Alanine methyl ester, complex

Oxidation of 4-methoxycatechol with Ag20 in the presence of /3-alanine methyl ester resulted in the formation of a complex mixture from which compound 57 was isolated in 0.4% yield (82HCA1279). 

Wulff and his collaborators reported, in 1989, the preparation of imprinted polymers able to perform enantioselective synthesis [11, 12]. The imprinting complex was prepared by reacting 3,4-di-hydroxy-phenyl-alanine methyl-ester (l-DOPA methyl ester) (16) with the 4-vinyl-salicylaldehyde (17) to form the corresponding Schiff s base (18), which was further reacted with the 4-vinyl-phenyl-boronic acid (19) to afford to the corresponding ester (20) (Scheme 4). The imprinting complex obtained was then polymerised and the template removed. The resulting polymers were incubated with sodium glycinate to allow formation... 

A synthesis of a-arylamino acids has been reported using Schiff-base anions 61 derived from amino esters, which are arylated with fluorobenzene complex la to give a-aryl imino esters 62 in 48-76 % yield (R = H, Me, CH2Ph) [49]. Using the same procedure, these authors reported a convenient synthesis of optically pure a-aryl amino acid precursors 64 by enantioselective substitution of fluorobenzene complex la using the Schiff base of L-alanine methyl ester with f 1 R.2R.5 R -2-hydroxy-3-pinanone 63 in the presence of LDA (Scheme 30) [50]. 

Enantiomerically pure aldehydes 287 were obtained by DIBAL reduction of the corresponding o-alanine methyl esters. Coupling with t-butyl glycinate quantitatively gave the ( )-imines 288 (Scheme 85). Peracid oxidation did not allow the isolation of oxaziridines 289 which spontaneously decomposed to give complex mixtures of products [156]. This was probably due to a deprotonation a to the ester group accompanied by cleavage of the weak N-O bond. Imines 290, derived from aldehydes 287 and P-alanine esters, could be indeed oxidised into stable oxaziridines 291 which were isolated as mixtures of two dia-stereoisomers (Scheme 86) [157]. 

Sheldrick and Heeb [98] reported the preparation of the amino acid complex [(ri -benzene)Ru(L-alanine-N,0)Cl]. The crystals contained enantiomers with opposite chirality at the Ru centre. This complex reacted with 9EtG to give [(r -benzene)Ru(L-alanine)(9EtG)] which contains N7-bound 9EtG stabilized by a C60 H-N H-bond. Reaction of [(r] -benzene)Ru(L-alanine-methyl ester)Cl2] with 9EtG led to displacement of coordinated monodentate L-alanine methyl ester. These workers observed that aquation of the Ru-Cl bonds occurs readily in water, as noted by Dersnah and Baird [99]. 

North and coworkers have investigated application of Cu(II)/salen complex (405) and derivatives to enantioselective alkylation of alanine methyl ester imine (403) (Scheme 17.91) [128]. Numerous variations on the aryl rings of the salen ligand... 

Extractions of aqueous solutions of racemic amino-acid ester salts with solutions of / -6/s(dinaphthyl)-22-crown-6 [284] in chloroform revealed the dependence of the enantiomeric distribution constant on the structure of the amino acid ester (Table 64). In order to limit the concentrations of complex in the aqueous phase, inorganic salts were added. In the case of tyrosine, serine and alanine no extraction of salt was observed obviously these salts form very hydrophilic complexes. The highest degree of chiral recognition was found with [284] and p-hydroxyphenylglycine methyl ester hexafluorophosphate [A(AG°)... 

The chiral cavitands 3.109 have been developed by combining the amino acid residue L-alanine with macrocyclic cavitands (calixarenes - Section 3.14).51 These ammonium ion receptors are able to complex a range of amino acids and their methylester hydrochloride salts, all of which contain an -NH3+ functionality capable of interaction with the carboxylate residues of the host. In general amino acids are bound only very weakly in aqueous solution, while association constants with the chiral methyl esters range from 620 M-1 for L-tryptophan methylester to 110 M-1 for L-alanine methylester. The methylester of glycine is not bound at all. Receptors related to 3.109 with variable four peptide loops arrayed around a central calixarene core have been used to bind to the surfaces of proteins. The... 

