Racemization homochiral amines

It has recently been shown that aminotransferases can be used to produce homochiral amine products that do not contain an a-carboxylic add (17,18,48). Enzymes capable of catalyzing such reactions belong to the group of (o-aminotransferases. The reversible nature of the transamination reaction makes it possible for both enantiomers of a given amine to be produced using a single enzyme (Fig. 18). The racemic amine can be... 

Chiral phosphoramides, particularly C2-symmetric examples, are widely used in asymmetric synthesis (see section 3.2). One example is the asymmetric catalysis of Aldol reactions, where the phosphoramide catalyst is used in combination with a Lewis base. A solid state and solution study of the structure of chiral phosphoramide-tin complexes used in such reactions has now been reported. A number of chiral, non-racemic cyclic phosphoramide receptors (387) have been synthesised and their interactions with homochiral amines studied using electrospray ionisation MS. Although (387) bind the amines strongly, no evidence of chiral selectivity was found. Evidence from a combination of its X-ray structure, NMR, and ab initio calculations suggests that the cyclen phosphorus oxide (388) has an N-P transannular interaction in the solid state. A series of isomers of l,3,2-oxazaphosphorino[4,3-a]isoquinolines(389), containing a novel ring-system, have been prepared and their stereochemistry and conformation studied by H, C, and P NMR spectroscopy and X-ray crystallography... 

Allyl amines 611 and pyrazoles 612 could be obtained by hydrazinolysis of 2-ketoaziridines 610 (Equation 127) <2006TL255>. A variety of aziridines, including N-unprotected, N-substituted, as well as bicyclic enamine and aminal types, were transformed into diversely substituted linear or cyclic products. The hydrazinolysis of homochiral aziridines proceeded without racemization and usually allylamines are obtained in greater yields than the pyrazoles in each case. Addition of hydrazines to /3-hydroxy acylsilanes 613 afforded 3-trimethylsilyl pyrazoles 614 (Equation 128) (TMS = trimethylsilyl group) <2000TL9791>. 

The reaction of a homochiral derivatizing agent with a heterochiral sample to yield covalently linked diastereoisomeric products is a precolumn technique used for the analysis of the individual enantiomers. The diastereoisomeric products are separable under a variety of chromatographic conditions (GC and LC), including both normal and reversed-phase procedures. Fig. 23 shows the LC separation of two diastereoisomeric products formed by the reaction of a heterochiral amine and a homochiral derivatization reagent. The derivatization reaction involves the formation of an amide by treating an A-substituted 5-prolyl chloride with racemic amphetamine (Fig. 24). 

In this reaction, partial racemization of some homochiral amino acids was observed. In addition, the combination of a hindered amino acid and an electronically deactivated aldehyde may lead to low yields. Bis-alkylation side reactions of aliphatic aldehydes may generate 1-10% of tertiary amines. 

Observation of the stereoselective manner of chiral substrates binding to these asymmetric metal-salen complexes was not confined to [VO(l,3)] or chiral epoxides. Recently we showed how asymmetric copper salen complexes, [Cu(l)] and [Cu(4)] (Fig. 1), could also discriminate between chiral amines (R-IS-methylbenzylamine, MBA) as evidenced by multi-frequency CW and pulsed EPR, ENDOR, HYSCORE and DPT [45]. The discrimination of the MBA enantiomers was directly observed by W-band EPR. By simulating the W-band EPR spectra of the individual diastereomeric adduct pairs (i.e. R,R -[Cu(4)]+R-MBA and R,/ -[Cu(4)]-l-5-MBA), accurate spin-Hamiltonian parameters could be extracted for each adduct. The EPR spectmm of the racemic combinations (i.e. ra -[Cu(4)]+rac-MBA) was then simulated using a linear combination of the g/A parameters for the homochiral (R,R -[Cu(4)]+R-MBA) and heterochiral (R,R -[Cu... 

A series of l-(isoquinolin-l-yl)naphthalen-2-amines 239 was prepared. The atropisomers of the NH2, N-Me and N,N-diMe2 derivatives were separated on various CSPs and the barriers to racemization in toluene were experimentally determined AG = 125.4, 130.8, and 124.5 kj mol respectively. Molecular mechanics calculation showed that the most favorable transition state is the anti one in which the amino group is opposite to the isoquinoline nitrogen (04H223). When racemic 239 (R = Me, = H) and zirconium tetrakis(dimethylamide) were combined in a 2 1 ratio. X-ray data of the complex showed that a selection of identical ligand antipodes by the metal had occurred (homochiral complex) (02AG(IE)345). 

Subcomponent substitution of a racemic mixture of isomers of 1 1 cage complex of 826 with encapsulated triflate anion in the presence of optically active primary amine 462 by Scheme 5.84 allowed to obtain an optically active AAAA form of this complex [84], The use of a racemic mixture of / ,S-isomers of the amine subcomponent afforded / ,S-imine capsules 828 but not its homochiral analogs. Therefore, chiral selfsorting is not observed in this system. 

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