Amino acids, isolation Ammonia, hydrolysis

In 1959 a new non-protein L-a-amino acid was isolated from the seeds of Acacia willardiana and later from other species of Acacia-, it proved to be l-/3-amino-/3-carboxyethyluracil (977) (59ZPC(316)164). The structure was confirmed by at least four syntheses in the next few years. The most important involves a Shaw synthesis (Section 2.13.3.1.2e) of the acetal (975) and hydrolysis to the aldyhyde (976) followed by a Strecker reaction (potassium cyanide, ammonia and ammonium chloride) to give DL-willardiine (977) after resolution, the L-isomer was identical with natural material (62JCS583). Although not unambiguous, a Principal Synthesis from the ureido acid (978) and ethyl formylacetate is the most direct route (64ZOB407). 

On the other hand, the esters of the polypeptides are of the greatest importance and they are prepared by the action of alcoholic hydrochloric acid. Hydrolysis of the polypeptide does not occur if prolonged heating be avoided, nor does hydrolysis occur when the esters are saponified by dilute cold caustic alkali. The esters have served in particular for the further synthesis of polypeptides and for the isolation of dipeptides from mixtures on treatment with alcoholic ammonia, the dipeptide esters are converted into their diketopiperazines. They are not soluble in petroleum ether and they are soluble with difficulty in ether, and they thus differ from amino acid esters. Chloroform dissolves them, and in this solvent their combination with acid chlorides has been generally effected. 

The hydrolysis of these compounds by the enzyme was determined by the isolation of the individual substances. The isolation of the amino acids soluble with difficulty in water, namely, tyrosine and cystine, presented no great difficulty, since those compounds crystallised out during the process of hydrolysis, but in the other cases the amino acids required separation from unchanged dipeptide. The ester method here again proved its usefulness the esters of the simple monoamino acids are easily volatile in vacuo and can be characterised by the methods previously described those of the dipeptides are not volatile and are characterised by conversion into their diketopiperazines or anhydrides by the action of ammonia, which compounds are less soluble than the dipeptides themselves and are thus capable of separation by filtration. 

During digestive processes, nucleoprotein is split into nucleic acids and protein, the latter then being broken down into amino acids. The nucleic acids are attacked by ribonuclease and deoxyribonuclease enzymes to form nucleotides, which are further hydrolysed by nucleotidases to form nucleosides and phosphates. In the intestines these nucleosides are split by nucleosidases into ribose, deoxy-ribose, purine and pyrimidine bases, which later undergo oxidation and decomposition to ammonia, carbon dioxide and water, to be finally expelled as urea. Nucleotide hydrolysis products are conveniently identified and isolated by chromatographic methods (Chapter 14.2). 

Diazotization of (5-amino-6-chloropyrimidin-4-yl-amino)cyclopentane derivatives followed by acid hydrolysis yielded the 8-azahypoxanthine 230 without isolation of the 6-chloropurine derivatives, whereas treatment with anhydrous ammonia gave the 8-azaadenosine 232 (73JHC601 73JPS858) (Scheme 48). 

Doering and Odum have examined the photoreaction of phenyl azide in the presence of bases and other nucleophiles. On irradiation of phenyl azide in either aniline, diethylamine or liquid ammonia, 2-anilino-3H-azepine (137), 2-diethylamino-3H-azepine (139) and 2-amino-3H-azepine (140) were isolated respectively. Treatment of phenyl azide with hydrogen sulphide gave a very small yield of 2-thio-3H-azepine. The structure of the cyclic amidines was established chemically by hydrogenation and subsequent hydrolysis to the e-aminocaproic acid and the corresponding base. The u.v. spectra were similar to that of acetamidine and also the absence of —NH— absorption in the infrared together with a strong absorption at 1600 cm are in accord with the proposed structure. Most important, the n.m.r. spectrum of the product proved unequivocally the presence of a 3H-azepine. 

Additional evidence was obtained for the structure (110) of the compound derived from D-mannose, ammonia, and ethyl acetoacetate. This substance, when suspended in water and kept at room temperature, is slowly hydrolyzed, giving di-n-mannosylamine, isolated in the crystalline state, and n-mannose, characterized as its phenylhydrazone. Acetylation gives a tetra-O-acetyl derivative (111). The infrared spectrum of this acetate shows bands at 3280 cm. , attributable to the presence of an intramolecularly bonded NH group, and at 1658 cm. S probably due to the carbonyl group of the /3-amino a, 8-unsaturated ester also involved in a hydrogen bond. Mild, acid hydrolysis of (111) gives 2,3,4,6-tetra-O-acetyl-D-mannose. 

The reaction of the methyl ester of the racemic epoxide 101 with acetone and aluminum chloride gave a 4,S-0-isopropylidene derivative 108. Michael addition of ammonia to the conjugated double bond of 108 with concomitant ammonolysis of the ester group afforded a mixture of 3-amino-2,3,6-trideoxy-4,5-0-isopro-pylidene-OL-arabino- and -r/Z o-hexonamides (109). For the purpose of isolation the mixture was N-acetylated. Acidic hydrolysis of the amide groupings gave a mixture of y- and 8-aminolactone hydrochlorides (110 and 111). Careful N-acetylation and reduction of the lactone carbonyl groups in 112 and 113 afforded N-acetyl-DL-acosamine (115) in 36% yield. The stereoisomeric potential partner of 115, N-acetyl-DL-ristosamine (116), was not isolated in this procedure. 

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