHN L E E
AKD
Received October $8, 1946
The hydrolytic decomposition of arylamine-N-glycosides as a method for the prepara,tion of rare sugars and their derivatives has not been reported, although the ease of hydrolysis and decomposition of aromatic N-glycosides is well known. Irvine and Moodie (1) determined the N-glycoside nature of glucose anilide by hydrolyzing a methylated glucose anilide with mineral acid and identifying the methyhtted glucose obtained. Irvine and McNicoll (2) reported that mannose anilide could be hydrolyzed with technical wet ether and in a later paper Irvine and Hynd (3) reported that glucose alanide could not be recrystallized, as it decomposed immediately on heating. Weygand (4)reported that p-toluidineD-glucoside decomposed to a tarry mass when exposed to the vapors of a drop of glacial acetic acid in a vacuum desiccator. As a result of a study of the rate of hydrolysis of various substituted anilineN-glycosides, Hanaoka (5) reported that the introduction of the hydroxyl, methoxyl, ethoxyl, or methyl group on the ring decreased the stability of the N-glycoside linkage to acids, while chlorine, and especially the carboxyl group increased the stability. This has been confirmed with a study of the stability of the aniline ribosides and 3,4-dimethylaniline ribosides, whether in the pyranoside or furanoside form. The latter are comparatively unstable while the anilineN-ribosides were stable for several weeks at room temperature and have been kept without noticeable decomposition in a sealed container at 5" for over six months. Traces of impurities, moisture, as well as high temperature accelerated the decomposition. By a selection of mild conditions it was found that the hydrolysis of arylaminecould be effected pracN-D-ribopyranosides and arylamine-N-D-ribofuranosides tically quantitatively and the sugar easily obtained in a crystalline condition. The hydrolysis was effected by refluxing in water or aqueous alcohol solution or suspension, catalyzed by small amounts of dilute acetic acid. It was found convenient to remove the aniline formed by steam distillation, or by binding up with aldehydes such as formaldehyde and benzaldehyde in Schiff bases. The resultant aqueous sugar solution was concentrated to a clear syrup in vacuo and crystallized from absolute ethyl alcohol. The presence of a non-oxidizing atmosphere (as nitrogen) was advantageous but not necessary. The Schiff base formed when aldehydes were used, was extracted with benzene or ether, and subsequently hydrolyzed to regenerate aniline and the aldehyde. Recovery of these materials reduced the cost of operation in the preparation of large batches of ribose in this manner. The pyranoside was hydrolyzed also in the form of the 91
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BERGER, SOLMSSEN, LEOPU’ARD, W E N S , AND LEE
“complex salt” obtained from the condensation of the aromatic amine and D-ribose in the presence of alkali metal salts (6). The sugar obtained crystallized readily from ethyl alcohol in yields of 70-900/, of pure crystalline D-ribose, m.p. 86-87’; [ai:’ - 19.6’; (c = 4.0% in HzO.) D-Ribose has been prepared by hydrolysis of nucleic acid, nucleotides, nucleosides, and their degradation products as guanosine or adenosine. Chemically, it has been synthesized from D-arabinose according to the method of Fisher and Piloty (7) and Alberda v. Ekenstein and Blanksma (8) by reduction of D-ribonolactone (prepared by epimerization of D-arabonic acid in aqueous pyridine) with sodium amalgam; or according to the method of Gehrke and Aichner (9), modified by Austin and Humoller (lo), and Steiger (ll),by oxidation of D-arabinal with perbenzoic acid to give a mixture of D-arabinose and D-ribose. The syrupy ribose obtained by these methods could not be crystallized directly even in the presence of mere traces of impurities. The sugar was obtained in a crystalline state through decomposition of its p-bromophenylhydrazone, or diphenylhydrazone derivatives with formaldehyde or benzaldehyde. The yields of crystalline ribose obtained were low and the product obtained wag usually of a low grade of purity and required several recrystallizations. The quality of the D-ribose obtained was improved when pure p-bromphenylhydrazine was prepared and condensed with the crude ribose and the hydrazone isolated was purified carefully by crystallizations (11). In contrast, crystalline 1)-ribose was obtained directly in good yields from crude syrups obtained by the reduction of D-ribonolactone, by conversion to a-aniline-N-D-ribofuranoside (prepared in excellent yield by boiling the syrup in alcohol with a slight excess of aniline) and subsequent hydrolysis. D-Ribose was also isolated in a pure crystalline state in good yield from reduction liquors containing D-ribose and electrolyte salts by means of the cu-aniline-X-D-ribopyranoside “complex salt” and direct hydrolysis of the “complex salt” obtained. The hydrolysis method was applied to triacylated K-ribosides derived from two isomeric aniline ribosides (a-aniline-N-D-ribopyranosideand a-aniline-SD-ribofuranoside) (12). These yielded triacyl derivatives which are tentatively designated as 2 , 3 ,4- or 2,3,5-triacyl derivatives of ribose depending upon whether they were derived from the pyranoside or the furanoside form, on the assumption that no acyl migration occurred during acylation of the ribosides or the subsequent hydrolysis. The acylated riboses were obtained in good yield. The products mere hygroscopic syrups or glasses and could not be brought to crystallization. The exact structure of these acylated riboses has not as yet been determined. The close agreement of the optical rotations of the two triacetylriboses obtained might seem to indicate that ring opening and acyl migration may have occurred in one of the ribosides. Methylation studies of these acylriboses gave mixtures of partially methylated syrups of undetermined structure, from which conclusions as the structure of the acyl sugars could not be drawn. The designation of the
ARYLAMINE-W-GLYCOSIDES.
