D-Threonine

The L-threonine (EC 4.1.2.5), D-threonine (EC 4.1.2.-) or L-allothreonine aldolases (EC 4.1.2.6 synonymous to S1IMT) can be used for resolution of racemic (allo)threonine mixtures by highly selective cleavage of the unwanted isomers42, but can also efficiently direct the anabolic pathways. The substrate spectrum includes propanal, butanal and dodecanal43. 

Ah + H2N OH (2R JS)-2-amino-3-hydroxypentanoir acid D-threonine aldolase "f COOH OH 6... 

High-pressure [4 + 2] cycloaddition of 1-methoxy-1,3-butadiene to A/,0-protected D-threoninals and D-allo-threoninals [91]... 

Extension of this strategy enables syntheses of both protected D-threonine and L-allo-threonine, in which reagent-controlled stereoselective epoxidation of a common intermediate is the key step (Scheme 4.8).53... 

Other aldolases, from microorganisms, have been cloned and overexpressed. For instance, L-threonine aldolase from Escherichia coli and D-threonine aldolase from Xanthomonus orysae have been obtained and used to prepare 0-hydroxy-a-amino acid derivatives1122. ... 

Differently from serine, ESI-MS analysis of homoserine (HSer) solutions reveals an unusually abundant diprotonated homoserine octamers [(HSer)g-2H], but not the expected monoprotonated [(HSer)g H]" one." A 3/1 mixture of L-serine and L-homoserine yields abundant mixed serine octamers with the incorporation of one or two homoserine molecules into the cluster. CID of the isolated [(Ser)6(HSer)2-H] cluster leads to the preferentially loss of two neutral serine molecules. Homoserine is always retained. The ESl-MS spectral patterns of threonine and allothreonine solutions is similar to that of homoserine. A 1/1 mixture of D-serine and D-threonine yields abundant mixed singly- and doubly-charged octamers incorporating from 2 to 6 threonine molecules. Their relative abundance indicates that threonine may incorporate freely into serine clusters because the additional methyl group does not interfere with the bonding of the cluster. 

Stereoisomers with more than one chiral center and which are not mirror images of each other hence, stereoisomers that are not enantiomers of each other. For example, L-threonine and D-threonine are an enantiomeric pair whereas L-threonine and D-allothreonine are a diastereomeric pair (as is L-threonine and L-allothreo-nine). Diastereomers will have similar physical, chemical, and spectral properties but those properties will not be identical. If n is the number of chiral centers, then the maximum number of stereoisomers will be equal to 2. However, the actual number for a given set of isomers may be less than 2 due to the presence of meso forms. See Enantiomer Epimer Meso Form... 

This observation is in accordance with the phenomena of the crystallization in the resolution operation mentioned above in the following points. There are no clear, definite critical supersaturations above which nucleation of D-threonine occurs. Ohtsuki (2), however, reported supersolubility curve for this system, who gave the value of the supersaturation width At=7 C at 50 C. Their definition of the metastablllty was that no nucleation of the enantiomer other than seeded one was observed for two hours of resolution experiments. According to this definition, the supersolubility can be determined to lie somewhere between At=8 and 5 C from the present experimental data, this being in agreement with his result. If the crystallization proceeds further, however, D-threonine crystals may start to crystallize from the solution even if the initial supersaturation is 5 C. In this sense it is no longer the metastablllty limit. 

From the consecutive measurements of solution concentrations and crystal purities during the optical resolution by preferential crystallization, the crystallization of D-threonlne other than the seeded component (L-threonine) was observed In the later stage of the resolution. Washing of the seed crystals was found to be effective to delay the purity decrease. D-threonine was believed to be Introduced... 

Researchers at the University of Graz, in collaboration with scientists from DSM, have developed an elegant and novel approach to the synthesis of P-amino alcohols using two different enzymes in one pot (Scheme 2.35). For example, a threonine aldolase-catalyzed reaction was initially used, under reversible conditions, to prepare L-70 from glycine 69 and benzaldehyde 68. L-70 was then converted to (R)-71 by an irreversible decarboxylation catalyzed by L-tyrosine decarboxylase. In a second example, D/L-syn-70 was converted to (R)-71 using the two enzymes shown combined with a D-threonine aldolase in greater than 99% e. e. and 67% yield ]37, 38]. 

Ij is an indicator variable which takes a value of 1 for the data determined by Mazur et al. to correct parallel difference from those by Ariyoshi et al. Those by Fujino et al. need no correction. Examination of the data by Ariyoshi et al. indicated that there is a parallel difference in the sweetness between compounds derived from D-threonine and the alio counterparts [3 7 R1=CH(OH)Me]. I2 is the indicator variable taking care of the alio compounds. The negative coefficient of this term indicates that the alio configuration within the R1 moiety is sterically unfavorable. 

A. Gotfbiowski and J. Jurczak, High-pressure [4+2]cycloaddition of 1 -methoxy-1,3-butadiero to N.O-protected D-threoninals and D-a//o-threoninals, Tetrahedron 47 1037 (1991). 

Sometimes the subscript s or g is added to a d or l prefix to indicate whether the chirality of a compound is being related to that of serine, the traditional configurational standard for amino acids, or to that of gly-ceraldehyde. In the latter case the sugar convention (Chapter 4) is followed. In this convention the configurations of the chiral centers furthest from Cl are compared. Ordinary threonine is ls- or d -threonine. The configuration of dextrorotatory (+)-tartaric acid can be described as 2R, 3R, or as ds, or as l. ... 

Glycine-dependent threonine aldolases have been used to synthesize a number of /-halogenated and long-chain fi-hydroxy-a-amino acids. For D-threonine aldolase. vvn-selectivity was observed exclusively. Further chemical conversion yielded the 2-amino-l,3-diols, potential precursors for the synthesis of short-chain sphingo-sine-derivatives (Fig. 35c) [193]. 

Overproduction of E (isoleucine) inhibits enzyme E6 (threonine deaminase), and the consequent rise of D (threonine) reduces the rate of production of C (homoserine) via enzyme E3 (homoserine dehydrogenase). The concentration of B (aspartate semialdehyde) rises, and this in turn inhibits Ej (aspartokinase). It is therefore obvious why the control system is called a negative feedback network, or sequential feedback system. 

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