Allothreonin

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. 

C( H, 02 99-93-4) see Bamethan Bufexamac Paracetamol Pifoxime Salbutamol 4-hydroxy-L-allothreonine monosodium salt (C4H,NNa04 117095-55-3) see Carumonam 4 -hydroxy-2-aminoacetophenone (CSH9NO2 77369-38-1) see Octopamine... 

A number of other chiral catalysts can promote enantioselective conjugate additions of silyl enol ethers, silyl ketene acetals, and related compounds. For example, an oxazaborolidinone derived from allothreonine achieves high enantioselectivity in additions of silyl thioketene acetals.323 The optimal conditions for this reaction also include a hindered phenol and an ether additive. 

Figure 22. Photographs of (R,S)-serine crystals (a) Pure (b)-(d) grown in the presence of (b) (R)-threonine, (c) (S)-threonine, (d)-(R,5)-threonine (e) grown in the presence of resolved or (R,S) allothreonine.

These principles are nicely illustrated by the contrast between the serine-threonine and serine-allothreonine (allothr) systems. The relative orientation of molecular serine vis-a-vis its various crystal faces suggests that allothr can be adsorbed on the homotopic 100 faces as well as on the enantiotopic 011 faces (Figure 21). 

Rat liver aminomalonate decarboxylase has recently been identified with cytoplasmic serine hydroxymethylase and allothreonine aldolase 17>. Most references in this narrative have been omitted, since they can all be found in Popjack s review t). 

Palekar, A. G., Tate, S. S., Meister, A. Rat liver aminomalonate decarboxylase. Identity with cytoplasmic serine hydroxymethylase and allothreonine aldolase. J. Biol. Chem. 248, 1158-1167 (1973). 

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. 

In the enzymatic part of the process, a one-pot conversion was achieved by using Candida lipase (Lip) to hydrolyze the ester and then LeuDH to catalyze the reductive amination (with or without N labeling). In this case, the coenzyme recycling was accomplished by adding FDH and formate. The same group used a similar enzymatic strategy to prepare labeled L-threonine and L-allothreonine starting from the a-keto methyl ester. ... 

Decomposition of the copper complex with HjS in acid leads to allothreonine and (in about 2-fold excess) threonine. Following the pioneering work of Akabori et this reaction has been extended to a variety of metals and aldehydes and to complexes such as A- and A-Co(en)2gly with intriguing stereoselectivity behavior (optically-active allothreonine and threonine products). ... 

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... 

A cycloaddition analogous to that in Eq. 12 also occurs with aminocarbene 9. Thus, addition of formaldehyde to the cocondensate of C - - NH3 generates serine 18 by the mechanism in Eq. 13. This reaction is the key step in the formation of serine when water is added to the C + NH3 reaction (with C + H2O producing the CH2=0). Addition of acetaldehyde to the C - - NH3 cocondensate results in threonine and allothreonine (Eq. 14). ... 

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