Valine anhydride

That being said, it must be recognized that the evidence that the (V-acy I isourea is the precursor of the 2-alkoxy-5(4//)-oxazolone is only circumstantial because experiments starting from the former have yet to be achieved. The oxazolone could theoretically come from the symmetrical anhydride. The latter generates 2-alkoxy-5(4//)-oxazolone in the presence of tertiary amines (see Section 4.16) even dicy-clohexylcarbodiimide (DCC) was basic enough to generate 2-t< rt-butoxy-5(4 )-oxazolone from Boc-valine anhydride. However the weight of evidence points to O-acylisourea as the precursor of the 2-alkoxy-5(4//)-oxazolone. In the absence of. V-nucleophile, such as in the preparation of esters, the major precursor of product is the symmetrical anhydride.7,8... 

By the careful hydrolysis of certain proteins, peptids of definite structure have been obtained. From silk-fibroin have been obtained the anhydrides of glycyl-d-alanine and glycyl-Z-tyrosine, and a tetrapeptid which consists of two molecules of glycine, one molecule of alanine, and one molecule of tyrosine. It has been shown that the products of the partial hydrolysis of elastin contain cZ-alanyl-Z-leucine, alanyl-proline anhydride, and glycyl-valine anhydride. Other peptids have been obtained from gliadin and casein. 

Glycyl-valine anhydride, which was identical in its properties, except the melting-point, with the synthetical compound. 

From gliadin Fischer and Abderhalden have also isolated a dlpep-tide by these methods, namely, 1-leucyl-d-glutamic acid, which they identified with the synthetical substance Abderhalden and Funk have isolated leucinimide, 1-phenylalanyl-d-alanine anhydride by acid hydrolysis from casein, and probably also leucyl-valine anhydride. 

Typical procedure. N-Carboxy-L-valine anhydride [894] To a solution of N-Boc-l-valine (500 mg, 2.3 mmol) and triphosgene (273 mg, 0.92 mmol) in anhydrous ethyl acetate (55 mL), distilled triethylamine (353 mL, 2.5 mmol) was added over a period of 30 s at room temperature EtaN-HCl precipitated immediately. The vessel was connected to a manometer in order to monitor CO2 evolution while maintaining vigorous stirring of the reaction mixture. The requisite amount of CO2 was generated in 3 h, whereupon the suspension was filtered. The solid EtsN HCl was washed with a small portion of ethyl acetate (10 mL), and the filtrate was concentrated to dryness. The residue obtained was crystallized from dichloromethane and petroleum ether at -20 °C to give the title compound as white crystals (330 mg, 75%). 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

FIGURE 1.18 2-AI koxy-5(4/7)-oxazol ones as intermediates in reactions of IV-alkoxycarbo-nylamino acids.22 After removal of the symmetrical anhydride from a reaction mixture containing Boc-valine and ethyl-(3-dimethylaminopropyl)-carbodiimide hydrochloride, the filtrate contained a novel activated form of Boc-valine (20% yield) that was established to be the 2-alkoxy-5(4H)-oxazolone. Slow addition of Boc-valine to ethyl-(3-dimethylamino-propyl)-carbodiimide hydrochloride in dilute solution gave a 55% yield. Petrol = petroleum ether, bp 40-60°. 

FIGURE 7.34 Decomposition of the symmetrical anhydride of A-methoxycarbonyl-valine (R1 = CH3) in basic media.2 (A) The anhydride is in equilibrium with the acid anion and the 2-alkoxy-5(4//)-oxazolone. (B) The anhydride undergoes intramolecular acyl transfer to the urethane nitrogen, producing thelV.AT-fcwmethoxycarbonyldipeptide. (A) and (B) are initiated by proton abstraction. Double insertion of glycine can be explained by aminolysis of the AA -diprotected peptide that is activated by conversion to anhydride Moc-Gly-(Moc)Gly-0-Gly-Moc by reaction with the oxazolone. (C) The A,A -diacylated peptide eventually cyclizes to the IV.AT-disubstituted hydantoin as it ejects methoxy anion or (D) releases methoxycarbonyl from the peptide bond leading to formation of the -substituted dipeptide ester. 

FR Ahmed, FMF Chen, NL Benoiton. The crystal structure of N,N-bismethoxycar-bonyl-L-valyl-L-valine, a product of the rearrangement of the symmetrical anhydride of N-methoxycarbony I -1.-valine. Can J Chem 64, 1396, 1986. 

Valine.—This amino acid is contained mixed with leucine in the fractions of the esters which boil between 6o° and 90° C. Its isolation and separation from leucine is of extreme difficulty, since these compounds, as well as their copper salts into which they are converted by boiling with freshly precipitated cupric oxide, tend to form mixed crystals. Its isolation was only effected by these means in certain cases, and its amount is really much more than the figures represent from its yield. It is best characterised by conversion into its phenylhy-dantoine derivative by treatment with phenyl isocyanate in alkaline solution. The phenylureido acid is first formed, and this loses a molecule of water, as shown by Mouneyrat, and is changed into its anhydride or phenylhydantoine by treatment with hydrochloric acid. The following reactions occur —... 

Oxazolin-5-ones have also proven to be important intermediates in the homologation of carboxylic acids (71AG(E)655). The IV-acyl-DL-valine derivative (402), prepared from the acid chloride of the carboxylic acid and DL-valine by the Schotten-Baumann procedure, was treated with excess acetic anhydride to afford (403). Reaction of (403) with acrylonitrile and triethylamine led to (404) in good yield. Hydrolysis of (404) with dilute alkali or acid gave the y-keto nitrile or y-keto acid (Scheme 89). 

Bei der Reaktion von N-Trifluoracetyl-valin mit Trifluoressigsaure-anhydrid kann das 2-Trifluormethyl-4-isopropyl-A2-oxazolinon-(5) durch vorsichtige Aufarbeitung des Reaktionsgemisches isoliert werden. Es ist bei Raumtemperatur bestandig, lagert sich aber bei Sanre- oder Basen-zusatz rasch in das A3-Oxazolinon am 199). 

Rate Constants (l.mol. s 1 x 10 ) for the Disproportionation of Z-Valine-Phosphinic Acid Anhydrides... 

An alternative approach for the analysis of blood samples from the same group of Iranian mustard gas victims has been described (50). As mustard gas alkylates amino acids in hemoglobin, adducts will be formed, which remain in the bloodstream for some time. Selective cleavage of the alkylated N-terminal valine of the a-chain of hemoglobin was carried out by using the modified Edman reagent pentafluorophenyl isothiocyanate. After derivatiza-tion of the adduct-derived pentafluorophenylthio-hydantoin with heptafluorobutyric anhydride, the... 

When the second amino acid (valine) is added to the protected, activated alanine, the nucleophilic amino group of valine attacks the activated carbonyl of alanine, displacing the anhydride and forming a peptide bond. (Some procedures use an ester of the new amino acid to avoid competing reactions from its carboxylate group.)... 

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