Proline, complex with

Metal ion complexes. These classic CSPs were developed independently by Davankov and Bernauer in the late 1960s. In a typical implementation, copper (II) is complexed with L-proline moieties bound to the surface of a porous polymer support such as a Merrifield resin [28-30]. They only separate well a limited number of racemates such as amino acids, amino alcohols, and hydroxy acids. 

The values of x = 0.5 and = 1 for the kinetic orders in acetone [1] and aldehyde [2] are not trae kinetic orders for this reaction. Rather, these values represent the power-law compromise for a catalytic reaction with a more complex catalytic rate law that corresponds to the proposed steady-state catalytic cycle shown in Scheme 50.3. In the generally accepted mechanism for the intermolecular direct aldol reaction, proline reacts with the ketone substrate to form an enamine, which then attacks the aldehyde substrate." A reaction exhibiting saturation kinetics in [1] and rate-limiting addition of [2] can show apparent power law kinetics with both x and y exhibiting orders between zero and one. 

The most widely used approach for the separation of enantiomers by TLC is based on a ligand exchange mechanism using commercially available reversed-phase plates impregnated with a solution of copper acetate and (2S,4R,2 RS)-4-hydroxy-l-(2-hydroxydodecyl)proline in optimized amounts. Figure 7.9 (10,97,98,107-109). Enantiomers are separated based on the differences in the stability of the diastereomeric complexes formed between the sample, copper, and the proline selector. As a consequence, a prime requirement for separation is that the seumple must be able to form complexes with copper. Such compounds include... 

Selectivity studies with DTU indicated marked discrimination in the clathrate formation 23,45). As in other types of clathrates, the steric factor is important in differentiation between compounds of similar functionality but different shape. For example, DTU forms crystalline complexes with some alcohols (methanol, ethanol, propanol, 1-butanol) but not with others (2-butanol). It complexes the ethyl esters of N-acetyl derivatives of glycine, alanine, methionine and aspartic acid, but not of proline, serine, phenylalanine and glutamic acid. 

Corma and coworkers tested a number of rhodium and other transition metal complexes with ligands based on proline (Fig. 29.23). These authors reported ee-values of 54—90% for the hydrogenation of dehydroamino acid derivatives with a catalyst prepared from ligand 38 [51]. With ligand 39, an ee-value of 34% was recorded for the hydrogenation of ethyl acetamidocinnamate 10 [52]. 

Tzeng, S. R., et ak. Solution structure of the human BTK SH3 domain complexed with a proline-rich peptide from pl20cbk J Biomol NMR, 2000, 16(4), 303-12. 

To support the proposed hydride transfer as shown for the substrate geranylacetone 68 in Fig. 30 proline was linked to the primary face of P-CD yielding the tertiary amine 101 which was complexed with ruthenium and employed to ATH under standard conditions. No product was formed at all which is in good agreement with observations by other groups (31,49,50). The presence of a hydrogen... 

Fluoral has been condensed with an equivalent of chiral glycinate anion. The chirality stems from a chiral nickel complex with a chiral Schiff base derived from proline as hgand (Figure 5.17). (25, 35)-Difluorothreonine has thus been obtained with an excellent selectivity (de > 95%). This method also allows preparation of numerous fluoroalkyl and fluoroaryl analogues of threonine. Enantiopure difluorothreonine could also be prepared from ascorbic acid. ... 

In late 1975, Enders et al.156) started a research project directed towards the development of a new synthetic method for asymmetric carbon-carbon bond formation. A new chiral auxiliary, namely the (S)-proline derivative SAMP (137), was allowed to react with aldehydes and ketones to give the hydrazones (138), which can be alkylated in the a-position in an diastereoselective manner 157,158). Lithiation 159) of the SAMP hydrazones (138), which are formed in excellent yields, leads to chelate complexes of known configuration 160). Upon treatment of the chelate complexes with alkyl halogenides the new hydrazones (139) are formed. Cleavage of the product hydrazones (139) leads to 2-alkylated carbonyl compounds (140). 

They further observed the stereoselective effect in several other systems containing other amino acids as the polymer ligands74, and identified certain prerequisites for effective resolution (i) mixed complexes are more stable and it is better to use Cu(II) or Ni(II), (ii) the sum of the dentation of the polymer ligands and the mobile ligands (amino acids) should be equal to the coordination number of the central metal ion. The difference in free energy of formation of the two dia-stereomeric complexes with L- and D-proline was estimated to be 0.4 to 0.5 kcal/mol for the L-proline-Cu resin. It was emphasized that the stereoselectivity of this process was sufficient for the complete resolution of racemic a-amino acids74. ... 

A crystal structure of the all-tram isomer of [Cr2(gly)4(OH)2] has been reported.1162 Its low temperature magnetic susceptibility has been fitted to both the Van Vleck and modified Van Vleck models. The uncorrected model leads to, uef = 3.80BM with 2/= 8.4 cm-1 1162,1163,1164 with the inclusion of quadratic exchange 2/=7.4 cm-1.1162 Related studies of alanine,1153,1163 valine, phenylalanine, leucine,1163,1149 proline1166,1167 and histidine1168 complexes have appeared. The proline complex is unusual in that it is soluble in methanol and DMSO. Circular dichroism spectra have been measured the X-ray structure shows the complex to be the L-bms(N), L-tram(0) isomer.1166 More complicated dimers of unusual stoichiometry have been reported.1169... 

The asymmetric epoxidation of allylic alcohols with cumene hydroperoxide or rerf-butyl hydroperoxide (TBHP) was first examined by using chiral amino alcohol-Mo complexes 45) and V complexes with chiral hydroxamic acid ligands (Scheme 20) 46). The highest optical yields were 33% with geraniol and 50% with 2-phenylcinnamyl alcohol. Combined use of VO(acac)2 and a hydroxamic acid derived from proline led to 80% optical yield with 2-phenylcinnamyl alcohol 47). 

O-Methylation of N-methylated derivatives under basic conditions is disappointing, 5063 but improved results are obtained using trimethyloxonium tetrafluoroborate (Scheme 13), or boron trifluoride-diethyl ether complex with diazomethane. 671 Conversely, methylation of the proline derived P-hydroxy acid using sodium hydride and iodomethane, as well as using trimethyloxonium tetrafluoroborate, gives the dolaproine unit (8) of dolastatin 10 in good yield. 68,691... 

Rather earlier but still recent studies include those of zinc complexes with glycine,270,273 alanine,272,274 /5-alanine,272 norleudne,271 phenylalanine,272 proline, methionine, serine,274 histidine,271 asparagine,276 adrenaline,277 noradrenaline,277 terizidone,278 S-ethyl-L-cysteine,279 5,5 -methylenebis(L-cysteine),280 ornithine, lysine, 2,4-diaminobutyric add and 2,3-diaminopropionic acid.281... 

Cadmium complexes with glycine,271-273,282-284 alanine,272,284 norleudne,271 phenylalanine,272 proline,285 serine,286 histidine, 71 asparagine,276 leudne, tyrosine, norvaline, arginine, and... 

For small peptides, the amount of color increases with the size of the peptide. The presence of any of five amino acid residues (tyrosine, tryptophan, cysteine, histidine, and asparagine) in the peptide or protein backbone further enhance the amount of color produced, because they contribute additional reducing equivalents for further reduction of the phos-phomolybdic/phosphotungstic acid complex. With the exception of tyrosine and tryptophan, free amino acids will not produce a colored product with the Lowry reagent however, most dipeptides can be detected. In the absence of any of the five amino acids listed above, proteins containing proline residues have a lower... 

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