W-Acylamino

A typlciil regioselecdvity and endo/exo selecdvity has been reported in the Diels-Alder reacdon of 2-W-acylamino -l,3-diene v/ith nitroalkenes fEq 8 21) Thus, exo products are predominandy formed, which is generiil for the Diels-Alder reacdon of nitroalkenes v/ith sterically hmdered dienes... 

Exercise 25-21 How could an optically pure W-acylamino acid racemize and lead to racemic W-acylpeptides as the result of a peptide coupling reaction wherein the carboxyl group of the amino acid was converted to an anhydride group (Review Section 25-5A.)... 

With the exception of glycine, all proteinogenic a-amino acids are chiral. The prevention of racemiza-tion in the case of the most commonly used a-protected amino acids is a prerequisite of successful peptide synthesis. W-acylamino acids might lose their stereochemistry according to the mechanism shown in Scheme 1. The proper choice of the protection group (e.g. urethane-derived), activation method and additives has to be made carefully. 

Rearrangements. Ireland-Claisen rearrangement of allyl fluoroacetates, formation of /3-(W-acylamino)aldehydes from 0-vinyl-N,0-acetals, 1,2-group migra-tion/trapping are some of the useful transformations initiated by TMSOTf. ... 

When the penicillins are treated with dilute alkali, or with the enz une penicillinase, the /3-lactam ring is opened and products known as peni-cilloates are formed. Early attempts to synthesise penicillins by ring-closure of the corresponding penicilloic acids (II) were unsuccessful, mainly because the W-acylamino acid substituent on the thieizolidine ring underwent an alternative cyclisation to form an oxazolone. Sheehan and Henery-... 

W Williams, GT Young. Amino acids and peptides. XXXV. Effect of solvent on the rates of racemization and coupling of acylamino acid p-nitrophenyl esters. Base strengths of amines in organic solvents, and related investigations. J Chem Soc Perkin Trans 1 1194, 1972. 

U. Westerlind, P. Hagback, B. Tidback, L. Wiik, O. Blixt, N. Razi, and T. Norberg, Synthesis of deoxy and acylamino derivatives of lactose and use of these for probing the active site of Neisseria meningitidis W-acetyltransferase, Carbohydr. Res., 340 (2005) 221-233. 

The fourth chapter, 14-Amino-4,5-epoxymorphinan Derivatives and Their Pharmacological Actions, by John W. Lewis and Stephen M. Husbands, presents the recent extensive studies on the chemistry, structure-activity relationships, and pharmacology of 14-acylamino- and 14-alkylamino-derivatives. 

In the development of mixed anhydrides the year 1951 was indeed an annus mirabilis . In England G.W. Kenner (Plate 27) invented the interesting and efficient method of peptide bond formation via anhydrides of acylamino acids with sulfuric acid [12]. The reactive intermediates prepared from the blocked amino acid and the anhydride of sulfuric acid applied in the form of a complex... 

A new method for synthesis of W-alkyl- and N,iV-dialkyl-derivatives of 2-amino-2-deoxy-D-glucose is shown in Scheme 19. Oxazolidine derivatives such as 61 related to muramic acids, but with conformational restrictions, wrae synthesized by alkylation of the corresponding 2-acylamino-2-deoxy-3-hydroxy-sugars with dichloroacetic acid. ... 

FIG. 13 Structures of methyl-2-acylamino-2-deoxy-D-glucopyranosides (XLV, XLVl), M-alkyl-2-acetylamino-2-deoxy-D-glucopyranosides (XLVII, XLVIII), and w-alkyl-2-amino-2-deoxy-D-glucopyranoside hydrochlorides (XLIX, L). (Adapted from Ref. 117.)... 

But the formation of azlactones as intermediates cannot explain all the observations made in this field. Thus it has been mentioned already that ketene racemizes AT-methyltryptophan. Carter and Stevens (1940) state that certain acyl derivatives of ir-proline and W-methyl-n-phenyl-alanine are rapidly racemized by the action of acetic anhydride in glacial acetic acid. In the same paper it is also reported that the addition of various azlactones to a solution of benzoyl-p-methoxyphenylalanine in acetic acid produces fairly rapid racemization of the acyl derivative. An azlactone can obviously not be formed from a compound such as proline, and there is no evidence that structures such as XLIII exist and even if they exist, there is no apparent reason why they should be so easily racemized. There is a possibility of the transient formation of a dipolar structure such as XLV, which is analogous to the formula proposed for sydnones (Baker and Ollis, 1946). But a more likely explanation is that both ketene and acetic anhydride can form mixed anhydrides with acylamino acids, which can then rearrange to form azlactones and acetic acid. Reference has already been made to the action of ketene on carboxylic acids to produce mixed anhydrides and similar reactions have been observed with acetic anhydride. The marked racemization of such structures is partly explained by the strongly electronegative character of the anhydride group. Such an explanation is supported by the findings... 

Hunter, S.W., T. Fujiwara, R.C. Murphy, and P.J. Brennan N-Acyl Kansosamine. A Novel Acylamino Sugar from the Trehalose-Containing Lipooligosaccharide Antigens of Mycobacterium Kansasii. J. Biol. Chem. 259, 9729 (1984). 

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