Glutamine esters

A new toxic alkaloid, marinobufagin 3-suberoyl-L-glutamine ester (36a), has been isolated from the skin of the poison toad (Bufo americanus). The partial synthesis of the toxin from the ester (36b) was also reported.80... 

Household bleach has been used to carry out the Hofmann rearrangement of 3-nitrobenzamide to 3-nitroaniline, while the Hofmann rearrangement of N(2)-protected glutamine esters of N(2)-protected (25 )-4-[(2,2,2-trifluoroethoxy)carbonylamino]-2-aminobutyric acid esters has been successfully achieved by an electrochemical method using a trifluoroethanol-methyl cyanide solvent system." ... 

The interaction with both synthetic and naturally occurring amino acids has been studied extensively glycine (138, 173, 219-221), a-(173, 219) and /3-alanine (138, 220), sarcosine (219), serine (222), aspartic acid (138, 173, 222-226), asparagine (222), threonine (222), proline (219), hydroxyproline (219), glutamic acid (138, 222-225), glutamine (222), valine (219, 227), norvaline (219), methionine (222, 226), histidine (228, 229), isoleucine (219), leucine (219, 230), norleu-cine (219), lysine (222), arginine (222), histidine methyl ester (228), phenylalanine (138, 222), tyrosine (222), 2-amino-3-(3,4-dihydroxy-phenyl jpropanoic acid (DOPA) (222), tryptophan (222), aminoiso-butyric acid (219), 2-aminobutyric acid (219,231), citrulline (222), and ornithine (222). 

The Ras proteins are synthesized as biologically inactive, cytosolic precursor proteins. They are then modified by several post-translational processing steps at the carboxyl terminal end and thereby converted into biologically active proteins localized at the plasma membrane. The cysteine of the C-terminal CAAX sequence (C is cysteine, A is generally an aliphatic amino acid, and X is methionine, serine, alanine, or glutamine) is first enzymatically S-farnesylated the AAX part is then cleaved off by a specific protease, and the free C-terminal cysteine is finally converted into a methyl ester (Scheme 1). 

A second method of activating the acid for esterification (see Section 7.6) is as the mixed anhydride. The mixed-anhydride reaction had been employed decades ago for preparing activated esters. However, it was never adopted because of its unreliability and the modest yields obtained. The method was fine-tuned (Figure 7.12), after reliable information on the properties of mixed anhydrides was acquired (see Section 2.8). Tertiary amine is required for esterification of the mixed anhydride to occur. The method is generally applicable, except for derivatives of asparagine, glutamine, and serine with unprotected side chains. The base also prevents decomposition that occurs when the activated derivative is a Boc-amino acid (see... 

Escherichia coli, glutamine synthetase, 28 350 ESR, see Electron spin resonance Ester enolates, Michael addition to ynoates, 38 275, 278... 

L-Glutamine methyl ester was used in the synthesis of the alkaloid histri-onicotoxin ring system. After condensation with 1,3-cyclohexanedione and photocyclization, the intermediate 149 was obtained (86TL5177). 

The biosynthesis of sulfate esters with the help of phosphoadenosine phosphosulfate (PAPS), the active sulfate , (see p. 110) and amide formation with glycine and glutamine also play a role in conjugation. For example, benzoic acid is conjugated with glycine to form the more soluble and less toxic hippuric acid (N-benzoylglycine see p. 324). 

Two of these glutamates are initially glutamines and can undergo methylation only if they are deaminated first.72 An esterase encoded by the cheB gene72 removes the methyl ester groupings as methanol. 

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