Chiral calix[4]arene podands were made using A-benzyl histidine methyl ester.33 These histidyl calixarenes 12a,b were studied in complexation experiments with Co(H), but no use was made of their chirality. The same is true for a chiral calix[4]arene capped tetraphenyl porphyrin which is C4-symmetrical due to the four L-alanine derived linkers.34... 

Aminophosphines. - The bis(V-pyrrolidinyl)phosphines (139), prepared conventionally by treatment of the appropriate organodichlorophosphine with an excess of pyrrolidine, have proved to be unusually electron-rich <7-donor ligands when compared to either tris(V-pyrrolidinyl)phosphine, or trialkyl-and triaryl-phosphines. Full details of a route to the polycylic aminophos-phirane systems (140) have now appeared. The bis(aminophosphine) (141) has been prepared and used in the synthesis of macrocyclic metal complexes. Two new chiral aminophosphine systems (142) and (143) have been prepared by transamidation of related aryl bis(dimethylamino)phosphines with a chiral amine. The chiral aminophosphine (144) has been obtained from the reaction of chlorodiphenylphosphine with the methyl ester of alanine. A range of ether-functionalised aminophosphines (145) has also been prepared. 

The synthesis of the chiral copper catalyst is very easy to reproduce. The complex catalyses the asymmetric alkylation of enolates of a range of amino acids, thus allowing the synthesis of enantiomeric ally enriched a,a disubstituted amino acids with up to 92% ee. The procedure combines the synthetic simplicity of the Phase Transfer Catalyst (PTC) approach, with the advantages of catalysis by metal complexes. The chemistry is compatible with the use of methyl ester substrates, thus avoiding the use of iso-propyl or ferf-butyl esters which are needed for cinchona-alkaloid catalyzed reactions[4], where the steric bulk of the ester is important for efficient asymmetric induction. Another advantage compared with cinchona-alkaloid systems is that copper(II)(chsalen) catalyses the alkylation of substrates derived from a range of amino acids, not just glycine and alanine (Table 2.4). 

An alternative strategy for binding amines is to use a Lewis acidic metal atom. Zn-porphyrin complexes prove especially useful in this context. For example, the doubly bridged a,a,p,P-systern 12 bound the methyl esters of a-amino acids with moderate but fairly general enantio-selectivities (7.5 1 for valinate, 4 1 for alaninate) in dichloromethane. The Troger s-base-linked bis-porphyrin 13 was designed to make two ZimA interactions and was shown to bind histidine methyl ester 14 with an enantioselectivity of 13 1 in CDCls. Recently, the... 

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... 

Diels-Alder reactions of cyclopentadiene and methacrolein with crotonaldehyde are also catalyzed by complexes formed in situ between NbCls or TaCls and bidentate ligands (2 equiv.) such as L-tartrate esters, or a-amino acids (e.g. tryptophan, alanine). Yields with the Ta catalysts are often somewhat better (14-78 %) than with the Nb catalysts. Good exo. endo ratios are obtained but enantioselectivities are still low (7-40 % ee) [185]. Methylrhenium trioxide is an efficient catalyst in these reactions and its best performance is in aqueous solution. Acrolein derivatives and methyl vinyl ketones react with a variety of dienes to give single diastereoisomers in very high yield with as little as 1 % catalyst loading [186]. Examples are shown in Sch. 49. The reaction is sluggish with disubstituted dienophiles and dienes. 

Glucose ester conjugates can be formed very rapidly in plants m-phenoxybenzolc acid was metabolized in 81% yield to a glucose ester conjugate within 18 hr in excised cotton leaves (51 ), N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine was metabolized in 85% yield to simple and complex glucose esters within 24 hr in oat ( ), and dlclofop-methyl was metabolized by hydrolysis and glucose ester conjugation in 54% yield within 24 hr in oat root (32). 

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