D-threonine aldolase

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

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. ... 

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]. 

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]. 

A second catabolic reaction of L-threonine (Eq. 24-37, step b) is cleavage to glycine and acetaldehyde. The reaction is catalyzed by serine hydroxymethyl-transferase (Eq. 14-30). Some bacteria have a very active D-threonine aldolase. A quantitatively more important route of catabolism in most organisms is dehydrogenation (Eq. 24-37, step to form 2-amino-3-oxobutyrate. This intermediate can be cleaved by another PLP-dependent enzyme to acetyl-CoA plus glycine (Eq. 24-38, step d). It can also be decarboxylat-ed (Eq. 24-38, step e) to aminoacetone, a urinary excretion product, or oxidized by amine oxidases to methylglyoxal (Eq. 24-37, The latter can... 

Threonine aldolases have been also successfully applied in the resolution of racemates of (3-hydroxyamino acids. An interesting example is the use of a D-threonine aldolase from Alcaligenes xylooxidans to resolve DL-threo- 3-(3,4-methylenedocyphenyl)serine, a synthetic intermediate for parkinsonism dmg (Liu et al. 2000b). 

As mentioned before, one of the main drawbacks in the application of threonine aldolases is their lack of erithro/threo selectivity (kinetic limitation) and their equilibrium position (thermodynamic limitation). Recently, a tandem use of LD-threonine aldolases with low selectivity and L-amino acid decarboxylases with high selectivity has demonstrated to overcome the kinetic and thermodynamic limitations in the synthesis of phenyl serine (Steinreiber et al. 2007). Starting with benzalde-hyde and glycine, i -phenyl ethanol was obtained in 58% isolated yield and R enantiomeric excess higher than 99% by the action of L-threonine aldolase (L-TA) from Pseudomonas putida, D-threonine aldolase (D-TA) from Alcaligenes xylosoxidans and L-tyrosine decarboxylase (L-TyrDC) from Enterococcus faecalis following the scheme depicted in Fig. 6.5.17. 

Liu JQ, Odani M, Yasuoka T et al. (2000b) Gene cloning and overproduction of low-specificity D-threonine aldolase from Alcaligenes xylosoxidans and its application for production of a key intermediate for parkinsonism drug. Appl Microbiol Biotechnol 54 44-51 Machajewski TD, Wong CH (2000) The catal)rtic asymmetric aldol reaction. Angew Chem Int Ed... 

Another screening study uncovered a natural L-aZZo-threonine aldolase from Aeromoms jandaei (L-aZZoThrA jandae) D-threonine aldolase from Pseudomonas sp. 

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. 

Whereas SHMT in vivo has a biosynthetic function, threonine aldolase catalyzes the degradation of threonine both l- and D-spedfic ThrA enzymes are known [16,192]. Typically, ThrA enzymes show complete enantiopreference for their natural a-D- or a-t-amino configuration but, with few exceptions, have only low specificity for the relative threo/erythro-configuration (e.g. (122)/(123)) [193]. Likewise, SHMT is highly selective for the L-configuration, but has poor threo/erythro selectivity [194]. For biocatalytic applications, the knovm SHMT, d- and t-ThrA show broad substrate tolerance for various acceptor aldehydes, notably induding aromatic aldehydes [193-196] however, a,P-unsaturated aldehydes are not accepted [197]. For preparative reactions, excess of (120) must compensate for the unfavorable equilibrium constant [34] to achieve economical yields. 

Scheme 5.51. L-Threonine aldolase approach to mycestericin D. X, Rj, R2 = protecting groups.

As discussed previously, the major route of threonine degradation in humans is by threonine dehydratase (see section 111.D.2.). In a minor pathway, threonine degradation by threonine aldolase produces glycine and acetyl CoA in the liver. 

Synthetic applications of threonine aldolase have been hampered due to the poor capacity for erythro/threo discrimination. Erythro-sdective threonine aldolase from Candida humicola has been used for the preparation of a key chiral building block in the synthesis of the immunodepressive lipid mycestericin D (Fig. 6.5.16). The conversion was purposely low to ensure a kinetic control and therefore maximizing the yield of the erythro product. 

Fig. 6.5.16 Threonine aldolase-mediated chemo-enzymatic synthesis of immunodepressive lipid mycestericin D...

D- and L-Threonine Aldolase. These enzymes are involved in the biosynthesis/... 

Aldol reactions have been catalyzed by aldolases as well as by catalytic antibodies. For example, L-threonine aldolase was applied to C—C bond formation of an aldehyde with glycine. The resulting adduct could be further converted to a precursor of N-acetyl-4-deoxy-D-mannosamine, a potent inhibitor of N-acetylneuraminic acid synthetase (Fig. 10.39(a)). "... 

I. Steinreiber, K. Fesko, C. Reisinger, M. Schiirmann, F. Van Assema, M. Wolbei D. Mink, H. Griengl, Threonine aldolases - an emerging tool for organic synthesis. Tetrahedron 63 (2007) 918-926. 

T. Kimura, V.P. Vassilev, G.l. Shen, G.-H. Wong, Enzymatic synthesis of p-hydroxy-a-amino acids based on recombinant D- and L-threonine aldolases, 1. Am. Ghem. Soc. 119 (1997) 11734-11742. 

Example of multistep chemo-enzymatic synthesis of pipecolic acid derivatives (60) and homoiminocyclitols (61) by two consecutive enzymatic aldol addition reactions (a) i-serine hydroxy-methyltransferase from Streptococcus thermophilus (lSHMTj ) (b) Cbz-OSu CHjCN/aqueous HCI (c) Cbz-OSu MeOH/SO CIj CaCI, NaBH, EtOH/THF CHjCN/aqueous HCI (d) o-threonine aldolase from Achromobacterxylosoxidans (oThrA j (e) FucA F131A (f) RhuA wild-type (g) acid phosphatase from potato type II and (h) H Pd/C. 

Giger, L., Toscano, M. D., Bouzon, M., Marli re, R, and Hilvert, D., A novel genetic selection system for RLR-dependent threonine aldolases. Tetrahedron 2012,68 (37), 7549-7557. 

Shibata, K., Shingu, K., Vassilev, V. R, Nishide, K., Fujita, T., Node, M., Kajimoto, T., and Wong, C.-H., Kinetic and thermodynamic control of L-threonine aldolase catalyzed reaction and its application to the synthesis of mycestericin D. Tetrahedron Lett. 1996,37 (16), 2791-2794. 

Glycine-Dependent Aldolases (ThrA) The group of the glycine-dependent aldolases affords the synthesis of (S-hydroxy-a-amino-acids, d- and L-threonine and serine, most of them are known as L-threonine aldolases (ThrA). They catalyzed the addition of glycine 31 to various aldehyde substrates with pyridoxal-5 -phosphate (PLP) as cofactor. The formed products contain two stereogenic centers whose stereochemistry is controlled by the choice of D- or L-threonine and corresponding d- or L-a//o-threo-nine aldolases (Scheme 28.16). 

Different ThrAs possessing variable stereoselectivities are described in the literature (c/review ). The L-threonine aldolases can be divided into three different subgroups, the L-ThrA (catalyzing the formation of L-threonine), the L-allo-ThiA, and the l-1ow specific enzymes (L-low-ThrA, catalyzing the formation of both L-Thr and L-allo-Thr), whereas only low specific D-aldolase (o-ThrA, catalyzing... 

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