D-Allothreonine

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... 

An additional bulky group on the dioxanone moiety was not required for stereoinduction, and an excellent diastereomeric excess was obtained starting from 59 when R = H. Enantioselective synthesis of D-allothreonine 61 has been achieved from 60 (R = CH2CH2Ph) with 42 % yield [22]. (S)-Trifluorothreonine methyl ester 63 has also been synthesized in 57 % yield from the 2-f-butyl-1,3-dioxan-4-ones 62 using a related approach [30] (Scheme 29). 

Alkylene bromide, 20, 24 Alkylene thioureas, 26, 35 Alkylidenecyanoacetic esters, 25, 48 Alkyl lactate, 26, 6 Alkyl phenyl selenides, 24, 91 S-Alkylthiuronium halides, 22, 60 d/-ALLOTHREONINE, 20, 104 Alloxan, 23, 3... 

Rhodium and ruthenium complexes of CHIRAPHOS are also useful for the asymmetric hydrogenation of p-keto esters. Dynamic kinetic resolution of racemic 2-acylamino-3-oxobutyrates was performed by hydrogenation using ((5,5)-CHIRAPHOS)RuBr2 (eq 3). The product yields and enantiomeric excesses were dependent upon solvent, ligand, and the ratio of substrate to catalyst. Under optimum conditions a 97 3 mixture of syn and anti p-hydroxy esters was formed, which was converted to o-threonine (85% ee) and D-allothreonine (99% ee) by hydrolysis and reaction with propylene oxide. 

C-N.m.r. Chemical-shift Data for the Anomeric-Carbon Atom (C-1) and the Threonine Methyl Carbon Atom (O) of Diastereomeric a- and/S o-Calactopyranosyl-L-threonine, -D-threonine, -L-allothreonine, and -D-allothreonine ... 

Among the amino acids, threonine, hydroxylysine, cystine, isoleucine, the two hydroxyprolines, and others possess two optically active centers. Therefore, the synthetic compounds are mixtures of four diastereoisomers the l- and d- forms, and the L-allo- and D-allo- forms, respectively. For example, threonine can have these four forms L-threonine (XLI), D-threonine (XLII), L-allothreonine (XLIII), and D-allothreonine (XLIV). 

Isoleucine and threonine both have two chiral centers. According to official nomenclature the names L-isoleucine and L-threonine both designate only one optically active diastereoisomer. The mirror images are named D-isoleucine and o-threonine, whereas the diastereoisomers are named l-and D-alloisoleucine and l- and D-allothreonine. The configurations of L-isoleucine and L-threonine are shown in the formulas in Table I. The table also contains notation of the configuration at the two centers according to the R,S system and according to traditional nomenclature for amino acids (lUPAC-IUB, 1975). 

Konno, H., Takabayashi, Y, Nosaka, K., and Akaji, K. (2010) Synthetic studies on caUipeltins Stereoselective syntheses of (3S,4R)-3,4-dimethyl-L-pyroglutamic acid and Fmoc-D-allothreonine from serine derivatives. Heterocycles. 81,79-89. 

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