I11
93
products obtained as 2,3,4- or 2,3,5-triacylriboses is therefore to be regarded as tentative. EXPERIMENTAL
Hydrolysis of a-aniline-N-n-riboside (pyranoside or furanoside). Method I . Four grams of a-aniline-N-D-ribopyranoside was suspended in 200 cc. of water containing 0.25% acetic acid. Steam was injected until all the aniline was removed. The light yellow solution was treated with a small amount of h'orit, filtered, and concentrated t o dryness i n vacuo a t 30-35'. The residual syrup was dissolved in absolute alcohol and dried by concentration in uacuo. A light yellow syrup weighing 3.0 g. was obtained. It was dissolved in 4-5 cc. of absolute alcohol with slight warming, seeded, and set in the refrigerator for crystallization. The whole mass crystallized in several hours, was filtered off, and washed with cold alcohol and ether There was obtained 2.3 g. of crystalline D-ribose (86% yield), melting a t 86-87"; [a]::-19.6'; ( c = 4% in water); [a]: -43.3'; (c = 1.5% in pyridine). Method IZ. Forty-five grams of a-aniline-l\rT-n-ribofuranoside was suspended in 2250 cc. of hot water in a 5-liter 3-neck flask equipped with a stirrer, dropping-funnel, and a condenser. The reaction mixture was heated until the glycoside dissolved, and 35 cc. of benzaldehyde was added a t this point. The mixture was refluxed for one-half hour under nitrogen, cooled, and the solid benzalaniline filtered off. The aqueous layer was extracted with ether t o remove the final traces of benzalaniline, decolorized withNorit, and concentrated t o dryness in uacuo a t 30-35". The residual syrup was dried by alcohol reconcentrations and crystallrzed from absolute alcohol in the ratio of 5 g. of syrup t o 5.6 cc. of absolute ethyl alcohol. On seeding, crystalline ribose was obtained in excellent yield (90%) melting at 86-87 Hydrolysis of a-aniline-N-D-ribopyranoside-sodiumsulfate complex. To 200 cc. of water containing 0.25% acetic acid was added 16.0 g. of a-aniline-K-D-ribopyranoside-sodium sulfate "complex salt," equivalent t o 7.9 g. of pure riboside. The solution was steam distilled under nitrogen until all the aniline was removed. The aqueous liquors were treated with a small amount of Norit, filtered, and concentrated t o dryness in uucuo a t 30-35". The residue was extracted twice with warm alcohol, filtered, and evaporated t o dryness in vacuo. The syrup obtained crystallized immediately on seeding t o yield pure crystal11,neD-ribose in 73% yield, m.p. 84-86"; [a],"-19.4'; (c = 1% in water). The pyranoside complex was hydrolyzed according to method I1 t o yield pure ribose in 71% yield. Hydrolysis of ~~-$,3,4-triacetyl aniline-N-D-ribopyranoside. Ten grams of a-2,3,4triacetyl aniline-x-D-ribopyranoside was dissolved in 25 cc. of ethyl alcohol and added to 400 cc. of a 0.5% acetic acid solution. The solution was steam distilled until all the aniline mas removed. The aqueous solution was treated with h'orit, filtered, and concentrated t o dryness in vacuo as previously. The resultant syrup was dried via repeated alcohol distillations. There was obtained 5.0 g. of a clear colorless thick syrup t h a t could not be crystallized. The syrup was readily soluble in alcohol and ethyl acetate (D-ribose is insoluble i n cold alcohol and ethyl acetate). The syrupy 2,3,4-triacetylribose was dried a t 100" for six hours and analyzed. A n a l . Calc'd for CllHleOs: C, 47.82; H, 5.80; Acetyl, 46.7. Found: C, 47.58; H, 5.86;Acetyl, 40.9.' The 2,3,4-triacetylribose was very hygroscopic and adsorbed %lo% of water on standing. Dried a t room temperature in uucuo over P20j, i t retained 1/2 mole of water; [CY]: -26.3"; (c = 1.3% in water). Hydr
