Alanyle complexes

Terminally bound alanyle complexes of the type L M-A1R2 contain an electron-deficient A1 center that, in principle, may act as a Lewis acid moiety. Such complexes therefore tend to form intra- or intermolecularly coordinated structures as observed in base-stabilized complexes such as [( 7 -C5H5)(CO)2Fe-Al (CH2)3NMe2)/-Bu] and in dimeric complexes such as [(C5H4Me)(p-77 77 -C5H3Me)Mo(p-Al(H)/-Bu)]. Compound [Cp(CO)2Fe-Al(tmp)2] is the only... 

Alanyle complexes with terminal AIR2 groups ... 

Structurally characterized alanyle complex containing a planar and three-coordinate A1 center (Fig. 22). 

Fig. 8.2 Interaction of transpeptidase (Enz) with its natural substrate, acyl-D-alanyl-D-alanine in the first stage of the transpeptidation reaction to form an acyl-enzyme intermediate. A similar reaction with a penicillin results in the formation of an inactive penicilloyl-enyme complex.

FIGURE 1.19 X-ray crystal structures of selector-selectand complexes (ion-pairs) (a) O-9-(P-chloro-fert-butylcarbamoyl)quinine with iV-(3,5-dinitrobenzoyl)-(5)-leucine, (b) tbe pseudoenantiomeric complex of 0-9-( 3-cbloro-tert-butylcarbamoyl)quinidine with N-(3,5-dinitrobenzoyl)-(i )-leucine, (c) 0-9-( 3-cbloro-terf-butylcarbamoyl)quinine with N-(3,5-dinitrobenzoyl)-(5)-alanyl-(5)-alanine, and (d) comparison of tbe complexes of (a) and (c). Most hydrogens have been omitted for the purpose of clarity. (Reprinted from C. Czerwenka et al., Anal. Chem., 74 5658 (2002). With permission.)... 

Nieto, M. and Perkins, H.R., Physicochemical properties of vancomycin and iodovancomycin and their complexes with diacetyl-L-lysyl-D-alanyl-D-alanine, Biochem. /., 123, 773, 1971. 

Sheldrick, G.M. et al.. Structure of vancomycin and its complex with acetyl-D-alanyl-D-alanine, Aafare, 271, 223, 1978. 

The presence of a covalent acyl-enzyme intermediate in the catalytic reaction of the serine proteases made this class of enzymes an attractive candidate for the initial attempt at using subzero temperatures to study an enzymatic mechanism. Elastase was chosen because it is easy to crystallize, diffracts to high resolution, has an active site which is accessible to small molecules diffusing through the crystal lattice, and is stable in high concentrations of cryoprotective solvents. The strategy used in the elastase experiment was to first determine in solution the exact conditions of temperature, organic solvent, and proton activity needed to stabilize an acyl-enzyme intermediate for sufficient time for X-ray data collection, and then to prepare the complex in the preformed, cooled crystal. Solution studies were carried out in the laboratory of Professor A. L. Fink, and were summarized in Section II,A,3. Briefly, it was shown that the chromophoric substrate -carbobenzoxy-L-alanyl-/>-nitrophenyl ester would react with elastase in both solution and in crystals in 70 30 methanol-water at pH 5.2 to form a productive covalent complex. These... 

Incubation of Pseudomonas putida with anthracene-labeled carbon-base ferrichrome analog Fe(lll) complex 173 resulted in cellular iron uptake and the appearance of anthracene fluorescence in the culture medium identical to the Fe-ferrichrome uptake. Incubation with the alanyl analog 174 failed to show any significant iron uptake or fiuorescence. This is consistent with the tests described above on the unlabeled analogs. Remarkably, other strains such as Pseudomonas fluorescens S680 or WCS3742 also did not show any iron uptake or culture fluorescence. 

The incorporation of the D-alanine ester groups is, presumably, the last stage in the biosynthesis of teichoic acids. Several organisms possess enzymes which activate D-alanine, that is, which form a D-alanyl-adenosine 5-phosphate-enzyme complex but, so far, there has been no demonstration of incorporation, in cell-free systems, of D-alanine into teichoic acid or any... 

The dipeptide camosine, /J-alanyl-i.-histidinc, is one of the most abundant N compounds present in the non-protein fraction of vertebrate skeletal muscles. It constitutes, for example, 50, 150, and 276 mg per 100 g of muscle tissue from chicken leg, bovine leg, and porcine shoulder, respectively. Chen and Ho138 examined its effects on volatile generation in a model system of ribose and cysteine (180 °C, 2 h, pH 5 and 8.5). These were complex the levels of thiophenes and some meaty compounds, such as 2-methyl-3-furanthiol, 2-furfurylthiol, and their associated dimers, were generally lowered, but those of important N compounds, such as pyrazines and thiazoles, which are known to elicit roasty and nutty flavours, were enhanced. 

Pestka, S., Studies on the formation of transfer ribonucleic add-ribosome complexes. XI. Antibiotic effects on phenyl-alanyl-oligonucleotide binding to ribosomes. Proc. Natl. Acad. Sci. USA 1969, 64, 709-714. 

M. Nieto and H. R. Perkins, Modifications of the acyl-D-alanyl-D-alanine terminus affecting complex formation with vancomycin, Biochem. J. 123 (1971), 789. 

A number of investigations have been based on the conclusions of Strominger and Tipper [183,215]. It was estimated that by structural analogy between the terminal D-alanyl-D-alanine moiety of N-acetylmuramylpentapeptide and 6a-methylpenicillin the latter should possess an enhanced bioactivity. The first experiments aimed at obtaining this compound were unsuccessful [216,217], as the copper complex (112) could not be split after alkylation. Starting from 6-APA, Reiner and Zeller [216] were able to introduce the hydroxymethyl function into C-6, but the low activity of the end-product suggested the presence of (113) in the epi-conformation. The use 4>f formaldehyde yielded the spiro derivative (114). 

Fig. 12.3 The action of transpeptidase (TPase) with its natural substrate (upper) and penicillin G (lower). The OH group on a serine residue at the active site of the TPase attacks the peptide bond between the terminal D-alanyl-D-alanine in the peptidoglycan precursor, releasing the terminal D-alanine and forming a new peptide cross-link with existing peptidoglycan in the cell wall. Penicillin G blocks this process by forming a stable penicilloyl-TPase complex.

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